The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(...The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.展开更多
We use 15 seismic stations, crossing the Qinling orogen （QO）, Weihe graben （WG） and Ordos block （OB）, to study the crustal structures by receiver functions （RFs） methods. The results show quite a difference in...We use 15 seismic stations, crossing the Qinling orogen （QO）, Weihe graben （WG） and Ordos block （OB）, to study the crustal structures by receiver functions （RFs） methods. The results show quite a difference in crustal structures and materials of three tectonic units （orogenic belt, extentional basin and stable craton）. The average crustal thickness in the northern QO is 37.8 km, and Poisson ratio is 0.247, which indicates the increase of felsic materials in QO. In the southern OB, the average crustal thickness is 39.2 km and Poisson ratio is 0.265. Comparatively high value of Poisson ratio is related with old crystallized base in the lower crust and shallow sediments. The artificial RFs reveal that low-velocity and thick sediments have a significant ef fect on phases of the MohoroviEi6 discontinuity （Moho）. As a result, the Moho phases in WG are tangled. S-wave velocity （Vs） inversion shows that there are shallow sediment layers with 4-8 km＇s thickness and high velocity zones in the middle-lower crust in WG. Complex Moho structure and high velocity zone may have been induced by the activities of the Weihe faults series.展开更多
In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquak...In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008,which occurred in the central part of the Longmenshan.The profile also passes through the northwestern Sichuan Plateau,along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded.Seismic wave phase records that reflect the structural characteristics of different tectonic blocks,especially the complicated phase features associated with the Wenchuan earthquake,were calculated and analyzed in detail.A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined,and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were characterized.Lithological variations within the upper and lower crust in the interior of the plateau,especially a great velocity decrease and plastic rheological properties associated with strong lithologic weakening in lower crust,were detected.From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau,a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part;this is inferred to be related to the fault systems in the central Longmenshan.An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement beneath a central fault system in the Longmenshan.The data,combined with an understanding of the regional tectonic stress field and previous geological results,enable a discussion of basin-and-range coupling,orogenic tectonics,the crustal fault system,and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.展开更多
The Tibetan Plateau has been known for its highest elevation and thickest crust on earth,and become a key region for comprehending the rheology and tectonic evolution of continental plates and associated dynamic proce...The Tibetan Plateau has been known for its highest elevation and thickest crust on earth,and become a key region for comprehending the rheology and tectonic evolution of continental plates and associated dynamic processes.Over the past years,numerous geophysical studies have been conducted to explore the deep structure of the Tibetan Plateau,resulting in significant advancements in understanding the formation and growth of the Plateau.This paper aims to provide a comprehensive summary and discussion of the geophysical observations and underlying mechanisms of the plateau uplift.First,major relevant tectonic models are reviewed,and the corresponding features of crustal structures and related deformation are presented.Then,recent observations,including the identification of a high-velocity layer in the lower crust of the Lhasa block,the spatial distribution of crustal channel flow,and the decoupling of shallow and deep crustal deformation,are synthesized to gain insights into the crustal structures,and multidisciplinary data are integrated to discuss the potential mechanisms of the plateau uplift.Lastly,some pertinent suggestions are put forward for future research on the Tibetan Plateau.展开更多
Seismic tomography is one of the main tools to explore the interior of the earth.In this study,the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital r...Seismic tomography is one of the main tools to explore the interior of the earth.In this study,the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital region of China.3-D highresolution V_P,V_S and the Poisson’s ratio models are generated by inverting 29839 direct P-and 29972 direct S-wave traveltimes selected from 3231 local earthquakes.The results reveal strong crustal heterogeneities.The velocity anomalies at shallow depths are well consistent with surface geologic structures.The relatively low-velocity anomaly layer in the middle crust may be the result of multiple phases of tectonic activity.Earthquakes generally occurred on the boundaries of high-and low-velocity and Poisson’s ratio anomalies.There are obvious low-velocity anomalies below the hypocenters of the Tangshan earthquake and the historical Sanhe-Pinggu earthquake,implying the existence of fluids.The similar velocity structures around the hypocenters of the two earthquakes indicate that the occurrences of the two earthquakes may be related to the same mechanism.The highresolution velocity models provide important observational constraints on the small-scale heterogeneities and dynamic mechanism of the crust in the capital region of China.展开更多
To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-...To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-scale structures,Moho depth,crustal density structures,and isostatic state are modelled using Bouguer gravity anomaly data,topography,and earthquake focal mechanisms.We obtained homogeneous crustal densities and deviations of<1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block,the Inner Mongolia Suture Zone,the Sichuan Basin,and the Jizhong Depression.These results provide new evidence for relatively simple and stable continental crustal structures,and indicate that these regions will remain stable in both the vertical and lateral directions.The Hetao Graben,Yinchuan Graben,Weihe Basin,and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated.In contrast,the crust beneath the Yinshan Uplift,Lvliang Uplift,and northern and central Taihang Uplift is thin and under-compensated.The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions.Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia,we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces.The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.展开更多
The deep crustal structure is closely related to oil and gas reserves.Predicting the oil and gas enrichment of depressions based on the Moho depth and crustal thickness is a promising research topic with significant i...The deep crustal structure is closely related to oil and gas reserves.Predicting the oil and gas enrichment of depressions based on the Moho depth and crustal thickness is a promising research topic with significant implications for guiding exploration in petroliferous basins.In this study,seismic data were used as a constraint on the use of satellite gravity anomaly inversion to obtain the distribution of Moho depth and crustal thickness in the Bohai Basin.Stretching factors were calculated to analyze the differential distribution of deep crustal structural activity.Four indicators,including the minimum Moho depth,minimum crustal thickness,sum of Moho stretching factors,and sum of crustal stretching factors,were selected.Principal component analysis was applied to reduce the dimensionality of the multi-indicator system and obtain an oil and gas enrichment score for quantitative prediction of favorable prolific depressions.The deviation between the inverted Moho depth and seismic constraints was small;thus,the data effectively reflect the variations in the characteristics of each depression.The analysis revealed significant statistical features related to the minimum Moho depth/crustal thickness and the sum of Moho/crustal stretching factors associated with prolific depressions.Based on the oil and gas enrichment score,the depressions were classified into four categories related to their different deep crustal structural characteristics.Highly active ClassⅠ,ClassⅡ,and ClassⅢdepressions are predicted to be favorable prolific depressions.This study expands the research on quantitatively predicting favorable prolific depressions in the Bohai Basin using the deep crustal structure and can contribute to reducing production costs and improving exploration efficiency in future explorations.展开更多
The eastern Tibetan plateau has been getting more and more attention because it combines active faults,uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most ...The eastern Tibetan plateau has been getting more and more attention because it combines active faults,uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus,a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative（THD） had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks,including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the SongpanGarze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion,which is coincident with the flowing direction indicatedfrom the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.展开更多
The Red Sea-Gulf of Suez-Cairo-Alexandria Clysmic-Trend in northern Egypt is the main earthquake zone in the country,with a moderate-to-high seismic hazard and a history of significant earthquakes caused by rifting an...The Red Sea-Gulf of Suez-Cairo-Alexandria Clysmic-Trend in northern Egypt is the main earthquake zone in the country,with a moderate-to-high seismic hazard and a history of significant earthquakes caused by rifting and active faulting.To improve our understanding of the tectonic and seismic processes in this area,more comprehensive imaging of the crustal structure is required.This can be achieved by increasing the number of receiver functions(RFs)recorded by the seismic stations in northern Egypt and the southeastern Mediterranean.Data handling and processing should also be automated to increase process efficiency.In this study,we developed a capsule neural network for automated selection of RFs.The model was trained on a dataset containing RFs(both selected and unselected)from five broadband stations in northern Egypt.Stations SLM,SIWA,KOT,NBNS,and NKL are located in the unstable shelf region of Egypt,where limited knowledge of the deep crustal structure is available.The proposed capsule neural network achieved an average precision of 80%on the test set.The automated selection of RFs using a capsule neural network has the potential to significantly improve the efficiency and accuracy of RF analysis,as demonstrated by the stacking test.This could lead to a better understanding of crustal structure and tectonic processes in northern Egypt and the southeastern Mediterranean.展开更多
Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian li...Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian lithospheric subduction are still controversial.Answering these questions requires additional information regarding crustal structure.In this study,the 2-D normalized full gradient(NFG)of the Bouguer gravity anomaly was used to investigate anomalous sources and interpret the crustal structure underneath the Qiangtang and Songpan-Ganzi terranes.The NFG-derived structures with loworder harmonic numbers(N=33 and N=43)showed that an anomalous source beneath the southern Qiangtang terrane had a characteristic northeastward-dipping shape,suggesting the northeastward motion of the crustal material induced by underthrusting Indian lithospheric mantle.The NFG images with harmonic number N=53 showed a large-scale anomalous source in the lower crust of the transformational zone from the Qiangtang terrane to the Songpan-Ganzi terrane,consistent with thickening crust and resistance of lower crustal flow.The anomalous source demonstrated by the NFG results with harmonic number N=71,located in the upper crust underneath the Ganzi-Yushu fault,suggested a seismogenic body of the 2010 M6.9 Yushu event.展开更多
Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their sourc...Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their source mechanisms,which is partially essential for a deeper understanding of intraplate geodynamics.The epicentral zones of earthquakes are situated in hard-toreach areas,so,using active seismic methods for such purposes is unreasonable or even impossible because of high cost and logistical difficulties.We propose a novel approach that combines diverse passive seismic methods,which allows us to get sufficient information about geological environment structure for such task solutions.As an example,we investigated the inner structure of platform earthquake epicentral zone originated up north of Russia.We used four passive seismic methods:microseismic sounding method,passive seismic interferometry,HVSR method,and microseismic activity method.We show that passive seismic data,recoded in the same installation and processed by these different methods,can provide sufficient information about structure of studied environment,needed to explain source mechanism.In sum,the hypocenter zone is presented by intersection of vertical faults and a lateral fractured zone in the middle crust.Results were confirmed by comparison with results by active seismic methods.展开更多
