Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

A long paleoseismic record at Hog Lake on the central San Jacinto fault in southern California documents evidence for 18 surface ruptures in the past 3.8-4 ka. This yields a long-term recurrence interval of about 210 years, consistent with its slip rate of ~15 mm/yr and field observations of 3-3.5 m of displacement per event. However, during the past 3800 years, the fault has switched from a quasiperiodic mode of earthquake production, during which the recurrence interval is similar to the long-term average, to clustered behavior with the inter-event periods as short as a few decades (five surface ruptures occurred between about AD 1043 and 1383). There are also some periods as long as 450 years during which there were no surface ruptures, and these periods are commonly followed by one to several closely-timed ruptures. The coefficient of variation (CV) for the timing of these earthquakes is about 0.6 for the past 4000 years (17 intervals). Similar behavior has been observed on the San Andreas Fault (SAF) at Wrightwood, where clusters of earthquakes have been followed by periods of lower seismic production, and the CV is as high as 0.7 for some portions of the fault zone. In contrast, the central North Anatolian Fault (NAF) in Turkey, which ruptured in 1944, appears to have produced ruptures with similar displacement at fairly regular intervals for the past 1600 years. With a CV of 0.16 for timing, and close to 0.1 for displacement, the 1944 rupture segment near Gerede appears to have been both periodic and characteristic. The San Jacinto and San Andreas faults are part of a broad plate boundary system with multiple parallel strands with significant slip rates. Additional faults lay to the east (Eastern California shear zone) and west (faults of the LA basin and southern California Borderland), which makes the southern San Andreas fault system a complex and broad plate boundary zone. In contrast, the 1944 rupture section of the NAF is simple, straight and highly localized, which contrasts to the complex system of parallel faults in southern California. These observations suggest that the complexity of the southern California fault network is partly responsible for the apparent increase in “noise” and non-periodic behavior, perhaps resulting from stress transfer to adjacent faults after a large earthquake on one fault. The simplicity of the central NAF may account for its relatively simple behavior. If correct, the study of simple plate boundary faults may provide new insights into the constitutive elements of fault zones, and aid in identifying those components that are critical in better forecasting future seismicity in complex systems.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Fifth Conference

Publisher

Missouri University of Science and Technology

Publication Date

5-24-2010

Document Version

Final Version

Rights

© 2010 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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May 24th, 12:00 AM May 29th, 12:00 AM

The Non-Regularity of Earthquake Recurrence in California: Lessons from Long Paleoseismic Records from the San Andreas and San Jacinto Faults in Southern California, and the North Anatolian Fault in Turkey

San Diego, California

A long paleoseismic record at Hog Lake on the central San Jacinto fault in southern California documents evidence for 18 surface ruptures in the past 3.8-4 ka. This yields a long-term recurrence interval of about 210 years, consistent with its slip rate of ~15 mm/yr and field observations of 3-3.5 m of displacement per event. However, during the past 3800 years, the fault has switched from a quasiperiodic mode of earthquake production, during which the recurrence interval is similar to the long-term average, to clustered behavior with the inter-event periods as short as a few decades (five surface ruptures occurred between about AD 1043 and 1383). There are also some periods as long as 450 years during which there were no surface ruptures, and these periods are commonly followed by one to several closely-timed ruptures. The coefficient of variation (CV) for the timing of these earthquakes is about 0.6 for the past 4000 years (17 intervals). Similar behavior has been observed on the San Andreas Fault (SAF) at Wrightwood, where clusters of earthquakes have been followed by periods of lower seismic production, and the CV is as high as 0.7 for some portions of the fault zone. In contrast, the central North Anatolian Fault (NAF) in Turkey, which ruptured in 1944, appears to have produced ruptures with similar displacement at fairly regular intervals for the past 1600 years. With a CV of 0.16 for timing, and close to 0.1 for displacement, the 1944 rupture segment near Gerede appears to have been both periodic and characteristic. The San Jacinto and San Andreas faults are part of a broad plate boundary system with multiple parallel strands with significant slip rates. Additional faults lay to the east (Eastern California shear zone) and west (faults of the LA basin and southern California Borderland), which makes the southern San Andreas fault system a complex and broad plate boundary zone. In contrast, the 1944 rupture section of the NAF is simple, straight and highly localized, which contrasts to the complex system of parallel faults in southern California. These observations suggest that the complexity of the southern California fault network is partly responsible for the apparent increase in “noise” and non-periodic behavior, perhaps resulting from stress transfer to adjacent faults after a large earthquake on one fault. The simplicity of the central NAF may account for its relatively simple behavior. If correct, the study of simple plate boundary faults may provide new insights into the constitutive elements of fault zones, and aid in identifying those components that are critical in better forecasting future seismicity in complex systems.