Slip Rate Modulation Caused by Ocean Loading on Glacial Timescales
Abstract
We propose that variations in sea level associated with glacial cycles affect the slip rate of strike-slip faults by perturbing the normal stress. As sea level rises, the differential loading across a shoreline will flex the lithosphere. Downward flexure landward of the shoreline induces extensional stress at seismogenic depths, which promotes strike-slip faulting. Two cases are considered, the San Andreas Fault (SAF) zone located within 200 km of the Pacific shoreline and the North Anatolian Fault (NAF) located within 100 km of the Black Sea. We model the 3-D deformation and stress in an elastic plate overlying a viscoelastic halfspace in response to 145 m of ocean loading from well known eustatic sea-level rise during the past 25k years. High-resolution land and ocean topography are used to provide a geometrically accurate loading history. The model is computed at 1 km grid spacing and verified against analytic solutions of thin elastic plate flexure in response to a step load. We calculate fault-normal stress at seismogenic depths (5 km) and find a 1-3 MPa reduction along the SAF zone. Present-day stress perturbation is largely independent of halfspace viscosity because the loading time is much greater than the Maxwell time (viscosity 1017 to 1020 PA's). The location of maximum extensional stress moves landward with increasing plate thickness although plates between 30 and 70 km thick all have large extension along the SAF zone. The model predicts a rapid increase in slip rate along the NAF 7000 years ago associated with the abrupt 135 m increase in the level of the Black Sea from the breaching of the Bosporus Straight.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.G53A0866L
- Keywords:
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- 4901 Abrupt/rapid climate change (1605);
- 8106 Continental margins: transform;
- 8138 Lithospheric flexure;
- 8164 Stresses: crust and lithosphere;
- 8177 Tectonics and climatic interactions