Friday's earthquake in Bam, Iran, that killed more than 50,000 reminds us that earthquakes are still a major cause of death and destruction throughout the world, and the United States may not be spared. The Bam quake measured 6.8 on the Richter scale, but scientists say a monster quake as high as 9.0 is likely to occur in the Pacific Northwest. California's San Andreas Fault, the most popular locale for the feared "Big One," is also causing renewed concern.
A recent article in the
Tri-Valley Herald says "the Pacific Northwest could be struck by a magnitude 9 quake, shaking the region 10 times more violently than San Francisco's famous 1906 quake and for 12 times longer. Scientists call it a 'mega-thruster' and say the Seattle area is especially vulnerable."
That is because Seattle rests on loose, liquefiable dirt and the downtown straddles the Puget Sound area's largest fault. "Researchers foresee instantaneous damage deep into Southwest Canada and Northern California. Seattle, Vancouver and Portland are loaded with buildings not outfitted for earthquakes.
"It will extend from Cape Mendocino to Vancouver. And all of those folks will experience two to three minutes of strong shaking. The (1989) Loma Prieta earthquake lasted 15 seconds and that felt like an eternity."
Within minutes of the quake, tsunamis up to 60 feet high could slam the coast. In the century's three largest quakes -- 1964 in Alaska, 1960 in Chile and 1952 quake in Kamchatka -- tsunamis and landslides killed more people than ground shaking.
Oregon State University geophysicist Chris Goldfinger said the Puget Sound cores revealed two monster quakes roughly every 300 to 400 years, then a longer interval, then a single big quake. The last one was in January 1700. Japanese records at that time say rice farmers saw waves up to 15 feet high charge out of the east without warning, wrecking homes and swamping fields.
A recent article in the
Los Angeles Times says many scientists say the Coachella Valley, part of the 750-mile San Andreas Fault, seems most prone for a giant earthquake. In 1994, "subsidiary faults" in Loma Prieta and Northridge generated quakes that flattened buildings and buckled interstates while the San Andreas remained relatively quiet as it has since 1906, but now "scientists again are highlighting the San Andreas as the rupture without rival - a slumbering beast napping on borrowed time," the article said.
"The primary fault in California - the big dog - is the San Andreas, and it's important for people to remember that," said Doug Yule, a geologist at Cal State Northridge, which was badly damaged in the Jan. 17, 1994, disaster. "The San Andreas will produce the largest earthquakes."
The good news is that most of the San Andreas is remote from major cities in Southern and Central California. The bad news is that the San Andreas runs through the fast-growing Inland Empire and Antelope Valley, which last felt major quakes in 1812 and 1857, meaning that they may be due for a repeat.
The U.S. Geological Survey said that the Iran's Bam quake was not unusual and is part of a normal pattern that included quakes in California, New Caledonia, Panama, Mexico and Indonesia in the last two weeks.
"We are in the norm of earthquake activity," seismologist Jim Devine said in a telephone interview. "We would need several more large earthquakes before we start considering something unusual."
Devine said there is no indication that the quakes are related. Earthquakes occur when two or more of the dozen tectonic plates that slowly drift over the earth collide and release energy, but a quake on one side of the Earth does not trigger one on the other side.
Between 1890 and 1906, an unusually high number of large earthquakes including ones in California and Chile occurred that were higher than level 8 on the Richter scale, while in the 1980s, "We were 'energy deficient,"' Devine said.
The Bam quake was about the same size as the Dec. 22 California tremor that killed two people, but Bam's buildings, many of which were made of mud and straw, were not as earthquake-resistant as the structures in California. The relative destructiveness of a quake, therefore, has more to do with building standards and economic development than magnitude.
The largest earthquake in the recent series occurred southeast of the Loyalty Islands, New Caledonia, on Dec. 27 at a 7.3 magnitude, but caused little damage. Other recent quakes were in Indonesia (6.1 magnitude) and in a remote area of Panama (6.1 magnitude) killing at least one person.
