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Tomographic inversion of OBS converted shear waves:case study of profile EW6 in the Dongsha area

Acta Oceanologica Sinica 2024年第8期43卷 13-25页

作者： Genggeng Wen Kuiyuan Wan shaohong xia Xiuwei Ye Huilong Xu Chaoyan Fan Jinghe Cao Shunshan Xu CEA Key Laboratory of Earthquake Monitoring and Disaster Mitigation Technology Guangdong Earthquake AgencyGuangzhou 510070China Guangdong Science and Technology Collaborative Innovation Center for Earthquake Prevention and Disaster Mitigation Guangzhou 510070China MOE Key Laboratory of Disaster Forecast and Control in Engineering-Urban Earthquake Safety Laboratory Guangzhou 510070China CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China 6 Centro de Geociencias Universidad Nacional Autónoma de MéxicoQuerétaroC.P.76230Mexico

Studies of converted S-wave data recorded on the ocean bottom seismometer(OBS)allow for the estimation of crustal S-wave velocity,from which is further derived the Vp/Vs ratio to constrain the crustal lithology and geophysical *** a precise S-wave velocity model is important for deep structural research,and inversion of converted S-waves provides a potential ***,the inversion of the converted S-wave remains a weakness because of the complexity of the seismic ray path and the inconsistent conversion *** this study,we introduced two travel time correction methods for the S-wave velocity inversion and imaged different S-wave velocity structures in accordance with the corresponding corrected S-wave phases using seismic data of profile EW6 in the northeastern South China Sea(SCS).The two inversion models show a similar trend in velocities,and the velocity difference is<0.15 km/s(mostly in the range of 0–0.1 km/s),indicating the accuracy of the two travel time correction methods and the reliability of the inversion *** to simulations of seismic ray tracing based on different models,the velocity of sediments is the primary influencing factor in ray tracing for S-wave *** the sedimentary layer has high velocities,the near offset crustal S-wave refractions cannot be *** contrast,the ray tracing of Moho S-wave reflections was not significantly impacted by the velocity of the *** two travel time correction methods have their own advantages,and the application of different approaches is based on additional *** works provide an important reference for future improvements in converted S-wave research.

关键词： converted S-wave S-wave velocity structure inversion ocean bottom seismometer northeastern South China Sea

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Tomographic inversion of OBS converted shear waves:case study of profile EW6 in the Dongsha area

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Acta Oceanologica Sinica 2024年第08期 13-25页

作者： Genggeng Wen Kuiyuan Wan shaohong xia Xiuwei Ye Huilong Xu Chaoyan Fan Jinghe Cao Shunshan Xu CEA Key Laboratory of Earthquake Monitoring and Disaster Mitigation Technology Guangdong Earthquake Agency Guangdong Science and Technology Collaborative Innovation Center for Earthquake Prevention and Disaster Mitigation MOE Key Laboratory of Disaster Forecast and Control in Engineering-Urban Earthquake Safety Laboratory CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of Oceanology Chinese Academy of Sciences Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) Centro de Geociencias Universidad Nacional Autónoma de México

Studies of converted S-wave data recorded on the ocean bottom seismometer(OBS) allow for the estimation of crustal S-wave velocity, from which is further derived the Vp/Vs ratio to constrain the crustal lithology and geophysical properties. Constructing a precise S-wave velocity model is important for deep structural research,and inversion of converted S-waves provides a potential solution. However, the inversion of the converted S-wave remains a weakness because of the complexity of the seismic ray path and the inconsistent conversion *** this study, we introduced two travel time correction methods for the S-wave velocity inversion and imaged different S-wave velocity structures in accordance with the corresponding corrected S-wave phases using seismic data of profile EW6 in the northeastern South China Sea(SCS). The two inversion models show a similar trend in velocities, and the velocity difference is <0.15 km/s(mostly in the range of 0–0.1 km/s), indicating the accuracy of the two travel time correction methods and the reliability of the inversion results. According to simulations of seismic ray tracing based on different models, the velocity of sediments is the primary influencing factor in ray tracing for S-wave phases. If the sedimentary layer has high velocities, the near offset crustal S-wave refractions cannot be traced. In contrast, the ray tracing of Moho S-wave reflections was not significantly impacted by the velocity of the sediments. The two travel time correction methods have their own advantages, and the application of different approaches is based on additional requirements. These works provide an important reference for future improvements in converted S-wave research.

