Collaborative Research: Continuation Of A GPS and Seismic Study of the Subduction Earthquake Cycle: Jalisco, Mexico

请求经费用于对墨西哥西部科利马-哈利斯科地区进行为期四年、第三阶段和最后阶段的基于gps的研究。自1995年初以来，两次大地震（M=8.0和M=7.6）直接从30个站点的GPS网络上破坏了中美洲的俯冲界面，最近一次是在2003年1月。这些地震为研究大俯冲地震的同震和震后效应提供了难得的机会，包括震后断层后滑和粘弹性流动的逐渐衰减以及震间弹性应变积累的重新出现。研究这些地震及其后果有许多智力上的价值，概述如下。建议项目的具体目标如下：(1)继续对1995年10月9日发生的Mw=8.0 Colima-Jalisco地震和2003年1月22日发生的m_w =7.6 Tecoman地震进行区域速度场测量，以表征黏弹性流和余震的空间变化特征；(2)建立6站连续gps网络，以更好地表征这些黏弹性和余震响应的时间演变，并更好地将它们与潜在的线弹性应变积累区分离。连续的测量将能够确定Cocos/Rivera俯冲界面是否存在类似于最近在卡斯卡迪亚、日本和墨西哥南部描述的下倾瞬态地震滑动事件。(3)利用现有和新的观测资料完成2003年Tecoman地震的同震和震后效应建模，包括大地测量和地震约束的联合反演，余震重新定位的局部地震数据的协同分析，以及我们假设的弹性常数、层厚和俯冲界面几何形状的敏感性分析。(4)利用测量到的地震间应变积累方向和量级的变化来估计里维拉和科科斯板块俯冲界面的锁定程度，并将陆上应变积累与海洋板块运动联系起来。(5)确定1995年科利马-哈利斯科地震和随后的过程是如何改变邻近Tecoman地震爆发带的应力水平的。(6)从GPS、地震和shuttlradar地形任务数据中提取本区与大陆裂谷相关的上板块变形信息。正如该项目的前几个阶段的情况一样，现阶段的项目将产生许多更广泛的影响。墨西哥国立自治大学的Osvaldo sanchezo、瓜达拉哈拉大学的Bertha Marquez和科利马大学的Gabriel Reyes，以及来自三所大学的墨西哥本科生和研究生将作为官方合作者参与研究。此外，还要求支持一名华盛顿大学研究生继续他的大地测量数据有限元建模论文，一名加州理工学院研究生将与Gabriel Reyes一起研究当地地震数据，以及两名REU本科生将在Stock的指导下工作。来自新的连续站点的数据将为其他研究人员提供有用的遗产，特别是用于检测和表征与俯冲界面沿线地震滑动相关的瞬态信号。

Funds for a four-year, third and final phase of a GPS-based study of theColima-Jalisco region of western Mexico are requested. Since early 1995,two large magnitude earthquakes (M=8.0 and M=7.6) have ruptured the MiddleAmerica subduction interface directly offshore from a 30-station GPS network,most recently in January of 2003. These earthquakes have afforded an exceptionalopportunity to study the coseismic and postseismic effects of largesubduction earthquakes, including the gradual decay of postseismic faultafterslip and viscoelastic flow and re-emergence of interseismic elasticstrain accumulation. Studying these earthquakes and their after effectshave numerous intellectual merits, outlined below. Specific goals forthe proposed project are as follows: (1) Continue annual measurements of theregional velocity field to characterize spatial variations in viscoelasticflow and afterslip triggered by the Mw=8.0 Oct. 9, 1995 Colima-Jalisco andM_w=7.6, 1.22.2003 Tecoman earthquakes, (2) Construct a six-station continuousGPS network to better characterize the temporal evolution of these viscoelasticand afterslip responses and better separate them from the underlying linearelastic strain accumulation. Continuous measurements will enable determine ofwhether the Cocos/Rivera subduction interfaces accommodate downdip transientaseismic slip events similar to those recently described for Cascadia, Japan,and southern Mexico. (3) Complete modeling of the coseismic and post-seismiceffects of the 2003 Tecoman earthquake using existing and new observations,including a joint inversion of the geodetic and seismic constraints,collaborative analysis of local seismic data for aftershock relocations, andsensitivity analysis for our assumed elastic constants, layer thickness,and subduction interface geometry. (4) Employ measured variations inthe direction and magnitude of interseismic strain accumulation toboth estimate the degree of locking along the Rivera and Cocos platesubduction interfaces and relate onshore strain accumulation tothe oceanic plate motion. (5) Determine how the 1995 Colima-Jalisco earthquakeand subsequent processes altered stress levels in the adjacent Tecoman earthquakerupture zone. (6) Extract information about upper plate deformation associatedwith the continental rifts in our field area from GPS, seismic, and ShuttleRadar Topographic Mission data. As has been the case in previous stages ofthis project, the present phase of the project will have numerous broader impacts.Three Mexican scientists will participate as official collaborators: Osvaldo Sanchezof UNAM, Bertha Marquez of the Universidad de Guadalajara, and Gabriel Reyes ofthe University of Colima, as well as Mexican undergraduate and graduate studentsfrom three universities. In addition, support is requested for a UW graduate studentto continue his finite element modeling of the geodetic data for his dissertation,a Caltech graduate student who will work with Gabriel Reyes on local seismic data,and two REU undergraduates who will work under Stock's guidance. Data from the newcontinuous sites will constitute a useful legacy for other investigators, particularlyfor detecting and characterizing transient signals related to aseismic slip alongthe subduction interface.