title: Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea.
abstract: 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° 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.
authors.affiliation: Marine Physical Laboratory, Scripps Institution of Oceanography, 291 Rosecrans Street, University of California San Diego, Scripps Institution of Oceanography, Marine Physical Laboratory Building 4, San Diego, California 92106.
authors.forename: Simon E
authors.initials: SE
authors.lastname: Freeman
authors.forename: Gerald L
authors.initials: GL
authors.lastname: D'Spain
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Lynch
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Stephen
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Heaney
authors.forename: James J
authors.initials: JJ
authors.lastname: Murray
authors.forename: Arthur B
authors.initials: AB
authors.lastname: Baggeroer
authors.forename: Peter F
authors.initials: PF
authors.lastname: Worcester
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Dzieciuch
authors.forename: James A
authors.initials: JA
authors.lastname: Mercer
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D004867:Equipment Design; D005583:Fourier Analysis; D008962:Models, Theoretical; D009038:Motion; D009791:Oceanography / Q000295:instrumentation / Q000379:methods*; D009792:Oceans and Seas; D010679:Philippines; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012623:Seawater; D013016:Sound; D013018:Sound Spectrography; D013997:Time Factors; D014159:Transducers