澜沧-耿马地震的震源机制研究

本文利用中国数字化地震台网（CDSN）记录的2°-40°范围内的长周期P波垂直分量波形资料,通过理论地震图拟合的方法,研究了1988年云南澜沧-耿马地震主震及两个余震的震源机制.结果表明,主震由三个震源机制不尽相同的子事件组成.第一个子事件的震源机制为:走向N30°W,倾角88°,错动角185°,地震矩为0.55×10²⁰Nm.第二个子事件的震源机制为:走向N33°W,倾角90°,错动角209°,地震矩0.24×10²⁰Nm,延迟时间为25s.第三个子事件的震源机制为:走向N65°W,倾角82°,错动角172°,地震矩为0.14×10²⁰Nm,延迟时间为70s.这种在空间上相距甚小而在时间上有分离、子事件的震源机制相差较为显著的复杂震源过程,与现场综合考察所见的地表裂缝分布一致,可以解释为单一裂缝的X型共轭剪切破裂,两个余震震源机制均为:走向N10°W,倾角86°,错动角185°,地震矩分别为0.54×10¹⁸Nm和4.29×10¹⁸Nm.

SOURCE MECHANISM OF THE 1988 LANCANG-GENGMA CHINA EARTHQUAKE

The source mechanisms of the main shock and two aftershocks of the 1988 Lancang-Gengma, Yunnan Province, P. R. C., earthquake sequence have been determined using CDSN long-period P waveforms in the range of 2°-40°. Our analysis shows that the main shock is composed ;of motions of three subevents, each wtih a different mechanism. The first sub-event has a mechanism with a strike of N30 °W, dip of 88° , a rake of 185°, and a seismfc moment of 0.55×1020Nm. The second iubevent has a mechanism with a strike of N33° W, dip of 90°, a rake of 209°, a seismic moment of 0.24×1020Nm. and delay time of 25s. The third subevent has a mechanism with a strike of N65° W, dip of 82° , a rake of 172° , a seismic moment of 0.14×1020Nm, and a delay time of 70s. There are little seperation in space and significant seperation in time for these three subevents, the mechanisms of these three subevents are different. This complex source process is consistent with the surface rupture characteristics. This phenomina may be a X-type shear fracture. The two aftershocks have the same mechanism with a strike of N10° W, dip of 86°, a rake of 185° and seismic moments of 0.54 and 4.29×1018Nm, respectively.