Identification Criteria for Sources of T Waves Recorded in French Polynesia

Abstract

Ð From a data set of 150 digital records of T phases from 71 sources obtained on seismometers of the Polynesian Seismic Network, we de®ne a discriminant separating earthquake and explosion sources, which uses the maximum amplitude of recorded ground velocity, measured on its envelope, e Max (in lm/s), and the duration of the phase measured at 1/3 of maximum amplitude, s 1=3 (in seconds). Earthquake sources and man-made explosions are eectively separated in a log-log space by the straight line log 10 e Max 4:9 log 10 s 1=3 À 4:1 :Other criteria in both the time and frequency domains fail to reliably separate the populations of the various kinds of events. The application of this technique to analog records of large-scale man-made explosions carried out in the 1960s con®rms that it provides an adequate discriminant over 3.5 orders of magnitude of ground velocity.

T Waves from the 1998 Papua New Guinea Earthquake and its Aftershocks: Timing the Tsunamigenic Slump

“…However, WADATI and INOUYE (1953) countered this suggestion based on the observation of T waves from on-land sources, and we now know that the complex mechanics of T -wave generation can result in substantial T waves even from the deepest earthquakes TALANDIER, 1997, 1998). Also, TALANDIER (1966) has shown in the case of the Kuriles event of 20 October 1963 that a ''tsunami earthquake,'' characterized by enhanced tsunami generation (relative to its surface waves) was actually deficient in T -wave excitation, a conclusion confirmed in the case of recent tsunami earthquakes such as Nicaragua (1992) or Peru (1996) (OKAL et al, 2001). In summary, in the case of elastic dislocations, little if any correlation can be expected between the excitation of T waves (by the highest-frequency components of the source spectrum), and tsunamis (by their static or lowest-frequency components).…”

Underwater acoustic records from the March 2009 eruption of Hunga Ha'apai-Hunga Tonga volcano in the Kingdom of Tonga

“…These properties are consistent with the T-waves derived from shallow seismicity along oceanic spreading centers and transforms (cf., Yang and Forsyth, 2003;Dziak et al, 2004) and suggest that the initial Hunga Ha'apia activity is sourced at similarly shallow depths (b~10 km) within overriding Tofua Arc. By contrast, for deeper plate-interface events, which are common along the subduction zone, higher frequency energy is preferentially stripped out as the signals traverse longer solid-Earth paths through the arc crust (e.g., Salzberg, 2006), and a broader zone T-wave conversion commonly gives rise to more emergent arrivals (e.g., Talandier and Okal, 2001).…”

Hydroacoustic Signals from Presumed CHASE Explosions off Vancouver Island in 1969-1970: A Modern Perspective

“…As shown in Figure 2, the T-phase paper record at station TPT, facing northeast on Rangiroa atoll, is heavily saturated, but its amplitude can be extrapolated from other stations on the atoll, as discussed in Talandier and Okal (2001) and . For Events 1 and 2, predating the full development of the RSP subarray on Rangiroa, a further extrapolation is necessary between the high island of Tahiti and the atoll of Rangiroa.…”

“…In Talandier and Okal (2001), we used a set of 44 announced underwater explosions at sea recorded on Polynesian atolls to derive the empirical relation log10 Y= 1.30 log10 ema x + 2.64…”