Table of Content

20 June 2017, Volume 39 Issue 3

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INFLUENCE OF PRESSURE HEAD CHANGE AND ITS CHANGE RATE ON RESERVOIR TRIGGERED SEISMICITY -A CASE STUDY OF ZIPINGPU RESERVOIR

LIU Yuan-zheng, MA Jin, MA Wen-tao, JIANG Tong

2017, 39(3):  437-450.  DOI: 10.3969/j.issn.0253-4967.2017.03.001

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For analyzing the role that reservoir impounding plays in triggering earthquake, the process of diffusion of pore pressure and its mechanism of action should be understood firstly. The temporal distribution of seismicity, which occurred before the M_S8.0 Wenchuan earthquake, following the impoundment of Zipingpu reservoir is studied in this paper. Then the mechanisms of the occurrence and development of reservoir triggered seismicity are discussed. A comparative analysis of the temporal distribution of seismicity and the submerged area by reservoir impounding is carried out firstly. Then the influence of various factors on modeling is analyzed in detail. After calculating, the pore pressure change by the Zipingpu reservoir impoundment is obtained. The following observations are made:(1)Conspicuous swarms of earthquakes, of which the sources are located on the same fault of the M_S8.0 Wenchuan earthquake, occurred orderly with the impoundment of Zipingpu reservoir.(2)Because of the influences of the terrain and the medium, the range of effect of pore pressure change by the impoundmemt is limited and anisotropic. Hydraulic diffusivities(D)of 0.7 and 0.35m²/s along the fault strike and the fault dip are reached respectively by a semi-quantitative assessment. Of course, the qualitative pressure constraints on the surface are also applied for the modeling.(3)The calculation results show that the temporal distribution of seismicity near the Zipingpu reservoir is related with the pore pressure change. After the pore pressure reached the threshold of triggering earthquake, whether the pressure head change is high or not, the change rate of pressure head change plays a key role in the decrease or increase of seismicity. It means that the triggered seismicity by pore pressure is a dynamic triggering process.

COULOMB STRESS EVOLUTION AND SEISMIC HAZARD ALONG THE EASTERN BOUNDARY OF THE SICHUAN-YUNNAN BLOCK

XU Jing, JI Ling-yun, JI Cun-wei, SUN He, ZHAO Qiang

2017, 39(3):  451-469.  DOI: 10.3969/j.issn.0253-4967.2017.03.002

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Using a more realistic model of multi-layered viscoelastic media, and considering the effects of the coseismic dislocation and the postseismic viscoelastic relaxation caused by the 34 great earthquakes occurring along the eastern boundary of the Sichuan-Yunnan block since 1480 and the interseismic stress accumulation caused by the tectonic loading generated by plate motions which were modeled by introducing "virtual negative displacements" along the major fault segment in the region under study, we calculated the evolution of the Coulomb stress change in each fault plane of 18 major fault segments along the eastern boundary caused by the coseismic, postseismic and interseismic effects. We studied the interactions of the Xianshuihe, Anninghe, Zemuhe and Xiaojiang fault zones on the eastern boundary of the Sichuan-Yunnan block. By evaluating if the previous earthquake could bring another earthquake closer to or farther from failure, we analyzed the interactions of the earthquakes which occurred in the different segments in the same fault zone, or in the different fault zones respectively. And further based on the calculation results of the Coulomb stress change on the fault planes, we analyzed the seismic hazard of each fault segment.The results show that the previous earthquake may trigger another earthquake which can occur in the same fault zone or in the different fault zone. And the calculation results on the evolution of the cumulative Coulomb stress change in the each fault segment show that, the Coulomb stress increases significantly in the middle section and the Moxi segment of the Xianshuihe fault zone, the Mianning-Xichang segment of the Anninghe fault zone, the Qiaojia-dongchuan segment and the Jianshui segment of the Xiaojiang fault zone, and the seismic hazard in these fault segments is worthy paying attention to.

SPATIAL AND TEMPORAL DISTRIBUTION OF SLIP RATE DEFICIT ACROSS HAIYUAN-LIUPAN SHAN FAULT ZONE CONSTRAINED BY GPS DATA

HAO Ming, LI Yu-hang, QIN Shan-lan

2017, 39(3):  471-484.  DOI: 10.3969/j.issn.0253-4967.2017.03.003

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As the northeast boundary of the Tibetan plateau, the Haiyuan-Liupan Shan fault zone has separated the intensely tectonic deformed Tibetan plateau from the stable blocks of Ordos and Alxa since Cenozoic era. It is an active fault with high seismic risk in the west of mainland China. Using geology and geodetic techniques, previous studies have obtained the long-term slip rate across the Haiyuan-Liupan Shan fault zone. However, the detailed locking result and slip rate deficit across this fault zone are scarce. After the 2008 Wenchuan M_S8.0 earthquake, the tectonic stress field of Longmen Shan Fault and its vicinity was changed, which suggests that the crustal movement and potential seismic risk of Haiyuan-Liupan Shan fault zone should be investigated necessarily.
Utilizing GPS horizontal velocities observed before and after Wenchuan earthquake(1999~2007 and 2009~2014), the spatial and temporal distributions of locking and slip rate deficit across the Haiyuan-Liupan Shan fault zone are inferred. In our model, we assume that the crustal deformation is caused by block rotation, horizontal strain rate within block and locking on block-bounding faults. The inversion results suggest that the Haiyuan fault zone has a left-lateral strike-slip rate deficit, the northern section of Liupan Shan has a thrust dip-slip rate deficit, while the southern section has a normal dip-slip rate deficit. The locking depths of Maomao Shan and west section of Laohu Shan are 25km during two periods, and the maximum left-lateral slip rate deficit is 6mm/a. The locking depths of east section of Laohu Shan and Haiyuan segment are shallow, and creep slip dominates them presently, which indicates that these sections are in the postseismic relaxation process of the 1920 Haiyuan earthquake. The Liupan Shan Fault has a locking depth of 35km with a maximum dip-slip rate deficit of 2mm/a. After the Wenchuan earthquake, the high slip rate deficit across Liupan Shan Fault migrated from its middle to northern section, and the range decreased, while its southern section had a normal-slip rate deficit.
Our results show that the Maomao Shan Fault and west section of Laohu Shan Fault could accumulate strain rapidly and these sections are within the Tianzhu seismic gap. Although the Liupan Shan Fault accumulates strain slowly, a long time has been passed since last large earthquake, and it has accumulated high strain energy possibly. Therefore, the potential seismic risks of these segments are significantly high compared to other segments along the Haiyuan-Liupan Shan fault zone.

THE 2008 AND 2009 QAIDAM, CHINA EARTHQUAKES:INSAR ANALYSIS FOR COSEISMIC DISPLACEMENTS AND INVERSION FOR FAULT MODELS

XU Xiao-bo, SHAN Xin-jian, QU Chun-yan, ZHANG Guo-hong, MA Chao, SONG Xiao-gang, ZHANG Gui-fang, WEN Shao-yan

2017, 39(3):  485-496.  DOI: 10.3969/j.issn.0253-4967.2017.03.004

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This study focuses on four moderate-sized earthquakes in the northern margin of the Qaidam Basin, northeastern Tibet Plateau, China, of which one occurred in 2008, and three in 2009, respectively. We obtain coseismic displacement fields of these four events using Envisat descending ASAR data and D-InSAR technology. The results show that the 2008 earthquake has only one deformation center and the 2009 earthquakes have three deformation centers in their fields. The maximum displacement of 2008 and 2009 earthquakes are 0.097m and 0.41m in the LOS(line of sight), respectively. We invert ground displacements of these earthquakes based on elastic dislocation models to estimate slip distribution on fault planes. For the 2008 event, using a one-segment fault model, the inversion reveals peak slip of about 0.47m occurring at a depth of 19km. For the 2009 earthquakes, the ground displacement pattern observed by InSAR can be fitted by a three-segment fault model with smallest RMS of residuals. The three sectional fault model is considered the most reliable.

DETRITAL ZIRCON U-PB DATING OF MODERN RIVERS' DEPOSITS IN PAMIR, SOUTH TIAN SHAN AND THEIR CONVERGENCE ZONE

LIU Lang-tao, CHEN Jie, LI Tao

2017, 39(3):  497-516.  DOI: 10.3969/j.issn.0253-4967.2017.03.005

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By dating detrital zircon U-Pb ages of deposition sequence in foreland basins, we can analyze the provenance of these zircons and further infer the tectonic history of the mountain belts. This is a new direction of the zircon U-Pb chronology. The precondition of using this method is that we have to have all-around understanding to the U-Pb ages of the rocks of the orogenic belts, while the varied topography, high altitude of the zircon U-Pb ages of the orogenic belts are very rare and uneven. This restricts the application of this method. Modern river deposits contain abundant geologic information of their provenances, so we can probe the zircon U-Pb ages of the geological bodies in the provenances by dating the detrital zircon U-Pb ages of modern rivers' deposits. We collected modern river deposits of 14 main rivers draining from Pamir, South Tian Shan and their convergence zone and conducted detrital zircon U-Pb dating. Combining with the massive bed rock zircon U-Pb ages of the magmatic rocks and the detrital zircon U-Pb ages of the modern fluvial deposit of other authors, we obtained the distribution characteristics of zircon U-Pb ages of different tectonic blocks of Pamir and South Tian Shan. Overlaying on the regional geological map, we pointed out the specific provenance geological bodies of different U-Pb age populations and speculated the existence of some new geological bodies. The results show that different tectonic blocks have different age peaks. The main age peaks of South Tian Shan are 270~289Ma and 428~449Ma, that of North Pamir are 205~224Ma and 448~477Ma, Central Pamir 36~40Ma, and South Pamir 80~82Ma and 102~106Ma. The Pamir syntaxis locates at the west end of the India-Eurasia collision zone. The northern boundary of the Pamir is the Main Pamir Thrust(MPT)and the Pamir Front Thrust(PFT). In the Cenozoic, because of the squeezing action of the India Plate, the Pamir thrust a lot toward the north and the internal terranes of the Pamir strongly uplifted. For the far-field effect of the India-Eurasia collision, the Tian Shan on the north margin of the Tarim Basin also uplifted intensely during this period. Extensive exhumation went along with these upliftings. The material of the exhumation was transported to the foreland basin by rivers, which formed the very thick Cenozoic deposition sequence. These age peaks can be used as characteristic ages to recognize these tectonic blocks. These results lay a solid foundation for tracing the convergence process of Pamir and South Tian Shan in Cenozoic with the help of detrital zircon U-Pb ages of sediments in the foreland basin.

PRINCIPAL COMPONENT ANALYSIS AND LOCAL CORRELA-TION TRACKING AS TOOLS FOR REVEALING AND ANALYZING SEISMO-ELECTROMAGNETIC SIGNAL OF EARTHQAUKE

LI Jian-kai, TANG Ji

2017, 39(3):  517-535.  DOI: 10.3969/j.issn.0253-4967.2017.03.006

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This study provides new seismo-electromagnetic data processing methods to extract the anomalous signals by combining the principal component analysis(PCA)and local correlation tracking(LCT)methods. The PCA method can separate signals of different frequencies by projecting them to different axes according to their energy. So it can solve the problems of identifying the relatively weak signals in strong interference background to a certain extent. The LCT method is more suitable for non-stationary signal processing compared with classical cross-correlation method. This method is based on the good spatial correlation between the magnetic field components of different ELF stations to pick up the correlation coefficient, so as to achieve the purpose of weak anomalies signals identification. As a case study of the M4.6 Jinggu earthquake in Yunnan, China, we investigated the electromagnetic data observed by ELF stations near the epicenter. First, we applied the PCA method to the magnetic-filed data and got the temporal variation of percentage of each principal component. The results indicate that the contribution of the second principal components, which may relate with the earthquake, increased significantly about a week before the earthquake. Then, we applied the LCT method to the magnetic-filed data processing as well, and the results of both north-south and east-west magnetic field components showed that local correlation coefficient saw anomalies about a week before the earthquake, which had a good corresponding relationship with the former results by PCA method. Both means for the same earthquake case got a consistent conclusion, which not only enhanced the reliability of the results, but also confirmed the effectiveness of two methods applied in the earthquake-related electromagnetic anomalies extraction. We also discussed the possible relationship between these anomalies and the earthquake. Although there are no direct evidence and supporting theories in terms of the relationship between abnormal electromagnetic signals and earthquakes at present, the studies in this paper may strengthen the understanding of seismoelectromagnetic phenomena and promote further research.

