You probably already know this. One hundred years ago, on April 18, at 5:12 in the morning, San Francisco and the rest of the Bay Area were very rudely awakened by an enormous earthquake. Richter scale 7.9, that's the rough estimate. It grabbed the City by the Bay, along with San Jose, San Rafael, Sebastopol, Santa Rosa and a bunch of other horse-and-buggy towns, and collectively shook them all like a great big clothesline full of old, wet rags. The quake knocked San Francisco off its pre-building-code pedestal and sparked a fiery maelstrom that killed scores of city dwellers and destroyed more than 28,000 buildings.

It hit Santa Rosa the hardest, destroying every brick building in town, leveling the business district for blocks and blocks. Like San Francisco, fire broke out instantly and burned down a swathe of those structures not already destroyed by the initial tremor. It was the largest earthquake in California's recorded history, and when the dust settled, after the fires had finally been put out, more than 600 people were dead on both sides of the Golden Gate, the ground spectacularly ruptured up and down the Northern end of the state.

Immediately, almost as soon as the shaking stopped, people began asking questions: "Why did this happen? What caused the earthquake? How can we protect ourselves from future earthquakes?"

It has become an annual California custom every April 18 and in the days and weeks leading up to the anniversary of the quake to ask such questions. Each year, as people gather to commemorate the moment that the earth shook in Northern California, and to honor the heroes who put out the fires and banded together to pull strangers from the rubble, newspapers, radio shows and television specials explore the same ground and ask the same trillion-dollar question: "When is the next big earthquake going to strike?"

Contrary to some people's belief, the Loma Prieta quake of 1989 was not the Big One. The 1906 quake was eight times stronger than Loma Prieta, which in comparison was a mere roller coaster ride.

Now the Great Earthquake of 1906 is about to celebrate another anniversary, the big one-zero-zero. California's most infamous natural disaster has returned to the spotlight in a large way, basking in the glow of geological notoriety as it is ceremoniously awarded one more opportunity to shake us up all over again. The earthquake--long the focus of books, movies, television shows, interactive ground-shaking county fair attractions, and illuminating scientific experiments featuring simulated earthquake shocks like those of the original--is about to be commemorated up and down the state of California with ceremonies, memorials, candlelight vigils, museum exhibits, lectures, power point presentations, dance recitals, sock-puppet extravaganzas and who knows what else.

Along with the usual questions, the usual recitations of the names of victims, the usual telling of stories about firemen hauling children from burning buildings and hard-drinking dance-hall owners searching the early-morning rubble for survivors, a large number of California geologists are hoping that 2006 will be the year to honor a man whose actions in the wake of the quake are rarely discussed. He is Andrew C. Lawson, a geology professor at UC Berkeley, who, in 1906, was the first person to take action to try and find answers to the questions everyone was asking.

"It's a fascinating story," says Thomas Anderson, a professor of geology at Sonoma State University. "What Lawson did in 1906 is, for geologists and people who know about it, the stuff of legend. It's a lot more interesting than all the same questions I get every year about predicting earthquakes."

Rock Hounds and Sky Watchers

In the early part of the century, geologists knew very little about earthquakes and the mechanisms that caused them. Seismology was a relatively new science, and there had been scant first-hand research done in the wake of a large earthquake.

On April 18, 1906, immediately after the earthquake, Lawson formally challenged California governor George C. Pardee to set up a commission for the purpose of mapping the entire length of the earthquake rupture and collecting observations and evidence that could significantly expand the public and scientific understanding of earthquakes. Three days later, on April 21, 2006, the governor established the Earthquake Investigation Commission and appointed Lawson as its head, charging him with conducting an exhaustive scientific investigation of the earthquake.

Lawson pulled together a crack team of eight, featuring some leading geologists, engineers and astronomers of the time, including the directors of the Chabot and Lick observatories. Of the eight, only two had experience studying earthquakes, Lawson not among them. The governor had provided no money to fund the new mandate. Lawson and his team took on the job, anyway. They worked for free.

The initial ground work done by Lawson and his horse-riding, sketch-pad-carrying (pistol-packing? probably!) scientists was as crammed with derring-do and danger as any adventure novel. There were few roads in California at the time, and the wilderness was still a dangerous place, the habitat of perils natural and criminal. On horseback, in small groups and sometimes solo, the men worked their way up and down the San Andreas Fault, which they could identify by tracing the spots where the earthquake had ruptured the ground.