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Submarine volcanism in the southern margin of the South China Sea

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Journal of Oceanology and Limnology 2023年第2期41卷 612-629页

作者： Chenglong ZHANG shaohong xia Chaoyan FAN Jinghe CAO CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China University of Chinese Academy of Sciences Beijing 100049China

Submarine volcanism is widely developed in the South China Sea(SCS).However,the characteristics,distribution,and genesis of submarine volcanoes in the southern margin of the SCS remain *** this study,we analyzed the characteristics of submarine volcanoes and identified a total of 43 submarine volcanoes in the southern margin of the SCS,based on a newly acquired 310-km seismic reflection profile,along with previous 45 multi-channel seismic(MCS)profiles,petrological results from volcanic rocks sampled by dredging and drilling,nearby ocean bottom seismometer(OBS)wide-angle seismic profiles,and gravity and magnetic *** study ascertains that most of these volcanoes are located in fault-block belts and graben-horst zones with strong crustal stretching and *** volcanoes exhibit positive high-amplitude external seismic reflections,weak and chaotic internal seismic reflections,and are accompanied by local deformation of the surrounding sedimentary ***,they have higher positive gravity anomalies and higher magnetic anomalies than the background *** petrological dating results show that volcanic ages are primarily in the Pliocene-Pleistocene,with geochemical characteristics indicating dominance of oceanic island basalt(OIB)-type *** faults have obviously spatial correspondence with post-spreading volcanism,suggesting these faults may provide conduits for submarine *** high-velocity bodies(HVBs)in the lower crust and magma underplating exist in the southern SCS,which could provide a clue of genesis for submarine *** inference is that the intensity of post-spreading volcanism in the southern margin might be affected by stretching faults,crustal thinning and magma underplating.

关键词： submarine volcanoes magmatism extensional fault Nansha Block South China Sea(SCS).

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Three-dimensional S-wave velocity structure of the upper crust in the Guangdong-Hong Kong-Macao Greater Bay Area:insights into the basins structure and genesis of hot springs

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Journal of Oceanology and Limnology 2023年第2期41卷 575-591页

作者： Yingchen LIU shaohong xia Changrong ZHANG Xinyang WANG Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China University of Chinese Academy of Sciences Beijing 100049China

As one of the four largest bay areas with strong economic activities in the world,the Guangdong-Hong Kong-Macao Greater Bay Area(GHMGBA)is located in the zone of interaction between the South China Block(SCB)and the South China Sea(SCS).Under the influence of complex geologic evolution,basin-range structures,fault systems and hot springs are well developed ***,the characteristics of geological structures and the genetic mechanism of these geological phenomena are still ***,we performed ambient noise tomography to obtain 3-D upper crust(0-7.5 km)S-wave velocity structures of the GHMGBA by using 40-day continuous waveform data from 130 seismic stations in the *** results show that sedimentary basins in the GHMGBA are mainly characterized by low-velocity anomalies.S-wave velocities of sediment formation in basins are about 2.8-3.1 km/*** changes in velocity appear at the edges of the basins,which correspond to the NE-,NEE-,and NW-trending faults,indicating prominent basin-controlling effects of the *** Sanshui Basin(SSB),the largest in the GHMGBA,has a developmental depth of about 4 km,and there is a significant difference in velocity gradient between the east and west sides of the basin,indicating that SSB has experienced east-west asymmetric ***,there are prominent low-velocity anomalies at a depth of about 4.5 km beneath the hot springs at the west of the Zhujiang(Pearl)River estuary(ZRE).We infer that the low-velocity anomalies are fluid reservoirs of the hot springs,which lead to the development of the hot springs on the *** addition,the distribution of main cities in the GHMGBA shows a spatial correlation with low-velocity areas at shallow depths(<3 km).The population development trend in the GHMGBA in the past 20 years is also mainly concentrated in the structural province of relatively *** combination with the GHMGBA basin structures and drainage distribution characteristics,we suggest t

