剪切破裂源及其近场影响

THE SHEAR RUPTURE SOURCES AND ITS NEAR-FIELD INFLUENCE

摘要:

本文利用有限差分法对垂直走滑断层和垂直倾滑断层两种剪切破裂源在不同埋深和不同破裂尺度(指垂直于地面方向上断层尺度)情况下的近场理论地震图进行了讨论,并得到了地表不同震中距处的加速度付氏谱。
通过对上述两种源所产生的近场效应的对比分析,本文得到了以下初步结果:
(1)在埋深相同,断层面宽度相同的情况下,垂直走滑断层源对近场地表的影响比垂直倾滑断层源大。
(2)在垂直倾滑断层源的埋深、破裂尺度相同的情况下,在地表同一震中距处产生的水平位移要比垂直位移大。
(3)两种破裂源在地表同一震中距处产生的位移的最大振幅随破裂尺度的增大而增大,且近似为线性关系;在极震区内不同震中距处产生的位移的最大振幅随震中距的增大而减小,且随震中距的变化率在减小;在地表不同震中距处产生的加速度的付氏谱的主峰周期随震中距的增大而变长,随破裂的增大,付氏谱中主峰周期也加长,且长周期成份愈多;随着破裂源埋深的增加,地表不同震中距处产生的位移的最大振幅变小,即等震线变疏。
(4)走滑断层源产生的加速度付氏谱的主峰周期比倾滑断层源长。

Abstract:

In this paper, the near-field synthetic seismogram for vertical strike slip fault and dip slip fault is discussed with finite difference method in the case of different source depth and fault rupture size (refer to fault rupture size perpendicular to the ground). The acceleration fourier spectrum of different epicentral distance is discussed too.
The following inital results have been obtained through analysing near-field effect of two kinds of sources:
(1) If the source depth and the fault rupture size, are the same, the effect of vertical strike slip fault on near-field surface is larger than the effect of vertical dip slip fault.
(2) For vertical dip slip fault, if the source depth and the fault rupture size are the same, the largest amplitude of the horizontal displacement is larger than one of the vertical displacement in the same epicentral distance.
(3) The largest displacement amplitude produced by anyone of two kinds of sources in the same epicentral distance increases along with the enlargement of rupture size.
(4) The largest displacement amplitude produced by anyone of two kinds of sources in different epicentral distance decreases along with the increasing of epicentral distance, the rate of change along with the increasing of epicentral distance decreases too.
(5) The dominant period of acceleration fourie rspectrum produced by anyone of two kinds of sources in different epicentral distance changes longer along with the increasing of epicentral distance, the dominant period changes longer too along with the increasing of fault rupture size, and long period composition is much too along with the increasing of rupture size.
(6) For anyone of two kinds of sources, owing to the different source depth, the effect on near-field surface is different too. The largest displacement amplitude along with the rate of change of epicentral distance decreases, namely, isoseisms is getting thin. This relation is very useful in determing source depth by isoseisms density.
(7) The dominant period of acceleration fourier spectrum produced by vertical strike slip fault is longer than dip slip fault.