Notes for Geoacoustic_TDFD

These notes were written to help users run the WHOI TDFD (Time Domain Finite Difference) elastic wave equation code that was prepared for distribution through the ONR Ocean Acoustics Library (http://www.hlsresearch.com/oalib/). The code and documentation are based on materials that were developed for a Numerical Wave Propagation class given at MIT in the Fall of 2000. The code used is the full two-dimensional time-domain finite-difference code developed at WHOI over the past 25 years, but in order to reduce the number of variables to a manageable size, we consider a two dimensional, isotropic problem with fixed parameters in time and space. For example, the source waveform in time for both beam and point sources is a RICKER wavelet, time units have been normalized to periods (defined at the peak frequency for pressure in water), space units have been normalized to water speed and density of 1! .5km/sec and 1000kg/m3) and the domain size has been fixed at 72 x 12 water wavelengths.Funding was provided by the Office of Naval Research under Contract No. N00014-04-1-0090

User's guide for PLOT_FINDIF

PLOT_FINDIF is a MATLAB script which is used to plot output from the Woods Hole Oceanographic Institution (WHOI) Time Domain Finite Difference (TDFD) program called "Geoacoustic_TDFD" Both Geoacoustic_TDFD and PLOT_FINDIF are available from the ONR Ocean Acoustics Library (http://www.hlsresearch.com/oalib/). This script will plot both the snapshot and time series output from Geoacoustic_TDFD. To run this script you must have a MATLAB license and the complete suite of 32 m-files contained in the PLOT_FINDIF package. This code has been tested with MATLAB versions 6 and 7.Funding was provided by the Office of Naval Research under Contract No. N00014-04-1-0090

A graphical user interface for processing data from the high resolution profiler (HRP)

The High Resolution Profiler (HRP) is one of the only oceanographic instruments that is capable of measuring turbulent velocity and temperature fluctuations in the abyssal ocean. It is a unique device, and consequently specialized communications, data conversion and analysis software are employed to examine the data it collects. This document describes a major upgrade of the software and hardware systems used to process data from the HRP. The bulk of the conversion occurred in 1996 prior to the Brazil Basin Tracer Release Experiment (BBTRE). During the upgrade process, a Graphical User Interface (GUI) was designed and implemented for accomplishing routine HRP data processing tasks.Funding was provided by the National Science Foundation through Grant No. OCE-94- 15589

Site synthesis report of DSPP sites 417 and 418

This document summarizes information relevent to planning, execution, and interpretation of results from a study of the interaction of sound in the 2-30Hz band with deep ocean seafloor using sea-surface sources, seafloor receivers, and borehole seismometers emplaced by wireline re-entry at Deep Sea Drilling Project sites 417 and 418 in the western North Atlantic. We summarize published scientific results from borehole sampling of water, sediment, and rock, from wire line logging, and from borehole seismic experiments. We present new results from analysis of total power recorded by receivers clamped in basement during the borehole seismic experiment on DSDP Leg 102. We document non-drilling investigations of the site and the nature and location of re-entry cones and transponders. We describe the physical oceanography of the region and the speed of sound in water. We provide an extensive bibliography on published results from scientific investigations at 417/418. This document was completed prior to 1989 surveys of sites 417 and 418.Funding was provided by the Johns Hopkins University, Applied Physics Laboratory under contract Number 602809-0

Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Solid Earth 6 (2015): 1075-1085, doi:10.5194/se-6-1075-2015.The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10−8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel–iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4–10 packet, and are an order of magnitude smaller than those from the core–mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and conservation of angular momentum. Since mountain building we now know results from changes in momentum, we have calculated an experimental deformation index value (1–1000) based on a world topographic grid at 5 arcmin spacing and displayed those results for viewing

Three-dimensional bottom diffraction in the North Pacific

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3), (2019): 1913-1922, doi:10.1121/1.5125427.A significant aspect of bottom-interaction in deep water acoustic propagation, from point sources to point receivers, is the diffraction (or scattering) of energy from discrete seafloor locations along repeatable, deterministic paths in three-dimensions. These bottom-diffracted surface-reflected (BDSR) paths were first identified on the North Pacific acoustic laboratory experiment in 2004 (NPAL04) for a diffractor located on the side of a small seamount. On the adjacent deep seafloor, ambient noise and propagation in the ocean sound channel were sufficiently quiet that the BDSRs were the dominant arrival. The ocean bottom seismometer augmentation in the North Pacific (OBSANP) experiment in June–July 2013 studied BDSRs at the NPAL04 site in more detail. BDSRs are most readily identified by the arrival time of pulses as a function of range to the receiver for a line of transmissions. The diffraction points for BDSRs occur on the relatively featureless deep seafloor as well as on the sides of small seamounts. Although the NPAL04 and OBSANP experiments had very different geometries the same diffractor location is consistent with observed arrivals in both experiments within the resolution of the analysis. On OBSANP the same location excites BDSRs for 77.5, 155, and 310 Hz transmissions.We greatly appreciate the support from Captain Curl, the officers, and crew of the R/V Melville (MV1308). The OBS data used in this research was acquired on instruments from the ocean bottom seismograph instrument pool (OBSIP) at Scripps Institution of Oceanography. Ernie Aaron (SIO) was responsible for shipboard OBS operations. The multi-beam data was processed using the MB-System (Caress and Chayes, 1996). Figure 1 was prepared using the generic mapping tool (Wessel and Smith, 1998). Feedback and reviews from an anonymous reviewer and the editorial staff of JASA are also greatly appreciated. The OBSANP experiment was funded by the ONR Ocean Acoustics Program (Code 322 OA) under Grant Nos. N00014-10-1-0987 and N00014-10-1-0510. Analysis was carried out under ONR Grant Nos. N00014-14-1-0324, N00014-16-1-2337, and N00014-17-C-7043.2020-03-3

