Seismicity and sedimentation rate effects on submarine slope stability
Abstract
Large submarine mass-transport scars are commonly observed on continental margins, but are noticeably less abundant on margins that experience frequent earthquakes than on those that seldom experience them. This is a surprising observation, given that horizontal acceleration from earthquakes and associated strength loss from cyclic loading and liquefaction are commonly thought to provide the primary triggers for inducing failures and subsequent mass movements. Mapping submarine failure scars in ten margins worldwide, we find decreasing scar abundance with both increasing frequency of earthquakes and decreasing sedimentation rate. The decrease in scar abundance is interpreted to represent increasing slope stability. The increase in stability is non linear (power law with b<0.5), accelerating with decreasing inter-seismic sediment accumulation, a parameter combining earthquake recurrence with sedimentation rate. The correlation is interpreted as evidence for sediment densification and associated shear strength gain induced by repeated seismic shaking. This conclusion is supported by the correlation of higher mean margin gradient with higher earthquake frequency and with lower scar abundance and by published in-situ measurements showing over consolidation of shallow sediments in areas of frequent earthquakes. Outliers to this correlation likely identify margins where tectonic activity (salt diapirs, seamount subduction, etc.) leads to relatively rapid oversteepening of the slope, implying that the morphology of most margins is in fact, stable over many earthquake cycles. Note that the above correlation averages scar area and sedimentation rate over entire margin areas. Variations in sedimentation rate with time, such as over glacial-interglacial cycles, and intra-margin variations in seismic attenuation, sedimentation rate, composition, and pore pressure, have likely affected the abundance of slope failures in time and space.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMOS21A1936T
- Keywords:
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- 4306 Multihazards;
- NATURAL HAZARDSDE: 4313 Extreme events;
- NATURAL HAZARDSDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8110 Continental tectonics: general;
- TECTONOPHYSICS