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San Francisco Bay Area Fault Map

View earthquakes for the last 30 days

San Francisco, Oakland, Palo Alto, San Mateo, Fremont, and Hayward Faults

San Francisco, situated on the complex tectonic landscape of Northern California, is surrounded by several significant fault zones that play crucial roles in the area's seismic activity. Understanding these faults and their types helps in assessing the earthquake hazards the city might face.

San Andreas Fault Zone

The San Andreas Fault is one of the most well-known fault systems in the world and is a right-lateral strike-slip fault. It stretches over 800 miles from Southern California to northern California. Near San Francisco, the fault runs through the San Francisco Peninsula and is known for its significant seismic activity. Its most recent major event was the 1906 San Francisco earthquake, which caused widespread devastation.

Hayward Fault Zone

This is another major right-lateral strike-slip fault, running parallel to the San Andreas Fault but located on the eastern side of the San Francisco Bay. It extends from the southern end of San Pablo Bay to the northern end of Fremont. The Hayward Fault has a history of major earthquakes, including the 1868 Hayward earthquake, which was one of the largest in the Bay Area's recorded history.

San Gregorio Fault Zone

The San Gregorio Fault is a right-lateral strike-slip fault that runs along the coast south of San Francisco, extending from the San Francisco Peninsula to the southern part of the Bay Area. It is less studied compared to the San Andreas and Hayward faults but still poses a significant seismic risk, especially in the coastal regions.

Pilarcitos Fault

This fault is a lesser-known right-lateral strike-slip fault located west of San Francisco, near the coast. It is considered less active than the San Andreas and Hayward faults but still contributes to the regional seismic hazard.

Serra Fault Zone

The Serra Fault is a right-lateral strike-slip fault located in the Santa Cruz Mountains, running parallel to the San Andreas Fault. It is considered a significant fault in terms of seismic hazard due to its proximity to the densely populated Bay Area.

San Jose Fault

This is a minor right-lateral strike-slip fault located near San Jose. While not as well-known as the San Andreas or Hayward faults, it still contributes to the region's seismic activity.

Hermit Fault

Located in the southern part of the San Francisco Bay Area, the Hermit Fault is a right-lateral strike-slip fault. It is relatively minor compared to the more prominent faults but adds to the overall seismic complexity of the region.

Stanford Fault

This fault is another minor right-lateral strike-slip fault in the Bay Area. It is less significant in terms of seismic hazard but is part of the region's complex fault network.

Monte Vista-Shannon Fault Zone

This is a right-lateral strike-slip fault zone located in the eastern Bay Area, stretching from Monte Vista to Shannon. It is considered less active than the Hayward and San Andreas faults but still contributes to regional seismic risk.

Chabot Fault

A right-lateral strike-slip fault located near the eastern side of the Bay Area, the Chabot Fault is part of the region’s intricate fault system. It is considered less active but still relevant for understanding regional seismic hazards.

Moraga Fault

This is a right-lateral strike-slip fault located in the East Bay region. It is relatively minor compared to the more prominent faults but is part of the Bay Area’s seismic risk profile.

Franklin Fault

This is another minor right-lateral strike-slip fault located in the Bay Area, adding to the complexity of the region’s fault network.

Most Active Faults

The San Andreas and Hayward Faults are the most active and significant in terms of seismic hazard. They have a well-documented history of producing large earthquakes and are closely monitored by seismologists.

Earthquake Hazards

In the event of a major quake, San Francisco faces several hazards. Liquefaction is a significant risk, particularly in areas with loose, water-saturated soils, which can lead to ground failure. Landslides are another concern, especially in hilly areas. Tsunamis could be generated if the quake triggers underwater landslides or if there is a significant offshore rupture. Building and freeway collapse is a major concern due to the age and construction standards of many structures in the city. Fires can also result from damaged gas lines and electrical systems.

