If You're Going To Sink California, Do It Right

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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How It Began

One of the most popular catastrophes in recent decades was the one described by Curt Gentry in The Last Days of the Late, Great State of California, published in 1967. In this book a titanic series of earthquakes ruptured the entire length of the San Andreas Fault, resulting in catastrophic loss of life and the first magnitude 9 rating ever given an earthquake (on the Richter Scale as then defined-on the modified version now in use many large quakes have exceeded magnitude 9). South of Los Angeles, a hitherto-unknown fault branched off and curved out to sea just south of San Diego. A few days later the initial earthquake was dwarfed as all of coastal California west of the fault plunged beneath the waves. The book ended on an upbeat note (!) as new gold veins in the Sierra Nevada, freshly exposed by the quakes, lured thousands of immigrants daily in a modern Gold Rush. The California Dream lives on.

Although The Last Days of the Late, Great State of California was entirely a work of fiction, and the notion was probably around before Gentry's book, the phrase "California falling into the sea" has entered into American mythology, and the book was a major contributor to the myth. I have had many people ask me about the theory in absolute seriousness. When the book came out, I was majoring in geology at the University of California; it was truly a fun time to be a geology major. Californians had a ball with the idea. After the 1906 San Francisco Earthquake, Californians simply denied earthquakes for many years, (they referred to the "San Francisco Fire" instead - after all, you can put out a fire) but now a cavalier attitude toward seismic disaster is part of the laid-back California mystique. Columnist Art Hoppe of the San Francisco Chronicle (my nominee for most underrated newspaper humorist ever) described the opening of great fissures in the Sierra Nevada; then, as a Salvation Army band in Boise played Nearer My God to Thee, the rest of the United States slid majestically into the sea. Californians could now buy European cars at East Coast port-of-entry prices and, while the war in Vietnam continued, "it was now a fairer fight." The new President of the United States (State?) was--Ronald Reagan. 

The Doobie Brothers produced a record album entitled Living on the Fault Line whose cover depicted a San Francisco skyscraper, the TransAmerica Building, half-submerged in the ocean. The TransAmerica Building is actually on the mainland side of the San Andreas Fault. (The building was still new and hotly controversial when Gentry's book came out. A group of wealthy San Franciscans set up a charity pool. Contributors drew a number from 1 to 360. If the building fell, whoever had the compass bearing it fell would win the kitty.)

Geologic Reality

Earthquakes occur when rocks, stressed to the breaking point, rupture. Most of the world's earthquakes occur at the edges of the earth's crustal plates. The plates move a few inches per year and either pull apart, slide past one another, or collide. The Pacific Plate, which underlies most of the Pacific Ocean, is sliding parallel to the West Coast, carrying a sliver of California and all of Baja California northward at about three inches a year. Part of the boundary between the Pacific Plate and North America is the San Andreas Fault. Now we see the reason for Gentry's hitherto-unknown fault south of San Diego - he only wanted to sink California, not a large part of Mexico as well!

Magnitude (the Richter Scale) is a measure of energy release. Each unit of magnitude increase corresponds to roughly a 30-fold energy increase. Mathematically the Richter Scale can go arbitrarily high or low. It is perfectly possible to have negative magnitudes. A magnitude zero earthquake releases about as much energy as a stick of dynamite or dropping an average-sized car 30 feet. An average-sized man jumping off a stool a foot high generates a magnitude -2 earthquake when he hits the ground. Dropping a quarter from waist height is about equal to a magnitude -5 quake, and so on. It does not pay, except for specialized research, to try to record very tiny quakes because the instruments would be swamped by vibrations from storms, automobiles, footsteps, burrowing by earthworms, and so on. (One practical application of ultra-sensitive seismology is detecting tiny vibrations in mines and quarries that might signal an impending cave-in.) At the high end of the scale, there have been many quakes in the high eights but never a nine. If we plot the number of earthquakes in the world per year against magnitude, we get a very consistent relationship between frequency of occurrence and magnitude right up to the largest observed quakes. If nines and tens occur at all, we should have seen a few by now. It appears that the earth's crust cannot store up enough energy to produce extremely large quakes; nine seems to be about the practical upper limit to the Richter Scale.

It turns out that the original Richter Scale underestimates the energy released by the very greatest earthquakes. In the 1980's a modification called the seismic-moment magnitude scale came into use. On this scale, the very largest earthquakes do exceed Magnitude 9. But this revised scale wasn't in use when Gentry wrote his book.

The first quakes described in The Last Days of the Late Great State of California, rupturing the entire length of the San Andreas Fault, are conceivable. What about the second one? There's a major mechanical problem involved. Coastal California is supposed to drop several thousand feet; where does all the rock beneath California go? How do we make room for a gigantic block of crust to drop thousands of feet in only a few minutes? If the rock beneath the crust--the mantle--somehow moves out of the way we have to move many thousands of cubic miles of rock in a few minutes. How does it move so fast? Where does it go? We have evidence that movements of the plastic mantle drive the motion of the plates, but at a few inches a year. There is not the slightest evidence for movements of thousands of feet in a single spasm, now or in the geologic past. We can store up enough strain in the crust to produce a few feet of movement when the stress is relieved, but not enough for thousands of feet.

