Friday, November 6, 2015

Inside a tsunami lab

by Lauren Ellis:

Scientists are creating monster waves and slamming them into structures to prepare for the next big one.

Just miles off the coast in the Pacific Northwest is the Cascadia Subduction Zone, a 700 mile long mega fault with a pleasant sounding named that’s capable of anything but. This silent, submerged region is slowly building friction as the oceanic Juan de Fuca plate dives down below the North American continent. That friction eventually needs to give and will release an enormous amount of energy and wallop the coastline.

Subduction zones, like the ones found off the coasts of Chile and Japan, are capable of producing a one-two punch for the Pacific Northwest: a magnitude 9.0 earthquake followed by a 100 ft. wave tsunami. Vancouver, Washington, Oregon, and parts of California are all in the splash zone, and scientists are working quickly to understanding the fault’s mechanics and prepare for the consequences of its future rip. As the saying goes, it’s not a matter of if, but when.  

On this upcoming episode of TechKnow, we visited Professor Dan Cox at the O.H. Hinsdale Wave Research Laboratory, one of the largest test beds for coastal hazard & tsunami research. The team spoke to Dr. Cox about tsunamis, disaster preparedness, and the best designs to minimize damage from this looming event. 

Editor’s Note: The following was adapted from an interview with Phil Torres. It has been edited for length and clarity.

TechKnow: How would a rupture in the Cascadia Subduction Zone turn into a tsunami?

Dan Cox: When the Cascadia Subduction Zone ruptures, the plates lift up and they create a large volume of water that heads to our coast. The reason why this is so dangerous is that it hits our coast in a matter of minutes, maybe 20-40 minutes depending on where you live.

So that’s not a lot of time to evacuate.

It doesn’t give us a lot of time to evacuate and if you are thinking about evacuation for the first time, its going to be too late. You have to have a lot of plans in place.

How big would this wave be? How fast?
When it hits the coast it'll probably be somewhere around 30 feet high and in some cases higher than that.  So it come quickly in 20-40 minutes and when it moves over the land, its going to move faster than you can run. Usain Bolt won't be able to outrun it when first hits the beach…its big, its fast and we have almost no time to react.

Phil Torres and Professor Dan Cox touring the wave lab

So what is the best thing? What needs to be done the second we know a tsunami is coming?

The second we feel the ground shaking, make sure that we know we are safe from the earthquake. Be in a building or in a place where we are not going to get hurt from the earthquake, and then immediately after the earthquake, we have to get to high ground as fast as possible

Are there specialized buildings for this?

One of the big problems on the Oregon and Washington coast is there are a lot of places where there isn’t a lot of high ground. And it turns out that a lot of places that are developed early on are the low-lying coastal areas. But those areas are the most vulnerable and that's where we have to think about other options aside from just moving to high ground.

What would a tsunami evacuation building look like?

A tsunami evacuation building has to be open and accessible to the public 24 hours a day. That’s the most important quality of this building. If it locked up, what good is it? The other thing is, it has to have some ability to resist the tsunami. One way is to make it open so that the tsunami can sort of flow through the building. 

What happens when you add debris to a tsunami wave?

Debris makes the problem a lot more complicated because the force that you can get from a shipping container or tractor trailer or a school bus can be big enough to take out the column support of a building, and then if the building isn't designed right, the building is gong to collapse.

Setting up toy cars and structures in the flume lab

Mini Phil bracing for a tsunami wave

So we did a demonstration, we put a little figurine up on top and he survived the tsunami.  Why does a structure like this help?

They are designed in such a way that the water is going to flow underneath the building and doesn't try to resist the full brunt of the tsunami. It’s not trying to push the water out of the way. It’s just trying to stand up tall and let the water flow underneath. The difficulty is that's probably the worst thing for an earthquake design to put a very heavy mass up high in the air. The best thing for the earthquake is to put it low to the ground. The best thing for the tsunami is raise it up high. We have to figure out the optimum way to put this building together.

How do you find that balance?

Well you have to work with the earthquake engineer and you have to work with a tsunami engineers. They have to both come up with their design and kind of meet in the middle.

So you guys don’t just make buildings, you’ve made entire replicas of towns

We’ve made replicas of typical coastal towns because you might have a building or two that are close together that are massive, and the water is going to flow in between, channeling the water and making the force stronger on buildings that are behind it. So if your evacuation structure is located right behind these big buildings, initially you might think oh its going to be fine its going to be sheltered but the reality is its worse because of the funneling effect. You have to study the building, not just in isolation, but within the entire community.

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