海南省东方地区1992年小震群剪切波分裂研究

SHEAR WAVE SPLITTING STUDY ON SMALL EARTHQUAKE SWARM OF 1992 IN DONGFANG OF HAINAN，SOUTH CHINA

１９９２年１月海南省东方县发生小震群活动，本文利用在震中附近设立的５台ＤＣＳ－３０２数字磁带加速度地震仪记录的近场资料，进行了剪切波分裂的研究采用相关函数方法，通过对１８个做了精确定位的地震事件共４２条有效记录的分析，计算出了快剪切波的偏振方向为１１３°±１８Ｏ°，慢剪切波的时间延迟为（３．１±１．１）ｍｓ／ｋｍ，裂隙密度的平均值为０．００９７±０．００３３．结合该地区的地震活动性，分析了区域应力变化对时间延迟的影响，并根据ＥＤＡ理论讨论了分裂剪切波的时间延迟的变化特征，发现快、慢剪切波的到时差（时间延迟）随地震活动性及应力积累而变化，并推断出该区的主压应力场为北西西方向．

Abstract:A small earthquake swarm occurred in Dongfang region of Hainan province，South China since January of 1992．Five DCS-302 digital accelerotype seismometer were set up there from June 1，1992 and kept up observation for 3 months by Insritute of Geophysics,Stare Seismolgical Bureau.From 18 earthquakes which were well located，42 local seismic data were used for shear wave splitting analysis．Polarization azimuth（Paz）of fast shear wave，time delay（△t )of slow shear wave and cracks density（ε）were estimated，their aerage values and standard deviation are 113°±118°，3．1±1．1（ms／km）and 0．0097±0．0033 respectively．Combining with earthquake activity in this region，this paper analyses the effect on time delay from regional stress change，and discusses the variation feature of time delay of splitting shear wave using EDA theory．In this paper，we find the variation of the rime delaywith earthquake activity and stress accumulation and deduce the direction of principal compressive stress field may be the NWW in this region．Ksywords: Dongfang region，Shear wave splitting，Time delay，Crack density，Aspect ratio of crack．