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In a recent paper, Chapman and Marrett [J. Acoust. Soc. Am. 119, 3669-3675 (2006)] examined the tertiary (T-) waves associated with three subduction-related earthquakes within the South Fiji Basin. In that paper it is argued that acoustic energy is radiated into the sound channel by downslope propagation along abyssal seamounts and ridges that lie distant to the epicenter. A reexamination of the travel-time constraints indicates that this interpretation is not well supported. Rather, the propagation model that is described would require the high-amplitude T-wave components to be sourced well to the east of the region identified, along a relatively flat-lying seafloor.

Low‐frequency (1–100 Hz) hydroacoustic recordings can provide a wealth of information on earthquake characteristics in the shallow marine environment. This frequency band, considered low frequency for acousticians, is actually high frequency for regional or global seismologists who commonly work with frequencies of a few Hz and below. In some cases this higher frequency data may provide higher resolution of some earthquake characteristics than traditional seismic methods. The 2004 Great Sumatra‐Andaman earthquake provides an example where detailed analysis of the T‐wave arrival has allowed detailed characterization of changes in rupture velocity that have not proven easy to resolve in traditional seismic data. Our single‐station interpretation of the T‐wave data shows that the fault ruptured northward from the epicenter in at least two phases with lower rupture velocity in the north. The methods behind this single station approach will be discussed along with possible future uses of this type of data for ...

Seismically generated tertiary (T‐) waves can be used to detect and locate the shallow hypocenter earthquakes associated with mid‐ocean ridge spreading centers and oceanic transforms. During the last several years, regional seismic catalogs, which contain estimates of T‐wave source regions, origin times and acoustic source levels, have been generated from continuous hydroacoustic monitoring along the northern Mid‐Atlantic Ridge and equatorial East Pacific Rise. As the mechanics of T‐wave generation remain poorly understood, critics of these datasets have questioned the correlation between T‐wave source regions and seismic epicenters, as well as the usefulness of acoustic source level as a proxy for earthquake size. Recent analyses, however, suggest that these data provide a reasonably complete record of seismicity within the mid‐ocean ridge environment, yielding significant improvements in location accuracy and catalog completeness level, relative to global seismic catalogs. Most importantly, it appears that many fundamental and well‐established properties of seismic distributions can be studied using T‐wave catalogs, including the modified Omori decay law of aftershocks, a power‐law size frequency distribution (Gutenberg–Richter law), a fractal time‐clustering behavior (1/f noise) and fractal spatial distribution of epicenters. These observations show that T‐wave derived earthquake catalogs can be used for quantitative seismo‐tectonic studies in the ridge setting.