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Observations of ambient noise and signal coherency on the Island of Hawaii for teleseismic studies

Department of Earth, Atmospheric, and Planetary Sciences Massachusetts Institute of Technology, Cambridge, Massachusetts 02142
Department of Geological Sciences University of California at Santa Barbara, Santa Barbara, California 93106
Department of Geology and Geophysics University of Wisconsin-Madison, Madison, Wisconsin 53706
Global Seismographic Network, IRIS, Arlington, Virginia 22209

Abstract

Ambient seismic noise conditions at several sites on the Island of Hawaii have been studied by analyzing noise power spectral density (PSD) and signal-to-noise ratio (SNR) of teleseisms. Broadband digital waveform data used in this study were collected during Project ALOHA. Direct comparison of noise PSD and SNR of teleseisms simultaneously recorded at stations on Hawaii and at station KIP on Oahu indicates that the stations on Hawaii are quieter than station KIP on Oahu in the frequency band of 0.1 to 1 Hz, suggesting that the Island of Hawaii can provide better noise conditions than station KIP. Our interpretation of this observation is that the area and volume of Hawaii are much larger than those of Oahu and distances to the coast for the stations on Hawaii are larger than that for station KIP on Oahu. Stronger attenuation and relatively low coherency for teleseismic signals on Hawaii in frequencies of 0.4 to 1.2 Hz are attributed to the presence of partial melt in the upper mantle. Teleseismic signal coherency is very low at frequencies above 2 Hz for a small array with a radius about 2 km. The relatively high coherency of the tangential component is strongly indicative of severe scattering effects caused by the heterogeneity in structure of the active volcanic area.