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.