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

在大俯冲带地震期间形成的地表裂缝，如果保存下来，可能会提供过去大地震的记录。然而，在大多数情况下，这些细微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大地震相关的变形。最近发生在智利的8.2级地震提供了一个机会，可以直接检验在这些大事件中形成裂缝的想法，并且裂缝可以用来估计地震期间发生的滑动量和震源区域上方经历的变形量。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）与大型逆冲地震相关的地震危害的认识。与智利研究人员合作开展的RAPID项目的目标是收集2014年4月1日发生在智利海岸科迪勒拉的8.2 Mw Pisagua地震产生的同震I型地表裂缝的扫描线数据。裂缝通常在松散的沉积物中形成，必须在地震发生后大约六个月内测量，以便确定是在地震期间产生的。裂缝孔径的精确测量对于确定表面应变也同样重要，以便与即将从这次事件中获得的GPS数据进行比较。由于裂缝壁随着时间的推移而退化，精确测量孔径变得越来越困难。目的是重新测量地震前在蓬塔德洛沃斯已经测量过的扫描线，并测量在伊基克市和皮萨瓜普韦布洛北部之间地区至少三个独立地点的新扫描线数据。最初的InSAR数据显示，伊基克和皮萨瓜之间的地表变形最大。同震地表裂缝提供了数千次板块边界地震活动周期的独特长期记录。Pisagua地震提供了一个很好的机会来记录在一次地震中形成的裂缝数量，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）反映可恢复的弹性变形和不可恢复的塑性变形的基本问题。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.