Reliable thickness of sedimentary layers is essential for seismic hazard assessment in active fault zones, especially in regions prone to strong earthquakes. This study analyzed the seismic ambient noise data recorded...Reliable thickness of sedimentary layers is essential for seismic hazard assessment in active fault zones, especially in regions prone to strong earthquakes. This study analyzed the seismic ambient noise data recorded by 60 short-period seismic stations deployed at the Jishishan earthquake source and adjacent areas. The base-order resonance frequencies of sedimentary layers beneath the stations were determined using the horizontal-to-vertical spectral ratio method on ambient noise with diff erent frequencies. Then, a resonance-thickness formula was applied to estimate the sedimentary layer thickness at each station. Finally, the entire regional sediment thickness was obtained via interpolation. The thickness of the sedimentary layer beneath each station was estimated using the equation of the relationship between resonance frequency and sedimentary layer thickness, and fi nally, the distribution of sedimentary layer thickness in the whole region was obtained by interpolation. Results reveal notable spatial variations in sediment thickness in the source and adjacent areas. The shallow sedimentary layer in the source area is relatively thick at approximately 100 m, whereas that in Liugou Village, which is the most severely damaged area, is approximately 150-180 m. In the western region, specifically along the western edge of the Jishishan Mountain rupture and the Pourouliuhe-Cheunhua Nanshan rupture zone, the shallow sedimentary layer is approximately 30-60 m. A comparison between the distribution of seismic secondary hazards and sedimentary layer thickness highlights a strong correlation between these hazards and the amplifi cation eff ects of seismic waves. In regions with thicker sedimentary layers, ground shaking is signifi cantly amplifi ed, resulting in more serious seismic secondary hazards. In addition, the study confi rmed that secondary hazards, such as landslides and liquefaction, were more prevalent in regions with thicker sedimentary layers. These fi ndings provide an important reference for post-earthquake reconstruction, seismic risk assessment, and the development of regional disaster prevention and mitigation strategies..展开更多
The aftershocks of the 1975 M_(S)7.3 Haicheng and 1999 M_(S)5.4 Xiuyan earthquakes have persisted for a long time.The ChinArray-III dense stations,deployed in eastern North China from 2018 to 2020,increased seismic mo...The aftershocks of the 1975 M_(S)7.3 Haicheng and 1999 M_(S)5.4 Xiuyan earthquakes have persisted for a long time.The ChinArray-III dense stations,deployed in eastern North China from 2018 to 2020,increased seismic monitoring capability in the Haicheng-Xiuyan region,which can facilitate the construction of high-precision earthquake catalogs to better clarify the fault structures and seismogenic mechanisms of the two earthquakes.In this study,we selected 15 permanent stations and 37 ChinArray-III stations within 150 km of the epicenter of the Haicheng Earthquake.Next,we used deep learning methods to pick P-and S-wave phases from continuous waveforms recorded at these stations from January 2018 to July 2020.Based on these picks,we constructed an automatic earthquake catalog of the Haicheng-Xiuyan region.Compared with the routine manual catalog by China Earthquake Networks Center(CENC),our catalog contains 9.7 times more seismic events,including 98.3%of the seismic events in the CENC catalog,and has a lower magnitude of completeness(M_(c)=1.1 vs M_(c)=1.8 for the CENC catalog).The relocated events indicate that the strike of the Haichenghe-Dayanghe fault varies considerably from northwest to southeast,indicating that the fault bends slightly around the hypocenter of the 1975 M_(S)7.3 Haicheng earthquake which may act as a channel for fluid migration.The weak seismicity in the area between Haicheng and Xiuyan indicates that the fault section may be locked.Furthermore,the 1999 M_(S)5.4 Xiuyan earthquake and its aftershock sequence occurred on the Kangjialing fault and its ENE-trending conjugate fault,and the intersection of the two faults coincides with the source areas of the 1999 M_(S)5.4 and 2000 M_(S)5.1 Xiuyan earthquakes.Therefore,the Xiuyan earthquake sequence may be controlled by the Kangjialing fault and its conjugate fault.This study shows that the automatic earthquake catalog,obtained by deep learning methods and dense seismic array,can provide valuable information for fault structures and the seismogenic mechanisms of moderate-to-strong earthquakes.展开更多
The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins ca...The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.展开更多
Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western...Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He’nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional(3D)shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region,while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.展开更多
The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthqu...The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.展开更多
Both earthquake seismology and structural seismology rely on observations, which in turn contribute critically to the development of seismology, especially in recent years.In order to understand specific geologic stru...Both earthquake seismology and structural seismology rely on observations, which in turn contribute critically to the development of seismology, especially in recent years.In order to understand specific geologic structures and interior processes of the Earth, seismic arrays are widely展开更多
The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ning...The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ningdu basin can provide important information for geothermal resource exploration.In this study,we deployed a dense seismic array in the Ningdu basin to investigate the 3D velocity structure and discuss implications for geothermal exploration and geological evolution.Based on the dense seismic array including 35 short-period(5 s-100 Hz)seismometers with an average interstation distance of~5 km,Rayleigh surface wave dispersion curves were extracted from the continuous ambient noise data for surface wave tomographic inversion.Group velocity tomography was conducted and the 3D S-wave velocity structure was inverted by the neighborhood algorithm.The results revealed obvious low-velocity anomalies in the center of the basin,consistent with the low-velocity Cretaceous sedimentary rocks.The basement and basin-controlling fault can also be depicted by the S-wave velocity anomalies.The obvious seismic interface is about 2 km depth in the basin center and decreases to 700 m depth near the basin boundary,suggesting spatial thickness variations of the Cretaceous sediment.The fault features of the S-wave velocity profile coincide with the geological cognition of the western boundary basincontrolling fault,which may provide possible upwelling channels for geothermal fluid.This study suggests that seismic tomography with a dense array is an effective method and can play an important role in the detailed investigations of sedimentary basins.展开更多
