A comparison of slip rate, recurrence interval, and slip per event on several well-characterized faults (Invited)
Abstract
Rapid growth in the application of LiDAR and other modern geodetic techniques has led to an explosion in the number of micro-geomorphic offsets along faults that can be interpreted as displacement in one or several earthquakes. As a result of this new data there are an increasing number of places along faults for which data are available for the slip rate (based on the dated offset of a feature that is old enough to average out the seismic cycle), recurrence interval (based on a representative number of dated paleo-earthquakes), and slip per event (based on an adequate sample of micro-geomorphic or 3D-excavated offsets). Because these three datasets are largely independent, but related by accumulation and release of strain across the fault, comparing them can provide insight into how faults balance size and frequency of earthquakes. We discuss several examples of faults with closely co-located slip rate, recurrence interval, and slip per event data, including the Ana River fault, a small normal fault in Central Oregon, and portions of the San Andreas fault, the principal plate boundary fault in California. The Ana River fault offsets more than 11 Pleistocene shorelines different amounts that we have measured using a combination of LiDAR, ground-based surveying, and a DEM generated from a USGS topographic map with 5 foot contours. The ages of ~10 paleo-earthquakes are determined from trenches and other exposures into deep-water lacustrine deposits that contain ~50 dated volcanic ashes. The long-term slip rate, 0.05 mm/yr, is known from the total offset of dated late Pliocene basalts. We also use new data from the Santa Cruz segment of the northern San Andreas fault (NSAF) and the southern San Andreas fault (SSAF: Parkfield to Bombay Beach). On the NSAF, earthquakes in 1838, 1890, and 1906 have a total slip of 4 - 6 m while the slip rate (17 mm/yr) suggests it would take 2 - 3 centuries to accumulate this much strain. Data for the SSAF, which have recently been compiled for UCERF-3, include 12 sites with recurrence intervals, hundreds of micro-geomorphic offsets, including at least 7 places with closely-spaced progressively larger offsets that allow one to estimate the average slip per event, and slip rate estimates that vary from about 34 to 12 mm/yr, decreasing from Parkfield to San Gorgonio Pass and then increasing to the southern end of the SSAF. In general the 3 types of data are reasonably consistent (i.e. slip rate (mm/yr) = slip per event (mm) X recurrence interval (1/yr)). Recurrence intervals seem to be more variable than displacements, although displacement variability may be biased by difficulty resolving small offsets with geomorphic markers. Assuming slip rate is constant through time, in places where (or periods of time when) there are inconsistencies between the three parameters it appears to be due to the intervals between earthquakes varying more than displacements, i.e. short intervals are not associated with small enough displacements and long intervals do not yield unusually large displacements. Similarly, as the SSAF changes slip rate along strike the recurrence interval varies more than the size of slip events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.T21D..02W
- Keywords:
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- 7221 SEISMOLOGY Paleoseismology;
- 8118 TECTONOPHYSICS Dynamics and mechanics of faulting;
- 8175 TECTONOPHYSICS Tectonics and landscape evolution