青藏高原北缘地震波特征量动态变化与强震活动关系的研究

RESEARCH ON THE RELATION BETWEEN DYNAMIC CHANGES OF THE CHARACTERSTICS OF SEISMIC WAVES AND THE ACTIVITIES OF STRONG EARTHQUAKES IN NORTHERN MARGIN REGION OF QINGHAI-TIBET PLATEAU

本文利用甘肃河西地震台网观测到的肃南南部地区１９８７年１月至１９９２年１０月间的地震记录资料，分析研究了青藏高原北缘地震波特征量动态变化与该区及邻近地区强震活动的关系。所研究的地震波特征量有Ｐ、Ｓ波速度Ｖｐ／Ｖｓ及其比值Ｖｐ／Ｖｓ；振幅比Ａｐ／Ａｓ；Ｐ波初始部分波形时间线性度ｒ和空间线性度α１、α２以及平均半周期Ｔｈ。所得结果表明，包括河西走廊中部及祁连山中段在内的青藏高原北缘地区的地震波特征量的动态变化可反映出震中距约在３００公里。内的７级强震及震中距约在２００公里以内的５～６级中强震前，由构造应力场变化引起的大面积介质性质的变化，因而可把它们视为强震和中强震的近源区或远场区地震波前兆异常。

By using the seismic records of earthquakes occurred in Southern Sunan region during January,1987 - October, 1992 observed at Hexi Seismic Network, Gansu Province, the relation between dynamic changes of the characteristics of seismic waves and the avtivities of strong earthquakes in Northern Margin region of Qinghai-Tibet plateau has been analyzed and studied. The studied characteristicsof seismic waves are:Velocities of P and S waves Vp and Vs,seismic velocity ratioVp/Vs, amplituderatio of S and P waves Ap/As, recti-linearities in time and space of the waveform of p-wave's initial part r, a1, a2, and average half Period of P wave Th. The results show that the dynamic change ofseismic waves in the Northern Margin region of Qinghai-Tibet Plateau including the middle port ofGansu(Hexi)corridor and the middle segment of Mt.Qilian may reflect the changes of medium's characters in a large area caused by the variations of tectonic stress field before strong earthquake of magnitude 7 at the epicentral distance within about 300km and moderate earthquake of magnitude 5-6 atthe epicentral distance within about 200km. Therefore,these dynamic changes can be considered asthe precursory anomalies of seismic waves in the near source region or far field region of strong andmoderate earthquakes.