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2008 UNAVCO Science Workshop
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Abstract Information
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Abstract Title
Toward Real-Time GPS for Tsunami Warning Systems and Post-Earthquake Damage Assessment and Emergency Response (INVITED TALK)
Abstract Author
Geoffrey
Blewitt(1), Corne Kreemer(1), William Hammond(1), Hans-Peter Plag(1),
Seth Stein(2), Emile Okal(2), Yoaz Bar-Sever(3), Richard Gross(3),
Vindell Hsu(4), Kenneth Hudnut(5), Mark Simons(6), Tony Song(3) and
Frank Webb(3)
(1) University of Nevada, Reno, Nevada
(2) Northwestern University, Department of Geological Sciences, Evanston, Illinois
(3) Jet Propulsion Laboratory, Pasadena, California
(4) NOAA / NWS, Hawaii
(5) United States Geological Survey, Pasadena, California
(6) California Institute of Technology, Pasadena, California
Abstract Text
The
26 December 2004 Sumatra earthquake (Mw 9.2-9.3) generated the most
deadly tsunami in history. Yet within the first hour, the true danger
of a major ocean wide tsunami was not indicated by seismic magnitude
estimates, which were far too low (Mw 8.0-8.5). This problem relates to
the inherent saturation of seismic wave methods designed to estimate
magnitude with minutes of the event. We have shown that the
earthquake's true size and tsunami potential could have been determined
using Global Positioning System (GPS) data up to only 15 min after
earthquake initiation, by tracking the mean displacement of the Earth's
surface associated with the arrival of seismic waves. Within minutes,
displacements of >10 mm are detectable as far away as India,
consistent with results using weeks of data after the event. These
displacements imply Mw 9.0 ± 0.1, indicating a high tsunami potential.
This suggests existing GPS infrastructure could be developed into an
effective component of tsunami warning systems. We present our recent
findings on the design specifications a real-time GPS component of
future tsunami warning systems.
It is now being proposed
jointly by NASA, NOAA and USGS to exploit the increasingly available
global and regional real-time GPS data from NASA's operational Global
Differential GPS (GDGPS) System to enable more accurate and timely
assessment of the magnitude and mechanism of large earthquakes, as well
as the magnitude and direction of resulting tsunamis. The idea is to
use GPS-based information, in addition to existing data types, to
enhance the USGS operational system for post-earthquake damage
assessment and emergency response, and to improve tsunami warnings by
NOAA's Pacific Tsunami Warning Center (PTWC).
In addition, we
note that the IGS Real-Time Pilot Project is just underway, which will
provide real-time access to precise satellite orbits and clocks to
enable rapid precise point positioning. As current geodetic techniques
approach the ability to monitor ground movements with millimeter
accuracy over the broadband range of ~1 second to ~10 years, it becomes
apparent that IGS, and more generally the Global Geodetic Observing
System (GGOS), should be exploited for geohazard prediction and early
warning systems. Broadly speaking, successful prediction and early
warning require two very different system designs. On the one hand,
prediction systems are characterized by high accuracy measurements,
detailed modeling and understanding, and long term stability to provide
a standard frame of reference as a basis for prediction. On the other
hand, early warning systems are characterized by real-time sensitivity
and automatic response to events, and robustness against false alarms.
Since
geohazards are often associated with long-term cumulative processes
leading to precipitously damaging events, there is an obvious advantage
if the two systems being used for prediction and early warning are
developed within a self-consistent framework, as could be provided by
GGOS. This way, the early warning system design can be better informed
by the understanding gained from the prediction system. Prediction also
helps to target the warning systems more efficiently. Precise
positioning using GPS/GNSS can be done at high rate in real-time, and
so can bridge the bandwidth from seconds to decades, enabling an early
warning capability, while providing a connection to the more long-term
stable components of GGOS required for prediction.
We suggest
that the EarthScope PBO/PANGA array in the Cascadia subduction zone
provides an ideal candidate location to begin implementing the concept
of combined prediction/early warning systems. Our simulations (Figure
1) suggest that an Mw 9.0 earthquake in this region would generate
>10 cm static displacements over a broad area covered by PBO/PANGA,
which would be easily detectable within minutes of the earthquake
origin time. We would therefore recommend to upgrade the PBO network to
provide data in real time.
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