Rapid estimation of shaking over the entire southern California region
is accomplished by spatially interpolating ground motions recorded by TriNet using
frequency and amplitude-dependent site corrections based on surface geology.
Ground motions in areas of sparse station coverage are inferred from the data by
using the centroid for forward estimation. As the real-time TriNet station density
increases, the importance of the centroid for gap-filling will diminish,
but currently it is imperative for the robust generation of ground motion maps.
Fortunately, as planned, TriNet stations are more concentrated in heavily populated
regions, so the most reliable recovery of the shaking distribution should be where potential
losses and the need for concerted emergency response efforts could be the greatest.
Newly developed relationships
between recorded ground-motion parameters and expected shaking intensity [Wald et al., 1999a]
allow us to also produce an instrumentally derived intensity map. This additional map allows
us to rapidly portray the extent of shaking
in a simplified form suitable for immediate post-earthquake decision-making.
We have found that a relationship that follows acceleration for
<VII and follows velocity for >VII works fairly well in reproducing the
observed for a number of moderate to large earthquakes which have occurred
in southern California.
One of the most important advances in loss estimation in recent years has been the
development of methods such as HAZUS [Kircher et al., 1997, NIBS, 1997] that directly use
instrumental ground motion observations in place of .
ShakeMap will provide a much clearer picture of the nature and extent of
ground motion following the next significant southern California earthquake and will
provide a sound starting point for immediate loss estimation using such methods.
A critical component in successfully generating ``ShakeMap'' is a system that is robust; that is, it must function under the adverse conditions present during a damaging earthquake including strong shaking of computer equipment, power failures, communication problems, Internet bottlenecks, etc. Efforts have been ongoing to address these concerns. The World Wide Web uniform resource locator for the ``ShakeMap'' is http://www.trinet.org/shake.html