Earthquakes keep hitting inhabited areas on the planet, and they have nothing to do with human activities and carbon emissions, not even with the offshore oil drilling that my grandmother used to blame for all the destruction caused by quakes.
They are the result of adjustments in the earth’s crust. One commonly thinks of it as an incredibly solid layer of rock, with mountains on top made of even more rock. But in reality, most of the earth is in a molten state. The solid crust on top is, by comparison, paper-thin. When you think of the globe as a boiling sphere, it’s easier to visualize how its cold outer skin is broken up into large and small segments, called plates.
Prepare a pot of pudding on the stove (which makes for great comfort food while watching news about natural disasters) and observe how trouble zones develop when the mixture starts to boil. In some places, bubbles form and hot pudding squirts up, like little volcanoes. When it cools, you can often see seams in the upper layer where larger portions are joined.
Such seams exist on the earth all around the Pacific Ocean, which makes its outline the No. 1 trouble zone in the world.
For the U.S., this means that San Francisco remains at great risk of a devastating quake. The 1906 quake, destroying most of the city, was roughly the strength of the 1985 quake in Mexico City that killed 10,000.
Apart from the weaker Loma Prieta quake in 1989, the San Andreas fault has been quiet. This type of fault, which is produced by the Pacific Plate moving northward and rubbing against the American Plate, tends to make a major jolt every few decades.
The U.S. Geological Survey has free preparedness handbooks available (www.usgs.gov) but many of the structures in the city are old and unable to withstand strong shaking. Once-fashionable accessories like ledges and porticos are prone to breaking off and bringing a hail of stonework down on whomever is in the street.
In addition to San Francisco, the Oregon Coast has been added to the “endangered” list. According to a recent article on www.wunderground.com, the plate boundary there mirrors the conditions on Japan’s east coast. As awareness is slowly growing in Oregon’s coastal towns, the Oregon Seismic Safety Policy Advisory Commission is making vigorous efforts to point out the growing danger to that part of the country.
Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.