Holocene slip rate along the Hayward fault northern California
The aseismic surface slip (creep) rate along most of the Hayward fault generally has ranged from 5 to 6 mm/yr for several decades (between central Fremont and Point Pinole). In southern Fremont, however, slip since the 1920s has been much higher, 8-10 mm/yr. Regional strain data in recent decades permit as much as 10-12 mm/yr dextral strain rate to be associated with the Hayward fault. Because large earthquakes (about M 6.8) have occurred on the fault historically, in 1868 and 1836( ), it is important to know if the historic creep rate (5-6 mm/yr) is lagging behind a long-term or geologic slip rate for the fault zone. In April 1989 a trench 130 m long by 4 to 6 m deep was cut parallel to and about 20 m from the fault. The trench showed at least 6 buried (beheaded) apexes of an alluvial fan offset by the fault that will be used to measure Holocene and latest Pleistocene slip rates. These 6 apexes indicate net slip of: 20{plus minus}7 m; 46{plus minus}5 m; 66{plus minus}5 m, 88{plus minus}5 m; 131{plus minus}6; and 167{plus minus}6 m. More trenching and field work within the next year will verify and improve these preliminary values. Twenty-four carbon-14 samples have been submitted for slip rates. Thus far one apex (66{plus minus}6 m) has been dated, 7,435{plus minus}60 yr before present (radiocarbon), yielding average slip rate of 8.8{plus minus}0.7 mm/yr, similar to the southern Fremont creep rate, and thus indicating a higher earthquake risk on the Hayward fault than previously assumed.
- OSTI ID:
- 6225203
- Journal Information:
- California Geology (California Division of Mines and Geology); (USA), Vol. 43:2; ISSN 0026-4555
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALIFORNIA
GEOLOGIC FAULTS
CREEP
AGE ESTIMATION
CARBON 14
EARTHQUAKES
FORECASTING
GEOLOGIC HISTORY
GROUND MOTION
HISTORICAL ASPECTS
ISOTOPE DATING
PLEISTOCENE EPOCH
QUATERNARY PERIOD
REGIONAL ANALYSIS
SLIP
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON ISOTOPES
CENOZOIC ERA
EVEN-EVEN NUCLEI
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
ISOTOPES
LIGHT NUCLEI
MECHANICAL PROPERTIES
MOTION
NORTH AMERICA
NUCLEI
RADIOISOTOPES
SEISMIC EVENTS
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences