Debate has persisted over whether the metamorphic basement of the Zhoushan Islands,easternmost Cathaysia Block,is Precambrian.Here,representative metamorphic rocks from the Qushan Islands were investigated using petro...Debate has persisted over whether the metamorphic basement of the Zhoushan Islands,easternmost Cathaysia Block,is Precambrian.Here,representative metamorphic rocks from the Qushan Islands were investigated using petrography,mineral chemistry,phase equilibria modeling and SHRIMP zircon U-Pb dating to constrain their metamorphic evolution and tectonic significance.Both the pelitic granulites(garnet-kyanite-perthite-biotite-quartz)and the mafic granulites(garnet-clinopyroxene-amphibole-plagioclase-quartz)reached high-pressure granulite-facies conditions of 1.2-1.4 GPa/820-900℃,and recorded three metamorphic stages along a clockwise P-T path with post-peak isothermal decompression.This trajectory indicated rapid exhumation of thickened continental crust during collisional orogeny.Metamorphic ages of 254±3 Ma,262±4 Ma and 259±3 Ma were obtained for mafic granulite,pelitic granulite and marble,respectively,and were consistent with the emplacement age of 259±4 Ma for a pegmatite vein.Detrital zircons in metasediments spanned 2706-330 Ma,which constrained the latest deposition to~330 Ma;thus represented mid-Paleozoic sediment metamorphosed during the late Paleozoic rather than Precambrian basement.We conclude that the Indosinian tectonothermal event in the Cathaysia Block had originated from late Paleozoic-early Mesozoic collisional orogeny between the South China Plate to the north and the Indochina Block to the south.展开更多
We investigated the influence of historical earthquakes on the 2022 Luding M_(S)6.8 earthquake and its subsequent effects.We computed the viscoelastic Coulomb stress changes induced by these historical seismic events ...We investigated the influence of historical earthquakes on the 2022 Luding M_(S)6.8 earthquake and its subsequent effects.We computed the viscoelastic Coulomb stress changes induced by these historical seismic events using the rupture model of historical earthquakes and the layered Maxwell viscoelastic medium model.Our findings indicate that the Luding earthquake was brought forward approximately 29 years because of several historical earthquakes.Specifically,the 1923 Renda M_(S)7.3 earthquake,the 1933 Diexi M_(S)7.5 earthquake,the 1973 Luhuo M_(S)7.3 earthquake,the 2008 Kangding M_(S)5.1 earthquake,the 2008 Wenchuan M_(S)8.0 earthquake,the 2014 Kangding M_(S)6.3 earthquake,and the 2014 Kangding M_(S)5.8 earthquake advanced the occurrence of the event by 117.61,26.67,84.51,0.27,0.91,7.64,and 3.17 years,respectively.Conversely,the 1936 Mabian earthquake swarm,the 1948 Litang M_(S)7.3 earthquake,the 1955 Kangding M_(S)7.5 earthquake,and the 2013 Lushan M_(S)7.0 earthquake delayed its occurrence by 39.89,22.43,144.23,and 4.89 years,respectively.Furthermore,by employing the halfspace homogeneous elastic model and the rupture characteristics of the Luding earthquake,we computed the coseismic Coulomb stress changes in neighboring faults.Our results reveal increased Coulomb stress on the Xianshuihe fault(excluding its southern segment),the Anninghe fault,the Zemuhe fault,the Daliangshan fault,the southern segment of the Longmenshan fault,the northern segment of the Mabian-Yanjin fault,and the Xiaojinhe fault.Conversely,we observed stress decreases in the southern segment of the Jinshajiang fault,the central and eastern segments of the Longriba fault,the Mabian-Yanjin fault(excluding its northern segment),and the southern segment of the Xianshuihe fault.展开更多
The Microwave Land Surface Emissivity(MLSE)atlas and instantaneous simulation of all-sky/all-surface MLSE are important prerequisites for satellite data assimilation.A ten-day/month synthesized FengYun-3D MLSE atlas(N...The Microwave Land Surface Emissivity(MLSE)atlas and instantaneous simulation of all-sky/all-surface MLSE are important prerequisites for satellite data assimilation.A ten-day/month synthesized FengYun-3D MLSE atlas(New_FY3D)was constructed by the two global MLSE daily product datasets,clear-sky(FY-3D1)and clear/cloudy(FY-3D2),which were retrieved from the same FY-3D MicroWave Radiation Imager(MWRI)Level-1 brightness temperature(BT)data from 2021 to 2022,respectively.Then,a set of global MLSE label samples based on the New_FY3D,including 14 surface geophysical parameters,was obtained for an instantaneous global MLSE simulation at a 0.10°spatial resolution by adopting the extreme gradient boosting(XGBoost)machine learning method.Finally,the FengYun-3F(FY-3F)MWRI-II BT simulations using the Advanced Radiative Transfer Modeling System(ARMS)based on the above different MLSE products were evaluated.The results show that the New_FY3D atlas performs well,and the BT simulation at the top of atmosphere is better than that of FY-3D1,FY-3D2,and the international mainstream TELSEM2(Version 2.0 for a Tool to Estimate Land Surface Emissivities in the Microwaves)atlas.Surface roughness,vegetation coverage,land cover type,and snow cover are vital parameters for MLSE simulation.The XGBoost model can accurately simulate all-sky/all-surface MLSE instantaneously over the frequency range 10.65–89.0 GHz.The average simulation determination coefficients(R^(2))under clear-sky and cloud-sky conditions are 0.925 and 0.901,respectively,and the average root-mean-square errors(RMSEs)are 0.018 and 0.021,respectively.Large simulation errors occur in permanent wetland,ice and snow,and urban and built-up areas.With a standard deviation of 6.6 K,the BT simulation based on an XGBoost simulated MLSE is better than those based on New_FY3D and TELSEM2.展开更多
At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused subst...At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused substantial social impact.To reveal the seismogenic structure of the M4.7 Feidong earthquake sequence and assess seismic risks,we use data from both the permanent seismic network and a temporary dense nodal array deployed in the epicentral region prior to the mainshock for:(1)accurate location of the earthquake sequence and determination of the focal mechanisms;(2)obtaining the spatiotemporal distribution,b-value,and half-day occurrence frequency of the earthquake sequence.The Sentinel-1 satellite data are used to analyze the coseismic displacement.Additionally,velocity models from regional tomography and local high-resolution 2D active-and passive-source surveys across the Tanlu fault zone in the epicentral area are also used to reveal the detailed geometry of the seismogenic fault.The results indicate:(1)the M4.7 Feidong earthquake sequence is concentrated around 10.5 km in depth along a NW-dipping,subvertical fault which trends NE and is approximately 5 km in length;the focal mechanism solution also reveals that the fault hosting the mainshock is a subvertical strike-slip fault,driven by the regional compressional stress in ENE-WSW;the coseismic horizontal displacement on the surface caused by the M4.7 mainshock has a maximum value close to 1 mm;(2)the regional velocity model shows significant lateral variation in v_(S) in the source region,with the mainshock occurring in the area with higher velocity;high-resolution P-wave velocity structures obtained by full waveform inversion from active sources,and S-wave velocity structures from passive-source ambient noise tomography indicate that the mainshock occurred along the boundary between high-and low-velocity bodies,and the seismogenic fault dips NW;the deep seismic reflection profiling shows that the mainshock occurred within the Jurassic strata;(3)based on these results,we suggest the seismogenic fault for the M4.7 Feidong earthquake is either the Zhuding-Shimenshan fault,one of the major faults in the Tanlu fault zone,or a hidden fault to the east;the intersection of the NE-trending Tanlu fault zone and the WNW-trending Feizhong fault,along with significant velocity variations,likely create local stress concentrations which could have triggered the M4.7 Feidong earthquake sequence;(4)the strong aftershocks following the M4.7 Feidong mainshock did not further extend the fault rupture zone;the active period of the Zhuding-Shimenshan fault was the late Early Pleistocene to Middle Pleistocene,and the imaging results indicate that this fault does not cut through the shallow Feidong depression.In conjunction with the small coseismic rupture area,it is inferred that the probability of surface-rupturing earthquakes in the future is relatively low.展开更多
