SEISMO-TECTONIC STRESS FIELD IN EAST CHINA
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Abstract
On the basis of P wave first motion data of 1211 micro-earthquakes which were widespread over northeastern, central and southern part of the continent of eastern China during 1973—1982, we have used the grid testing method to deduce the mean P, B and T axis corresponding to composite fault plane solutions for each of 23 subregions. Combined with the results of principal stress axes studies of 23 additional sub-regions in North China and around the Ordos Massif, which were obtained previously by other authors, the features of the seismo-tectonic stress field have been analysed more completely for the continent of eastern China (to the east of 105°E).The overall features of stress field are as follow: the mean P axes are nearly horizontal and orientate radially from the central part of the continent to eastern coastal region; the mean T axes are horizontal and lie along arcs which are convex eastwards. This indicates that the stress field here is not likely to be generated by some local sources within this region. Since all earthquakes of this region have occurred in the crust and most of them showed vertical strike slip faulting, it is inferred that the dominant deformation associated with the earthquake occurrence is of horizontal type. The vertical mean P axis in the southern part of Fen-Wei Graben indicates tensional tectonic movement there.Although the stress field shows clearly the overall feature, the seismic activity is inhomogeneous in the whole area. This implies that differences in regional seismic activity may be attributed to differences in the tectonic provinces rather than differences in stress field.
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