Investigations of Spatial and Temporal Variations in Strain Accumulation at the Sumatra Subduction Zone from Continuous GPS Measurements

0001090号块，苏门答腊岛西海岸和明打威群岛为研究苏门答腊岛断裂和俯冲带的应变积累和释放过程提供了一个独特的机会。两次历史上的大地震(1833年和1861年)表明，苏门答腊岛俯冲带的应变缓解主要是罕见的超大型地震。众所周知，苏门答腊岛断层也曾发生过几次Mw7级地震。1989~1993年的GPS测量揭示了地表形变的空间分布，表明俯冲界面沿着1833年大地震的震源区是完全锁定的，而沿着1861年大地震的震源区只是部分锁定。这些数据还导致了苏门答腊岛断层几个部分的滑移率估计。调查人员计划对他们在苏门答腊岛和明打威群岛建立的大约50个GPS纪念碑进行运动式调查。这些地点的新测量数据将与其早期数据一起进行分析，以获得苏门答腊岛前弧和苏门答腊岛断层的一段最新的时间平均速度场。通过这一分析，他们希望解决关于苏门答腊岛断层和俯冲带的两个重要问题。首先，他们希望确定1989年至1994年观测到的苏门答腊岛俯冲带的应变分段是一个长期信号，还是由例如无地震滑动事件引起的瞬时效应。他们希望解决的第二个问题是位于大约1S的苏门答腊岛断层段的滑动速率。他们目前对那里滑动速率的估计为235毫米/年，远远大于从水流偏移量估计的11毫米/年。这是加州大学圣地亚哥分校斯克里普斯海洋研究所(SIO)和印度尼西亚国家测绘协调机构(BAKOSURTANAL)之间的一项合作提案。

Bock 0001090 The west coast of Sumatra and the Mentawai Islands offer a unique opportunity to study the process of strain accumulation and release along the Sumatran fault and subduction zone. Two giant historical earthquakes (1833 and 1861) suggest that infrequent very-large earthquakes dominate strain relief at the Sumatra subduction zone. The Sumatran fault has also been known to produce several Mw7 earthquakes. GPS measurements collected from 1989 to 1993 revealed the spatial distribution of surface deformation, suggesting that the subduction interface is completely locked along the source region of the 1833 giant earthquake, but is only partially locked along the source region of the 1861 event. The data have also resulted in slip rate estimates for several segments of the Sumatran fault. The investigators plan to conduct campaign-style surveys at approximately fifty of their established GPS monuments on Sumatra and the Mentawai islands. The new measurements from these sites will be analyzed in conjunction with their earlier data to obtain an updated, time-averaged velocity field for the Sumatra forearc and one segment of the Sumatran fault. With this analysis they hope to resolve two important questions about the Sumatran fault and subduction zone. First, they hope to determine whether the strain segmentation of the Sumatran subduction zone observed by the 1989-1994 measurements is a long-term signal, or if it was a transient effect caused by, for example, an aseismic slip event. The second question they hope to resolve is the slip rate for the Sumatran fault segment located about 1 S. Their current estimate of the slip rate there is 235 mm/yr, considerably larger than the 11 mm/yr estimated from stream offsets. This is a collaborative proposal between UCSD's Scripps Institution of Oceanography (SIO) and the Indonesian National Coordination Agency for Surveying and Mapping (BAKOSURTANAL).