The 18^(th)Academic Conference of the Seismological Society of China was held in Guiyang,China,on August 7,2023,fostering academic exchanges on the latest advancements in earthquake science.The conference featured 170...The 18^(th)Academic Conference of the Seismological Society of China was held in Guiyang,China,on August 7,2023,fostering academic exchanges on the latest advancements in earthquake science.The conference featured 170 abstracts and nearly 300 academic presentations.In this paper,we classify and summarize the scholars'presentations,analyzing the current state and progress of earthquake science in China from four key perspectives:crustal structure dynamics,earthquake mechanisms,seismic resilience of urban and rural infrastructure,and innovative earthquake services.The presentations reveal that research primarily focuses on detecting crustal structures in southwest China,with seismic imaging technology and magnetotelluric detection being the most commonly used methods.Studies on earthquake mechanisms are centered on recent destructive events,such as the 2023 M_(W)7.8 and M_(W)7.6 Türkiye earthquakes,the 2022 M_(W)6.7 Luding earthquake,and the 2021 M_(W)7.4 Madoi earthquake.Regarding seismic resilience,the focus is on shock resistance and seismic isolation experiments involving large-scale hybrid structures,as well as the formation mechanisms and risk assessments of earthquake-triggered disaster chains.Additionally,significant progress has been made in smart earthquake services,particularly in rapid disaster assessment,earthquake disaster information extraction technology,the China Seismic Experimental Site,and the strong-motion Flatfile database for China's Mainland.Overall,this conference highlighted that earthquake science in China has reached a new level of development.However,numerous scientific challenges and critical technologies remain to be addressed,such as acquiring higher-resolution crustal structures and applying big data and artificial intelligence to diverse seismic models and earthquake services,which requires the continued collaboration of researchers in the field.展开更多
This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South Chi...This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.展开更多
We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of t...We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China. Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s. Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 kin. The phase velocities at short periods （〈20 s） are lower in the Sichuan basin, the northwest segment of the Ordos block and the Weihe graben, and outline sedimentary deposits. At intermediate and long periods （〉25 s）, strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau, reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east. Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau, the Sichuan basin and the Ordos block. The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle. There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau, whose width narrows towards the eastern margin of the plateau. No low velocity zone is apparent beneath the Qinling orogen, suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.展开更多
This paper presents the survey and research work of two land-sea profiles in the Bohai Sea, China, carried out in 2010-2011, including the seismic sources on land and in the sea, the ocean bottom seismographs （OBS） ...This paper presents the survey and research work of two land-sea profiles in the Bohai Sea, China, carried out in 2010-2011, including the seismic sources on land and in the sea, the ocean bottom seismographs （OBS） and their recovery, the coupling of OBS and the environment noise in sea area, the data quality of OBSs, and the result of data analysis. We focused on the investigation of crustal structures revealed by the two NE／EW-trending joint land-sea profiles. In combination with the Pn-velocity distribution and gravity- magnetic inversion results in the North China Craton, we propose that the undulation of the Moho interface in the Bohai and surrounding areas is not strong, and the lithospheric thinning is mainly caused by the thinning of its mantle part. The research result indicates that obvious lateral variations of Moho depth and seismic velocity appear nearby all the large-scale faults in Bohai Sea, and there is evidence of underplating and reforming of the lower crust by mantle material in the Bohai area. However, geophysical evidence does not appear to support the ＂mantle plume＂ or ＂delamination＂ model for the North China Craton destruction. The crustal structure of the Bohai Sea revealed ＂a relatively normal crust and obviously thinned mantle lid＂, local velocity anomalies and instability phenomena in the crust. These features may represent a combined effect of North China-Yangtze collision at an early stage and the remote action of Pacific plate subduction at a late stage.展开更多
Based on the integrative interpretation of travel-time data and amplitude information obtained from the deep seismic sounding experiment on the Chuxiong-Luoping profile, eastern Yunnan province, carried out in January...Based on the integrative interpretation of travel-time data and amplitude information obtained from the deep seismic sounding experiment on the Chuxiong-Luoping profile, eastern Yunnan province, carried out in January of 2005, we present a 2-D P wave velocity structure along the profile. The crustal structure shows remarkable contrasts between the two sides of the Xiaojiang fault zone, although the whole profile is situated within the Yangtze platform. The average P wave velocities of the crust on the west and east sides of the fault zone are 6.21 km/s and 6.32 km/s, respectively, and the crustal thicknesses are 41 km and 45 km, respectively. These results imply that the crust to the east of the Xiaojiang fault zone presents characteristics of crustal structure in a stable platform, while the crust to the west is complicated with a lower velocity zone in middle of the upper crust. The average velocity of 6.21 km/s is lower than the global continental crustal average （6.30 km/s）, indicating that the region is tectonically active. According to the lateral variation of velocity and depth of interfaces （including the Moho）, it is inferred that the Xiaojiang fault zone has cut through the whole crust. It is also deduced that existence of low velocity zone in middle of the upper crust is conducive to the south-southeastern sliding of the Sichuan- Yunnan （Chuan-Dian） rhombus block.展开更多
A profile of shallow crustal velocity structure(1–2 km) may greatly enhance interpretation of the sedimentary environment and shallow tectonic deformation.Recent advances in surface wave tomography, using ambient noi...A profile of shallow crustal velocity structure(1–2 km) may greatly enhance interpretation of the sedimentary environment and shallow tectonic deformation.Recent advances in surface wave tomography, using ambient noise data recorded with high-density seismic arrays, have improved the understanding of regional crustal structure. As the interest in detailed shallow crustal structure imaging has increased, dense seismic array methods have become increasingly efficient. This study used a high-density seismic array deployed in the Xinjiang basin in southeastern China, to record seismic data, which was then processed with the ambient noise tomography method. The high-density seismic array contained 203 short-period seismometers, spaced at short intervals(～ 400 m). The array collected continuous records of ambient noise for 32 days. Data preprocessing,cross correlation calculation, and Rayleigh surface wave phase-velocity dispersion curve extraction, yielded more than 16,000 Rayleigh surface wave phase-velocity dispersion curves, which were then analyzed using the direct-inversion method. Checkerboard tests indicate that the shear wave velocity is recovered in the study area, at depths of 0–1.4 km,with a lateral image resolution of ～ 400 m. Model test results show that the seismic array effectively images a 50 m thick slab at a depth of 0–300 m, a 150 m thick anomalous body at a depth of 300–600 m, and a 400 m thick anomalous body at a depth of 0.6–1.4 km. The shear wave velocity profile reveals features very similar to those detected by a deep seismic reflection profile across the study area. This demonstrates that analysis of shallow crustal velocity structure provides high-resolution imaging of crustal features.Thus, ambient noise tomography with a high-density seismic array may play an important role in imaging shallow crustal structure.展开更多
Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai （莺歌海） basin （YGHB） with ocean bottom hydrophones （OBHs） and piggyback recorded by onshore stations located...Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai （莺歌海） basin （YGHB） with ocean bottom hydrophones （OBHs） and piggyback recorded by onshore stations located on the Hainan （海南） Island. Detailed velocity-depth models were obtained through traveltime modeling and partially constrained by amplitude calculations. More than 15 km Tertiary sedimentary infill within the YGHB can be divided in to three layers with distinct velocity-depth distribution. Overall, the upper layer has a high velocity gradient with 3.8--4.1 km/s at its bottom, consistent with progressive compaction and diagenesis. Its thickness increases gradually towards the basin center, reaching 4.5 km along the southern profile. The middle layer is characterized in its most part as a pronounced low velocity zone （LVZ） with average velocity as low as 3.0 km/s. Its thickness increases from 3.0 to over 4.5 km from NW towards SE. The primary causes of the velocity inversion are high accumulation rate and subsequent under-compaction of sediments. The velocity at the top of the lower layer is estimated at about 4.5 km/s. Despite strong energy source used （4 × 12L airgun array）, no reflections can be observed from deeper levels within the basin. Towards NE the basin is bounded sharply by a clear and deep basement fault （Fault No. 1）, which seems to cut through the entire crust. A typical continental crust with low-velocity middle crust is found beneath the coast of the western Hainan Island. Its thickness is determined to be 28 km and shows no sign of crustal thinning towards the basin. The sharp change in crustal structure across Fault No. 1 indicates that the fault is a strike-slip fault. The crustal structure obtained in this study clearly favors the hypothesis that the YGHB is a narrow pull-apart basin formed by strike-slip faulting of the Red River fault zone.展开更多
The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern...The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern South China Sea （SCS）. These profiles are of good penetration that Moho is recognizable in -70% length of the lines. Seismostratigraphic interpretation and time-depth conversion were conducted. A power function D = ath ＋ c was used in the time-depth conversion, which avoided the under- or over-estimation of the depths of deep-seated interfaces by cubic or quadratic polynomial functions. Contour maps of basement depth, Moho depth, crustal thickness, and crustal stretching factor were obtained for the study area. In the dip direction, the Mobo depth decreases stepwisely from 28 km in the outer shelf southwards to 19, 15, and 12 km in the deepsea basin, with ramps at the shelf break, lower slope, and the continent ocean boundary （COB）, respectively. Accordingly, the crustal thickness decreased southwards from 25 to 15, 13, and 7 km, respectively. Under the center of the Baiyun （白云） sag, the crust thins significantly to 〈 7 km. The crustal stretching factor βc was calculated by assuming the original crust thickness of 30 km. In the centers of the Baiyun sag, βc exceeds 5. Tertiary and Quaternary volcanic activities show a general trend of intensifying towards the COB. An important finding of this study is the along-strike variation of the crustal structure. A Moho rise extends from the COB NW-ward until the shelf break, about 170 km long and 50-100 km wide, with Moho depth 〈 20 km. This is called the Baiyun Moho Nose, which is bounded to the east, west, and north by belts of high Moho gradients indicative of crustal or even lithospheric faults. The doming of Moho in the nose area might be the cause of the W-E segmentation of the crustal and geological structures along the slope of the northern South China Sea, and the cause of the strong crustal stretching in the Baiyun and Liwan （荔湾） sags.展开更多
Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the bord...Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the border between China and Mongolia and its structure, composition and tectonic evolution have been revealed, and abundant information about the deep structures has been provided. Based on the research into the geotransect, it is suggested that the crust in this area was formed by the assembly of the terranes in different geological stages. Following the formation of the Palaeo-Asian continent, the north part of the corridor of the transect became a part of the huge unifying continent by the end of the Early Permian. In the Mesozoic and Cenozoic, as a result of the compression mainly by the push of the Qinghai-Tibet plateau on the south, the unique crustal structure and geomorphologic features on the northern Qinghai-Tibet plateau were formed. This geotransect together with the Yadong-Golmud geotransect constitutes a long geotransect which runs across the western Chinese continent.展开更多
基金supported by the National Key R&D Program of China(No.2023YFC3012002)the National Natural Science Foundation of China(42374073)。
文摘The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.
基金supported by National Natural Science Foundation of China(Grant Nos.41174038 and 40474017)
文摘We use 15 seismic stations, crossing the Qinling orogen （QO）, Weihe graben （WG） and Ordos block （OB）, to study the crustal structures by receiver functions （RFs） methods. The results show quite a difference in crustal structures and materials of three tectonic units （orogenic belt, extentional basin and stable craton）. The average crustal thickness in the northern QO is 37.8 km, and Poisson ratio is 0.247, which indicates the increase of felsic materials in QO. In the southern OB, the average crustal thickness is 39.2 km and Poisson ratio is 0.265. Comparatively high value of Poisson ratio is related with old crystallized base in the lower crust and shallow sediments. The artificial RFs reveal that low-velocity and thick sediments have a significant ef fect on phases of the MohoroviEi6 discontinuity （Moho）. As a result, the Moho phases in WG are tangled. S-wave velocity （Vs） inversion shows that there are shallow sediment layers with 4-8 km＇s thickness and high velocity zones in the middle-lower crust in WG. Complex Moho structure and high velocity zone may have been induced by the activities of the Weihe faults series.
