Characteristics of Recent Horizontal Crustal Movement and Tectonic Deformation in the Northwest China Region

Making use of observation data of GPS in the Northwest China region and infrared distancemeasurements crossing the Qilian-Longshoushan fault zone up to 2004, aided by the least square collocation and inversion of negative dislocation model for the boundaries of elastic blocks and the singular force-source, the dynamic evolution features of deformation and strain fields before and after the Ms = 8. 1 earthquake on the west of Kunlun Mountains Pass, especially the recent tectonic deformation and stress field status three years after this earthquake are studied. The possible regions or segments of active blocks and their boundaries reflecting accumulation background of high strain energy of producing earthquakes over middle magnitude, are obtained, as well as the potential epicenter. The results show that after shortterm relaxation and adjustment in the northern margin of Qinghai-Xizang （Tibet） block after the Ms = 8. 1 earthquake, the main control action of background field of northeastward pushing of Indian plate is now recovering. Moreover, the following regions are found to have the background of high strain energy accumulation. They are the middle segment of the northern Tianshan fault zone and its meeting region with the western segment, the middle and western segments of southern Tianshan fault zone and the meeting region with Western Kunlun fault zone, the middle segment of Altun fault, the middle-eastern segment of Qilianshan fault zone and its meeting region with Haiyuan fault, the meeting region of northern margin fault of west Qinling Range and the southeastward expanding line of Zhuanglanghe fault; The Linze and Haiynan areas also see accumulation of strain energy to some degree.

Deformation Model Inferred from Focal Mechanisms in the Chinese Mainland and Its Adjacent Areas

We collect seismic moment tensors of the earthquakes occurring from 1900 to 2013 in and around the Chinese mainland and summarize the surface ruptures and displacements of 70 earthquakes with M S≥7. 0. We divide these large earthquakes into three types. Type A contains earthquakes with surface ruptures and displacements. Type B is earthquakes without displacements and Type C is those without any of this data. We simulate a triangular distribution of displacements for Type B and C. Then,we segment these large earthquakes by using their displacements and surface ruptures. Finally,kinematic models are determined from earthquake data and Bicubic Bessel spline functions. The results show that,first of all,the reasonability and spatial consistency of defined models are advanced.Strain rates have better continuity and are comparable with geologic and geodetic results in Himalaya thrust fault zones. The strain rates decrease in the Tarim basin and the Altun Tagh fault zones because of their low seismicity. The direction of compressional deformation in Gobi-Altay is changed from SE to NE and its extensional direction is changed from NE to NW. The extensional deformation in the Ordos block is diminished obviously. Secondly,earthquakes account for 30- 50% of expected motion of India relative to Eurasia determined from the NUVEL-1A model,with a missing component of 20 mm / a which may contain aseismic deformation such as fault creep and folds,the missing parts of earthquake data and elastic strain energy released by potential earthquakes.

GPS observation in Sichuan-Yunnan and its vicinity before and after the Wenchuan earthquake in a decade

Based on the horizontal velocity data observed by GPS during 2004-2007,2007-2009,and 2011-2017 before,during,and after the Wenchuan earthquake in Sichuan-Yunnan and its vicinity,we analyze evolution features of the tectonic deformation caused by crustal movement in main active fault belts,and its possible influence.We conclude:the Wenchuan earthquake area showed obvious co-seismic thrust and dextral deformation from 2007 to 2009.The earthquake,to a certain extent,promoted tectonic movements on the Gansu-Sichuan boundary,Western Qinling fault zone,Anninghe-Zemuhe fault zone,and southern Xianshuihe fault zone.The vectors and strain filed acquired by GPS during Lushan and Jiuzhaigou earthquakes period may indicate that the southwest segment in the Longmenshan fault zone still has the possibility of larger earthquakes.