High-resolution imaging of fault zone structure and its temporal changes can not only advance our understanding of earthquake physics,but is also critical for better seismic hazard preparation and mitigation.In the pa...High-resolution imaging of fault zone structure and its temporal changes can not only advance our understanding of earthquake physics,but is also critical for better seismic hazard preparation and mitigation.In the past a few years,we deployed multi-scale dense arrays across the Chenghai fault system in Binchuan,Yunnan,China.The first array consisted of 381 intermediate-period three-component seismometers with an average station spacing of~2 km.The array has been deployed in the field for~3 months in 2017 and recorded numerous local and teleseismic earthquakes.Travel time analyses based on teleseismic earthquakes and an airgun source in the region indicated clear signature of low-velocity fault zones in the southern branch of the Chenghai fault system.In 2018 we deployed two other linear arrays using the same instruments with much smaller inter-station spacing,e.g.30-50 m,across the southern branch the Chenghai fault.The profile lengths were 8 and 5 km,respectively.Record sections of the airgun source on the two linear arrays clearly marked a low-velocity zone(LVZ)within the southern array but no such signature in the northern array,suggesting along-strike variation of the LVZ.Although the instruments within our dense arrays had an intermediate frequency band,we demonstrated that they were capable of characterizing crustal structure with techniques commonly applied to broadband signals such as receiver functions.To our best knowledge,this was the first time to have multi-scale across-fault dense arrays with three-component seismometers in such apertures.These results lay out the pavement to comprehensively investigate fault zone structures as well as to derive subsurface structural changes using dense arrays and the airgun source.展开更多
The complex Red River fault zone(RRFZ),which is situated in the southwestern region of China and separates the Indochina plate and South China blocks,has diverse seismic activities in different segments.To reveal the ...The complex Red River fault zone(RRFZ),which is situated in the southwestern region of China and separates the Indochina plate and South China blocks,has diverse seismic activities in different segments.To reveal the detailed geometric characteristics of the RRFZ at different sections and to better understand the seismogenic environment,in 2022 and 2023 we deployed 7 seismic dense linear arrays,consisting of 574 nodal stations,across the RRFZ in the northern and southern segments near the towns Midu,Gasa,Zhega,Dazhai,Xinzhai,and Taoyuan.The linear arrays,which extend from 2.4 to 12.5 km in length with station intervals ranging between 40 and140 m,recorded seismic ambient noise for approximately one month.Using the extended range phase shift method,we extract the phase velocity dispersion curves of the Rayleigh waves between 0.9 and 10 Hz,which are then used to invert for the high resolution shearwave velocity structures across the RRFZ beneath the linear arrays.The key findings are:(1)the 7 imaged sections of the RRFZ exhibit quite similar structures,with higher velocities on the SW side and lower velocities on the NE side;the velocity variation is consistent with the surface geological structures along the RRFZ;(2)the shear-wave velocities on the SW side of the RRFZ at the northern Midu section and southern Gasa-Dazhai sections are generally higher than their counterparts in the southern Xinzhai-Taoyuan sections,which reflects lithological variations from the marble-dominated Paleoproterozoic Along basement to the gneiss dominated Paleoproterozoic Qingshuihe basement;(3)from the northern Midu section to the southern region where the RRFZ intersects with the Xiaojiang Fault,the major faults of the RRFZ exhibit a consistent high-angle,NE-dipping structure;(4)the low shear-wave velocities immediately to the NE of the velocity boundary may indicate a faulted zone due to long-term shearing,where excessive amplifications of ground motions could occur.This study provides new insights into the characteristics of the shallow structures of the RRFZ.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
In this study, we conducted ambient noise tomography(ANT), with 33-day data, to investigate the nearsurface shear-velocity structure in downtown Ji’nan, Shandong Province, China. The cross-correlation functions with ...In this study, we conducted ambient noise tomography(ANT), with 33-day data, to investigate the nearsurface shear-velocity structure in downtown Ji’nan, Shandong Province, China. The cross-correlation functions with quiet clear Rayleigh waves are obtained with more symmetrical energy distribution which indicates that strong human activities, such as moving vehicles and municipal engineering construction, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surfacewave tomographic method with period-dependent ray-tracing is used to invert all surface-wave dispersion data in the period band 0.2–1.5 s simultaneously for 3D variations of shear-velocity structure. The study result can help us better understand the local geologic structures, evaluate the distribution and geometry of the fracture-karst media, and assess hazards of the concealed active fault and its effect on the springs in the future.展开更多
With the rapid increase of dense seismic array deployment, more and more ambient noise studies have been applied on short period surface waves tomography. For arrays with inter-station distance of several hundred mete...With the rapid increase of dense seismic array deployment, more and more ambient noise studies have been applied on short period surface waves tomography. For arrays with inter-station distance of several hundred meters,the effect of surface topography has to be considered. In this study, we investigate topography effect on ambient noise surface wave tomography using synthetic data from different topographic models. Our travel times are synthetized considering surface topography, and shear wave inversions are performed by incorporating and not incorporating topography respectively. Our inversion results suggest that topography does affect subsurface shear wave velocity inversion. If topography is not considered, although the pattern of the structure may be recovered reasonably well, the depth distribution of velocity structure can be distorted. The maximum distortion depth is generally correlated with the relief of the topography and the amplitude of the velocity anomalies. Finally, our example of real data inversion in a mountain area demonstrates good correlation between shear velocity and the geological settings, as well as the core sample in that area.展开更多
The phase identification and travel time picking are critical for seismic tomography,yet it will be challenging when the numbers of stations and earthquakes are huge.We here present a method to quickly obtain P and S ...The phase identification and travel time picking are critical for seismic tomography,yet it will be challenging when the numbers of stations and earthquakes are huge.We here present a method to quickly obtain P and S travel times of pre-determined earthquakes from mobile dense array with the aid from long term phase records from co-located permanent stations.The records for 1768 M≥2.0 events from 2011 to 2013 recorded by 350 ChinArray stations deployed in Yunnan Province are processed with an improved AR-AIC method utilizing cumulative envelope and rectilinearity.The reference arrivals are predicted based on phase records from 88 permanent stations with similar spatial coverage,which are further refined with AR-AIC.Totally,718573 P picks and 512035 S picks are obtained from mobile stations,which are 28 and 22 times of those from permanent stations,respectively.By comparing the automatic picks with manual picks from 88 permanent stations,for M≥3.0 events,81.5%of the P-pick errors are smaller than 0.5 second and 70.5%of S-pick errors are smaller than1 second.For events with a lower magnitude,76.5%P-pick errors fall into 0.5 second and 69.5%S-pick errors are smaller than 1 second.Moreover,the Pn and Sn phases are easily discriminated from directly P/S,indicating the necessity of combining traditional auto picking and integrating machine learning method.展开更多
