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seismic anisotropy and upper mantle dynamics in Alaska:A review of shear wave splitting analyses

Earthquake Research Advances 2024年第2期4卷 72-81页

作者： Zhaofeng Jin Yuchen Yang Muhammad Ishaidir Siregar Zihao Mu S.M.Ariful Islam Qichao Zhao Dan Wang Fan Zhang Xugang Yang Liwei Song School of Earth Sciences Northeast Petroleum UniversityDaqing163318China Department of Geoscience University of IndonesiaDepok16424Indonesia School of Computer and Information Technology Northeast Petroleum UniversityDaqing163318China Center for Earthquake Research and Information University of MemphisMemphis38152USA College of Environment and Civil Engineering Chengdu University of TechnologyChengdu610059China School of Petroleum Engineering China University of PetroleumQingdao266555China School of Physics and Electronic Engineering Northeast Petroleum UniversityDaqing163318China

Shear wave splitting(SWS)is regarded as the most effective geophysical method to delineate mantle flow fields by detecting seismic azimuthal anisotropy in the earth's upper mantle,especially in tectonically active regions such as subduction *** Aleutian-Alaska subduction zone has a convergence rate of approximately 50 mm/yr,with a trench length reaching nearly 2800 *** a long subduction zone has led to intensive continental deformation and numerous strong earthquakes in southern and central Alaska,while northern Alaska is relatively *** sharp contrast makes Alaska a favorable locale to investigate the impact of subduction on mantle ***,the uniqueness of this subduction zone,including the unusual subducting type,varying slab geometry,and atypical magmatic activity and composition,has intrigued the curiosity of many *** identify different sources of seismic anisotropy beneath the Alaska region and probe the influence of a geometrically varying subducting slab on mantle dynamics,extensive SWS analyses have been conducted in the past ***,the insufficient station and azimuthal coverage,especially in early studies,not only led to some conflicting results but also strongly limited the in-depth investigation of layered anisotropy and the estimation of anisotropy *** the completion of the Transportable Array project in Alaska,recent studies have revealed more detailed mantle structures and characteristics based on the dense station coverage and newly collected massive seismic *** this study,we review significant regional-and continental-scale SWS studies in the Alaska region and conclude the mantle flow fields therein,to understand how a geometrically varying subducting slab alters the regional mantle *** summarized mantle flow mechanisms are believed to be conducive to the understanding of seismic anisotropy patterns in other subduction zones with a complicated tectonic setting.

关键词： seismic anisotropy Shear wave splitting Mantle flow Alaska subduction zone Slab

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Segmental nature of the Red River fault revealed by seismic anisotropy and geological structures

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Science China Earth Sciences 2024年第8期67卷 2423-2443页

作者： Ying LI Yuan GAO School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China Key Laboratory of Earthquake Prediction Institute of Earthquake ForecastingChina Earthquake AdministrationBeijing 100036China

As the western boundary of the Sichuan-Yunnan block(SYB),the Red River fault(RRF)is a major fault that controls deep crustal movement and deformation in the southeast margin of the Tibetan Plateau and regulates middle-lower crustal *** data suggest that the RRF is segmented and exhibits distinct variations in seismicity,velocity structure and crustal deformation from north to *** anisotropy reveals a complex pattern of lateral spatial and vertical stratified distributions.(1)From the perspective of crustal stratification,in the upper crust,the fast wave polarization in the north segment of the RRF is complex and possibly influenced by the Sanjiang lateral collision zone and adjacent faults with varying *** fast wave polarization in the middle segment is in the NW-SE direction,indicating a localized area of closed down or locked up with consistent *** in the south segment,it presents a disordered pattern,signifying complex deep tectonics and stress conditions at the wedged intersection *** the middle-lower crust in the north and south segments of the RRF,the azimuthal anisotropy is strong and consistent with the spatial strike of the weak zone characterized by low-velocity and *** suggests a connection between the anisotropy and the material migration.(2)In the whole crustal scale,the fast wave directions in two sides of the RRF are consistent with the NW-SE tectonic *** indicates that the RRF,as a large fault potentially cutting through the whole crust,strongly controls the surrounding media.(3)In the lithospheric scale,the fast wave polarizations are oriented nearly E-W and independent of the fault strike,consistent with the low P-and S-wave velocity structures and positive radial anisotropy in the upper *** fast wave directions could be related to lithospheric olivine deformation and asthenospheric *** paper suggests a decoupling of deformation between the crust and the lithospheri

