High-amplitude seismic waves radiated from the bright spot of an earthquake
High-amplitude seismic waves radiated from the bright spot of an earthquake
复制标题
从地震亮点辐射出的高振幅地震波
DOI：
10.1016/0040-1951(90)90131-q
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发表时间：
1990
期刊：
影响因子：
2.9
通讯作者：
Y. Umeda
中科院分区：
文献类型：
--
作者：
Y. Umeda
在大浅源地震的震源区，很可能存在一个小点，其特点是产生高加速度和余震间隙。在大多数大浅源地震的地震图上，以及在一些中度主震的地震图上，可以检测到两种类型的P波：P1相之后的相对低幅度的波和P2之后的主要高频波。P1相之后的地震波的持续时间（P1−P2时间）与地震震级成比例地增加。这一事实有力地表明，初步破裂周期与主要高频地震波的辐射密切相关。为了解释上述观察结果，计算了移动破裂辐射的剪切应变波。由于地震波速度一般高于破裂传播速度，地震波产生的最大剪应变通常先于破裂前缘。如果总剪应变（等于震前静态剪应变加上地震波激发的动态剪应变）超过临界剪应变（~10−4），则二次破裂从初始破裂向前方向爆发。大中型地震的破裂过程分两个阶段：一是P1相对应的破裂萌生，二是破裂发展。地震剪切应变波引发的二次破裂。后一个过程会产生辐射高振幅地震波的地震亮点。
In the source region of a large shallow earthquake, there is likely to be a small spot characterized by the production of high accelerations and a gap in the aftershocks. On the seismograms of most large shallow earthquakes, and on some seismograms of moderate main shocks, two types of P-waves may be detected: the relatively low-amplitude waves following phase P1and the predominant high-frequency waves following phase P2.The duration of the seismic waves following phase P1(the P1−P2time) increases proportionately with the earthquake magnitude. This fact strongly suggests that the preliminary rupture period is closely related to the radiation of the predominant high-frequency seismic waves.To explain the above observation, the shear strain waves radiated from a moving rupture are calculated. Because the seismic wave velocity is generally higher than the rupture propagation velocity, maximum shear strains by seismic waves usually precede the rupture front.If the total shear strain, which is equal to the static pre-earthquake shear strain plus dynamic shear strain excited by seismic waves, exceeds the critical shear strain (~ 10−4), the secondary ruptures break out in the forward direction from the initial rupture.The rupture processes of large or moderate earthquakes occur in two stages: one is the initiation of rupture corresponding to phase P1, and the other is the development of secondary ruptures triggered by seismic shear strain waves. The latter process generates an earthquake bright spot which radiates high-amplitude seismic waves.