关键词： Guangdong-Hong Kong-Macao Greater Bay Area(GHMGBA) ambient noise tomography crustal structure basin hot spring

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Hyperextended crustal structure of the Qiongdongnan Basin and subsequent magmatic influence from the Hainan mantle plume

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Science China Earth Sciences 2022年第5期65卷 845-862页

作者： shaohong xia Chaoyan FAN Dawei WANG Jinghe CAO Fang ZHAO Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China Sanya Institute of Oceanology SCSIOSanya 572100China Institute of Deep-sea Science and Engineering Chinese Academy of SciencesSanya 572000China

The Qiongdongnan Basin(QDNB)is a rift basin located in the extension direction of the oceanic ridge of the Northwest Subbasin of the South China *** basin is surrounded by Late Cenozoic Ocean Island Basalts(OIBs)magmatism associated with the putative Hainan mantle ***,how the Hainan mantle plume has affected the QDNB has not been studied in *** reveal the crustal structure of the QDNB and the possible influence of the Hainan mantle plume,we conducted a wide-angle seismic exploration from Hainan Island across the QDNB to the Xisha Block,and obtained the crustal structure by travel-time *** results show that the crustal stretching factors of the Northern and Southern Rises of the QDNB are estimated to be 1.3-2.0,indicating slight or moderate crustal ***,the crustal stretching factor in the Central Depression of the QDNB is estimated to be more than 3.0,which means that the crust has been *** by two detachment faults(F2 and F11),the upper and lower crust show brittle and ductile thinning,*** anomalous low-velocity conduits penetrating the crystalline crust are developed in the Songnan Uplift and the Southern Rise of the *** P-wave velocities are 5.5-6.0 km s^(−1),which are significantly lower than those of the surrounding crust(6.0-6.8 km s^(−1)).The Late Cenozoic magmatic intrusions(e.g.,sills and dikes)and hydrothermal activities can be observed in the sedimentary strata above these low-velocity *** interpret that the low-velocity conduits might be the crustal magmatic footprints of the Hainan mantle plume,due to the correlated distributions of OIB-type magmatism,the magmatic intrusion patterns,the deep structure of the Hainan mantle plume and the high heat flow of 95 mW m^(−2).Thus,we propose that the crustal structure of the QDNB is the product of crustal hyperextension in the rifting stage and subsequently affected by the Hainan mantle plume *** study provide

关键词： Crustal structure Hyperextension Magmatism Hainan mantle plume Qiongdongnan Basin

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Characteristics of PmP phases from earthquakes and their role in crustal tomography:An active volcanic area example,northeastern Japan

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Science China Earth Sciences 2011年第5期54卷 640-646页

作者： xia shaohong QIU XueLin XU HuiLong ZHAO MingHui SHI xiaoBin Chinese Academy of Sciences Key Laboratory of Marginal Sea Geology South China Sea Institute of Oceanology Chinese Academy of Sciences Guangzhou 510301 China

Later earthquake-sourced PmP phases have the potential to significantly improve ray coverage and resolution of crustal tomography methods,as their trajectories are quite different from those of shallower P *** paper analyzes the characteristics of later PmP arrival times from earthquakes with different focal *** results show that PmP arrival time differences from earthquakes at a range of focal depths are gradually lowered with increasing *** found that where the first recorded P-wave phase was the intra-crustal refraction phase(Pg),the differences in arrival time between Pg and PmP phases decreased with increasing focal depth at an offset of less than 120 *** the first P-wave phase is the upper mantle refraction phase(Pn),the difference in arrival times between Pn and PmP phases became larger with an increase in focal depth at an offset of more than 150 km.A total of 394 PmP phases and 3356 first P phases were picked from seismograms in the active volcanic area of northeastern Japan,according to the characteristics of calculated arrival times,amplitudes and particle *** were used to investigate the role of PmP phases in crustal tomography beneath an active volcanic *** of the detailed resolution analysis show that the addition of PmP data can improve significantly the resolution of the lower crustal structure in tomographic *** the PmP data were included in the tomographic inversion,the path of upwelling magma,along which a series of low-frequency microearthquakes is clearly distributed,was better *** results suggest that the PmP phase has an important role in detailed crustal tomography.

关键词： PmP phase crustal structure tomography earthquake active volcanoes

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Offshore Fault Geometrics in the Pearl River Estuary,Southeastern China:Evidence from Seismic Reflection Data

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Journal of Ocean University of China 2018年第4期17卷 799-810页

作者： CAO Jinghe xia shaohong SUN Jinlong ZHAO Fang WAN Kuiyuan XU Huilong CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesCruangzhou 510301China University of Chinese Academy of Sciences Beijing 100049China

The Pearl River Estuary(PRE) is located at the onshore-offshore transition zone between South China and South China Sea Basin, and it is of great significant value in discussing tectonic relationships between South China block and South China Sea block and seismic activities along the offshore active faults in PRE. However, the researches on geometric characteristics of offshore faults in this area are extremely lacking. To investigate the offshore fault distribution and their geometric features in the PRE in greater detail, we acquired thirteen seismic reflection profiles in 2015. Combining the analysis of the seismic reflection and free-air gravity anomaly data, this paper revealed the location, continuity, and geometry of the littoral fault zone and other offshore faults in PRE. The littoral fault zone is composed of the major Dangan Islands fault and several parallel, high-angle, normal faults, which mainly trend northeast to northeast-to-east and dip to the southeast with large displacements. The fault zone is divided into three different segments by the northwest-trending faults. Moreover, the basement depth around Dangan Islands is very shallow, while it suddenly increases along the islands westward and southward. These has resulted in the islands and neighboring areas becoming the places where the stress accumulates easily. The seismogenic pattern of this area is closely related to the comprehensive effect of intersecting faults together with the low velocity layer.

关键词： offshore active faults littoral fault zone Pearl River Estuary earthquake seismic reflection data

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Western fault zone of South China Sea and its physical simulation evidences

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Acta Oceanologica Sinica 2006年第3期25卷 58-67页

作者： SUN Longtao SUN Zhen ZHAN Wenhuan SUN Zongxun ZHAO Minghui xia shaohong Key Laboratory of Marginal Sea Geology South China Sea Institute of Oceanology Chinese Academy of Sciences Guangzhou 510301 China Graduate School of the Chinese Academy of Sciences Beijing 100039 China

The western fault zone of the South China Sea is a strike-slip fault system and consists of four typical strike-slip faults. It is the western border of the South China Sea. The formation of the system is due to the extrusion of Indo - China Peninsula caused by the collision of India with Tibet and the spreading of the South China Sea in Cenozoic. There are five episodes of tectonic movement along this fault zone, which plays an important role in the Cenozoic evolution of the South China Sea. By the physical modeling experiments, it can be seen the strike-slip fault undergoes the sinistral and dextral movement due to the relative movement velocity change between the South China Sea block and the Indo - China block. The fault zone controls the evolution of the pull basins locating in the west of the South China Sea.

