Ma, Bo , Geersen, Jacob , Klaeschen, Dirk , Petersen, Florian , Kopp, Heidrun , Trehu, A. and Contreras-Reyes, E. (2021) Seismic reflection character of the plate interface in the rupture zone of the 2014 Iquique earthquake sequence. [Poster] In: 81. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG). , 01.03.-05.03.2021, Kiel (online) .

Abstract

On 1 April 2014, the Mw 8.1 Iquique earthquake broke the plate-boundary along the North Chilean margin in the region between 19.5°S and 21°S. During this event, seismic rupture concentrated under the marine forearc with an updip limit at a plate-boundary depth of 17 km under the middle continental slope. In late 2016, wide-aperture seismic reflection and refraction data were acquired aboard the R/V Marcus G. Langsethoffshore Northern Chile as part of the “Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source” (PICTURES) project. Utilizing multiple suppression techniques and ray-based tomographic inversion, we have achieved enhanced pre-stack depth migrated images to a depth of 40 km. Seismic lines MC23 and MC25, located in the southern part of the 2014 rupture area, display a pronounced plate boundary reflection that can be tracked to a depth of ~16 km. In contrast, on line MC04, located north of the 2014 rupture area, a plate boundary reflection is clearly visible to ~40 km depth. We consider that changes in fluid pressure cause the observed spatial variations in the downdip extent of the reflective plate boundary and thus may exert an influence on seismic rupture. However, the processes that control the spatial variations in fluid pressure over short distances remain enigmatic. Temperature controlled dehydration processes within the shallow subduction zone are expected to change only gradually along the margin and may therefore not explain short wavelength changes in the downdip extent of high reflectivity between line MC04 in the north and the other lines farther south. We notice, however, that the vertical displacement induced by bending related normal faults in the oceanic plate is significantly smaller along line MC04 compared to lines MC23 and MC25. This may lead to a delayed vertical flow of pore-fluids from the oceanic basement towards the plate boundary along line MC04. In contrast to lines MC23 and MC25, where fluids are expelled from the oceanic basement at relatively shallow depth along the plate boundary (i.e. under the outermost wedge), they are subducted to greater depths at the location of line MC04.

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