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| Here is how the basic tsunami warning
system works in the Pacific Northwest area. First, a key concept
- there are two sources of tsunami for Washington coastal waters
- a distant source and a local source. |
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A local source - if you feel violent
shaking for several minutes, head for higher ground. The earthquake
is your warning. The most likely source for a violent earthquake
of this magnitude is from the Cascadia
Subduction Zone just off our coast. The last associated earthquake
was estimated to be 9.0 in magnitude on Jan 26, 1700, and was similar
to the Dec 26, 2004 Sumatra 9.0 magnitude earthquake and subsequent
Indian Ocean Basin tsunami.
What To Do? - Simulations show the initial tsunami wave from the 1700 event reached the coast in 20 to 30 minutes - so time is limited. Geologic history showed waves with this event were as high as 30 feet. So you must get at least that high above sea level.
To top it off, the earthquake will also result in the coastal area subsiding as much as six feet, meaning the ground and roadways will likely be very uneven, and you are now that much lower to sea level. Since the roads will be in pieces, evacuation must be on foot. Another form of evacuation is vertical evacuation into a sturdy building of at least three stories and climb to at least the third story.
Other area earthquake faults could produce such strong violent quakes, such as the Seattle fault that produced a tsunami in Puget Sound about 1100 years ago. Yet, the most likely source for a local tsunami is the Cascadia Subduction Zone off our coast. |
A Distant Source - The perimeter of the Pacific Ocean Basin, nicknamed the Ring of Fire, has a number of earthquake sources that can produce strong earthquakes of 7.0 magnitude or greater. During the 20th century, there were three 9.0 magnitude or greater quakes, the last was the 1964 Alaskan quake of 9.2 magnitude that produced a tsunami throughout the Pacific Basin. These kind of earthquakes permit a lead time of hours before their subsequent tsunami reaches the Washington coastline. Tsunamis from distant locations like Japan or Chile will take over 10 hours to get here, while from Alaska, only three to six hours.
Tsunamis generated from both sources of earthquakes do penetrate into the Puget Sound region via the Strait of Juan de Fuca and up coastal rivers, harbors and bays, but lose energy as they move further inland.
What To Do? - A Tsunami Warning System has been put into place to help minimize loss of life and property. The West Coast/Alaska Tsunami Warning Center in Palmer, Alaska monitors for earthquakes and subsequent tsunami events. If a tsunami is generated, they issue tsunami watches and warnings, as well as tsunami information bulletins for Alaska, British Columbia and Washington, Oregon and California.
The Pacific Tsunami Warning Center in Ewa Beach, Hawaii provides the same service for the Aloha state as well as all other American territories in the Pacific. They also serve as the International Tsunami Warning Center for 25 other member countries in the Pacific Ocean Basin. |
Both of the tsunami warning centers use earthquake information, tide gauges and now a new tool from NOAA - tsunami detection buoys, developed by NOAA's Pacific Marine Environmental Laboratory. Six of these buoys are now deployed in the north Pacific to help scientists determined whether a tsunami has been generated and moving across the Pacific before reaching North American coastlines - another tool in the tsunami warning centers warning toolbox to help avoid any false alarms. More of these buoys would help detection as well as provide backup to each other since the buoys suffer outages in the harsh north Pacific Ocean.
Upon receipt of tsunami watches and warnings, coastal National Weather Service (NWS) offices such as those in Seattle and Portland, activate the Emergency Alert System (EAS) via NOAA Weather Radio. All broadcasters (TV, AM/FM radio, cable TV) receive the tsunami EAS message simultaneously as well as those with weather radio receivers in homes, businesses, schools, health care facilities, etc. NOAA Weather Radio also activates the All-Hazard Alert Broadcast (AHAB) units located in remote coastal areas, alerting people in those isolated locations.
Upon receipt of tsunami watch and warning messages, local emergency management officials (see Clallam County, WA as an example) can decide to activate the Emergency Alert System (EAS) to evacuate low-lying coastal areas in advance of the initial tsunami wave. Their EAS messages are also received by broadcasters, weather radio receivers and All Hazard Alert Broadcasts (AHABs) to help provide widespread dissemination of these messages. Follow the directions provided by your area emergency management officials - they will help save your life and those of your loved ones.
If you want your own tsunami warning message receipt system, obtain a NOAA weather radio receiver with EAS-programmable features. They are available from most radio electronic retailers and on the Internet.
Education is another key element in the tsunami warning system. Many coastal areas have designated tsunami inundation zones and marked evacuation routes to assist residents and visitors to higher ground. Emergency management officials also distribute tsunami education information, conduct community meetings and workshops, and many more awareness activities.
The National Weather Service recognizes communities with strong
tsunami warning and awareness programs through the TsunamiReady
Community program. Such communities are recognized for their efforts
to enhance their tsunami warning system, widespread use of weather
radio receivers and community awareness activities. TsunamiReady
road signs are also a part of NWS recognition.
Provided by Ted Buehner, NOAA/NWS
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