Main active faults and seismic activity along the Yangtze River Economic Belt:Based on remote sensing geological survey

The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Active faults and seismic activity are important geological factors for the planning and development of the YREB.In this paper,the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings,using both remote-sensing data and geological survey results.The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed.The main active fault zones in the western YREB,together with the neighboring regional active faults,make up an arc fault block region comprising primarily of Sichuan-Yunnan and a“Sichuan-Yunnan arc rotational-shear active tectonic system”strong deformation region that features rotation,shear and extensional deformation.The active faults in the central-eastern YREB,with seven NE-NNE and seven NW-NWW active faults(the“7-longitudinal,7-horizontal”pattern),macroscopically make up a“chessboard tectonic system”medium-weak deformation region in the geomechanical tectonic system.They are also the main geological constraints for the crustal stability of the YREB.

Seismic activity and active faults in Huailai basin

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Formation mechanism of fault accommodation zones under combined stress in graben basin:Implications from geomechanical modeling

A fault accommodation zone is a type of structure that is defined as regulating displacement and strain between faults structure.Increasing numbers of fault accommodation zones are being identified in graben basins,indicating the potential exploration target and petroleum accumulation areas.This study aims to analyze the formation mechanism and development of fault accommodation zones under combined stress by a numerical simulation method considering geomechanical modeling.Using three-dimensional(3-D)seismic interpretation and fractal dimension method,exampled with the Dongxin fault zone,the fault activity and fault combination pattern were conducted to quantitatively characterize the activity difference in fault accommodation zones.Combined with mechanical experiment test,a geomehcanical model was established for fault accommodation zones in a graben basin.Integrating the paleostress numerical simulations and structural physical simulation experiment,the developmental characteristics and genetic mechanism of fault accommodation zones were summarized.Influenced by multi movements and combined stresses,three significant tectonic evolution stages of the Dongxing Fault Zone(DXFZ)were distinguished:During the E_(s)^(3)sedimentary period,the large difference in the stress,strain,and rupture distribution in various faults were significant,and this stage was the key generation period for the prototype of the DXFZ,including the FAZ between large-scale faults.During the E_(s)^(2)sedimentary period,the EW-trending symmetric with opposite dipping normal faults and the NE-SW trending faults with large scale were furtherly developed.The junction area of two secondary normal faults were prone to be ruptured,performing significant period for inheriting and developing characteristics of fault accommodation zones.During the Es1 sedimentary period,the high-order faults in the DXFZ exhibited the obvious fault depressions and strike-slip activity,and the fault accommodation zones were furtherly inherited and developed.This stage was the molded and formative period of the FAZ,the low-order faults,and the depression in the DXFZ.

Dynamic response of mountain tunnel,bridge,and embankment along the Sichuan-Tibet transportation corridor to active fault based on model tests

The Sichuan-Tibet transportation corridor is prone to numerous active faults and frequent strong earthquakes.While extensive studies have individually explored the effect of active faults and strong earthquakes on different engineering structures,their combined effect remains unclear.This research employed multiple physical model tests to investigate the dynamic response of various engineering structures,including tunnels,bridges,and embankments,under the simultaneous influence of cumulative earthquakes and stick-slip misalignment of an active fault.The prototype selected for this study was the Kanding No.2 tunnel,which crosses the Yunongxi fault zone within the Sichuan-Tibet transportation corridor.The results demonstrated that the tunnel,bridge,and embankment exhibited amplification in response to the input seismic wave,with the amplification effect gradually decreasing as the input peak ground acceleration(PGA)increased.The PGAs of different engineering structures were weakened by the fault rupture zone.Nevertheless,the misalignment of the active fault may decrease the overall stiffness of the engineering structure,leading to more severe damage,with a small contribution from seismic vibration.Additionally,the seismic vibration effect might be enlarged with the height of the engineering structure,and the tunnel is supposed to have a smaller PGA and lower dynamic earth pressure compared to bridges and embankments in strong earthquake zones crossing active faults.The findings contribute valuable insights for evaluating the dynamic response of various engineering structures crossing an active fault and provide an experimental reference for secure engineering design in the challenging conditions of the Sichuan-Tibet transportation corridor.

Present-day Block Movement and Fault Activity on the Eastern Margin of the Tibetan Plateau

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008–2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are（17.02±0.60） mm/a,（8.77±1.51） mm/a,（13.85±1.31） mm/a and（6.84 ± 0.74） mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are（7.30±1.25–8.30±1.26） mm/a,（10.07±0.97–11.79±0.89） mm/a,（0.96±0.74–2.98±1.73） mm/a,（2.03±0.49–3.20±0.73） mm/a,（3.45±0.40–6.02±0.50） mm/a and（6.23±0.56） mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show leftlateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strikeslip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism.

Lateral migration of fault activity in Weihe basin

Lateral migration of fault activity in Weihe basin is a popular phenomenon and its characteristics are also typical. Taking the activity migrations of Wangshun Mountain piedmont fault toward Lishan piedmont fault and Weinan platform front fault, Dabaopi-Niujiaojian fault toward Shenyusi-Xiaojiazhai fault, among a serial of NE-trending faults from Baoji city to Jingyang County as examples, their migration time and process are analyzed and discussed in the present paper. It is useful for further understanding the structure development and physiognomy evolution history of Weihe basin.

Analyses of active faults, seismic activities and sea floor unstable factors of the Zhujiang River Mouth Basin and its adjacent areas

-On the basis of the data of geophysics and seismic activities, the analyses of the active faults, seismic activities and the sea floor unstable factors of the Zhujiang River Mouth Basin have been made so as to study the characteristics of the compressional subactive continental margin of Cathaysian system, arc littoral strongly active fracture zone, the division of seismic subzone and seismic zone of the continental margin of northern South China Sea, the potential focal area, and to analyze the regional stability. We consider that the Zhujiang River Mouth Basin belongs to a stable or a moderately stable region.

Numerical modeling of tectonic stress field and fault activity in North China

On the basis of a 3-dimension visco-elastic finite element model of lithosphere in North China, we numerically simulate the recent mutative figures of tectonic stress field. Annual change characteristics of stress field are： 1 ） Maximum principal tensile stress is about 3 -9 kPaa-1 and its azimuth lie in NNW-SSE. 2） Maximum principal compressive stress is about 1 - 6 kPaa-1 and its azimuth lie in NEE-SWW. 3 ） Maximum principal tensile stress is higher both in the west region and Liaoning Province. 4） Variation of tectonic stress field benefits fault movement in the west part and northeast part of North China. 5 ）Annual accumulative rates of Coulomb fracture stress in Tanlu fault belt have segmentation patterns： Jiashan-Guangji segment is the high- est （6 kPaa - 1 ） , Anshan-Liaodongwan segment is the second （5 kPaa - l ） , and others are relatively lower （ 3 - 4 kPaa-1 ）.

Active Depths of Main Faults in the Ying-Qiong Basin Investigated by Multi-Scale Wavelet Decomposition of Bouguer Gravity Anomalies and Power Spectral Methods

The Ying-Qiong Basin is located on the northwestern margin of the South China Sea and at the junction of the South China Block and the Indochina Block.It is characterized by complex geological structures.The existing seismic data in the study area is sparse due to the lack of earthquake activities.Because of the limited source energy and poor coverage of seismic data,the knowledge of deep structures in the area,including the spatial distribution of deep faults,is incomplete.Contrarily,satellite gravity data cover the entire study area and can reveal the spatial distribution of faults.Based on the wavelet multi-scale decomposition method,the Bouguer gravity field in the Ying-Qiong Basin was decomposed and reconstructed to obtain the detailed images of the first-to sixth-order gravitational fields.By incorporating the known geological features,the gravitational field responses of the main faults in the Ying-Qiong Basin were identified in the detailed fields,and the power spectrum analysis yielded the depths of 1.4,8,15,26.5,and 39 km for the average burial depths of the bottom surfaces from the first-to fifth-order detailed fields,respectively.The four main faults in the Yinggehai Basin all have a large active depth range:fault A(No.1)is between 5 and 39 km,fault B is between 26.5 and 39 km,and faults C and D are between 15 and 39 km.However,the depth of active faults in the Qiongdongnan Basin is relatively shallow,mainly between 8 and 26.5 km.

Influence of 2008 Wenchuan earthquake on earthquake occurrence trend of active faults in Sichuan-Yunnan region

The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults＇ slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake.

The neotectonic deformation and earthquake activity in Zhuanglang river active fault zone of Lanzhou

Lanzhou Institute of Seismology, China Seismological Bureau, Lanzhou 730000, China 2) Institute of Geology, China Seismological Bureau, Beijing 100029, China

New Discovery of Holocene Activity along the Weixi-Qiaohou Fault in Southeastern Margin of the Tibetan Plateau and its Neotectonic Significance

Objective The lateral extrusion eastward of the Tibetan Plateau leads to the formation of the Sichuan–Yunnan block, which is the most representative active block in the southeastern margin of the Tibetan Plateau, characterized by strong and frequent seismicity(Li Ping et al., 1975; Zhang Peizhen et al., 2003; Li Yong et al., 2017). Its eastern boundary is composed of sinistral faults including the Xianshuihe, Xiaojiang faults, etc., and the western

Discussion of the Horizontal Intensity of Late Quaternary Fault Activity Along the Tianjingshan Fault Zone in Different Time Intervals and Fault Segments

By computing and classifying the data of gully offset obtained from field surveys along the Tianjingshan fault zone and estimating the ages of three types of gullies,the strike-slip rates along the fault zone are discussed in different time intervals and fault segments.The results suggest that the intensity of activity along the fault zone is not strong,but the differences between different time intervals and fault segments since the late Pleistocene have been obvious.The average rates range from 0.23 mm/a to 1.62 mm/a.The largest average rate is 1.40 mm/a,which occurred in the early and middle of late Pleistocene along the western segment of the fault zone.Since the late stage of the late Pleistocene,the center of faulting activity of the fault zone has shifted to the middle segment,and the average slip rates range have changed from 1.30 mm/a to 1.63 mm/a.

Fission Track Method to Date Fault Activity—As Exemplified by the Three Gorges Dam Area of the Yangtze River Valley, China

The Xiannushan and Jiuwanxi are the two major fracture belts adjacent to the Three Gorges Dam Site. Apatites are selected from fracture clay and fracture\|cliff rock in the fracture belts and examined with the fission track dating method. Our study shows that the Xiannushan and Jiuwanxi fracture belts were tectonically active at 0.60±0.04Ma and 0.29±0.04Ma ago, respectively. Their ages are close to those obtained by the U\|series method.

The historic evolution of Zhouyuan and the newest activity of the great Wei River fault

The rate of vertical differential movement of the great Weihe fault (west segment) in different periods is analyzed by using the data of the historic evolution of the Zhouyuan plateau surface. Results show that the rate reached a maximum in the Ming Dynasty, about 6. 4 mm/a, which corresponded well to the period of strongearthquake on the Wei River fault in the 15-16th centuries. Based on such a correspondence, the time separation between active periods of Ms=8. 0 strong earthquakes in the Wei River fault depression is investigated.

Active faults and seismogenic models for the Urumqi city,Xinjiang Autonomous Region, China

We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings, seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated, and have revealed the primary features of the thrust-fold- nappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are inter- preted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, con- sisting of the lower （root） thrust fault, middle detachment, and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east, which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases, this section of the nappe structure near the city has an earthquake risk of M6.5-7, An earthquake Ms6.6, 60 km east to Urumqi city occurred along the structure in 1965.

Seismic active faults in the northwestern Beijing by seismic tomography

Using the arrival times of 197 earthquakes well recorded by the Beijing Seismic Network and the China-Germany cooperative Yanqing Digital Seismic Array in the period from October of 2001 to December of 2005, we accurately relocate these earthquakes by the joint-inversion program for hypocentral position and 3-D velocity structure The distribution of hypocenters shows that there are two major seismic active belts in the northwestern Beijing. The first belt stretches from Qinghe, Wenquan to the NW direction and the second extends from Nankou, Changping to the ENE direction.

Kinematics of faults in Bengal Basin:Constraints from GPS measurements

The crustal deformation of Bengal Basin is constrained by motion on faults within the basin and those along the basin boundaries on all sides except the southern margin.Eocene Hinge Zone(EHZ),the most prominent structure within Bengal Basin,running through Kolkata-Ranaghat-Mymensingh,shows present day reactivation by hosting 8 earthquakes of magnitude 5.3 to 7.2 on or near its vicinity since 1906.Analysis of GPS derived velocities of stations around the hinge belt reveals a change in crustal kinematics across the belt.The predicted fault model that best fits the observed GPS station velocities on the surface shows that EHZ is a low angle east dipping fault which is locked to a depth of 10 km below the alluvium cover with a maximum slip rate deficit of 1.6±0.7 mm/yr in its northern part at a shallow depth from surface while the deficit in the southern part of EHZ is 1.0±0.6 mm/yr.The Garh-Moyna Khandaghosh fault running almost parallel to the western basin-shield margin does not show significant slip rate deficit.The basin-bounding faults are more active than the faults within and therefore they are greater sources of seismic hazard in the basin.The model results reveal that the Sylhet trough region in the northeastern corner is most vulnerable to future earthquakes as it undergoes deformation due to a maximum slip rate deficit of 9.5±2.4 mm/yr on the shallowly dipping locked megathrust along the eastern margin of the basin plus that of 7.4±2.6 mm/yr on the over thrusting Dapsi thrust and Dauki fault in the north.

A reappraisal of active faults in central-east Iran(Kerman province)

Fault lineaments are the main input data in earthquake engineering and seismology studies.This study presents a digitally-based active fault map of the Kerman region in central-east Iran which experienced several devastating earthquakes on poorly exposed and/or not identified active faults.Using Landsat 8 data,we have carried out the image-based procedures of fault mapping,which include applying the contrast stretching technique,the principal component analysis,the color composite technique,the spectral rationing,and creating the false-color composite images.Besides,we have cross-checked the resulting map with the geological maps provided by the Geological Survey of Iran to decrease the associated uncertainties.The resulting map includes 123 fault segments,still,a part of which has been expressed in the previously compiled active-fault maps of Iran.Indeed,the new one is mapping the poorly exposed active faults,so-called secondary faults,which are able to produce strong events.These faults are primarily associated with poorly defined areas that accommodate low levels of seismicity;however,sporadic strong events are likely to occur.It has also been investigated that these kinds of faults are seismogenic and are able to produce destructive events.In total,the outcome of this study can also be jointed with seismic studies for investigating parts of the earthquake activity in central-east Iran,in particular for the fault-based approaches in impending earthquake-resistant buildings.

Soil Gas Radon Measurement for Identifying Active Faults in Thua Thien Hue (Vietnam)

The solid-state nuclear track detectors have long been applied to assess the activity of tectonic faults. We measured the Radon (Rn) concentration in soil gas on 09 profiles with a total of 245 measurement points in Thua Thien Hue area (Vietnam). Measurement results show that the Rn concentration in soil gas ranges from ~10 Bq/m3 to 144,570 Bq/m3. There is a clear difference in the Rn concentration on the granite rock of Dai Loc complex compared to the remaining rocks. The calculated background value and anomaly threshold of Rn concentration on the granite rock of Dai Loc complex and on the remaining rocks are 33,488 Bq/m3, 82,839 Bq/m3 and 5313 Bq/m3, 24,850 Bq/m3 respectively. Spatial distribution of Rn concentration in soil gas reflects the existence of faults since Rn concentration increases at the points above or near fault lines. The level of expression of fault activity is assessed by radon activity index (KRn), which is calculated by the ratio of anomaly value to background value of Rn concentration. According to KRn, in Thua Thien Hue area, only the Dakrong-Hue fault shows a strong expression of activity with high and very high KRn (the maximum KRn = 27.21). The Truong Son, Huu Trach River, Ta Trach River and Bo River fault zones do not show clear activity with low and medium KRn. There is no Rn anomaly value recorded on the Rao Trang fault, demonstrating that it is likely to be inactive at present. The study results indicate that the Rn concentration in soil gas is a strong evidence of the existence of faults or tectonic fracture zones as the Rn concentration always increases at the points above or near the fault line.