When Nature Strikes: Earthquakes

Air Date: 09/24/2015
Source:
NBC Learn
Creator:
Dr. Marshall Shepherd
Air/Publish Date:
09/24/2015
Event Date:
09/24/2015
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2015
Clip Length:
00:05:59

John Vidale and his team at the Pacific Northwest Seismic Network are monitoring ground motion across Washington State and Oregon to prepare residents for one of the most powerful natural hazards on the planet - a magnitude 9 "megathrust" earthquake. "When Nature Strikes" is produced by NBC Learn in partnership with the National Science Foundation and The Weather Channel. For a classroom activity related to this video, please click the Links section below.

When Nature Strikes -- Earthquakes

MARSHALL SHEPHERD reporting: 

When we think about seismic activity in the United States, we often think of California. But one of the strongest earthquakes in U.S. history happened in 1700 in the Pacific Northwest, and it will happen again. John Vidale, a University of Washington seismologist, is leading a team of scientists that is helping residents prepare for the next big quake to hit the region. 

On February 28, 2001 at 10:54 am, a 6.8 magnitude earthquake jolted Washington State, cracking roads, damaging buildings in Olympia and Seattle, and injuring 400 people. Known as the Nisqually earthquake, it served as a wake-up call for Pacific Northwest residents who at some point may face one of the most powerful and destructive natural hazards on Earth, a magnitude 9 or greater "megathrust" earthquake. 

JOHN VIDALE (University of Washington): It's a place where about every 600 years, we have a magnitude 9 earthquake so that whole region shifts about 10 or 20 meters in an earthquake that generates enormous amounts of energy and causes, you know, widespread destruction along the coast. 

SHEPHERD: National Science Foundation-funded researcher John Vidale is director of the Pacific Northwest Seismic Network, a group that is monitoring and recording earthquakes across Washington State and Oregon in order to better understand and prepare for a "megathrust" earthquake. 

A magnitude 9 megathrust earthquake would release about 2,000 times more energy than the magnitude 6.8 Nisqually earthquake. It could trigger a tsunami, landslides, and volcanic eruptions, causing billions of dollars in damages and untold numbers of casualties. Thankfully, earthquakes of this great magnitude are rare. 

Earthquakes are the result of sudden, violent movements of tectonic plates in the Earth's surface. Where two plates meet, called a fault, they rub together and stick until the fault breaks, releasing energy in the form of seismic waves. Millions of earthquakes occur around the world every single year, the majority of which go unnoticed because their magnitudes are small, usually magnitude 5 or below. 

But the Pacific Northwest is susceptible to stronger earthquakes because of an 800-mile-long "megathrust" fault just 60 miles off the coast. Stretching from Northern Vancouver Island to Northern California, it's called the Cascadia Subduction Zone. 

VIDALE: The hazard in the Pacific Northwest is the Cascadia Subduction Zone. It's a place where the rock mass under the ocean, something called the Juan de Fuca Plate that's connected to the Pacific Plate, is pushing underneath the North American Plate.

SHEPHERD: A subduction zone earthquake could trigger a devastating tsunami. Waves up to 30 feet high claimed thousands of lives along the coast of Japan following a magnitude 9 earthquake on March 11, 2011. To better understand the geology of this region and its susceptibility to megathrust earthquakes, the Pacific Northwest Seismic Network has over 50 ground motion stations around the city of Seattle, including this one at a wastewater treatment plant. These stations measure shaking and other movements in the ground generated from seismic waves that can wreak havoc on communities and structures above. 

VIDALE: We'd like to have data from this particular location to try to understand why west Seattle was hard hit in the Nisqually earthquake. We have a strong motion instrument here. It's all wired up to a modem so it's sent over a telephone line back to the University of Washington. 

SHEPHERD: At another monitoring station in downtown Seattle, seismometers and pressure sensors have been placed 100 feet underground to measure shaking before it reaches the surface. This area has soft soil, consisting of sand and gravel, which is prone to a phenomenon called liquefaction. When there is intense shaking, the ground loses its strength and stiffness causing it to behave like a liquid. In a worst case scenario, liquefaction could cause a building to tip over. 

VIDALE: We like this location because we know that in the last 100 years, it's liquefied three times, and if we have another earthquake like we had in 2001, we'll be able to record the fluid pressures and the shaking and just understand that process well enough to tell the engineers how to deal with the problem better. 

SHEPHERD: The Pacific Northwest Seismic Network is in the process of developing an early earthquake warning system that could alert people of shaking before it reaches them, giving the public a few crucial moments to react-- time that can save lives and property.

VIDALE: With a few seconds, you know, you can do things like turn the traffic lights yellow and red to slow down the cars and slow down the trains and have airplanes not land. 

SHEPHERD: These few extra seconds to divert airplanes and stop traffic could help keep people out of harm’s way and prevent loss of life. Even though there is still no way to predict the exact time and location of an earthquake, Vidale and his team hope data gathered by the Pacific Northwest Seismic Network will help prepare residents and issue an alert that could save thousands of lives when the next megathrust earthquake rocks the Pacific Northwest.

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