Mar 29, 2011

Discovery Files: Earth Wake

The potential for a huge Pacific Ocean tsunami on the West Coast of America may be greater than previously thought, according to a new study of geological evidence along the Gulf of Alaska coast.

Credit: NSF/Karson Productions

Audio Transcript:

Finding fault[1]-- From Sendai to the San Andreas.

I'm Bob Karson with the discovery files -- new advances in science and engineering from the National Science Foundation.

The magnitude[2] 8.9 Japan earthquake and destructive tsunami cause many to be concerned about whether similar events could occur on our own west coast. Research led by the University of Texas at Austin following the Haiti quake is kind of a "sorta-good-news -- not-so-good-news" kind of thing. The sorta good news is that the San Andreas Fault is a "strike-slip" fault[3]. The two plates are passing each other moving in opposite directions. The Sendai quake occurred on a subduction[4] fault -- one plate riding under the other.

Traditionally, tsunami risk is considered to be higher in these subduction areas because they displace huge amounts of water when they rupture.

Which brings us to the not-so-good-news for the U.S. the research team found that you do not need a large quake to produce a large wake. In strike-slip areas like those around the San Andreas Fault, large tsunamis can occur through "submarine landslides." Sediment slides along the seafloor and displaces the water above it.

The team conducted geological surveys on and off shore around the epicenter[5] of the Haitian earthquake. They found that tsunamis around Haiti are about 10 times more likely to be generated by submarine landslides than previously thought. Meaning higher risk of destructive tsunamis in places near strike-slip faults -- like Kingston, Istanbul, and Los Angeles.

"The Discovery Files" covers projects funded by the government's National Science Foundation. Federally sponsored research -- brought to you, by you! Learn more at or on our podcast.

[1] Fault
--A mistake.
--In geology, a fault(斷層) is a planar fracture in rock in which the rock on one side of the fracture has moved with respect to the rock on the other side.

[2] Magnitude規模
--The size of an earthquake.

Intensity of earthquake motion震度
--the strength of ground motion

[3] Strike-slip fault 平移斷層
--The fault surface is usually near vertical and the footwall(下磐) moves either left or right or laterally with very little vertical motion.

[4] Subduction 隱沒
--The sideways and downward movement of the edge of a plate(板塊) of the earth's crust into the mantle beneath another plate

[5] Epicenter震央
--The point on the earth's surface vertically above the focus(震源) of an earthquake.

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