Real-time determination of "Tsunami Earthquakes"
Andrew V. Newman
Along with Emile Okal, I have worked to develop Real-Time Determinations of "tsunami earthquakes" from teleseismic P-waves. "Tsunami earthquakes" are oceanic events that rupture at a significantly slower rate than do normal tectonic earthquakes. These events are considerably more effective at generating tsunamis (either by inducing oceanic landslides, or by setting up a resonance effect through the water column). Since "tsunami earthquakes" rupture at a slower rate, they radiate much less energy in the body waves (high frequency energy) than they do in surface waves (low frequency energy).

By utilizing the deficiency in energy radiated in the body waves we have developed a method for determining in real-time, the impending danger these earthquakes may bring in the form of tsunami waves. Currently this work is for stations that are between 30 and 80 degrees from the event; future work will include local warning.
We have also been working on determining whether the slow nature of recent tsunami earthquakes (92 Nicaragua, 94 Java, 96 Chimbote) is seen in the other recent large oceanic events in the respective areas.

The following three figures show the locations of the three recent "tsunami earthquakes" as well surrounding oceanic events with seismic moments greater than 1026. The colors of the beach balls represent the relative Energy/Moment ratio, going from low (red) to high (blue).
The Nicaraguan Earthquake of Sept. 2, 1992 (large red beach ball) occurred in a region of significant trench seismicity. With the exception of a small earthquake in 1987, there are no other significantly deficient events, however there are a large number of intermediately deficient events (shown with orange beach balls).
The Java Earthquake of June 2, 1994 (large red beach ball) was in an area where no other deficient earthquakes were found. All other events had moderate to high energy; even the five aftershocks (all with normal focal mechanism solutions) are rich in radiated energy (blue).
Similar to the Nicaraguan event, the Chimbote Earthquake of Feb. 21, 1996 (large red beach ball) occurred in a region where other intermediately deficient events have occurred (orange).
I have included a figure showing the radiated energy compared to the CMT published seismic moment. Events that are lower and more to the right are considered to be deficient in body wave energy. Note: The Indonesian tsunamigenic event that generated a large tsunami in Papua New Guinea shows to be moderately deficient. More information about this earthquake and tsunami can be found in the August 1st and October 3rd issues of Science News or from USC's PNG tsunami page.

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