Imperial Valley, CA Faults - Seismic Activity and Geothermal Energy

Brawley, California, is situated in a seismically active region of Southern California where multiple earthquake faults intersect. The area around Brawley features several significant fault zones, each characterized by different fault types and levels of activity. Here’s a detailed overview of the faults in the region, their types, and the associated earthquake hazards:

Faults and Their Types

San Andreas Fault Zone: This is a major transform fault that forms the boundary between the Pacific and North American tectonic plates. It is a right-lateral strike-slip fault that accommodates horizontal motion between these plates. While the San Andreas Fault Zone is not directly under Brawley, it influences the regional stress field.
San Jacinto Fault Zone: Another significant fault in the area, the San Jacinto Fault is a right-lateral strike-slip fault, similar to the San Andreas Fault. It is one of the most active faults in Southern California and plays a critical role in the regional seismic activity.
Brawley Seismic Zone: This area is characterized by a complex interaction of multiple fault types, including strike-slip and normal faults. It is known for its high seismic activity and is directly associated with the seismic hazard in the Brawley region.
San Felipe Fault Zone: This fault is primarily a right-lateral strike-slip fault, which is part of the larger system of transform faults in the region. It contributes to the seismic activity around Brawley.
Elsinore Fault Zone: This is another transform fault, with both strike-slip and normal fault components. It runs parallel to the San Andreas Fault and affects the seismic activity in the region.
Imperial Fault: The Imperial Fault is a right-lateral strike-slip fault located to the east of Brawley. It is a significant contributor to the seismic activity in the Imperial Valley region.
Coachella Fan Fault Zone: This zone contains a mix of fault types, including normal and strike-slip faults. It plays a role in the complex tectonic setting around Brawley.
Mecca Hills Fault Zone: This zone features a variety of fault types, including normal and strike-slip faults. It is situated to the west of Brawley and contributes to the seismic hazards in the area.
Yuha Basin Faults: These faults are primarily normal faults and contribute to the tectonic complexity of the region. They are part of the broader seismic activity in the Imperial Valley.
Northern Centinela Fault Zone: This fault zone includes a mix of strike-slip and normal faults. It adds to the overall seismic risk in the Brawley area.
Extra Fault Zone: Less well-known compared to other fault zones, the Extra Fault Zone has a complex fault system with various types, including normal and strike-slip faults.

Fault Activity and Hazards

In the Salton Sea area, the most active faults include the San Andreas Fault, the San Jacinto Fault, and the Imperial Fault. The Brawley Seismic Zone is particularly notable for its frequent seismic activity, making it a high-risk area for earthquakes. The region experiences significant shaking due to the interaction of these faults, especially during large seismic events.

Earthquake Hazards in Brawley:

Liquefaction: This is a significant hazard in areas with loose, water-saturated soils, like those around the Salton Sea. In a major quake, these soils can lose their strength and behave like a liquid, causing substantial damage to structures.
Tsunamis: The Salton Sea is an inland lake and not directly connected to the ocean. Therefore, tsunamis are not a concern for Brawley. However, if there were a significant seismic event, the main concern would be ground shaking rather than tsunamis.
Landslides: While landslides are a common hazard in hilly or mountainous regions, Brawley’s relatively flat terrain means this is less of a concern compared to other hazards.
Building and Structure Collapse: With high seismic activity, building and structure collapse is a significant concern. Older structures or those not built to modern seismic codes are at higher risk.
Fires: Earthquakes can cause gas line ruptures and electrical faults, leading to fires. This is a potential hazard in the aftermath of a significant quake.

Areas Facing Worst Shaking:

The areas around Brawley most likely to experience severe shaking include those closest to the major fault lines, such as near the Imperial Fault and Brawley Seismic Zone. The intensity of shaking decreases with distance from these active faults.

Major Earthquakes in the Last 100 Years:

Significant earthquakes in the region include the 1940 Imperial Valley earthquake, which had a magnitude of 7.1 and was centered near the Imperial Fault. More recent earthquakes include events in the 1980s and 1990s related to the Brawley Seismic Zone.

Unzipping Scenario of the San Andreas Fault:

The "unzipping" scenario refers to the potential for a major earthquake to propagate along the San Andreas Fault from the Salton Sea area to the north. This scenario involves a rupture that starts in the southern part of the fault near the Salton Sea and could extend northward, causing widespread damage along the fault zone. This scenario is a concern for seismologists because it would involve a significant release of seismic energy along a major fault line, affecting a large region.

The Salton Sea area is also known for its significant geothermal activity due to the presence of the Imperial Fault and other geological features. The region is one of the most geologically active areas in the United States, and this activity has led to the development of a substantial geothermal power industry.

The Salton Sea Geothermal Field, located to the east of the Salton Sea, is a major source of geothermal energy. Several power plants in the area harness this geothermal activity to produce electricity. The geothermal resources in the Salton Sea region are considered among the most promising in the world due to their high temperature and productivity.

The power plants in the area use the steam and hot water from underground geothermal reservoirs to generate electricity. This makes geothermal energy a significant part of the renewable energy mix for the region, contributing to its energy needs while also helping reduce greenhouse gas emissions.

Summary

In summary, Brawley faces significant seismic hazards due to its proximity to several active fault zones. The most pressing concerns are related to ground shaking, potential building collapse, and liquefaction in certain areas. The unzipping scenario for the San Andreas Fault highlights the potential for large-scale seismic events that could have far-reaching impacts across Southern California. While, on the flipside, the geothermal energy is a major energy resource and job creator.

Salton Sea Faults Map

Imperial Valley Fault Map

The Salton Sea and surrounding basin sits over the San Andreas Fault, Brawley seismic zone, Indio Hills fault zone, Imperial Fault Zone, and nearby and very large San Jacinto fault zone. Area geologists have estimated that previous flooding episodes from the Colorado River have been linked to increases in earthquakes along the area’s San Andreas Fault. Ground instruments were used to survey the Salton Sea's underwater faults during this study. During the geologic historic period when the basin was filled by the large Lake Cahuilla, (a larger inland sea), more earthquakes higher than magnitude 7 occurred about every 180 years, the last one occurring around the decades in the 1700s.

Computer stress models conclude that the normal faults in the area are vulnerable to special deviatoric stress loading by filling in of water. Currently, a risk still exists for an earthquake of magnitude 7 or 8 due to man lowering the huge natural aquifer tables in the region. Simulations also showed, in the Los Angeles area, shaking and thus damage would be more severe for a San Andreas earthquake that propagated along the fault from the south, rather than from the north due to fault directions, depth, and it being much closer than the 1857 mega quake. Such a large earthquake also raises the risk for soil liquefaction in the Imperial Valley filled in regions and sandy soils.

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.

Click on the fault lines for more information.
Note* The earthquake faults are color coded by unique name and section not type.

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