RAPID: GPS and InSAR Observations in Bolivia and Chile of the Co-seismic and Post-seismic Deformation Associated with the 1 Apr, 2014 Mw 8.2 Pisagua, Chile, Earthquake

2014年3月16日，智利北部俯冲带发生了一系列不寻常的地震，持续10天的地震群向北移动。这种模式类似于2011年日本东北9.0级地震的前兆，那次地震引起了智利的担忧，因为这个巨型逆冲带上一次在1877年的8.8级地震中失败，被认为有能力再次发生9级地震。迄今为止，该序列中最大的地震是2014年4月1日发生在智利皮萨瓜的8.2级地震。这次大地震造成的地面变形将在地震后很长一段时间内持续存在，并在一段时间内衰减。对地震期间和之后地表变形的测量可以提供有关该地区地球性质的重要信息，提高对变形过程的理解，并有助于确定产生大余震的可能性很高的地区。由美国、德国、法国、秘鲁和智利的团队在智利安装的大型密集GPS网络将记录地震震中附近的这种变形，但在玻利维亚，一个仪器设备非常差的地区，预计会有明显的变形。这个快速反应项目将在玻利维亚安装新的GPS网络，从智利和玻利维亚现有的GPS站点收集数据，并分析卫星合成孔径雷达数据，以便全面捕捉与该事件相关的地面运动。这些数据将有助于了解智利和其他地方（如卡斯卡迪亚、阿拉斯加和日本）大型逆冲地震的物理和潜在危害。2014年4月1日智利皮萨瓜发生的8.2级地震是一系列不寻常地震中最大的一次，该地震于2014年3月16日开始于智利北部的俯冲带。根据美国地质勘探局初步的远震和面波反演，智利大逆冲断层沿走向约250公里，下倾约150公里发生滑动，上一次在1877年的8.8级地震中失败。美国、智利、秘鲁、德国和法国集团在该地区建立了相对密集的连续运行GPS （CGPS）和测量模式GPS （SGPS）台站网络，因此在智利北部可以很好地观测到近场地震间、地震同震和地震后瞬态信号。然而，在距离主震700公里的范围内，将会有明显的同震和震后瞬态运动，包括几乎所有的Altiplano和玻利维亚科迪勒拉东部的大部分地区，以及阿根廷西北部的普纳地区。测量Altiplano及其他地区的中远场共震和震后信号对任何地球动力学建模工作都至关重要。然而，玻利维亚高原的仪器设备很差，因此目前无法提供精确反演余震和岩石圈松弛所需的观测资料。为了快速应对2014年4月1日智利Pisagua发生的8.2 Mw地震，研究小组将：(1)在玻利维亚安装10个新的CGPS站；(2)重新占领玻利维亚和智利的SGPS站点；(3)从玻利维亚和智利的PLUTONS网内的5个CGPS站检索数据；(4)从Radarsat-2和TerraSAR-X卫星上获取和分析约100个SAR场景。数据将通过联安援助团设施档案立即提供给国际地球科学界。将对SAR数据进行分配，并按照外国空间机构所要求的密码保护限制，通过联阿援助办事处设施托管的WinSAR档案向社区提供。低延迟大地测量数据处理对于确定发生大余震的可能性高的地区和减灾工作至关重要，因为最大的余震（4月3日7.7级）比预期的要大，这可能表明持续的异常活动，邻近的部分被认为保留了很大的滑动赤字。

An unusual sequence of earthquakes began in the northern Chile subduction zone on March 16, 2014 with a 10-day long swarm of earthquakes that migrated to the north ? a pattern similar to the swarm of earthquakes that presaged the 2011 magnitude 9.0 Tohoku Japan earthquake, which provoked concern in Chile because this megathrust zone last failed in a magnitude 8.8 earthquake in 1877 and is thought capable of producing a magnitude 9 earthquake again. So far, the largest event in the sequence is the April 1, 2014 magnitude 8.2 Pisagua, Chile earthquake. The ground deformation caused by this large earthquake will persist long after the earthquake and decay over a period of years. Measurements of the surface deformation during and after the event can provide important information about the properties of the earth in the region, improve understanding of deformation processes, and aid in determining regions with a high likelihood of producing large aftershocks. Large dense GPS networks installed by U.S., German, French, Peruvian, and Chilean groups in Chile will record this deformation close to the earthquake epicenter but significant deformation is expected farther away in Bolivia, a very poorly instrumented region. This rapid response project will install new GPS networks in Bolivia, collect data from existing GPS sites in Chile and Bolivia, and analyze satellite synthetic aperture radar data in order to fully capture the ground motion associated with this event. These data will contribute to understanding the physics and hazard potential of large megathrust earthquakes in Chile and elsewhere, such as Cascadia, Alaska, and Japan.The April 1, 2014 Mw 8.2 Pisagua, Chile earthquake was the largest event in an unusual sequence of earthquakes, which began in the northern Chile subduction zone on March 16, 2014. Based on the USGS preliminary teleseismic and surface wave inversion, slip occurred along a 250 km along-strike and about 150 km down-dip section of the Chile megathrust that last failed in an M 8.8 earthquake in 1877. U.S., Chilean, Peruvian, German, and the French groups have built relatively dense continuously operating GPS (CGPS) and survey mode GPS (SGPS) station networks in this region, thus the near-field inter-, co- and post-seismic transient signals will be well observed in northern Chile. However, there will be significant co-seismic and post-seismic transient motion up to 700 km from the main event, incorporating nearly all of the Altiplano and at least much of eastern Cordillera in Bolivia, and the Puna of northwestern Argentina. Measuring the mid- and far-field co- and post-seismic signals in the Altiplano and beyond will be critical to any geodynamic modeling effort. The Bolivian Altiplano, nevertheless, is very poorly instrumented and so cannot, at present, provide the observations required for accurate inversions of afterslip and lithospheric relaxation. In rapid response to the April 1, 2014 Mw 8.2 Pisagua, Chile earthquake, the research team will: (1) install 10 new CGPS stations in Bolivia; (2) reoccupy SGPS sites in Bolivia and Chile; (3) retrieve data from 5 CGPS stations within the PLUTONS network in Bolivia and Chile; and (4) acquire and analyze about 100 SAR scenes from Radarsat-2 and TerraSAR-X. Data will be made immediately available to the international earth science community through the UNAVCO Facility Archive. SAR data will be tasked and made available to the community with the password-protected restrictions required by the foreign space agencies through the WinSAR archive hosted by the UNAVCO Facility. Low latency geodetic data processing could be critical in determining regions with a high likelihood of producing large aftershocks and for hazard mitigation efforts because the largest aftershock (M 7.7 on April 3) was larger than expected, potentially indicating continued unusual activity with the neighboring segments thought to retain a large slip deficit.