Earthquake activity in the Southern Vanuatu arc recorded by the Texas digital OBS |
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Authors: | Cliff Frohlich Remy Louat Yosio Nakamura |
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Institution: | (1) University of Texas Institute for Geophysics, 8701 N. Mopac, 78759 Austin, Texas, USA;(2) ORSTOM, Noumea BP A5, New Caledonia |
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Abstract: | We have reconfigured the Texas digital ocean bottom seismograph (OBS) to operate in a triggered mode and record regional earthquake
signals. This paper reports the results of a deployment program designed to test these digital OBS, by moni toring earthquake
activity in and near the trench in southern Vanuatu (formerly, the New Hebrides). We successfully recorded hundreds of earthquakes,
including 133 located regional earth quakes recorded by three or more stations. We also report J-B residuals for 21 earthquakes
reported and located by the ISC. Fourier analysis of seismograms from regional earthquakes suggest that the frequencies of
spectral peaks at any station were nearly the same for large, small, nearby, and distant events. However, we obtained very
disparate frequencies when we analyzed seismograms for the same earthquake recorded at different stations. The most plausible
interpretation is that spectral peaks do not depend on the characteristics of the earthquake source, but instead on site characteristics,
or, more specifically, on the coupling of the instrument to the seafloor. To record reliable spectral data, we need to overcome
this problem. |
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Keywords: | Ocean bottom seismograph Vanuatu earthquake spectra |
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