Tsunami earthquakes: the quest for a regional signal

Using the technique developed by Newman and Okal [J. Geophys. Res. 103 (1998) 26885], a dataset of digital records from 84 earthquakes is analyzed to investigate their source slowness in the quest for a possible regional signal in three subduction zones which experienced recent tsunami earthquakes (Nicaragua, 1992; Java, 1994; Peru, 1996). The dataset is augmented by analog seismograms from historical events, including major tsunamigenic earthquakes of the past 65 years. We fail to detect a regional trend for slowness, which suggests that the latter may be controlled on a more local scale by morphological structures of the subducting plate. No correlation is found between slowness and either depth, focal mechanism, or seismic moment. Tn Nicaragua, we document two slow historical earthquakes located on the slab down-dip from the 1992 shock. The most interesting results are in Peru, where a local area of slowness is tentatively defined around the source of the 1960 tsunami earthquake, and where both the 1996 and 1960 tsunami earthquakes occur at the intersection of the trench with major topographic features on the Nazca plate, the Mendana fracture zone and the Trujillo trough, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.