Fine Structure of Fault Zones from Modeling High-frequency Body-wave Waveforms of Aftershocks

地震是地壳块体在断层上快速运动的结果，断层的标志是一个宽度为几百米的狭窄断裂带。大多数地震破裂模型，包括粗糙和粘滑模式，表明FZ结构（几何地形和材料特性）控制地震破裂的开始、传播和终止。然而，在地震成核和大部分滑动发生的发震深度，确定FZ结构已被证明是极其困难的。在这个项目中，圣路易斯大学的地震学家使用FZ附近余震的高频体波波形来确定精细尺度。波形特性使他们能够设计一种新的策略，其中FZ宽度和速度是分开确定的，从而消除了两者之间的权衡。此外，利用FZ反射波可以精确定位FZ内的位置，从而获得FZ宽度和速度参数。这给了他们一个前所未有的高深度分辨率的fz结构。此外，他们能够以相对于FZ边界几十米的精度重新定位余震。他们计划将该方法应用于加利福尼亚各种断层带的数据集，包括兰德斯、赫克托矿、圣哈辛托和帕克菲尔德的圣安德烈亚斯断层，以确定FZ参数（走向、宽度、速度和密度下降以及Q）和可能的临时变化。更广泛的影响：获得的信息对建立震源模型至关重要。在这项研究中获得的经验将有助于设计未来的FZ地震实验，并且开发的方法可以很容易地应用于其他地区和数据集，例如正在进行的USArray。

Earthquakes are the result of rapid movement of crustalblocks on faults, which are marked by a narrow fault zone(FZ) with a width of several hundred meters. Mostearthquake rupture models, including the asperity andstick-slip paradigms, suggest that FZ structure (geometricaland material properties) controls earthquake ruptureinitiation, propagation, and termination. However,determining FZ structure at seismogenic depths whereearthquakes nucleate and the majority of slip occurs hasbeen shown to be extremely difficult. In this project,seismologists at Saint Louis University use high-frequencybody-wave waveforms from aftershocks near the FZ todetermine fine-scale. Waveform characteristicsenables them to design a new strategy in which the FZ widthand velocities are determined separately, thus eliminatingthe trade-off between the two. Furthermore, by using FZreflected waves, they can pinpoint the locations in the FZwhere they have obtained FZ width and velocity parameters.This gives them a unprecedented high depth resolution of FZstructure. In addition, they are able to relocateaftershocks with an accuracy of a few tens of metersrelative to the FZ boundaries. They plan to apply themethod to data sets of various fault zones in California,including the Landers, Hector Mine, San Jacinto, and SanAndreas Fault at Parkfield to determine FZ parameters(strike, width, velocity and density drops, and Q) andpossible temporary variations. Broader Impacts: The information obtained is crucialto developing models of the earthquake source. Experiencegained in this study will help design future FZ seismicexperiments and the methodologies developed can be easilyapplied to other regions and data sets, such as those fromthe on-going USArray.