Long-period free oscillations provide robust information for the spatio-temporal characteristics of large earthquakes.In this study,we employ a normal-mode summation algorithm to generate threecomponent seismograms wi...Long-period free oscillations provide robust information for the spatio-temporal characteristics of large earthquakes.In this study,we employ a normal-mode summation algorithm to generate threecomponent seismograms within an aspherical,anelastic,and rotating Earth model,focusing on the excitation of seismic normal modes by the 2011 Tohoku megathrust earthquake.Specifically,we analyze the effects of seismic source parameters,including fault geometry,focal depth,and rupture duration.By comparing synthetic free oscillation spectra with observed data,we validate several source mechanisms and emphasize the need for horizontal observations to improve seismic mechanism inversions.Our quantitative analyses reveal that among fault geometry parameters,dip and slip angles have a more pronounced impact on excitation amplitudes than fault strikes.Certain fault configurations enhance the detectability of specific modes,underscoring the relationship between fault geometry and mode excitation.Normal modes also exhibit varying sensitivity to focal depth,with significant excitation amplitude changes at discontinuity boundaries.Additionally,we demonstrate that while rupture duration can be inferred by minimizing differences between observed and synthetic spectra,more extensive records and modes should be included.展开更多
An earthquake of magnitude 6.9 occurred in Tajikistan on February 23,2023.Studying this earthquake is the key to understanding the seismogenic structure of this area.The slip distribution of the M_(W)6.9 earthquake wa...An earthquake of magnitude 6.9 occurred in Tajikistan on February 23,2023.Studying this earthquake is the key to understanding the seismogenic structure of this area.The slip distribution of the M_(W)6.9 earthquake was inverted using InSAR technology and a distributed slip model.The results showed that the seismogenic fault was dominated by a dextral strike-slip motion with a small number of normal fault components.The average strike is 124°,the dip angle is 86°,the maximum slip is 0.7 m,and the moment magnitude is M_(W)6.85.The epicenter is located in the gradient zone of the effective elastic thickness of the lithosphere and the edge of the high-value zone of the GNSS shear strain.Simultaneously,the Coulomb stress generated by strong historical earthquakes had a certain degree of loading on the seismogenic fault of this earthquake,and these factors trigger the earthquake.The static Coulomb stress caused by the 2023 Tajikistan M_(W)6.9 earthquake indicated that the NW direction along the strike direction of the fault is a risk area for medium-strong earthquakes in the future.展开更多
The Arab Conference on Astronomy and Geophysics is a prominent biennial event that has been convening for 16 years.Hosted by the National Research Institute of Astronomy and Geophysics(NRIAG),the conference serves as ...The Arab Conference on Astronomy and Geophysics is a prominent biennial event that has been convening for 16 years.Hosted by the National Research Institute of Astronomy and Geophysics(NRIAG),the conference serves as a unique platform for presenting and discussing the latest advancements in astronomy and geophysics.Attended by representatives from Arab and international institutions,the conference facilitates knowledge sharing,collaborative research,and the dissemination of cuttingedge scientific findings.The 8th edition,held from October 9 to 12,2023,brought together leading scientists,researchers,and academics from across the globe.Participants included keynote speakers.展开更多
We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The resu...We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.展开更多
In the Mesoproterozoic time, the northern part of the Sino-Korean Plate experienced a period of intensive tectonic extension and breakup. 1. An abundance of sedimentary earthquake records is preserved in the Chuanling...In the Mesoproterozoic time, the northern part of the Sino-Korean Plate experienced a period of intensive tectonic extension and breakup. 1. An abundance of sedimentary earthquake records is preserved in the Chuanlinggou, Tuanshanzi and Gaoyuzhuang formations in the Mesoproterozoic Changcheng System （1800-1400 Ma） and in the Mesoproterozoic Wumishan Formation of the Jixian System （1400-1000 Ma）. These earthquake records are characterized by various liquefied sand-veins, carbonate microspar and coarser spar veins, limestone dikes, liquefied breccia and various forms of liquefied contorted bedding. This deformation is always associated with synsedimentary faults and igneous activity. 2. Three liquefaction models for soft carbonate sediments are recognized, including liquefaction in laminated carbonate rocks, liquefaction in thin-bedded carbonates and large-scale liquefaction along huge carbonate dikes. 3. Based on the record of earthquake and volcanic activities, the Sino-Korean Plate experienced at least twice intraplate breakups. One occurred between 1800-1400 Ma, and the other occurred at about 1200 Ma. The last breakup resulted in formation of the Yan-Liao aulacogen, a tectonic zone characterized by deeper material vibrancy, active faults, major igneous activity and frequent earthquakes.展开更多
The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define thos...The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define those problems,a 1:50000 active tectonic mapping was carried out along the northern segment of the Chenghai-Binchuan fault zone.The result shows that there is an at least 25 km-long surface rupture and a series of seismic landslides distributed along the Jinguan fault and the Chenghai fault.Radiocarbon dating of the 14C samples indicates that the surface rupture should be a part of the deformation zone caused by the Yongsheng earthquake in the year 1515.The distribution characteristics of this surface rupture indicate that the macroscopic epicenter of the 1515 Yongsheng earthquake may be located near Hongshiya,and the seismogenic fault of this earthquake is the Jinguan-Chenghai fault,the northern part of the Chenghai-Binchuan fault zone.Striations on the surface rupture show that the latest motion of the fault is normal faulting.The maximum co-seismic vertical displacement can be 3.8 m,according to the empirical formula for the fault displacement and moment magnitude relationship,the moment magnitude of the Yongsheng earthquake was Mw 7.3-7.4.Furthermore,combining published age data with the 14C data in this paper reveals that at least four large earthquakes of similar size to the 1515 Yongsheng earthquake,have taken place across the northern segment of the Chenghai-Binchuan fault zone since 17190~50 yr.BP.The in-situ recurrence interval of Mw 7.3-7.4 characteristic earthquakes in Yongsheng along this fault zone is possibly on the order of 6 ka.展开更多
We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, includ...We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, including 54 525 seismograms from 1 376 local earthquakes over Ms3.5 between 12 May 2008 and 3 August 2008. The cross-correlation technique used in this paper has greatly improved the relocation precision by giving much more accurate P-wave differential travel-time measurements than those obtained from routinely picked phase onsets. At the same time, we pick P-wave polarity observations of the Wenchuan earthquake series （hereafter referred to as WES） from 1023 stations in China and 59 IRIS （Incorporated Research Institutions of Seismology） stations. Then, employing a newly developed program CHNYTX, we obtain 83 well-determined focal mechanism solutions （hereafter referred to as FMSs）. Based on spatial distribution and FMSs of the WES, we draw following conclusions： （1） The region near the main shock exhibits a buried low-angle northwest-dipping seismic zone with the main shock at its upper end and two conjugated seismic zones dipping southeast with roughly equal dip-angle; （2） The compressional directions of all kinds of FMSs of the WES are subhorizontal, which reflects the dominant stress in this area is eompressional; （3） The principal compressional direction of the regional stress around Wenchuan is roughly perpendicular to the strike of Beichuan-Yingxiu fault, while around Qingchuan it is roughly parallel to the strike of Qingehuan fault. In intermediate part of the Longmenshan area, the principal compressional direction of the stress should be in-between; （4） The possibly existed molten materials in the lower crust of Songpan-Garze terrain have small contribution to the local stress state in Longmenshan area. The listric geometries of the Longmenshan faults most probably resulted from subhorizontal compression along NW-SE direction in history.展开更多
