10/20/2017 - 3:30pm
IGPP Conference Room (Munk 303)
Probing plate boundaries rheology during the seismic cycle using GPS data
GPS is commonly used to study crustal deformation related to the seismic cycle in different contexts such as subduction zones, strike slip fault zones and many others. During this seminar, I will be reviewing my previous works focusing first on the Chilean subduction zone and then on the North Anatolian fault in Turkey. The 2 contexts are quite different but the final goal remains similar: better understand the processes that lead to major earthquakes along plate boundaries.
Megathrust earthquakes of magnitude close to 9 are followed by large-scale (thousands of km) and long-lasting (decades), significant crustal and mantle deformation. I report on deformation observed with GPS during the 5 yr time span after the 2010 Mw 8.8 Maule Megathrust Earthquake (2010 February 27) over the whole South American continent. With the first 2 yr of those data, a finite element modelling (FEM) was used to relate this deformation to slip on the plate interface and relaxation in the mantle, using a realistic layered Earth model and Burgers rheologies. A combined model of viscoelastic relaxation and afterslip is necessary to reproduce the different patterns of deformation, both horizontal and vertical, observed at different distances from the rupture zone. Relaxation both in the asthenosphere and in a low-viscosity channel along the deepest part of the plate interface is required to fit the horizontal deformation and the intense and quick uplift over the Cordillera.
In Turkey, ever since the Mw 7.4 Izmit earthquake in 1999, evaluation of seismic hazard associated with the last unbroken segments of the North Anatolian strike slip fault is capital. But a strong controversy remains over whether Marmara fault segments are locked or are releasing strain aseismically. Using a Bayesian approach, we propose a preliminary probabilistic interseismic model which reveals large model uncertainties, mainly resulting from the sparsity of current geodetic observations. Therefore, we implemented a network optimization procedure to identify the most favorable distribution of stations to better measure strain accumulation in the Marmara Sea.
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