Shan Xinjian

Extracting coseismic deformation of the 1997 Mani earthquake with differential interferometric SAR

Interferometry Synthetic Aperture Radar (InSAR) is a kind of new earth observation technique and great development has been made in the recent ten years. In the paper, InSAR and Differential Interferometric Synthetic Aperture Radar (D-InSAR) are generally introduced; then the factors affecting the data accuracy are primarily discussed. The 1997 Mani earthquake was selected as an example to obtain the coseismic deformation field with the three-pass differential interferometric processing method. The results show that the coseismic deformation field is about 200 km in length and 115 km in width. The interferometric fringes spread in the area with the NEE-trending seismogenic fault — the Margaichaka fault as the center and they are primarily parallel to the fault. Based on the analysis to the interferogram, the seismogenic fault can be divided into three segments. The whole fault is about 110 km and the length of each segment from the west to the east is about 23 km, 60 km and 26 km. The maximum uplifting displacement in the side-looking direction near the seismic center is about 162.4 cm, the maximum subsiding displacement in the side-looking direction in the western part of the fault is about 103.6 cm, and the maximum horizontal surface dislocation near the seismic center is about 7.96 m.

Multiparameter seismo-ionospheric anomaly observation before the 2008 Wenchuan, China, Mw7.9 earthquake

Abstract The atmosphere-ionosphere response before 2008 Mw7.9 Wenchuan earthquake based on global positioning system (GPS), detection of electro-magnetic emission transmitted from earthquake regions (DEMETER), and National Oceanic and Atmospheric Administration—advanced very high resolution radiometer (NOAA/AVHRR) satellite data is analyzed. It is found that GPS total electron content (TEC) above the epicenter continuously decreased in the afternoon periods from 6 to 10 May but increased in the afternoon of 9 May. Contour analysis on ionospheric plasma using Instrument Sonde de Langmuir data onboard DEMETER satellite showed that electron density (Ne) and ion density (Ni) was also reduced from 6 to 10 May, the anomalous region mainly distributed in the south of the epicenter, conforming to the anomalous TEC area. The brightness temperature ( T b ) from NOAA/AVHRR data, calculated by K index method, shows a noticeable enhancement on the northwest side of the epicenter on 7 May, while ion temperature ( T i ) from DEMETER data increased on 9 May with the order of ∼ 12.5 % . The energetic particle flux presents an obvious enhancement for the spectrum at 100 to 600 keV energy range on 6 May. Preliminary study suggests the perturbations of these parameters (TEC, Ne, Ni, T b , and T i ) before the Wenchuan earthquake may be related to the changes of vertical electric field in the atmosphere and ionosphere, induced by the enhancement of stress in tectonic regions and the electromagnetic signal propagation from the earthquake preparation area.

Slow crustal deformation of Haiyuan fault in the northeast Tibetan plateau observed by PS-InSAR

We attempted to detect tiny interseismic crustal deformation on the Haiyuan fault using the PS-InSAR method and 17 ENVISAT/ASAR images in descending orbit. The result shows that homogeneity and consistency in space, and stability and linear variance in time characterize deformation rates of PS points in study area. Mean while conspicuous contrast of deformation rates is present on opposite sides of the Haiyuan fault, with a relative motion rate in line of sight about 5mm/a in the central segment. These estimates are in accordance with the results of 2~10mm/yr determined by geological and geodetic methods.

A Model of In-depth Displacement under Ms8.1 at Kunlun Earthquake with D-InSAR Co-seismic Deformation Field

