Earthquake Storms

by John Dvorak

  Lawson was struck by the sameness of the reports. Dislocated fences, roads, railway bridges, tunnels, dams, and pipes were found from Point Arena on the coast north of San Francisco to the Spanish mission at San Juan Bautista east of Monterey Bay, a distance of 190 miles. Moreover, every dislocation was in the same direction—an offset to the right—though the amounts of offset varied from a maximum of 20 feet near the Skinner ranch in Bear Valley to lesser amounts to the north and the south.

  And because buildings in the remote community of Petrolia, sited in the redwoods a few miles south of Eureka in Humboldt County and lying along a projection of the rupture northward from Point Arena, were severely damaged, Lawson suggested the total length of the rupture was probably 270 miles—a speculation that would be confirmed decades later.

  To put this in perspective, though dozens of earthquakes since 1906 have released more energy and have caused more seismic damage than the San Francisco earthquake, none have produced a longer line of surface rupture. In 1939, an earthquake in eastern Turkey approached that distance when the ground broke for almost 200 miles. Four years later, again in Turkey, another broke the ground a similar distance. Not until 2001 did an earthquake produce a surface rupture comparable in length to that in 1906: the Kokoxili earthquake along the Kunlun Fault in western China and northern Tibet, which created a line of surface rupture 240 miles long.

  Lawson also took particular pleasure in noting the location of the rupture. Gilbert had traced it as a straight line through Bear Valley as far south as the sandy spit at Bolinas Lagoon, where it disappeared under the sea. Others found that it reappeared on land near Mussel Rock. From there, the rupture ran for several miles, as a mole track, through the line of small ponds found by Palache and Lawson a decade earlier and continued along the San Andreas Valley. And so the conclusion was inescapable: The fault Lawson had discovered in 1892 and declared active had slipped and slid during the 1906 earthquake.

  Moreover, he now realized that what had ruptured in 1906 was only a segment of a much longer feature, one that he and his former student Fairbanks had followed across southern California just months before the earthquake. As Lawson took out his maps, he must have been amazed: Cutting obliquely across the entire length of the Coast Ranges and continuing across southern California from Humboldt County to the Salton Basin in the Colorado Desert, a distance of more than 800 miles, was a single geologic feature—the longest one known at the time—the San Andreas Fault.

  Two months after the earthquake, the other committee, comprised of the two astronomers Leuschner and Burkhalter and charged with compiling and analyzing all information related to the time of passage of the earthquake wave across California, had made little progress, so Lawson gave their task to someone else who was added to the commission: Harry Fielding Reid of Johns Hopkins University in Baltimore.*

  At first glance, Reid seemed to be an odd choice. He was from the East Coast and as far as can be determined had never been to California. He was an expert on glaciers, having done fieldwork in the Swiss Alps and in Alaska, but did have a minor association with earthquakes. Since 1902 he had been hired by the United States Weather Bureau to examine seismographs collected at a handful of weather stations, of which one was at Johns Hopkins. For that work, to cover his salary and his expenses, Reid was paid $100 a year, an indication of how minor this work was perceived to be.

  Reid arrived in California in late June and began to sift through the scores of timing reports, mainly of pendulum clocks stopped by earthquake shaking, finding that the vast majority were known to an accuracy of a minute or so. Because of the great speed of the wave, in order to calculate the earthquake’s place of origin, Reid knew he needed the time of passage to be within one or two seconds in order to compute where the most violent shaking had originated. By that requirement, only four records qualified: one maintained by the time inspector of the North Shore Railroad in San Rafael, located 20 miles north of San Francisco, and those of the standard clock used at the Navy Yard at Mare Island to set ship chronometers, located near the north edge of the bay, and two clocks at astronomical observatories, one at the Students’ Observatory on the Berkeley campus and the other a small clock that had sat on the director’s desk at Lick Observatory.