关键词： Red River fault seismic anisotropy Geological structures Lithosphere Fault segmentation

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Major methods of seismic anisotropy

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Earthquake Research Advances 2024年第3期4卷 82-91页

作者： Xinai Zhao Jing Wu State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing100049China

seismic anisotropy reveals that seismic wave velocity, amplitude, and other physical properties show variations in different directions, which can be divided into lattice-preferred orientation(LPO) and shape-preferred orientation(SPO) according to its physical mechanisms. The main methods for studying seismic anisotropy include shearwave splitting analysis, P-wave travel time inversion and surface-wave tomography, etc. There are some differences and correlations among these methods. seismic anisotropy is an important way to reveal the dynamic processes of crust-mantle evolution, and it is significant for monitoring crustal stress changes and improve seismic exploration studies. With the help of long-term observation, the application of machine learning techniques and combining inversion based on multiple phases would become potential developments in seismic anisotropy studies. This may improve the understanding of complex seismic anisotropic models, such as multiple layers anisotropy with an oblique axis of symmetry.

关键词： seismic anisotropy Shear-wave splitting P-wave travel time inversion Surface-wave tomography

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seismic anisotropy of the crust in Yunnan,China:Polarizations of fast shear-waves

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Acta Seismologica Sinica(English Edition) 2006年第6期19卷 620-632页

作者：石玉涛高原吴晶罗艳苏有锦 Institute of Earthquake Science China Earthquake AdministrationBeijing 100036 China Earthquake Administration of Yunnan Province Kunming 650041 China

Using seismic data recorded by Yunnan Telemetry seismic Network from January 1, 2000 to December 31, 2003, the dominant polarization directions of fast shear-waves are obtained at 10 digital seismic stations by SAM technique, a systematic analysis method on shear-wave splitting, in this study. The results show that dominant directions of polarizations of fast shear-waves at most stations are mainly at nearly N-S or NNW direction in Yunnan. The dominant polarization directions of fast shear-waves at stations located on the active faults are consistent with the strike of active faults, directions of regional principal compressive strains measured from GPS data, and basically consistent with regional principal compressive stress. Only a few of *** complicated polarization pattern of fast shear-waves, or are not consistent with the strike of active faults and the directions of principal GPS compressive strains, which are always located at junction of several faults. The result reflects complicated fault distribution and stress field. The dominant polarization direction of fast shear-wave indicates the direction of the in-situ maximum principal compressive stress is controlled by multiple tectonic aspects such as the regional stress field and faults.

关键词： seismic anisotropy polarization of fast shear-wave principal compressive stress active faults GPS

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seismic anisotropy beneath the Chinese mainland

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Earthquake Science 2010年第6期23卷 583-595页

作者： Yuanyuan V. Fu Yongshun John Chen Aibing Li Department of Geosciences University of Houston TX 77204 USA Department of Geophysics School of Earth and Space Sciences Peking University Beijing 100871 China

We investigated the upper mantle anisotropy beneath China by applying teleseismic shear wave splitting measurements at 119 seismic stations from CDSN and GSN//RIS networks in China. The splitting observations are characterized by apparent diversity of anisotropy pattern in adjacent tectonic domains, including the Tianshan orogenic belt, Tibetan plateau, the Yangtze craton, the North China craton and northeastern region. In western China （Tianshan orogenic belt and Tibetan plateau）, fast polarization directions of split SKS waves coincide strikingly well with the dominating trend of deformational crustal features and delay times range from 0.5 s to 1.6 s. While in eastern China, seismic anisotropy deduced from shear wave splitting reveals a homogeneous NW-SE trending structure, almost perpendicular to the strike of large-scale surface structures. The observed delay times of 1.5 s to more than 2 s favor consistent mantle flow over large mantle thicknesses Based upon the straightforward relationships between seismic anisotropy and the development of lattice preferred orientation of mineral in upper mantle rocks, we interpret the splitting results in terms of tectonic fabric within the upper mantle. Since the lithosphere is less than 100 km thick beneath eastern China and the observed fast directions are subparallel to the trend of the absolute plate motion （APM） of Eurasian plate, we propose that the asthenosphere may mainly contribute to the anisotropic effects beneath eastern China. However, the upper mantle anisotropy beneath western China may have developed more recently in the subcrustal lithosphere because of rather small delay times and thick lithosphere. We also use the opportunity of the dense geodetic measurements available in China to discuss the coupling between the crust and mantle. In the Eura- sia-fixed reference frame, GPS and shear wave splitting both depict a similar trend beneath eastern China, suggesting a lithospheric block ＂escaping＂ toward the ea

