Accumulation of Permanent Deformation and Topography over Multiple Timescales, Cascadia Subduction Zone (USA)
Abstract
The formation and maintenance of mountain topography requires the accumulation of permanent deformation at a rate faster than surface processes can remove it. Traditional mechanical models of the earthquake cycle assume that interseismic elastic deformation is completely recovered during earthquakes, closing the deformation budget of steady slip on the deep subduction interface and different types of episodic slip on the shallow subduction interface. However, at Cascadia, the presence of persistent, elevated topography in the Olympic Peninsula requires that some tectonic deformation is not recovered over the elastic cycle. Here, we compare estimates of deformation from various timescales with each other to disentangle the contributions from elastic (recoverable) and permanent deformation within the Olympic Mountains. Elevated topography and high denudation rates from 14 cosmogenic nuclides and >61 thermochronometric samples (integrating over 103 -104 and 106 years, respectively) all yield similar patterns, suggesting that on long timescales most permanent deformation is accumulated in the center of the mountain range. High values from these long-term observations are spatially coincident with geodetically (GPS) observed residual tilting (integrating over 101 years), overlapping with a published area of negative shear stress rates on the subduction interface. We attribute the observed tilting to time-dependent stresses and a spectrum of different slip types on the plate interface of the subduction zone. Viscoelastic deformation at the top of the episodic slip zone causes the dissipation of stress over time and initiates tilting in the overriding plate, which in turn leads to the accumulation of deformation, topography, and focused denudation observed today.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP21A..04E
- Keywords:
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- 1815 Erosion;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS