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，特别是沿着浅俯冲巨型逆冲断层，在那里巨大的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，以便与中美洲海沟沿着一个小地理区域内的特定构造和地质变化进行比较，该区域过去曾产生过大海啸和地震，并且存在大量地震目录的独特陆上和海上地震记录。研究人员假设，震源特征，如视应力与沿着断层的物质条件有关，因此在俯冲带内会有所不同。 沿着俯冲巨型逆冲断层，有许多潜在的罪魁祸首改变断层条件。俯冲海山、海脊、断裂带、板块弯曲断层和俯冲板块上的可变沉积物包可使巨型逆冲断层的几何形状发生重大变化。变化的孔隙流体压力可以通过改变有效正应力来影响沿着断层的强度条件。压缩波与剪切波速度之比（Vp/Vs）对断层条件的变化敏感，如孔隙和裂缝中存在的流体、温度和成分，但对板几何形状不敏感。因此，为了确定这些条件如何影响地震破裂，需要关于断层条件的高质量数据以及广泛的地震目录，这两者都是沿着该研究区域可用的。 它们将是：1）确定地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两个参数，用于描述地震破裂特性; 2）使用波形互相关计算近源Vp/Vs，该波形互相关采用创新技术导出微分时间。研究人员将把震源参数与中美洲已有的丰富地球物理数据以及Vp/Vs的新估计值进行比较，以帮助确定板间断层段是否具有异常的流体压力或物质成分。这将使他们能够推进关于流体在地震破裂中的作用的想法。研究人员将研究一个有大（7级）地震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危险的理解，也将对沿着其他俯冲边缘的地震和海啸危险有更广泛的理解。该项目还将支持2名研究生的参与，继续开展国际合作，并产生成果，这些成果将在国家会议、国际出版物上以及通过在线海洋地球物理数据库和公众参与者支持的网页广泛传播。

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.