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，断层以宽度为几百米的狭窄断层带（FZ）为标志。 大多数地震破裂模型，包括粗糙体和粘滑范例，表明FZ结构（几何和材料属性）控制地震破裂的开始，传播和终止。 然而，确定FZ结构的孕震深度，地震成核和大多数滑动发生已被证明是极其困难的。 在这个项目中，圣刘易斯大学的地震学家们使用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宽度和速度分别确定，从而消除了两者之间的权衡。 此外，利用FZ反射波，还可以精确定位FZ中已获得FZ宽度和速度参数的位置，从而获得了前所未有的FZ构造深度分辨率。 此外，他们能够重新定位余震的精度为几十米相对于FZ的边界。 他们计划将该方法应用于加州各种断层带的数据集，包括Landers，Hector Mine，San Jacinto和Parkfield的SanAndreas Fault，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：所获得的信息对于开发地震源模型至关重要。 在这项研究中获得的经验将有助于设计未来的FZ地震实验和开发的方法可以很容易地应用到其他地区和数据集，如那些从正在进行的美国阵列。

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.