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

Bock 0001090 苏门答腊岛西海岸和明打威群岛为研究沿苏门答腊断层和俯冲带的应变积累和释放过程提供了独特的机会。历史上的两次大地震（1833 年和 1861 年）表明，罕见的特大地震主导了苏门答腊俯冲带的应力释放。据了解，苏门答腊断层也曾发生过数次 Mw7 地震。 1989年至1993年收集的GPS测量揭示了地表变形的空间分布，表明俯冲界面完全锁定在1833年大地震的震源区，但仅部分锁定在1861年事件的震源区。这些数据还对苏门答腊断层的几个部分的滑动率进行了估计。调查人员计划对苏门答腊岛和明打威群岛上大约 50 个已建立的 GPS 纪念碑进行活动式调查。这些地点的新测量结果将与其早期数据结合起来进行分析，以获得苏门答腊弧前和苏门答腊断层一段更新的时间平均速度场。通过这项分析，他们希望解决有关苏门答腊断层和俯冲带的两个重要问题。首先，他们希望确定1989-1994年测量观测到的苏门答腊俯冲带应变分割是否是一个长期信号，或者是否是由地震滑动事件等引起的瞬态效应。他们希望解决的第二个问题是位于约 1 S 的苏门答腊断层段的滑移率。他们目前估计的滑移率为 235 毫米/年，远大于根据河流偏移量估计的 11 毫米/年。这是加州大学圣地亚哥分校斯克里普斯海洋学研究所 (SIO) 和印度尼西亚国家测绘协调局 (BAKOSURTANAL) 之间的合作提案。

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).