They camped out along the rift, sketching and collecting samples, facts, figures, anecdotal stories and detailed measurements. They collected an immense amount of data, eventually mapping nearly 300 miles of ruptured fault line. It took them a solid year to complete their research, and another year to put it together in book form. The result was The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission, known to most geologists simply as the "Lawson Report."

"I've got that volume sitting right here on my desk," says Anderson. "Most of what we do know about earthquake science today really started with the work that Andrew Lawson did after the 1906 earthquake."

"It's an incredible study," agrees Mary Lou Zoback, a senior research scientist at the U.S. Geological Survey in Menlo Park. "Whenever we talk about earthquakes today, we're still drawing from that report." In fact, Lawson gave the fault its name in 1895, in honor of San Andreas Lake, now one of San Francisco's primary water sources.

Zoback has been capitalizing on the interest surrounding the 1906 centennial to call attention to the little-known fact that the 1906 quake was the birth of modern earthquake science. "It was such an important and interesting project," she says. "You have to understand how exciting this was at the time. No one had ever had the opportunity to do this kind of research [so soon after an earthquake]. I don't think you could have kept the interested scientists away from it. The fact that there was no money and that most of them were working without pay for a while didn't seem to bother them at all."

Scum of the Earth

Remember, this was pre-Richter scale. Effective measurement of earthquakes was nonexistent, and people still held a lot of simplistic ideas about what caused quakes, believing in everything from the pull of the tides to the manic-depressive temperament of a heavenly creator.

As the adventurer-scientists spread out, working up and down the fault, the team began to piece together some previously unknown facts: They confirmed, for instance, that the San Andreas was a major active fault, recognizing that it was part of the same fault that ran through parts of Southern California, making it the longest fault in California. They proved that the 1906 quake wasn't a random event, but part of a recurring process. They eventually discovered that along the fault zone, the ground seemed to be moving very slowly in horizontally opposite directions, with the fault more or less in the middle. Using a marker on one side of the fault and another planted on the other side, they could measure the slow movement of the ground.

At that time, the notion of plate tectonics was unheard of, and only decades later would it be shown that what Lawson and his team had discovered was evidence of two massive earth plates moving past each other. The data that the commission provided eventually supported the notion that earthquakes happen when seismic energy, stored in a fault that is under pressure, is suddenly released.

"We call it the elastic rebound hypothesis," explains Zoback. Imagine a sheet of thick rubber on a table in front of you, with both of your hands palm down on it. Now imagine using your left hand to push the rubber sheet away from you while your right hand is pulling it toward you. There will be a point in between where the rubber begins to experience stress, stretching and building pressure until the sheet rips and the pressure is released. That point in between is the fault zone.

"The forces of loading here in California are plate motion," Zoback says. "It's going on all the time, and it's driven by the internal heat of the earth. What it's doing is causing the outermost scum of the earth, if you will, which is where we live--a scum that is cold and hard and moves around driven by convection bubbling from underneath--to behave elastically."

If California is that thick sheet of rubber, with the two sides moving horizontally past one another, at some point it's going to exceed the strain of the fault, which becomes locked up between earthquakes, and when it reaches a certain point, all the energy that has been put into the fault by the two plates moving past one another is suddenly released as seismic energy.

Boom. Ladies and gentlemen, say hello to an earthquake.

Lawson didn't fully understand all of this at that point, but the evidence he published has been used over and over, combined with more recent discoveries, to build a picture of what happens before, during and after a quake. One thing is certain. The "locking up" is a major part of the process that produces the earthquakes; faults that are not locked do not produce major quakes.

The San Andreas Fault has been completely locked since 1906.

Not If, but When

Since the underlying question as we approach the 1906 centennial is "When's the next one?" a person has to wonder: Did the work Lawson move us any closer to being able to predict when an earthquake will take place?

