Discriminants and Detectors: Seismological Studies of Tsunami Earthquakes and Hurricane Microseisms

High energy natural hazards have potential to cause great damage and significant loss of life, but understanding of many lags behind what is required to mitigate their impacts. Of specific concern here are the estimation of tsunami hazard in the eastern Mediterranean; the more timely identification of tsunami earthquakes; and the use of microseisms to identify “missing” hurricanes, thus augmenting the traditional—but short, incomplete, and biased—observational hurricane record. Earthquake energy estimation and time- and frequency-domain time-series analyses applied to an array of historical analog and modern digital seismological data are used to address these problems.;Improved estimations of the location, depth, moment magnitude, and focal mechanism of four of the largest Hellenic Arc earthquakes in the last century help to better understand seismic hazard there. Seismological reassessments combined with hydrodynamic simulations show that the tsunamis associated with two of them were not triggered by the earthquakes themselves but instead involved submarine slumping.;Moments and estimates of radiated energy from 67 earthquakes taking place in the last twenty years in oceanic environments and recorded at regional and teleseismic distances are used to develop an empirical correction to the robust tsunami earthquake discriminant Theta. This extends its applicability to regional distances, thereby allowing earlier discrimination of tsunami earthquakes.;Microseisms, which result from the interaction of ocean swell generated by energetic storms, are shown here to carry information about parent hurricanes and under favorable conditions can be used to detect them. Power variations of microseisms recorded at the Harvard, Massachusetts seismic station demonstrate that Saffir-Simpson category 5 hurricane Andrew (1992) can be identified when it is ∼2,000 km from the station and still at sea. Applied to an expanded data set of 66 hurricanes between 1992 and 2007 with Saffir-Simpson categories ranging from 2 to 5, microseism power and frequency content analyses indicate that some additional energetic hurricanes can be detected. However, because these methods detect even the most intense hurricanes inconsistently and do not reject non-hurricane storms, a robust detection methodology cannot be based on them alone. These methods do have the potential to improve understanding of the microseism wavefield in general.