基金supported by the Chinese Mainland Active Fault Exploration Project 2010-Deep Seismic Sounding Profile in the central Longmenshan,CEAthe National Natural Science Foundation of China(Grant No.40974033)
文摘In 2010,a 500-km-long wide-angle reflection/refraction seismic profile was completed,running northwest from the central Sichuan Basin.This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008,which occurred in the central part of the Longmenshan.The profile also passes through the northwestern Sichuan Plateau,along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded.Seismic wave phase records that reflect the structural characteristics of different tectonic blocks,especially the complicated phase features associated with the Wenchuan earthquake,were calculated and analyzed in detail.A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined,and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were characterized.Lithological variations within the upper and lower crust in the interior of the plateau,especially a great velocity decrease and plastic rheological properties associated with strong lithologic weakening in lower crust,were detected.From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau,a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part;this is inferred to be related to the fault systems in the central Longmenshan.An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement beneath a central fault system in the Longmenshan.The data,combined with an understanding of the regional tectonic stress field and previous geological results,enable a discussion of basin-and-range coupling,orogenic tectonics,the crustal fault system,and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.
基金supported by the Supercomputing Laboratory at the Institute of Geology and Geophysics,Chinese Academy of Sciencessupported by the National Natural Science Foundation of China(Grant No.42074067)the Key Research Program of the Institute of Geology and Geophysics,CAS(Grant No.IGGCAS-202204)。
文摘The Tibetan Plateau has been known for its highest elevation and thickest crust on earth,and become a key region for comprehending the rheology and tectonic evolution of continental plates and associated dynamic processes.Over the past years,numerous geophysical studies have been conducted to explore the deep structure of the Tibetan Plateau,resulting in significant advancements in understanding the formation and growth of the Plateau.This paper aims to provide a comprehensive summary and discussion of the geophysical observations and underlying mechanisms of the plateau uplift.First,major relevant tectonic models are reviewed,and the corresponding features of crustal structures and related deformation are presented.Then,recent observations,including the identification of a high-velocity layer in the lower crust of the Lhasa block,the spatial distribution of crustal channel flow,and the decoupling of shallow and deep crustal deformation,are synthesized to gain insights into the crustal structures,and multidisciplinary data are integrated to discuss the potential mechanisms of the plateau uplift.Lastly,some pertinent suggestions are put forward for future research on the Tibetan Plateau.
基金supported by the National Natural Science Foundation of China(Grant No.41704047)supported by the National Natural Science Foundation of China(Grant No.11871297)Tsinghua University Initiative Scientific Research Program。
文摘Seismic tomography is one of the main tools to explore the interior of the earth.In this study,the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital region of China.3-D highresolution V_P,V_S and the Poisson’s ratio models are generated by inverting 29839 direct P-and 29972 direct S-wave traveltimes selected from 3231 local earthquakes.The results reveal strong crustal heterogeneities.The velocity anomalies at shallow depths are well consistent with surface geologic structures.The relatively low-velocity anomaly layer in the middle crust may be the result of multiple phases of tectonic activity.Earthquakes generally occurred on the boundaries of high-and low-velocity and Poisson’s ratio anomalies.There are obvious low-velocity anomalies below the hypocenters of the Tangshan earthquake and the historical Sanhe-Pinggu earthquake,implying the existence of fluids.The similar velocity structures around the hypocenters of the two earthquakes indicate that the occurrences of the two earthquakes may be related to the same mechanism.The highresolution velocity models provide important observational constraints on the small-scale heterogeneities and dynamic mechanism of the crust in the capital region of China.
基金supported by National Key Research and Development Program of China (Grant No. 2016YFC0600501)National Basic Research Program of China (Grant No. 2015CB452605)+2 种基金National Natural Science Foundation of China (Grant Nos. 41702075 and 41572315)Geological Survey Project of China (Grant No. DD20160045)the State Key Program of National Natural Science of China (Grant No. 41430320)
文摘To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-scale structures,Moho depth,crustal density structures,and isostatic state are modelled using Bouguer gravity anomaly data,topography,and earthquake focal mechanisms.We obtained homogeneous crustal densities and deviations of<1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block,the Inner Mongolia Suture Zone,the Sichuan Basin,and the Jizhong Depression.These results provide new evidence for relatively simple and stable continental crustal structures,and indicate that these regions will remain stable in both the vertical and lateral directions.The Hetao Graben,Yinchuan Graben,Weihe Basin,and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated.In contrast,the crust beneath the Yinshan Uplift,Lvliang Uplift,and northern and central Taihang Uplift is thin and under-compensated.The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions.Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia,we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces.The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.