Ross ice shelf vibrations

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 7589–7597, doi:10.1002/2015GL065284.Broadband seismic stations were deployed across the Ross Ice Shelf (RIS) in November 2014 to study ocean gravity wave-induced vibrations. Initial data from three stations 100 km from the RIS front and within 10 km of each other show both dispersed infragravity (IG) wave and ocean swell-generated signals resulting from waves that originate in the North Pacific. Spectral levels from 0.001 to 10 Hz have the highest accelerations in the IG band (0.0025–0.03 Hz). Polarization analyses indicate complex frequency-dependent particle motions, with energy in several frequency bands having distinctly different propagation characteristics. The dominant IG band signals exhibit predominantly horizontal propagation from the north. Particle motion analyses indicate retrograde elliptical particle motions in the IG band, consistent with these signals propagating as Rayleigh-Lamb (flexural) waves in the ice shelf/water cavity system that are excited by ocean wave interactions nearer the shelf front.Bromirski, Diez, and Gerstoft were supported by NSF grant PLR 1246151. Stephen and Bolmer were supported by NSF grant PLR-1246416. Wiens, Aster, and Nyblade were supported under NSF grants PLR-1142518, 1141916, and 1142126, respectively. Bromirski also received support from the California Department of Parks and Recreation, Division of Boating and Waterways under contract 11-106-107. The NIB data were collected under NSF grant OPP-0229546 and were downloaded from the IRIS DMC archives.2016-03-1

A high-resolution bathymetry map for the Marguerite Bay and adjacent west Antarctic Peninsula shelf for the Southern Ocean GLOBEC Program

One objective of the U.S. Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program is to gain a better understanding of the sea floor bathymetry in the program study area. Much of Marguerite Bay and the adjacent shelf west of the Antarctic Peninsula were poorly charted when the SO GLOBEC program started in 2000. Before the first SO GLOBEC cruise, an improved local area version (ETOPO8.2A) was created from the Smith and Sandwell (1997) topo_8.2.img 2-minute digital gridded bathymetry for the study area. The first SO GLOBEC mooring cruise on the R/V Lawrence M. Gould (March 2001) showed that the 2-minute spatial resolution of ETOPO8.2A did not resolve many of the canyons and abrupt changes in topography that characterize Marguerite Bay and the inner- to mid-shelf region. It also was not particularly accurate in the more uniform terrain regions. We then decided to collect as much multibeam bathymetry data as possible during the SO GLOBEC broad-scale survey cruises on the R/VIB Nathaniel B. Palmer and combine these data with all other available multibeam and trackline bathymetry data to construct a digital bathymetry database and map for the study area. The resulting database has high-resolution data over much of the shelf and parts of Marguerite Bay gridded at 2 seconds in latitude and 6 seconds in longitude spacing between 65° to 71° S and 65° to 78° W. This technical report describes the steps taken to assemble and construct this database and how to access the data via the Internet.Funding was provided by the Office of Naval Research under Contract No. N00014-99-1-0213

Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) - cruise report

The Ocean Bottom Seismometer Augmentation in the North Pacific Experiment (OBSANP, June-July, 2013, R/V Melville) addresses the coherence and depth dependence of deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we observed "deep seafloor arrivals" (DSFA) that were dominant on the seafloor Ocean Bottom Seismometer (OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line Array (DVLA) (above 4250m depth). At least a subset of these arrivals correspond to bottomdiffracted surface-reflected (BDSR) paths from an out-of-plane seamount. BDSR arrivals are present throughout the water column, but at depths above the conjugate depth are obscured by ambient noise and PE predicted arrivals. On the 2004 NPAL/LOAPEX experiment BDSR paths yielded the largest amplitude seafloor arrivals for ranges from 500 to 3200km. The OBSANP experiment tests the hypothesis that BDSR paths contribute to the arrival structure on the deep seafloor even at short ranges (from near zero to 4-1/2CZ). The OBSANP cruise had three major research goals: a) identification and analysis of DSFA and BDSR arrivals occurring at short (1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03 to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths. On OBSANP we deployed a 32 element VLA from 12 to 1000m above the seafloor, eight short-period OBSs and four long-period OBSs and carried out a 15day transmission program using a J15-3 acoustic source.Funding was provided by the Office of Naval Research under contract #'s N00014-10-1-0987 and N00014-10-1-051

Analysis of Deep Seafloor Arrivals observed on NPAL04

This report gives an overview of the analysis that was done on Deep Seafloor Arrivals since they were initially presented in Stephen et al (2009). All of the NPAL04/LOAPEX (North Pacific Acoustic Laboratory, 2004/ Long Range Ocean Acoustic Propagation Experiment) data on three ocean bottom seismometers (OBSs) at ~5,000m depth and the deepest element of the deep vertical line array (DVLA) at 4250m depth has been analyzed. A distinctive pattern of late arrivals was observed on the three OBSs for transmissions from T500 to T2300. The delays of these arrivals with respect to the parabolic equation predicted (PEP) path were the same for all ranges from 500 to 2300km, indicating that the delay was introduced near the receivers. At 500km range the same arrival was observed throughout the water column on the DVLA. We show that arrivals in this pattern converted from a PEP path to a bottom-diffracted surface reflected (BDSR) path at an off-geodesic seamount.Funding was provided by the Office of Naval Research under Contract No. N00014-10-1-0510