Collaborative Research: A Study of Transient Aseismic Slip and Non-Volcanic Tremor in Southern Mexico With Large Aperture Seismic and GPS Arrays

智力优势：申请资金用于中美洲俯冲带瓦哈卡-格雷罗段的联合大地测量和地震研究，这是地球上为数不多的可以使用陆基GPS和地震观测来研究俯冲界面的锁定发震区和更深的过渡滑动区域的地方，在那里可能发生间歇性震颤和滑动。主要的科学目标是更好地理解最近发现的幕式滑动瞬变现象，以及它在减轻或增加沿俯冲界面发震部分积累的应变方面的作用。去年的一项初步研究表明，这种瞬变现象在该地区每隔12-24个月就会频繁发生，一些瞬变现象（1998年和2004年）发生在格雷罗地震间隙很远的地方，而且这些瞬变现象可能伴随着非火山地震。基于这些之前未被认识到的结果，计划在24个月内部署8个站点的宽带地震阵列，并扩展区域连续GPS阵列，包括在可能发生瞬变的区域内的4个关键位置站点。作为加州理工学院/UNAM中美洲地震实验的一部分，新的地震阵列将跨越两个密集地震横断面之间的国外间隙，将允许检测和定位研究区域的任何偶发性地震。从现有的GPS站和由该小组及其合作者UNAM的Enrique Cabral建造的9个新站进行的连续GPS测量将提供有关周期性滑动的震源区域、震级和时间的关键补充信息。DeMets和cabrala在cocos -北美俯冲界面上方的瓦哈卡州运行的现有30个站点连续和运动GPS阵列的数据也将用于更详细地研究一个明显的地震间隙内的变形，类似于众所周知的格雷罗地震间隙，但比它小。GPS和地震阵列的结合将成为研究俯冲瞬变和非火山性地震的有力工具，并可成像网络下沿锁定带和过渡带的摩擦耦合的时空变化。布鲁津斯基将于2005年8月成为俄亥俄迈阿密大学的新教员，他将用其教员职位上的启动资金购买必要的地震设备，并将在2006年初为两年的部署做好准备。威斯康星大学麦迪逊分校的DeMets将与Cabral博士协调GPS站的安装，以及瓦哈卡GPS网络的适度扩展，以提高上述地震间隙的覆盖范围。威斯康星大学麦迪逊分校地球物理小组在部署地震和GPS网络方面有着悠久的历史，他们将免费提供两名专家技术人员来帮助建立和维护地震和GPS网络。DeMets和Brudzinski将分别负责大地测量和地震观测的建模工作。更广泛的影响：间断性震颤和滑动是一种新观察到的现象，似乎与地球科学的许多不同方面（地震学、构造学、岩石学和地球动力学）有关，可能对理解特大逆冲地震的触发产生影响。迈阿密大学的学生将有一个独特的机会参加一个现场研讨会课程，该课程将与最初的地震部署同时进行，从而使学生接触到地球物理现场研究。对威斯康星大学麦迪逊分校更广泛的影响将包括墨西哥研究生Francisco Correa-Mora的教育，他的论文将主要研究中美洲海沟俯冲的力学。新的连续和运动GPS和地震数据对更广泛的地球物理社区的可用性也将扩大这项工作的影响，超出我们的小组，特别是一旦记录未来的瞬变滑动事件和/或震颤序列。

Intellectural merit: Funds are requested for a joint geodetic and seismic study ofthe Oaxaca-Guerrero segment of the Middle America subduction zone, one of the few placeson earth where land-based GPS and seismic observations can be used to study both thelocked, seismogenic area of a subduction interface and region of deeper transitionalslip, where episodic tremor and slip may originate. The principal scientific goal isto better understand the recently discovered phenomenon of episodic slip transientsand its role in either relieving or increasing strain accumulating along the seismogenicportion of a subduction interface. A pilot study during the past year shows that suchtransients are occurring as frequently as every 12-24 months in this region, thatsome transients (1998 and 2004) originate far outside the Guerrero seismic gap, andthat the transients may be accompanied by non-volcanic seismic tremors. Based on thesepreviously unrecognized results, deployment for 24 months of an 8-station broadbandseismic array and expansion of a regional continuous GPS array to include 4 criticallylocated stations in a region where the transients appear to occur are planned. Thenew seismic array, which will span abroad gap between two dense seismic transects being installed as part of the alreadyfunded Caltech/UNAM Middle America Seismic Experiment, will allow detection and locationof any episodic tremors in the study area. Continuous GPS measurements from thepre-existing GPS stations and nine new stations constructed by this group andcollaborator Enrique Cabral of UNAM will provide critical complementary informationabout the source regions, magnitude, and timing of episodic slip. Data from an existingsmaller-footprint 30-station continuous and campaign GPS array that DeMets and Cabraloperate in Oaxaca above the Cocos-North America subduction interface will also be usedto study in more detail deformation within a conspicuous seismic gap analogous to,but smaller than the well-known Guerrero seismic gap. The combined GPS and seismicarrays will be a powerful tool for studying subduction transients and non-volcanictremor, and for imaging spatial and temporal variations in frictional couplingalong the locked and transitional zones beneath our network. Brudzinski, who will bea new faculty member at Miami University of Ohio in August of 2005, will purchase thenecessary seismic equipment with start-up funds from his faculty position and willhave it prepared for a two-year deployment in early 2006. DeMets at UW-Madison willcoordinate the GPS station installation with Dr. Cabral, as well as a modest expansionof the Oaxaca GPS network to improve coverage of the aforementioned seismic gap. TheUW-Madison geophysics group has a long history of deploying seismic and GPS networksand will provide at no cost two expert technicians to help build and maintain thecombined seismic and GPS network. Responsibilities for modeling of the geodetic andseismic observations will lie respectively with DeMets and Brudzinski.Broader impacts: Episodic tremor and slip are a newly observed phenomenon that appearsto be related to many different aspects of earth science (seismology, tectonics,petrology, and geodynamics), with possible ramifications for understanding triggeringof megathrust earthquakes. Students at Miami University will be offered a unique opportunityto participate in a field workshop course that will coincide with the initial seismicdeployment, thereby exposing students to a geophysics field research. Broader impacts atUW-Madison will include education of Mexican graduate student Francisco Correa-Mora,who will do a substantial portion of his dissertation research on the mechanics ofsubduction along the Middle America trench. The availability of new continuous andcampaign GPS and seismic data to the broader geophysical community will alsoextend the impact of this work beyond our group, particularly once future transientslip episodes and/or tremor sequences are recorded.