关键词： China shear wave splitting seismic anisotropy GPS

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seismic anisotropy IN THE LOWER CRUST INDUCED BY THE LATTICE PREFERRED ORIENTATIONS OF MINERALS

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地震地质 1989年第4期 24-30页

作者： David Mainpric 34060 Montpellier Cedex Franoe Laboratoire de Tectonophysique Place Eug.Bataillon U.S.T.L.

To identify the physical properties responsible for the seismic reflections from the deep ductile shear zones, we have undertaken a study on the effect of lattice preferred orientation (LPO) on the seismic velocity anisotropy. LPO has been quantitatively determined by U-stage measurement for plagioclase (An 49), diopside and hornblende from an extensively deformed basic mylonite from Jotun Nappe, Norway. The typical plagioclase fabrics are produced by plastic flow on (010) [001], and the normal diopside and hornblende fabrics are produced by (100)[001] slip. The complete seismic properties (VP, VS, VSS and △VS) with respect to structural frame (foliation and lineation) have been calculated for hypothetical monomineralic and polymineralic aggregates from the elasstic stiffness coefficients and LPO data. The calculations show that the strongest Vp anisotropies develop in monomineralic rocks with values between 5% and 14%, compared with 5.6% and 7.8% for granulite (50% P1, 50% Di) and amphibolite (50% P1,

关键词： LPO seismic anisotropy Basic mylonite Ductile shear zones in the lower crust

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Mantle flow underneath the South China Sea revealed by seismic anisotropy

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National Science Review 2023年第10期10卷 54-61页

作者： Fansheng Kong Rui Gao Stephen S.Gao Kelly H.Liu Weiwei Ding Xiongwei Niu Aiguo Ruan Pingchuan Tan Jianke Fan Shaoping Lu Zhengyi Tong Liqun Cheng Wenfei Gong Yanghui Zhao Jiabiao Li Key Laboratory of Submarine Geosciences Second Institute of OceanographyMinistry of Natural Resources Southern Marine Science and Engineering Guangdong Laboratory Geology and Geophysics Program Department of Geosciences and Geological and Petroleum Engineering Missouri University of Science and Technology School of Earth Sciences and Engineering Sun Yat-sen University Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of Sciences

It has long been established that plastic flow in the asthenosphere interacts constantly with the overlying lithosphere and plays a pivotal role in controlling the occurrence of geohazards such as earthquakes and volcanic ***,accurately characterizing the direction and lateral extents of the mantle flow field is notoriously difficult,especially in oceanic areas where deployment of ocean bottom seismometers(OBSs) is expensive and thus *** this study,by applying shear wave splitting analyses to a dataset recorded by an OBS array that we deployed between mid-2019 and mid-2020 in the South China Sea(SCS),we show that the dominant mantle flow field has a NNW-SSE orientation,which can be attributed to mantle flow extruded from the Tibetan Plateau by the ongoing Indian-Eurasian *** addition,the results suggest that E-W oriented flow fields observed in South China and the Indochina Peninsula do not extend to the central SCS.

关键词： mantle flow South China Sea Tibetan Plateau seismic anisotropy shear wave splitting

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Reservoir stress path and induced seismic anisotropy： results from linking coupled fluid-flow/geomechanical simulation with seismic modelling

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Petroleum Science 2016年第4期13卷 669-684页

作者： D.A.Angus Q.J.Fisher J.M.Segura J.P.Verdon J.-M.Kendall M.Dutko A.J.L.Crook School of Earth and Environment University of LeedsLeeds UK Formerly School of Earth and Environment University of Leeds Leeds UK Department of Earth Sciences University of Bristol BristolUK Rockfield Software Ltd. Swansea UK Three Cliffs Geomechanics Swansea UK Repsol Madrid Spain ESG Solutions Kingston Canada

