Department of Geology and Geological Engineering Van Tuyl Lecture Series- Fall 2014

1. Department of Geology and Geological Engineering Van Tuyl Lecture Series- Fall 2014 4:00-5:00 p.m. in Berthoud Hall Room 241 Thursday, September 25, 2014 Dr. Gavin Hayes United States Geological Survey “Mind the Gap – the Iquique, Northern Chile Earthquake Sequence of March-April 2014” Abstract: The seismic gap theory, which identifies regions of elevated hazard based on a lack of recent seismicity in comparison to other portions of a fault, has successfully explained past earthquakes and is useful for qualitatively describing where future large earthquakes might occur. Prior to 2014, the subduction zone adjacent to northern Chile – the northern Chile seismic gap - had not ruptured in a megathrust earthquake since a M~8.8 event in 1877. On April 1 2014, a M 8.2 earthquake occurred within this gap; the size and spatial extent of the rupture indicate it was not the earthquake that had been anticipated. Here, we present a rapid assessment of the seismotectonics of the March-April 2014 seismic sequence offshore northern Chile, including analyses of earthquake (fore- and aftershock) relocations, moment tensors, finite fault models, moment deficit calculations, and cumulative Coulomb stress transfer calculations over the duration of the sequence. This ensemble of information allows us to place the sequence within the context of historic seismicity in the region, and to assess areas of remaining and/or elevated hazard. Our results indicate that while accumulated strain has been released for about one third of the northern Chile seismic gap, significant sections have not ruptured in almost 150 years. These observations indicate that potential remains for large-to-great sized megathrust earthquakes north and south of the 2014 Iquique sequence in the near future.