T waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy up the slab

Abstract

Abstract. We report the observation of T phases recorded at a number of Pacific island sites, following the great Bolivian deep earthquake of June 9, 1994. By studying their arrival times at the various stations, we unravel the process of conversion from seismic to acoustic energy at the South American coastline. We find that the maxima of amplitude of the phase are incompatible with propagation along the great circle from source to receiver but rather require the generation of the acoustic wave at a common point at the Arica Bight for all stations in the South Pacific, and even farther south for stations in Hawaii and the Bonin Islands. The timing of these conversions corresponds to the arrival of regional S waves at the conversion points. The high-frequency nature of the T phase requires the channeling of the S wave from the seismic source to conversion point through low-attenuation material, which in tums adds supportive evidence for the mechanical continuity of the downgoing slab under that section of South America, despite the observed gap in seismicity between 300 and 600 kmo

T‐waves excited by S‐waves and oscillated within the ocean above the Southeastern Taiwan Forearc

“…However, the results differ from those obtained by Talandier A detailed comparison of the results of this study with those of previous research shows that whether the T-waves were converted from P-or S-waves, they were consistently dependent on the incidence angles of the seismic waves. In the studies of both Okal and Talandier (1997) as well as in the present study, the seismic waves had an almost vertical incidence before being converted into T-waves, even though the seismic waves had been generated at different hypocentral distances. Consequently, the T-waves were converted from S-waves in both studies.…”

“…Recently, more detailed investigations into the conversion processes of acoustic energy (T-waves) from and to seismic waves based on the downslope conversion mechanism have been more numerous (Okal and Talandier, 1997;Talandier and Okal, 1998). For one, the T-phases that were generated by the great 1994 Bolivian deep earthquake and recorded at a number of Pacific island sites significantly corresponded to the arrivals of regional S-waves at the conversion points (Okal and Talandier, 1997).…”

“…For one, the T-phases that were generated by the great 1994 Bolivian deep earthquake and recorded at a number of Pacific island sites significantly corresponded to the arrivals of regional S-waves at the conversion points (Okal and Talandier, 1997). In another study, high-frequency seismic records in the Polynesian Seismic Network showed that the T-waves were generated in a steep slope, which allowed for an efficient conversion from P-waves by shallow events (Talandier and Okal, 1998).…”

Hydroacoustic contributions to understanding the December 26th 2004 great Sumatra–Andaman Earthquake

“…By exploiting these characteristics, regional hydroacoustic arrays can provide significant improvements in detection threshold and location accuracy, relative to land-based seismic monitoring (Fox et al 1994;. Importantly, T-wave studies have done much to define mid-ocean ridge eruptive processes (e.g., Fox et al 1995;Dziak and Fox 1999), illuminate the complex structure of subduction zones and slabs (e.g., Fox and Dziak 1999;Okal and Talandier 1997), provide insights into transform fault dynamics (e.g., Dziak et al 1997;McGuire et al 2005) and shown great promise as a tool in addressing a variety of other tectonic problems (e.g., Smith et al 2002;Bohnenstiehl et al 2002Escartín et al 2003).…”

Operational Processing of Hydroacoustics at the Prototype International Data Center

“…For example, an earthquake generated signal which propagates through the ocean and is then recorded on a T-phase station might have been called``PTP''. The problem with this approach is that the mode of propagation on land is not known and probably includes compressional, shear and surface type waves (PISERCHIA et al, 1998;OKAL and TALANDIER, 1997;STEVENS et al, 1998). It would be similar to separating the regional seismic Lg phase into its various components.…”