Collaborative research: A study of transient aseismic slip and non-volcanic tremor in southern Mexico with large aperture seismic and GPS arrays

智力上的优点：要求提供资金，对中美洲俯冲带的瓦哈卡-格雷罗段进行大地测量和地震联合研究，这是地球上为数不多的几个地方之一，可以利用陆基全球定位系统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，这些地区可能产生幕式震颤和滑动。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及其在减轻或增加沿俯冲界面的孕震部分沿着积累的应变中的作用。过去一年的一项试点研究表明，这种瞬变在该地区每12-24个月发生一次，一些瞬变（1998年和2004年）起源于格雷罗地震空区以外，瞬变可能伴随着非火山地震震颤。 根据这些以前未确认的结果，计划部署一个8个台站的宽带地震阵列，为期24个月，并扩大一个区域连续GPS阵列，以包括出现瞬变的区域内的4个关键台站。新的地震阵列将跨越两个密集地震断面之间的间隙，作为已经资助的加州理工学院/UNAM中美洲地震实验的一部分，将允许检测和定位研究区域的任何偶发性震颤。从现有的GPS站和九个新的站由这个小组和合作者恩里克卡布拉尔的墨西哥国立自治大学的连续GPS测量将提供关键的补充信息的来源地区，规模和时间的幕滑。DeMets和Cabral在科科斯-北美俯冲界面上方的瓦哈卡操作的现有较小足迹30站连续和活动GPS阵列的数据也将用于更详细地研究类似于但小于众所周知的格雷罗地震间隙的明显地震间隙内的变形。结合GPS和地震阵列将是一个强大的工具，用于研究俯冲瞬变和非火山震颤，以及成像的空间和时间变化的摩擦couplingalong锁定和过渡区下我们的网络。Brudzinski将于2005年8月成为俄亥俄州迈阿密大学的新教员，他将用他的教员职位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，以提高上述地震缺口的覆盖范围。威斯康星大学麦迪逊分校的地球物理小组在部署地震和GPS网络方面有着悠久的历史，并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。更广泛的影响：幕式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，可能对理解巨型逆冲断层地震的发生产生影响。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相吻合，从而使学生接触到地球物理学现场研究。在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弗朗西斯科科雷亚莫拉，谁将做他的论文研究的大部分力学俯冲沿着中美洲海沟的教育。向更广泛的地球物理界提供新的连续和活动GPS和地震数据也将扩大这项工作的影响，特别是一旦记录了未来的瞬时滑动事件和/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.