With the development of unconventional shale gas in the southern Sichuan Basin,seismicity in the region has increased significantly in recent years.Though the existing sparse regional seismic stations can capture most...With the development of unconventional shale gas in the southern Sichuan Basin,seismicity in the region has increased significantly in recent years.Though the existing sparse regional seismic stations can capture most earthquakes with ML≥2.5,a great number of smaller earthquakes are often omitted due to limited detection capacity.With the advent of portable seismic nodes,many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed,and the magnitudes of those earthquakes are key to understand the local fault reactivation and seismic potentials.However,the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity,utilizing a calibration function with a minimal resolution of 5 km in the epicentral distance.That is,the current national standard tends to overestimate the local magnitudes for stations within short epicentral distances,and can result in discrepancies for dense arrays.In this study,we propose a new local magnitude formula which corrects the overestimated magnitudes for shorter distances,yielding accurate event magnitudes for small earthquakes in the Changning-Zhaotong shale gas field in the southern Sichuan Basin,monitored by dense seismic arrays in close proximity.The formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3 C nodes deployed from the end of February 2019 to early May 2019 in the Changning-Zhaotong shale gas field.The magnitude of completeness(MC)using the dense array is-0.1,compared to MC 1.1 by the sparser Chinese Seismic Network(CSN).In addition,using a machine learning detection and picking procedure,we successfully identify and process some 14,000 earthquakes from the continuous waveforms,a ten-fold increase over the catalog recorded by CSN for the same period,and the MC is further reduced to-0.3 from-0.1 compared to the catalog obtained via manual processing using the same dense array.The proposed local magnitude formula can be adopted for calculating accurate local magnitudes of future earthquakes using dense arrays in the shale gas fields of the Sichuan Basin.This will help to better characterize the local seismic risks and potentials.展开更多
In this paper,the densely arrayed bonded particle model is proposed for simulation of granular materials with discrete element method(DEM)considering particle crushing.This model can solve the problem of pore calculat...In this paper,the densely arrayed bonded particle model is proposed for simulation of granular materials with discrete element method(DEM)considering particle crushing.This model can solve the problem of pore calculation after the grains are crushed,and reduce the producing time of specimen.In this work,several one-dimensional compressing simulations are carried out to investigate the effect of particle crushing on mechanical properties of granular materials under a wide range of stress.The results show that the crushing process of granular materials can be divided into four different stages according to er-logσy curves.At the end of the second stage,there exists a yield point,after which the physical and mechanical properties of specimens will change significantly.Under extremely high stress,particle crushing will wipe some initial information of specimens,and specimens with different initial gradings and void ratios present some similar characteristics.Particle crushing has great influence on grading,lateral pressure coefficient and compressibility of granular materials,and introduce extra irreversible volume deformation,which is necessary to be considered in modelling of granular materials in wide stress range.展开更多
The left-lateral Altyn Tagh Fault(ATF) system is the northern boundary of the Qinghai-Xizang Plateau, separating the Tarim Basin and the Qaidam Basin. The middle section of ATF has not recorded any large earthquakes s...The left-lateral Altyn Tagh Fault(ATF) system is the northern boundary of the Qinghai-Xizang Plateau, separating the Tarim Basin and the Qaidam Basin. The middle section of ATF has not recorded any large earthquakes since1598 AD, so the potential seismic hazard is unclear. We develope an earthquake catalog using continuous waveform data recorded by the Tarim-Altyn-Qaidam dense nodal seismic array from September 17 to November23, 2021 in the middle section of ATF. With the machine learning-based picker, phase association, location, match and locate workflow, we detecte 233 earthquakes with M_L-1–3, far more than 6 earthquakes in the routine catalog. Combining with focal mechanism solutions and the local fault structure, we find that seismic events are clustered along the ATF with strike-slip focal mechanisms and on the southern secondary faults with thrusting focal mechanisms. This overall seismic activity in the middle section of the ATF might be due to the northeastward transpressional motion of the Qinghai-Xizang Plateau block at the western margin of the Qaidam Basin.展开更多
Dense array seismology, which is characterized by large number, densely deployed autonomous geophone/seismographs, has received great concerns worldwide recently, especially after the great success of dense array in L...Dense array seismology, which is characterized by large number, densely deployed autonomous geophone/seismographs, has received great concerns worldwide recently, especially after the great success of dense array in Long Beach. One of the biggest curiosity is that if the great success in Long Beach is replicable in China. Hence, we analyze the seismic records from a dense array in Binchuan basin, Yunnan province, which consists of three-component short-period seismographs of three most common domestic models. The Binchuan basin is located near the intersection between the Chenghai-Binchuan fault and the Red River fault,with the latter being the major fault accommodating significant tectonic deformation resulting from eastern extrusion of the Tibetan plateau. Both faults pose serious seismic threats to local residents in Binchuan basin. Basinrange differences, faults, local earthquakes, and a Fixed Airgun Seismic Transmitting Station(FASTS), make the Binchuan basin a perfect experiment site for dense array experiment. The array is named Array of Binchuan(ABC)and the main target is imaging the shallow crustal structure,especially the structure of the basin. To examine the monitoring capability of ABC, we analyze the seismograms to check if they can reveal the basin, the most significant geological feature in the area. Power spectral density analysis,travel time and amplitude analysis of FASTS signals, and amplitude analysis of earthquakes and noise cross-correlation functions are used in the analysis. All the results show correlation with the basin and clear difference between basin and non-basin area. Therefore, the preliminary results support that the ABC has the potential to provide constraints on local structures.展开更多
Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structur...Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structure through teleseismic receiver function analysis by using the amplitude of direct P-wave.The results reveal that the epicentral area(Liugou Township and surroundings)exhibits markedly low S-wave velocities of 400-600 m/s,with a mean value of(500±50)m/s.In contrast,intermountain basins-Guanting Basin and Dahejia Basin-demonstrate significantly elevated velocities,exceeding the epicentral zone by 100-300 m/s,with values concentrated at 600-900 m/s.Notably,localized areas such as Jintian Village and Caotan Village maintain stable S-wave velocities of(700±30)m/s.The western margin tectonic belt of Jishishan displays distinctive velocity differentiation:A pronounced velocity gradient zone along the 35.8°N latitude boundary separates northern areas(<550 m/s)from southern regions(>750 m/s).These findings demonstrate significant spatial heterogeneity in shallow S-wave velocity structures,primarily controlled by three factors:(1)topographic-geomorphic units,(2)stratigraphic lithological contrasts,and(3)anthropogenic modifications.The persistent low-velocity anomalies(<600 m/s)in the epicentral zone and northern Yellow River T2 terrace likely correlate with Quaternary unconsolidated sediments,enhanced groundwater circulation,and bedrock weathering.These results provide critical geophysical constraints for understanding both the seismogenic environment of the Jishishan earthquake and its damage distribution patterns.Furthermore,they establish a foundational framework for regional seismic intensity evaluation,site amplification analysis,and secondary hazard risk assessment.展开更多
Seismic networks have significantly improved in the last decade in terms of coverage density,data quality,and instrumental diversity.Moreover,revolutionary advances in ultra-dense seismic instruments,such as nodes and...Seismic networks have significantly improved in the last decade in terms of coverage density,data quality,and instrumental diversity.Moreover,revolutionary advances in ultra-dense seismic instruments,such as nodes and fiber-optic sensing technologies,have recently provided unprecedented high-resolution data for regional and local earthquake monitoring.Nodal arrays have characteristics such as easy installation and flexible apertures,but are limited in power efficiency and data storage and thus most suitable as temporary networks.Fiber-optic sensing techniques,including distributed acoustic sensing,can be operated in real time with an in-house power supply and connected data storage,thereby exhibiting the potential of becoming next-generation permanent networks.Fiber-optic sensing techniques offer a powerful way of filling the observation gap particularly in submarine environments.Despite these technological advancements,various challenges remain.First,the data characteristics of fiber-optic sensing are still unclear.Second,it is challenging to construct software infrastructures to store,transfer,visualize,and process large amount of seismic data.Finally,innovative detection methods are required to exploit the potential of numerous channels.With improved knowledge about data characteristics,enhanced software infrastructures,and suitable data processing techniques,these innovations in seismic instrumentation could profoundly impact observational seismology.展开更多
A rapidly deployable dense seismic monitoring system which is capable of transmitting acquired data in real time and analyzing data automatically is crucial in seismic hazard mitigation after a major earthquake.Howeve...A rapidly deployable dense seismic monitoring system which is capable of transmitting acquired data in real time and analyzing data automatically is crucial in seismic hazard mitigation after a major earthquake.However,it is rather difficult for current seismic nodal stations to transmit data in real time for an extended period of time,and it usually takes a great amount of time to process the acquired data manually.To monitor earthquakes in real time flexibly,we develop a mobile integrated seismic monitoring system consisting of newly developed nodal units with 4G telemetry and a real-time AI-assisted automatic data processing workflow.The integrated system is convenient for deployment and has been successfully applied in monitoring the aftershocks of the Yangbi M_(S) 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali,Yunnan in southwest China.The acquired seismic data are transmitted almost in real time through the 4G cellular network,and then processed automat-ically for event detection,positioning,magnitude calculation and source mechanism inversion.From tens of seconds to a couple of minutes at most,the final seismic attributes can be presented remotely to the end users through the integrated system.From May 27 to June 17,the real-time system has detected and located 7905 aftershocks in the Yangbi area before the internal batteries exhausted,far more than the catalog provided by China Earthquake Networks Center using the regional permanent stations.The initial application of this inte-grated real-time monitoring system is promising,and we anticipate the advent of a new era for Real-time Intelligent Array Seismology(RIAS),for better monitoring and understanding the subsurface dynamic pro-cesses caused by Earth's internal forces as well as anthropogenic activities.展开更多
基金jointly supported by the National Natural Science Foundation of China (42204061)Special Fund for Basic Research Operations of the Institute of Geophysics,China Earthquake Administration (0419501)+1 种基金the Gansu Jishishan6.2 magnitude earthquake scientific investigation (DQJB23Y45) programthe Sichuan Provincial Natural Science Foundation (2023NSFSC0768,2023NSFSC0770)。
文摘Reliable thickness of sedimentary layers is essential for seismic hazard assessment in active fault zones, especially in regions prone to strong earthquakes. This study analyzed the seismic ambient noise data recorded by 60 short-period seismic stations deployed at the Jishishan earthquake source and adjacent areas. The base-order resonance frequencies of sedimentary layers beneath the stations were determined using the horizontal-to-vertical spectral ratio method on ambient noise with diff erent frequencies. Then, a resonance-thickness formula was applied to estimate the sedimentary layer thickness at each station. Finally, the entire regional sediment thickness was obtained via interpolation. The thickness of the sedimentary layer beneath each station was estimated using the equation of the relationship between resonance frequency and sedimentary layer thickness, and fi nally, the distribution of sedimentary layer thickness in the whole region was obtained by interpolation. Results reveal notable spatial variations in sediment thickness in the source and adjacent areas. The shallow sedimentary layer in the source area is relatively thick at approximately 100 m, whereas that in Liugou Village, which is the most severely damaged area, is approximately 150-180 m. In the western region, specifically along the western edge of the Jishishan Mountain rupture and the Pourouliuhe-Cheunhua Nanshan rupture zone, the shallow sedimentary layer is approximately 30-60 m. A comparison between the distribution of seismic secondary hazards and sedimentary layer thickness highlights a strong correlation between these hazards and the amplifi cation eff ects of seismic waves. In regions with thicker sedimentary layers, ground shaking is signifi cantly amplifi ed, resulting in more serious seismic secondary hazards. In addition, the study confi rmed that secondary hazards, such as landslides and liquefaction, were more prevalent in regions with thicker sedimentary layers. These fi ndings provide an important reference for post-earthquake reconstruction, seismic risk assessment, and the development of regional disaster prevention and mitigation strategies..