  From those four time records, Reid determined that the most violent shock had originated beneath the town of Olema near the Skinner ranch, a place, he noted, where, according to eyewitness accounts, “the violence of the shock was probably as great as anywhere,” and where investigators, primarily Gilbert, had reported the largest amount of surface offset. For years Reid’s determination was accepted as the earthquake’s origin—its epicenter—and today, people who live in Olema take a measure of pride in announcing that they live where the 1906 disaster began. But they are wrong.

  Ninety-six seismographs around the world recorded the passage of the earthquake wave on April 18, 1906. The most distant station was on the island of Mauritius in the Indian Ocean, a direct-line distance through the earth from San Francisco of 7,827 miles. It took 84 minutes for the first disturbance to reach this station. That was followed by more than three hours of vibrations, many appearing as distinct wave trains.

  Reid knew of these records, but he did not know how to analyze them; he did not know how to identify a specific wave train on one record with the same wave train on others. Today, we do. A sophisticated analysis of the wave trains recorded on these distant seismographs shows that Reid and his four time records gave an epicenter that was 20 miles too far north of the actual one.

  The main shock in 1906 originated beneath the sea 2 miles west of the shoreline at Golden Gate Park—8 miles west of downtown San Francisco—at a depth of 6 miles. Furthermore, from the individual scratches and squiggles traced out on the seismographs, which may seem incomprehensible to the layperson but are decipherable by a specialist, it is now possible to show that once the earthquake began, the rupture propagated both north and south at a speed of about 2 miles per second, about ten times the cruising speed of a commercial jetliner—though for some unknown reason that is still debated, the rupture grew slightly faster to the north than to the south—reaching the far ends at Petrolia and at San Juan Bautista in about one minute.

  In the weeks immediately after the earthquake, some scientists, notably Branner at Stanford, voiced the standard explanation that the earthquake had been caused either by a local heating and expansion of the crust by rising hot rock or by a slow cooling and contraction of the crust to produce a strain in the other direction. But those opinions soon changed after it was realized how low the rupture was and how consistent the horizontal slip. By late May, Branner was telling audiences that it was his belief “that the recent shock was caused by the slipping of an old fault.” Seldom has a disaster produced such a dramatic shift in scientific opinion, but after 1906, most scientists accepted Gilbert’s suggestion made in 1884—and restated in 1893 by Bunjiro Koto after the Mino-Owari earthquake in central Japan—that the rupture had been the cause, not the effect, of the earthquake. But that introduced a new question: If neither the earth’s internal heat nor its slow and steady cooling and contraction was the source of seismic energy, then what was? Reid soon provided the answer.

  Because of the early economic importance of San Francisco Bay, accurate maps of the region were essential. They were prepared twice, first in the 1860s and again in the 1890s. Both times, they were based on determining, through land surveys, the precise locations of a network of control points, most sited on hilltops. Because of the dramatic shift in ground positions recorded by Gilbert and others along the 1906 rupture, a third survey was conducted. It was completed in the spring of 1907.

  Reid compared the position of all points surveyed in the 1890s and again in 1907. He found that every point on the west side of the San Andreas Fault had moved north with respect to those on the east side of the fault. Furthermore, the amount of movement decreased with distance from the fault, s
o that if a point a mile west of the fault had moved 11 feet to the north, one 4 miles west had moved 8 feet, and on the Farallon Islands, 23 miles west of the rupture, a point had moved northward nearly 6 feet.

  Then came the surprise.

  When Reid compared how points had moved between the 1860s and the 1890s, he found that most points showed little or no movement except for the westernmost point on the Farallon Islands—which had moved a remarkable 5 feet north without an earthquake. Reid knew immediately what this meant.

