Earthquake cycle modulation via the redistribution of surface water mass
Abstract
Surface water bodies, from individual lakes to the global ocean, change in extent and mass over timescales ranging from a single year to a Milankovich cycle. Stress changes within the solid earth as a result of the redistribution of water mass have the potential to affect the seismic cycle on nearby faults through a combination of mechanisms, including deformation from the weight of the load and changes to effective normal stress via pore pressure diffusion. We present a model that quantifies these effects and their roles in modulating the seismic cycle. 3-D stress change from rebound is calculated using a semi-analytic method for a two-layer model including a thick elastic plate overlying a viscoelastic halfspace. The computational efficiency of the semi-analytic solution allows the true shape of the surface load to be accounted for without simplification. Effective normal stress from pore pressure diffusion is constrained by the hydrostatic end member. Two case studies are considered: 1) eustatic sea level rise since the Last Glacial Maximum and its ability to influence fault slip-rate in coastal regions during the late Pleistocene and early Holocene; and 2) intermittent floods of ancient Lake Cahuilla over the last 1200 years and their influence on fault rupture along the southern terminus of the San Andreas Fault. The sensitivity of a particular fault to water loading is highly dependent on both its geometry and its earthquake recurrence interval. The stresses imposed by these loads are generally an order of magnitude smaller than the tectonic stress accumulation over the same time period, such that redistributed surface loads can affect the timing of fault rupture but do not alter the structural or tectonic setting of a region. However, by advancing or delaying fault rupture, surface loads are able to perturb the apparent fault slip rate over the timescale of the redistribution. In particular, the long-term seismic cycle of a fault is more likely to be affected when a nearby flooding event recurs over a time period similar to the earthquake recurrence interval. These models are therefore helpful for understanding observations of fault slip-rate variability on a variety of systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T43I..03L
- Keywords:
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- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 8164 TECTONOPHYSICS / Stresses: crust and lithosphere