基金supported by the National Natural Science Foundation of China(No.U2239206)Selfinitiated Project of the Institute of Geophysics of the China Earthquake Administration(JY2022Z48)+1 种基金the Dedicated Fundamental Research Funds of the Institute of Geophysics of the China Earthquake Administration(No.DQJB23X16)the Science and Technology Support Project of Guizhou Province(QKHZC[2022]General 238).
文摘The aftershocks of the 1975 M_(S)7.3 Haicheng and 1999 M_(S)5.4 Xiuyan earthquakes have persisted for a long time.The ChinArray-III dense stations,deployed in eastern North China from 2018 to 2020,increased seismic monitoring capability in the Haicheng-Xiuyan region,which can facilitate the construction of high-precision earthquake catalogs to better clarify the fault structures and seismogenic mechanisms of the two earthquakes.In this study,we selected 15 permanent stations and 37 ChinArray-III stations within 150 km of the epicenter of the Haicheng Earthquake.Next,we used deep learning methods to pick P-and S-wave phases from continuous waveforms recorded at these stations from January 2018 to July 2020.Based on these picks,we constructed an automatic earthquake catalog of the Haicheng-Xiuyan region.Compared with the routine manual catalog by China Earthquake Networks Center(CENC),our catalog contains 9.7 times more seismic events,including 98.3%of the seismic events in the CENC catalog,and has a lower magnitude of completeness(M_(c)=1.1 vs M_(c)=1.8 for the CENC catalog).The relocated events indicate that the strike of the Haichenghe-Dayanghe fault varies considerably from northwest to southeast,indicating that the fault bends slightly around the hypocenter of the 1975 M_(S)7.3 Haicheng earthquake which may act as a channel for fluid migration.The weak seismicity in the area between Haicheng and Xiuyan indicates that the fault section may be locked.Furthermore,the 1999 M_(S)5.4 Xiuyan earthquake and its aftershock sequence occurred on the Kangjialing fault and its ENE-trending conjugate fault,and the intersection of the two faults coincides with the source areas of the 1999 M_(S)5.4 and 2000 M_(S)5.1 Xiuyan earthquakes.Therefore,the Xiuyan earthquake sequence may be controlled by the Kangjialing fault and its conjugate fault.This study shows that the automatic earthquake catalog,obtained by deep learning methods and dense seismic array,can provide valuable information for fault structures and the seismogenic mechanisms of moderate-to-strong earthquakes.
基金funded by the National Key R&D Program of China(No.2017YFC1500202)supported by the National Natural Science Foundation of China(No.41604048)China Earthquake Science Experiment(No.2016CESE0103)
文摘The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.
基金supported by the China Spark Program(No.XH17055Y)the National Natural Science Foundation of China(No.41574084)
文摘Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He’nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional(3D)shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region,while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.
基金This work is jointly supported by the National Natural Science Foundation of China(No.41904057)the National Key Research and Development Program of China(No.2018YFC1503402).
文摘The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.
文摘Both earthquake seismology and structural seismology rely on observations, which in turn contribute critically to the development of seismology, especially in recent years.In order to understand specific geologic structures and interior processes of the Earth, seismic arrays are widely
基金supported by China Geological Survey (DD20190083, DD20221662)National Natural Science Foundation of China (41904044, 41974064, 42174076, 41874069)Youth Innovation Promotion Association CAS (2019330).
文摘The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ningdu basin can provide important information for geothermal resource exploration.In this study,we deployed a dense seismic array in the Ningdu basin to investigate the 3D velocity structure and discuss implications for geothermal exploration and geological evolution.Based on the dense seismic array including 35 short-period(5 s-100 Hz)seismometers with an average interstation distance of~5 km,Rayleigh surface wave dispersion curves were extracted from the continuous ambient noise data for surface wave tomographic inversion.Group velocity tomography was conducted and the 3D S-wave velocity structure was inverted by the neighborhood algorithm.The results revealed obvious low-velocity anomalies in the center of the basin,consistent with the low-velocity Cretaceous sedimentary rocks.The basement and basin-controlling fault can also be depicted by the S-wave velocity anomalies.The obvious seismic interface is about 2 km depth in the basin center and decreases to 700 m depth near the basin boundary,suggesting spatial thickness variations of the Cretaceous sediment.The fault features of the S-wave velocity profile coincide with the geological cognition of the western boundary basincontrolling fault,which may provide possible upwelling channels for geothermal fluid.This study suggests that seismic tomography with a dense array is an effective method and can play an important role in the detailed investigations of sedimentary basins.