RESEARCH OF SEISMOGENIC STRUCTURE OF THE MENYUAN M_S6.4 EARTHQUAKE ON JANUARY 21, 2016 IN LENGLONGLING AREA OF NE TIBETAN PLATEAU

JIANG Wen-liang, LI Yong-sheng, TIAN Yun-feng, HAN Zhu-jun, ZHANG Jing-fa

2017, 39(3):  536-549.  DOI: 10.3969/j.issn.0253-4967.2017.03.007

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On January 21 2016, an earthquake of M_S6.4 hit the Lenglongling fault zone(LLLFZ)in the NE Tibetan plateau, which has a contrary focal mechanism solution to the Ms 6.4 earthquake occurring in 1986. Fault behaviors of both earthquakes in 1986 and 2016 are also quite different from the left-lateral strike-slip pattern of the Lenglongling fault zone. In order to find out the seismogenic structure of both earthquakes and figure out relationships among the two earthquakes and the LLLFZ, InSAR co-seismic deformation map is constructed by Sentinel -1A data. Moreover, the geological map, remote sensing images, relocation of aftershocks and GPS data are also combined in the research. The InSAR results indicate that the co-seismic deformation fields are distributed on both sides of the branch fault(F₂)on the northwest of the Lenglongling main fault(F₁), where the Earth's surface uplifts like a tent during the 2016 earthquake. The 2016 and 1986 earthquakes occurred on the eastern and western bending segments of the F₂ respectively, where the two parts of the F₂ bend gradually and finally join with the F₁. The intersections between the F₁ and F₂ compose the right-order and left-order alignments in the planar geometry, which lead to the restraining bend and releasing bend because of the left-lateral strike-slip movement, respectively. Therefore, the thrust and normal faults are formed in the two bending positions. In consequence, the focal mechanism solutions of the 2016 and 1986 earthquakes mainly present the compression and tensional behaviors, respectively, both of which also behave as slight strike-slip motion. All results indicate that seismic activity and tectonic deformation of the LLLFZ play important parts in the Qilian-Haiyuan tectonic zone, as well as in the NE Tibetan plateau. The complicated tectonic deformation of NE Tibetan plateau results from the collisions from three different directions between the north Eurasian plate, the east Pacific plate and the southwest Indian plate. The intensive tectonic movement leads to a series of left-lateral strike-slip faults in this region and the tectonic deformation direction rotates clockwise gradually to the east along the Qilian-Haiyuan tectonic zone. The Menyuan earthquake makes it very important to reevaluate the earthquake risk of this region.

THE NEW ACTIVITY OF TAN-LU FAULT ZONE IN SEGMENT OF DAHONGSHAN SINCE LATE QUATERNARY

ZHAO Peng, YAO Da-quan, YANG Yuan-yuan, ZHENG Hai-gang, FANG Liang-hao

2017, 39(3):  550-560.  DOI: 10.3969/j.issn.0253-4967.2017.03.008

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The relationship between the latest activity of active fault and seismic events is of the utmost importance. The Tan-lu fault zone in eastern China is a major fault zone, of which the active characteristics of the segments in Jiangsu, Shandong and Anhui has been the focus of research. This study takes the Dahongshan segment of the Tanlu Fault in Sihong County as the main research area. We carried out a detailed geological survey and excavated two trenches across the steep slope on the southwest side of the Dahongshan. Each trench shows fault clearly. Combining the comparative analysis of previous work, we identified and cataloged the late Quaternary deformation events and prehistoric earthquake relics, and analyzed the activity stages and behavior of this segment.
Fault gonge observed in the trench profiles shows that multiple earthquake events occurred in the fault. The faulting dislocated the Neogene sandstone, black gravel layer and gray clay layer. Brown clay layer is not broken. According to the relations of dislocated stratums, corresponding ¹⁴C and OSL samples were collected and dated. The result indicates that the Dahongshan segment of the Tanlu Fault has experienced strong earthquakes since the late Quaternary. Thrust fault, normal fault and strike-slip fault are found in the trenches. The microscopic analysis of slices from fault shows that there are many stick-creep events taking place in the area during the late Quaternary. Comprehensive analysis shows that there have been many paleoearthquakes in this region since the late Quaternary, the recent active time is the late Pleistocene, and the most recent earthquake event occurred in(12~2.5ka BP).
The neotectonic activity is relatively weak in the Anhui segment(south of the Huaihe River)of Tanlu fault zone. There are difficulties in the study of late Quaternary activity. For example, uneven distribution of the Quaternary, complex geological structure, larger man-made transformation of surface and so on. The progressive research may be able to promote the study on the activity of the Anhui segment of Tanlu fault zone.

