Probing the transient rheology of accretionary prisms and megathrust earthquake hazard in the Indian Ocean basin

世界上最大的地震发生在俯冲带，板块构造边界，一个板块潜入另一个板块之下。这些地震有可能引发海啸，影响震源地数千英里外的居民和城市。然而，对俯冲带及其地震和海啸潜力的研究往往是困难的，因为诊断俯冲带行为的地球物理和地质信号发生的大部分地区都在水下。这种限制反过来又要求研究人员对地球的行为进行简化，比如地球的行为是像橡皮筋一样有弹性，还是像蜡烛蜡一样有粘性，这可能会对地震和海啸潜在的估计产生负面影响。该项目将利用对巴基斯坦南部和伊朗的一个俯冲带——马克兰俯冲带的独特观测，更好地量化俯冲带断层周围的岩石随时间的变化。这个位置提供了一个独特的机会，可以更好地描述世界各地的俯冲带，因为这个俯冲带的大部分都暴露在海洋表面之上。这意味着研究人员将能够使用卫星监测工具以前所未有的细节量化俯冲带的行为。该项目的更广泛影响包括量化Makran俯冲带未来发生地震的可能性，地震引发的海啸将影响整个西印度洋盆地的城市，包括孟买、pop等大城市。2390万，还有卡拉奇。1690万年。该项目还支持EPSCoR州的研究生和研究。为了实现上述目标，研究人员将使用干涉合成孔径雷达（InSAR）时间序列分析来量化Mw7.7级地震在Makran吸积棱镜内引起的震后变形。对这一变形信号的初步分析表明，大多数吸积棱镜本身在相对较浅的深度（20公里）经历了粘弹性松弛。通过将InSAR时间序列分析与有限元建模方法相结合，我们将量化Makran吸积棱镜的流变结构和粘度，幂律粘弹性行为是否需要解释大地测量观测，以及什么变形机制是活跃的，以适应震后松弛。由于InSAR观测错过了震后变形的前15个月，而在这段时间里，余震预计是主要的变形过程，因此研究人员将探索利用Landsat-8图像进行光学图像时间序列分析的新方法，目的是量化早期余震。后滑估计将被纳入粘弹性松弛模拟，以提供一个更完整和无偏的Makran增生棱镜流变结构模型。最后，本项目将把该流变模型整合到Makran俯冲带的地震间耦合模型中，以更好地估计Makran巨型逆冲构造的锁定分布和锁定速率。这些结果将进一步证明，在世界其他地方的俯冲带锁定模型中加入粘弹性增生棱镜的重要性，或者缺乏这种重要性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The world's largest earthquakes occur in subduction zones, plate tectonic boundaries where one plate dives beneath another. These earthquakes have the potential to generate tsunamis that impact people and cities many thousands of miles from the location of the earthquake. The study of subduction zones and their earthquake and tsunami potential is often difficult, though, because much of the region where the geophysical and geological signals occur that are diagnostic of subduction zone behavior is underwater. This limitation in turn requires researchers to make simplifications of Earth behavior, such as whether the Earth behaves elastically like a rubber band or viscously like candle wax, that can negatively impact estimates of earthquake and tsunami potential. This project will use unique observations of a subduction zone in southern Pakistan and Iran, the Makran Subduction Zone, to better quantify how the rocks surrounding a subduction zone fault behave over time. This location provides a unique opportunity to better characterize subduction zones around the world because much of this subduction zone is exposed above the surface of the ocean. This means that the researchers will be able to quantify the behavior of the subduction zone with unprecedented detail using satellite monitoring tools. The Broader Impacts of the project include quantifying the future earthquake potential of the Makran Subduction Zone where an earthquake-generated tsunami would impact cities throughout the western Indian Ocean basin, including the megacities of Mumbai, pop. 23.9 million, and Karachi, pop. 16.9 million. The project also supports a graduate student and research in an EPSCoR state.To accomplish the goals above, the researchers will use interferometric synthetic aperture radar (InSAR) time series analysis to quantify post-seismic deformation caused by an Mw7.7 earthquake in within the Makran accretionary prism. Preliminary analysis of this deformation signal indicates that most of the accretionary prism itself undergoes viscoelastic relaxation at relatively shallow depths (20 km). By combining InSAR time series analysis with finite element modeling approaches, we will quantify the rheological structure and viscosities of the Makran accretionary prism, whether power-law viscoelastic behavior is required to explain the geodetic observations, and what deformation mechanisms are active to accommodate the post-seismic relaxation. Because InSAR observations miss the first 15 months of post-seismic deformation, a period when afterslip is expected to be a dominant deformation process, the researchers will explore new approaches in optical imagery time series analysis using Landsat-8 imagery, with the goal of quantifying early afterslip. Afterslip estimates will be incorporated into viscoelastic relaxation simulations to provide a more complete and unbiased model of the rheological structure of the Makran accretionary prism. Finally, this project will incorporate this rheological model into interseismic coupling models of the Makran Subduction Zone in an effort to better estimate the locking distribution and locking rate of the Makran megathrust. These results will additionally demonstrate the importance, or lack thereof, of including viscoelastic accretionary prisms in subduction zone locking models elsewhere in the world.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.