According to the China Earthquake Networks Center,a strong earthquake of M6.8 occurred in Luding County,Ganzi Tibetan Autonomous Prefecture,Sichuan Province,China(102.08°E,29.59°N),on September 5,2022,with a...According to the China Earthquake Networks Center,a strong earthquake of M6.8 occurred in Luding County,Ganzi Tibetan Autonomous Prefecture,Sichuan Province,China(102.08°E,29.59°N),on September 5,2022,with a focal depth of 16 km.Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue,disaster assessment,and scientific research.Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters.The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data.Using these near-field observations and conventional mid-and far-field seismic waveform records,we obtained the focal mechanism solutions of the mainshock and M≥3.0 aftershocks through the waveform fitting method.We were further able to rapidly invert the rupture process of the mainshock.Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting,we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake.The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms,reflecting the segmented nature of the Xianshuihe fault.As more high-frequency information has been applied in this study,the absolute location of the fault rupture is better constrained by the near-field strong-motion data.The rupture process of the mainshock correlates well with the spatial distribution of aftershocks,i.e.,aftershock activities were relatively weak in the maximum slip area,and strong aftershock activities were distributed in the peripheral regions.展开更多
Because ambient seismic noise provides estimated Green’s function （EGF） between two sites with high accuracy, Rayleigh wave propagation along the path connecting the two sites is well resolved. Therefore, earthquak...Because ambient seismic noise provides estimated Green’s function （EGF） between two sites with high accuracy, Rayleigh wave propagation along the path connecting the two sites is well resolved. Therefore, earthquakes which are close to one seismic station can be well located with calibration extracting from EGF. We test two algorithms in locating the 1998 Zhangbei earthquake, one algorithm is waveform-based, and the other is traveltime-based. We first compute EGF between station ZHB （a station about 40 km away from the epicenter） and five IC/IRIS stations. With the waveform-based approach, we calculate 1D synthetic single-force Green’s functions between ZHB and other four stations, and obtain traveltime corrections by correlating synthetic Green’s functions with EGFs in period band of 10–30 s. Then we locate the earthquake by minimizing the differential travel times between observed earthquake waveform and the 1D synthetic earthquake waveforms computed with focal mechanism provided by Global CMT after traveltime correction from EGFs. This waveform-based approach yields a location which error is about 13 km away from the location observed with InSAR. With the traveltime-based approach, we begin with measuring group velocity from EGFs as well as group arrival time on observed earthquake waveforms, and then locate the earthquake by minimizing the difference between observed group arrival time and arrival time measured on EGFs. This traveltime-based approach yields accuracy of 3 km, Therefore it is feasible to achieve GT5 （ground truth location with accuracy 5 km） with ambient seismic noises. The less accuracy of the waveform-based approach was mainly caused by uncertainty of focal mechanism.展开更多
Abstract The 2008 Wenchuan earthquake, a major intraplate earthquake with Mw 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge o...Abstract The 2008 Wenchuan earthquake, a major intraplate earthquake with Mw 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions （FMSs） of the 2008 Wenchuan earthquake sequence （WES） using both P-wave first-motion polarity data and SH/P amplitude ratio （AR） data. As P-wave polarities are more reliable information, they are given priority over SH/ PAR, the latter of which are used only when the former has loose constraint on the FMSs. We collect data from three categories： （1） permanent stations deployed by the China Earthquake Administration （CEA）; （2） the Western Sichuan Passive Seismic Array （WSPSA） deployed by Institute of Geology, CEA; （3） global stations from Incorporated Research Institutions for Seismology. Finally, 129 events with magnitude over Ms 4.0 in the 2008 WES are identified to have well-constrained FMSs. Among them, 83 are well constrained by P-wave polarities only as shown by Cai et al. （Earthq Sci 24（1）：115-125,2011）, and the rest of which are newly constrained by incorporating SH/P AR. Based on the spatial distribution and FMSs of the WES, we draw following conclusions： （1） the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. （2011） but with a few modifications that the compressional directions are WNW-ESE around Wenchuan and ENE-WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a leftlateral rotation, which agrees well with regional stress field inverted by former researchers （e.g., Xu et al., Acta Seismol Sin 30（5）, 1987; Acta Geophys Sin 32（6）, 1989; Cui et al., Seismol Geol 27（2）：234-242, 2005）; （2） the FMSs of the events not only reflected the regional stress state of the Longmenshan region, but also were obviously controlled by the faults to some extent, which was pointed out by Cai et al. （2011） and Yi et al. （Chin J Geophys 55（4）：1213-1227, 2012）; （3） while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmen- shan fault, some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008 Wenchuan earthquake and some of its strong aftershocks. （4） Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly propose that there is less probability for great earthquakes in the middle part of the Longmenshan fault in the near future, although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future.展开更多
In January 2010, the Suining Ms5.0 earthquake occurred in central Sichuan Basin, with the epicenter in Moxi-Longnvsi structural belt and a focal depth of 10 km. Based on structural interpretations of seismic profiles ...In January 2010, the Suining Ms5.0 earthquake occurred in central Sichuan Basin, with the epicenter in Moxi-Longnvsi structural belt and a focal depth of 10 km. Based on structural interpretations of seismic profiles in this area, we recognized a regional detachment fault located at a depth of 9-10 km in the Presinian basement of the Suining area, transferring its slipping from NW to SE orientation. This detachment fault slipped from NW to SE, and underwent several shears and bends, which caused the basement to be rolled in and the overlaying strata fold deformation. It formed a fault-bend fold in the Moxi area with an approximate slip of 4 km. Correspondingly, the formation of the Moxi anticline is related to the detachment fault. With the earthquake＇s epicenter on the ramp of the detachment fault, there is a new point of view that the Suining earthquake was caused by re-activation of this basement detachment fault. Since the Late Jurassic period, under the influence of regional tectonic stress, the detachment fault transfered its slip from the Longmen Mountains （LMS） thrust belt to the hinterland of the Sichuan Basin, and finally to the piedmont zone of southwest Huayingshan （HYS）, which indicates that HYS might be the final front area of the LMS thrust belt.展开更多
The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our unde...The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth.Here,static calculations demonstrate that the pyrite-type FeO2 H-FeO2 system has a high density and Poisson's ratio and ultra-low seismic velocities at conditions of Earth's lowermost mantle.It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth's D″layer.The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity(VS)but increase the bulk sound velocity(VΦ),and can potentially explain the observed anti-correlation of VS and VΦin the lowermost mantle.Additionally,FeO2 H exhibits nearly isotropic whereas Fe O2 is highly anisotropic,which may help understand some seismic anisotropies at the core-mantle boundary.展开更多
On May 12,2008,an Mw7.9 earthquake occurred in Wenchuan County,Sichuan Province,China.Movement of Yingxiu–Beichuan Fault in the Longmenshan Fault Zone was considered to be the main cause of the earthquake.Earthquakes...On May 12,2008,an Mw7.9 earthquake occurred in Wenchuan County,Sichuan Province,China.Movement of Yingxiu–Beichuan Fault in the Longmenshan Fault Zone was considered to be the main cause of the earthquake.Earthquakes are closely related to fault activities.Therefore,studying the strain distribution and evolution process around active fault zones is important to the understanding of seismic activities.In this study,we conduct laboratory experiments with uniaxial compression applied to marble sheets with intentionally fabricated cracks.The speckle patterns of the rock samples under different loading conditions are recorded in real time by a digital camera.To calculate the deformation fields of the deliberately cracked marble sheets during different stages of the loading processes,the recorded images are processed by the digital image correlation method.The distribution and variation of the displacement and strain are further analyzed in order to understand the strain localization of and observed damage in the experimental fracture zones.Finally,we compare these laboratory results with the GPS-observed coseismic displacements during the 2008 Wenchuan earthquake,to assess the consistency between our laboratory observations and the field observations of the earthquake,but also to suggest how laboratory results can improve thinking about how earthquake patterns do and do not reflect fault patterns.展开更多
The Tan-Lu Fault Zone is a large NNE-trending fault zone that has a substantial effect on the development of eastern China and its earthquake disaster prevention efforts. Aiming at the azimuthally anisotropic structur...The Tan-Lu Fault Zone is a large NNE-trending fault zone that has a substantial effect on the development of eastern China and its earthquake disaster prevention efforts. Aiming at the azimuthally anisotropic structure in the upper crust and seismogenic tectonics in the Hefei segment of this fault, we collected phase velocity dispersion data of fundamental mode Rayleigh waves from ambient noise cross-correlation functions of ~400 temporal seismographs in an area of approximately 80 × 70 km along the fault zone. The period band of the dispersion data was ~0.5–10 s. We inverted for the upper crustal three-dimensional(3-D) shear velocity model with azimuthal anisotropy from the surface to 10 km depth by using a 3-D direct azimuthal anisotropy inversion method. The inversion result shows the spatial distribution characteristics of the tectonic units in the upper crust. Additionally, the deformation of the Tan-Lu Fault Zone and its conjugated fault systems could be inferred from the anisotropy model. In particular, the faults that have remained active from the early and middle Pleistocene control the anisotropic characteristics of the upper crustal structure in this area. The direction of fast axes near the fault zone area in the upper crust is consistent with the strike of the faults, whereas for the region far away from the fault zone, the direction of fast axes is consistent with the direction of the regional principal stress caused by plate movement. Combined with the azimuthal anisotropy models in the deep crust and uppermost mantle from the surface wave and Pn wave, the different anisotropic patterns caused by the Tan-Lu Fault Zone and its conjugated fault system nearby are shown in the upper and lower crust. Furthermore,by using the double-difference method, we relocated the Lujiang earthquake series, which contained 32 earthquakes with a depth shallower than 10 km. Both the Vs model and earthquake relocation results indicate that earthquakes mostly occurred in the vicinity of structural boundaries with fractured media, with high-level development of cracks and small-scale faults jammed between more rigid areas.展开更多
The complex tectonic background of East Asia makes it an ideal region for investigating the evolution of the continental lithosphere,for which high-resolution lithospheric structural models are essential.In this study...The complex tectonic background of East Asia makes it an ideal region for investigating the evolution of the continental lithosphere,for which high-resolution lithospheric structural models are essential.In this study,we measured Rayleigh-wave phase-velocity dispersion curves at periods of 10-120 s and group velocity dispersion curves at periods of 10-140 s using event records from more than 1,000 seismic stations in and around China.By jointly inverting new and previously published dispersion data from ambient noise and earthquakes,we developed a high-resolution shear-wave velocity model down to a depth of~300 km beneath East Asia.Our model revealed heterogeneous lithospheric structures beneath East Asia,and allowed us to investigate the velocity structure of the entire lithosphere.We also derived crustal and lithospheric thickness models from the three-dimensional(3D)shear-wave model,revealing strong spatial heterogeneity and a general thinning trend of lithospheric thickness from west to east across the study region.Overall,our models reveal important lithospheric features beneath East Asia and provide a valuable baseline dataset for understanding continental-scale dynamics and evolution.展开更多
The Longmenshan(LMS)fault zone is located at the junction of the eastern Tibetan Plateau and the Sichuan Basin and is of great significance for studying regional tectonics and earthquake hazards.Although regional velo...The Longmenshan(LMS)fault zone is located at the junction of the eastern Tibetan Plateau and the Sichuan Basin and is of great significance for studying regional tectonics and earthquake hazards.Although regional velocity models are available for the LMS fault zone,high-resolution velocity models are lacking.Therefore,a dense array of 240 short-period seismometers was deployed around the central segment of the LMS fault zone for approximately 30 days to monitor earthquakes and characterize fine structures of the fault zone.Considering the large quantity of observed seismic data,the data processing workflow consisted of deep learning-based automatic earthquake detection,phase arrival picking,and association.Compared with the earthquake catalog released by the China Earthquake Administration,many more earthquakes were detected by the dense array.Double-difference seismic tomography was adopted to determine V_(p),V_(s),and V_(p)/V_(s)models as well as earthquake locations.The checkerboard test showed that the velocity models have spatial resolutions of approximately 5 km in the horizontal directions and 2 km at depth.To the west of the Yingxiu–Beichuan Fault(YBF),the Precambrian Pengguan complex,where most of earthquakes occurred,is characterized by high velocity and low V_(p)/V_(s)values.In comparison,to the east of the YBF,the Upper Paleozoic to Jurassic sediments,where few earthquakes occurred,show low velocity and high V_(p)/V_(s)values.Our results suggest that the earthquake activity in the LMS fault zone is controlled by the strength of the rock compositions.When the high-resolution velocity models were combined with the relocated earthquakes,we were also able to delineate the fault geometry for different faults in the LMS fault zone.展开更多
基金supported by the National Natural Science Foundation of China(42072223)Geological Survey project(DD20221649,DD20231429).
