Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea

TitleEstimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea
Publication TypeJournal Article
Year of Publication2013
AuthorsFreeman S.E, D'Spain G.L, Lynch S.D, Stephen R.A, Heaney K.D, Murray J.J, Baggeroer A.B, Worcester P.F, Dzieciuch M.A, Mercer J.A
JournalJournal of the Acoustical Society of America
Date Published2013/10
Type of ArticleArticle
ISBN Number0001-4966
Accession NumberWOS:000330119700077
Keywordsarray; hydrophones; magnitude submarine earthquakes; mid-atlantic ridge; ocean sound-channel; p-wave; scattering; soc. am. 119; t-phase signals; Thresholds; wave detection

Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer adaptiveness levels. Ninety T-phases from unique azimuths were recorded between Yeardays 107 to 119. T-phase azimuth and S-minus-P-phase time-of-arrival range estimates were validated using United States Geological Survey seismic monitoring network data. Analysis of phases from a seismic event that occurred on Yearday 112 near the east coast of Taiwan approximately 450 km from the arrays revealed a 22 degrees clockwise evolution of T-phase azimuth over 90 s. Two hypotheses to explain such evolution-body wave excitation of multiple sources or in-water scattering-are presented based on T-phase origin sites at the intersection of azimuthal great circle paths and ridge/coastal bathymetry. Propagation timing between the source, scattering region, and array position suggests the mechanism behind the evolution involved scattering of the T-phase from the Ryukyu Ridge and a T-phase formation/scattering location estimation error of approximately 3.2 km. (C) 2013 Acoustical Society of America.

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