Long dormancy, low slip rate, and similar slip-per-event for the Emerson fault, eastern California shear zone
Rubin, Charles M.
Date of Issue1997
Excavations in a playa along the 1992 rupture of the Emerson fault reveal evidence of two paleoseismic events, with only one large prehistoric rupture in the past 15 millennia. Accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault-scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka. Trench-wall exposures revealed clear evidence of at least one pre-9 ka rupture at the playa site. The event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14.8 ka and 24.1 ka, implying that the earthquake occurred about 20,000 years B.P. The actual bracketing ages for this rupture are likely a few thousand years older because of the mean residence time for the pedogenic carbonate and calibration of the 14C ages by 230Th dating. Despite the large uncertainties, a dormant period of at least 6 kyr to as much as 13 kyr separates the older event from the 9 ka event. Because the scarp formed by the penultimate event is similar in height to the scarp formed by the 1992 Mw 7.3 Landers earthquake, the penultimate rupture was, at least locally, similar in size to the most recent rupture. This similarity supports the concept of characteristic slip for the Emerson fault. Preliminary results from paleoseismic studies at other sites on the 1992 rupture suggest that large ruptures occurred on other nearby faults within a few hundred years of this penultimate event on the Emerson fault. The interseismic period that preceded the 1992 earthquake on the Emerson fault was about 40 times longer than the average interval between large events on the nearby San Andreas fault. Therefore, in comparison to events on the San Andreas fault, the 1992 Landers earthquake was an exceedingly rare event
DRNTU::Science::Geology::Volcanoes and earthquakes
Journal of geophysical research
© 1997 American Geophysical Union. This paper was published in Journal of Geophysical Research and is made available as an electronic reprint (preprint) with permission of American Geophysical Union. The paper can be found at the following official URL: http://dx.doi.org/10.1029/97JB00265. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.