关键词： western margin of South China Sea fault zone physical modeling experiments

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Spatial Variations of b-Values in the Coastal Area of Guangdong

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Journal of Ocean University of China 2018年第1期17卷 177-185页

作者： ZHOU Pengxiang xia shaohong SUN Jinlong CAO Jinghe XU Huilong ZHAO Fang CHEN Chuanxu CAS Key Laboratory of Ocean and Marginal Sea Geology South ChinaSea Institute of OceanologyChinese Academy of Sciences College of Earth Sciences University of Chinese Academy of Sciences Institute of Deep-Sea Science and Engineering Chinese Academy of Sciences

We used earthquake catalogs recorded by Guangdong Seismological Network from 2008 to 2014 to resolve the spatial variations of b-values in the coastal area of Guangdong, particularly in three key research areas(Yangjiang, Heyuan, and offshore Nanao Island) with strong seismicity. Our results revealed that b-values exhibited significant spatial variations, and zones with low b-values could indicate the most likely seismogenic area of large earthquakes. We observed three clear low b-value patches in the offshore Nanao Island. We found a distinct high b-value peak at the depth of 11 km and two minimum peaks at about 14 and 7–8 km in the Yangjiang area. The overall b-values generally decrease with depth in the Heyuan area. The spatial variations of b-values reflect tectonic anomalies; that is, the ‘low-high-low' distribution of b-values in the offshore Nanao Island and the Yangjiang area may indicate the anomaly of the crustal structure with a weak layer. The b-values of reservoir-induced seismicity are obviously lower than that induced by tectonism. This finding indicates that the reservoir area is generally at high stress state under the condition of high pore pressure. We inferred that large earthquakes might be prone to occur at 10–12 km depth in the offshore Nanao Island, at 12–15 km depth in the Yangjiang area, and at the lower part of the seismic activity zone in the Heyuan area. Moreover, the upstream area of the Xinfengjiang reservoir is the most likely area of future large earthquakes in the Heyuan area.

关键词： b-values earthquake Guangdong seismogenic area stress

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Seismotectonics of the Taiwan Shoal Region in the Northeastern South China Sea:Insights from the Crustal Structure

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Journal of Ocean University of China 2018年第1期17卷 156-168页

作者： WAN Kuiyuan SUN Jinlong XU Huilong XIE xiaoling xia shaohong ZHANG xiang CAO Jinghe ZHAO Fang FAN Chaoyan CAS Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China University of Chinese Academy of Sciences Beijing 100049China Earthquake Administration of Hainan Province Haikou 570203China Earthquake Administration of Guangdong Province Guangzhou 510070China

A cluster of earthquakes occurred in the Taiwan Shoal region on the outer rise of the Manila Trench. Although most were of small to medium magnitudes, one strong earthquake occurred on September 16, 1994. Several previous studies have provided important information to progress our understanding of this single earthquake. However, little is currently known about the earthquake cluster, and it is necessary to investigate the deep crustal structure of the Taiwan Shoal region to understand the mechanisms involved in controlling and generating it. This study presents a two-dimensional seismic tomographic image of the crustal structure along the OBS2012 profile based on ocean-bottom seismograph(OBS) data, which exhibits a high-velocity anomaly flanked by low-velocity anomalies in the upper crust beneath the Taiwan Shoal. In this study, 765 earthquakes(Richter magnitude ML > 1.5) occurring between 1991 and 2015 were studied and analyses of earthquake epicenters, regional faults, and the crustal structure provides an improved understanding of the nature of active tectonics in this region. Results of analyses indicate firstly that the high-velocity area represents major asperities that correspond to the location of the earthquake cluster and where stress is concentrated. It is also depicted that the earthquake cluster was influenced by fault interactions. However, the September 1994 earthquake occurred independently of these seismic activities and was associated with reactivation of a preexisting fault. It is also determined that slab pull is resisted by the exposed precollision accretionary prism, and the resistive force is causing accumulation of inplane compressive-stress. This may trigger a future damaging earthquake in the Taiwan Shoal region.

关键词： earthquake cluster crustal structure fault interactions outer rise Taiwan Shoal

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