基金The Scientific and Technological Project of China National Offshore Oil Corporation(CNOOC)Research Institute Co.,Ltd.under contract No.CCL2021RCPS0167KQNthe Open Fund Project for the year 2022 of National Engineering Research Center of Offshore Oil and Gas Exploration under contract No.CCL2022RCPS0794RQN。
文摘The deep crustal structure is closely related to oil and gas reserves.Predicting the oil and gas enrichment of depressions based on the Moho depth and crustal thickness is a promising research topic with significant implications for guiding exploration in petroliferous basins.In this study,seismic data were used as a constraint on the use of satellite gravity anomaly inversion to obtain the distribution of Moho depth and crustal thickness in the Bohai Basin.Stretching factors were calculated to analyze the differential distribution of deep crustal structural activity.Four indicators,including the minimum Moho depth,minimum crustal thickness,sum of Moho stretching factors,and sum of crustal stretching factors,were selected.Principal component analysis was applied to reduce the dimensionality of the multi-indicator system and obtain an oil and gas enrichment score for quantitative prediction of favorable prolific depressions.The deviation between the inverted Moho depth and seismic constraints was small;thus,the data effectively reflect the variations in the characteristics of each depression.The analysis revealed significant statistical features related to the minimum Moho depth/crustal thickness and the sum of Moho/crustal stretching factors associated with prolific depressions.Based on the oil and gas enrichment score,the depressions were classified into four categories related to their different deep crustal structural characteristics.Highly active ClassⅠ,ClassⅡ,and ClassⅢdepressions are predicted to be favorable prolific depressions.This study expands the research on quantitatively predicting favorable prolific depressions in the Bohai Basin using the deep crustal structure and can contribute to reducing production costs and improving exploration efficiency in future explorations.
基金supported by the National Natural Science Foundation of China (Grant Nos.41430213 and 41304064)
文摘The eastern Tibetan plateau has been getting more and more attention because it combines active faults,uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus,a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative（THD） had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks,including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the SongpanGarze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion,which is coincident with the flowing direction indicatedfrom the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.
文摘The Red Sea-Gulf of Suez-Cairo-Alexandria Clysmic-Trend in northern Egypt is the main earthquake zone in the country,with a moderate-to-high seismic hazard and a history of significant earthquakes caused by rifting and active faulting.To improve our understanding of the tectonic and seismic processes in this area,more comprehensive imaging of the crustal structure is required.This can be achieved by increasing the number of receiver functions(RFs)recorded by the seismic stations in northern Egypt and the southeastern Mediterranean.Data handling and processing should also be automated to increase process efficiency.In this study,we developed a capsule neural network for automated selection of RFs.The model was trained on a dataset containing RFs(both selected and unselected)from five broadband stations in northern Egypt.Stations SLM,SIWA,KOT,NBNS,and NKL are located in the unstable shelf region of Egypt,where limited knowledge of the deep crustal structure is available.The proposed capsule neural network achieved an average precision of 80%on the test set.The automated selection of RFs using a capsule neural network has the potential to significantly improve the efficiency and accuracy of RF analysis,as demonstrated by the stacking test.This could lead to a better understanding of crustal structure and tectonic processes in northern Egypt and the southeastern Mediterranean.
基金financially supported by the National Natural Science Foundation of China(Grant No.42074090)
文摘Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian lithospheric subduction are still controversial.Answering these questions requires additional information regarding crustal structure.In this study,the 2-D normalized full gradient(NFG)of the Bouguer gravity anomaly was used to investigate anomalous sources and interpret the crustal structure underneath the Qiangtang and Songpan-Ganzi terranes.The NFG-derived structures with loworder harmonic numbers(N=33 and N=43)showed that an anomalous source beneath the southern Qiangtang terrane had a characteristic northeastward-dipping shape,suggesting the northeastward motion of the crustal material induced by underthrusting Indian lithospheric mantle.The NFG images with harmonic number N=53 showed a large-scale anomalous source in the lower crust of the transformational zone from the Qiangtang terrane to the Songpan-Ganzi terrane,consistent with thickening crust and resistance of lower crustal flow.The anomalous source demonstrated by the NFG results with harmonic number N=71,located in the upper crust underneath the Ganzi-Yushu fault,suggested a seismogenic body of the 2010 M6.9 Yushu event.
基金funded by the Russian Federation Ministry of Science and Higher Education according to the research project FUUW-2025-0033 of the FECIAR UrB RASthe Arkhangelsk branch of the Territorial Fund of Geological Information for the North-Western Federal District for providing geological and geophysical reports for the objects under consideration。
文摘Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their source mechanisms,which is partially essential for a deeper understanding of intraplate geodynamics.The epicentral zones of earthquakes are situated in hard-toreach areas,so,using active seismic methods for such purposes is unreasonable or even impossible because of high cost and logistical difficulties.We propose a novel approach that combines diverse passive seismic methods,which allows us to get sufficient information about geological environment structure for such task solutions.As an example,we investigated the inner structure of platform earthquake epicentral zone originated up north of Russia.We used four passive seismic methods:microseismic sounding method,passive seismic interferometry,HVSR method,and microseismic activity method.We show that passive seismic data,recoded in the same installation and processed by these different methods,can provide sufficient information about structure of studied environment,needed to explain source mechanism.In sum,the hypocenter zone is presented by intersection of vertical faults and a lateral fractured zone in the middle crust.Results were confirmed by comparison with results by active seismic methods.
基金supported by research grants from National Institute of Natural Hazards,Ministry of Emergency Management of China(ZDJ2024-16,2023-JBKY-57)the National Natural Science Foundation of China(42077259,42002225).