We present a workflow linking coupled fluid-flow and geomechanical simulation with seismic modelling to predict seismic anisotropy induced by non-hydrostatic stress changes. We generate seismic models from coupled simulations to examine the relationship between reservoir geometry, stress path and seismic anisotropy. The results indicate that geometry influences the evolution of stress,which leads to stress-induced seismic anisotropy. Although stress anisotropy is high for the small reservoir, the effect of stress arching and the ability of the side-burden to support the excess load limit the overall change in effective stress and hence seismic anisotropy. For the extensive reservoir, stress anisotropy and induced seismic anisotropy are high. The extensive and elongate reservoirs experience significant compaction, where the inefficiency of the developed stress arching in the side-burden cannot support the excess *** elongate reservoir displays significant stress asymmetry,with seismic anisotropy developing predominantly along the long-edge of the reservoir. We show that the link betweenstress path parameters and seismic anisotropy is complex,where the anisotropic symmetry is controlled not only by model geometry but also the nonlinear rock physics model used. Nevertheless, a workflow has been developed to model seismic anisotropy induced by non-hydrostatic stress changes, allowing field observations of anisotropy to be linked with geomechanical models.

关键词： Coupled fluid-flow/geomechanics Reservoir characterization seismic anisotropy Stress path

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Lattice Preferred Orientation, Water Content, and seismic anisotropy of Orthopyroxene

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Journal of Earth Science 2010年第5期21卷 555-568页

作者： Haemyeong Jung Munjae Park Sejin Jung Jaeseok Lee Tectonophysics Laboratory School of Earth and Environmental Sciences Seoul National University Seoul 151-747 Korea

Lattice preferred orientation （LPO） and seismic anisotropy of orthopyroxene （enstatite） in mantle xenoliths from Spitsbergen, Svalbard, near the Arctic, are studied. LPOs of enstatite were determined using electron backseattered diffraction （EBSD）. We found four types of LPOs of orthopyroxene and defined them as type-AC, -AB, -BC, and -ABC. Type-AC LPO of orthopyroxene is defined as （100） plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-AB LPO is defined as （100） plane aligned subparallel to foliation and [010] axis aligned subparallel to linea- tion. Type-BC LPO is defined as （010） plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-ABC LPO is defined as both （100） and （010） planes aligned subparallel to foliation with a girdle distribution of both [100] and [010] axes normal to lineation and [001] axis aligned subparallel to lineation. We report for the first time the type-AB, -BC, and -ABC LPO of orthopyroxerie. We found that the LPO pattern has a correlation with the content of orthopyroxene in the specimen. Nicolet 6700 FTIR （Fourier transformation infrared） study of enstatite showed that type-AC LPO was observed mostly in the samples of enstatite with low water content. It is found that the strength of the LPO of enstatite decreases with increasing water content and has a correlation with the strength of the LPO of olivine： the stronger the LPO of enstatite, the stronger the LPO of olivine. seismic anisotropy of enstatite was smaller than that of olivine in the same specimen.

关键词： orthopyroxene lattice preferred orientation seismic anisotropy mantle xenolith Spitsbergen FTIR.

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Crustal seismic anisotropy in southeastern Capital area, China

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Earthquake Science 2008年第1期21卷 1-10+108页

作者：吴晶高原陈运泰 Beijing 100081 China Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Institute of Geophysics China Earthquake Administration Institute of Geophysics China Earthquake Administration

Shear-wave splitting parameters of 24 stations in southeastern Capital area of North China （38.5°N;9.85°N, 115.5°E;18.5°E） are obtained with systematic analysis method of shear-wave splitting （SAM） based on the data recorded by Capital Area Seismograph Network （CASN） from 2002 to 2005. The results show that the average polarization of fast shear-wave in southeastern Capital area is consistent with regional maximum horizontal prin- cipal compressive stress in the area, and is also consistent with maximum horizontal principal compressive strain from GPS in North China. The average shear-wave splitting in southeastern Capital area （in basin） is different from that in northwestern Capital area where uplifts and basin exist, which means that tectonics can be related to shear-wave splitting results. Research also shows that the distribution of faults around stations can obviously affect the shear-wave splitting results, and complicated distribution of faults can result in much more scatter of shear-wave splitting. Moreover, in the north and south of the studied area （southeastern Capital area）, the polariza- tions of fast shear-wave are not very consistent, which may be related to differences in tectonic and stress for the two areas.

关键词： southeastern Capital area seismic anisotropy shear-wave splitting crust stress

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