Plate tectonics reveal earth's precarious state

WASHINGTON — Earth, that living, seething, often inhospitable and not altogether intelligently designed thing, has again shrugged, and tens of thousands of Pakistanis are dead. That earthquake struck 10 months after the undersea quake that caused the December 2004 tsunami that killed 285,000 in Asia. Americans reeling from Katrina, and warned of scores of millions of potential deaths from avian flu, have a vague feeling — never mind the disturbing rest of the news — of pervasive menace from things out of control. Too vague, according to Simon Winchester.

His timely new book, "A Crack in the Edge of the World: America and the Great California Earthquake of 1906," teaches — reminds, really — that we should have quite precise worries about the incurably unstable ground on which scores of millions of Americans live. This almost certainly will result in a huge calamity, probably in the lifetime of most people now living.

Before the study of plate tectonics revolutionized geology just 40 years ago, that science, Winchester writes, was concerned with "rocks, fossils, faults and minerals that were scattered around simply and solely on the surface of the earth." But the surface consists of between — depending how they are defined — six and 36 floating plates, which Winchester calls "rafts of solid rock," forming a band 1,800 miles thick. The plates' slow movements are powered by earth's molten innards, the boiling and bubbling radioactive residue of the planet's formation 4.5 billion years ago.

The plates grind against — and slide up on, or plunge below — one another. But not smoothly, which is the lethal problem. When friction freezes them for a while, stupendous kinetic energy builds up until, suddenly, plates unlock and the energy is released, sometimes in ways that seem to involve related spasms around the world.

On the last day of January 1906, that seismically dangerous year, an earthquake in Ecuador and Colombia of perhaps 8.8 magnitude on the Richter Scale killed about 2,000. Sixteen days later there was a large Caribbean quake, followed five days later by one in the Caucuses, and on March 17 by one that killed 1,228 on the island of Formosa. On April 6 a 10-day eruption of the volcano Vesuvius began with rocks blown 40,000 feet into the air over Naples. Two days after Vesuvius subsided, San Francisco was knocked down, and 2,600 acres of it were then devoured by three days of fires. About 3,000 San Franciscans died then, four months before a Chilean quake killed 20,000.