There were huge life and property losses during the M_(s)8.0 Wenchuan earthquake on May 12,2008.Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its su...There were huge life and property losses during the M_(s)8.0 Wenchuan earthquake on May 12,2008.Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake.This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations.In particular,data of 174 earthquakes(M_(s)4.0-M_(s)8.5)were processed and analyzed with various methods,which were recorded at the Shandan station from August 2007 to December 2008.The results were compared with other seismic data,and further analyses were done for the recoded strain seismic waves,co-seismic strain stepovers,pre-earthquake strain valleys,Earth's free oscillations before and after the earthquake and their physical implications.During the Wenchuan earthquake,the strainmeter recorded a huge extensional strain of 70 seconds,which shows that the Wenchuan earthquake is a rupture process predominated by thrusting.Significant precursory strain anomalies were detected 48 hours,30 hours,8 hours and 37 minutes before the earthquake.The anomalies are very high and their forms are very similar to that of the main shock.Similar anomalies can also be found in strain curves of other shocks greater than M_(s)7.0,indicating that such anomalies are prevalent before a great earthquake.In this paper,it is shown that medium aftershocks(M_(s)5.5-6.0)can also cause Earth's free oscillations.Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks,thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.展开更多
In recent years, the fluid-injection-induced seismicity tests within the WFSD-3P borehole belonging to the Wenchuan Earthquake Fault Science Drilling （WFSD） project, have made remarkable progress. This study has bee...In recent years, the fluid-injection-induced seismicity tests within the WFSD-3P borehole belonging to the Wenchuan Earthquake Fault Science Drilling （WFSD） project, have made remarkable progress. This study has been supported by the Science and Technology Project of China （No. WFSD-00003）.展开更多
This study, supported by the Science and Technology Project of China （grant no. WFSD-00003）, focuses on the in-situ stress measurements in the WFSD-I borehole and has achieved considerable progress. Stress is defin...This study, supported by the Science and Technology Project of China （grant no. WFSD-00003）, focuses on the in-situ stress measurements in the WFSD-I borehole and has achieved considerable progress. Stress is defined as the natural stress existing between rocks in the Earth＇s crust, and in-situ stress measurements are the main methods used to obtain records of the stress state. The Wenchuan Fault Scientific Drilling （WFSD） project used differential strain analysis （DSA） to confirm in-situ stress measurements.展开更多
基金supported by Project of Ministry of Science and Technology:"Scientific drilling in Wenchuan earthquake fault zone"and Project of China Geological Survey(1212010916064)
文摘There were huge life and property losses during the M_(s)8.0 Wenchuan earthquake on May 12,2008.Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake.This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations.In particular,data of 174 earthquakes(M_(s)4.0-M_(s)8.5)were processed and analyzed with various methods,which were recorded at the Shandan station from August 2007 to December 2008.The results were compared with other seismic data,and further analyses were done for the recoded strain seismic waves,co-seismic strain stepovers,pre-earthquake strain valleys,Earth's free oscillations before and after the earthquake and their physical implications.During the Wenchuan earthquake,the strainmeter recorded a huge extensional strain of 70 seconds,which shows that the Wenchuan earthquake is a rupture process predominated by thrusting.Significant precursory strain anomalies were detected 48 hours,30 hours,8 hours and 37 minutes before the earthquake.The anomalies are very high and their forms are very similar to that of the main shock.Similar anomalies can also be found in strain curves of other shocks greater than M_(s)7.0,indicating that such anomalies are prevalent before a great earthquake.In this paper,it is shown that medium aftershocks(M_(s)5.5-6.0)can also cause Earth's free oscillations.Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks,thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.
文摘In recent years, the fluid-injection-induced seismicity tests within the WFSD-3P borehole belonging to the Wenchuan Earthquake Fault Science Drilling （WFSD） project, have made remarkable progress. This study has been supported by the Science and Technology Project of China （No. WFSD-00003）.
文摘This study, supported by the Science and Technology Project of China （grant no. WFSD-00003）, focuses on the in-situ stress measurements in the WFSD-I borehole and has achieved considerable progress. Stress is defined as the natural stress existing between rocks in the Earth＇s crust, and in-situ stress measurements are the main methods used to obtain records of the stress state. The Wenchuan Fault Scientific Drilling （WFSD） project used differential strain analysis （DSA） to confirm in-situ stress measurements.
