A Spectral Expansion Approach for Geodetic Slip Inversion: Implications for the Down-dip Rupture Limits of Oceanic and Continental Megathrust Earthquakes
Abstract
We have developed a new data-driven spectral expansion inversion method to place bounds on the down-dip rupture depth of large megathrust earthquakes having good InSAR and GPS coverage. Application of this method to the 2010 Mw 8.8 Maule Earthquake shows slip tapering to zero at 40 km depth. In contrast, the continent-continent megathrust earthquakes of the Himalayas (e.g., 2015 Mw7.8 Gorkha Earthquake) have slip tapering to zero at a very shallow depth of 20 km. Bassett and Watts [2015] noted that many ocean megathrust zones have gravity and topographic ridges directly above the down-dip transition from a interseismically locked to steadily creeping megathrust. The Himalayas frontal ridge is also located directly above the transition zone at 20 km depth. Following Savage 1983, we propose that both types of topographic ridges are caused by long-term inelastic deformation of the overriding plate directly above the frictional transition zone. The main question is why is the depth of the continental transition zone of 20 km only one half the depth of the ocean transition zone of 40 km. To understand this difference we have developed a simple 1-D heat conduction model that includes the effects of uplift and surface erosion. The relatively low erosion rates along the ridges of the ocean megathrust zones results in a geotherm where the 450°-600°C transition is centered at 40 km depth. The relatively high average erosion rates of the Himalayas area of 1.2 mm/yr results in a geotherm where the 450°-600°C transition is centered at 20 km. Based on these new observations and models we suggest that the effects of erosion rate on temperature may explain the difference in the maximum depth of the seismogenic zone between Chile and the Himalayas.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T22B..08X
- Keywords:
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- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS