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PresentationThree-dimensional numerical modeling of bottom-diffracted surface-reflected arrivals in the North Pacific [poster]( 2015-12-15) Stephen, Ralph A. ; Udovydchenkov, Ilya A. ; Bolmer, S. Thompson ; Komatitsch, Dimitri ; Tromp, Jeroen ; Casarotti, Emanuele ; Xie, Zhinan ; Worcester, Peter F.Bottom-diffracted surface-reflected (BDSR) arrivals were first identified in the 2004 Long-range Ocean Acoustic Propagation Experiment (Stephen et al, 2013, JASA, v.134, p.3307-3317). The BDSR mechanism provides a means for acoustic signals and noise from distant sources to appear with significant strength on the deep seafloor. At depths deeper than the conjugate depth ambient noise and PE- predicted arrivals are sufficiently quiet that BDSR paths, scattered from small seamounts, can be the largest amplitude arrivals observed. The Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) Experiment in June-July 2013 was designed to further define the characteristics of the BDSRs and to understand the conditions under which BDSRs are excited and propagate. The reciprocal of the BDSR mechanism also plays a role in T-phase excitation. To further understand the BDSR mechanism, the SPECFEM3D code was extended to handle high-frequency, deep water bottom scattering problems with actual bathymetry and a typical sound speed profile in the water column. The model size is 38km x 27km x 6.5km. The source is centered at 10Hz with a 5Hz bandwidth. Work supported by NSF and ONR.
PresentationThree-dimensional numerical modeling of sound propagation and scattering in the deep ocean with elastic bottoms [poster]( 2014-02-25) Udovydchenkov, Ilya A. ; Stephen, Ralph A. ; Komatitsch, Dimitri ; Xie, Zhinan ; Tromp, JeroenA challenging problem in bottom-interacting ocean acoustics and marine seismology is to accurately describe environmental variability in a computationally feasible model. Wave field predictions are often difficult in environments with strong range dependence, with rapid bathymetric variations, with multiple scattering regions, with interface waves at fluid/solid boundaries, and/or with shear waves in the bottom. In this presentation, we are using an existing three-dimensional spectral-finite-element code (SPECFEM3D, distributed and supported by the NSF funded program, Computational Infrastructure for Geodynamics), originally developed for simulations of seismic wave propagation at the local or regional scale, to bottom interaction problems in underwater acoustics. Recent developments of the SPECFEM3D model include full compressional attenuation in elastic media and improved transparent boundary conditions. Numerical results from SPECFEM3D are compared with wave fields simulated using acoustic propagation model based on the parabolic equation (PE) method, for a 10 Hz broadband acoustic pulse propagating in the deep ocean. The importance of out-of-plane scattering and bottom shear properties on resulting wave fields are investigated.