How To Do It Right (Or At Least Less Wrong)

NOTE: This scenario is an attempt to create a plausible outline for a script dealing with submerging the California coast. It's fiction, okay?

The TV movie 10.5 pictured a series of massive quakes as a series of deep faults ruptured in sequence. A scheme to lock the San Andreas Fault by melting rocks along the fault mostly worked, but the southernmost charge failed to lock one segment of the fault and a chunk of Southern California broke away to become an island.

The irritating thing about movies like 10.5 is that they almost go out of their way to be illiterate. I'm sure they had some scientist on hand to review some of their ideas (probably recognizable at meetings by the paper bag over his head), then they invented gibberish like "preactivity" and "lateral skips."

Nobody likes a critic who talks about what's wrong but won't say what's right. So what might a believable script be like, one that merely requires suspension of disbelief, not bludgeoning it into a coma? First, forget about sinking California. The San Andreas Fault slices diagonally from the Imperial Valley, up the Coast Ranges, then out to sea just south of San Francisco. It comes onshore again, clipping off Point Reyes, Bodega Head, and a sliver of coast from Fort Ross to Cape Mendocino. At Cape Mendocino it ends in a triple junction of the North American, Pacific, and Gorda Plates. So Los Angeles, San Diego and Monterey are on the Pacific side, but not San Francisco or the Golden Gate.

Also, not that many people live in the higher elevations of the Coast Ranges. So you don't have to submerge the Pacific sliver entirely, just drop it a thousand feet to flood the urban areas. Even so, that's hugely more than any known fault motion, and you still have the mechanical problem of displacing the crust under the coast.

Also, we need to do something about Baja California. At the south end the San Andreas Fault joins the East Pacific Rise. The segment in the Gulf of California consists of long faults connecting short segments of spreading center. This sort of thing is called a transtensional plate boundary. Mostly the plates are sliding past one another but with a small component of separation as well. Sinking Baja California will probably create an international incident as well as starting the Politically Correct types harping about racism. Curt Gentry solved this by invoking a hitherto unknown fault that sliced out to sea south of San Diego. Another possibility might be to have the crust flex downward, leaving Baja California unscathed.

If we can't simply drop coastal California downward, that leaves one possible direction: seaward. We'd need a nearly horizontal fault plane sloping from near the surface along the San Andreas Fault to the base of the continental slope. That's about 11,500 feet below sea level off California. At the widest, around Los Angeles, we're talking a 1% slope. And is there such a thing? Well, yes, there is. It's called a listric normal fault. A normal fault is a fault where one of the two opposing blocks drops down the fault plane so the overall length of the crust increases. As the amount of extension increases the fault plane curves to near horizontal. With a simple, steeply dipping fault plane you can get a measly few percent extension, but with a listric fault the extension can be almost unlimited. As the extension increases, a gap opens along the steep segment of the fault and the upper fault block sags into the gap. Also, friction will cause the upper fault block to break up internally along subsidiary faults.

So we'd need to postulate such a fault connecting to the San Andreas and dipping seaward. Rather than pull it out of thin air, we can have a geologic reason for it. Before there was a San Andreas, the whole West Coast was bordered by an oceanic trench like the one still off Mexico. The Coast Ranges are basically stuff scraped off the Pacific Plate onto North America. It's not hard to picture the whole complex being shoved upward along a gently dipping thrust fault, and what goes up can come down.

Of course, we need a reason for it to start sliding. We can picture the Pacific Plate starting to move more westerly than it now does and thereby relieving compressional stresses along the San Andreas Fault, enabling the block to begin slipping. Confined fluids are great for reducing friction along faults, and major thrust faults in the Coast Ranges are commonly associated with serpentine. Serpentine is a wonderfully slippery rock for fault zones.

Assuming the deep part of the fault has a 1% slope, then if the upper block slips 10 kilometers seaward, it will drop 100 meters. That will nicely submerge all the coastal cities. Given the way the upper block will sag and fragment internally as it pulls away from the steep segment of the fault, we can probably submerge San Bernardino (300 meters above sea level). The internal breakup of the block will thoroughly devastate the surface. The block will essentially be an extremely large landslide. It will be way bigger than anything known, but not impossible. It will be similar to, but far larger, than the big submarine landslides around the Hawaiian Islands. And the only thing we have to displace is sea water.

The tsunamis this thing creates will be something else. They will demolish the whole Pacific Rim and possibly cause damage in the Atlantic. They might well make two or three circuits of the earth before dying out. Even though the San Andreas Fault nicks the southern end of the San Joaquin Valley, there's enough high ground on the Pacific side of the fault to make a tsunami incursion at that end unlikely. But the Bay Area should be inundated, with enough water entering the Central Valley to cause widespread flooding. And hey, this is a movie.

Final Words

The above scenario is fiction, an attempt to create a reasonably scientifically literate scenario. There is no evidence for any undiscovered fault dipping seaward under Southern California.

You bloody well better believe this is copyrighted. My campus can use a major expansion of its library, some new buildings, and a bunch of endowed professorships if you want to make use of these ideas.

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Created 8 July 1998, Last Update 30 Aug 2011

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