关键词: 地震异常, 水汽含量, 汶川地震, 松潘震群, 玉树地震

Abstract:

The spatial-temporal variations of atmospheric water vapor in western Sichuan Province and its vicinity during the mid-and long-term earthquake preparation process are studied.The M_S 8.0 Wenchuan earthquake in 2008,the Songpan-Pingwu earthquake sequence in 1976 and the Yushu M_S 7.1 earthquake in 2010 are selected as cases of the study regions.The result shows the frequency of atmospheric water vapor anomalies will decrease at first, then increase quickly during the mid-and long-term process of strong earthquake.The decreasing of the frequency of atmospheric water vapor anomalies begins relatively early,mostly over 10 years before earthquake and will last more than 9 years,which is considered as mid-and long-term precursor.The rapid increase appears 4 years before earthquake,as a kind of mid-and short-term precursor.The frequency of atmospheric water vapor anomalies over epicentral region of Wenchuan earthquake began to decline slowly 18 years before the earthquake and continued for 15 years, then increased rapidly 2 years before the earthquake.The atmospheric water vapor anomalies in the epicenter area changed from lowest frequency to high frequency 1 year before the earthquake,then the event occurred.It continued to increase until 2009 then resumed to normal state.14 years before Songpan-Pingwu earthquake,the frequency of atmospheric water vapor anomalies over the epicenter region began declining and it continued for 9 years,and then increased 4 years before the event.The anomalies in the epicenter region changed from lowest frequency in 1971 to high frequency in 1973,and reached the highest in 1976,and then the main shock happened.After the earthquake,it resumed to normal state.Similarly to the above two cases,there had been atmospheric water vapor anomalies before the M_S 7.1 Yushu earthquake in 2010,the frequency of anomalies declined from 1997 to 2008 when the lowest value was reached.It increased quickly in 2009 till the event occurred in 2010.The atmospheric water vapor anomalies over epicentral region may be due to the opening-closing movement of pores and fractures in the rock layer before the earthquake,resulting in the migration of underground fluid and underground heat energy,and then causing the change of the surface temperature and surface latent heat flux.During the mid-and long-term process of earthquake preparation,the rate of latent heat exchange decreases due to the reduction of the hot water vapor from underground caused by the closing of pore and fracture when the crustal rocks undergo compression deformation,so the frequency of atmospheric water vapor anomalies begins to decline.While during the mid-and short-term process of earthquake preparation,the accelerating of the crustal rocks deformation and the expanding of micro fractures will lead to increasing the hot water vapor from underground,accelerating the latent heat exchange,and quickly increasing the frequency of atmospheric water vapor anomalies.Analyses of the above three cases prove preliminarily that this assumption is reasonable.

Key words: earthquake anomaly, atmospheric water vapor, Wenchuan earthquake, Songpan-Pingwu earthquake sequence, Yushu earthquake