A little bit. The best a scientist can do is to calculate the probability of a quake occurring within a certain time frame. Those probabilities, in large part, come from noting when earthquakes have taken place in the past along a certain part of a particular fault and determining the average number of years between quakes in that area, and then waiting to see how close the next quake is to the average. This requires significant historical knowledge of a fault's earthquake history, and in the end, is a little like predicting what kind of pitch a baseball player is going to throw at the bottom of the ninth based on which pitches he threw in that situation in his last two or three games.

Asked how possible it is to predict an earthquake with any accuracy today, 10 decades after the 1906 quake, Thomas Anderson has a succinct answer.

"Not," he says. "Geographically, it's possible to predict more or less where an earthquake is likely to occur, but temporally, it's just not possible to say when an earthquake will happen."

Not that people don't try.

Over the last several months, plenty of maverick quake "experts" have cropped up on television and in the papers, espousing alternative methods of quake prediction and claiming to have predicted various earthquakes in the past. Anderson remains skeptical.

"When they start predicting 'em before they happen, when they establish a success rate, then I'll put more credence in those people," he says. "Right now, all of these people just wait till an earthquake happens and then they say they knew it was coming. The bottom line is, nobody can predict the occurrence of an earthquake with any accuracy. Not yet, anyway."

Not yet. Then does Anderson believe that accurate advance earthquake prediction will be possible in the future?

"Some day, sure, it could probably happen," he says. "Of course, I am the eternal optimist."

Everybody's Fault

As we stand at the brink of the earthquake centennial, with all of its attendant fresh interest in earthquakes, geology and seismology, Zoback hopes that some of the heightened attention will result in a better public understanding of science and the mysterious ways of earth. She recognizes, however, that some people are likely to become alarmed and anxious by all of this earthquake talk. Zoback suggests that that might not be a completely bad thing. After all, in order to adequately prepare for the Big One--and Zoback and her colleagues are certain that it is coming--people need to really believe that something like 1906 could happen again.

But where? Anderson points out that it's easier to predict where the next quake will happen than it is to predict when. With seven major fault zones, can modern science tell us which of the North Bay's faults can be expected to hand us an earthquake in the future?

"All of them," Zoback says. "Eventually, all of them will have strong earthquakes, so there is essentially no safe place, in terms of avoiding the shaking. You might think, 'Well, I don't live anywhere near the Hayward Fault,' but I guarantee, in this area, you live near enough to some fault to potentially experience the effects of an earthquake, should the next one occur along that fault."

Preparation, ultimately, is the best way that Californians could choose to honor the centennial of the 1906 earthquake. According to Zoback, Hurricane Katrina demonstrated that it is not wise to rely on the government to have made the proper preparations for a major emergency. We must prepare for a disaster on our own, and we can do that by asking all the questions right now.

"Ask your landlord when your building was built, whether it was retrofitted, and make them show you what was done," she says. "We can either choose to ignore this and not ask the questions, or wait to be outraged when an earthquake happens and the hospital collapses and our house falls over. There's a lot we should be asking, and once we do have the answers, we all need to work together to figure out how we're going to address the vulnerabilities we've uncovered.

"It's important for us to educate people and to talk about these things," she concludes. "I hope we can do that without terrifying people, but the images from Katrina are burned into all of our minds. We do have to be self-reliant, because there are more people in the Bay Area now than in 1906. There are more buildings and roads and bridges.

"When the next huge earthquake happens in the Bay Area, it won't just be a disaster. It will be a catastrophe."

Various and many North Bay events mark the centenary of the 1906 earthquake. At Copperfield's Books on Wednesday, April 5, Cal Orey and Jim Berkland present a reading and discussion of 'The Man Who Predicts Earthquakes.' Also at Copperfield's on Tuesday, April 11, is Richard Schwartz with 'Earthquake Exodus, 1906.' 2316 Montgomery Drive, Santa Rosa. Both free events are at 7pm. 707.578.8938. The American Red Cross and the city of Santa Rosa sponsor a 'Be a Survivor' event reenacting the events of April 18, during which some 119 residents perished, in downtown Santa Rosa at 5:18am. Volunteers are still needed. For details, call 707.569.87856, ext. 29. The Sonoma County Museum launches its 'Force of Nature' centennial exhibition on Saturday, April 22, as an interdisciplinary look at history, the natural world and the fine arts. 425 Seventh St., Santa Rosa. 707.579.1500.

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