Worst Shaking Areas

Areas closest to the active faults, such as the San Francisco Peninsula, parts of the East Bay near the Hayward Fault, and coastal regions near the San Gregorio Fault, would experience the most severe shaking. The intensity of shaking diminishes with distance from the fault lines but can still be significant throughout the Bay Area.

Major Earthquakes

Notable historical earthquakes include the 1906 San Francisco earthquake, which caused extensive damage and loss of life. The 1989 Loma Prieta earthquake, while centered in the Santa Cruz Mountains, also affected San Francisco significantly. Other significant events in the region’s history include the 1868 Hayward earthquake and various pre-instrumental quakes that have been inferred from historical accounts and geological evidence.

Understanding these faults and the associated risks helps in preparing for and mitigating the impacts of future earthquakes in the San Francisco Bay Area.

Fault Attributes Key

NAME is an 80-character field for the name of the fault (including section name,
i.e., Denali fault, Holitna section). Fault and section are lower case.

CODE is a three-integer field.that defines certainty or reliability of field mapping
(integer one), time of most recent movement (integer two), and amount or rate of slip (integer three).
CODE is composite of the single integer fields ACODE, SLIPCODE, and FCODE
and determines the line type (fault trace) to be plotted.

NUM is a six-character unique USGS identifier that defines a fault or section id. Simple fault
ids are only numeric; section ids are alpha numeric.

AGE is the upper bounding time of the most recent surface-deforming earthquake. The allowable
choices are provided in a pull-down menu.

ACODE is the second integer in CODE and defines the upper bounding time of the most recent
surface-deforming earthquake.
Permissible values are between 1 and 6: 1=historic «150 years; red =cmyk 1096680);
2= post glacial (15,000 years; orange = cmyk 1 38 1000);
3 = late Quaternary «130,000 years; green> cmyk 1002500);
4 =middle and late Quaternary «750,000 years: blue > cmyk 1004440);
5 =Quaternary «1,600,000 years; black 5);
6 = Class B (black halftone)
In the text documentation, Quaternary faults (integer two, 1-5) are Class A structures. Questionable or
suspected structures are Class B (integer two, 6).

SLIPRATE is the assigned slip rate category.

SLIPCODE is the third integer in CODE and defines the assigned slip rate category. Permissible
values are between 1 and 4 and determines line width:
1=>5 mm/year (extra wide; .048):
2 =1-5 mm/year (wide; .0325):
3 =0.2-1 mm/year (medium; .025);
4 =<.2 mm/year (thin; .015)

SLIPSENSE is normal, reverse, strike slip, thrust

DIPDIRECTION is one of the eight quadrant dip directions for the entire fault or section, not the
individual arc. C = center E =east N_ =north NE =northeast NW =northwest S =south SE =southeast SW =
southwest W_ =west
SLIPDIRECT (we are not using that field anymore and can be left empty) FCODE is the first integer
in CODE and defines how well the fault is located and expressed in the landscape. Permissible values are

between 1 and 3:
1 = fault landforms are more continuous than discontinuous and mapping is accurate at
given MAPPEDSCALE (solid);
2 = fault landforms are more discontinuous than continuous and mapping is accurate at
given MAPPEDSCALE (dashed);
3 = location of fault is inferred (dotted)
FTYPE is one of three allowable choices provided in a pull-down menu: Well constrained (FCODE 1),
Moderately constrained (FCODE 2), and Inferred (FCODE 3)

MAPPEDSCALE is one of four allowable choices provided in a pull-down menu.
Mapped scale will control visualization of the fault at various scales.
1:24,000, fault should be more continuous than discontinuous and mapping is accurate at <10,000 scale.
1:50,000, fault should be more continuous than discontinuous and mapping is accurate at <25,000 scale.
1:100,000, fault could be more discontinuous than continuous and mapping is accurate at <50,000 scale.
1:250,000, fault location may be inferred or is poorly constrained.



Data source: USGS
CCCarto is not responsible for data errors or omissions, use as reference only.
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