文摘Debate has persisted over whether the metamorphic basement of the Zhoushan Islands,easternmost Cathaysia Block,is Precambrian.Here,representative metamorphic rocks from the Qushan Islands were investigated using petrography,mineral chemistry,phase equilibria modeling and SHRIMP zircon U-Pb dating to constrain their metamorphic evolution and tectonic significance.Both the pelitic granulites(garnet-kyanite-perthite-biotite-quartz)and the mafic granulites(garnet-clinopyroxene-amphibole-plagioclase-quartz)reached high-pressure granulite-facies conditions of 1.2-1.4 GPa/820-900℃,and recorded three metamorphic stages along a clockwise P-T path with post-peak isothermal decompression.This trajectory indicated rapid exhumation of thickened continental crust during collisional orogeny.Metamorphic ages of 254±3 Ma,262±4 Ma and 259±3 Ma were obtained for mafic granulite,pelitic granulite and marble,respectively,and were consistent with the emplacement age of 259±4 Ma for a pegmatite vein.Detrital zircons in metasediments spanned 2706-330 Ma,which constrained the latest deposition to~330 Ma;thus represented mid-Paleozoic sediment metamorphosed during the late Paleozoic rather than Precambrian basement.We conclude that the Indosinian tectonothermal event in the Cathaysia Block had originated from late Paleozoic-early Mesozoic collisional orogeny between the South China Plate to the north and the Indochina Block to the south.
基金supported by the National Natural Science Foundation of China(Nos.42174074,and 41674055).
文摘We investigated the influence of historical earthquakes on the 2022 Luding M_(S)6.8 earthquake and its subsequent effects.We computed the viscoelastic Coulomb stress changes induced by these historical seismic events using the rupture model of historical earthquakes and the layered Maxwell viscoelastic medium model.Our findings indicate that the Luding earthquake was brought forward approximately 29 years because of several historical earthquakes.Specifically,the 1923 Renda M_(S)7.3 earthquake,the 1933 Diexi M_(S)7.5 earthquake,the 1973 Luhuo M_(S)7.3 earthquake,the 2008 Kangding M_(S)5.1 earthquake,the 2008 Wenchuan M_(S)8.0 earthquake,the 2014 Kangding M_(S)6.3 earthquake,and the 2014 Kangding M_(S)5.8 earthquake advanced the occurrence of the event by 117.61,26.67,84.51,0.27,0.91,7.64,and 3.17 years,respectively.Conversely,the 1936 Mabian earthquake swarm,the 1948 Litang M_(S)7.3 earthquake,the 1955 Kangding M_(S)7.5 earthquake,and the 2013 Lushan M_(S)7.0 earthquake delayed its occurrence by 39.89,22.43,144.23,and 4.89 years,respectively.Furthermore,by employing the halfspace homogeneous elastic model and the rupture characteristics of the Luding earthquake,we computed the coseismic Coulomb stress changes in neighboring faults.Our results reveal increased Coulomb stress on the Xianshuihe fault(excluding its southern segment),the Anninghe fault,the Zemuhe fault,the Daliangshan fault,the southern segment of the Longmenshan fault,the northern segment of the Mabian-Yanjin fault,and the Xiaojinhe fault.Conversely,we observed stress decreases in the southern segment of the Jinshajiang fault,the central and eastern segments of the Longriba fault,the Mabian-Yanjin fault(excluding its northern segment),and the southern segment of the Xianshuihe fault.
基金supported by the National Natural Science Foundation of China(Grant No.U2242211)the Hunan Provincial Natural Science Foundation Major Project(Grant No.2021JC0009).
文摘The Microwave Land Surface Emissivity(MLSE)atlas and instantaneous simulation of all-sky/all-surface MLSE are important prerequisites for satellite data assimilation.A ten-day/month synthesized FengYun-3D MLSE atlas(New_FY3D)was constructed by the two global MLSE daily product datasets,clear-sky(FY-3D1)and clear/cloudy(FY-3D2),which were retrieved from the same FY-3D MicroWave Radiation Imager(MWRI)Level-1 brightness temperature(BT)data from 2021 to 2022,respectively.Then,a set of global MLSE label samples based on the New_FY3D,including 14 surface geophysical parameters,was obtained for an instantaneous global MLSE simulation at a 0.10°spatial resolution by adopting the extreme gradient boosting(XGBoost)machine learning method.Finally,the FengYun-3F(FY-3F)MWRI-II BT simulations using the Advanced Radiative Transfer Modeling System(ARMS)based on the above different MLSE products were evaluated.The results show that the New_FY3D atlas performs well,and the BT simulation at the top of atmosphere is better than that of FY-3D1,FY-3D2,and the international mainstream TELSEM2(Version 2.0 for a Tool to Estimate Land Surface Emissivities in the Microwaves)atlas.Surface roughness,vegetation coverage,land cover type,and snow cover are vital parameters for MLSE simulation.The XGBoost model can accurately simulate all-sky/all-surface MLSE instantaneously over the frequency range 10.65–89.0 GHz.The average simulation determination coefficients(R^(2))under clear-sky and cloud-sky conditions are 0.925 and 0.901,respectively,and the average root-mean-square errors(RMSEs)are 0.018 and 0.021,respectively.Large simulation errors occur in permanent wetland,ice and snow,and urban and built-up areas.With a standard deviation of 6.6 K,the BT simulation based on an XGBoost simulated MLSE is better than those based on New_FY3D and TELSEM2.
基金supported by the Anhui Province Science and Technology Breakthrough Plan Project(Key Project,No.202423l10050030)the National Natural Science Foundation of China(Fundamental Science Center Category B,No.4248830017)+4 种基金the Joint Funds of National Natural Science Foundation of China(No.U2139204)the National Natural Science Foundation of China Project(No.42104063)the Hefei Government Key Construction Project(No.2024BFFFD02048)the Earthquake Science and Technology Spark Program of the China Earthquake Administration(Nos.XH23020YA,XH24020B)the Anhui Mengcheng National Geophysical Observatory Joint Open Fund(No.MENGO-202307).
文摘At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused substantial social impact.To reveal the seismogenic structure of the M4.7 Feidong earthquake sequence and assess seismic risks,we use data from both the permanent seismic network and a temporary dense nodal array deployed in the epicentral region prior to the mainshock for:(1)accurate location of the earthquake sequence and determination of the focal mechanisms;(2)obtaining the spatiotemporal distribution,b-value,and half-day occurrence frequency of the earthquake sequence.The Sentinel-1 satellite data are used to analyze the coseismic displacement.Additionally,velocity models from regional tomography and local high-resolution 2D active-and passive-source surveys across the Tanlu fault zone in the epicentral area are also used to reveal the detailed geometry of the seismogenic fault.The results indicate:(1)the M4.7 Feidong earthquake sequence is concentrated around 10.5 km in depth along a NW-dipping,subvertical fault which trends NE and is approximately 5 km in length;the focal mechanism solution also reveals that the fault hosting the mainshock is a subvertical strike-slip fault,driven by the regional compressional stress in ENE-WSW;the coseismic horizontal displacement on the surface caused by the M4.7 mainshock has a maximum value close to 1 mm;(2)the regional velocity model shows significant lateral variation in v_(S) in the source region,with the mainshock occurring in the area with higher velocity;high-resolution P-wave velocity structures obtained by full waveform inversion from active sources,and S-wave velocity structures from passive-source ambient noise tomography indicate that the mainshock occurred along the boundary between high-and low-velocity bodies,and the seismogenic fault dips NW;the deep seismic reflection profiling shows that the mainshock occurred within the Jurassic strata;(3)based on these results,we suggest the seismogenic fault for the M4.7 Feidong earthquake is either the Zhuding-Shimenshan fault,one of the major faults in the Tanlu fault zone,or a hidden fault to the east;the intersection of the NE-trending Tanlu fault zone and the WNW-trending Feizhong fault,along with significant velocity variations,likely create local stress concentrations which could have triggered the M4.7 Feidong earthquake sequence;(4)the strong aftershocks following the M4.7 Feidong mainshock did not further extend the fault rupture zone;the active period of the Zhuding-Shimenshan fault was the late Early Pleistocene to Middle Pleistocene,and the imaging results indicate that this fault does not cut through the shallow Feidong depression.In conjunction with the small coseismic rupture area,it is inferred that the probability of surface-rupturing earthquakes in the future is relatively low.
