Serra Fault
Encyclopedia
The Serra Fault is the northernmost fault in a zone of northwest-striking range front thrust faults adjacent to and northeast of the San Francisco Peninsula
segment of the San Andreas Fault
, in eastern San Mateo County
, California
.
The Serra Fault is positioned approximately 1.5–3 km (0.93205910497471–1.9 mi) northeast of the San Andreas Fault; moreover the Serra Fault extends for more than 20 km (12.4 mi) from the town of Hillsborough
to a point near Daly City
.
fluvial
channel deposits inset into the Merced Formation along the forelimb of the fold seem to be deformed, illustrating that the folding is active.
The Serra Fault is a low angle imbricate fault that has thrust older Franciscan
Assemblage rocks and soils of the Merced Formation over the younger Colma Formation. The Serra Fault was originally zoned as potentially active by the State of California under the mandated special studies for surface fault rupture. 1980s studies concluded that evidence for active Holocene age faulting (displacement within past 11,000 years) along the Serra Fault is lacking. The Serra Fault is, therefore, not zoned for Special Studies by the State of California and is classified as Quaternary
in age: that is, fault displacement within the past two million years.
San Francisco Peninsula
The San Francisco Peninsula is a peninsula in the San Francisco Bay Area that separates the San Francisco Bay from the Pacific Ocean. On its northern tip is the City and County of San Francisco. Its southern base is in Santa Clara County, including the cities of Palo Alto, Los Altos, and Mountain...
segment of the San Andreas Fault
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
, in eastern San Mateo County
San Mateo County, California
San Mateo County is a county located in the San Francisco Bay Area of the U.S. state of California. It covers most of the San Francisco Peninsula just south of San Francisco, and north of Santa Clara County. San Francisco International Airport is located at the northern end of the county, and...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
The Serra Fault is positioned approximately 1.5–3 km (0.93205910497471–1.9 mi) northeast of the San Andreas Fault; moreover the Serra Fault extends for more than 20 km (12.4 mi) from the town of Hillsborough
Hillsborough, California
Hillsborough is an incorporated town in San Mateo County, California, in the San Francisco Bay Area. Hillsborough is one of the wealthiest communities in America and has the highest income of places in the United States with populations of at least 10,000...
to a point near Daly City
Daly City, California
Daly City is the largest city in San Mateo County, California, United States, with a 2010 population of 101,123. Located immediately south of San Francisco, it is named in honor of businessman and landowner John Daly.-History:...
.
Serra geology
According to Kennedy: "Three angular unconformities within the Merced and overlying Colma Formations have formed on the steeply dipping fold forelimb". Mid to later HoloceneHolocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
fluvial
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
channel deposits inset into the Merced Formation along the forelimb of the fold seem to be deformed, illustrating that the folding is active.
The Serra Fault is a low angle imbricate fault that has thrust older Franciscan
Franciscan
Most Franciscans are members of Roman Catholic religious orders founded by Saint Francis of Assisi. Besides Roman Catholic communities, there are also Old Catholic, Anglican, Lutheran, ecumenical and Non-denominational Franciscan communities....
Assemblage rocks and soils of the Merced Formation over the younger Colma Formation. The Serra Fault was originally zoned as potentially active by the State of California under the mandated special studies for surface fault rupture. 1980s studies concluded that evidence for active Holocene age faulting (displacement within past 11,000 years) along the Serra Fault is lacking. The Serra Fault is, therefore, not zoned for Special Studies by the State of California and is classified as Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
in age: that is, fault displacement within the past two million years.
Regional geology
Age constraints for coastal exposures of the Pleistocene Colma and uppermost Merced Formations have prior to 2005 been primarily correlative, generating uncertainty about the depositional history of these units as well as the timing of fault activity responsible for lifting them to elevations up to seventy meters along the northwestern coast of the San Francisco Peninsula. Yi notes that: "Recent studies have suggested that Merced and Colma deposits, as well as younger Holocene inset channel deposits, show fault-propagation fold growth and tilting" related to activity on the Serra Fault itself.Reference notes
- Kennedy, Drew G., LATE PLEISTOCENE TO HOLOCENE FOLD GROWTH ABOVE THE SERRA FAULT, NORTHERN SAN FRANCISCO PENINSULA, CALIFORNIA, Sanders & Associates Geostructural Engineering, Geological Society of America (2005)
- California Division of Mines and Geology, Special Studies Zone:Serra Fault, (1974) Sacramento, California
- Earth Metrics, (1989) Marc. Papineau, Ballard. George, Jill Buxton et al., Environmental Impact Report for the Metro Center, Colma, California, Rpt Number 10062, city of Colma Planning Department and published by the California State Clearinghouse, December, 1989
- Chimi Yi, Karen Grove, John Caskey, Drew Kennedy, and Glenn Berger, Depositional and Deformational History of the Colma and Uppermost Merced Formations, Southwest San Francisco, (2005), Geological Society of America