Holocene slip rate along the Hayward fault northern California

Journal Article · Mon Jan 01 04:00:00 EST 1990 · California Geology (California Division of Mines and Geology); (USA)

OSTI ID:6225203

Borchardt, G; Lienkaemper, J J; Wilmesher, J F

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), Journal Name: California Geology (California Division of Mines and Geology); (USA) Vol. 43:2; ISSN 0026-4555; ISSN CGEOA
• Country of Publication: United States
• Language: English

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