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移动的结果，断层上有一个几百米宽的狭窄断裂带(FZ)。大多数地震破裂模型，包括粗糙和粘滑范例，表明FZ构造(几何和材料性质)控制着地震破裂的萌生、传播和终止。然而，在地震成核和大多数滑动发生的孕震深度确定FZ构造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。波形特征使他们能够设计一种新的策略，其中FZ带宽和速度是单独确定的，从而消除了两者之间的权衡。此外，通过利用FZ反射波，他们可以精确地定位他们在FZ中获得FZ宽度和速度参数的位置，这使他们获得了前所未有的FZ构造的高深度分辨率。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。他们计划将这种方法应用于加州不同断裂带的数据集，包括帕克菲尔德的兰德斯、赫克托矿、圣哈辛托和桑安德烈亚斯断层，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：所获得的信息对建立震源模型至关重要。这项研究的经验将有助于设计未来的FZ地震实验，所开发的方法可以很容易地应用于其他地区和数据集，如正在进行的美国阵列的那些。

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.