基金supported by the National Natural ScienceFoundation of China(42204003,42274011,42388102,42192533,42192531)the Natural Science Foundation of Wuhan(2024040701010027)+1 种基金the Open Fund Supported by the State KeyLaboratory of Precision Geodesy,Innovation Academy for PrecisionMeasurement Science and Technology,Chinese Academy of Sci-ences(SKLGED2024-1-1)the Open Fund Supported by KeyLaboratory of Polar Environment Monitoring and Public Gover-nance(Wuhan University),Ministry of Education(202401)。
文摘Long-period free oscillations provide robust information for the spatio-temporal characteristics of large earthquakes.In this study,we employ a normal-mode summation algorithm to generate threecomponent seismograms within an aspherical,anelastic,and rotating Earth model,focusing on the excitation of seismic normal modes by the 2011 Tohoku megathrust earthquake.Specifically,we analyze the effects of seismic source parameters,including fault geometry,focal depth,and rupture duration.By comparing synthetic free oscillation spectra with observed data,we validate several source mechanisms and emphasize the need for horizontal observations to improve seismic mechanism inversions.Our quantitative analyses reveal that among fault geometry parameters,dip and slip angles have a more pronounced impact on excitation amplitudes than fault strikes.Certain fault configurations enhance the detectability of specific modes,underscoring the relationship between fault geometry and mode excitation.Normal modes also exhibit varying sensitivity to focal depth,with significant excitation amplitude changes at discontinuity boundaries.Additionally,we demonstrate that while rupture duration can be inferred by minimizing differences between observed and synthetic spectra,more extensive records and modes should be included.
基金sponsored in part by the National Natural Science Foundation of China(No.42274014,41874015)National Key R&D Projects of China(No.2022YFC3003703)+3 种基金the State Administration of Foreign Experts Affairs Talent Introduction Project(No.G2022045013L)Key R&D Program of Xinjiang Uygur Autonomous Region(No.2022B03001-1,2020B03006-2)Third Xinjiang Scientific Examination(No.2022xjkk1305)the Open Fund for Xinjiang Key Laboratory of Geological Disaster Prevention and Control(No.XKLGP2022K01)。
文摘An earthquake of magnitude 6.9 occurred in Tajikistan on February 23,2023.Studying this earthquake is the key to understanding the seismogenic structure of this area.The slip distribution of the M_(W)6.9 earthquake was inverted using InSAR technology and a distributed slip model.The results showed that the seismogenic fault was dominated by a dextral strike-slip motion with a small number of normal fault components.The average strike is 124°,the dip angle is 86°,the maximum slip is 0.7 m,and the moment magnitude is M_(W)6.85.The epicenter is located in the gradient zone of the effective elastic thickness of the lithosphere and the edge of the high-value zone of the GNSS shear strain.Simultaneously,the Coulomb stress generated by strong historical earthquakes had a certain degree of loading on the seismogenic fault of this earthquake,and these factors trigger the earthquake.The static Coulomb stress caused by the 2023 Tajikistan M_(W)6.9 earthquake indicated that the NW direction along the strike direction of the fault is a risk area for medium-strong earthquakes in the future.
文摘The Arab Conference on Astronomy and Geophysics is a prominent biennial event that has been convening for 16 years.Hosted by the National Research Institute of Astronomy and Geophysics(NRIAG),the conference serves as a unique platform for presenting and discussing the latest advancements in astronomy and geophysics.Attended by representatives from Arab and international institutions,the conference facilitates knowledge sharing,collaborative research,and the dissemination of cuttingedge scientific findings.The 8th edition,held from October 9 to 12,2023,brought together leading scientists,researchers,and academics from across the globe.Participants included keynote speakers.
基金supported by the Basic Research Fund of the Institute of Earthquake Forecasting,China Earthquake Administration(2015IES010302)the State Key Laboratory of Geodesy and Earth’s Dynamics,Institute of Geodesy and Geophysics,Chinese Academy of Sciences(SKLGED2018-4-3-E)
文摘We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.
文摘In the Mesoproterozoic time, the northern part of the Sino-Korean Plate experienced a period of intensive tectonic extension and breakup. 1. An abundance of sedimentary earthquake records is preserved in the Chuanlinggou, Tuanshanzi and Gaoyuzhuang formations in the Mesoproterozoic Changcheng System （1800-1400 Ma） and in the Mesoproterozoic Wumishan Formation of the Jixian System （1400-1000 Ma）. These earthquake records are characterized by various liquefied sand-veins, carbonate microspar and coarser spar veins, limestone dikes, liquefied breccia and various forms of liquefied contorted bedding. This deformation is always associated with synsedimentary faults and igneous activity. 2. Three liquefaction models for soft carbonate sediments are recognized, including liquefaction in laminated carbonate rocks, liquefaction in thin-bedded carbonates and large-scale liquefaction along huge carbonate dikes. 3. Based on the record of earthquake and volcanic activities, the Sino-Korean Plate experienced at least twice intraplate breakups. One occurred between 1800-1400 Ma, and the other occurred at about 1200 Ma. The last breakup resulted in formation of the Yan-Liao aulacogen, a tectonic zone characterized by deeper material vibrancy, active faults, major igneous activity and frequent earthquakes.
基金supported by National Natural Science foundation of China(grants No.41571013)China Geology Survey project(grants No.DD20160268)Institute of Geomechanics,Chinese academy of geological sciences basal research fund(grants No.DZLXJK201702)
文摘The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define those problems,a 1:50000 active tectonic mapping was carried out along the northern segment of the Chenghai-Binchuan fault zone.The result shows that there is an at least 25 km-long surface rupture and a series of seismic landslides distributed along the Jinguan fault and the Chenghai fault.Radiocarbon dating of the 14C samples indicates that the surface rupture should be a part of the deformation zone caused by the Yongsheng earthquake in the year 1515.The distribution characteristics of this surface rupture indicate that the macroscopic epicenter of the 1515 Yongsheng earthquake may be located near Hongshiya,and the seismogenic fault of this earthquake is the Jinguan-Chenghai fault,the northern part of the Chenghai-Binchuan fault zone.Striations on the surface rupture show that the latest motion of the fault is normal faulting.The maximum co-seismic vertical displacement can be 3.8 m,according to the empirical formula for the fault displacement and moment magnitude relationship,the moment magnitude of the Yongsheng earthquake was Mw 7.3-7.4.Furthermore,combining published age data with the 14C data in this paper reveals that at least four large earthquakes of similar size to the 1515 Yongsheng earthquake,have taken place across the northern segment of the Chenghai-Binchuan fault zone since 17190~50 yr.BP.The in-situ recurrence interval of Mw 7.3-7.4 characteristic earthquakes in Yongsheng along this fault zone is possibly on the order of 6 ka.
