Bottom interacting acoustics in the north Pacific

During the 2004 Long-range Ocean Acoustic Propagation Experiment (LOAPEX), a new class of acoustic arrivals was observed on ocean bottom seismometers (OBSs) for ranges from 500 to 3200 km. The arrivals were called deep seafloor arrivals (DSFAs), because they were the dominant arrivals on the ocean bottom seismometers (OBSs), but were very weak on the deep vertical line array (Deep VLA), located above 750 m from the seafloor. Stephen et al. [JASA 134, 3307–3317 (2013)] attributed some of these arrivals to bottom-diffracted, surface-reflected (BDSR) energy that scattered from a seamount near the Deep VLA and subsequently reflected from the sea surface before arriving at the OBSs. In the Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) Experiment in June to July 2013, we returned to the Deep VLA site with a near-seafloor Distributed Vertical Line Array (DVLA) that extended upward 1000 m from the seafloor and 12 OBSs. We transmitted to the instruments with a ship-suspended J15-3 acoustic source. The receiver locations and transmission program were designed to test the hypothesis that DSFAs correspond to BDSR energy, to further define the characteristics of the DSFAs, and to understand the conditions under which DSFAs are excited and propagate.