2008������Ms7.3����ǰ��������̬�仯������

????1998?????????й??????????????????????????2008??3?????????7.3?????????????????????仯?????????????????????????????????????????????????????г????2~10???????????????????????????????????????????????????仯?????????????????????仯????????????????????????????????????????????????????????????????????????????????仯?????????????????????????????1976?????7.8????????????????????????й?????8?????????????仯??200??10 _-8 ms ^-2 ??

CHARACTERISTIC ANALYSIS OF DYNAMIC GRAVITY CHANGE BEFORE YUTIAN Ms7.3 EARTHQUAKE,2008

On the basis of the data and results of the repeated gravity observation network in Chinese mainland since 1998, the evolution characteristics of dynamic gravity field changes in the seismogenic region before Yutian Ms7.3 earthquake in Mar, 2008 has been analyzed and summarized. The dynamic evolution images of regional gravity field reflects the middle long term (two to ten years) essential information during the earthquake preparation. The notable gravity symbols of the earthquake preparation are positive gravity change (rise) lasted for many years and relatively large scale gradient zone of gravity change that the former is in favor of continuous accumulation of seismic energy and the latter makes for occurrence of seismic rupture. The related gravity change during the process of the earthquake preparation have the characteristics: increase accelerated increase decelerated increas which is similar to that of Tangshan Ms7.8 earthquake in 1976. The maximum accumulative gravity change related to the earthquake can reach 200×10^-8 ms ^-2 .