Geoscience Reference
In-Depth Information
The TWCs in-house analysis offers the beneit of obtaining solutions much faster than
the NEIC's publicly available solution, which might take tens of minutes longer. In addition,
the TWCs' assessment of the tsunami potential of any given earthquake depends on knowing
the depth of the earthquake and the earthquake's geometry, neither of which are as high of a
priority for the NEIC.
Regardless, there are many beneits to leveraging research and development at the TWCs
and the NEIC and to more broadly ind synergies in the tsunami and earthquake hazard reduc-
tion programs.
Conclusion:
The current global seismic network is adequate and suficiently reliable for
the purposes of detecting likely tsunami-producing earthquakes. Because the majority of
the seismic stations are not operated by the TWCs, availability of this critical data stream is
vulnerable to changes outside of NOAA's control. Furthermore, as discussed in Appendix G,
many of the STS-1 seismographs in the GSN are now more than two decades old, and
because the STS-1 is no longer manufactured, spares are not available.
Recommendation:
NOAA and the USGS could jointly prioritize the seismic stations
needed for tsunami warnings. These needs could be communicated with partner agencies
and organizations to advocate for upgrading and maintenance of these critical stations
over the long-term.
Conclusion:
The complex seismic processing algorithms used by the TWCs, given the
available seismic data, quickly produce adequate estimates of earthquake location, depth,
and magnitude for the purpose of tsunami warning. The methodologies are inexact, partly
because of the physically variable nature of tsunami-generating earthquakes (one model
does not it all), and partly because of the need for rapid determination of earthquake
parameters that may not be certain until the entire rupture process is complete (potentially
minutes). For example, the methodologies applied by the TWCs do not properly relect the
tsunami-generating potential of mega-earthquakes or tsunami earthquakes.
Conclusion:
In parallel with their own analyses, staff at the TWCs and at the Tsunami Program
could avail themselves of earthquake locations and magnitudes that are estimated within
minutes of an event from the USGS's NEIC. An interagency agreement could be established
to make these initial estimates available on secure lines between the USGS and NOAA.
Recommendation:
Among the methodologies employed by the NEIC is the W-phase
algorithm for estimating earthquake magnitude. The committee recommends that the
TWCs work jointly with the NEIC to test the potential utility of the W-phase algorithm in
the tsunami warning process, using both a suficient dataset of synthetic seismograms
and a set of waveforms from past great earthquakes, paying particular attention to the
algorithm's performance during tsunami earthquakes and to the assessment of a lower-
magnitude bound for its domain of applicability.