  For an unknown reason—which would not be explained for another 60 years—the Farallon Islands, situated out in the Pacific Ocean more than 20 miles west of the San Andreas Fault, were constantly moving north at about two inches a year with respect to other points measured around San Francisco Bay, but without earthquakes. That slow and steady movement set up a strain of captured energy that continued to build and build until it exceeded the finite strength of the rock. Then, in Reid’s words, there is a “sudden fling” as the rock fractures—along the San Andreas Fault—and the opposite sides of the fault slide to new positions of no strain, releasing the pent-up energy. It was, again according to Reid, similar to winding an elastic spring inside a watch. As the spring is wound tighter and tighter, elastic energy builds until the spring breaks. The same happens inside the Earth. As the Farallon Islands and their surroundings continue to move north, elastic energy builds until it is released as an earthquake. Then the process starts again.

  Reid called his idea “the elastic rebound theory of earthquakes,” and it has been at the heart of understanding—and attempts to predict—earthquakes for more than a century. A simple calculation shows that if the Farallon Islands are moving north at a rate of 2 inches a year, then after a century the islands are about 16 feet farther north—the same as the amount of horizontal slip at Olema during the 1906 earthquake. And so—and this was a big step forward—major earthquakes should repeat along the San Andreas on average every hundred years or so. Furthermore, Reid realized, as Lawson and Gilbert and others did, the buildup to an earthquake could now be recorded by placing a line of survey points across the fault and measuring how they moved. When the strain came close to the breaking strength of rock, an earthquake was imminent.

  In practice—as an additional century of scientific studies have shown—earthquakes are much more complicated than this. But this was a start—a crucial start. And so it is not a stretch to claim that our basic knowledge of earthquakes—what they are, the source of the energy they release, how they might be predicted—comes from the remarkably long and remarkably straight 1906 rupture of the San Andreas Fault.

  Two massive scientific reports were prepared for the 1906 earthquake, the first published in 1908 by Lawson and the second in 1910 by Reid. These tomes set the standard for future studies of earthquakes. Eyewitness accounts are abundant. The type and location of seismic destruction is described in detail and illustrated by hundreds of photographs. There are detailed descriptions of the faulting and reports on shaking intensity. The ground rupture is also described, as are the results of the land surveys conducted before and immediately after the earthquake. There are brief reports from the 96 stations where the earthquake waves were recorded on seismographs. Of special value, provided as an atlas, are tracings of the waves from the 96 seismographs and 40 detailed maps that show exactly where the ground rupture was found.

  In 1909, Lawson was elected the second president of the Seismological Society of America. The society officially organized on August 30, 1906, while aftershocks were still rocking the region. The founding membership numbered almost 300; today there are more than 2,000 members. In 1911, he taught the first university course in seismology in the United States.

  Reid’s life took an unusual turn in 1922 when a close friend, Edith Hamilton—the famed classicist and headmistress of Bryn Mawr School for Girls in Baltimore—took up residence in the Reid household. Hamilton was having a dispute with the school’s benefactor, M. Carey Thomas, and after a shouting match with Thomas at Reid’s house, Hamilton resigned as headmistress.

  The next summer, Hamilton and Reid bought a summer house in Maine, where Hamilton and Reid’s eldest daughter, Doris Fielding Reid, resided. Their relationship was described, according to the vernacular of the time, as a “Boston marriage,” which meant two women were living together without the financial support of a man. Doris Reid took work as an investment banker, in which she succeeded, and Hamilton began writing her famous series of books on mythology. The first book, The Greek Way, was dedicated to Doris Fielding Reid. Both women were at Harry Reid’s bedside when he died in 1944. One wonders whether any discussions with Reid about geology—and about his experiences in San Francisco after the earthquake and his groundbreaking (no pun intended) conclusion on elastic wave theory—crept into the mythological imagery used by Hamilton in her writings.

  Alice Eastwood worked as a volunteer at the University of California for a year after the earthquake. She then set off traveling, using for financial support a small amount of money she was earning from a hotel in Colorado in which she had invested before she moved to California. For a while she worked, again as a volunteer, at the Smithsonian Institution, the New York Botanical Garden, and an arboretum near Boston. She also found time, and money, to visit botanical collections in London and Paris. In 1912, she was called back to California to resume her position at the newly rebuilt California Academy of Sciences, working at the new botanical garden in Golden Gate Park.

