Shen Xu-Hui

General characteristics of the recent horizontal crustal movement in Chinese mainland

In this paper, the horizontal crustal movement obtained from GPS observations in 1998 and 2000 at basic and fiducial stations in the Crustal Movement Observation Network of China (CMONOC) is introduced. A brief introduction of the field observations, the data processing with GAMIT/GLOBK software and the accuracy of the GPS observations is given. In average the accuracy of the results for each year is about 2 mm in the horizontal components and 5 mm in the vertical component, and the average accuracy of horizontal displacements at a station is about 3 mm. The results of crustal movement during the period from early September 1998 to mid June, 2000, including the displacements at each station with datum definition of a group of stable stations of insignificant relative movements among themselves in the eastern part of China, strains in different parts of the network and rotations in some parts, are obtained. Based on the crustal movement maps which are more complete and detailed than previous ones, the general characteristics of the recent crustal movement in Chinese mainland are discussed. During the above mentioned period of observations, the crustal deformation in the eastern part of China was relatively small and quite stable. With reference to a group of stable stations with small relative movement in the eastern part of China, the northeastern China block moved northward for about 10 mm, the South China block moved southeastward for about 9 mm. In reference to the eastern part the northwestern part of China moved northward for about 26 mm, the Tibetan area in southwestern part of China moved mainly northward for about 32 mm. The area in Yunnan and east Tibet showed significant clockwise tectonic rotation of 0.0045″ or average rotational displacement of 12 mm with the rotation center at 26.5°N and 95.5°E. The North-South Seismic Belt in the middle part of China is of active and complicated deformation. The observation results show that the northward pushing by the Indian plate has still played the dominant role in the crustal movement in Chinese mainland.

VLF radio signal anomalies associated with strong earthquakes

The VLF (Very Low Frequency) radio signal receiving network of Russian Alpha radio navigation system has been established in China since 2010. We applied a quartile-based method to study the variations of VLF signal propagation before the M≥6.0 shallow earthquakes in the network. Results found that possible anomalies occurred around the two strong earthquakes, 2010 M7.1 Yushu and 2013 M7.0 Lushan earthquake, respectively. For earthquakes with magnitude 5.0≥M≥7.0, such anomalies are not detected. Preliminary statistical analysis with Dst and Kp indices show that there exists a good correlation between geomagnetic storms and VLF propagation anomaly.

Strong paleoearthquakes along the Talas-Fergana Fault, Kyrgyzstan

Abstract: The Talas-Fergana Fault, the largest strike-slip structure in Centred. Asia, forms an obliquely oriented boundary between the northeastern and southwestern parts of the Tianshan mountain belt. The fault underwent active right-lateral strike-slip during the Paleozoic, with right-lateral movements being rejuvenated in the Late Cenozoic. Tectonic movements along the intracontinental strike-slip faults contribute to absorb part of the regional crustal shortening linked to the India-Eurasia collision; knowledge of strike-slip motions along the Talas-Fergana Fault are necessary for a complete assessment of the active deformation of the Tianshan orogen. To improve our understanding of the intracontinental deformation of the Tianshan mountain belt and the occurrence of strong earthquakes along the whole length of the Talas-Fergana Fault, we identify features of relief arising during strong paleoearthquakes along the Talas-Fergana Fault, fault segmentation, the length of seismogenic ruptures, and the energy and age of ancient catastrophes. We show that during neotectonic time the fault developed as a dextral strike-slip fault, with possible dextral displacements spreading to secondary fault planes north of the main fault trace. We determine rates of Holocene and Late Pleistocene dextral movements, and our radiocarbon dating indicates tens of strong earthquakes occurring along the fault zone during arid interval of 15800 years. The reoccurrence of strong earthquakes along the Talas-Fergana Fault zone during the second half of the Holocene is about 300 years. The next strong earthquake along the fault will most probably occur along its southeastern chain during the next several decades. Seismotectonic deformation parameters indicate that M > 7 earthquakes with oscillation intensity I > IX have occurred.

Preliminary analysis on characteristics of co-seismic deformation field of the Gêrzê earthquake (Ms6.9) from ascending and descending pass ASAR radar interferometry

We process the ascending and descending mode ASAR radar data that covers the same area using 2-pass D-InSAR technology, and get the co-seismic deformation field, which provides us information on the seismic activity in the study area, in LOS direction of the Gêrzê (Tibet) earthquake (Ms6.9), which happened on 9 January 2008, followed by 40 aftershocks including the largest one on 16 January 2008. The result shows that it is double earthquakes caused by two buried normal faults. The LOS deformation is from −46.0cm to 11.4cm by descending interferometry pair, and −47.8cm by ascending interferometry pair.

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.