^{The carbonate crust called tufa coats a high boulder over the Salton Sea, testifying that the Colorado River fed mighty Lake Cahuilla there in the geologically recent past. Photo by Andrew Alden.}

Geologic research is a remote and dusty undertaking that can look tedious to most people. But if it bears on subjects we fear, like earthquakes, even painstaking background projects can be blown out of proportion. A recent example from Southern California went from an intriguing journal article to "we're all gonna die" TV stories in the space of a day. Maybe it will help you spot the next time this happens in the Bay Area.

The article, published in the prestigious Nature Geoscience on June 26, presented the fruits of years of heat and tedium on the foul waters of the Salton Sea, in southernmost California. The Salton Sea occupies a sinking basin, the Salton Trough, that would rather be part of the Sea of Cortez except that the Colorado River has built a delta that dams it dry. As the river wanders over its delta, draining sometimes south and sometimes north, it periodically creates a geologically temporary lake in the Salton basin that has filled and dried out many times in the last few million years. (A short video by the University of Redlands illustrates the process.)

The repeating lake is known as Lake Cahuilla, and the Salton Sea is today's version of it. The Salton Sea is actually a terrible blunder, formed in 1905 when an irrigation canal tapping the Colorado River burst its banks and flooded a huge area of farmland in the dry bed of Lake Cahuilla. The breach was eventually fixed before the reborn lake could drown everything from Mexicali to Indio, but floods continued to be a problem until Hoover Dam was built upstream 30 years later.

The Salton Sea covers up the southern end of the San Andreas fault, and that's where our science story begins. A research team from Scripps Institution of Oceanography crisscrossed the drowned land in a small boat with a state-of-the-art CHIRP sonar system. They mapped a swarm of short faults running from the end of the San Andreas toward the end of the Imperial fault lying to the south—a tectonic configuration called a stepover. Here's the figure showing how it all fits together.

_{Tectonic setting of the Salton Trough and Salton Sea. SJF is San Jacinto fault, SSAF is southern San Andreas fault and IF is Imperial fault. Green grid is ship tracks in the dashed box; awz (acoustic wipeout zone) marks disturbed sediments. (Scripps)}

From their sonar database the researchers extracted a decent record of recent ruptures on some of these stepover faults. My figure below shows, schematically, how the sediment record is built as downdrops on the fault combine with sediment being deposited on top.

The researchers ran this process backward to reconstruct the history of faulting for a few thousand years into the past.

What made things interesting was how this record of stepover quakes meshed with records of lake floods and San Andreas mega-quakes. The correlation is imperfect, but intriguing: every time the lake was reborn in a flood, the stepover faults gave way, and half of the recent mega-quakes coincided with stepover quakes. To connect the dots further, the researchers said that "at least one of the last three dry-basin floods coincides with an earthquake on the SSAF (southern San Andreas fault)." In their cautious words, "We propose that loading by (Lake Cahuilla) may have induced failure on faults beneath the Salton Sea that, in turn, has the potential to trigger an earthquake rupture on the SSAF."

That's all ingenious science (seismic oceanography, in the desert!), but not news. To get news takes a press officer with a nose for a hook, and the hook is that the SSAF hasn't broken in some 300 years when we might (given the recent record) expect it to happen more often. Has our failure to let Lake Cahuilla be reborn held off triggering the next Big One? Well, has it??

That question is something for geologists to wave their arms about at meetings and parties, not hold out to the world as a sure thing. But between the paper, whose abstract is world-readable, and the press release from Scripps we can see the story begin to morph. It's a scattershot press release, meant to serve any news angle, that immediately confuses today's managed Salton Sea with wild prehistoric Lake Cahuilla. It includes a great hook, a quote about the "overdue" SSAF likening it to "a woman who is 15 months pregnant." The quote is only part of the background to the science, just a tangential part of the paper itself, but irresistible to the troutlike mind of the news reporter.

