Lateral offsets and revised dates of large prehistoric earthquakes at Pallett creek, Southern California
Date of Issue1984
Recent excavation and new radiocarbon dates of sediments at Pallett Creek are the basis for new conclusionsr egarding the late Holocene history of the San Andreas fault. Systematicd issectiono f a 50-m-long, 15-m-wide, 5-m-deep volume of earth, centered on the fault, enables documentation in three dimensions of fault patterns, lateral offsets, and vertical deformation associated with large earthquakes of the past. The excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 A.D., with an average recurrence interval of about 145 years. Prehistoric slip events that occurred in 1720 ± 50, 1550 ± 70, 1350 ± 50, 1080 ± 65, and 845 ± 75 A.D. have lateral offsets that are comparable to those of the most recent great earthquake of 1857. Thus all of these events represent earthquakes of large magnitude. The lateral offsets of two other events, in 935 ± 85 and 1015 ± 100 A.D., are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events. The new data constraint he average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years. On the basis of these data, the probability of a large earthquake with surficial fault rupture at this site is between 0.2 and 5% during 1984 and 7 and 60% by the year 2000.
DRNTU::Science::Geology::Volcanoes and earthquakes
Journal of geophysical research
© 1984 the American Geophysical Union. This paper was published in Journal of Geophysical Research and is made available as an electronic reprint (preprint) with permission of the American Geophysical Union. The paper can be found at the following official DOI: http://dx.doi.org/10.1029/JB089iB09p07641. 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.