RAPID: Investigation of Co-seismic Surface Cracks Produced during the April 1, 2014, Magnitude 8.2 Pisagua, Chile, Earthquake

如果保存完好，在大型俯冲带地震中形成的表面裂缝可能会提供过去大地震的记录。然而，在大多数情况下，这些微妙的表面特征在几天内就会消失。由于智利阿塔卡马沙漠的干旱，这些裂缝被保存下来，可以用来估计智利俯冲带沿线与大地震相关的形变。最近在智利发生的8.2级地震提供了一个机会，可以直接检验裂缝是在这些大地震期间形成的，裂缝可以用来估计地震期间发生的滑动量和震源区上方经历的变形量。如果成功，该项目将增加一种新的方法，以提高对智利和其他地方(如卡斯卡迪亚、阿拉斯加和日本)大地震危险性的了解。这个快速项目的目标是与智利研究人员合作，收集2014年4月1日8.2兆瓦皮萨瓜地震在智利海岸科迪勒拉产生的同震I类表面裂缝的扫描线数据。裂缝通常形成在松散的沉积物中，必须在地震发生后约六个月内测量，才能确定为在地震期间产生的。准确测量裂隙开度对于确定表面应变也同样重要，以便与这次事件将获得的GPS数据进行比较。由于裂缝的壁面随着时间的推移而退化，准确测量孔径变得越来越困难。目标是重新测量地震前在Punta de Lobos已经测量的扫描线，并测量伊基克市和皮萨瓜村以北地区至少三个不同地点的新扫描线数据。最初的InSAR数据表明，伊基克和皮萨瓜之间的地表形变最大。同震表面裂缝提供了板块边界地震活动数千个周期的独特长期记录。皮萨瓜地震提供了一个绝佳的机会来记录在一次地震中形成的裂缝群，以帮助完善同震裂缝产生的模型，并探索同震大地测量信号(主要是GPS)在多大程度上反映了可恢复的弹性变形和不可恢复的塑性变形这一基本问题。这些数据将有助于完善同震地表变形和平均破裂段的模型，这是地震危险性评估的关键输入。

Surface cracks, if preserved, formed during large subduction zone earthquakes potentially provide records of past large earthquakes. However, these subtle surface features disappear within days in most settings. Due to the aridity of the Atacama Desert in Chile, these cracks are preserved and can be used to estimate deformation associated with large earthquakes along the Chilean subduction zone. The recent magnitude 8.2 earthquake in Chile affords an opportunity to directly test the idea that cracks form during these large events and that the cracks can be used to estimate the amount of slip that occurred during an earthquake and the amount of deformation experienced above the earthquake source region. If successful, the project would add a new method to improve understanding of earthquake hazards associated with large megathrust earthquakes in Chile and elsewhere, such as Cascadia, Alaska, and Japan.The goal of this RAPID project, carried out in collaboration with Chilean researchers, is to collect scan line data of co-seismic Mode I surface cracks in the Chilean Coastal Cordillera produced by the April 1, 2014 Mw 8.2 Pisagua earthquake. Cracks commonly form in unconsolidated deposits and must be measured within about six months from the time of the earthquake in order to be identified as having been produced during the earthquake. Accurate measurement of crack apertures is likewise important for determination of surface strain for comparison with GPS data that will be forthcoming from this event. As the walls of the cracks degrade over time, accurate measurement of aperture becomes more and more difficult. The objectives are to re-measure scan lines that have already been measured, pre-earthquake, at Punta de Lobos and to measure new scan line data for at least three separate sites in the region between the city of Iquique and north of the pueblo of Pisagua. Initial InSAR data suggest that the highest surface deformation will be encountered between Iquique and Pisagua. Co-seismic surface cracks provide a unique long term record of thousands of cycles of plate boundary seismicity. The Pisagua earthquake provides an outstanding opportunity to document the crack population developed during a single earthquake to help refine models of co-seismic crack generation as well as explore the basic question of how much of the co-seismic geodetic signal (predominantly GPS) reflects recoverable elastic deformation and non-recoverable plastic deformation. These data will help refine models of co-seismic surface deformation and average rupture segments, which are key inputs into seismic hazard assessment.