Monterey, CA, and Its Surrounding Earthquake Faults

Monterey, CA, and its surrounding region are influenced by several notable earthquake faults, each with its characteristics and seismic activity. Here's an overview of the faults around Monterey, their types, activity levels, associated earthquake hazards, areas prone to shaking, and major historical earthquakes:

Faults Around Monterey and Their Types:

San Andreas Fault: This major transform fault runs roughly northwest-southeast through California. While not directly adjacent to Monterey, its proximity influences seismic activity in the region, particularly regarding the potential for large earthquakes affecting nearby faults.
San Gregorio fault zone: Located offshore, this fault zone is a complex system of faults primarily characterized as strike-slip faults. It plays a significant role in regional seismic activity.
Monterey Bay-Tularcitos fault zone: This zone consists of several faults, including the Tularcitos and Monterey Bay faults, primarily characterized as strike-slip faults.
Chupines fault zone: This fault zone is relatively minor compared to others in the region and is primarily characterized as a strike-slip fault.
Laureles fault: A local fault in the Monterey area, its type and activity are less well-documented but are likely to be strike-slip or normal faults.
Reliz fault zone: Located inland, this fault zone includes faults of various types, likely including strike-slip and possibly some thrust faults.
Zayante-Vergeles fault zone: Located north of Monterey Bay, this fault zone is primarily characterized as a right-lateral strike-slip fault.

Most Active Faults:

The most active faults in the region include the San Andreas Fault and its associated fault systems, such as the San Gregorio fault zone and the Monterey Bay-Tularcitos fault zone. These faults have experienced significant historical seismic activity and continue to pose seismic hazards.

Earthquake Hazards:

In the event of a major earthquake near Monterey, several hazards could affect the region:

Ground Shaking: The primary hazard, capable of causing structural damage to buildings, infrastructure, and lifelines.
Liquefaction: Areas with loose, water-saturated soils could experience liquefaction, where the ground temporarily loses strength, potentially causing buildings to sink or tilt.
Landslides: Steep slopes around Monterey are prone to landslides triggered by ground shaking, particularly in areas with vulnerable soils.
Tsunami: Depending on the earthquake's location and magnitude, a tsunami could affect the coastline, causing flooding and damage.
Building and Freeway Collapse: Older buildings and bridges not designed to modern seismic standards could collapse, posing risks to occupants and transportation routes.
Fires: Earthquakes can rupture gas lines and electrical systems, leading to fires that could spread rapidly if emergency services are disrupted.

Areas Most Prone to Shaking:

Areas closest to active faults, such as along the San Andreas Fault and its associated fault systems (San Gregorio fault zone, Monterey Bay-Tularcitos fault zone), would experience the most intense shaking. Coastal areas could also experience amplified shaking due to soft sediments and proximity to fault lines.

Major Earthquakes in the Last 100 Years:

Historically, Monterey and its vicinity have experienced notable earthquakes:

1906 San Francisco Earthquake: While not centered on Monterey, this earthquake significantly impacted the region and influenced seismic understanding.
1989 Loma Prieta Earthquake: Centered near Santa Cruz, this earthquake caused shaking and damage throughout Monterey County, including the collapse of a portion of the Bay Bridge and damage in Santa Cruz and Watsonville.
2004 Parkfield Earthquake: Although not as directly impactful on Monterey, it underscored seismic hazards along the San Andreas Fault.

These earthquakes highlight the ongoing seismic risk in the Monterey region, driven by the complex fault systems nearby. Preparedness and seismic resilience efforts are crucial for mitigating potential future impacts from earthquakes in this seismically active area.

Monterey Bay Fault Map

Monterey and Carmel 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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