Santa Rosa, CA: Overview of Nearby Earthquake Faults

Santa Rosa, CA, is situated in an area with several significant earthquake faults nearby. Here's a detailed overview of the faults around Santa Rosa, their types, activity levels, associated earthquake hazards, vulnerable areas, and historical seismic events:

1. Faults Around Santa Rosa and Their Types:

Rodgers Creek Fault: This is a major strike-slip fault that runs close to Santa Rosa. It is capable of producing significant earthquakes.
San Andreas Fault Zone: Although not directly adjacent to Santa Rosa, the San Andreas Fault is nearby and poses a significant seismic hazard. It is a major transform fault system.
Alexander-Redwood Hill Fault Zone: This is a complex fault system including both strike-slip and reverse fault components.
Maacama Fault Zone: Another significant strike-slip fault in the region.
Tolay Fault: This fault is a reverse fault (thrust fault) capable of generating moderate to large earthquakes.
Healdsburg Fault: A strike-slip fault that can produce earthquakes with moderate magnitudes.
Knights Valley Fault Zone: This fault system includes both strike-slip and reverse fault segments.
Bidwell Creek Fault Zone: This fault zone includes both strike-slip and normal fault segments.
West Napa Fault: A strike-slip fault that can generate earthquakes of moderate size.
Geyser Peak Fault Zone: This fault zone includes both strike-slip and reverse fault components.

2. Most Active Faults:

The most active faults in the region include the Rodgers Creek Fault, San Andreas Fault Zone, Maacama Fault Zone, and the West Napa Fault. These faults have produced historical earthquakes and are monitored closely for seismic activity.

3. Earthquake Hazards for Santa Rosa:

In the event of a major earthquake, Santa Rosa could face several hazards:

Ground Shaking: The primary hazard, causing damage to buildings, infrastructure, and potential injuries.
Liquefaction: Areas with loose, water-saturated soils are susceptible to liquefaction, where the ground temporarily loses strength and can cause buildings to sink or tilt.
Landslides: Steep slopes and hillsides around Santa Rosa could experience landslides triggered by strong shaking.
Building and Freeway Collapse: Older buildings and infrastructure not built to modern seismic standards could collapse.
Fires: Earthquakes can rupture gas lines and cause fires, particularly in urban areas with dense infrastructure.

4. Areas Facing the Worst Shaking:

Areas closest to active faults like the Rodgers Creek Fault, San Andreas Fault, and other local faults would experience the strongest shaking. Additionally, neighborhoods with softer soils prone to amplifying seismic waves could face more severe shaking effects.

5. Major Earthquakes in the Last 200 Years:

Several significant earthquakes have affected the Santa Rosa area in the past two centuries:

1906 San Francisco Earthquake: Although centered south of Santa Rosa, it was felt strongly in the region and caused damage.
1969 Santa Rosa Earthquake: A magnitude 5.6 earthquake that caused moderate damage in Santa Rosa and surrounding areas.
1980 Livermore Earthquake: This earthquake, although not directly in Santa Rosa, was felt in the region and highlighted seismic vulnerability.

These earthquakes underscore the seismic activity and potential risks faced by Santa Rosa due to its proximity to active fault systems. Ongoing monitoring and preparedness efforts are crucial to mitigate future seismic hazards in the area.

Santa Rosa Fault Map

North Bay Area Fault Map

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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