Reprinted by courtesy of The Sentinel newspaper, Coquille OR

BY ROBERT JUMP Staff Reporter - The Sentinel, Coquille.

With seismic equipment and ocean buoys placed around the Pacific Rim to detect earthquakes and distant tsunamis, south coast residents are relatively safe from the type of disaster that struck countries bordering the Indian Ocean last week. However, should a quake large enough to generate a tsunami occur along the Cascadia Subduction Zone which lies less than 100 miles off the west coast, the waves would arrive within minutes, leaving no time for a warning.

"If it were a locally generated tsunami from the Cascadia fault that's off shore, a subduction zone earthquake, there would only be minutes," Jay Wilson, Earthquake and Tsunami Program coordinator with the Oregon Office of Emergency Management told The Sentinel. "The earthquake would be the warning for people. There wouldn't be time to wait for an announcement."

According to experts, it's not a matter of if an earthquake will take place along the subduction zone, but when. According to experts at Oregon State University, an earthquake along the Cascadia Subduction Zone may occur at any time.

"The Cascadia Subduction Zone has the longest recorded data about its earthquakes of any major fault in the world," said Chris Goldfinger, an associate professor of marine geology at OSU and one of the leading experts on this fault zone. "So we know quite a bit about the periodicity of this fault zone and what to expect. But, the key point we don't know is whether the current cluster of earthquake activity is over yet, or does it have another event left in it."

The two most recent major earthquakes on this fault occurred in the year 1700 and approximately the year 1500, Goldfinger said. Those two events were only 200 years apart, and it's now been 305 years since the last one. From this perspective, there's some reason to believe the next major earthquake could happen soon.

According to Goldfinger, there are only two places in the United States with active subduction zones, or major areas where one of the Earth's great plates are being subducted, or forced underneath the other. One is in Alaska, the site of the great earthquake of 1964. The other is the Cascadia zone, a 600-mile long fault zone that runs from Cape Mendocino in California to Vancouver Island in southern British Columbia.

Major studies have been done on this fault zone, many of them at OSU, and they have identified 19-21 major earthquake events during the past 10,000 years. During at least 17 of these events, the entire fault zone appears to have ruptured at once, causing an earthquake around magnitude nine, and major tsunamis.

"There's some variation in intensity, the last event in 1700 appeared to be about average," Goldfinger said. "To track these events we use radiocarbon dating of deposits of sand called turbidites, which come from marine landslides. These deep-sea cores give us a pretty accurate picture of when and where an earthquake event happened."

According to Goldfinger, there are remarkable geologic parallels between what just happened in East Asia and what could happen in the Pacific Northwest. The Asian event happened where the India plate was being subducted beneath the Burma microplate, and it ruptured – for the first time since 1833 - along a 600-mile front that is just about the same length as the Cascadia Subduction Zone.

That earthquake happened as the Indian plate moved towards the northeast beneath Asia, just like the Juan de Fuca plate is in the Pacific Northwest before it disappears beneath the North American plate.

What happened in Asia may give a vivid demonstration of the geologic future of the Pacific Northwest. For hundreds of years, these subduction zone plates remain locked, releasing little of their tension. The plate which is being subducted is forced down, while the plate above bulges upwards. Then, in a few minutes of violence every few centuries, the forces are released. The upper plate moves seaward, and a massive tsunami can be produced along with catastrophic destruction from earthquake shaking.

"In the case of the Cascadia Subduction Zone, you could have an area of ocean sea floor that's 50 miles wide and 500-600 miles long suddenly snap back up, causing a huge tsunami," Goldfinger said. "At the same time, we could expect some parts of the upper, or North American plate to sink one to two meters. These are massive tectonic events. Subduction zones produce the most powerful earthquakes and tsunamis in the world."

The question, Goldfinger says, is not whether or not the Cascadia Subduction Zone will break again. It's when. And that's where the study of past events may shed light on the present. When that earthquake happens there is only one piece of advice: seek higher ground.

The quake that struck the island of Sumatra was so close there was no time for a tsunami warning, even if a warning system had been in place. That quake and resulting tsunami left tens of thousands dead in it's wake. In addition, with no warning system in place, other countries surrounding the Indian Ocean were caught unaware a giant wave was looming over the horizon.

The folks in Sumatra after the earthquake was over, which lasted for minutes, they only had minutes to prepare for the tsunami," Wilson said. "In India they had hours before this thing arrived and if there were a system in place they could have received a message."

According to Wilson, much was learned from the earthquake that struck Anchorage, Alaska in 1964. During that quake, which struck on Good Friday, March 27, at 5:36 p.m. and registered 8.6 on the Richter Scale, a tsunami was generated that caused damage thousands of miles away.

"By the time it got here (the tsunami) I think there were warnings that were coming down and certainly in Seaside and Cannon Beach and these places some people were aware of it and others weren't," Wilson said. "People didn't know what to expect and so there were people down on the waterfront watching. It was kind of a spectator thing and there people like the family that were hit on Beverly Beach in 1964. Their four children were killed because they weren't in the notification scheme. They didn't know that this was coming."

There were relatively few deaths due to the 1964 Anchorage quake which claimed 115 lives. The fact is attributed to the quake occurring at a time when most families were at home and the sparse population of the area.

