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Title: Earthquake geology of the northern San Andreas Fault near Point Arena, California

Abstract

Excavations into a Holocene alluvial fan provided exposures of a record of prehistoric earthquakes near Point Arena, California. At least five earthquakes were recognized in the section. All of these occurred since the deposition of a unit that is approximately 2000 years old. Radiocarbon dating allows constraints to be placed on the dates of these earthquakes. A buried Holocene (2356-2709 years old) channel has been offset a maximum of 64 {plus minus} 2 meters. This implies a maximum slip rate of 25.5 {plus minus} 2.5 mm/yr. These data suggest that the average recurrence interval for great earthquakes on this segment of the San Andreas fault is long - between about 200 and 400 years. Offset marine terrace risers near Point Arena and an offset landslide near Fort Ross provide estimates of the average slip rate since Late Pleistocene time. Near Fort Ross, an offset landslide implies a slip rate of less than 39 mm/yr. Correlation and age estimates of two marine terrace risers across the San Andreas fault near Point Arena suggest slip rates of about 18-19 mm/yr since Late Pleistocene time. Tentative correlation of the Pliocene Ohlson Ranch Formation in northwestern Sonoma County with deposits 50 km to themore » northwest near Point Arean, provides piercing points to use in calculation of a Pliocene slip rate for the northern San Andreas fault. A fission-track age 3.3 {plus minus} 0.8 Ma was determined for zicrons separated from a tuff collected from the Ohlson Ranch Formation. The geomorphology of the region, especially of the two major river drainages, supports the proposed 50 km Pliocene offset. This implies a Pliocene slip rate of at least 12-20 mm/yr. These rates for different time periods imply that much of the Pacific-North American plate motion must be accommodated on other structures at this latitude.« less

Authors:
Publication Date:
Research Org.:
California Inst. of Tech., Pasadena, CA (USA)
OSTI Identifier:
7011185
Resource Type:
Miscellaneous
Resource Relation:
Other Information: Thesis (Ph. D.)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; GEOLOGIC FAULTS; EARTHQUAKES; GEOLOGIC HISTORY; AGE ESTIMATION; CARBON 14; CORRELATIONS; DEPOSITION; FISSION TRACKS; GEOLOGIC AGES; GEOLOGIC FORMATIONS; ISOTOPE DATING; PLATE TECTONICS; SLIP; TUFF; ZIRCON; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; CARBON ISOTOPES; EVEN-EVEN NUCLEI; FEDERAL REGION IX; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; ISOTOPES; LIGHT NUCLEI; MINERALS; NORTH AMERICA; NUCLEI; OXYGEN COMPOUNDS; PARTICLE TRACKS; RADIOISOTOPES; SEISMIC EVENTS; SILICATE MINERALS; SILICATES; SILICON COMPOUNDS; TECTONICS; TRANSITION ELEMENT COMPOUNDS; USA; YEARS LIVING RADIOISOTOPES; ZIRCONIUM COMPOUNDS; ZIRCONIUM SILICATES; 580000* - Geosciences

Citation Formats

Prentice, C S. Earthquake geology of the northern San Andreas Fault near Point Arena, California. United States: N. p., 1989. Web.
Prentice, C S. Earthquake geology of the northern San Andreas Fault near Point Arena, California. United States.
Prentice, C S. 1989. "Earthquake geology of the northern San Andreas Fault near Point Arena, California". United States.
@article{osti_7011185,
title = {Earthquake geology of the northern San Andreas Fault near Point Arena, California},
author = {Prentice, C S},
abstractNote = {Excavations into a Holocene alluvial fan provided exposures of a record of prehistoric earthquakes near Point Arena, California. At least five earthquakes were recognized in the section. All of these occurred since the deposition of a unit that is approximately 2000 years old. Radiocarbon dating allows constraints to be placed on the dates of these earthquakes. A buried Holocene (2356-2709 years old) channel has been offset a maximum of 64 {plus minus} 2 meters. This implies a maximum slip rate of 25.5 {plus minus} 2.5 mm/yr. These data suggest that the average recurrence interval for great earthquakes on this segment of the San Andreas fault is long - between about 200 and 400 years. Offset marine terrace risers near Point Arena and an offset landslide near Fort Ross provide estimates of the average slip rate since Late Pleistocene time. Near Fort Ross, an offset landslide implies a slip rate of less than 39 mm/yr. Correlation and age estimates of two marine terrace risers across the San Andreas fault near Point Arena suggest slip rates of about 18-19 mm/yr since Late Pleistocene time. Tentative correlation of the Pliocene Ohlson Ranch Formation in northwestern Sonoma County with deposits 50 km to the northwest near Point Arean, provides piercing points to use in calculation of a Pliocene slip rate for the northern San Andreas fault. A fission-track age 3.3 {plus minus} 0.8 Ma was determined for zicrons separated from a tuff collected from the Ohlson Ranch Formation. The geomorphology of the region, especially of the two major river drainages, supports the proposed 50 km Pliocene offset. This implies a Pliocene slip rate of at least 12-20 mm/yr. These rates for different time periods imply that much of the Pacific-North American plate motion must be accommodated on other structures at this latitude.},
doi = {},
url = {https://www.osti.gov/biblio/7011185}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 1989},
month = {Sun Jan 01 00:00:00 EST 1989}
}

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