One of the most popular catastrophes in recent decades was the one described by CurtGentry 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 AndreasFault, resulting in catastrophic loss of life and the first magnitude 9 rating ever givenan earthquake (on the Richter Scale as then defined-on the modified version now in usemany large quakes have exceeded magnitude 9). South of Los Angeles, a hitherto-unknownfault branched off and curved out to sea just south of San Diego. A few days later theinitial earthquake was dwarfed as all of coastal California west of the fault plungedbeneath the waves. The book ended on an upbeat note (!) as new gold veins in the SierraNevada, freshly exposed by the quakes, lured thousands of immigrants daily in a modernGold Rush. The California Dream lives on.
Although The Last Days of the Late, Great State of California was entirely awork 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 thebook was a major contributor to the myth. I have had many people ask me about the theoryin absolute seriousness. When the book came out, I was majoring in geology at theUniversity of California; it was truly a fun time to be a geology major. Californians hada ball with the idea. After the 1906 San Francisco Earthquake, Californians simply deniedearthquakes 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 ispart of the laid-back California mystique. Columnist Art Hoppe of the San FranciscoChronicle (my nominee for most underrated newspaper humorist ever) described the opening of great fissures in the Sierra Nevada; then, as aSalvation Army band in Boise played Nearer My God to Thee, the rest of the United Statesslid majestically into the sea. Californians could now buy European cars at East Coastport-of-entry prices and, while the war in Vietnam continued, "it was now a fairerfight." The new President of the United States (State?) was--Ronald Reagan.
TheDoobie Brothers produced a record album entitled Living on the Fault Line whosecover depicted a San Francisco skyscraper, the TransAmerica Building, half-submerged inthe ocean. The TransAmerica Building is actually on the mainland side of the SanAndreas Fault. (The building was still new and hotly controversial when Gentry'sbook 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 thecompass bearing it fell would win the kitty.)
Earthquakes occur when rocks, stressed to the breaking point, rupture. Most of theworld's earthquakes occur at the edges of the earth's crustal plates. The plates move afew inches per year and either pull apart, slide past one another, or collide. The PacificPlate, 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 inchesa year. Part of the boundary between the Pacific Plate and North America is the SanAndreas Fault. Now we see the reason for Gentry's hitherto-unknown fault south of SanDiego - 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 magnitudeincrease corresponds to roughly a 30-fold energy increase. Mathematically the RichterScale can go arbitrarily high or low. It is perfectly possible to have negativemagnitudes. A magnitude zero earthquake releases about as much energy as a stick of dynamite or dropping anaverage-sized car 30 feet. An average-sized man jumping off a stool a foot high generatesa magnitude -2 earthquake when he hits the ground. Dropping a quarter from waist height isabout equal to a magnitude -5 quake, and so on. It does not pay, except for specializedresearch, to try to record very tiny quakes because the instruments would be swamped byvibrations from storms, automobiles, footsteps, burrowing by earthworms, and so on. (Onepractical application of ultra-sensitive seismology is detecting tiny vibrations in minesand quarries that might signal an impending cave-in.) At the high end of the scale, therehave been many quakes in the high eights but never a nine. If we plot the number ofearthquakes in the world per year against magnitude, we get a very consistent relationshipbetween frequency of occurrence and magnitude right up to the largest observed quakes. Ifnines and tens occur at all, we should have seen a few by now. It appears that the earth'scrust cannot store up enough energy to produce extremely large quakes; nine seems to beabout the practical upper limit to the Richter Scale.
It turns out that the original Richter Scale underestimates the energy released by thevery greatest earthquakes. In the 1980's a modification called the seismic-momentmagnitude scale came into use. On this scale, the very largest earthquakes do exceedMagnitude 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 thesecond one? There's a major mechanical problem involved. Coastal California is supposed todrop several thousand feet; where does all the rock beneath California go? How dowe make room for a gigantic block of crust to drop thousands of feet in only a fewminutes? If the rock beneath the crust--the mantle--somehow moves out of the way we haveto 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 motionof the plates, but at a few inches a year. There is not the slightest evidence formovements of thousands of feet in a single spasm, now or in the geologic past. We canstore up enough strain in the crust to produce a few feet of movement when the stress isrelieved, but not enough for thousands of feet.
NOTE: This scenario is an attempt to create a plausible outline for ascript dealing with submerging the California coast. It's fiction, okay?
