Professor says Portland not ready for a major earthquake

In light of the recent devastation in Japan, students may be wondering how ready Portland is for a major earthquake.

In light of the recent devastation in Japan, students may be wondering how ready Portland is for a major earthquake.

As it turns out, this is a very difficult question to answer, according to Dr. Kenneth Cruikshank, an assistant professor in Portland State’s geology department. Depending on a number of factors, a potential earthquake could have a minimal or very severe effect on the city.

Cruikshank said that depending on the “resonant frequency” of a building, an earthquake could either have little effect on a building, or completely destroy it. If the waves of energy that an earthquake creates vibrate at the same resonant frequency as the building, the building doesn’t stand much of a chance.

Because of differing resonant frequencies, “half a dozen buildings will be affected differently,” Cruikshank said.

Scientists have informed the public that the west coast is overdue for a major earthquake. PSU geology Professor Scott Burns said that along the Cascadia Margin, which exists off the coast where the North American Plane meets the Juan De Fuca Plate, quakes usually occur every 500 years. The last one occurred on January 2, 1700.

Because of this, the next major subduction earthquake—caused by the slipping of these two plates—could happen tomorrow or even hundreds of years from now. Scientists have no way of predicting when it will hit, Burns said.

Subduction zone earthquakes are predicted to be the most devastating earthquakes because they are caused by an entire tectonic plate slipping under another. This type of earthquake tends to generate significantly more energy than the frequent earthquakes in California, which are caused by rapidly shifting rock around fault lines—the most famous being the San Andreas Fault.

Dr. Franz Rad, a professor in the College of Civil and Environmental Engineering, pointed out that one of the major problems with subduction earthquakes is that they last much longer than earthquakes along fault lines.

“[Subduction earthquakes] can go for two or three minutes. It’s a very different phenomenon,” Rad said. “They are very different in the nature of the damage that they can do. They are not like the fault earthquake that we see in California.”

Cruikshank said that during a subduction earthquake taller buildings are particularly at risk. Additionally, as the waves created by the earthquake increase in length, the more severe the effect will be on taller buildings.

At PSU, a number of buildings have been upgraded to be more earthquake-resistant. Michael Cummings, a geology professor at PSU, said that buildings such as Shattuck Hall, Lincoln Hall, Smith Memorial Student Union and the newest science building have all been seismically upgraded.

Walking along the north side of SMSU, one can see the most noticeable seismic improvement on campus: the large “X” beams on the north side of the building were installed to prevent floors from collapsing during an earthquake, Burns said.

Rad said that while much improvement has been made, it is not nearly enough to get us ready for the major subduction earthquake that is inevitably coming.

“You can’t say that we’re ready,” Rad said. “But we’re making some progress.”

Rad said that buildings built in the last 20 years have been constructed with updated codes and therefore are more “ductile,” or flexible. When it comes to making earthquake-resistant structures, this is one of the most important factors. According to Rad, the idea behind these seismic codes is to allow the buildings enough flexibility so they don’t simply crumble when a large earthquake hits them.

“We may have to eliminate those [collapsed] buildings after the quake is over,” Rad said, “but at least we haven’t killed anybody, and that’s the idea.”

Surprisingly, the fact that Oregon doesn’t have many major earthquakes is of very serious concern to Rad. He said the abundance of earthquakes in other areas such as California does two important things: one, “it wakes people up” and makes them more aware of earthquakes, he said. When people are more aware of recurring phenomenon like this, they usually take more steps to be prepared; and two, an abundance of larger earthquakes eliminates the weaker buildings in populated areas.

“[Oregon doesn’t] have any purging that goes on,” he said. “California is way ahead of us. Every decade they get these big earthquakes. So they have a very strong set of policies regarding the retrofitting of major structures such as hospitals.”

Rad added that the best thing to increase preparedness in Portland would be to have around a 5.5 magnitude earthquake hit the city.

“We could eliminate a lot of the weaker buildings without killing a lot of people,” Rad said.

According to Burns, the last time that Portland had an earthquake of this size in recent years was the Scotts Mill earthquake in 1993. Also known as the “Spring Break Quake,” this particular earthquake caused $25 million worth of damage in the northern Willamette Valley. ?