基金This work is supported by National Key R&D Program of China(2018YFC1503400)China Earthquake Science Experiment Project,CEA(grants no.2018CSES0101,2018CSES0102,2019CSES0107)+1 种基金HKSAR Research Grant Council GRF Grant 14305617,National Science Foun-dation of China(grants 41774071,41974069,41790463,and 41674058)Chen Yong Academician Workstation of Yunnan Province in China(2014IC007).
文摘High-resolution imaging of fault zone structure and its temporal changes can not only advance our understanding of earthquake physics,but is also critical for better seismic hazard preparation and mitigation.In the past a few years,we deployed multi-scale dense arrays across the Chenghai fault system in Binchuan,Yunnan,China.The first array consisted of 381 intermediate-period three-component seismometers with an average station spacing of~2 km.The array has been deployed in the field for~3 months in 2017 and recorded numerous local and teleseismic earthquakes.Travel time analyses based on teleseismic earthquakes and an airgun source in the region indicated clear signature of low-velocity fault zones in the southern branch of the Chenghai fault system.In 2018 we deployed two other linear arrays using the same instruments with much smaller inter-station spacing,e.g.30-50 m,across the southern branch the Chenghai fault.The profile lengths were 8 and 5 km,respectively.Record sections of the airgun source on the two linear arrays clearly marked a low-velocity zone(LVZ)within the southern array but no such signature in the northern array,suggesting along-strike variation of the LVZ.Although the instruments within our dense arrays had an intermediate frequency band,we demonstrated that they were capable of characterizing crustal structure with techniques commonly applied to broadband signals such as receiver functions.To our best knowledge,this was the first time to have multi-scale across-fault dense arrays with three-component seismometers in such apertures.These results lay out the pavement to comprehensively investigate fault zone structures as well as to derive subsurface structural changes using dense arrays and the airgun source.
基金funded by the National Key Research and Development Project of China(Grant No.2021YFC3000600)the China Earthquake Science Experiment Field-Cross-fault Observation Array-Red River Fault Scientific Drilling Project Geophysical Prospecting Site Selection Project+2 种基金Anhui Province Science and Technology Breakthrough Plan Project(Key Project,202423l10050030)the Earthquake Science and Technology Spark Program of the China Earthquake Administration(XH23020YA)the Anhui Mengcheng National Geophysical Observatory Joint Open Fund(MENGO-202307)。
文摘The complex Red River fault zone(RRFZ),which is situated in the southwestern region of China and separates the Indochina plate and South China blocks,has diverse seismic activities in different segments.To reveal the detailed geometric characteristics of the RRFZ at different sections and to better understand the seismogenic environment,in 2022 and 2023 we deployed 7 seismic dense linear arrays,consisting of 574 nodal stations,across the RRFZ in the northern and southern segments near the towns Midu,Gasa,Zhega,Dazhai,Xinzhai,and Taoyuan.The linear arrays,which extend from 2.4 to 12.5 km in length with station intervals ranging between 40 and140 m,recorded seismic ambient noise for approximately one month.Using the extended range phase shift method,we extract the phase velocity dispersion curves of the Rayleigh waves between 0.9 and 10 Hz,which are then used to invert for the high resolution shearwave velocity structures across the RRFZ beneath the linear arrays.The key findings are:(1)the 7 imaged sections of the RRFZ exhibit quite similar structures,with higher velocities on the SW side and lower velocities on the NE side;the velocity variation is consistent with the surface geological structures along the RRFZ;(2)the shear-wave velocities on the SW side of the RRFZ at the northern Midu section and southern Gasa-Dazhai sections are generally higher than their counterparts in the southern Xinzhai-Taoyuan sections,which reflects lithological variations from the marble-dominated Paleoproterozoic Along basement to the gneiss dominated Paleoproterozoic Qingshuihe basement;(3)from the northern Midu section to the southern region where the RRFZ intersects with the Xiaojiang Fault,the major faults of the RRFZ exhibit a consistent high-angle,NE-dipping structure;(4)the low shear-wave velocities immediately to the NE of the velocity boundary may indicate a faulted zone due to long-term shearing,where excessive amplifications of ground motions could occur.This study provides new insights into the characteristics of the shallow structures of the RRFZ.
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.
基金supported by China Geological Survey's project(Nos.and DD20189132)Basic Scientific Research project from Chinese Academy of Geological Sciences(No.YWF201901-02)The National Key Research and Development Program of China(Nos.2016YFC0600201,2016YFC0600208 and 2016YFC0600209)
文摘In this study, we conducted ambient noise tomography(ANT), with 33-day data, to investigate the nearsurface shear-velocity structure in downtown Ji’nan, Shandong Province, China. The cross-correlation functions with quiet clear Rayleigh waves are obtained with more symmetrical energy distribution which indicates that strong human activities, such as moving vehicles and municipal engineering construction, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surfacewave tomographic method with period-dependent ray-tracing is used to invert all surface-wave dispersion data in the period band 0.2–1.5 s simultaneously for 3D variations of shear-velocity structure. The study result can help us better understand the local geologic structures, evaluate the distribution and geometry of the fracture-karst media, and assess hazards of the concealed active fault and its effect on the springs in the future.
基金supported by Guangzhou Science and Technology Planning Project Fund(No.201707020029)the joint research project by GIGCAS and Sino Shaanxi Nuclear Industry Group(No.2016–2017)
文摘With the rapid increase of dense seismic array deployment, more and more ambient noise studies have been applied on short period surface waves tomography. For arrays with inter-station distance of several hundred meters,the effect of surface topography has to be considered. In this study, we investigate topography effect on ambient noise surface wave tomography using synthetic data from different topographic models. Our travel times are synthetized considering surface topography, and shear wave inversions are performed by incorporating and not incorporating topography respectively. Our inversion results suggest that topography does affect subsurface shear wave velocity inversion. If topography is not considered, although the pattern of the structure may be recovered reasonably well, the depth distribution of velocity structure can be distorted. The maximum distortion depth is generally correlated with the relief of the topography and the amplitude of the velocity anomalies. Finally, our example of real data inversion in a mountain area demonstrates good correlation between shear velocity and the geological settings, as well as the core sample in that area.