Since that time, a tsunami warning system has been placed around the Pacific Rim to provide warnings should an earthquake of large enough magnitude and frequency to generate a tsunami.

The Tsunami Warning System in the Pacific monitors seismological and tidal stations throughout the Pacific Basin to evaluate earthquakes that could potentially generate a tsunami. The warning system also disseminates tsunami warning information. The Pacific Tsunami Warning Center is the operational center of the Pacific TWS. Located near Honolulu, Hawaii, PTWC provides tsunami warning information to national authorities in the Pacific Basin. The Alaska Tsunami Warning Center in Palmer, Alaska, serves as the regional Tsunami Warning Center for Alaska, British Columbia, Washington, Oregon, and California.

In addition to monitoring earthquake activity, the TWS also monitors ocean buoys that are able to detect a tsunami. The information comes into the centers in real time and a warning can be issued almost simultaneously.

The information comes through a variety of channels," Wilson said. "They send it out over the Internet within a matter of minutes."

According to Wilson, he receives information regarding Alaskan earthquakes several times a day.

Our Oregon Emergency Response System monitors all of that seismic activity and is able to turn that around to all of the local emergency managers almost instantaneously from when that message comes in," he said. "If there were a tsunami, that information would be put out on the emergency alert system, which gets translated into all of the media."

According to Wilson, the National Weather Service helps coordinate the messages and operate the system. NWS radio stations automatically broadcast the alert messages over their weather radio stations.

Along the coast, a lot of schools, libraries and city halls have NOAA (National Oceanic and Atmospheric Administration) weather radios and alert messages are automatically broadcast to those folks," Wilson said. "Then the local emergency managers then assume the responsibility to use their sirens or whatever systems they have for doing emergency broadcasts."

According to Wilson, beach tsunami sirens are locally controlled.

With many radio stations in Coos County using automated broadcasting after business hours, 911 dispatchers would have the responsibility of getting information to the public should a warning be issued after regular business hours.

According to Coos County Sheriff Andy Jackson, the sheriff's office, in times of emergency can break into broadcasting at local radio stations and get the word out.

The radio stations that we are connected with, we have an override that can override their programming," Jackson told The Sentinel. In addition, Jackson said programming on local television stations would have a ticker tape placed on the bottom of the screen to issue warnings and instruction. However, if there is time, other ways to warn the public may have to be used.

If it came down to it and there was enough time, you might have emergency officials actually, law enforcement, actually go and drive the major highway routes with public address systems to get into campgrounds and things like that just to get the word out," Wilson said. "This would be for a distant tsunami that might come from Alaska or across the Pacific Basin where you have hours."

The TWS has also been used to rescind warnings that had been issued. According to Wilson, seismic information has been generated that necessitated a tsunami warning to be issued. However, information received from buoys monitoring water pressures and wave fronts indicated that no tsunami was generated and warnings were rescinded.

The buoy system that's in place off the coast of Alaska, Oregon and Washington, it's proven its worthiness, because it's allowed us to call off a warning that's been put into place," Wilson said. "It let them avert an evacuation that could have cost a lot of money."

In addition, Wilson said that when people go through false alarms it becomes counter productive by eroding confidence in the system.

However, tsunamis are only one worry for Oregon coastal residents should a large quake strike along the Cascadia Subduction Zone, according to Wilson, who said two other factors would also cause major damage: liquefaction and subsidence.

According to Wilson, many areas along the coast are marsh land that has been developed. Should a quake as large as the one that struck Sumatra take place along the Cascadia Subduction Zone, in many areas along the coast the ground would liquefy and infrastructure on the top would just suddenly disappear.

The ground basically becomes a liquid and foundations and buildings and infrastructure are going to sink and settle into them and that can cause a lot of damage," Wilson said.

Where subsidence occurs, areas would then be left under water as the ground falls below sea level, Wilson said.

That's what happened near the epicenter on Sumatra," Wilson said. "Some of the local villages along the coast actually sank below sea level. There's a certain amount of deflection that happens on the plate on top of the one that's going down. Once the underlying plate slips it's like the tension is released and there's a lot of historic evidence along the Oregon and Washington coastlines that some areas along the coast actually sink a foot or a few feet and become inundated with seawater."

According to Wilson, maps have been produced showing areas that need to be evacuated should an event along the Cascadia Subduction Zone take place. Wilson again stressed that should that quake take place, the quake itself would be the warning to leave the area as the first wave would strike within minutes.

Those are really kind of a conservative estimate of water to make sure people get out of the way," he said. "What's really happening the most is the face that faces along the ocean and at the mouth of the bay because by the time the water gets up and gets around a lot of the velocity is gone, but you still have the water level."

According to Wilson, there are usually sets of tsunami waves rather than a single wave, and many times those coming later are larger.

Depending on the height of the dunes that form that outer barrier there, if it can crest those it will also erode those dunes and so there will usually be sets of these waves and the second and third waves, if they are as big or bigger, they'll roll right over those," Wilson said.

According to Jackson, he is concerned that in case of a tsunami there won't be enough time to warn the public.

"My thoughts are, if we get a tsunami we'll be lucky if we get everybody warned in time. It may only be a mile out before we figure out what's going on. That's not much time to get things moving. It's right in your back pocket," he said. "We're looking at the feasibility of putting sirens and stuff around the county and what that cost would be. But even with the best laid plans there's always going to be something that you didn't prepare for."