Feeds:
Posts
Comments

Posts Tagged ‘cascadia subduction zone’

The following items are derived from a phone conversation I recently had with James Roddey, public relations head for the Department of Oregon Geology and Mineral Industries (DOGAMI), and most of the quotes are from Roddey:

Seawalls and Japan: Building seawalls along the coast has the danger of giving citizens behind the seawall a false sense of security. If the seawalls aren’t built high enough, they will do little good. No one in Japan expected a 1,000-year event to happen off their northeastern coast. An 8.1 earthquake had been forecast as the maximum for the area, and a 7.5 at the Fukushima plant. We’ve learned about the cost of that underestimation.

Chile: The difference between Japan’s subduction zone tsunami and the one in Chile in February 2010 is that in Chile, there were no seawalls, and no warning systems to sound the tsunami alarm. The tsunami that hit Chile was somewhat smaller than the one that hit Japan. But more importantly, Chile had a different style of building: using concrete, with deep foundations anchored into the ground. In Japan, the homes and other buildings were generally not built to sustain tsunami damage. Many wood-frame houses were broken off their bases by the tsunami: without an anchor in the ground, the homes were carried off by the rushing waters. Also, in Chile, people knew exactly what to do after their earthquake: the people had grown up hearing scary stories of the 1964 quake and tsunami. They knew not to wait for an announcement or an evacuation order from the authorities: they just dropped everything and ran inland.

Oblivion and ignorance and denial: Roddey said the basic problem he faces in getting out the word about the earthquake danger is that “we don’t get a lot of earthquakes of sizable magnitude, and so people are oblivious to the danger.” So, agencies are focusing on a tsunami outreach and education program for coastal dwellers. (Check this website to see how busy Roddey is with events on the coast.) He said people on the coast are much better prepared than they used to be, but many communities are still in denial.

The media—including Portland tv stations and papers like the Oregonian—is really good at getting the word out, but most of the stories are background noise. You have to try to convince people that the danger is there. It is: there have been 40 large subduction zone quakes in the last 10,000 years. That’s an average of one every 250 years: the last one happened in 1700. Draw your own conclusions.

Roddey said a lot of places on the coast are woefully unprepared. He gets, with alarming frequency, angry calls from hotel and motel owners asking him, “Why are you doing this? You’re hurting our business! No one’s going to come to the coast if you scare them off!” His counter to that “bottom line” argument is that the hotels and motels simply need to get prepared, and they can make their preparedness a selling point for their tourist guests by being able to say, “You’ll be safe here, our place is rock solid.”

The Oregon coast: On the coast, there are 50,000 people living in the expected inundation zone for a subduction zone tsunami. Another 250,000 people are in state parks in the summer, during tourist season, and would be vulnerable to a tsunami. A lot of coastal communities are very vulnerable to a tsunami, with flat terrain and no easy evacuation route. They include Seaside, Gearhart, and Warrenton.

The Washington coast sirens: Washington’s Emergency Management Division has central control of a network of sirens along its coast. That is, when someone at their head quarters sees an earthquake off the coast, he can press a button and make all the sirens on the coast sound the alarm.

The Oregon coast sirens: The sirens on the Oregon coast are not centrally controlled. They’re an ad hoc response built and managed by individual municipalities. They don’t have good coverage; they’re activated locally, on a piecemeal basis. And, some of the sirens may not work when needed. So, sirens, like seawalls, give people a false sense of security.

The sirens are really only good for warning about a tsunami that’s begun a long ways away. People need to know that this kind of warning gives you lots of time to head inland, and the tsunami probably will not be a big event. 99% of people on the coast would not need to evacuate for a distant tsunami.

The really deadly tsunami, the one people on the Northwest coast have to prepare for, is one that will happen locally. If a tsunami starts near the coast, you’ll need to take the initiative and not wait for a siren to tell you what to do.

NOAA radios: As the above indicates, instead of relying on sirens, tv or regular radio, you should use NOAA weather radios to keep yourself informed in a disaster.

Portland earthquakes: There are three known major faults in the Portland area. The apparent recurrence period for large earthquakes on the faults is once every 2500 years. And, the experts think the faults can produce at most a 6.5 magnitude quake. The Portland hills fault slipped 10,000 years ago. But, keep in mind that these figures are based on a sliver of evidence, one or two trenches dug in a parking lot or highway construction site. You shouldn’t think that these are fail-safe assurances of safety and that no bad earthquakes can happen in and around Portland.

Tsunami damage around Brookings and Oregon’s south coast: The Japan tsunami did $25 million of damage to the port at Brookings, quite a bit of damage at Gold Beach, a little bit at Port Orford, and a minuscule amount as far north as Depoe Bay. The Brookings area was hit so hard because the oceanic shelf is much shallower around Brookings. It funnels the wave into a smaller area and lets it build up as it hits the coast. For an analogy on land, think of how the Colorado River or Rouge River turn into whitewater rapids in places where the river channel narrows and the terrain drops sharply. Pretty much the same thing happens as the ocean floor turns up toward the coast. When a tsunami comes along, it surges into the narrow, rising funnel near shore and hits the shore with more violence because all that water has to squeeze into a much smaller area.

Read Full Post »

Follow

Get every new post delivered to your Inbox.

Join 97 other followers