ON THE FOCAL MECHANISMS OF EARTHQUAKES AND REGIONAL STRESS FIELD OF THE FUJIAN-TAIWAN REGION

In this paper, the focal mechanisms of the earthquakes of M 6, occurred in Taiwan Province and on the sea east of it, from 1933 to 1969 have been critically collected and compiled. In addition, the focal mechanisms of the earthquakes M 6 occurred in Taiwan and Fujian provinces, and in the Strait of Taiwan from 1970 to 1978 and of the earthquake of Magnitude 8 of 1604 are reexamined. After analyzing all these focal mechanism data of the two provinces, it is pointed out that: (1) the focal plane solutions obtained are closely related to the recent crustal movement at depth; (2) most of the directions of principal axis of compressive stress are perpendicular to the major fault zone; (3) on the sea east of Taiwan province, earthquakes moderate in size form three parallel seismic gaps elliptical in shape. Around the gaps, about 83% of the earthquakes of magnitude 6.0-6.9 have their major P axis nearly at right angles to the periphery of the gaps on which most earthquakes of magnitudes equal or greater than 7 occurred; (4) taking the Bashi strait as the center, facing Fujian province, the stress field consists of fan-like pattern toward NW.