Application of High-Resolution Remote Sensing Technology in Quantitative Study on Coseismic Surface Rupture Zones: An Example of the 2008 M_w7.2 Yutian Earthquake

Objective Nowadays, high-resolution remote sensing technology has brought new changes to surveys of earthquakes, and the quantitative study of seismic faults based on this technology has become a trend in the world(Barzegari et al., 2017). An Mw 7.2 earthquake occurred in Yutian of Xinjiang on the western end of the Altyn Tagh fault on March 21 st, 2008. It is difficult to access this depopulated zone because of the high altitude and only 1–2 months of snowmelt. This study utilized high-resolution

Quantitative analysis on tectonic deformation of active rupture zones

Based on the regional GPS data of high spatial resolution, we present a method of quantitative analysis on the tectonic deformation of active rupture zones in order to predict the location of forthcoming major earthquakes. Firstly we divide the main fault area into certain deformation units, then derive the geometric deformation and relative dislocation parameters of each unit and finally estimate quantitatively the slip and strain rates in each segment of the rupture zone. Furthermore, by comparing the consistency of deformation in all segments of the whole rupture zone, we can determine the possible anomalous segments as well as their properties and amplitudes. In analyzing the eastern boundaries of Sichuan-Yunnan block with the GPS velocity data for the period of 1991-2001, we have discovered that the Mianning-Ningnan-Dongchuan segment on the Zemuhe-Xiaojiang fault zone is relatively locked and the left-lateral shear strain rate here is higher.

Parameters of Coseismic Reverse- and Oblique-Slip Surface Ruptures of the 2008 Wenchuan Earthquake,Eastern Tibetan Plateau

On May 12th, 2008, the Mw7.9 Wenchuan earthquake ruptured the Beichuan, Pengguan and Xiaoyudong faults simultaneously along the middle segment of the Longmenshan thrust belt at the eastern margin of the Tibetan plateau. Field investigations constrain the surface rupture pattern, length and offsets related to the Wenchuan earthquake. The Beichuan fault has a NE-trending rightlateral reverse rupture with a total length of 240 km. Reassessment yields a maximum vertical offset of 6.5±0.5 m and a maximum right-lateral offset of 4.9±0.5 m for its northern segment, which are the largest offsets found; the maximum vertical offset is 6.2±0.5 m for its southern segment. The Pengguan fault has a NE-trending pure reverse rupture about 72 km long with a maximum vertical offset of about 3.5 m. The Xiaoyudong fault has a NW-striking left-lateral reverse rupture about 7 km long between the Beichuan and Pengguan faults, with a maximum vertical offset of 3.4 m and left-lateral offset of 3.5 m. This pattern of multiple co-seismic surface ruptures is among the most complicated of recent great earthquakes and presents a much larger danger than if they ruptured individually. The rupture length is the longest for reverse faulting events ever reported.

Deformation of the Most Recent Co-seismic Surface Ruptures Along the Garzê–Yushu Fault Zone(Dangjiang Segment)and Tectonic Implications For the Tibetan Plateau

The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.

Analysis of Remote Sensing Images of Ground Ruptures Resulting from the Kunlun Mountain Pass Earthquake in 2001

On November 14, 2001, an earthquake measuring a magnitude of 8.1 occurred to the west of the Kunlun Mountain Pass which is near the border between Xinjiang and Qinghai of China. Since its epicenter is located in an area at an elevation of 4900 m where the environment is extremely adverse, field investigation to this event seems very difficult. We have performed interpretation and analysis of the satellite images of ETM, SPOT, Ikonos, and ERS-1/2SAR to reveal the spatial distribution and deformation features of surface ruptures caused by this large earthquake. Our results show that the rupture zone on the ground is 426 km long, and strikes N90-110°E with evident left-lateral thrusting. In spatial extension, it has two distinct sections. One extends from the Bukadaban peak to the Kunlun Mountain Pass, with a total length of 350 km, and trending N95-110°E. Its fracture plane is almost vertical, with clear linear rupture traces and a single structure, and the maximum left-lateral offset is 7.8 m. This section is the main rupture zone caused by the earthquake, which is a re-fracturing along an old fault. The other is the section from Kushuihuan to the Taiyang Lake. It is 26 km long, trending N90-105°E, with the maximum strike-slip displacement being 3 m, and is a newly-generated seismic rupture. In a 50 km-long section between the Taiyang Lake and the Bukadaban peak, no rupture is found on the ground. The eastern and western rupture zones may have resulted from two earthquakes. The macroscopic epicenter is situated at 65 km east of the Hoh Sai Lake. The largest coseismic horizontal offset in the macroscopic epicenter ranges from 7 m to 8 m. Based on the dislocation partition of the whole rupture zone, it is suggested that this rupture zone has experienced a process of many times of intensification and fluctuation, exhibiting a remarkable feature of segmentation.

Surface rupture zone of the 1303 Hongtong M=8 earthquake, Shanxi Province

Based on the latest displacement of Huoshan piedmont fault, Mianshan west-side fault and Taigu fault obtained from the beginning of 1990s up to the present, the characteristics of distribution and displacement of surface rup-ture zone of the 1303 Hongtong M = 8 earthquake, Shanxi Province are synthesized and discussed in the paper. If Taigu fault, Mianshan west-side fault and Huoshan piedmont fault were contemporarily active during the 1303 Hongtong M = 8 earthquake, the surface rupture zone would be 160 km long and could be divided into 3 segments, that is, the 50-km-long Huoshan piedmont fault segment, 35-km-long Mianshan west-side fault segment and 70-km-long Taigu fault segment, respectively. Among them, there exist 4 km and 8 km step regions. The surface rupture zone exhibits right-lateral features. The displacements of northern and central segments are respectively 6~7 m and the southern segment has the maximum displacement of 10 m. The single basin-boundary fault of Shanxi fault-depression system usually corresponds to M 7 earthquake, while this great earthquake (M = 8) broke through the obstacle between two basins. It shows that the surface rupture scale of great earthquake is changeable.

Recent advances in imaging crustal fault zones: a review

Crustal faults usually have a fault core and surrounding regions of brittle damage, forming a low-velocity zone （LVZ） in the immediate vicinity of the main slip interface. The LVZ may amplify ground motion, influence rupture propagation, and hold important information of earthquake physics. A number of geophysical and geodetic methods have been developed to derive high-resolution structure of the LVZ. Here, I review a few recent approaches, including ambient noise cross-correlation on dense across-fault arrays and GPS recordings of fault-zone trapped waves. Despite the past efforts, many questions concerning the LVZ structure remain unclear, such as the depth extent of the LVZ. High-quality data from larger and denser arrays and new seismic imaging technique using larger portion of recorded waveforms, which are currently under active development, may be able to better resolve the LVZ structure. In addition, effects of the alongstrike segmentation and gradational velocity changes across the boundaries between the LVZ and the host rock on rupture propagation should be investigated by conducting comprehensive numerical experiments. Furthermore, high-quality active sources such as recently developed large-volume airgun arrays provide a powerful tool to continuously monitor temporal changes of fault-zone properties, and thus can advance our understanding of fault zone evolution.

The Surface Rupture Zone and Coseismic Deformation Produced by the Yutian Ms7.3 Earthquake of 21 March 2008,Xinjiang

On 21 March 2008, a Ms7.3 earthquake occurred at Quickbird, Yutian County, Xinjiang. We attempt to reveal the features of the causative fault of this shock and its coseismic deformation field. Our work is based on analysis and interpretation to high-resolution satellite images as well as differential interferometric synthetic aperture radar （D-InSAR） data from the satellite Envisat SAR, coupled with seismicity, focal mechanism solutions and active tectonics in this region. The result shows that the 40 km-long, nearly NS trending surface rupture zone by this event lies on a range-front alluvial platform in Qira County. It is characterized by distinct linear traces and simple structure with 1-3-m-wide individual seams and maximum 6.5 m width of a collapse fracture. Along the rupture zone many secondary fractures and fault-bounded blocks are seen, exhibiting remarkable extension. The eoseismic deformation affected a large area 100~100 km2. D-InSAR analysis indicates that the interferometric deformation field is dominated by extensional faulting with a small strike-slip component. Along the causative fault, the western wall fell down and the eastern wall, that is the active unit, rose up, both with westerly vergence. Because of the big deformation gradients near the seismogenic fault, no interference fringes are seen on images, and what can be determined is a vertical displacement 70 cm or more between the two fault walls. According to the epicenter and differential occurrence times from the National Earthquake Information Center, China Earthquake Network Center, Harvard and USGS, it is suggested that the seismic fault ruptured from north to south.

Relocating ruptures of two M6 earthquakes in Zhongba, South-central Tibet in 2004 and 2005 with seismological and geodetic methods

To better understand repeatability of strong earthquakes in previously ruptured zones during one seismogenic period, we studied the rupture zones of the doublet of M6 earthquakes in Zhongba region of southcentral Tibet, China, in 11 July 2004 and 7 April 2005, respectively. We focused on the overlapping degree of two strong quakes’ aftershock areas one week after the mainshocks by using the SQH station in China Seismic Network and a 68-stations temporary broadband seismic array, a part of the international HI-CLIMB project. About 115 local earthquakes were recorded in one week after the mainquakes, and we located these earthquakes by master event relative location （MERL） method. We also used this method to relocate 31 other M3.7 ＋ earthquakes from 1 July 2004 to 1 July 2005. Meanwhile, we studied two mainshocks’ coseismic ruptures with satellite interferometric synthetic aperture radar （InSAR）. Our results show that the ruptured zones of the two earthquakes do not overlapp substantially, either from early aftershock data or from InSAR inversions.

Rock Damage Structure of the South Longmen-Shan Fault in the 2008 M8 Wenchuan Earthquake Viewed with Fault-Zone Trapped Waves and Scientific Drilling

This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.

Fault zone structures of northern and southern portions of the main central fault generated by the 2008 Wenchuan earthquake using fault zone trapped waves

The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170-200 m and 200-230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of MS.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.

Holocene activities of the Taigu fault zone,Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

No abstract available