Geoscience Reference
In-Depth Information
Tsunami Decision Support
Detection of a signiicant earthquake leads to a series of critical decisions by TWC watch-
standers: What type of product needs to be issued? When and how can the initial message be
reined, based on real-time observations? Basic tools available in the decision making process
include:
•
Threshold criteria for an initial warning, which are based on historical events;
•
Software for monitoring relevant data and visualizing the tsunami event; and
•
Pre-run models that provide scenarios of inundation and impacts, also based on
historical events.
The type of notiication product issued from each TWC is based on an earthquake's loca-
tion, magnitude, and depth. These “bulletin threshold” criteria differ for different regions of an
AOR, as seen in Table 5.2. However, some regional differences in the threshold criteria could
result in confusion. For example, in the case of a 6.5 magnitude earthquake in the vicinity of
Puerto Rico, the WC/ATWC would issue a warning for Puerto Rico, but based on PTWC back-
up criteria from the WC/ATWC user's guide, the PTWC would issue an information statement
for the Caribbean Sea (National Oceanic and Atmospheric Administration, 2009). It is not clear
what factors have contributed to this difference in threshold criteria between Puerto Rico and
rest of the Caribbean Sea. As previously discussed, issuing messages with potentially con-
licting or confusing content—as would be the result from issuing a warning for Puerto Rico
and an information statement for the remaining Caribbean Sea—is counter to the science of
effective warning messaging. Thus, harmonizing threshold criteria to yield consistent warning
products for regions in close proximity would reduce a potential source of confusion.
As discussed in Chapter 4, the initial warning is based on seismic information alone and
relies on fairly conservative thresholds. Therefore, in the case of most earthquakes—except for
“mega-” and “tsunami” earthquakes (see Appendix G and H)—these thresholds result in the
tendency to over-warn. Given the potential consequences of failing to warn, that is, the loss of
lives, over-warning is the preferred outcome for the initial product, which can be reined based
on the subsequent detection of sea level changes. However, as previously noted, tsunami
earthquakes (i.e., slow earthquakes—see Appendix H) might not be recognized quickly
enough based on the current analysis and might not result in the correct warning decision.
Even this early decision process could beneit from reinement as more advanced methods
have been developed and are discussed in greater detail in Chapter 4.
Product Generation and Warnings
Once a watchstander decides to issue a message, s/he ills out a pre-generated checklist
that is incorporated into a pre-written or “canned” message. After the product is generated,
it is carefully reviewed by the watchstander prior to issuance. Checklists and tsunami warn-