基金supported by the Wenchuan Fault Scientific Drilling Program(WFSD),the Key Projects in the National Science and Technology Pillar Program during the Eleventh Five-year Plan Period under grant No. 2008BAC38B02-4the National Natural Science Foundation of China under grant No. 40821062
文摘We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, including 54 525 seismograms from 1 376 local earthquakes over Ms3.5 between 12 May 2008 and 3 August 2008. The cross-correlation technique used in this paper has greatly improved the relocation precision by giving much more accurate P-wave differential travel-time measurements than those obtained from routinely picked phase onsets. At the same time, we pick P-wave polarity observations of the Wenchuan earthquake series （hereafter referred to as WES） from 1023 stations in China and 59 IRIS （Incorporated Research Institutions of Seismology） stations. Then, employing a newly developed program CHNYTX, we obtain 83 well-determined focal mechanism solutions （hereafter referred to as FMSs）. Based on spatial distribution and FMSs of the WES, we draw following conclusions： （1） The region near the main shock exhibits a buried low-angle northwest-dipping seismic zone with the main shock at its upper end and two conjugated seismic zones dipping southeast with roughly equal dip-angle; （2） The compressional directions of all kinds of FMSs of the WES are subhorizontal, which reflects the dominant stress in this area is eompressional; （3） The principal compressional direction of the regional stress around Wenchuan is roughly perpendicular to the strike of Beichuan-Yingxiu fault, while around Qingchuan it is roughly parallel to the strike of Qingehuan fault. In intermediate part of the Longmenshan area, the principal compressional direction of the stress should be in-between; （4） The possibly existed molten materials in the lower crust of Songpan-Garze terrain have small contribution to the local stress state in Longmenshan area. The listric geometries of the Longmenshan faults most probably resulted from subhorizontal compression along NW-SE direction in history.
基金supported by the China Spark Program of Earthquake Science and Technology(No.XH23051B)National Key R&D Program on Monitoring,Early Warning and Prevention of Major Natural Disaster(No.2017YFC1500304)。
文摘According to the China Earthquake Networks Center,a strong earthquake of M6.8 occurred in Luding County,Ganzi Tibetan Autonomous Prefecture,Sichuan Province,China(102.08°E,29.59°N),on September 5,2022,with a focal depth of 16 km.Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue,disaster assessment,and scientific research.Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters.The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data.Using these near-field observations and conventional mid-and far-field seismic waveform records,we obtained the focal mechanism solutions of the mainshock and M≥3.0 aftershocks through the waveform fitting method.We were further able to rapidly invert the rupture process of the mainshock.Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting,we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake.The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms,reflecting the segmented nature of the Xianshuihe fault.As more high-frequency information has been applied in this study,the absolute location of the fault rupture is better constrained by the near-field strong-motion data.The rupture process of the mainshock correlates well with the spatial distribution of aftershocks,i.e.,aftershock activities were relatively weak in the maximum slip area,and strong aftershock activities were distributed in the peripheral regions.
基金supported by Chinese Acadmy of Sciences Fund(No.KCZX-YW-116-1)Joint Seismological Science Fundation of China (Nos.20080878 and 200708035)
文摘Because ambient seismic noise provides estimated Green’s function （EGF） between two sites with high accuracy, Rayleigh wave propagation along the path connecting the two sites is well resolved. Therefore, earthquakes which are close to one seismic station can be well located with calibration extracting from EGF. We test two algorithms in locating the 1998 Zhangbei earthquake, one algorithm is waveform-based, and the other is traveltime-based. We first compute EGF between station ZHB （a station about 40 km away from the epicenter） and five IC/IRIS stations. With the waveform-based approach, we calculate 1D synthetic single-force Green’s functions between ZHB and other four stations, and obtain traveltime corrections by correlating synthetic Green’s functions with EGFs in period band of 10–30 s. Then we locate the earthquake by minimizing the differential travel times between observed earthquake waveform and the 1D synthetic earthquake waveforms computed with focal mechanism provided by Global CMT after traveltime correction from EGFs. This waveform-based approach yields a location which error is about 13 km away from the location observed with InSAR. With the traveltime-based approach, we begin with measuring group velocity from EGFs as well as group arrival time on observed earthquake waveforms, and then locate the earthquake by minimizing the difference between observed group arrival time and arrival time measured on EGFs. This traveltime-based approach yields accuracy of 3 km, Therefore it is feasible to achieve GT5 （ground truth location with accuracy 5 km） with ambient seismic noises. The less accuracy of the waveform-based approach was mainly caused by uncertainty of focal mechanism.
基金supported by the Wenchuan Fault Scientific Drilling Program(WFSD)
文摘Abstract The 2008 Wenchuan earthquake, a major intraplate earthquake with Mw 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions （FMSs） of the 2008 Wenchuan earthquake sequence （WES） using both P-wave first-motion polarity data and SH/P amplitude ratio （AR） data. As P-wave polarities are more reliable information, they are given priority over SH/ PAR, the latter of which are used only when the former has loose constraint on the FMSs. We collect data from three categories： （1） permanent stations deployed by the China Earthquake Administration （CEA）; （2） the Western Sichuan Passive Seismic Array （WSPSA） deployed by Institute of Geology, CEA; （3） global stations from Incorporated Research Institutions for Seismology. Finally, 129 events with magnitude over Ms 4.0 in the 2008 WES are identified to have well-constrained FMSs. Among them, 83 are well constrained by P-wave polarities only as shown by Cai et al. （Earthq Sci 24（1）：115-125,2011）, and the rest of which are newly constrained by incorporating SH/P AR. Based on the spatial distribution and FMSs of the WES, we draw following conclusions： （1） the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. （2011） but with a few modifications that the compressional directions are WNW-ESE around Wenchuan and ENE-WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a leftlateral rotation, which agrees well with regional stress field inverted by former researchers （e.g., Xu et al., Acta Seismol Sin 30（5）, 1987; Acta Geophys Sin 32（6）, 1989; Cui et al., Seismol Geol 27（2）：234-242, 2005）; （2） the FMSs of the events not only reflected the regional stress state of the Longmenshan region, but also were obviously controlled by the faults to some extent, which was pointed out by Cai et al. （2011） and Yi et al. （Chin J Geophys 55（4）：1213-1227, 2012）; （3） while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmen- shan fault, some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008 Wenchuan earthquake and some of its strong aftershocks. （4） Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly propose that there is less probability for great earthquakes in the middle part of the Longmenshan fault in the near future, although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future.
