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Brief Report for Hayward fault zone, Southeast Extension section (Class A) No. 55c

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Compiled in cooperation with the California Geological Survey

citation for this record: Bryant, W.A., and Cluett, S.E., compilers, 2000, Fault number 55c, Hayward fault zone, Southeast Extension section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 07/25/2014 12:47 AM.

Synopsis General: Historically active dextral strike-slip fault zone that is part of the larger San Andreas fault system. The Hayward fault zone is located along the eastern margin of San Francisco Bay and generally forms the western front of the East Bay Hills. The fault zone has three sections (Working Group on Northern California Earthquake Probabilities, 1996 #1216; Petersen and others, 1996 #4860). The Northern [55a] and Southern Hayward [55b] sections are principally characterized by historically active dextral strike-slip displacement (Herd, 1977 #5484; 1978 #5485; Smith, 1980 #5497; 1980 #5498; 1981 #5499; Lienkaemper, 1992 #5486). The Southeast Extension section [55c] is characterized by late Quaternary and Holocene dextral, dextral-reverse, and reverse displacement (Bryant, 1982 #5475). The Hayward fault is characterized by fault creep along the Northern and Southern sections. A preferred average creep rate of 4.6 mm/yr was reported by Lienkaemper and Galehouse (1997 #5488). Most of the fault creeps between 3 mm/yr and 6 mm/yr (Galehouse, 1995 #4853; Lienkaemper and Galehouse, 1997 #5488; 1999 #5500), although the historic creep rate has been as high as 9 mm/yr near the southern part of the Southern Hayward fault [section 55b] (Lienkaemper and others, 1991 #5487; Lienkaemper and Galehouse, 1997 #5488). The MW ~7 1868 earthquake (Lawson, 1908 #4969; Yu and Segall, 1996 #5492) occurred on the Southern Hayward fault [section 55b] and extended into the Northern Hayward fault [section 55a]. Fault creep has not been observed along the Southeast Extension section [55c]. Toppozada and Borchardt (1998 #5493) showed that the June 10, 1836 earthquake, previously thought to have been on the Northern Hayward fault [section 55a], occurred further south, somewhere east of Monterey Bay. Cumulative dextral offset of the 6 Ma Roblar Tuff is 28?3 km (Sarna-Wojcicki, 1992 #5265). Lienkaemper and Borchardt (1996 #5297) reported a preferred Holocene slip rate (minimum) of 8.0?0.7 mm/yr based on dextral offset of an alluvial-fan apex in Union City. A dated recurrence interval has not been determined for the Northern and Southern Hayward faults (sections 55a and 55b, respectively), but there have been at least four surface faulting earthquakes in the past 2,250 radiocarbon years along the Northern Hayward section (Leinkaemper and others, 1997 #5482). Williams (1992 #5495) reported that at least 6 and as many as eight events have occurred in the past 2.1 k.y. along the Southern Hayward section.

Sections: This fault has 3 sections. There is insufficient data to determine seismogenic segments. The segment boundary between the Northern and Southern Hayward faults was long considered to be delineated by the location of the northern boundary of rupture associated with the Mw~7 1868 earthquake and the southern boundary of rupture associated with the 1836 (Working Group on California Earthquake Probabilities, 1988 #5494; 1990 #549). Toppozada and Borchardt (1998 #5493) re-evaluated the 1836 earthquake and demonstrated that it did not occur on the Hayward fault. Yu and Segall (1996 #5492) and Working Group on Northern California Earthquake Potential (1996 #1216) suggest that 1868 rupture may have extended as far north as northern Oakland. Petersen and others (1996 #4860) and Working Group on Northern California Earthquake Potential (1996 #1216) modeled the Hayward fault zone with two segments of equal length. The Northern and Southern sections of the Hayward fault zone were considered to rupture characteristically, with a dextral strike-slip slip rate of 9 mm/yr. A possible third segment, the Southeast Extension, was modeled with a dextral reverse oblique slip rate of 3 mm/yr. The section boundaries proposed by Petersen and others (1996 #4860) and Working Group on Northern California Earthquake Potential (1996 #1216) are adopted here: from north to south they are the Northern Hayward [55a], Southern Hayward [55b], and Southeast Extension [55c] sections.
County(s) and State(s) ALAMEDA COUNTY, CALIFORNIA
SANTA CLARA COUNTY, CALIFORNIA
Physiographic province(s) PACIFIC BORDER
Length (km) This section is 30 km of a total fault length of 107 km.
Average strike N46°W (for section) versus N39°W (for whole fault)
Sense of movement Dextral
Dip Direction NE; V
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)
Slip-rate category Between 1.0 and 5.0 mm/yr
Date and Compiler(s) 2000
William A. Bryant, California Geological Survey
Sereyna E. Cluett, California Geological Survey