Silent witnesses seismic sagas: Chilean scientists are studying historic accounts of earthquakes for clues that will help them predict the size and timing of future eruptions.

"... and as God was pleased that on the sixteenth of December, two hours before sunset, within the time it takes to recite three credos, with a tremble and earthquake all this city fell down, without leaving any house where one could dwell or dare to enter ..."

Report to the Lieutenant Governor, Town Council of Imperial, Chile January 8,1576

This obscure report buried deep in Chile's colonial archives has recently become a key piece of seismological data. The Apostles' Creed in the Catholic mass takes roughly thirty seconds to recite, and the writer was presumably on his knees as soon as the shaking started. Thus we know that the Chilean earthquake of December 16, 1575, lasted about ninety seconds. This is of interest because duration of motion partly determines how much stored energy an earthquake releases, and therefore helps to predict the timing and magnitude of the next one.

In a study published last year in the prestigious scientific journal Nature, Marco Cisternas at the Catholic University in Valparaiso and his co-authors used this and other eyewitness accounts of the 1575 earthquake, along with reports of nearby earthquakes in 1737 and 1837, to help explain why the 1960 quake centered near Concepcion was so surprisingly powerful.

The 1960 quake's magnitude was the equivalent of an estimated 250-350 years of stored energy, yet that fault's previous earthquake had occurred only 123 years earlier. Why? Using both documents and field data, Cisternas determined that the previous two quakes in 1737 and 1837 had been insufficiently strong producing little if any land subsidence or tidal wave--to fully release the energy that the fault had stored until they struck. The fault line thus remained a half-cocked gun waiting additional centuries to be fired with full force in 1960.

Seismologists routinely sift through eyewitness records of earthquakes that occurred before the modern era in search of such tell-tale detail. According to Leonardo Seeber, a senior earthquake researcher at New York's Columbia University, the accuracy of seismic data actually decreased when recording instruments were first introduced because they were more error prone than word-of-mouth accounts. "Seismologists finally realized that there was still a lot of value in reports in newspapers, diaries, and the like--even of more recent events. Data does not have to be quantitative to be useful."

Although geologists do not have to read the Old Testament, for instance, to know that the Near East is seismically active, the prophets Samuel ("Then the earth shook and trembled, the foundations of heaven moved and shook" 22:8) and Isaiah ("The earth shall reel to and fro like a drunkard" 24:20) made this clear long ago. Useful scientific data can be gleaned even from laymen's reports of, say, in which direction buildings toppled, or how high the tide rose or fell, or in what orientation fissures opened in the ground.

Pliny the Younger, in a letter to the Roman historian Tacitus about the eruption of Mr. Vesuvius on August 24, A.D. 79--which killed his uncle, Pliny the Elder, the author--ironically--of the greatest scientific treatise of the classical era--wrote, "We saw the sea sucked away, apparently forced back by the earthquake; at any rate, it receded from the shore so that quantities of sea creatures were left stranded on dry sand." His description of the eruption's mushroom-shaped ash column--like an "umbrella pine"--holds valid today, as volcanologists still call such an ash cloud a pino, and any explosive eruption is called, in his honor, a plinian.

Even fictional eyewitnesses have been known to hazard a scientific guess or two. The Lisbon earthquake of November 1, 1755, spawned real tsunamis in the West Indies, but in Candide, Voltaire's naive Doctor Pangloss famously, and incorrectly, opined, "This earthquake is nothing new.

... The town of Lima in America experienced the same shocks last year. The same causes produced the same effects. There is certainly a vein of sulphur running under the earth from Lima to Lisbon." In fact, Pangloss was off by eight years--Lima was destroyed by a major quake in 1746, and before that in 1552, 1578, 1655, and again in 1687. His vein of sulphur, it goes without saying, was nothing but hot air.

Before the invention of seismographs to measure the magnitude of an earthquake, and particularly before 1935, when the Richter scale was introduced, seismologists relied on indirect measurements of intensity, by quantifying an earthquake's effect on manmade dwellings--from hairline cracks in walls to complete and utter destruction--and on human reactions--from barely a notice to absolute panic.

The most commonly used measure of earthquake intensity is the Mercalli scale, developed in 1902 by Giuseppe Mercalli and modified in 1931, which scores a quake on a range from I ("People do not feel any Earth movement") through VI ("Everyone feels movement. People have trouble walking. Trees and bushes shake") to XII ("Almost everything is destroyed. Objects are thrown into the air. The ground moves in waves or ripples").

One real eyewitness in Lisbon, an Englishman named Chase, told just how unhelpful some human reactions to an earthquake can be for accurately measuring its intensity. "Three times I thought myself inevitably lost!" he wrote. "The first, when I saw all the city moving like the water [level XII on the Mercalli scale!]; the second, when I found myself shut up between four walls; and the third time, when, with the fast fire before me, I thought myself abandoned.... As for the Portuguese, they were entirely employed in a kind of religious madness, lugging about saints without heads or limbs, and if by any chance they espied a bigger, throwing their own aside, they hauled away the greater weight of holiness."

Charles Darwin witnessed several Chilean earthquakes in 1835 on his voyage on the HMS Beagle. On May 17, while eating dinner in Coquimbo, another struck. "I heard the forthcoming rumble," he wrote, "but from the screams of the ladies, the running of the servants, and the rush of several of the gentlemen to the doorway, I could not distinguish the motion."

Lamenting that he had missed an opportunity to collect data, and noting that his hosts did not govern their fears sufficiently to observe scientifically, Darwin continued, "I heard of two Englishmen who, sleeping in the open air during a smart shock, knowing that there was no danger, did not rise. The natives cried out indignantly, 'Look at those heretics, they do not even get out of their beds!'"

The strongest earthquakes ever to strike the interior of a tectonic plate occurred in the U.S., in southern Missouri, on the New Madrid Fault, in three successive months, from December 1811 to February 1812. They rang church bells in Richmond, Virginia, and altered nearly eight thousand square miles of landscape in the Mississippi Valley. Dams made from fallen banks caused the Mississippi River to flow upstream.

The painter John James Audubon, then working across the river in western Kentucky, described the January quake in his diary, "I heard what I imagined to be the distant rumbling of a violent tornado, on which I spurred my steed.... The animal knew better than I what was forthcoming, and instead of going faster, so nearly stopped that I remarked he placed one foot after another on the ground with as much precaution as if walking on a smooth sheet of ice.... At that instant all the shrubs and trees began to move from their very roots [VI on the Mercalli scale!], and the ground rose and fell in successive furrows like the ruffled waters of a lake [XII!], and I became bewildered."

Closer to the epicenter, surveyor Louis Bringier wrote, "water rushed out in all quarters, which was ejected to the height of ten to fifteen feet and fell in a black shower mixed with sand. The surface was sinking and a black liquid was rising up to the belly of my horse who stood motionless, struck with terror. The whole surface of the country remained covered with holes which resembled so many craters."

The black geysers he described are known as "sand blows," which occur when subsurface sand and peat deposits are liquefied by sloshing groundwater and then forced under pressure up through surface fissures. One such hole blew out the fossilized skull of an extinct musk ox.

But it is South America, along its west coast, and not North, that is the globe's most seismically active region and the scene today of an ongoing tectonic smash-up that makes New Madrid look like a fender bender. Offshore Chile and Peru, the Nazca plate is moving eastward at the speed of two inches per year and diving under the continental South American plate, which itself is moving westward at a little over an inch per year. The result is an ultra-low speed but nonetheless devastating head-on collision, producing hundreds of tremors each year and uplifting the longest and one of the highest mountain chains in the world.

And it is here where seismicity is an everyday fact of life--where, in the words of Pablo Neruda, "every native carries in him the memory of an earthquake." Count Fernand de Montessus de Ballore, founding director of the Chilean Seismological Service, was also a student of Araucanian earthquake mythology. The Indians, he wrote, believed that forest spirits took the form of flaming stones, which humans would use as weapons. Earthquakes occurred when two armed men faced off and the one suffering defeat dropped his stone to the ground.

Chile has an enviable archive of earthquake-related documents to aid the modem researcher. Montessus de Ballore's six-volume Seismic History of the Southern Andes and eight-volume Bibliography of Chilean Earthquakes and Eruptions collects only a small sample of such reports. Many others still walt to be combed for the facts and figures that their authors may have inadvertently set down.

For instance, the January 1576 report from Imperial--near Temuco, where Neruda spent his childhood--provides details on the earthquake's effect on sea levels--"sea did not spare any crops, it rose through the valley upstream more than two leagues [over six miles] and left the fields full of many fish, the tide rose in this river up to Maquehua Island, and still does even after the sea has returned to its course."

We know from a letter sent to the king of Spain on February 12 of the same year what happened in the town of Valdivia, one hundred miles to the south. Wrote Martin Rosa de Gamboa, lieutenant general for the provinces of Arauco and Tucapel, "the sea left its limits and rose at Valdivia more than four leagues [over thirteen miles] upstream than usual, and in the provinces of Chiloe, where is inhabited the city of Castro, they write it rose ten estadales [about one hundred feet].

