论文部分内容阅读
地震震源机制(用等效于岩体破裂的力描述震源几何形状及其强度)通常被模拟为矩张量(MT),将震源描述为一个点。然而,有时这种近似是不够的,因为地震辐射会由于震源的有限范围而持有方向性。转换为矩张量就可能产生有偏差的机制。Adamov和íleny(2010)进行的综合研究说明即使是纯双力偶(DC)震源其机制中也出现假非双力偶分量。他们的方法设计了减少假震源分量,通过二阶矩方法来评估假分量在记录中的影响并将它们从数据中去除。在本文中,我们将这个方法应用到具有大非剪切分量的5个中等到大的区域地震事件。它们大多位于预计主要是纯剪切滑动的大构造断层。我们研究了著名的北安纳托利亚断层上的一个地震、太平洋地区的3个地震以及玻利维亚的一个地震。在多数情况下,非双力偶分量实质上减少了,机制的几何形状基本上保持不变。这证实了这样的假设,由于忽视了矩张量检索的常规程序中震源的有限性,区域矩张量解中的部分非双力偶分量可能是假的。此外,由二阶矩(震源椭球和破裂速度矢量)提供的震源的几何学和运动学特征多数与先前研究中的断层几何、余震分布及破裂速度估计一致。
The focal mechanism of the earthquake (describing the source geometry and its intensity in terms of force equivalent to the rupture of the rock mass) is usually modeled as a moment tensor (MT) describing the source as a point. However, sometimes this approximation is not sufficient, because seismic radiation will have directivity due to the limited range of sources. Converted to moment tensor may have biased mechanism. A comprehensive study by Adamov and íleny (2010) shows that even non-dual dual components occur in the mechanism of pure dual DC sources. Their approach was designed to reduce the amount of false source components and to evaluate the effect of false components in the records by the second-moment method and to remove them from the data. In this paper, we apply this method to five moderate to large regional seismic events with large non-shear components. Most of them are located in large structural faults that are predominantly purely shear-slip. We studied one of the famous earthquakes on the North Anatolian fault, three in the Pacific Ocean and one in Bolivia. In most cases, the non-dual-couple component is substantially reduced, and the geometry of the mechanism remains essentially unchanged. This confirms the hypothesis that some of the non-dual-couple components in a region moment tensor solution may be false due to neglecting the finiteness of the source in the conventional procedure of moment-tensor retrieval. In addition, most of the geometric and kinematic features of the hypocenter provided by the second moment (source ellipsoid and rupture velocity vector) are consistent with the previous estimates of fault geometry, aftershock distribution and fracture velocity.