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Summary of Proposal GEO1862

TitleInSAR observations Crustal deformation during the seismic cycle in the South-Central Chile margin
Investigator Motagh, Mahdi - Helmholtz Center Potsdam, GFZ, Geodesy and Remote Sensing
Team Member
Dr. Motagh, Mahdi - Helmholtz Center Potsdam, GFZ, Geodesy and Remote Sensing
Dr. Melnick, Daniel - University of Potsdam, Geology
SummarySubduction zones generate the largest earthquakes and tsunamis. In these regions, energy is accumulated during the inter-seismic period of the seismic cycle and then released during the coseismic phase. A post-seismic period follows the earthquake, lasting days to decades. Gaining insight into the physics of the earthquake cycle relies on combining surface deformation rates, geophysical data, and numerical modeling. Surface deformation rates are the first-order observables fed to numerical models, and thus obtaining high accuracy in such primary data is instrumental to obtain reliable results. The south-central Chile margin offers the opportunity to quantify surface deformation rates in regions affected by different phases of the earthquake cycle, but with very similar boundary conditions. We pretend to focus on three islands located near the trench characterized by the largest amplitudes of the surface deformation in all phases of the seismic cycle. A permanent GPS station is operating on each island. Guafoisland (43.5 S) was uplifted ~3.8 m during the 1960 earthquake (Mw9.5) and is rapidly subsiding at present as a result of inter-seismic coupling and post-seismic mantle relaxation. Deconvolving these two signals requires to quantify the local tilt rates, which could be obtained by combining GPS and TSX data. Isla Mocha (38.5 S) was uplifted during both the 1960 and 2010 (Mw 8.8) earthquakes. Raised strandlines suggest a very rapid Holocene uplift rate of ~7 mm/yr and landward tilting. Mocha was subsiding before 2010, uplifted during the earthquake and experienced rapid post-seismic uplift. Again deciphering the tilt rate will contribute to understanding the source of this rapid motion, which may be a splay fault in the upper plate,or very localized afterslip in the plate interface, and linking the short- and long-term signals. Santa Maria Island (37 S) was uplifted1.6-2.2 m and tilted parallel to the trench during the 2010earthquake, while remaining beyond the 1960 rupture. Based on the2010 tilt patterns and the occurrence of surface fault ruptures we proposed that a crustal splay fault slipped during the co-seismic phase of the 2010 earthquake. By monitoring the surface tilt after the earthquake we will attempt to resolve post-seismic motions on this splay fault, and differentiate it from the broader signal of afterslip on the plate interface. These three islands contain records of permanent uplift and tilt during the past few thousand years,which when compared with the modern deformation patterns may provide insight into the physics of the earthquake cycle and on mountain building processes in subduction zones.

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