Oceanic intraplate earthquakes: Implications for local and regional intraplate stress
Oceanic intraplate earthquakes: Implications for local and regional intraplate stress
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海洋板内地震：对局部和区域板内应力的影响
DOI：
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发表时间：
1980
期刊：
影响因子：
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通讯作者：
S. Solomon
中科院分区：
文献类型：
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作者：
E. Bergman;S. Solomon
板内地震的震源机制是目前唯一能够表征海洋岩石圈长波长构造应力场的手段。然而，从震源机制推断的应力方向可能不能准确地反映震中地区的应力状态，或者测得的应力可能由当地而不是区域源主导。为了建立一个研究这些可能性的数据集，自1963年以来，我们编制了159次mb 4.7或更大的海洋板内地震的综合目录。大约四分之一的活动有焦点机制，这里介绍几种新机制。对于本星表的代表子集，（83次），汇集了震中区的水深和构造历史，并根据它们与（1）先存断层带（可能使震源机制的P轴与最大压应力的真实方向解耦）和（2）大水深起伏的关系对地震进行了评级，这可能是大的局部应力的来源。海洋板内地震通常与以前的薄弱地带（通常是断裂带）有关，但它们与大的测深特征没有任何特殊的联系。在印度洋中部，有足够的震源机制可以为P轴建立明确的NW-SE方向，并推测为最大压应力的方向。在存在Ninetyeast Ridge的情况下，这些差异很大的机制的P轴的一致性是值得注意的，Ninetyeast Ridge是一个主要的板内变形和大的水深起伏的地点。一个可能的解释是，在存在大量的预先存在的断层的范围内的取向，滑动发生在这些断层上，具有较大的解决剪切应力从区域应力场。在这种情况下，震源机制的P轴往往与最大应力的真实方向一致。
Focal mechanisms of intraplate earthquakes provide the only means at present by which to characterize the long-wavelength tectonic stress field in oceanic lithosphere. Stress orientations inferred from focal mechanisms may not accurately reflect the state of stress in the epicentral area, however, or the measured stresses may be dominated by local rather than regional sources. To establish a data set with which to study these possibilities, a comprehensive catalog of 159 oceanic intraplate earthquakes has been compiled for events since 1963 with mb 4.7 or larger. Focal mechanisms are available for approximately one quarter of the events, and several new mechanisms are presented here. For a representative subset of this catalog (83 events), the bathymetry and tectonic history of the epicentral areas have been assembled, and the earthquakes have been rated according to their association with (1) a preexisting fault zone, which might decouple the P axis of the focal mechanism from the true orientation of maximum compressive stress, and (2) large bathymetric relief, which might be a source of large local stresses. Oceanic intraplate earthquakes are commonly found in association with zones of previous weakness (usually fracture zones), but they do not show any particular association with large bathymetric features. In the central Indian Ocean there are enough focal mechanisms available to establish a well-defined NW-SE orientation for P axes and presumably for the direction of greatest compressive stress. The consistency of the P axes of these widely varying mechanisms in the presence of the Ninetyeast Ridge, a site of major intraplate deformation and large bathymetric relief, is remarkable. A possible explanation is that in the presence of a large number of preexisting faults with a range of orientations, slip occurs on those faults which have large resolved shear stresses from the regional stress field. In such an instance the P axis of focal mechanisms will tend to show a consistent alignment with the true direction of maximum stress.