摘要
本文用WKBJ方法,计算了中国境内已知震源机制的六个地震——1973年7月14日西藏约基台错地震;1975年2月4日海城地震;1976年8月16日、1976年8月21日及1976年8月23日松潘地震和1976年11月15日宁河地震——的远震垂直向P波和PP波的理论地震图,并与观测波形进行对比,以检验计算方法。讨论了西藏地震的震源机制。 作者注意到,走滑型地震和倾滑型地震PP波与P波最大振幅的比值在一定的震中距范围内有不同的特征。为此,计算了走滑型和倾滑型地震在破裂方位角为330°,240°和0°,震源深度为8km,17km和24km,台站方主角为310°时,震中距由40°到80°间的P波与PP波理论地震图。给出了PP波与P波最大振幅比(A_(PP)/A_P)随震中距而变化的曲线。讨论了用(A_(PP)/A_P)值对地震震源机制类型给出粗略的估计的可能性。此项工作有助于确定一些资料不全,例如本世纪30年代到60年代间中国地震的震源机制类型。
Using the WKBJ approximatation method we calculate the synthetic teleseismograms of P and PP waves to match the observed ones of six large Chinese earthquakes with known focal mechanisms: Xizang earthquake of July 14, 1973; Haicheng earthquake of February 4, 1975; Songpan earthquakes of August 16, 1976, August 21, 1976 and August 23, 1976 and Ninghe earthquake of November 15, 1976. The focal mechanism of the Xizang earthquake is discussecussed to examine the technique used in the calculation.We note that the amplitude ratios of PP and P waves (App/Ap ) have different characteristics for dipslip events and strikslip events within certain epicentral distances. We ca-Iculate the synthetic teleseismograms of P and PP waves for the strike-slip and dip slip events with fault angles of 330°, 240° and 0°, focal depths of 8 km,, 17km and 24km, at the assumed station with an azimuth of 310° and epicentral distances from 40° to 80°. The diagrams of maximum amplitude ratios of PP to P waves (App/Ap) versus distences are given. The possibility to use the (App/Ap) values to give an approximate estimation for the focal mechanism type is discussed. This work may be useful for determining the focal mechanism type for those earthquakes which have only few records such as the Chinese earthquakes from the 1930's to 1960's.
出处
《地震学报》
CSCD
北大核心
1991年第2期150-160,共11页
Acta Seismologica Sinica