As with many earthquakes, it is not the shaking so much as the aftermath--tsunamis, fires, flooding, and avalanches--that do the most damage. In Valdivia it was a flood, caused by a temporarily dammed river upstream. An anonymous letter written from Valdivia in early 1576 describes the blockage with foreboding, "such a mighty river as it used to be that issued from a big lake, and where the lake drained were narrows, and in the middle of them a big hill fell and blocked it, and it has been more than forty days that the river carries no water but from the sea, which has seized the river, and the lake rises one codo [over fifteen inches] every day.... And it is frightening to see it because as the city is fourteen leagues [fifty miles] from it, they say if the dam suddenly lets loose, the city will be carried away.... The lake is big as the sea.... God help us...."

In April 1576, the inevitable came to pass. As witnessed by Pedro Marino de Lobera, corregidor of Valdivia, "it happened that at the end of the month of April it [the lake dam] came to blow out with such great fury. Finally the water was receding at the end of three days, having killed more than twelve hundred Indians and great numbers of cattle, without counting here the destruction of houses, fields, and orchards, which was difficult to reckon."

For the following two hundred years, this part of the southern coast remained relatively quiet. A quake on Christmas Eve 1737, according to a historical chronicle, destroyed the buildings on the island of Chiloe and shook the town of Valdivia ("such violent undulations that people could not remain standing and in many places the ground opened"), but did not damage the city of Concepcion.

Charles Darwin happened to be in Valdivia on February 20, 1835, when an earthquake struck, destroying much of Concepcion and its port of Talcahuano. He wrote in his journal of that day, in typically precise detail, "I happened to be on shore and was lying down in the wood to rest myself. It came on suddenly and lasted two minutes, but the time appeared much longer. The rocking of the ground was very sensible. The undulations appeared to come from the east, whilst others thought from the southwest.... There was no difficulty in standing upright but the motion made me almost giddy. It was like that felt by a person skating over thin ice which bends under the weight of the body."

Two weeks later, the Beagle entered Concepcion Bay. In the largely destroyed city ("the most awful yet interesting spectacle I ever beheld"), Darwin noted that the bricks from buildings had fallen to the northeast, and that walls that were aligned in a southwest-northeast direction had held firm, but that walls on the perpendicular had failed. The tide at the island of Santa Maria, southwest of the city, had risen three times higher than elsewhere in the bay, a fact that seems to accord with the perception that the quake had came from that quadrant.

On Quiriquina Island he noted the fissures were oriented north-south, some a yard wide.

This 1835 tremor, however, was just a warm-up for the killer quakes, all estimated as being 8+ on the Richter scale, that next visited Chile. In August 1868, in the north, an estimated twenty-five thousand people died. On August 17, 1906, Valparaiso, in the country's center, was decimated. Step by step, seismicity was moving south. In 1939, the farming town of ChillOn, near Concepcion, was largely destroyed, and then, in May 1960, the ground fell in six major quakes that struck within ten days in the same area. The largest, on May 22, killed six thousand people in Concepcion but has gone down in history for a different grim statistic. Its 9.5 Richter score is the highest ever directly measured. It released roughly three times more energy than the second strongest quake recorded, in Alaska's Prince William Sound in 1964.

Pablo Neruda was born two years before the 1906 Valparaiso earthquake that destroyed the coast where he later made his home. That shadow of doom, a kind of subconscious seismicity, was never far from his mind. "Sometimes it all begins with a vague stirring," he wrote in his memoirs, "and those who are sleeping wake up. Sleeping fitfully, the soul reaches down to profound roots, to their very depth under the earth ... and then, during the great tremor, there is nowhere to run, because the gods have gone away, the vainglorious churches have been ground up into heaps of rubble."

After the shaking, Neruda continued, the landscape "twitches like a wounded whale. It flounders in the air, is in agony, dies, and comes back to life.... Because in the memory there is defeat, the shudder of the earth as it quakes and the rumble that surfaces from deep down as if a city under the sea, under the land, were tolling bells in its buried towers to tell man that it's all over."

But it is not yet over. What came first from the earth, comes next from the sea--an "immense green arm," in Neruda's words, "like a final apparition, the mountainous wave ... that surges, tall and menacing, like a tower of vengeance, to sweep away whatever remains within its reach."

Colonial documents from 1575 describe this same terror--"the sea went out with such fierceness and power," and then "the seawater returned with so much pride and force that it carried trees and sticks and boards, and the river ran faster upstream than it does in flood downstream."

Professor Marco Cisternas found physical evidence, in the form of sea-sand deposits on high ground, showing that the 1575 earthquake's tsunami was even bigger than that of 1960, which was fifty feet in height when it struck Chile and twenty feet when it reached Japan. With the help of old written records, it is a remarkable story that a six-inch layer of sand, found where it does not belong, can tell--one of "fierceness and power," of "pride and force." Such is the way that silent stones can speak in the hands of a seismologist.

A documentary filmmaker residing in New York City, Louis Werner is a freelance contributor to Americas.