For a glimpse into California’s water future, consider the fate of a water destination from yesteryear.
Many of the tiny hamlets that surround the Salton Sea, a lake two hours east of San Diego, are mostly ghost towns. The resorts that made it a rival to Lake Tahoe in the 1950s have been replaced by junkyards and rusted signs with faded words like “pool” and “vacancy” on them.
Caught in the tug-of-war between metropolitan and agricultural demands for water, the sea itself is shrinking as evaporation is outpacing runoff. As a consequence, the salinity of the sea is increasing and that’s only part of the problem. Chemicals from agricultural runoff are also turning it into a concentrated broth.
The new dynamic has caused the ecosystem in the Salton Sea to shift. Algae blooms diminish oxygen concentrations in the water. Hardy tilapia are the last fish to survive here, but just barely. During hot summer months, gypsum crystals clog their gills and cause fish kills in the millions. Such large die-offs have prompted the state of California to hire people to skim dead fish off the surface.
The only movers and shakers left in this shrinking desert pool are hidden beneath it. Across the bottom of the lake are scars and cracks caused by the motion between two major faults — the San Andreas and San Jacinto. This motion accommodates 40 millimeters (1.6 inches) of slip between the Pacific and North American plates every year, making this region, known as the Salton Trough, one of the most tectonically active places in North America.
Such activity will manifest itself someday as the Big One, a spasm that will relieve stress on the San Andreas at the expense of some portion of Southern California. In fact, information being uncovered by scientists at Scripps Institution of Oceanography at UC San Diego suggests that this region of the San Andreas Fault system has a high probability for the Big One sooner rather than later. Earthquakes have recurred at the sea roughly every 200 years for the last thousand years, but it’s been 335 years since the last one.
Scripps geophysicist Graham Kent won’t say that the area is “overdue” for a seismic event. That would imply a certainty about earthquake behavior that scientists just don’t have.
“Imagine you’re 9 months pregnant,” Kent said by way of alternate explanation. “You’re somehow coming to the end of a process.”
Because of the Salton Sea’s potential to produce a major earthquake and its proximity to population centers, it has become the focus of intense study in the past year by a research team led by Kent and Scripps geologist Neal Driscoll. The team is using specialized sonar techniques to map the hidden fault lines beneath the lake floor.
In addition, they are digging trenches with colleagues at San Diego State University near Salt Creek to decipher the history of rupture exhibited in sediment layers. In addition, they are mapping topography at Mecca Hills with remote optical sensing equipment to measure the offset of gullies and streambeds to estimate the size, or horizontal displacement, of the past several large earthquakes. They are pinpointing how often seismic events have taken place throughout history, their horizontal displacement, and how the many lesser faults under the sea interact with the larger faults that bookend the region.
And now California legislators and the state Department of Water Resources are among the parties interested in what the researchers discover. With some urgency, they are looking for ways to save the sea (see sidebar) and need to know what are the likely seismic scenarios for earthquakes rupturing through the Salton Trough.
This water-starved, earthquake-prone region still needs the Salton Sea for several reasons, not the least among them being that the area is in the midst of a housing boom.
Longer Wait, Larger Quake?
The team, which also includes San Diego State geophysicist Gordon Seitz, who has researched seismic activity at the Salton Sea for several years, began the project’s first phase in 2004.
One of their initial findings had little to do with earthquakes: There were never hotel rooms available, because contractors erecting houses in a wave extending through nearby Indio always had them booked.
For the sake of efficiency, the researchers chose to live on a pontoon boat they had specially outfitted to accommodate their sonar CHIRP profiler. They would tow the CHIRP behind the boat through opaque waters in two- and three-day stretches, a practice known as capsuling. The CHIRP instrument created images of sediment layers beneath the seafloor that illuminated the location and size of otherwise invisible faults.
Seitz has already established some of the history of seismic activity in the Salton Trough. The area is an extensional basin that rests between two tectonic plates. Driscoll likens the movement there to the pulling apart of a Milky Way bar. One plate, the Pacific, moves northwest 50 millimeters (2 inches) a year as it pulls away from the North American plate.
Driscoll, Kent and Scripps graduate student Jeff Dingler added to the historical knowledge of quakes here during this project by estimating the size of the most recent seismic event. Using a technology called LIDAR (light detection and ranging) to measure deformation patterns in the hills overlooking the sea, they concluded that the quake from 335 years ago produced three meters (10 feet) of slip in one burst. Driscoll said that translates to an earthquake magnitude around 7.
The size of that quake gives scientists cause for concern. A magnitude 7 quake anywhere in Southern California is nearly guaranteed to do considerable property damage, but because the quiescent period between this last quake and today is longer than usual, the scientists fear that the extra time could mean an extra buildup of energy and an even larger quake when the energy is finally released.
The researchers are still analyzing the seismic CHIRP data collected from their fieldwork, which concluded early this summer. When done, they might be able to produce another key piece of information: what direction will the earthquake rupture travel when the next quake happens. The area has seen quakes on smaller faults trigger secondary quakes near the San Jacinto, most recently in a 1987 event known as the Elmore Ranch – Superstition Hills sequence.
The scientists hope to establish whether a similar event on the Extra Cross Fault in the Salton Sea will trigger an event along the southern San Andreas segment. In such a scenario, the earthquake rupture would radiate northward focusing more energy into the Los Angeles Basin than if it propagated in the opposite direction. If that happens, metropolitan Los Angeles could bear the worst of that energy.
Driscoll said the many implications of seismic activity at the Salton Sea argue for much more extensive study.
“Everyone wants to know how these faults link and communicate deformation,” said Driscoll. “What we’re seeing raises concern about the southern San Andreas Fault and future geohazards.”
Saving the Sea
In the 1950s and 1960s, the Salton Sea was a water recreation mecca, home to a thriving tourist industry and a holiday getaway for families and celebrities. But the former hotspots—at places with names such as “Bombay Beach” and “Desert Shores”—are now dilapidated and abandoned.
Scientists know that various bodies of water have existed at the current location of the Salton Sea for thousands of years. The existing lake, California’s largest at nearly 375 square miles, was created in 1905 when a poorly designed levee failed, sending the entire Colorado River to fill the Salton basin.
The sea became a thriving home to hundreds of bird and fish species and attracted a steady stream of wildlife seekers and recreational enthusiasts.
But in the second half of the century, the scene changed as a variety of problems emerged. Without a consistent water input, the lake began a losing battle with evaporation. The water supplied from the expansive adjacent agricultural industry contained high concentrations of fertilizers and salt.
Now public health officials fear that if the lake should dry out, contaminated dust kicked up from the lake’s former seafloor could create widespread respiratory illnesses and other health problems in the region.
“For decades the natural evaporation and the runoff of water from agriculture had been in balance, although the salinity and other chemicals increased in concentration over this time period,” said Scripps Institution of Oceanography geophysicist Graham Kent. “But the increasing appetite for water in the region has left the Salton Sea with an uncertain future and shrinking shorelines.”
While some say the lake should be left to run a natural course and dry out, there are many who believe the Salton Sea can be saved and returned to its former glory. The optimists envision a revitalized wetland haven that would preserve wildlife, attract new tourists, and lure business to the area.
Advocates, including California State Senator Denise Ducheny and state resources chief Mike Chrisman, are developing legislation that would launch a $9 billion restoration effort over 75 years. Through the California Resources Agency, Ducheny and Chrisman also have been supportive of Scripps research involving a new understanding of the geological makeup of the Salton Sea.
“There are multiple reasons for saving the Salton Sea, including its value as a resource to the region as a large wetland area,” said Ducheny. “Over 400 species of birds make their home there. If we were to allow it to disappear, there would be consequences in terms of air quality for the people of the Coachella and Imperial valleys, not to mention the fish and bird wildlife. We have a huge opportunity to save this beautiful sea in the middle of a desert and we’re working on a management plan that would do that.”
Neal Driscoll, a Scripps professor and the leader of the Salton Sea project, said he is impressed at the level of support and interest demonstrated by Ducheny and Chrisman in Scripps’ research.
Because the revitalization efforts will require new dikes, dams, or canals, Kent says it’s critical to develop a full geological profile of the region. The seismic maps Kent, Driscoll and their colleagues are producing will depict the faults underneath the lake, previously unknown data that will be critical to new construction efforts. They also will produce lake sediment profiles that could reveal where the deepest pockets of contaminated sediment may lie, vital details for determining which areas could be most at risk for airborne contaminants.
“In order to adequately proceed with designing a billion-dollar management system and fully understanding the risks and hazards involved, this information is essential,” said Kent.
--Mario C. Aguilera
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