Geoscience Reference
In-Depth Information
Although the use of
M
wp
is satisfactory for the majority of the (small, non-tsunamigenic,
and medium) events processed,
M
wp
has very serious shortcomings in its application to great
earthquakes (magnitude greater than 8.0), to mega-earthquakes (magnitude greater than 8.5;
Appendix G), and to the anomalous tsunami earthquakes (Whitmore et al., 2002; Appendix H).
Thus, the committee is concerned that the TWCs have relied on a single technique applied
without suficient attention to its limitations discussed above. Other approaches are presently
being studied including the “W-phase” algorithm, which could eventually be implemented
after both the theoretical and operational bases of the approach are established and the
limitations of current technologies are understood (Appendix G). Improvements are urgently
needed for the determination of the tsunami potential of mega- and tsunami earthquakes.
Potential Use of Earthquake Alerts from the NEIC
While NOAA and the NTHMP lead the efforts relevant to tsunamis, the USGS and the
National Earthquake Hazards Reduction Program (NEHRP) lead the efforts in research and re-
ducing impacts from earthquakes. The USGS' Earthquake Hazard Program provides and applies
earthquake science information to mitigate potential losses from earthquakes. This separa-
tion in mission runs the risk of developing tsunami efforts that neglect the earthquake hazard
within NOAA and vice versa within the USGS.
One service the USGS provides through its NEIC is to rapidly determine the location and
size of earthquakes around the world. The NEIC in Golden, Colorado, derives initial solutions,
not made public, within seconds after arrival of the seismic data. The NEIC monitors the GSN
and other stations and produces accurate seismic analysis within minutes of an event, which
it disseminates to a broad range of customers (national and international agencies, academia,
and the public). In a development that may inluence the methods and roles of the TWCs, U.S.
seismology is on the verge of being able to warn of earthquakes while they are still under way.
The drive toward such earthquake early warning includes the NEIC. USGS sources say that the
NEIC, which began operating 24/7 in January 2006, plans to support this warning function by
developing a back-up center at a site other than Golden. At present, the two TWCs do not use
the epicentral, hypocentral, or magnitude estimate provided by the NEIC. Instead, each TWC
uses its own mix of seismic processing algorithms and as described above develops its own
seismic solutions. The TWCs may correct their initial estimates, which are often made public
faster than the NEIC's solutions, to be more consistent with the NEIC's solutions and at times
confer with NEIC staff during an event to ensure consistency. With the availability of the new
tsunami forecasting methods and sea level observations (as described below), the TWCs rely
more on sea level data and numerical models than on details of earthquake parameters after
the issuance of the initial warning product. Therefore, the committee discussed whether it
remains necessary for the TWCs to run their own independent seismic analysis. For the forecast
models, the TWCs require little more than location, rough magnitude, and time of the event,
which could come directly from the NEIC.
