Collaborative Research: Examining the variation in earthquake parameters along the Nicaragua and Costa Rica subduction zone using onshore and offshore seismic data

了解断层条件如何影响地震破裂已被确定为地震学界的一个基本挑战，特别是沿浅层俯冲巨型逆冲断层，那里的大地震可以产生毁灭性的震动和海啸。该研究通过描述震源特征来解决这个问题，并将其与中美洲海沟附近一个小地理区域内的特定构造和地质变化进行比较，该区域过去曾发生过大海啸和地震，并且存在独特的陆上和海上地震记录，可以记录大量地震。研究人员假设，震源特征（如表观应力）与断层沿线的物质条件有关，因此在俯冲带内会有所不同。在俯冲巨型逆冲构造上，有许多潜在的改变断层条件的罪魁祸首。俯冲的海山、山脊、断裂带、板块弯曲断层和俯冲板块上的可变沉积物包体可以在大逆冲构造的几何形状上产生显著的变化。孔隙流体压力的变化可以通过改变断层的有效正应力来影响断层的强度状况。纵波速度与横波速度之比（Vp/Vs）对断层条件的变化很敏感，例如孔隙和裂缝中流体的存在、温度和成分，但对板的几何形状不敏感。因此，为了确定这些条件如何影响地震破裂，既需要断层条件的高质量数据，也需要广泛的地震目录，这两种数据都可以在本研究区域获得。它们将是：1)确定震源谱，以提供破裂时间和应力降的估计，这是全球研究中常用的描述地震破裂特性的两个参数；2)采用一种创新技术，利用波形互相关微分时间计算近源Vp/Vs。研究人员将把源参数与中美洲已有的丰富的地球物理数据进行比较，并与新的Vp/Vs估计进行比较，以帮助确定板间断层段是否存在不寻常的流体压力或物质成分。这将使他们进一步了解流体在地震破裂中的作用。研究人员将研究一个有大地震（7级）和海啸地震历史的地区。他们的研究结果将提高对当地地震和海啸灾害的认识，并对其他俯冲边缘的地震和海啸灾害有更广泛的认识。该项目还将支持2名研究生的参与，继续进行国际合作，并产生将在国家会议、国际出版物以及通过在线海洋地球物理数据库和PI支持的网页广泛传播的结果。

Understanding how fault conditions impact earthquake rupture has been identified as a fundamental challenge of the seismological community, especially along shallow subduction megathrust faults where giant earthquakes can produce devastating shaking and tsunami. The study addresses this issue by characterizing earthquake source characteristics for comparison to specific tectonic and geologic variations within a small geographic area along the Middle America Trench, an area that has produced past large tsunami and earthquakes and where unique onshore and offshore seismic recordings exist for a large catalog of earthquakes. The researchers hypothesize that earthquake source characteristics such as apparent stress are related to material conditions along faults and hence will differ within the subduction zone. Along the subduction megathrust, there are numerous potential culprits for altering the fault conditions. Subducted seamounts, ridges, fracture zones, plate-bending faults, and variable sediment packets riding on the subducting plate can provide significant variations in the megathrust geometry. Variable pore fluid pressure can affect the strength conditions along the fault by changing the effective normal stress. The ratio of compressional to shear wave speeds (Vp/Vs) is sensitive to changes in fault conditions, such as the presence of fluids in pores and cracks, temperature and composition, but not to slab geometry. Thus, to determine how these conditions affect earthquake rupture, both high quality data on fault conditions as well as extensive earthquake catalogs are need, both of which are available along this study area. They will be: 1) determining earthquake source spectra to provide estimates of the rupture time and stress drop, which are two parameters commonly used in global studies to describe earthquake rupture properties; and 2) calculating near source Vp/Vs using waveform cross-correlation derived differential times following an innovative technique. The Researchers will compare source parameters with the wealth of geophysical data already available in Middle America, as well as with the new estimates of Vp/Vs to help determine whether interplate fault segments have unusual fluid pressures or material composition. This will allow them to advance ideas about the role of fluids in earthquake rupture.The researchers will be studying a region that has a history of large (M7) earthquakes and tsunami earthquakes. Their results should improve understanding of local seismic and tsunami hazard and also bear on broader understanding of seismic and tsunami hazard along other subduction margins. The project will also support the participation of 2 graduate students, continue international collaborations, and produce results that will be disseminated widely at national meetings, international publications, and through online marine geophysical databases and PI supported webpages.