Tsunami Warning Procedure Based on Pre-computed Tsunami Forecast Models
Abstract
The mission of a Tsunami Warning Center (TWC) is to provide advance warning to coastal communities in the event of a tsunami. TWCs issue their initial warnings based on earthquake source region and magnitude criteria to accomplish this. For example, a magnitude 8.2 earthquake in the Gulf of Alaska will prompt a warning for all coastal areas within a three hour tsunami travel time from the source. Note that this approach bases warning extent exclusively on tsunami travel time or distance from the source which may lead to over-warning as some regions within the travel time or distance are not threatened. Tsunami forecast models can help limit the warning region extent by assessing the threat in advance. At the West Coast and Alaska Tsunami Warning Center (WCATWC), the Alaska Tsunami Forecast Model is executed and the output for likely earthquake sources along tectonic boundaries throughout the Pacific basin with magnitudes ranging from 7.5 to 9.5 is databased. The geographical extent of the initial tsunami warnings and/or advisories is then assessed using the pre-computed forecasts. The initial tsunami warning or advisory extent, established previously based on earthquake location and magnitude, is then either limited or expanded as necessary based upon the threat level. When portions of coastline are placed under a warning or an advisory, the WCATWC delineates them into sections through the use of “breakpoints.” Breakpoints are pre-defined end point locations for a specific section of coastline, and they coincide with the borders of National Weather Service public forecast zones. One or more public zones are included between two breakpoints, though not all the public zones may have the same threat. Public zones are then analyzed for threat by examining the forecasted amplitudes within the zone; amplitudes > 1 meter indicate a warning and amplitudes 0.3 to 1 meter indicate an advisory. The alert level (warning, advisory, or none) of the public zone is set to the highest forecasted threat level within that zone for a given earthquake. If there are multiple public zones between breakpoints, the alert level between the breakpoints corresponds to the alert level of the public zone with the highest forecasted threat; though non-threatened zones will not be included in the list of zones for the segment(s) under an alert. For example, a magnitude 8.2 Gulf of Alaska earthquake would trigger an advisory for the coast of Washington based on this procedure. However, only the public zones along the outer coast are threatened at the advisory level; the Puget Sound and Strait of Juan de Fuca zones are not threatened and would not be listed in the advisory zones. This procedure limits the length of coast put into an alert level to those coastlines threatened by the event, reducing the cost and impact of the public response.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMOS11B1194H
- Keywords:
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- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges