News

Rock and Roll: Disturbing New Earthquake Trends

Scott PikeEarthquakes have recently cut a devastating swath through the world, shaking up Pakistan, Japan, India, Peru, Chile, New Guinea and California. So what's going on?

"Nothing," said Scott Pike, earth science professor at Willamette University. It's business as usual for the earth, which sees about one and a half million earthquakes each year.

"We're seeing normal seismic activity," Pike said. "What's new is an increase in devastation due to increased population and environmental degradation."

Massive deforestation in Pakistan for the past half century has resulted in soil erosion and unstable mountainsides, he said. The recent quake displaced already loose soil, and rainfall caused soil and rocks to form river-like mudflows, which swallowed everything in their path. Boulders lost their grip and crashed down mountainsides, flattening houses below. In all, more than 79,000 people died as a result of the October quake.

"In Pakistan the earthquake itself caused severe damage," Pike said, "but the post-earthquake damage was just as devastating."

Could the same scenario unfold in the Pacific Northwest?

Pike said there are major differences between this region and Pakistan. The Himalayas have much steeper slopes than the population centers near the Cascades, and U.S. forest cuts tend to be less extensive and more controlled. But living in the Pacific Northwest isn't without risks.

"The rush for development in Oregon's coastal communities has led to construction on unstable slopes," Pike said. "You have to worry about erosion and landslides into the ocean, and about tsunamis, which are often caused by earthquakes."

Some Salem homes are at risk, Pike added. "If we were to have a major earthquake we could potentially see landslides in south Salem along the banks of the river. Salem's higher neighborhoods sit on top of Columbia basalts, a hard rock formation that overlays softer sedimentary rock. Normal erosion activities weaken the sandstone beneath the basalts. On Fairmont Hill, for instance, you can see some scarps from past landslides. There is potential for slippage there during a major quake."

The earth is like a giant jigsaw puzzle that's always in flux, said Pike. Tectonic plates float on top of the earth's plastic mantle, which flows much like a conveyor belt. Where the plates meet, stress builds until its force overcomes friction and the plates suddenly slip.

"The plates don't move gradually, but in jerky motions," he said. "They slam into or away from each other, or slide past each other, causing land displacement. When they occur at sea they can result in tsunamis like the one that occurred in Indonesia last December.

"Not all earthquakes are directly related to plate tectonics," Pike said. There have been large historical earthquakes far from plate boundaries. The earth's entire surface is always potentially volatile.

According to Pike, many minor quakes occur in Oregon each year.

"A large cluster is concentrated in the southern Cascades, with a small cluster east of Salem. We don't feel them because they're so small," he said. "About 300 years ago there was a major slippage in this area. We can expect a similarly powerful quake within the next 200 years. Unfortunately, our prediction tools are not very precise. We can't say when it will happen."

Earthquakes are sometimes a precursor to volcanic eruptions, he added. "An increase in seismic activity near Mount St. Helens tells us that magma is probably on the way up."

The science of seismology began after the 1906 quake flattened San Francisco.

"We began measuring seismic activity at that time and our understanding of the causes of earthquakes has drastically improved, but earthquakes are still fairly unpredictable."

In other words, he added, we understand the how but not the when.

11-04-2005