文摘The 18^(th)Academic Conference of the Seismological Society of China was held in Guiyang,China,on August 7,2023,fostering academic exchanges on the latest advancements in earthquake science.The conference featured 170 abstracts and nearly 300 academic presentations.In this paper,we classify and summarize the scholars'presentations,analyzing the current state and progress of earthquake science in China from four key perspectives:crustal structure dynamics,earthquake mechanisms,seismic resilience of urban and rural infrastructure,and innovative earthquake services.The presentations reveal that research primarily focuses on detecting crustal structures in southwest China,with seismic imaging technology and magnetotelluric detection being the most commonly used methods.Studies on earthquake mechanisms are centered on recent destructive events,such as the 2023 M_(W)7.8 and M_(W)7.6 Türkiye earthquakes,the 2022 M_(W)6.7 Luding earthquake,and the 2021 M_(W)7.4 Madoi earthquake.Regarding seismic resilience,the focus is on shock resistance and seismic isolation experiments involving large-scale hybrid structures,as well as the formation mechanisms and risk assessments of earthquake-triggered disaster chains.Additionally,significant progress has been made in smart earthquake services,particularly in rapid disaster assessment,earthquake disaster information extraction technology,the China Seismic Experimental Site,and the strong-motion Flatfile database for China's Mainland.Overall,this conference highlighted that earthquake science in China has reached a new level of development.However,numerous scientific challenges and critical technologies remain to be addressed,such as acquiring higher-resolution crustal structures and applying big data and artificial intelligence to diverse seismic models and earthquake services,which requires the continued collaboration of researchers in the field.
基金supported by the China Geological Survey Project(No.DD20243455)the National Natural Science Foundation of China(NSFC Project 41302046)。
文摘This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.
基金supported by Chinese Academy of Sciences grant kzcx2-yw-142 and Y009021002National Natural Science Foundation of China under grant No. 40974034+1 种基金NSF-EAR award 0944022NSF-OISE 0730154 at the University of Colorado at Boulder
文摘We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China. Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s. Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 kin. The phase velocities at short periods （〈20 s） are lower in the Sichuan basin, the northwest segment of the Ordos block and the Weihe graben, and outline sedimentary deposits. At intermediate and long periods （〉25 s）, strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau, reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east. Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau, the Sichuan basin and the Ordos block. The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle. There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau, whose width narrows towards the eastern margin of the plateau. No low velocity zone is apparent beneath the Qinling orogen, suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.
基金The National Natural Science Foundation of China under contract Nos 41210005,41074058 and 90814011the National High Technique R&D Program (863 Program) under contract Nos 2009AA093401 and 2011ZX05008-006-30
文摘This paper presents the survey and research work of two land-sea profiles in the Bohai Sea, China, carried out in 2010-2011, including the seismic sources on land and in the sea, the ocean bottom seismographs （OBS） and their recovery, the coupling of OBS and the environment noise in sea area, the data quality of OBSs, and the result of data analysis. We focused on the investigation of crustal structures revealed by the two NE／EW-trending joint land-sea profiles. In combination with the Pn-velocity distribution and gravity- magnetic inversion results in the North China Craton, we propose that the undulation of the Moho interface in the Bohai and surrounding areas is not strong, and the lithospheric thinning is mainly caused by the thinning of its mantle part. The research result indicates that obvious lateral variations of Moho depth and seismic velocity appear nearby all the large-scale faults in Bohai Sea, and there is evidence of underplating and reforming of the lower crust by mantle material in the Bohai area. However, geophysical evidence does not appear to support the ＂mantle plume＂ or ＂delamination＂ model for the North China Craton destruction. The crustal structure of the Bohai Sea revealed ＂a relatively normal crust and obviously thinned mantle lid＂, local velocity anomalies and instability phenomena in the crust. These features may represent a combined effect of North China-Yangtze collision at an early stage and the remote action of Pacific plate subduction at a late stage.
基金supported by the project "Exploration of Active Seismic Faults in Large Cities and Earthquake risk Assessment"National Natural Science Foundation of China (Grant No. 40774037)Contribution No.is 09FE3004 of Institute of Geophysics,China Earthquake Administration
文摘Based on the integrative interpretation of travel-time data and amplitude information obtained from the deep seismic sounding experiment on the Chuxiong-Luoping profile, eastern Yunnan province, carried out in January of 2005, we present a 2-D P wave velocity structure along the profile. The crustal structure shows remarkable contrasts between the two sides of the Xiaojiang fault zone, although the whole profile is situated within the Yangtze platform. The average P wave velocities of the crust on the west and east sides of the fault zone are 6.21 km/s and 6.32 km/s, respectively, and the crustal thicknesses are 41 km and 45 km, respectively. These results imply that the crust to the east of the Xiaojiang fault zone presents characteristics of crustal structure in a stable platform, while the crust to the west is complicated with a lower velocity zone in middle of the upper crust. The average velocity of 6.21 km/s is lower than the global continental crustal average （6.30 km/s）, indicating that the region is tectonically active. According to the lateral variation of velocity and depth of interfaces （including the Moho）, it is inferred that the Xiaojiang fault zone has cut through the whole crust. It is also deduced that existence of low velocity zone in middle of the upper crust is conducive to the south-southeastern sliding of the Sichuan- Yunnan （Chuan-Dian） rhombus block.
基金supported by the China Geological Survey Project“Deep Geological Survey of the Qin-Hang Belt”(No.DD20160082)the National Natural Science Foundation of China(No.41574048)
文摘A profile of shallow crustal velocity structure(1–2 km) may greatly enhance interpretation of the sedimentary environment and shallow tectonic deformation.Recent advances in surface wave tomography, using ambient noise data recorded with high-density seismic arrays, have improved the understanding of regional crustal structure. As the interest in detailed shallow crustal structure imaging has increased, dense seismic array methods have become increasingly efficient. This study used a high-density seismic array deployed in the Xinjiang basin in southeastern China, to record seismic data, which was then processed with the ambient noise tomography method. The high-density seismic array contained 203 short-period seismometers, spaced at short intervals(～ 400 m). The array collected continuous records of ambient noise for 32 days. Data preprocessing,cross correlation calculation, and Rayleigh surface wave phase-velocity dispersion curve extraction, yielded more than 16,000 Rayleigh surface wave phase-velocity dispersion curves, which were then analyzed using the direct-inversion method. Checkerboard tests indicate that the shear wave velocity is recovered in the study area, at depths of 0–1.4 km,with a lateral image resolution of ～ 400 m. Model test results show that the seismic array effectively images a 50 m thick slab at a depth of 0–300 m, a 150 m thick anomalous body at a depth of 300–600 m, and a 400 m thick anomalous body at a depth of 0.6–1.4 km. The shear wave velocity profile reveals features very similar to those detected by a deep seismic reflection profile across the study area. This demonstrates that analysis of shallow crustal velocity structure provides high-resolution imaging of crustal features.Thus, ambient noise tomography with a high-density seismic array may play an important role in imaging shallow crustal structure.
