Xinjian Shan

Depth segmentation of the seismogenic continental crust: The 2008 and 2009 Qaidam earthquakes

[1]xa0The seismic hazard in the immediate vicinity of an earthquake is usually assumed to be reduced after rupture of a continental fault, with along-strike portions being brought closer to failure and aftershocks being significantly smaller. This period of reduced hazard will persist as strain re-accumulates over decades or centuries. However, this is only realised if the entire seismogenic layer ruptured in the event. Here we use satellite radar measurements to show the ruptures of two Mw 6.3 earthquakes, occurring in almost the same epicentral location ten months apart in the Qaidam region, China, were nearly coplanar. The 2008 earthquake ruptured the lower half of the seismogenic layer, the 2009 event the upper half. Fault segmentation with depth allows a significant seismic hazard to remain even after a moderate and potentially devastating earthquake. This depth segmentation possibly exists in the case of the 2003 Bam earthquake where satellite radar and aftershock measurements showed that it ruptured only the upper half of the 15–20 km deep seismogenic region [Jackson et al., 2006], and that the lower, unruptured part may remain as a continuing seismic hazard.

Evidence of sudden rupture of a large asperity during the 2008 Mw7.9 Wenchuan earthquake based on strong motion analysis

[1]xa0We investigate the rupture process of the 12 May 2008 Wenchuan earthquake using the records of 26 strong-motion stations, located 20–120xa0km from the seismic fault and with a good azimuthal coverage. The wave velocity model required to conduct this analysis has been validated against aftershocks, for which the point source hypothesis is a very good approximation. The inversion of the main shock rupture process confirms the slip distribution and the average rupture velocity (∼3 km/s) previously determined. However, a very peculiar behavior is clearly resolved by the extensive data set used in this study: the major slip area of the Wenchuan earthquake, located at 20–50xa0km North-East of the epicenter, is shown to break almost simultaneously, 25xa0s after earthquake initiation. This implies that slip in this part of the fault cannot be understood by simple stress release at the rupture front. A more likely interpretation is the presence of a strong asperity, which could break only when it was completely surrounded by stress increase, resulting in a delayed but brutal rupture.

Study on the electronic density perturbation detected by DEMETER satellite before Wenchuan earthquake

We used slope analysis and sliding Median method to study the electron density data observed by Langmuir probe of DEMETER satellite since April 25, 2008 to May 11, 2008, and obvious perturbation phenomena of electron density(Ne) in ionosphere were found before Wenchuan earthquake on May 12, 2008. Considering the geomagnetic disturbances, there were some abnormal information in different degrees on May 3, 4, 7, 9, 10, 11 respectively. Furthermore, on May 3 and May 4, along with the change of electron density, electron temperature was also elevated at the latitude of 10∼30°N. Also on May 7, not only electron density increased, but also ion density did above the epicentral area.

Coseismic displacement field of the Wenchuan Ms 8.0 earthquake in 2008 derived using differential radar interferometry

We used the radar data from satellite ALOS/PALSAR of Japan and D-InSAR technology to derive the coseismic displacement produced by the Wenchuan, China Ms 8.0 earthquake on 12 May 2008. The result shows that the coseismic displacement primarily concentrated in a near-field range about 100km width on both sides of the Yingxiu-Beichuan fault. The incoherent zone about 250km long and 15~35km wide nearby the fault suffered the largest deformation with surface ruptures. The secondary deformed areas are 70km wide on each side of the incoherent zone, where the displacements exhibit a sunk northern wall with maximum -110~120cm and an uplifted southern wall with maximum 120~130cm, respectively. In the far-field range of the fault, displacements are less than 10cm. Using the offset tracking, we found clear rupture traces and coseismic displacement of 3m along the faults. With a model of four fault sections, we retrieved slip distribution on the faults. The inversion result reveals two slips of 10m at depths 5~20km beneath the Yingxiu-Beichuan fault and one slip of 2.3m at depth 5~20km below the Guanxian-Jiangyou fault, respectively. Thrust faulting dominates the southwestern Yingxiu-Beichuan fault and the entire Guanxian-Jiangyou fault, while right-slip is the primary component along the northeastern Yingxiu-Beichuan fault.

Coseismic surface deformation caused by the Wenchuan M8 earthquake from InSAR data analysis

The D-InSAR technology is used to aquired seven belts of coseismic surface deformation of Sichuan M8 earthquake of 12 May 2008 from the ALOS/PALSAR satellite data of Japan. The result covers Yinxiu, Dujiangyan, Wenchuan, Moxian, Beichuan, Pingwu and Qingchuan county, each 500km in north-south and 70km in east-west. The investigation indicates that the surface rupture zone caused by the earthquake coincides the Beichuan-Yingxiu fault, extending from nearby the epicenter southwest of the Yingxiu town to north of the Suhe, Qingchuan county for about 230km. The northwest wall of the seismogenic fault has uplifted, exhibiting a dominant thrust motion. The maximum relative LOS displacement at the epicenter reaches 260cm. A swell of LOS 120–180cm displacements is present from Beichuan to Pingtong. Another uplifted belt of displacements 70–80cm occurs nearby north of Suhe, Qingchuan. Around Yaan and Mount Emeishan, and from Shehong to north of Chongqing, there is a large area of subsidence. In Chongqing and its south is seen a small uplifted area of 20–30cm. From Qingchuan, eastward to Guangyuan and Ningqiang, uplift amplitudes are 60–70cm. The whole area of the deformation filed is fairly large, even in the Sichuan basin occurs surface deformation of different degrees.

Three-dimensional deformation field caused by the Gaize earthquake by Multi-LOS DInSAR measurement technology

This paper firstly presents the Multi-LOS DInSAR measurement result of the coseismic deformation field caused by the Gaize Ms6.9 mainshock and Ms6.0 aftershock in Tibet, China, and then obtain the 3D deformation field based on the 3D resolving mode. The characteristic analysis of coseismic deformation field shows the rupture of mainshock is majorly normal, left-lateral striking with a little rotation; and the aftershock is typical normal rupture nature. The mainshock and aftershock had induced the east and west rupture(maybe buried) successively, and produced the east and west two subsiding centers

The characteristics of post-seismic surface deformation of the Wenchuan M S 8.0 earthquake from InSAR

The D-InSAR technology is used to acquire four strips of post-seismic surface deformation of Wenchuan M8 earthquake of 2008 from the ALOS/PALSAR satellite data of Japan. The result covers the Yingxiu town, Wenchuan, Shifang, Maoxian county, Beichuan, Pingwu and Qingchuan county in Sichuan Province. Some post-deformation characteristics is showed in the final result. Around Yingxiu town, the epicenter of main shock, a area of uplift is present with small amplitude 0–5cm at the northern wall of the causative fault, while relative subsidence took place with the amplitude 0–15cm on the other wall. Near Shifang county, there are slightly arranged concentric fringes, reflecting another subsidence area with amplitude 0–20cm. Around the Beichuan and Anxian county, there exists a relatively small uplift of an strip area with 0–5cm along the causative fault on its both side. A small area of dense concentric fringes(indicated by a rectangle box) appeared in 30km northeast of Qingchuan, which coincide with the locations of the aftershocks Ms6.1 of 5 Aug. 2008. On the lower wall, we can see another large uplift area of sparse concentric fringes located in more than 100km southeast of Qingchuan, because it is far from the causative fault, its impossible so large deformation took place, and it should attribute to atmospheric component. the deformation characteristics of the whole area is complicated generally.