Characteristics of InSAR Coseismic Deformation and Slip Distribution of the Akto M_S6. 7 Earthquake,Xinjiang

The Akto MS6. 7 earthquake occurred near the western end of the Muji fault basin in the top of the Pamir syntaxis. The main shock of this earthquake is complicated and the focal mechanism solutions based on the seismic wave inversions are different. Based on the Sentinel-1 SAR data,the coseismal deformation field of the earthquake is obtained by In SAR technique. Based on the elastic half-space dislocation model,the geometrical parameters and the slip distribution model are determined by nonlinear and linear inversion algorithms. The results show that the distributed slip model can well explain the coseismic deformation field. The earthquake includes at least two rupture events,which are located at 7 km(74. 11°E,39. 25°N)and 33 km(74. 49°E,39. 16°N)east from the epicenter according to the CENC. The deformation field caused by the earthquake shows a symmetry distribution,with the maximum LOS deformation of 20 cm. The main seismic slip is concentrated in the 0-20 km depth,and the maximum slip is 0. 84 m. The seismic fault is the Muji fault,and this earthquake indicates that the northeastward push of the Indian plate is enhanced.

Intermediate to Long-term Estimation of Strong Earthquake Risk Areas in the Chinese Mainland Based on Geodesic Measurements

Based on previous research results,present-day crustal deformation and gravity fields in the Chinese mainland are analyzed using the GPS data,leveling,gravity and cross-fault deformations. We analyzed strain accumulation of the major faults,and identified locked or high strain accumulation segments. Combining the effects of large earthquakes in the study area,the long-term (decade) probability of large earthquakes in the Chinese mainland is estimated.

Research on Locating the Source of Abnormal Disturbances in the Border Region of Shaanxi and Gansu

Abnormal disturbances, s uch as sharp pulses, w ere observed by vertical pendulum tiltmeters in Wudu, Hanzhong and Ningshaan seismic stations on August 6, 2008.According to the time and spatial location of the anomalies,we build a"source precursor"propagator to calculate possible focal region by aid of quasi-Newton least squares and grid search methods. The calculated focal region is located at the aftershock area of the Wenchuan earthquake on the northern section of Longmenshan fault zone,which may be related to the 54km-away M S5. 0 Pingwu-Beichuan earthquake,with starting time of about thirty three hours before the earthquake.

Microseismic Concentration Zones before and after the February 12,2014 M_S 7.3 Yutian Earthquake and the Possible Indication of an Earthquake Risk Zone

Since 2001, there have occurred in succession the 2001 Kunlun Mountains M S8. 1earthquake,the 2008 Wenchuan M S8. 0 earthquake,the 2010 Yushu M S7. 1 earthquake and the 2012 Lushan M S7. 0 earthquake in the periphery of the Bayan Har block. By comparison of the characteristics of seismic strain release variations before and after the Kunlun Mountains M S8. 1 earthquake in the same time length in the geodynamical related regions,we found that the seismic strain release was obviously enhanced after the earthquake in the Longmenshan area,Batang area,and the NS-trending valleys at the west of the Hot Spring Basin. The Wenchuan earthquake occurred in the first area,and the Yushu earthquake is related to the second area. After the earthquake rupture occurred on the East Kunlun fault zone on the northern boundary of the Bayan Har Block,crustal materials on the south side of the fault zone migrated to the southeast,leading to a concentration of tectonic deformation in the Longmenshan thrust belt, e ventually rupturing on the Longmenshan thrust belt. This earthquake case illustrates that seismicity enhancement zones are possibly prone to long-term destructive earthquakes. After the M S7. 3 earthquake in Yutian,Xinjiang on February 12,2014,earthquake frequency and seismic strain release markedly increased in the junction area between the eastern Qilian Mountain tectonic belt and the Altun Tagh fault zone,where more attention should be paid to the long-term seismic risk.

Gravity variation associated with Wenchuan earthquake in western Sichuan

Based on the data of mobile gravity observation from 1998 to 2008 in western Sichuan, spatial dynamic variation results of regional gravity field are obtained. The relationship between the gravity variation features and Wenchuan Ms8.0 earthquake is systematically analyzed. The results show： 1 ） Gravity variation is closely related to active fault tectonics, and gravity measurement can better reflect material migration following crustal tectonic activity near active fault. 2）The gravity field appeared a wider range regional gravity variation during Wenchuan earthquake occurrence. The dynamic patterns of gravity field demonstrates the evolution process of gravity field ： quasi - homogeneous state non - homogeneous state-earthquake occurrence.

