Subsurface Geometry of the San Andreas Fault in Southern California: Results from the Salton Seismic Imaging Project (SSIP) and Strong Ground Motion Expectations

Seismological Society of America (SSA) | August 1st, 2017

The San Andreas fault (SAF) is one of the most studied strike‐slip faults in the world; yet its subsurface geometry is still uncertain in most locations. The Salton S

The San Andreas fault (SAF) is one of the most studied strike‐slip faults in the world; yet its subsurface geometry is still uncertain in most locations. The Salton Seismic Imaging Project (SSIP) was undertaken to image the structure surrounding the SAF and also its subsurface geometry. We present SSIP studies at two locations in the Coachella Valley of the northern Salton trough. On our line 4, a fault‐crossing profile just north of the Salton Sea, sedimentary basin depth reaches 4 km southwest of the SAF. On our line 6, a fault‐crossing profile at the north end of the Coachella Valley, sedimentary basin depth is ∼2–3km∼2–3  km and centered on the central, most active trace of the SAF. Subsurface geometry of the SAF and nearby faults along these two lines is determined using a new method of seismic‐reflection imaging, combined with potential‐field studies and earthquakes. Below a 6–9 km depth range, the SAF dips ∼50°–60°∼50°–60° NE, and above this depth range it dips more steeply. Nearby faults are also imaged in the upper 10 km, many of which dip steeply and project to mapped surface fault traces. These secondary faults may join the SAF at depths below about 10 km to form a flower‐like structure. In Appendix D, we show that rupture on a northeast‐dipping SAF, using a single plane that approximates the two dips seen in our study, produces shaking that differs from shaking calculated for the Great California ShakeOut, for which the southern SAF was modeled as vertical in most places: shorter‐period (⁠T<1sT<1  s⁠) shaking is increased locally by up to a factor of 2 on the hanging wall and is decreased locally by up to a factor of 2 on the footwall, compared to shaking calculated for a vertical fault.

Tectonic evolution of the Salton Sea inferred from seismic reflection data

Nature Portfolio (Springer Nature) | July 26th, 2009

Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The f

Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The formation of these basins has generally been studied using laboratory experiments or numerical models. Here we combine seismic reflection data and geological observations from the Salton Sea to understand the evolution of this nascent pull-apart basin. Our data reveal the presence of a northeast-trending hinge zone that separates the sea into northern and southern sub-basins. Differential subsidence (>10 mm yr−1) in the southern sub-basin suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline, which may control the spatial distribution of young volcanism. Rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull-apart basin began after ∼0.5 million years ago. We suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the Salton Sea. In contrast to previous models based on historical seismicity patterns, the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull-apart basins.

Testimony of Wade Crowfoot, California Secretary for Natural Resources House Natural Resources Committee Subcommittee on Water, Oceans and Wildlife

Salton Sea Authority | September 24th, 2020

Thank you, Chairman Huffman and members of the Subcommittee for the opportunity to testify today on how the federal government can partner with California to inve

Thank you, Chairman Huffman and members of the Subcommittee for the opportunity to testify today on how the federal government can partner with California to invest resources and efforts to improve and ultimately revitalize conditions at the Salton Sea. I serve as Secretary of the California Natural Resources Agency (CNRA), which is charged with stewarding California’s natural, historical, and cultural resources for current and future generations. As part of that work and under the direction of Governor Gavin Newsom, our Agency is advancing projects at the Salton Sea to tackle pressing environmental issues and improve conditions for the people who live near the Salton Sea. As California’s largest body of water, the Salton Sea has served as a critical wildlife habitat for nearly 100 years, providing a key stopover spot for many special species of resident and migratory birds along the Pacific Flyway. Flows into the Salton Sea have declined in recent years, and the result is a shrinking, increasingly saline lake. As the Sea recedes, previously submerged lakebed is being exposed, reducing habitat and creating dust that can be hazardous as it dries and becomes airborne. These dust emissions present air quality issues that exacerbate public health challenges experienced by local communities in the region, which already has some of the highest childhood asthma rates.

The disappearing Salton Sea: A critical reflection on the emerging environmental threat of disappearing saline lakes and potential impacts on children's health

Science of the Total Environment (Elsevier) | February 6th, 2019

Changing weather patterns, droughts and competing water demands are dramatically altering the landscape and creating conditions conducive to the production of wind-blown

Changing weather patterns, droughts and competing water demands are dramatically altering the landscape and creating conditions conducive to the production of wind-blown dust and dust storms. In California, such factors are leading to the rapid shrinking of the Salton Sea, a 345 mile2 land-locked “sea” situated near the southeastern rural border region known as the Imperial Valley. The region is anticipated to experience a dramatic increase in wind-blown dust and existing studies suggest a significant impact on the health and quality of life for nearby residents of this predominantly low-income, Mexican-American community. The discussion calls attention to the public health dimensions of the Salton Sea crisis. We know little about the possible long-term health effects of exposure to mobilized lakebed sediments or the numerous toxic contaminants that may become respirable on entrained particles. We draw on existing epidemiological literature of other known sources of wind-blown dust, such as desert dust storms, and related health effects to begin to understand the potential public health impact of wind-blown dust exposure. The increased production of wind-blown dust and environmental exposures to such non-combustion related sources of particulate matter are a growing health threat, due in part to drought coupled with increasing pressures on limited water resources. Recent population-based studies have linked dust storms with cardiovascular mortality, asthma hospitalization and decrease in pulmonary function in both adults and children. A growing number of studies provide evidence of the acute health effects of wind-blown dust exposures among children, which with repeated insults have the potential to influence respiratory health over time. The shrinking of the Salton Sea illustrates a public health and environmental justice crisis that requires action and attention to protect the health and well-being of local communities.