Numerical modeling can be used to obtain geophysical information for earthquake mechanism analysis. During the past decade, differential synthetic aperture radar interferometry (D-InSAR) technology has been applied successfully to research co-seismic field and hypocentral mechanism, which could offer more abundant boundary conditions with higher quality as compared with the conventional methodology of geodetic measurement. This paper reports a model of in-depth co-seismic displacement with this approach. On November 14, 2001, a Ms8.1 earthquake, one of the largest events hitting the Chinese mainland over the past 50 odd years, occurred at the Kunlun Mountains in the northern Tibetan plateau, China. In this model, a co-seismic field is established and a series of hypocentral parameters are extracted on the earthquake applying D-InSAR processing with 2Pass+external DEM mode to 20 pair’s ERS-2 SAR data and combined with field geology investigation as well as GPS observations on permanent stations. D-InSAR co-seismic field shows that the Kunlun Mountain Ms8.1 earthquake produced a 430-kilometer-long surface rupture zone, composed by the western section of Taiyang Lake-Kushuihuan with a length of 30km, the eastern section of Bukadaban Peak-Kunlun Mountain Pass with a length of 350km and a 50km long unbroken step area between the above-mentioned two sections. This rupture zone shows such obvious characteristics as distinct segmentation and a left-lateral slip with little reverse component. The maximum co-seismic sinistral horizontal dislocation is 7.38m, of which 4.30m on the south wall and 3.08m on north wall. The maximum vertical dislocation is 4.0m. By means of Poly3D, a geophysical boundary element method (BEM) developed by Stanford University, and based on the boundary conditions of D-InSAR hypocentral parameter, this paper simulates a 3D distribution of the co-seismic deformation and spatial trend of displacement vector over the shock surface area of 80,000 km2 and its underground areas of 20km in depth. The 3D displacement field shows that the maximum strike displacement Ux occurs at 15km below the surface of the Hoh sai Hu lake east-Yuxi peak segment, with a maximum dislocation of 6.424m, the maximum dip displacement Uy is located 10km below the surface of the Yuxi peak-Kunlun Mountain Pass segment, with a maximum dislocation of 2.067m, and the maximum dip displacement Uz is located 10km below the surface of the Yuxi peak-Kunlun Mountain Pass segment with a maximum dislocation of 3.701m. The simulation displacement vectors indicate that bounded by the almost vertical main rupture plane, the south wall thrusts northward with some subsidence, the north wall moves upwards, the south wall moves from west to east while the north wall does from east to west. As the horizontal offset is dominated by left-lateral vertical displacement, the earthquake is classified as a strike-slip dominant type. Thus it is concluded that the Ms8.1 Kunlun earthquake originated from the Kunlun fault with a set of steep dip, left-lateral and strike-slip reverse faults.

Precision evaluation and characteristics analysis of the coseismic deformation field of the 12 th may 2008 Wenchuan Ms8.0 earthquake

Based on the improved DInSAR technology, this paper obtained the whole coseismic deformation field of Wenchuan Ms8.0 earthquake by 128 frames of Lever1.0 data of ALOS PALSAR. By comparing with the continuous GPS survey results, the precision of coseismic deformation field was estimated as about 9.5cm, better than half-wavelength of L-band. The whole coseismic deformation stripe has a total length of about 300km, which encircles the NE-trend seismic ruptures, and is mostly distributed within 19–100km from the fault rupture. The spatial distribution of coseismic deformation gradually narrows down from southwest to northeast, owing to the fact that the seismic energy gradually decayed along the NE-trend from Yingxiu where the seismic fracture begins to Qingchuan where it ends. There is a weak coherence zone near the seismic rupture relating to strong displacements, such as landslide, mud and rock flow, etc. And this weak coherence zone obviously extends wider in south Beichuan than in north Beichuan, which is corresponding to the fact that two parallel rupture faults exist in south Beichuan while only one exists in north Beichuan. The 471-track deformation is produced mainly by Qingchuan Ms6.4 dextral-strike aftershock and other strong aftershocks, and therefore its deformation field is discontinuous with adjacent tracks. As a whole, northwest plate-Bayankala Block was uplifted, while southeast plate-rigid Sichuan Basin subsided, and both sides of the seismic rupture were uplifted. But there exist one subsided zone 10–30km away from the rupture in the Bayankala Block. Synthetically analysis shows that, under the effect of the huge eastward pushing force from Tibet, the Bayankala Block was resisted by the rigid Sichuan Basin when it thrust along the high-angle seismic rupture, and then its east margin bent to form a subsided zone to absorb and release the strong eastward thrusting force.

Correlation between movement of tectonic blocks and earthquakes in groups

The Chinese mainland is divided into some tectonic blocks by nearly NE- and EW-orientated faults. Meanwhile strong earthquakes in the Chinese mainland usually cluster in time and space. We call “earthquakes in groups”. Tectonic blocks separated by faults and earthquakes in groups are prominent features of the tectonics of the Chinese mainland. Correlation between movement of tectonic blocks and groups of earthquakes is discussed in this paper. The results show that earthquakes in groups often occurred at one or several block boundary faults. The released elastic strain energy is built up in the same periods and around blocks. It means that strong earthquakes in groups are mainly caused by movement of blocks. Four types of block movement are identified based on group earthquakes: movement along a single boundary of a block (or a combined blocks), movement of a single block, movement of multi-blocks, and movement in block interiors. If we consider distribution of all strong earthquakes occurred in the Chinese mainland, the movement along a single boundary of a block is more popular one inducing strong earthquakes. But if we only consider earthquakes in groups rather than single earthquakes the movement of a block dominates among four modes. Statistics with respect to group earthquakes show that the Taihangshan mountain and the North China block are much active in the eastern part of Chinese mainland, and in western part of Chinese mainland the active blocks are Sichuan-Yunnan and the Kunlun-Songpan ones.