Q&A: Earthquakes and Tsunamis

How far away from a continent does an earthquake have to be to generate a huge tsunami? 

Usually big tsunamis happen in subduction zones, which are located on the rim of fire around the Pacific Ocean. Unfortunately, those subduction zones are pretty close to the continents. The three biggest tsunamis: the Indonesian Tsunami, the Alaskan Tsunami, and the Chilean Tsunami occurred along the coastlines. There are usually no earthquakes in the middle of the ocean because nothing happens in the middle of the ocean. All the action happens where the subduction plate goes underneath the continent plate; all that happens at the coastlines. - Elena Suleimani, Tsunami Modeler/Research Analyst 

Does the size of an earthquake affect the speed of a tsunami?

The deeper, the faster. The formula for a tsunami wave is speed = [square root of] gravity x depth. Gravity is the gravitational constant of 9.82 meter/second square. Depth is the ocean depth. Which means that the only thing the speed of the wave depends on is the depth of the ocean. It doesn’t matter how strong the earthquake was, the speed of the wave only depends on the ocean depth. - Elena Suleimani, Tsunami Modeler/Research Analyst 

Which generates more a chance of a tsunami – earthquakes in land on the coast, or earthquakes in the ocean?

In order for a tsunami to be generated the earthquake has to be under the ocean bottom. If the  earthquake is on land, it is not going to generate any tsunami waves. - Elena Suleimani, Tsunami Modeler/Research Analyst 

How do the plates move to form the earthquake?

What happens, in terms of the North American plate (where Alaska is) and the Pacific plate, the Pacific Plate goes underneath the American plate and pushes it does. Stress is accumulated there over hundreds or thousands of years. They are stuck together. One day, it snaps and the stress is released. That upward motion pushes the water up and causes the tsunami. - Elena Suleimani, Tsunami Modeler/Research Analyst 

The earthquake in 1944; was the ‘quake really hard?

Oh yes, all day. Me and my cousin were hiding out by the door, bumping. - Phyllis Peterson, Kodiak Elder

I was in school in Afognak and it just shook the lights. They sent us all up the hill, into the mountains. During this other one, in ’64, my sister was going back home from the back bay where they keep their boats. The tidal wave starting coming so she turned around and went back to the mill. She says the water was right behind her; she was driving. She drove up the hill and then it stopped; she just made it. - Dennis Knagin, Kodiak Elder

We didn’t have a chance to grab one little thing when the water came. You just try to save your life; that’s all. You got no choice. - Phyllis Peterson, Kodiak Elder

The next day, I went down the beach below our house there, found a drum of gas. And I started to pump some out. Then, they announced another one coming, so I had to just drop everything and go. And I guess a while later someone else come and get that gas out of there. - Dennis Knagin, Kodiak Elder

What are some of the Alutiiq words for earthquake and tsunami?

Ulertuq is running away. - Dennis Knagin, Kodiak Elder

Ulertuq. And arulauq is earthquake. - April Laktonen Counceller, Quk'rtarmiut Alutiit Language Revitalization program manager, Alutiiq Museum & Archaeological Repository

How many aftershocks were there after the 1964 earthquake?

It shook every few minutes. - Phyllis Peterson, Kodiak Elder

Even after they took us to Anchorage, we hitch hiked on this crew, it took us 45 minutes to hitch hike down. We were riding there, and it started shaking. On 4th avenue in a bar in Anchorage, it started shaking and we run out, not waiting for anything. That area all collapsed. - Nick Alokli, Kodiak Elder

I guess [?] was coming into Ugak Island, you know the straits between Ugak island, he said it was all breakers. So he was going right up to it and taking pictures, and [it started shaking and] his legs buckled and he got all wet with his camera. His dad called and told him to get out of there. - Dennis Knagin, Kodiak Elder

Can volcanoes cause an earthquake?

The two are definitely interlinked. During an eruption, the movement of the magma will definitely cause earthquakes and sometimes it can be pretty large. Like when I showed the example of Mt. Pinatubo, that was a very large eruption. They had magnitude five earthquakes all the time. So they can definitely cause earthquakes. The big earthquakes that you feel elsewhere in Alaska - those would not be caused by volcanoes. So it would only be in the vicinity of the volcano, but yes they definitely do cause earthquakes. - Guy Tytgat, Geophysicist, Alaska Volcano Observatory


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