Publication Date:
2017-02-19
Description:
Postseismic surface deformation associated with great subduction earthquakes is controlled by asthenosphere rheology, frictional properties of the fault, and structural complexity. Here, by modeling GPS displacements in the six years following the 2010 Mw 8.8 Maule earthquake in Chile, we investigate the impact of heterogeneous viscosity distribution in the South American sub-continental asthenosphere on the 3-D postseismic deformation pattern. The observed postseismic deformation is characterized by flexure of the South America plate with peak uplift in the Andean mountain range and subsidence in the hinterland. We find that, at the timescale of observation, over two orders of magnitude gradual increase in asthenosphere viscosity from the arc area towards the cratonic hinterland is needed to jointly explain horizontal and vertical displacements. Our findings present an efficient method to estimate spatial variations of viscosity, which clearly improves the fitting to the vertical signal of deformation. Lateral changes in asthenosphere viscosity can be correlated with the thermomechanical transition from weak sub-volcanic arc mantle to strong sub-cratonic mantle thus suggesting a stationary heterogeneous viscosity structure. However, we cannot rule out a transient viscosity structure (e.g. power law rheology) with the short time span of observation.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