GPS AND LEVELING CONSTRAINED CO-SEISMIC SOURCE AND SLIP DISTRIBUTION OF THE LUSHAN M_S7.0 EARTHQUAKE ON 20 APRIL 2013

CHANG Liu, YANG Bo, ZHANG Feng-shuang, XU Ming-yuan, YANG Guo-hua

2017, 39(3):  561-571.  DOI: 10.3969/j.issn.0253-4967.2017.03.009

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Co-seismic deformation results calculated by the observations of GPS continuous sites and precise leveling are used as three-dimensional constraints for the deformation field of Lushan M_S7.0 earthquake on 20 April 2013.The inversion of seismic source parameters are calculated based on the consideration of different value-taking schemes and fault models. Seven data type selection schemes, three fault models and two data coverage selection schemes are designed in order to discuss the effect of data selection and fault model selection on the inversion results.
The results show that the fault model using blind reverse fault for the inversion is superior to the model using the fault that ruptures from its upper boundary to the earth'surface, which may indicate that the Lushan earthquake fault is most likely a blind reverse fault; there are no obvious differences in the inversion results between the blind listric reverse fault models and the rectangle blind reverse fault models.
The best inversion result of Lushan earthquake seismic moment is M_W6.7.And it also shows that the distribution of dislocations on the fault plane is concentrated in the range of 30km×30km, the northern flank of the seismogenic fault of Lushun earthquake is of dextral faulting and the southern flank of the fault is of sinistral faulting, the sinistral component is larger that dextral component, showing a wedge deformation mode.

ANALYSIS OF THE LATE QUATERNARY ACTIVITY ALONG THE WENCHUAN-MAOXIAN FAULT -MIDDLE OF THE BACK-RANGE FAULT AT THE LONGMENSHAN FAULT ZONE

WANG Xu-guang, LI Chuan-you, LÜ Li-xing, DONG Jin-yuan

2017, 39(3):  572-586.  DOI: 10.3969/j.issn.0253-4967.2017.03.010

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The Longmenshan fault zone is located in eastern margin of Tibetan plateau and bounded on the east by Sichuan Basin, and tectonically the location is very important. It has a deep impact on the topography, geomorphology, geological structure and seismicity of southwestern China. It is primarily composed of multiple parallel thrust faults, namely, from northwest to southeast, the back-range, the central, the front-range and the piedmont hidden faults, respectively. The M_S8.0 Wenchuan earthquake of 12^th May 2008 ruptured the central and the front-range faults. But the earthquake didn't rupture the back-range fault. This shows that these two faults are both active in Holocene. But until now, we don't know exactly the activity of the back-range fault. The back-range fault consists of the Pingwu-Qingchuan Fault, the Wenchuan-Maoxian Fault and the Gengda-Longdong Fault. Through satellite image(Google Earth)interpretation, combining with field investigation, we preliminarily found out that five steps of alluvial platforms or terraces have been developed in Minjiang region along the Wenchuan-Maoxian Fault. T₁ and T₂ terraces are more continuous than T₃, T₄ and T₅ terraces. Combining with the previous work, we discuss the formation ages of the terraces and conclude, analyze and summarize the existing researches about the terraces of Minjiang River. We constrain the ages of T₁, T₂, T₃, T₄ and T₅ surfaces to 3~10ka BP,~20ka BP, 40~50ka BP, 60ka BP and 80ka BP, respectively. Combining with geomorphologic structural interpretation, measurements of the cross sections of the terraces by differential GPS and detailed site visits including terraces, gullies and other geologic landforms along the fault, we have reason to consider that the Wenchuan-Maoxian Fault was active between the formation age of T₃ and T₂ terrace, but inactive since T₂ terrace formed. Its latest active period should be the middle and late time of late Pleistocene, and there is no activity since the Holocene. Combining with the knowledge that the central and the front-range faults are both Quaternary active faults, the activity of Longmenshan fault zone should have shifted to the central and the front-range faults which are closer to the basin, this indicates that the Longmenshan thrust belt fits the "Piggyback Type" to some extent.

