Constraining earthquake stress drop and mantle attenuation from teleseismic body-wave spectra

从远震体波谱中约束地震应力降和地幔衰减

基本信息

批准号：
2019379
负责人：
Jeroen Ritsema
金额：
$ 25.88万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-09-01 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2019379&HistoricalAwards=false
关键词：
Constraining earthquake stress drop mantle

项目摘要

Most earthquakes occur within plate-tectonic convergence zones. Earthquakes which occur at depths larger than ~50 km (30 miles) result from rupture events in oceanic plates that are sinking into the Earth’s mantle. These deep earthquakes have similar characteristics than shallow earthquakes, yet they are different. Observations suggest that deep earthquakes involve frictional sliding along planar faults, as the shallow ones. Yet it is still unclear how faults can break at the extreme pressure prevailing in the seismogenic mantle, reaching up to 250,000 times the atmospheric pressure. The mechanisms responsible for deep earthquakes have thus been debated for decades. Here, the researchers investigate these mechanisms using new analyses of seismic waves. Seismic waves travel away from the earthquakes that generated them, through the Earth’s mantle and crust. When they reach the surface, they can be used to investigate events in the deep Earth. Here, the team analyze the wave spectra, analogous to how astronomers analyze the electromagnetic spectra of stars. It tests the hypothesis that deep earthquakes rupture small fault planes with high rupture speeds. The researchers document the differences in shear-stress states of faults in the crust (at shallow depths) and in the mantle (at large depths). This project leverages national investments in seismological infrastructure, such as the IRIS Global Seismic Network (GSN) and the Earthscope USArray. It provides support for an early career female scientist and a female graduate student. It also provides training in seismology, geophysics, scientific computing, and big-data analytics for several undergraduate students at University of Michigan - Ann Arbor. Here, the analysis of the earthquake rupture process and seismic wave propagation are tightly linked, as both the earthquake source complexity and the heterogeneous properties of rock along the wave paths shape seismic wave spectra. The team follows a new two-step spectral-ratio approach aimed at optimally separating the source and propagation effects in teleseismic P-wave and S-wave spectra. Using the four-decade long IRIS database, the researchers select pairs of nearby earthquakes to determine rupture durations and stress drops of several hundred large earthquakes in the crust and mantle. From pairs of GSN and USArray ground-motion recordings, they estimate how seismic wave attenuation and scattering affect wave spectra. By processing the spectra consistently in both steps, they can compare the source characteristics and chart with robust statistics how stress drop varies with earthquake depth, magnitude, and tectonic plate boundary. Furthermore, they quantify wave propagation along several well-travelled paths to add new constraints on variations of wave scattering and attenuation in the Earth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大多数地震发生在板岩收敛区域内。地震发生在大于约50公里（30英里）的深度，这是由于海洋板的破裂事件导致的，这些盘子沉入地球的地幔中。这些深层地震的特征与浅层地震具有相似的特征，但它们是不同的。观察结果表明，深层地震涉及沿平面断层的摩擦滑动。然而，目前尚不清楚如何在地震生成地幔中盛行的极端压力下破裂，达到了大气压力的25万倍。因此，几十年来一直在辩论造成深层地震的机制。在这里，研究人员使用地震波的新分析研究了这些机制。地震波从地震中脱离地震，穿过地球的地幔和地壳。当它们到达表面时，它们可用于研究深地球中的事件。在这里，小组分析了波谱，类似于天文学家如何分析恒星的电子光谱。它检验了以下假设：深震破裂的小断层平面具有高破裂速度。研究人员记录了地壳（在浅深度）和地幔（大深度）中剪切压力状态的差异。该项目利用国家对地震基础设施的投资，例如IRIS全球地震网络（GSN）和EarthScope USArray。它为早期职业女科学家和女研究生提供了支持。它还为密歇根大学 - 安阿伯大学的几位本科生的地震学，地球物理学，科学计算和大数据分析提供了培训。在这里，对地震破裂过程和地震波传播的分析紧密相连，因为地震源复杂性和沿波道沿波路径的异质性质形状的地震波光谱。该团队遵循一种新的两步光谱比率方法，旨在最佳地分开远距离震动P-波和S波光谱中的源和传播效果。研究人员使用四个十年的长虹膜数据库选择附近的地震，以确定地壳和地幔中数百大地震的破裂持续时间和应力下降。从GSN和USARRAY地面录音中，它们估计地震波衰减和散射如何影响波光谱。通过在这两个步骤中始终如一地处理光谱，它们可以将源特性和图表与强大的统计数据进行比较应力下降如何随地震深度，幅度和构造板边界而变化。此外，他们沿着几条良好的路径量化了波浪传播，以增加地球中波散射和衰减变化的新约束。该奖项反映了NSF的法定任务，并被认为是通过基金会的智力优点和更广泛的影响审查标准通过评估来评估的。