基金support from the National Basic Research Program(No:2006CB202300)National Natural Science Foundation of China(Grant No:40739906)
文摘In January 2010, the Suining Ms5.0 earthquake occurred in central Sichuan Basin, with the epicenter in Moxi-Longnvsi structural belt and a focal depth of 10 km. Based on structural interpretations of seismic profiles in this area, we recognized a regional detachment fault located at a depth of 9-10 km in the Presinian basement of the Suining area, transferring its slipping from NW to SE orientation. This detachment fault slipped from NW to SE, and underwent several shears and bends, which caused the basement to be rolled in and the overlaying strata fold deformation. It formed a fault-bend fold in the Moxi area with an approximate slip of 4 km. Correspondingly, the formation of the Moxi anticline is related to the detachment fault. With the earthquake＇s epicenter on the ramp of the detachment fault, there is a new point of view that the Suining earthquake was caused by re-activation of this basement detachment fault. Since the Late Jurassic period, under the influence of regional tectonic stress, the detachment fault transfered its slip from the Longmen Mountains （LMS） thrust belt to the hinterland of the Sichuan Basin, and finally to the piedmont zone of southwest Huayingshan （HYS）, which indicates that HYS might be the final front area of the LMS thrust belt.
基金financial support from the National Natural Science Foundation of China (Nos. 41473056 and 41472037)
文摘The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth.Here,static calculations demonstrate that the pyrite-type FeO2 H-FeO2 system has a high density and Poisson's ratio and ultra-low seismic velocities at conditions of Earth's lowermost mantle.It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth's D″layer.The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity(VS)but increase the bulk sound velocity(VΦ),and can potentially explain the observed anti-correlation of VS and VΦin the lowermost mantle.Additionally,FeO2 H exhibits nearly isotropic whereas Fe O2 is highly anisotropic,which may help understand some seismic anisotropies at the core-mantle boundary.
文摘On May 12,2008,an Mw7.9 earthquake occurred in Wenchuan County,Sichuan Province,China.Movement of Yingxiu–Beichuan Fault in the Longmenshan Fault Zone was considered to be the main cause of the earthquake.Earthquakes are closely related to fault activities.Therefore,studying the strain distribution and evolution process around active fault zones is important to the understanding of seismic activities.In this study,we conduct laboratory experiments with uniaxial compression applied to marble sheets with intentionally fabricated cracks.The speckle patterns of the rock samples under different loading conditions are recorded in real time by a digital camera.To calculate the deformation fields of the deliberately cracked marble sheets during different stages of the loading processes,the recorded images are processed by the digital image correlation method.The distribution and variation of the displacement and strain are further analyzed in order to understand the strain localization of and observed damage in the experimental fracture zones.Finally,we compare these laboratory results with the GPS-observed coseismic displacements during the 2008 Wenchuan earthquake,to assess the consistency between our laboratory observations and the field observations of the earthquake,but also to suggest how laboratory results can improve thinking about how earthquake patterns do and do not reflect fault patterns.
基金financially supported by the National Key Research and Development Program of China (2022YFC3005600)the Foundation of the Anhui Educational Commission (2023AH051198)+1 种基金the National Natural Science Foundation of China (42125401 and 42104063)the Joint Open Fund of Mengcheng National Geophysical Observatory (MENGO-202201)。
文摘The Tan-Lu Fault Zone is a large NNE-trending fault zone that has a substantial effect on the development of eastern China and its earthquake disaster prevention efforts. Aiming at the azimuthally anisotropic structure in the upper crust and seismogenic tectonics in the Hefei segment of this fault, we collected phase velocity dispersion data of fundamental mode Rayleigh waves from ambient noise cross-correlation functions of ~400 temporal seismographs in an area of approximately 80 × 70 km along the fault zone. The period band of the dispersion data was ~0.5–10 s. We inverted for the upper crustal three-dimensional(3-D) shear velocity model with azimuthal anisotropy from the surface to 10 km depth by using a 3-D direct azimuthal anisotropy inversion method. The inversion result shows the spatial distribution characteristics of the tectonic units in the upper crust. Additionally, the deformation of the Tan-Lu Fault Zone and its conjugated fault systems could be inferred from the anisotropy model. In particular, the faults that have remained active from the early and middle Pleistocene control the anisotropic characteristics of the upper crustal structure in this area. The direction of fast axes near the fault zone area in the upper crust is consistent with the strike of the faults, whereas for the region far away from the fault zone, the direction of fast axes is consistent with the direction of the regional principal stress caused by plate movement. Combined with the azimuthal anisotropy models in the deep crust and uppermost mantle from the surface wave and Pn wave, the different anisotropic patterns caused by the Tan-Lu Fault Zone and its conjugated fault system nearby are shown in the upper and lower crust. Furthermore,by using the double-difference method, we relocated the Lujiang earthquake series, which contained 32 earthquakes with a depth shallower than 10 km. Both the Vs model and earthquake relocation results indicate that earthquakes mostly occurred in the vicinity of structural boundaries with fractured media, with high-level development of cracks and small-scale faults jammed between more rigid areas.
基金supported jointly by the National Natural Science Foundation of China (Nos. U1939204, 41774056, and 41704046)the Fundamental Research Funds for the Central Universities (No. 2042020kf0010)
文摘The complex tectonic background of East Asia makes it an ideal region for investigating the evolution of the continental lithosphere,for which high-resolution lithospheric structural models are essential.In this study,we measured Rayleigh-wave phase-velocity dispersion curves at periods of 10-120 s and group velocity dispersion curves at periods of 10-140 s using event records from more than 1,000 seismic stations in and around China.By jointly inverting new and previously published dispersion data from ambient noise and earthquakes,we developed a high-resolution shear-wave velocity model down to a depth of~300 km beneath East Asia.Our model revealed heterogeneous lithospheric structures beneath East Asia,and allowed us to investigate the velocity structure of the entire lithosphere.We also derived crustal and lithospheric thickness models from the three-dimensional(3D)shear-wave model,revealing strong spatial heterogeneity and a general thinning trend of lithospheric thickness from west to east across the study region.Overall,our models reveal important lithospheric features beneath East Asia and provide a valuable baseline dataset for understanding continental-scale dynamics and evolution.
基金supported by the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology under Grant 2024yjrc64the National Key R&D Program of China under Grant 2018YFC1504102。
文摘The Longmenshan(LMS)fault zone is located at the junction of the eastern Tibetan Plateau and the Sichuan Basin and is of great significance for studying regional tectonics and earthquake hazards.Although regional velocity models are available for the LMS fault zone,high-resolution velocity models are lacking.Therefore,a dense array of 240 short-period seismometers was deployed around the central segment of the LMS fault zone for approximately 30 days to monitor earthquakes and characterize fine structures of the fault zone.Considering the large quantity of observed seismic data,the data processing workflow consisted of deep learning-based automatic earthquake detection,phase arrival picking,and association.Compared with the earthquake catalog released by the China Earthquake Administration,many more earthquakes were detected by the dense array.Double-difference seismic tomography was adopted to determine V_(p),V_(s),and V_(p)/V_(s)models as well as earthquake locations.The checkerboard test showed that the velocity models have spatial resolutions of approximately 5 km in the horizontal directions and 2 km at depth.To the west of the Yingxiu–Beichuan Fault(YBF),the Precambrian Pengguan complex,where most of earthquakes occurred,is characterized by high velocity and low V_(p)/V_(s)values.In comparison,to the east of the YBF,the Upper Paleozoic to Jurassic sediments,where few earthquakes occurred,show low velocity and high V_(p)/V_(s)values.Our results suggest that the earthquake activity in the LMS fault zone is controlled by the strength of the rock compositions.When the high-resolution velocity models were combined with the relocated earthquakes,we were also able to delineate the fault geometry for different faults in the LMS fault zone.
