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

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 turns 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 km.