|Title||Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea|
|Publication Type||Journal Article|
|Year of Publication||2013|
|Authors||Freeman 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|
|Journal||Journal of the Acoustical Society of America|
|Type of Article||Article|
|Keywords||array; 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.