T053-0010
Marine forearc structure at the seismogenic up-dip end of the 2014 Iquique Mw 8.1 earthquake
Wednesday, 16 December 2020
Poster
Florian Petersen1, Dietrich Lange1, Bo MA1, Jacob Geersen1, Ingo Grevemeyer1, Heidrun Kopp1,2, Dirk Klaeschen1, Eduardo Contreras Reyes3, Sergio E Barrientos4, Anne M Trehu5 and PICTURES working group, (1)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (2)University of Kiel, Kiel, Germany, (3)Universidad de Chile, Department of Geophysics, Santiago, Chile, (4)Univ de Chile, Santiago, Chile, (5)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States
Abstract:
On April 1st, the Mw 8.1 Iquique earthquake ruptured the plate boundary in the North Chilean marine forearc. The earthquake did not cause enough shallow rupture in the updip area to trigger a significant tsunami in the Pacific Ocean. The segment of South American subduction-zone affected by the Iquique earthquake was previously considered a seismic gap, as it last ruptured entirely in 1877 during an M~9 earthquake, with a rupture area possibly extending from south of Arica at 19°S to the north of the Mejillones peninsula at 23°S. The smaller magnitude of the 2014 event and the reduced rupture area that only broke the central part of the seismic gap implies a seismo-tectonic segmentation of the marine forearc. To identify the structure of the marine forearc and the subduction plate interface at the shallow seismic/aseismic transition, we use two years of Ocean Bottom Seismometer (OBS) and permanent onshore seismic data recorded eight months after the Iquique mainshock.
The high-resolution aftershocks of the 2014 Mw 8.1 Iquique earthquake from the local OBS network together with a seismic reflection image acquired in 2016 of the marine forearc allow us to discuss the structural control on the up-dip extent of seismic rupture in the North Chilean subduction zone. Most aftershocks occur up-dip of a co-seismic shallow slip patch in the marine forearc in the vicinity of a large crustal normal fault. A second area of increased aftershocks at the plate interface coincidence with the crustal-scale normal fault that links to the coastal scarp. The up-dip limit under the marine forearc further correlates with a highly faulted upper-plate and the subduction of Iquique ridge related topography. By comparing the up-dip limits of the 2014 Iquique earthquake with previous events along the North Chilean margin (1995 Antofagasta and 2007 Tocopilla earthquakes), we suggest that the up-dip limit is spatially related either to normal faults in the marine forearc or to the coastal scarp in Northern Chile.
