Variation of stress field in the source region around a strong shock：an example

Ｖａｒｉａｔｉｏｎｏｆｓｔｒｅｓｓｆｉｅｌｄｉｎｔｈｅｓｏｕｒｃｅｒｅｇｉｏｎａｒｏｕｎｄａｓｔｒｏｎｇｓｈｏｃｋ：ａｎｅｘａｍｐｌｅＧｕｔ－ＬｉｎｇＤＩＡＯ（刁桂苓），Ｌｉ－ＭｉｎＹＵ（于利民）ａｎｄＱｉｎ－ＺｕＬＩ（李钦祖）（Ｓｅｉｓｍｏｌｏｇｉ...

Variation of stress field in the source region around a strong shock: an example

An earthquake with magnitude 6.6 occurred on November 16, 1983 in the Kaoiki, Hawii. The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes withM>-3.0 in this area from 1977 to 1985, it was found that each type of focal mechanism is roughly with invariable percentage, and that the strike-slip events including the mainshock, which did not appear in other stages, occurred in the stage aroundM=6.6 mainshock. The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena. Orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods. The results show that the stress field around the main shock withM=6.6 was more stable, its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively, the middle one is nearly vertical. The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip. The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field. The characteristic environment factors of Kaoiki region and its effects were discussed. The project is sponsored by the Earthquake Science Foundation under contract No. 91060.