Fluctuation in Ommastrephe bartrami yield in the North Pacific

The fluctuation in Ommastrephe bartrami yield from 1995 to 2001 in the North Pacific was shown obvious, on which this study was conducted using data of sea surface temperature （SST）, chlorophyll-a （chl-α） and statistical production. The study shows that, cool water and low food abundance caused by abnormal Kuroshio resulted in the reduction in abundance of O. bartrami, which was worsened by excessive catch and the unawareness to local fishery resources protection.

Anomaly Feature Extraction of the Gravity Field before the Jiuzhaigou Earthquake in 2017

The M_S7. 0 Jiuzhaigou earthquake occurred on August 8,2017. The earthquake occurred in the vicinity of the Tazang fault,the Minjiang fault and the Huya fault,where the focal mechanism is of the strike slip type. The static and dynamic anomalies of the gravity field can provide important physical field information for studying the structural properties of deep crust. Multi-scale decomposition techniques are used to separate Bouguer gravity at different depths and give some explanation to gravity variations at different time space scales. The results indicate that the wavelet multi-scale results of the EGM2008 model and the measured gravity data are consistent. Through comparative analysis,it is found that the Jiuzhaigou earthquake occurred in the stress enhanced region. The variation of gravity field at different time scales has a certain scientific significance for further understanding potential earthquake risk trend.

Study on Postseismic Impact of Wenchuan Earthquake on the Sichuan-Yunnan Region Based on Three-Dimensional Viscoelastic Finite Element Method

Based on the lateral segmentation and vertical stratification characteristics of the crustal medium in Sichuan-Yunnan region,and the asymmetry of the static dislocations on the coseismic fault plane of the Wenchuan M_S8.0 earthquake,we built a three-dimensional viscoelastic finite element model of the crust in the Sichuan-Yunnan region.The postseismic impact of the Wenchuan M_S8.0 earthquake on the Sichuan-Yunnan region was studied.The results show that:①The far-field horizontal deformation caused by the viscoelastic relaxation of the medium in the 10 years after the earthquake is about 0-20 mm within the Sichuan-Yunnan diamond-shaped block,which has a greater influence on north side and smaller on south side.②In the 10 years after the earthquake,the far-field vertical deformation caused by the viscoelastic relaxation effect of the medium is small,and it shows an increase of about 0-4 mm in most areas of the Sichuan-Yunnan diamond-shaped block.③The Xianshuihe fault and the eastern segment of the East Kunlun fault,which are close to the seismogenic fault,show a high gradient on deformation fields after the earthquake.④In order to compare with the strong earthquake activity in the SichuanYunnan region after the Wenchuan earthquake,the horizontal stress state and the Coulomb failure stress change of the active block boundary are also calculated.From the spatial distribution of the coseismic and postseismic displacement field,the fault activity characteristics reflected by the stress state and the stress loading of the fault layer reflected by the Coulomb failure stress change,there is a certain correlation with the spatial distribution of strong earthquake activity in this region.

The North-South Seismic Belt： Vertical Deformation Velocity Gradient Research

The vertical deformation gradient can reflect the rate of vertical change in unit distance,and the vertical deformation velocity gradient can reflect the strength of the earth's crust tectonic activities. In this paper,using long period leveling data combined with GPS data,the vertical deformation gradient values are calculated. Leveling data and GPS data are two different means of monitoring deformation,but the result is approximately the same vertical deformation gradient. The results show that the spatial distribution of the vertical deformation velocity gradient and tectonic distribution has an obvious correlation. The most significant gradient anomalies along the North-South Seismic Belt are Xianshuihe fault, Longmenshan fault and Xiaojiang-Zemuhe fault, while the second gradient anomalies in the northeastern Qinghai-Tibetan plateau are Zhuanglanghe fault and Lenglongling fault. The Menyuan M_S6. 4 earthquake in 2016 occurred in this abnormal area. However,according to the vertical deformation high gradient area distribution,there is also the possibility of an earthquake occurrence in the Tianzhu and Jingtai area.The area of convergence of three major fault zones is the strongest tectonically active region of the North-South Seismic Belt.