First out the chute on June 26 was the San Diego Union-Tribune's website, where Gary Robbins immediately removed all scientific uncertainty in his first sentence: "The Salton Sea east of San Diego is a deceptively dangerous backwater, hiding faults that repeatedly produce powerful earthquakes that jolt all of Southern California, says a new study by the Scripps Institution of Oceanography."

Later that day a Los Angeles TV station rewrote Robbins's story under the headline "Mega Quake Around the Corner?" with the lead sentence, "Man's interference with Colorado River floods that used to regularly flow to the Salton Sea may have 'stopped the clock' on a regular series of big earthquakes, setting the stage for a mega quake that could wreck Southern California, scientists said Sunday." The accidental flood of 1905 has become "interference" with regular flows to the Salton Sea, and the reasoning has turned upside-down: If we had let the Imperial Valley drown, Southern California's "Big One" might already have happened and been a few tenths of a magnitude unit smaller. How anyone wins under that scenario is not explained.

After a few days, more and better journalists weighed in. Some of them had actually studied the Nature paper (as I have). Many, including Discovery News's Tim Wall, apparently did not. USA Today's Dan Vergano did well. So did Chris Clarke on KCET's website. Charles Q. Choi did fresh reporting, as usual, for OurAmazingPlanet.com. Science News's Devin Powell wins my prize for his succinct, factual and well-written account. As you peruse the items collected by Google News under a search on "salton earthquake," look for those items that get the details right—specifically the fact that the Salton Sea arose by mismanagement, not on purpose.

The Bay Area has excellent media when it comes to our own earthquakes, with seasoned staff and good support from academic and government experts. But still—if scary news comes up, look around the science mediasphere and wait a few days before deciding what you think. Even better, track down the news at its source whenever you can. Learn who to trust.

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Topographic image of the Bay Area and continental shelf and slope. The coastline during the peak of the last ice age was at the shelf edge near the Farrallon Islands.

Before reading this post, make sure to check out QUEST’s video segment from last week about sea-level rise in the San Francisco Bay, which provides a nice overview of the problem low-lying areas in the greater Bay Area will face in the coming decades. As good as it is, the QUEST piece is really just an introduction to the problem of current sea-level rise. Sea-level rise is happening and more than 100 million people could be affected globally over the next century even under somewhat conservative projections. This is an tremendously complex problem that will require research across numerous scientific disciplines and creative problem-solving from engineers and urban planners. Like many of the posts I write for QUEST, I’d like to zoom out in terms of the timescales we are used to thinking about and share a little information about geologically recent sea-level changes in the Bay Area.

Over the past few million years, the Earth has flipped back and forth about 20 times between periods of significant continental glaciation, or ice ages, and briefer periods of much less ice. The peak of the most recent ice age was approximately 18,000 years ago. During this time, referred to as the Last Glacial Maximum by Earth scientists, the continental ice sheets that covered much of northern North America and northern Europe reached their largest extent in area. When such vast continental ice sheets grow they “borrow” water from the Earth’s water budget and, as a result, global sea level is lowered. Only 18,000 years ago sea level was 120 meters (400 ft) lower than it is at present.

The map above is a simple sketch map of the paleogeography of the Bay Area at this time*. Think about this for a moment — if you were standing at Land’s End Park on the northwest corner of San Francisco you would not be at the land’s end! The coast would be about 20 miles offshore of the current coast, just beyond the uplands that are now poking out as the Farallon Islands. What is now the Bay was a network of flat valleys with the ancestral Sacramento-San Joaquin River and tributary streams making their way through the narrow notch in the hills at Golden Gate. As temperatures warmed and the continental ice sheets began to melt sea level started to rise. That’s a simplified picture of what the landscape may have looked like at different stands of sea level, but what about the rate at which the sea rose?

The Pacific Institute, a nonprofit research institute based in Oakland, published a thoroughly researched and very readable report on sea-level rise and its impact on the California coast, which is also featured in the QUEST report. Estimates of future sea-level rise as stated in their report are between 1.0 and 1.4 meters (40-55 inches) by the year 2100. To be conservative (and to simplify a bit) let’s assume this present rate of sea-level rise is 1 meter per 100 years. If we now look at a reconstruction of sea-level changes since the Last Glacial Maximum we see the rise in sea level was not constant — depending on the rate of warming along with other factors the rate of rise varied. As you can see in the graph below the rate of rise slowed significantly about 8,000 years ago. From 18,000 years ago to 8,000 years ago sea-level rose approximately 100 meters (330 ft), which is an average rate of 1 meter per 100 years. In other words, the Earth will soon be experiencing a rate of sea-level rise it hasn’t experienced in several thousand years.

The most important uncertainties regarding our understanding of current and near-term sea-level rise are magnitude and rate — that is, how much and how fast. By studying the relatively recent past (geologically speaking) we can learn something about the effects varying rates of sea-level rise might have on the Bay Area. For example, how did bayshore ecosystems respond to rapid sea-level rise thousands of years ago? How will tidal marsh ecosystems respond to slow versus rapid sea-level change? The map below from the San Francisco Estuary Institute shows the different types low-lying bay shoreline that will be affected by future sea-level rise.

These environments, some of which are entirely human-made, will respond differently to sea-level rise. Further study of past environments and ecosystems and how they were affected by sea-level rise since the last ice age will play an important role in the broader goal to mitigate the consequences of a rising San Francisco Bay.

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UPDATE (9/2/2010):

Also check out this great video piece from QUEST a couple years ago to help you visualize what the Bay Area landscape was like 20,000 years ago and the kinds of animals that lived here. Definitely worth a look.

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* Check out this fantastic slide show from UC Berkeley Earth scientist Lynn Ingram here (link opens a PDF). This is  a great resource for learning more about the information scientists are collecting from the Bay’s sedimentary record to answer some of the questions I pose above.

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From left to right: Associate Producer, Joan Johnson, Sylvia Earle and Producer, Amy Miller

A turning point in her career came in 1970 when she led a team of woman Aquanauts in a two week research expedition in an underwater lab called Tektite. When the women emerged from their decompression chamber after living underwater for two weeks, the world embraced them as heroes. She was thrust into a spotlight as an ocean expert and pioneer of saturation diving and underwater research. Since then, she has continued to travel the globe and speak passionately and persuasively on ocean conservation.

We were thrilled to have a chance to meet Dr. Sylvia Earle and profile her on QUEST. Joan Johnson, the Associate Producer of the segment, was especially excited: Dr. Earle has been one of her idols since her former life as a marine biologist. Although I was also a burgeoning biologist at one point in my life, I had not heard of Dr. Earle until a couple of years ago when we featured her former husband and design partner, Graham Hawkes, in a earlier QUEST episode. We've wanted to feature her since then but she’s incredibly busy, traveling and speaking about ocean issues most of the year. In the two month window in which we wanted to film her, she was going to be on the road (in the air, under the water) no less than 50 days, with trips to Monaco, Rome, Mexico and the South Pacific.

Although I had envisioned a story where we actually get to know her, meet her family, spend time with her at her home in Oakland, cooking, playing with her dog on the beach; you know, find out what makes her "tick," I had to make due with three hours total in our KQED studio. So, Joan and I had to be VERY creative when figuring out the content of our story. Put another way, the only material that we shot of Sylvia Earle ourselves was a 2 hours interview. All the other footage in the story had to be researched, located, acquired and paid for. Thankfully, Sylvia Earle's life has been pretty well-documented in film and photography. But I know that if not for Joan's incredible resourcefulness and passion for the subject, this story would not have been possible. I had the easy part of the job: having a long conversation with an INCREDIBLE woman then writing about it. And I now have a new hero as well.

Watch the Profile: Sylvia Earle television story online.

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