The influence of large-magnitude earthquakes and fault zone damage on the spatial distribution of slow-moving landslides
Abstract
In areas of weak, clay-rich bedrock with low to moderate hillslope gradients, slow-moving landslides (earthflows) can be the primary drivers of hillslope lowering and the dominant source of sediment to river networks. Despite their importance, the controls on the spatial distribution of active earthflows are poorly understood. Here, we seek to isolate the effects of rock strength and the absence of large-magnitude earthquakes on earthflow spatial distribution. We use airborne interferometric synthetic aperture radar (InSAR) to map previously unrecognized slow-moving landslides along a ~145 km by 22 km long swath, centered on the "creeping section" of the San Andreas Fault (SAF), central California, USA. Although our data extend up to 10 km to either side of the fault, approximately 75% of detected landslides occur within 2 km of the SAF trace. We show variations in annual precipitation, topographic metrics (e.g., hillslope gradient and aspect), and lithology are small within the study area, and alone are not enough to explain the observed spatial distribution of earthflows. Instead, we hypothesize that earthflow occurrence proximate to the creeping section of the San Andreas Fault is governed by the width of the fault damage zone and lack of large-magnitude earthquakes. Within the fault damage zone rock is weak and highly fractured leading to reduced bulk rock strength which can increase hillslope susceptibility to failure. Similarly, the lack of large-magnitude earthquakes within the creeping section of the SAF limits the occurrence of co-seismic landslides which can preferentially remove fractured bedrock from hillslopes, thus limiting the availability of material for earthflows to form in. This latter point is supported by the observation that earthflow occurrence in fault damage zones is rare north of the creeping section of the SAF where lithology, climate, and topography are suitable for earthflow development, yet large-magnitude earthquakes and associated co-seismic landslides are common.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMEP44A..01S
- Keywords:
-
- 1810 HYDROLOGY / Debris flow and landslides;
- 1826 HYDROLOGY / Geomorphology: hillslope;
- 1855 HYDROLOGY / Remote sensing;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution