Relocation of the M_S≥2.0 Earthquakes in the Northern Tianshan Region, Xinjiang, Using the Double-Difference Earthquake Relocation Algorithm

We applied the double-difference earthquake relocation algorithm to 1348 earthquakes with M_S≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these M_S≥2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5≤M_S<2.0. Finally, we obtained the relocation results for 1253 earthquakes with M_S≥2.0, which account for 93% of all the 1348 earthquakes with M_S≥2.0 and includes all the M_S≥3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0≤M_S<3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N-S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 km, with 94% being from 5km to 35 km, 68.2% from 10 km to 25 km. The average hypocenter depth is 19 km.

A Preliminary Study on the New Activity Features of the Lajishan Mountain Fault Zone in Qinghai Province

The Lajishan Mountain fault zone consists of two NE_protruding arcuate faults, i.e. the northern and southern margin fault of Lajishan Mountain with the fault length of 230km and 220km respectively. The fault zone is located in the large_scale compressional structure zone and tectonic gradient zone in_between the NNW_trending right_lateral strike_slip Reshui_Riyueshan fault zone and the NWW_trending left_lateral strike_slip northern margin of west Qinling Ranges fault zone is also an important boundary fault zone, separating the Xining_Minhe basin and the Xunhua_Hualong basin at the southern and northern sides of the Lajishan Mountain respectively. Geologic geomorphic evidences of new activity revealed by field investigations indicate that the latest movement of the Lajishan fault zone was in late Epipleistocene (only a few segments were active in early Holocene) and is mainly of compressive thrusting with slightly left_lateral strike_slip component. The above movement has possibly resulted in the occurrence of about 20 moderate earthquakes of magnitude around 5.0. The Lajishan region can therefore be regarded as a seismotectonic window to reflect tectonic movement and earthquake activity.

Study on the Microstructure of Loess in Meizoseismal Zone

In this paper, quantitative study on the microstructure of loess is done based on the study of seismic subsidences of the Yongdeng M_S5.8 earthquake in 1995. Using SEM and image processing techniques, a comparison analysis on the microstructure of loess is done and distribution curves of loess pores are obtained. Based on laser grain analyzer test and trellis structure changes under earthquake effect, the dynamic properties of loess are explained. At the same time, pore distribution of loess from seismic zone and non-seismic zone is compared. The result shows that the pore distribution features of different meizoseismal zones are different, and even that loess at the similar depths has substantial differences, too.

Wenchuan earthquake:Brightness temperature changes from satellite infrared information

By using an alternative processing method for satellite infrared remote sensing data and adopting the China Geostationary Meteorological Satellite(FY-2C) infrared remote sensing brightness temperature data,we studied the great 2008 Wenchuan Ms8.0 earthquake.Results indicate the obvious characteristic period and amplitude,and distribution of thermal infrared anomalies before the Wenchuan earthquake.And we discussed the mechanism of the observed pre-earthquake thermal anomalies.The characteristics of observed thermal infrared anomalies are easy to be recognized and applied,and could provide a criterion for thermal anomalies of earthquakes.