1988年澜沧—耿马双主震型地震破裂与震区的现代构造运动

THE SEISMIC RUPTURE OF THE 1988 LANCANG-GENGMA EARTHQUAKE WITH DOUBLE MAIN SHOCK TYPE AND THE RECENT TECTONIC MOVEMENT IN THE SEISMIC REGION

本文在１９８８年澜沧──耿马地震震区野外考察和分析总结本组地震破裂基本特性的基础上，根据震区的大地形变测量资料和弹性理论，从现代构造运动的观点，探讨了本组地震破裂的成因，尤其是两次主震在破裂方面的联系和差异。研究结果表明：（１）自１９８５年至１９８９年，震区以２．１厘米／年的平均速率向北３７．４°东方向水平推挤了０．６４米；（２）与此同时，它还兼有绕铅垂轴的顺时针旋转运动，其平均角速度为９．４×１０^（－８）度／年，极点大的位于北纬２３°２０＇─２３°３０′，东经１００°１５＇─１００°２０＇；（３）震区的主压形变方位是北２３．３°东，最大右旋剪切形变方位是北２１．７°西，南北两主震区的最大右旋剪切形变的比值≥２．２；（４）震区的现代构造运动是导致本组地震破裂的重要原因之一，主震破裂在力学性质方面的差异与旋转运动的动力学效应有关。

Based on field investigation in the seismic region and analysis of basic rupture characteristics of the event group as well as survey data of geodetic deformation and elestic theory, from the view of recent tectonic movement,this paper preliminarily approaches tectonic origin of the 1988 LanchangGengma earthquake with double main shocks, especially the connection and difference in seismic rupture between the two main shocks. The results are shown as follows: 1. During 1958-89, the seismic region has been pushed horizontally towards 37.4 NE at an average rate of 2.1 cm/a by 0.4 meters.2.And at same time.the seismic segion has been clockwise rotated. round a vertical axis at an average angular velocity of 9.4 × 10￣(-8) degree/a, and the pole was located near 23°20'-23°30'N and 100°15'-100°20'E. 3. In the seismic region, the azimuth of principle compressive deformation was 23.3°NE and the azjmuth of maxium right-lateral shear deformation was 21.7°NW. The ratio of the maximum right-lateral shear strain in the earthquake area of magnitude 7.6 to in the magnitude 7.2 was 2.2 or more than.4. The recent tectonic movement in the seismic region is one of major origins causing the sismic rupture of the Lanchang-Gengma earthquake, and difference in mechanical behavior between the two main shocks relates to dynamical effect of rotation motion.