LATE QUATERNARY FAULTED LANDFORMS AND FAULT ACTIVITY OF THE HUASHAN PIEDMONT FAULT

XU Wei, YANG Yuan-yuan, YUAN Zhao-de, LIU Zhi-cheng, GAO Zhan-wu

2017, 39(3):  587-604.  DOI: 10.3969/j.issn.0253-4967.2017.03.011

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Based on the 1︰50000 active fault geological mapping, combining with high-precision remote imaging, field geological investigation and dating technique, the paper investigates the stratum, topography and faulted landforms of the Huashan Piedmont Fault. Research shows that the Huashan Piedmont Fault can be divided into Lantian to Huaxian section (the west section), Huaxian to Huayin section (the middle section) and Huayin to Lingbao section (the east section) according to the respective different fault activity.
The fault in Lantian to Huaxian section is mainly contacted by loess and bedrock. Bedrock fault plane has already become unsmooth and mirror surfaces or striations can not be seen due to the erosion of running water and wind. 10~20m high fault scarps can be seen ahead of mountain in the north section near Mayu gully and Qiaoyu gully, and we can see Malan loess faulted profiles in some gully walls. In this section terraces are mainly composed of T₁ and T₂ which formed in the early stage of Holocene and late Pleistocene respectively. Field investigation shows that T₁ is continuous and T₂ is dislocated across the fault. These indicate that in this section the fault has been active in the late Pleistocene and its activity becomes weaker or no longer active after that.
In the section between Huaxian and Huayin, neotectonics is very obvious, fault triangular facets are clearly visible and fault scarps are in linear distribution. Terrace T₁, T₂ and T₃ develop well on both sides of most gullies. Dating data shows that T₁ forms in 2~3ka BP, T₂ forms in 6~7ka BP, and T₃ forms in 60~70ka BP. All terraces are faulted in this section, combing with average ages and scarp heights of terraces, we calculate the average vertical slip rates during the period of T₃ to T₂, T₂ to T₁ and since the formation of T₁, which are 0.4mm/a, 1.1mm/a and 1.6mm/a, and among them, 1.1mm/a can roughly represent as the average vertical slip rate since the middle stage of Holocene. Fault has been active several times since the late period of late Pleistocene according to fault profiles, in addition, Tanyu west trench also reveals the dislocation of the culture layer of(0.31~0.27)a BP. 1~2m high scarps of floodplains which formed in(400~600)a BP can be seen at Shidiyu gully and Gouyu gully. In contrast with historical earthquake data, we consider that the faulted culture layer exposed by Tanyu west trench and the scarps of floodplains are the remains of Huanxian M_S8½ earthquake.
The fault in Huayin to Lingbao section is also mainly contacted by loess and mountain bedrock. Malan loess faulted profiles can be seen at many river outlets of mountains. Terrace geomorphic feature is similar with that in the west section, T₁ is covered by thin incompact Holocene sand loam, and T₂ is covered by Malan loess. OSL dating shows that T₂ formed in the early to middle stage of late Pleistocene. Field investigation shows that T₁ is continuous and T₂ is dislocated across the fault. These also indicate that in this section fault was active in the late Pleistocene and its activity becomes weaker or no longer active since Holocene.
According to this study combined with former researches, we incline to the view that the seismogenic structure of Huanxian M_S8½ earthquake is the Huashan Piedmont Fault and the Northern Margin Fault of Weinan Loess, as for whether there are other faults or not awaits further study.

THE INVERSION OF S-WAVE VELOCITY STRUCTURE IN NINGXIA AND ITS ADJACENT AREA USING BACKGROUND NOISE IMAGING TECHNOLOGY

XIE Hui, MA He-qing, JIAO Ming-ruo, MA Xiao-jun, ZHANG Nan, LI-Qing-mei

2017, 39(3):  605-622.  DOI: 10.3969/j.issn.0253-4967.2017.03.012

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In this paper, we use seismic waveform data of 90 seismic stations in Ningxia and its adjacent areas recorded between January 2012 and December 2013 to obtain the Rayleigh surface wave group velocity dispersion of the study area according to the noise imaging method and the 3-D S-wave velocity structure of the crust and upper mantle in Ningxia and its adjacent regions. The results show that within the depth range of 10~40km in Yinchuan graben and Liupanshan fault belt there exists a slow anomaly body, and with the increase of the depth this slow anomaly becomes an abnormal slow zone surrounding Lanzhou Basin between the massif arcuate structure of northeastern margin of Tibet Plateau and Alxa block. The 3-D S-wave velocity structure of the crust and upper mantle of the study area presents obvious lateral inhomogeneity. These results have important significance for the study of the dynamics of active tectonic zones and mechanism of strong earthquakes in Ningxia and its adjacent areas.