基金supported by the National Basic Research Program of China (No. 2007CB411706-05)the National Natural Science Foundation of China (No. 40576025)
文摘Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai （莺歌海） basin （YGHB） with ocean bottom hydrophones （OBHs） and piggyback recorded by onshore stations located on the Hainan （海南） Island. Detailed velocity-depth models were obtained through traveltime modeling and partially constrained by amplitude calculations. More than 15 km Tertiary sedimentary infill within the YGHB can be divided in to three layers with distinct velocity-depth distribution. Overall, the upper layer has a high velocity gradient with 3.8--4.1 km/s at its bottom, consistent with progressive compaction and diagenesis. Its thickness increases gradually towards the basin center, reaching 4.5 km along the southern profile. The middle layer is characterized in its most part as a pronounced low velocity zone （LVZ） with average velocity as low as 3.0 km/s. Its thickness increases from 3.0 to over 4.5 km from NW towards SE. The primary causes of the velocity inversion are high accumulation rate and subsequent under-compaction of sediments. The velocity at the top of the lower layer is estimated at about 4.5 km/s. Despite strong energy source used （4 × 12L airgun array）, no reflections can be observed from deeper levels within the basin. Towards NE the basin is bounded sharply by a clear and deep basement fault （Fault No. 1）, which seems to cut through the entire crust. A typical continental crust with low-velocity middle crust is found beneath the coast of the western Hainan Island. Its thickness is determined to be 28 km and shows no sign of crustal thinning towards the basin. The sharp change in crustal structure across Fault No. 1 indicates that the fault is a strike-slip fault. The crustal structure obtained in this study clearly favors the hypothesis that the YGHB is a narrow pull-apart basin formed by strike-slip faulting of the Red River fault zone.
基金supported by the National Natural Science Foundation of China (Nos. 40576027, 40876026)National Basic Research Program of China (Nos. 2007CB41170405, 2009CB219401)the Knowledge Innovation Program of South China Sea Institute of Oceanology, Chinese Academy of Sciences (No. LYQY200704)
文摘The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern South China Sea （SCS）. These profiles are of good penetration that Moho is recognizable in -70% length of the lines. Seismostratigraphic interpretation and time-depth conversion were conducted. A power function D = ath ＋ c was used in the time-depth conversion, which avoided the under- or over-estimation of the depths of deep-seated interfaces by cubic or quadratic polynomial functions. Contour maps of basement depth, Moho depth, crustal thickness, and crustal stretching factor were obtained for the study area. In the dip direction, the Mobo depth decreases stepwisely from 28 km in the outer shelf southwards to 19, 15, and 12 km in the deepsea basin, with ramps at the shelf break, lower slope, and the continent ocean boundary （COB）, respectively. Accordingly, the crustal thickness decreased southwards from 25 to 15, 13, and 7 km, respectively. Under the center of the Baiyun （白云） sag, the crust thins significantly to 〈 7 km. The crustal stretching factor βc was calculated by assuming the original crust thickness of 30 km. In the centers of the Baiyun sag, βc exceeds 5. Tertiary and Quaternary volcanic activities show a general trend of intensifying towards the COB. An important finding of this study is the along-strike variation of the crustal structure. A Moho rise extends from the COB NW-ward until the shelf break, about 170 km long and 50-100 km wide, with Moho depth 〈 20 km. This is called the Baiyun Moho Nose, which is bounded to the east, west, and north by belts of high Moho gradients indicative of crustal or even lithospheric faults. The doming of Moho in the nose area might be the cause of the W-E segmentation of the crustal and geological structures along the slope of the northern South China Sea, and the cause of the strong crustal stretching in the Baiyun and Liwan （荔湾） sags.
基金This paper is one of the results of the project"The Golmud-Ejin Geoscience Transect Interdisciplinary Research".The project was supported by the former Ministry of Geology and Mineral Resources(MGMR)and the National Natural Science Foundation of China(NNSFC).The leaders of the Project are Profs.Wang Zeju,Wu Gongjian and Xiao Xuchang.
文摘Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the border between China and Mongolia and its structure, composition and tectonic evolution have been revealed, and abundant information about the deep structures has been provided. Based on the research into the geotransect, it is suggested that the crust in this area was formed by the assembly of the terranes in different geological stages. Following the formation of the Palaeo-Asian continent, the north part of the corridor of the transect became a part of the huge unifying continent by the end of the Early Permian. In the Mesozoic and Cenozoic, as a result of the compression mainly by the push of the Qinghai-Tibet plateau on the south, the unique crustal structure and geomorphologic features on the northern Qinghai-Tibet plateau were formed. This geotransect together with the Yadong-Golmud geotransect constitutes a long geotransect which runs across the western Chinese continent.