基金This project is supported by the National Key Research and Development Program of China(2018YFC1503200)the Fundamental Research Funds for the Institute of Geophysics of China Earthquake Administration(DQJB19B29)+1 种基金the National Natural Science Foundation of China(41790463)the Science and Technology Projects of Zhejiang Earthquake Agency(2019zjj05)。
文摘The phase identification and travel time picking are critical for seismic tomography,yet it will be challenging when the numbers of stations and earthquakes are huge.We here present a method to quickly obtain P and S travel times of pre-determined earthquakes from mobile dense array with the aid from long term phase records from co-located permanent stations.The records for 1768 M≥2.0 events from 2011 to 2013 recorded by 350 ChinArray stations deployed in Yunnan Province are processed with an improved AR-AIC method utilizing cumulative envelope and rectilinearity.The reference arrivals are predicted based on phase records from 88 permanent stations with similar spatial coverage,which are further refined with AR-AIC.Totally,718573 P picks and 512035 S picks are obtained from mobile stations,which are 28 and 22 times of those from permanent stations,respectively.By comparing the automatic picks with manual picks from 88 permanent stations,for M≥3.0 events,81.5%of the P-pick errors are smaller than 0.5 second and 70.5%of S-pick errors are smaller than1 second.For events with a lower magnitude,76.5%P-pick errors fall into 0.5 second and 69.5%S-pick errors are smaller than 1 second.Moreover,the Pn and Sn phases are easily discriminated from directly P/S,indicating the necessity of combining traditional auto picking and integrating machine learning method.
基金supported by the National Natural Science Foundation of China under grants 41874048 and 41974068supported by the National Key Research and Development Projects 2018YFC0603500。
文摘With the development of unconventional shale gas in the southern Sichuan Basin,seismicity in the region has increased significantly in recent years.Though the existing sparse regional seismic stations can capture most earthquakes with ML≥2.5,a great number of smaller earthquakes are often omitted due to limited detection capacity.With the advent of portable seismic nodes,many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed,and the magnitudes of those earthquakes are key to understand the local fault reactivation and seismic potentials.However,the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity,utilizing a calibration function with a minimal resolution of 5 km in the epicentral distance.That is,the current national standard tends to overestimate the local magnitudes for stations within short epicentral distances,and can result in discrepancies for dense arrays.In this study,we propose a new local magnitude formula which corrects the overestimated magnitudes for shorter distances,yielding accurate event magnitudes for small earthquakes in the Changning-Zhaotong shale gas field in the southern Sichuan Basin,monitored by dense seismic arrays in close proximity.The formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3 C nodes deployed from the end of February 2019 to early May 2019 in the Changning-Zhaotong shale gas field.The magnitude of completeness(MC)using the dense array is-0.1,compared to MC 1.1 by the sparser Chinese Seismic Network(CSN).In addition,using a machine learning detection and picking procedure,we successfully identify and process some 14,000 earthquakes from the continuous waveforms,a ten-fold increase over the catalog recorded by CSN for the same period,and the MC is further reduced to-0.3 from-0.1 compared to the catalog obtained via manual processing using the same dense array.The proposed local magnitude formula can be adopted for calculating accurate local magnitudes of future earthquakes using dense arrays in the shale gas fields of the Sichuan Basin.This will help to better characterize the local seismic risks and potentials.
基金The authors wish to thank the National Natural Science Foundation of China(No.11772117)the Fundamental Research Funds for the Central Universities(No.2015B37414)+1 种基金Henan Scientific and Technical Project under Grant(No.192102310480)Key Scientific Research Project of Colleges and Universities in Henan Province(CN)(21B560015)for financial support.
文摘In this paper,the densely arrayed bonded particle model is proposed for simulation of granular materials with discrete element method(DEM)considering particle crushing.This model can solve the problem of pore calculation after the grains are crushed,and reduce the producing time of specimen.In this work,several one-dimensional compressing simulations are carried out to investigate the effect of particle crushing on mechanical properties of granular materials under a wide range of stress.The results show that the crushing process of granular materials can be divided into four different stages according to er-logσy curves.At the end of the second stage,there exists a yield point,after which the physical and mechanical properties of specimens will change significantly.Under extremely high stress,particle crushing will wipe some initial information of specimens,and specimens with different initial gradings and void ratios present some similar characteristics.Particle crushing has great influence on grading,lateral pressure coefficient and compressibility of granular materials,and introduce extra irreversible volume deformation,which is necessary to be considered in modelling of granular materials in wide stress range.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP, 2019QZKK0701-02)the National Natural Science Foundation of China (Grant 42104102 and 42130807)。
文摘The left-lateral Altyn Tagh Fault(ATF) system is the northern boundary of the Qinghai-Xizang Plateau, separating the Tarim Basin and the Qaidam Basin. The middle section of ATF has not recorded any large earthquakes since1598 AD, so the potential seismic hazard is unclear. We develope an earthquake catalog using continuous waveform data recorded by the Tarim-Altyn-Qaidam dense nodal seismic array from September 17 to November23, 2021 in the middle section of ATF. With the machine learning-based picker, phase association, location, match and locate workflow, we detecte 233 earthquakes with M_L-1–3, far more than 6 earthquakes in the routine catalog. Combining with focal mechanism solutions and the local fault structure, we find that seismic events are clustered along the ATF with strike-slip focal mechanisms and on the southern secondary faults with thrusting focal mechanisms. This overall seismic activity in the middle section of the ATF might be due to the northeastward transpressional motion of the Qinghai-Xizang Plateau block at the western margin of the Qaidam Basin.
