Reliability of Pressure and Tension Axes Determined by Initial Motions of P-Waves from Deep Earthquakes in and near Japan: The Use of J.M.A. Network
Reliability of Pressure and Tension Axes Determined by Initial Motions of P-Waves from Deep Earthquakes in and near Japan: The Use of J.M.A. Network
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由日本及其附近深部地震纵波初始运动确定的压力轴和张力轴的可靠性：J.M.A. 的使用
DOI：
10.4294/zisin1948.25.1_92
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
Tomowo Hirasawa
中科院分区：
文献类型：
--
作者：
S. Horiuchi;K. Emura;Tomowo Hirasawa
在日本及其附近的典型地震带的每个细分区域，估计了由p波初始运动确定的深地震双偶机制的压力轴和张力轴的可靠性。我们估计可靠性的方法解释如下：根据已知的结果，在一个小区域发生的地震机制彼此非常相似，我们可以在该区域定义一个代表性的机制，我们首先想象一个假设的地震，该机制位于每个适当划分的区域的一点上。接下来，我们将代表性机构理论期望的纵波初始运动方向数据分配给J.M.A.网的112个标准站。这些数据现在被视为这112个站点的观测数据。利用这些虚构的数据，我们可以反求出假定地震的震源机制，其中最初计算数据的代表性机制当然是完全符合数据的。然而，如果允许压力轴和张力轴在焦点球上向任何方向移动，只要不一致台站的数量小于规定的小数量，甚至为零，我们就可以计算压力轴和张力轴方向的允许变化，从而对可靠性进行估计。主要结果总结如下：在靠近苏联的日本海下面和本州岛（日本主岛）海岸以南的太平洋下面的地震带中，压力轴和张力轴的方向变化都是允许的，在这些地震带中，台站的方位角分布不是很好。在这些地区，两个轴都能够在焦点球上沿特定方向移动50至70度（在某些情况下为90度）的角距离，即使不一致站的数量被认为只有一个。在日本海岸以下靠近本州中部的地震带，压力轴和张力轴的测定都相当稳定，台站的方位角分布令人满意。
Reliability of the pressure and tension axes in double couple mechanisms of deep earhquakes determined from P-wave initial motions is estimated for each subdivided region of the typical seismic zones in and near Japan. Our method of estimating the reliability is explained as follows: Based on the known results that mechanisms of earthquakes occurring in a small region are so similar to one another that we may define a representative mechanism in the region, we first imagine a hypothetical earthquake of the mechanism located at a point in each of appropriately divided regions. We next assign data of P-wave initial motion directions expected theoretically for the representative mechanism to 112 standard stations of the J.M.A. Network. The data are now regarded as observational data at these 112 stations. We can calculate in reverse the focal mechanism of hypothetical earthquake by the use of these fictitious data, where the representative mechanism from which the data are originally computed, of course, satisfies the data completely. However, if the pressure and tension axes are allowed to move to any direction on a focal sphere as far as the number of inconsistent stations is less than a prescribed small number including even zero, we can calculate permissible variations in directions of the pressure and tension axes, leading to an estimation of the reliability. The main results are summarized as follows: A wide variation in orientation is permissible for both the pressure and tension axes in the seismic zones beneath the Japan Sea near U.S.S.R. and beneath the Pacific Ocean south off the coast of the Honshu (the main island of Japan), where distributions in azimuth of stations are not sufficiently good. In these regions both the axes are able to move on the focal sphere up to an angular distance of 50 to 70 degrees (90 degrees in some cases) in a particular direction, even though the number of inconsistent stations is taken to be only one. Determinations of both the pressure and tension axes are quite stable in the seismic zones beneath the Japan Sea coast near the central part of Honshu, where the azimuthal distribution of stations is satisfactory.