The TV movie 10.5 pictured a series ofmassive quakes as a series of deep faults ruptured in sequence. A scheme to lockthe San Andreas Fault by melting rocks along the fault mostly worked, but thesouthernmost charge failed to lock one segment of the fault and a chunk ofSouthern California broke away to become an island.
The irritating thing about movies like 10.5 is that they almost go outof their way to be illiterate. I'm sure they had some scientist on hand toreview some of their ideas (probably recognizable at meetings by the paper bagover 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'sright. So what might a believable script be like, one that merely requiressuspension of disbelief, not bludgeoning it into a coma? First, forget aboutsinking California. The San Andreas Fault slices diagonally from theImperial Valley, up the Coast Ranges, then out to sea just south of SanFrancisco. It comes onshore again, clipping off Point Reyes, Bodega Head, and asliver of coast from Fort Ross to Cape Mendocino. At Cape Mendocino it ends in atriple junction of the North American, Pacific, and Gorda Plates. So LosAngeles, San Diego and Monterey are on the Pacific side, but not San Franciscoor 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 athousand feet to flood the urban areas. Even so, that's hugely more than anyknown fault motion, and you still have the mechanical problem of displacing thecrust under the coast.
Also, we need to do something about Baja California. At the south end the SanAndreas Fault joins the East Pacific Rise. The segment in the Gulf of Californiaconsists of long faults connecting short segments of spreading center. This sortof thing is called a transtensional plate boundary. Mostly the plates aresliding past one another but with a small component of separation as well.Sinking Baja California will probably create an international incident as wellas starting the Politically Correct types harping about racism. Curt Gentrysolved this by invoking a hitherto unknown fault that sliced out to sea south ofSan Diego. Another possibility might be to have the crust flex downward, leavingBaja California unscathed.
If we can't simply drop coastal California downward, that leaves one possibledirection: seaward. We'd need a nearly horizontal fault plane slopingfrom near the surface along the San Andreas Fault to the base of the continentalslope. 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 afault where one of the two opposing blocks drops down the fault plane so theoverall length of the crust increases. As the amount of extension increases thefault plane curves to near horizontal. With a simple, steeply dipping faultplane you can get a measly few percent extension, but with a listric fault theextension can be almost unlimited. As the extension increases, a gap opens alongthe 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 alongsubsidiary faults.
So we'd need to postulate such a fault connecting to the San Andreas anddipping seaward. Rather than pull it out of thin air, we can have a geologicreason for it. Before there was a San Andreas, the whole West Coast was borderedby an oceanic trench like the one still off Mexico. The Coast Ranges arebasically stuff scraped off the Pacific Plate onto North America. It's not hardto picture the whole complex being shoved upward along a gently dipping thrustfault, and what goes up can come down.
Of course, we need a reason for it to start sliding. We can picture thePacific Plate starting to move more westerly than it now does and therebyrelieving compressional stresses along the San Andreas Fault, enabling the blockto begin slipping. Confined fluids are great for reducing friction along faults,and major thrust faults in the Coast Ranges are commonly associated withserpentine. Serpentine is a wonderfully slippery rock for fault zones.
Assuming the deep part of the fault has a 1% slope, then if the upper blockslips 10 kilometers seaward, it will drop 100 meters. That will nicely submergeall the coastal cities. Given the way the upper block will sag and fragmentinternally as it pulls away from the steep segment of the fault, we can probablysubmerge San Bernardino (300 meters above sea level). The internal breakup ofthe block will thoroughly devastate the surface. The block will essentially bean extremely large landslide. It will be way bigger than anything known, but notimpossible. It will be similar to, but far larger, than the big submarinelandslides around the Hawaiian Islands. And the only thing we have to displaceis sea water.
The tsunamis this thing creates will be something else. They will demolishthe whole Pacific Rim and possibly cause damage in the Atlantic. They might wellmake two or three circuits of the earth before dying out. Even though the SanAndreas Fault nicks the southern end of the San Joaquin Valley, there's enoughhigh ground on the Pacific side of the fault to make a tsunami incursion at thatend unlikely. But the Bay Area should be inundated, with enough water enteringthe Central Valley to cause widespread flooding. And hey, this is a movie.
The above scenario is fiction, an attempt to create a reasonablyscientifically literate scenario. There is no evidence for any undiscoveredfault dipping seaward under Southern California.
You bloody well better believe this is copyrighted. My campus can use a majorexpansion of its library, some new buildings, and a bunch of endowedprofessorships if you want to make use of these ideas.
Created 8 July 1998, Last Update 15 Jan 2020
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