HR: 0800h
AN: NG41B-0526    [Abstracts]
TI: Non-Poissonian Distribution of Tsunami Waiting Times
AU: * Geist, E L
EM: egeist@usgs.gov
AF: USGS, 345 Middlefield Rd., MS 999, Menlo Park, CA 94025, United States
AU: Parsons, T
EM: tparsons@usgs.gov
AF: USGS, 345 Middlefield Rd., MS 999, Menlo Park, CA 94025, United States
AB: Analysis of the global tsunami catalog indicates that tsunami waiting times deviate from an exponential distribution one would expect from a Poisson process. Empirical density distributions of tsunami waiting times were determined using both global tsunami origin times and tsunami arrival times at a particular site with a sufficient catalog: Hilo, Hawai'i. Most sources for the tsunamis in the catalog are earthquakes; other sources include landslides and volcanogenic processes. Both datasets indicate an over-abundance of short waiting times in comparison to an exponential distribution. Two types of probability models are investigated to explain this observation. Model (1) is a universal scaling law that describes long-term clustering of sources with a gamma distribution. The shape parameter (γ) for the global tsunami distribution is similar to that of the global earthquake catalog γ=0.63-0.67 [Corral, 2004]. For the Hilo catalog, γ is slightly greater (0.75-0.82) and closer to an exponential distribution. This is explained by the fact that tsunamis from smaller triggered earthquakes or landslides are less likely to be recorded at a far-field station such as Hilo in comparison to the global catalog, which includes a greater proportion of local tsunamis. Model (2) is based on two distributions derived from Omori's law for the temporal decay of triggered sources (aftershocks). The first is the ETAS distribution derived by Saichev and Sornette [2007], which is shown to fit the distribution of observed tsunami waiting times. The second is a simpler two-parameter distribution that is the exponential distribution augmented by a linear decay in aftershocks multiplied by a time constant T_a. Examination of the sources associated with short tsunami waiting times indicate that triggered events include both earthquake and landslide tsunamis that begin in the vicinity of the primary source. Triggered seismogenic tsunamis do not necessarily originate from the same fault zone, however. For example, subduction-thrust and outer-rise earthquake pairs are evident, such as the November 2006 and January 2007 Kuril Islands tsunamigenic pair. Because of variations in tsunami source parameters, such as water depth above the source, triggered tsunami events with short waiting times are not systematically smaller than the primary tsunami.
DE: 3245 Probabilistic forecasting (3238)
DE: 3265 Stochastic processes (3235, 4468, 4475, 7857)
DE: 4468 Probability distributions, heavy and fat-tailed (3265)
DE: 4564 Tsunamis and storm surges
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting