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  • 1
    Electronic Resource
    Electronic Resource
    3-D velocity structure of the San Jacinto fault zone near Anza, California—I. P waves (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 119 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismic arrival times from microearthquakes (ML 〈 4) on the San Jacinto fault near Anza, California, are used to find spatial variations in the seismic velocity that are related to the crustal structure of the fault zone. Preliminary modelling of the 1-D P-wave velocity structure of the upper 25 km of crust reveals that most of the variation in velocity is lateral rather than depth dependent. The traveltime anomalies due to lateral structure can be partially compensated for by applying station corrections, however the variance of the traveltime residuals is still 2.25 times larger than the variance of the picking error. The spatially correlated residuals show that this variance is due to localized velocity anomalies and that the data require further modelling using a 3-D velocity structure.Because the 3-D inverse problem is non-unique, smoothness constraints are applied to find the model that has the minimum structure required to fit the data to the picking error, where a smooth model is defined such that the gradient of the velocity perturbation from the original 1-D model is small. With small non-zero station corrections, a 3-D velocity model can be found that fits the data well. The structure is well resolved from 3 to 9 km depth where lateral perturbations of up to 7 per cent are determined independently of the trade-off between station corrections and poorly resolved near surface structure. The model shows a horizontal gradient with overall faster velocities in the north-east side of the fault zone. At 3–6 km depth, the signature of the fault zone is evident in the lower velocities beneath the surface trace of the fault. However, at 9 km depth. higher seismic velocities are found extending into the fault zone from the north-east block. This higher velocity region occurs where there is a distinct lack of seismicity on the fault. There is also a localized feature in the south-west of the modelled region that is more than 10 km from the main trace of the fault with velocities 3 per cent slower than average.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb00145.x
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  • 2
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    Multipurpose acoustic networks in the integrated Arctic Ocean observing system (2015)
    Arctic Institute of North America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Arctic Institute of North America, 2015. This article is posted here by permission of Arctic Institute of North America for personal use, not for redistribution. The definitive version was published in Arctic 68, supple.1 (2015): 11-27, doi:10.14430/arctic4449.
    Description: The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.
    Keywords: Arctic observing systems ; Arctic acoustics ; Acoustic tomography ; Cabled networks ; Passive acoustics ; Active acoustics
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 3
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    Ocean Seismic Network Pilot Experiment (2005)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2003. It is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 1092, doi:10.1029/2002GC000485.
    Description: The primary goal of the Ocean Seismic Network Pilot Experiment (OSNPE) was to learn how to make high quality broadband seismic measurements on the ocean bottom in preparation for a permanent ocean seismic network. The experiment also had implications for the development of a capability for temporary (e.g., 1 year duration) seismic experiments on the ocean floor. Equipment for installing, operating and monitoring borehole observatories in the deep sea was also tested including a lead-in package, a logging probe, a wire line packer and a control vehicle. The control vehicle was used in three modes during the experiment: for observation of seafloor features and equipment, for equipment launch and recovery, and for power supply and telemetry between ocean bottom units and the ship. The OSNPE which was completed in June 1998 acquired almost four months of continuous data and it demonstrated clearly that a combination of shallow buried and borehole broadband sensors could provide comparable quality data to broadband seismic installations on islands and continents. Burial in soft mud appears to be adequate at frequencies below the microseism peak. Although the borehole sensor was subject to installation noise at low frequencies (0.6 to 50 mHz), analysis of the OSNPE data provides new insights into our understanding of ocean bottom ambient noise. The OSNPE results clearly demonstrate the importance of sediment borne shear modes in ocean bottom ambient noise behavior. Ambient noise drops significantly at high frequencies for a sensor placed just at the sediment basalt interface. At frequencies above the microseism peak, there are two reasons that ocean bottom stations have been generally regarded as noisier than island or land stations: ocean bottom stations are closer to the noise source (the surface gravity waves) and most ocean bottom stations to date have been installed on low rigidity sediments where they are subject to the effects of shear wave resonances. When sensors are placed in boreholes in basement the performance of ocean bottom seismic stations approaches that of continental and island stations. A broadband borehole seismic station should be included in any real-time ocean bottom observatory.
    Description: This work was sponsored by the National Science Foundation (NSF Grant Numbers: OCE-9522114, OCE-9523541 and OCE-9819439) with additional support from Incorporated Research Institutions for Seismology (IRIS), Joint Oceanographic Institutions, Inc. (JOI Contract No: 12-94), Scripps Institution of Oceanography, a Mellon Grant from Woods Hole Oceanographic Institution, and the Earthquake Research Institute at the University of Tokyo (Visiting Professorship for RAS).
    Keywords: Ocean Seismic Network Pilot Experiment (OSNPE) ; Seismology ; Instruments and techniques ; Body wave propagation ; Surface waves and free oscillations
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 2963663 bytes
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  • 4
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    Field measurements of sonic boom penetration into the ocean (2008)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2000. 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 107 (2000): 3073-3083, doi:10.1121/1.429336.
    Description: Six sonic booms, generated by F-4 aircraft under steady flight at a range of altitudes (610–6100 m) and Mach numbers (1.07–1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30–50 m, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.
    Description: This work was funded by the NASA Langley Research Center (Technical Monitor, Dr. Kevin Shepherd).
    Keywords: Shock waves ; Oceanography ; Underwater acoustic propagation
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 5
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    Progress report on the development of the seafloor borehole array seismic system (phase II) : July 14, 1992 to January 31, 1996 (2016)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: The Seafloor Borehole Array Seismic System (SEABASS) was originally developed to record autonomously on the seafloor the signals received on a four-sonde three-component borehole geophone array in the VLF band (2-50Hz)(Stephen eta!., 1994). The system is designed to use the wireline re-entry capability (Spiess, 1993; Spiess eta!., 1992) to install and retrieve the seafloor instrumentation (Figures 1 and 2). Following the successful demonstration of this technology on the LFASE (Low Frequency Acoustic-Seismic Experiment) project in September 1989, it was decided to extend the capability to broadband (1000sec-5Hz) borehole seismometers which could be used for permanent seafloor seismic observatories in the Ocean Seismic Network (Orcutt and Stephen, 1993; Purdy and Dziewonski, 1988; Purdy and Orcutt, 1995; Stephen, 1995; Sutton and Barstow, 1990; Sutton eta!., 1988; Sutton eta!., 1965). The Broadband Borehole Seismic System (B3S2) is the prototype system for permanent broadband borehole seismic observatories on the seafloor. It has three major components: i) a broadband borehole seismometer, the Teledyne 54000, modified for seafloor operations by Scripps-IGPP; ii) the re-entry system provided by Scripps-MPL; and iii) the seafloor recording system developed by WHO I. Because of the similarity of the seafloor recording system to SEABASS we have named this new system SEABASS-ll. This report discusses the development of SEABASS-Il at WHOI in the period from July 14, 1992 to January 31, 1996. The motivation for the project and a work statement are contained in WHOI proposals 7016 and 7016.1. This report is a collection of documentation prepared while the work was being carried out. Some of the issues discussed in early memos were subsequently changed. Modifications and further testing of SEABASS-ll, as well as final system integration tests with the borehole andreentry systems (both of which are also still being modified and tested) have still to be carried out in preparation for the OSN Pilot Experiment Cruise in Spring 1997. This is a preliminary report only and presents work in progress. It will be useful to the engineering team as a historical reference of the sequence of events in the development of SEABASS-ll but it should not be considered as a technical manual for the instrumentation.
    Keywords: Seismology ; Borehole gravimetry ; Ocean bottom ; Oceanographic instruments
    Repository Name: Woods Hole Open Access Server
    Type: Working Paper
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  • 6
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    Tests of the broadband borehole seismic system (B³S²) at Scripps IGPP and the Pinon Flat Observatory : October 1994 to June 1995 (2016)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: The broadband borehole seismic system (B3S2) is being developed as one component of the Ocean Seismic Network (OSN) Pilot Experiment which will be carried out at the OSN-1 Site off Hawaii in Winter 1998. The other major instruments being developed for the experiment are a Broadband Ocean Bottom Seismometer and a Shallow Buried Broadband Ocean Bottom Seismometer. B3S2 consists of four major components: 1) a borehole sonde with a re-entry guide, Teledyne 54000 broadband seismometer, and REFTEK digitizing system, 2) a seafloor acquisition and recording system (SEABASS), 3) a control vehicle for deploying the sonde in a borehole, and 4) shipboard command and control electronics. The deployment system is very similar to the SEABASS configuration used on LFASE (Stephen eta!, 1994). The purposes of the tests at Pinon Flat were: 1) to integrate the borehole sonde and seafloor and shipboard electronics which had been constructed by different groups: WHOI and SIO/IGPP; 2) test the combined subsystem in a wet borehole environment using actual cables and simulating seafloor conditions; and 3) acquire seismic ambient noise and earthquake data over approximately a three month period for comparison with known stations at the Pinon Flat Observatory.
    Description: This work was carried out under NSF Grants No. OCE-91-18943 and OCE No. OCE-95-05730: "A Broadband Borehole Seismometer for the Deep Ocean - Development and Land Testing"
    Keywords: Seismology ; Borehole gravity meters ; Ocean bottom ; Oceanographic instruments
    Repository Name: Woods Hole Open Access Server
    Type: Working Paper
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  • 7
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    Broadband borehole seismic system integration tests : report of the system integration tests at MPL/SIO (2016)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: This report describes a series of tests performed at SIO/MPL, Point Lorna the week of 17 November 1997 designed to achieve integration of the Broadband Borehole Seismic System (BBBSS) in preparation for the OSN Pilot Experiment cruise on RN Thompson during January 1997. Representatives from all groups were present (see appendix A), with their respective parts of the system and support equipment. It was anticipated that these tests would result in the complete integration of the various components of the borehole seismometer system in preparation for the January cruise. The system would be assembled and tested following a plan (see appendix C) that would culminate in the fully integrated borehole seismometer being wet tested off the MPL pier.