  In March 1909, Grove Karl Gilbert developed a serious illness. It was diagnosed as apoplexy—a cerebral hemorrhage or stroke. “While my physician’s tone is optimistic,” he wrote to a friend, “my own impression is that my general physical condition is lowered.”

  But he did recover, slowly. Not until 1918 was he ready to declare his convalescence over, and when he did, he had something else to announce. In a letter to one of his sons, he finally confirmed what many had gossiped about. “Alice and I have been lovers for years.”

  He continued: “But for a long time I would not propose marriage because it seemed like asking her to give up a life that satisfied her to become the nurse of my broken health.” Here he was probably thinking of the difficult 18 years he had cared for his late wife during her prolonged illness. But now, “my general health has so far improved that I am less ashamed to impose myself on Alice.” And so he wrote to her and asked if she would marry him. She replied with a one-word answer: “Yes.”

  He left Washington, D.C., where he was then residing, and traveled to San Francisco to reunite with his new fiancée, stopping as he often did on a transcontinental trip for a short stay with his sister who lived in Jackson, Michigan. Here he suffered a second stroke. This time, he did not recover. He died on May 1, 1918.

  Eastwood lived another 35 years, continuing her work as curator of botany. By the time of her death in 1953, at age 94, she had named 125 species of California plants. In her honor, her colleagues had named eight plant species for her, including Salix eastwoodiae, a willow found in central California’s alpine regions, and Eastwoodia elegans, a yellow aster.

  But to those who study seismology and are familiar with the 1906 earthquake, she is the woman, often unidentified, in a photograph standing next to the “mole track” north of Olema, California.

  *****City officials had planned to fight any major fire in San Francisco with water piped from the reservoir in San Andreas Valley, but the earthquake had damaged the piping in several locations, namely where it ran across the San Andreas Fault, rendering the city without crucial water supply to fight the fires—or to supply drinking water after the disaster.

  ******The severity of seismic shaking depends on how close someone is to the source of an earthquake and to the nature of the ground underneath. Eastwood was living on Nob Hill, which is solid rock. The people who lived south of Market Street felt stronger shaking because the ground beneath them was fo
rmer marshland filled with loose debris.

  *******To understand why everything seemed to move to the right, consider this: Imagine you and a friend are on opposite sides of the San Andreas Fault and you ask your friend to stand directly in front of you and to face you. Now ask your friend to move to your right. Obviously, from your viewpoint, your friend has shifted to the right. More important, from your friend’s viewpoint on the other side of the fault, you seem to have moved to the right.

  *Reid was the eighth and last member added to the earthquake commission. In addition to Lawson, Gilbert, Leuschner, and Burkhalter, the other members were geologist John Branner of Stanford; the director of Lick Observatory, William Campbell; and George Davidson, the most august member of the commission—aged 81 at the time of the earthquake—who had conducted many of the original land surveys along the Pacific coast from Alaska to Panama and who was a past president of the California Academy of Sciences.

  Chapter 4

  Bridging “the Golden Gate”

  I was up on the tower when the earthquake hit.

  It was so limber the tower swayed sixteen feet each way.

  —Alfred “Frenchy” Gales,

  on the Golden Gate Bridge, 1934

  After the 1906 disaster, Lawson decided he would build a house that could withstand both earthquakes and fires. He consulted a study made of over 1,000 houses that were located in communities south of San Francisco and within four miles of the San Andreas Fault to determine what type of structure had suffered the least damage. By far, brick and stone buildings had faired the worst. Each one, according to the study, had either collapsed walls or huge cracks, and in some cases were totally demolished. The houses that had survived the best were single-storied wooden structures, though these, of course, were the most susceptible to fire. So Lawson decided he would risk a new type of construction—and build a new house of reinforced concrete.