基金supported by the National Natural Science Foundation of China(Grant Nos.41674058,41790463)Chen Yong Academician Workstation in Yunnan province(Grant No.2014IC007)
文摘Dense array seismology, which is characterized by large number, densely deployed autonomous geophone/seismographs, has received great concerns worldwide recently, especially after the great success of dense array in Long Beach. One of the biggest curiosity is that if the great success in Long Beach is replicable in China. Hence, we analyze the seismic records from a dense array in Binchuan basin, Yunnan province, which consists of three-component short-period seismographs of three most common domestic models. The Binchuan basin is located near the intersection between the Chenghai-Binchuan fault and the Red River fault,with the latter being the major fault accommodating significant tectonic deformation resulting from eastern extrusion of the Tibetan plateau. Both faults pose serious seismic threats to local residents in Binchuan basin. Basinrange differences, faults, local earthquakes, and a Fixed Airgun Seismic Transmitting Station(FASTS), make the Binchuan basin a perfect experiment site for dense array experiment. The array is named Array of Binchuan(ABC)and the main target is imaging the shallow crustal structure,especially the structure of the basin. To examine the monitoring capability of ABC, we analyze the seismograms to check if they can reveal the basin, the most significant geological feature in the area. Power spectral density analysis,travel time and amplitude analysis of FASTS signals, and amplitude analysis of earthquakes and noise cross-correlation functions are used in the analysis. All the results show correlation with the basin and clear difference between basin and non-basin area. Therefore, the preliminary results support that the ABC has the potential to provide constraints on local structures.
基金project is supported in part by Broadband Seismic 3D Array Detection(PhaseⅠ),Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(Grant No.2024ZD1000300)National Natural Science Foundation of China(42204061)Gansu Jishishan 6.2 magnitude earthquake scientific investigation(DQJB23Y45)program。
文摘Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structure through teleseismic receiver function analysis by using the amplitude of direct P-wave.The results reveal that the epicentral area(Liugou Township and surroundings)exhibits markedly low S-wave velocities of 400-600 m/s,with a mean value of(500±50)m/s.In contrast,intermountain basins-Guanting Basin and Dahejia Basin-demonstrate significantly elevated velocities,exceeding the epicentral zone by 100-300 m/s,with values concentrated at 600-900 m/s.Notably,localized areas such as Jintian Village and Caotan Village maintain stable S-wave velocities of(700±30)m/s.The western margin tectonic belt of Jishishan displays distinctive velocity differentiation:A pronounced velocity gradient zone along the 35.8°N latitude boundary separates northern areas(<550 m/s)from southern regions(>750 m/s).These findings demonstrate significant spatial heterogeneity in shallow S-wave velocity structures,primarily controlled by three factors:(1)topographic-geomorphic units,(2)stratigraphic lithological contrasts,and(3)anthropogenic modifications.The persistent low-velocity anomalies(<600 m/s)in the epicentral zone and northern Yellow River T2 terrace likely correlate with Quaternary unconsolidated sediments,enhanced groundwater circulation,and bedrock weathering.These results provide critical geophysical constraints for understanding both the seismogenic environment of the Jishishan earthquake and its damage distribution patterns.Furthermore,they establish a foundational framework for regional seismic intensity evaluation,site amplification analysis,and secondary hazard risk assessment.
基金the USTC Research Funds of the Double First-Class Initiative(No.YD2080002006)。
文摘Seismic networks have significantly improved in the last decade in terms of coverage density,data quality,and instrumental diversity.Moreover,revolutionary advances in ultra-dense seismic instruments,such as nodes and fiber-optic sensing technologies,have recently provided unprecedented high-resolution data for regional and local earthquake monitoring.Nodal arrays have characteristics such as easy installation and flexible apertures,but are limited in power efficiency and data storage and thus most suitable as temporary networks.Fiber-optic sensing techniques,including distributed acoustic sensing,can be operated in real time with an in-house power supply and connected data storage,thereby exhibiting the potential of becoming next-generation permanent networks.Fiber-optic sensing techniques offer a powerful way of filling the observation gap particularly in submarine environments.Despite these technological advancements,various challenges remain.First,the data characteristics of fiber-optic sensing are still unclear.Second,it is challenging to construct software infrastructures to store,transfer,visualize,and process large amount of seismic data.Finally,innovative detection methods are required to exploit the potential of numerous channels.With improved knowledge about data characteristics,enhanced software infrastructures,and suitable data processing techniques,these innovations in seismic instrumentation could profoundly impact observational seismology.
基金supported by the National Natural Science Foundation of China (under grants 41874048,41790464,41790462).
文摘A rapidly deployable dense seismic monitoring system which is capable of transmitting acquired data in real time and analyzing data automatically is crucial in seismic hazard mitigation after a major earthquake.However,it is rather difficult for current seismic nodal stations to transmit data in real time for an extended period of time,and it usually takes a great amount of time to process the acquired data manually.To monitor earthquakes in real time flexibly,we develop a mobile integrated seismic monitoring system consisting of newly developed nodal units with 4G telemetry and a real-time AI-assisted automatic data processing workflow.The integrated system is convenient for deployment and has been successfully applied in monitoring the aftershocks of the Yangbi M_(S) 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali,Yunnan in southwest China.The acquired seismic data are transmitted almost in real time through the 4G cellular network,and then processed automat-ically for event detection,positioning,magnitude calculation and source mechanism inversion.From tens of seconds to a couple of minutes at most,the final seismic attributes can be presented remotely to the end users through the integrated system.From May 27 to June 17,the real-time system has detected and located 7905 aftershocks in the Yangbi area before the internal batteries exhausted,far more than the catalog provided by China Earthquake Networks Center using the regional permanent stations.The initial application of this inte-grated real-time monitoring system is promising,and we anticipate the advent of a new era for Real-time Intelligent Array Seismology(RIAS),for better monitoring and understanding the subsurface dynamic pro-cesses caused by Earth's internal forces as well as anthropogenic activities.