    Description: This work is sponsored by the National Science Foundation Grant Nos. OCE 9522114and OCE 9523541 with additional support from Scripps Institute of Oceanography and Woods Hole Oceanographic Institution
    Keywords: Borehole gravimetry
    Repository Name: Woods Hole Open Access Server
    Type: Working Paper
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  • 8
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    A Comparison of Spectral Parameter Kappa from Small and Moderate Earthquakes Using Southern California ANZA Seismic Network Data (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-02-01
    Description: Kappa is a one-parameter estimator of the spectral amplitude decay with frequency of a seismogram. Low values (~5??ms) indicate limited attenuation of high-frequency energy whereas higher values (~40??ms) indicate high-frequency energy has been removed. Kappa is often assumed to be a site term and used in seismic designs. We address two key questions about kappa: (1) how to identify source, path, and site contributions to kappa; and (2) can kappa estimates from smaller earthquakes, and more readily accessible weak-motion recordings, be reasonably extrapolated to estimate kappa of larger earthquakes? The use of small earthquakes (ML 3.5 earthquakes inside the network. We find kappa from small earthquakes predicts the relative values of kappa for larger earthquakes (e.g., measurements at stations PFO and KNW are small compared with those at stations TRO and SND). For the SND and TRO data, however, kappa values from small earthquakes overpredict those from moderate and large earthquakes. Site effects are the most important contributor to kappa estimates, but the scatter within kappa measurements at a given station is likely caused by a significant contribution from near the source, perhaps related to near-source scattering. Because of this source-side variability, care is recommended in using individual small events as Green’s functions to study source-time effects of moderate and large events.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 9
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    Seismicity around the Hawaiian Islands Recorded by the PLUME Seismometer Networks: Insight into Faulting near Maui, Molokai, and Oahu (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-08-01
    Description: Instrumental limitations have long prevented the detailed characterization of offshore earthquakes around the Hawaiian Islands, and little is known about the spatial distribution of earthquakes in regions outside the vicinity of the well-monitored island of Hawaii. Here, we analyze data from the deployment of two successive networks of ocean-bottom seismometers (OBSs) as part of the Plume-Lithosphere Undersea Melt Experiment (PLUME) to better determine seismicity patterns along the Hawaiian Islands and their offshore regions. We find that earthquake detection rates are improved when seismograms are high-pass filtered above [~]5 Hz to reduce the background seismic noise. Hypocentral solutions have been determined for 1147 previously undetected microearthquakes, and an additional 2880 events correspond to earthquakes already in the catalog of the United States Geological Survey (USGS) Hawaiian Volcano Observatory (HVO). The spatial patterns of earthquakes identified solely on the PLUME network provide complementary information to patterns identified by the HVO network. A diffuse pattern of seismicity is found to the southeast of the island of Hawaii, and clusters of earthquakes are located west of the island. Many microearthquakes are observed in the vicinity of Maui and Molokai, including some located at mantle depths. A small number of microearthquakes are found to occur near Oahu. There is no evidence from our analyses that the Molokai fracture zone (MFZ) is seismically active at this time, and no evidence was found of a previously hypothesized Diamond Head fault (DHF) near Oahu. However, on the basis of both the PLUME and HVO locations, there is a northeast-southwest-trending swath of epicenters extending northeastward of Oahu that may indicate the locus of moderate-sized historic earthquakes attributed to the Oahu region.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 10
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    Quantifying Seismic Source Parameter Uncertainties (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-04-01
    Description: We use data from a small aperture array in southern California to quantify variations in source parameter estimates at closely spaced stations (distances ranging from [~]7 to 350 m) to provide constraints on parameter uncertainties. Many studies do not consider uncertainties in these estimates even though they can be significant and have important implications for studies of earthquake source physics. Here, we estimate seismic source parameters in the frequency domain using empirical Green's function (EGF) methods to remove effects of the travel paths between earthquakes and their recording stations. We examine uncertainties in our estimates by quantifying the resulting distributions over all stations in the array. For coseismic stress drop estimates, we find that minimum uncertainties of [~]30% of the estimate can be expected. To test the robustness of our results, we explore variations of the dataset using different groupings of stations, different source regions, and different EGF earthquakes. Although these differences affect our absolute estimates of stress drop, they do not greatly influence the spread in our resulting estimates. These sensitivity tests show that station selection is not the primary contribution to the uncertainties in our parameter estimates for single stations. We conclude that establishing reliable methods of estimating uncertainties in source parameter estimates (including corner frequencies, source durations, and coseismic static stress drops) is essential, particularly when the results are used in the comparisons among different studies over a range of earthquake magnitudes and locations.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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