Radiation of Teleseismic Body Waves from Dynamic Faults

本项目通过建立远震距离浅层逆冲断层地震的P和SH体波模型，研究断层不透明度（反射相位被困在断层上盘的趋势）对辐射能量的影响。采用三维有限元模型计算了多种摩擦模型下的断裂过程。这些滑动历史被用来计算由不同摩擦模型产生的远震体波。这些动态模型与通常用于确定地震矩的传统位错模型之间存在系统差异。主要目标是量化来自倾斜断层的远震P和SH体波如何受到地震波和动态滑动断层之间近源相互作用的影响。通常的做法是通过使用双偶震源表示对这些远震波形进行建模来估计地震矩。在这些模型中，介质被建模为具有由双偶体力分布引起的位移跳变的弹性连续体。虽然这些模型满足连续介质中的所有边界条件，但它们不一定与滑动断层（不连续介质）上的摩擦应力边界条件相容。特别是，从地球表面反射出来的剪切波通常可以通过滑动断层传播而不反射；这有时被称为透明的错误。一个长期存在的问题是，在确定地震大小时，使用透明断层模型是否引入了系统误差。这项研究应该对这种影响的重要性提供定量估计。

Thomas H. HeatonEAR-0208494This project is examining the effects of fault opacity (the tendency of reflected phases to be trapped in the hanging wall of the fault) on radiated energy by constructing models of P and SH body waves from shallow thrust fault earthquakes at teleseismic distances. Three-dimensional finite-element models are used to calculate rupture history assuming a variety of friction models. These slip histories are used to calculate the teleseismic body waves that results from the different friction models. Systematic differences are determined between these dynamic models and traditional dislocation models that are commonly used for determining seismic moments. The main goal is to quantify how teleseismic P and SH body waves from dipping faults are affected by near-source interactions between the seismic waves and a dynamically slipping fault. It has been common practice to estimate seismic moments by modeling these teleseismic waveforms using double-couple source representations. In these models, the medium is modeled as an elastic continuum with displacement jumps caused by distributions of double-couple body forces. While these models satisfy all boundary conditions within a continuous medium, they are not necessarily compatible with the frictional stress boundary conditions on the slipping fault (a discontinuous medium). In particular, shear waves that reflect off of the Earth's surface are generally allowed to propagate back through the slipping fault without reflection; this is sometimes referred to as a transparent fault. There is a long-standing question about whether or not systematic errors in determining earthquake sizes have been introduced by using transparent fault models. This study should provide quantitative estimates of the importance of this effect.