A high-resolution controlled-source seismic experiment to elucidate geologic controls on megathrust slip: the 2014 Pisagua, Chile earthquake sequence as a natural laboratory

高分辨率受控源地震实验，阐明巨型逆冲滑动的地质控制：2014 年智利皮萨瓜地震序列作为天然实验室

• 批准号: 1459368
• 负责人: Anne Tréhu
• 金额: $ 51.29万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-02-01 至 2020-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1459368&HistoricalAwards=false
• 关键词: resolution; controlled; source; seismic; experiment

Subduction zones, where one tectonic plate plunges beneath another, are the birthplace of many of Earth's more destructive earthquakes and volcanoes. Numerous studies reveal patchiness in the distribution of slip during these earthquakes; patches with the greatest slip can occur in pattern that is the opposite of where patches characterized by aseismic deformation occur along the fault. On April 1, 2014, a magnitude 8.2 earthquake occurred offshore Chile near the town of Pisagua. This region was identified in 1991 as one of two major seismic gaps in Chile. In anticipation of a future great quake, the international Integrated Plate Boundary Observatory Chile project started installing onshore seismic and geodetic instrumentation in the Pisagua/Iquique gap in 2007. Because the slip history of the fault prior to, during, and after the earthquake was well recorded, the rupture pattern can be compared with crustal structure. The largest foreshock preceding the earthquake and the patch of greatest slip during the mainshock are associated with a local increase in subsurface density. The boundary of the Pisagua aftershock activity coincided with the southern boundary of the broader, regional density low. The portion of the seismic 'gap' that did not slip during the Pisagua quake is marked by a distinct density high, indicating an abrupt change in crustal structure. The objective this project is to collect marine geophysical data to elucidate the geologic significance of this correlation between a crustal structure and earthquake slip. This project also has an important educational component. Students from the US, Chile, Germany will participate in an shipboard course in seismic reflection data processing. Advances in geodetic techniques and an increase in the number of high-resolution seismic networks have brought remarkable advances in documenting the distribution of slip on subduction zone plate boundary faults prior to, during, and after great earthquakes. The main Pisagua shock was preceded by two distinct foreshock sequences that occurred in the month prior to the main shock, and it was followed by many aftershocks, the largest of which had Mw 7.8. The sequence only ruptured the northern half of the gap, leaving significant unreleased strain accumulation according to plate tectonic and geodetic locking models. This study will acquire and analyze marine seismic data to characterize the Pisagua earthquake source region. A large-volume tuned airgun array and multichannel streamer (MCS) and 90 short-period ocean bottom seismometers (OBS) operated by the US Ocean Bottom Seismometer Instrumentation Pool and the German marine research institute GEOMAR. A 3D tomographic P-wave velocity model and a grid of 2D deep-crustal seismic reflection profiles will be obtained. The velocity model and positions of reflective boundaries will be integrated with high-resolution bathymetric data to generate a geologic model of the crust that can be compared to the seismologically and geodetically-determined slip history prior to, during and after the earthquake. The program will be accomplished in two phases. During phase 1, imaging will target the region that slipped during the 2014 earthquake and acquire reconnaissance data from the remaining gap to optimize the field program for phase 2. Earthquakes recorded by this and other OBS and onshore arrays will be incorporated into the data set for 3D tomography to increase the depth extent of imaging and improve determination of S-wave velocities and Poisson's ratio. Partners in this project include Oregon State University, GEOMAR, and the Universidad de Chile.

俯冲带，一个构造板在另一个构造板上坠落，是许多地球上许多更具破坏性的地震和火山的发源地。 大量研究揭示了这些地震期间滑动分布的斑块。具有最大滑动的斑块可以以图案形式发生，这与沿故障发生的斑块相反。 2014年4月1日，在皮萨瓜镇附近发生了8.2级地震。 该地区在1991年被确定为智利的两个主要地震差距之一。为了预期未来的地震，国际综合板边界智利智利项目开始在2007年在Pisagua/iquique Gap中安装陆上地震和地球仪器。由于地震前，期间和地震后，可以很好地记录过地震后的断裂模式，因此可以将破裂模式与甲壳结构进行比较。 在主震动期间地震和最大滑动片之前，最大的预种盘与地下密度的局部增加有关。 Pisagua余震活性的边界与较宽的区域密度低的南部边界相吻合。 在Pisagua地震期间没有滑动的地震“间隙”部分标志着明显的密度高，表明地壳结构的突然变化。 该项目的目的是收集海洋地球物理数据，以阐明地壳结构和地震滑动之间这种相关性的地质意义。 该项目还具有重要的教育组成部分。来自美国，智利，德国的学生将参加地震反思数据处理的船上课程。 大地测量技术的进步和高分辨率地震网络数量的增加在记录俯冲带板板边界断层上，期间和之后的俯冲带边界断层上的分布方面取得了显着进步。在主要冲击之前的一个月发生的两个不同的前壳序列之前，主要的Pisagua冲击是出现的，随后是许多余震，其中最大的是MW 7.8。该序列仅破裂了间隙的北半部，根据板块构造和大地测量锁定模型，留下了明显的未释放应变积累。这项研究将获取和分析海洋地震数据，以表征Pisagua地震源区域。由美国海洋底部地震计仪器池和德国海洋研究所GeoMar操作的大批量调谐气枪阵列和多通道彩带（MCS）和90个短期海洋底部地震仪（OBS）。 将获得3D断层扫描速度模型和2D深度地震反射曲线的网格。 速度模型和反射边界的位置将与高分辨率的测深数据集成，以生成地壳的地质模型，该模型可以与地震发生之前，期间和之后的地震学和地质确定的滑移历史进行比较。该计划将分为两个阶段。在第1阶段，成像将针对2014年地震期间滑倒的区域，并从剩余的差距中获取侦察数据，以优化第2阶段的现场计划。该和其他OBS和其他OBS和其他陆上阵列记录的地震将被纳入3D断层扫描的数据集中，以增加成像的深度和提高S-Wave Velocities和poisson and Poisson和Poisson的确定。该项目的合作伙伴包括俄勒冈州立大学，Geomar和De Chile大学。