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：需要资金对中美洲俯冲带的瓦哈卡-格雷罗段进行联合大地测量和地震研究，这是地球上少数几个可以使用陆基GPS和地震观测来研究俯冲界面的闭锁、地震孕育区和可能引发幕式地震和滑动的较深过渡滑动区的地方之一。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缓解或增加沿俯冲界面孕震部分积累的应变方面的作用。过去一年的一项初步研究表明，这类瞬变在该地区每隔12-24个月发生一次，有些瞬变(1998年和2004年)发生在远离格雷罗地震空区的地方，而且这些瞬变可能伴随着非火山地震震动。根据这些以前未被承认的结果，计划在24个月内部署8个台站的宽带地震台阵，并扩大区域连续全球定位系统台阵，以包括似乎发生瞬变的区域内4个关键位置的台站。新的地震阵列将跨越作为加州理工大学/北卡罗来纳大学中美洲地震实验的一部分而安装的两个密集地震横断面之间的广泛间隙，将允许检测和定位研究区域内的任何幕式地震。由该小组和UNAM的合作者恩里克·卡布拉尔建造的现有GPS站和九个新站的连续GPS测量将提供有关震源区域、震级和幕间滑动时间的关键补充信息。Demets和Cabral在瓦哈卡州Cocos-北美俯冲界面上方运行的现有的占地面积较小的30站连续和活动GPS阵列的数据也将用于更详细地研究与众所周知的格雷罗地震空区类似但更小的明显地震空区内的变形。组合的GPS和地震台阵将是研究俯冲瞬变和非火山地震的有力工具，并将用于成像摩擦耦合的时空变化，以及沿我们网络下面的锁定和过渡带的变化。Brudzinski将于2005年8月成为俄亥俄迈阿密大学的新教员，他将从教职岗位上用启动资金购买必要的地震设备，并将于2006年初为为期两年的部署做好准备。威斯康星大学麦迪逊分校的德梅茨将与卡布拉尔博士协调GPS站的安装，以及瓦哈卡GPS网络的适度扩张，以提高上述地震缺口的覆盖率。华盛顿大学麦迪逊分校的地球物理小组在部署地震和GPS网络方面有很长的历史，将免费提供两名专家技术人员来帮助建立和维护组合的地震和GPS网络。大地测量和地震观测的建模责任将分别由Demets和Brudzinski负责。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，可能会对理解大地震的触发产生影响。迈阿密大学的学生将获得一个独特的机会，参加与最初的地震部署同时进行的实地研讨会课程，从而使学生接触到地球物理实地研究。威斯康星大学麦迪逊分校的更广泛影响将包括墨西哥研究生Francisco Correa-Mora的教育，他将在论文中研究沿中美洲海沟俯冲的机制。向更广泛的地球物理界提供新的连续和动态全球定位系统和地震数据，也将扩大这项工作的影响范围，使其超出我们小组的范围，特别是在记录到未来的瞬变滑移事件和/或地震序列的情况下。

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.