The Effect of a Receding Saline Lake (The Salton Sea) on Airborne Particulate Matter Composition

American Chemical Society (ACS) | July 12th, 2017

The composition of ambient particulate matter (PM) and its sources were investigated at the Salton Sea, a shrinking saline lake in California. To investigate the influenc

The composition of ambient particulate matter (PM) and its sources were investigated at the Salton Sea, a shrinking saline lake in California. To investigate the influence of playa exposure on PM composition, PM samples were collected during two seasons and at two sites around the Salton Sea. To characterize source composition, soil samples were collected from local playa and desert surfaces. PM and soil samples were analyzed for 15 elements using mass spectrometry and X-ray diffraction. The contribution of sources to PM mass and composition was investigated using Al-referenced enrichment factors (EFs) and source factors resolved from positive matrix factorization (PMF). Playa soils were found to be significantly enriched in Ca, Na, and Se relative to desert soils. PMF analysis resolved the PM10 data with four source factors, identified as Playa-like, Desert-like, Ca-rich, and Se. Playa-like and desert-like sources were estimated to contribute to a daily average of 8.9% and 45% of PM10 mass, respectively. Additionally, playa sources were estimated to contribute to 38–68% of PM10 Na. PM10 Se concentrations showed strong seasonal variations, suggesting a seasonal cycle of Se volatilization and recondensation. These results support the importance of playas as a source of PM mass and a controlling factor of PM composition.

The Inundation of the Salton Basin by the Colorado River and How It Was Caused

Scientific American | April 14th, 1906

If the Colorado River continues to flow through the channel which it has been occupying during the last six months, the geography of the Southwest must be radically ch

If the Colorado River continues to flow through the channel which it has been occupying during the last six months, the geography of the Southwest must be radically changed, for at the present time but little water from the river reaches the Gulf of California, which until recently has formed its main estuary. Except when the river is in flood, the bulk of the water flows into what is known as the Salton Sink in southern California-a distance of fully 160 miles from the gulf.  The new channel of the Colorado takes a northwesterly course, while the channeI it formerly occupied is nearly south. It is perhaps needless to say that this watercourse is not only one of the most important in the Southwest, but is notable for the immense volume of water which it carries, especially during the flood seasons. But the quantity of detritus which it holds in solution is enormous, and is nearly equal to that carried down by the Mississippi at certain seasons of the year, owing to the topography of the region which drains into it. An idea of the quantity of water carried by the Colorado at different times of the year can be gained, when it is stated that actual measurements indicate a flow ranging as high as 30,000 cubic feet per second. It is estimated that if the silt and other material brought down the river in the course of a year were spread evenly over a given 'surface, it would cover no less than 35,000 acres to a minimum depth of one foot. Consequently, the Colorado is almost as much of a "land maker" as the Mississippi, acting like a gigantic suction dredge in carrying away the material in its vicinity and depositing it upon the lowlands near its mouth and in the Gulf of California.

The New Inland Sea

Scientific American | April 13th, 1907

The deep channel in the Alamo River, which passed Holtville in August, was gradually approaching Sharp's Heading, and it was recognized that when this cataract reached

The deep channel in the Alamo River, which passed Holtville in August, was gradually approaching Sharp's Heading, and it was recognized that when this cataract reached the heading it would be very difficult and expensive, and perhaps impossible, to maintain that heading. This, however, was not the only peril to the water supply of the valley. The channel of New River had eroded to such an extent that where the two streams separated it was estimated that four-fifths of the water was running down New River and only one fifth down the Alamo. While this proportion was favorable to the regimen of the Alamo and the safety of Sharp's Heading, it was very threatening in an other respect. It accelerated the cutting of the New River channel, in which was a great cataract four or five miles below the separation of the two streams, and this was, of course, advancing upstream. It was well recognized that when this cataract reached the Alamo the channel would be so deep that all of the water would run down New River and leave Sharp's Heading on dry land, without any water for the irrigation of the Imperial Valley. Threatened first with inundation, and next with the destruction of their entire water supply, the inhabitants of the Imperial Valley have naturally been almost in a state of panic for several months.

The Salton Sea: A Status Update

Legislative Analyst's Office (LAO) | August 29th, 2018

Torres Martinez Tribe Salton Sea Oral Testimony

Salton Sea Authority | September 24th, 2020

 Chairman and Ranking Member, I sincerely appreciate the opportunity to testify today. I am the Tribal Council Chairman of the Torres Martinez Desert Cahuilla (Tribe) an

 Chairman and Ranking Member, I sincerely appreciate the opportunity to testify today. I am the Tribal Council Chairman of the Torres Martinez Desert Cahuilla (Tribe) and a director on the Salton Sea Authority (SSA). I offer this testimony on behalf of both the Tribe and SSA.  I want to begin by thanking Congressman Ruiz (D-Calif.) and Congressman Vargas (D-Calif.) for their hard work to place this issue squarely before the Committee today. The Tribe and SSA view this hearing as a very important beginning of a more robust Congressional effort to drive federal action at the Salton Sea.