Interseismic Slip Deficit at the Edge of a Locked Patch: Shumagin Islands, Alaska

阿拉斯加是研究构造板块汇聚的边缘地区地震活动变化的首选地点。这是因为沿阿拉斯加俯冲带的不同区段，地震带的宽度是不同的。阿拉斯加半岛段包括从板块界面上宽阔的锁定区域过渡到以爬行为主的部分。一系列岛屿横跨这一段的事实为测量变形提供了理想的环境，这些数据将被用来确定最近滑动(或没有滑动)沿板块边界断层的分布。这将是第一次获得孕震带如何从锁定段到爬行段变化的详细视图。这些发现将为评估阿拉斯加半岛和美国西海岸因跨太平洋海啸而造成的地震和海啸危险提供参考。调查人员将在舒马金群岛阿拉斯加沙点当地社区的学区进行公开讲座，并与一名教师合作。将编写关于阿拉斯加地震和海啸、俯冲及其对当地环境影响等专题的课程材料。将在1990年代以来没有进行过调查的地点进行全球定位系统测量，提供新的高精度板块速度。大多数站点都测量过一次，新的测量将在第一次测量20年后进行，导致速度不确定度应为0.5毫米/年。这些数据将被用来估计板块界面断层的锁定和蠕动部分的分布，并将孕震带的空间变化与地震活动和下行板块性质的空间变化进行比较。结果将说明沿走向转换是多么突然，从Semidi段的宽闭锁区到舒马金段更窄的和/或蠕变主导的闭锁区。舒马金区段部分锁定区域内的结构将通过建模来解决。这项研究还将调查观测到的滑动变化与俯冲或下行板块上的特征、板块界面本身的反射特征、地震活动模式或其他地质观测之间的潜在相关性。

Alaska is a premier location for studying what controls variations in seismic activity along a margin where tectonic plates converge. This is because the width of the seismic zone is known to differ between segments along the Alaskan subduction zone. The Alaska Peninsula segment includes the transition from a wide, locked region on the plate interface to a dominantly creeping section. The fact that a chain of islandsruns across this segment provides an ideal setting for measuring deformation, and these data will be used to determine the distribution of recent slip (or lack thereof) along the plate boundary fault. This is the first time that a detailed view of how the seismogenic zone varies from a locked to a creeping section will be obtained. The findings will inform assessment of earthquake and tsunami hazards, both in relation to the Alaska Peninsula and along the US west coast due to trans-Pacific tsunamis. Investigators will conduct public lectures and work with a teacher in the school district of the local community of Sand Point, Alaska, in the Shumagin Islands. Lesson materials will be developed on the topics of earthquakes and tsunamis in Alaska, subduction and its impact on their local environment.GPS measurements will be made at sites that have not been surveyed since the 1990s, providing new highly precise plate velocities. Most of the sites have been measured once, and the new measurements will come 20 years after the first, resulting in velocity uncertainties that should be 0.5 mm/yr. These data will be used to estimate the distribution of locked and creeping parts of the plate interface fault, and spatial changes in the seismogenic zone will be compared with spatial changes in seismicity and properties of thedowngoing plate. Results will address how abrupt the along-strike transition is, from the wide locked region of the Semidi segment to the much narrower and/or creep-dominated locked region of the Shumagin segment. The structure within the partially locked region of the Shumagin segment will be addressed through modeling. The study will also investigate potential correlation between observed slip variations and features on the overriding or downgoing plates, the reflection character of the plate interface itself, seismicity patterns, or other geologic observations.