Journal articles on the topic 'Geophysical ows'
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Kilic, Lise, Catherine Prigent, Carlos Jimenez, and Craig Donlon. "Technical note: A sensitivity analysis from 1 to 40 GHz for observing the Arctic Ocean with the Copernicus Imaging Microwave Radiometer." Ocean Science 17, no. 2 (March 11, 2021): 455–61. http://dx.doi.org/10.5194/os-17-455-2021.
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Abstract. The Copernicus Imaging Microwave Radiometer (CIMR) is one of the high-priority missions for the expansion of the Copernicus program within the European Space Agency (ESA). It is designed to respond to the European Union Arctic policy. Its channels, incidence angle, precision, and spatial resolutions have been selected to observe the Arctic Ocean with the recommendations expressed by the user communities. In this note, we present the sensitivity analysis that has led to the choice of the CIMR channels. The famous figure from Wilheit (1979), describing the frequency sensitivity of passive microwave satellite observations to ocean parameters, has been extensively used for channel selection of microwave radiometer frequencies on board oceanic satellite missions. Here, we propose to update this sensitivity analysis, using state-of-the-art radiative transfer simulations for different geophysical conditions (Arctic, mid-latitude, tropics). We used the Radiative Transfer Model (RTM) from Meissner and Wentz (2012) for the ocean surface, the Round Robin Data Package of the ESA Climate Change Initiative (Pedersen et al., 2019) for the sea ice, and the RTM from Rosenkranz (2017) for the atmosphere. The sensitivities of the brightness temperatures (TBs) observed by CIMR as a function of sea surface temperature (SST), sea surface salinity (SSS), sea ice concentration (SIC), ocean wind speed (OWS), total column water vapor (TCWV), and total column liquid water (TCLW) are presented as a function of frequency between 1 and 40 GHz. The analysis underlines the difficulty to reach the user requirements with single-channel retrieval, especially under cold ocean conditions. With simultaneous measurements between 1.4 and 36 GHz onboard CIMR, applying multi-channel algorithms will be facilitated, to provide the user community with the required ocean and ice information under arctic environments.
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Giga, Yoshikazu, Matthias Hieber, and Edriss Titi. "Geophysical Fluid Dynamics." Oberwolfach Reports 10, no. 1 (2013): 521–77. http://dx.doi.org/10.4171/owr/2013/10.
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Giga, Yoshikazu, Matthias Hieber, and Edriss Titi. "Geophysical Fluid Dynamics." Oberwolfach Reports 14, no. 2 (April 27, 2018): 1421–62. http://dx.doi.org/10.4171/owr/2017/23.
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Klein, Rupert, Shafer Smith, and Jacques Vanneste. "Multiscale Interactions in Geophysical Fluids." Oberwolfach Reports 13, no. 3 (2016): 2225–68. http://dx.doi.org/10.4171/owr/2016/39.
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Giga, Yoshikazu, Matthias Hieber, Peter Korn, and Edriss S. Titi. "Mathematical Advances in Geophysical Fluid Dynamics." Oberwolfach Reports 17, no. 2 (July 1, 2021): 857–76. http://dx.doi.org/10.4171/owr/2020/15.
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Waldner, Jeffrey, Jeffrey Reidenauer, Lora Turner, Paul Knorr, and Leighann Brandt. "BUILDING A NATIONAL SAND RESOURCE INVENTORY FOR THE US CONTINENTAL SHELF." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 88. http://dx.doi.org/10.9753/icce.v36.sediment.88.
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The future of coastal resilience or restoration plans which implement natural or nature-based features largely depends upon the identification of proximate and compatible offshore sand and gravel material. BOEM’s Marine Minerals Program (MMP) is multi-faceted, focusing on coordinated leasing of sediment for extraction, inventorying sediment resources through geological and geophysical surveys of the Outer Continental Shelf (OCS), and environmental studies and reviews to inform decisions.
However, on a national scale, little is known about the character, quantity, and location of sand resources on the OCS and the habitat it provides for biological communities. BOEM places a high priority on creating a comprehensive national sand resource inventory to meet BOEM’s mandate as stewards of all federal mineral resources on the OCS. This stewardship responsibility will be realized by proactively planning for the increasing demands for OCS resources and emergency needs as they arise.
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Wang, Jing, Jianhe Guan, and Donglin Liu. "Research and Application of FAHP in Bidding Quotation for Petroleum Geophysical Prospecting Project." Open Journal of Statistics 07, no. 04 (2017): 589–98. http://dx.doi.org/10.4236/ojs.2017.74040.
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Carr, S., J. K. Pringle, P. Doyle, K. D. Wisniewski, and I. G. Stimpson. "Scallywag bunkers: geophysical investigations of WW2 Auxiliary Unit Operational Bases (OBs) in the UK." Journal of Conflict Archaeology 15, no. 1 (January 2, 2020): 4–31. http://dx.doi.org/10.1080/15740773.2020.1822102.
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Tian, Jinyu, Jian Lin, Fan Zhang, Min Xu, Yayun Zhang, Laiyin Guo, and Xin Zeng. "Time Correction of Ocean-Bottom Seismometers Using Improved Ambient Noise Cross Correlation of Multicomponents and Dual-Frequency Bands." Seismological Research Letters 92, no. 3 (January 13, 2021): 2004–14. http://dx.doi.org/10.1785/0220200358.
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Abstract An effective approach was developed for identifying and correcting ocean-bottom seismometer (OBS) time errors through improving ambient noise cross-correlation function (NCCF) analysis and combination with other methods. Significant improvements were illustrated through analyzing data from a passive-source seismic experiment in the southwestern sub-basin of the South China Sea. A novel method was first developed that can effectively identify errors in the sampling frequency of the OBS instruments. The traditional NCCF method was then expanded by increasing the analyzed data spectrum from a single-frequency band to dual-frequency band pairs, thus doubling the number of available data points and substantially improving the time correction quality. For data with relatively low signal-to-noise ratios, the average time errors were reduced from the original average values of 60–80 ms by the conventional methods to <40 ms using the improved approaches. The new multistep procedure developed in this study has general applicability to analysis of other OBS experiments. The demonstrated significant improvements in the data quality are critical for advancing seismic tomography and other modern marine geophysical studies that require high accuracy in the OBS data.
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Tonka, Şebnem Karul, and Ismail Ekmekci. "A Model Proposal for Occupational Health and Safety Performance Measurement in Geothermal Drilling Areas." Sustainability 14, no. 23 (November 24, 2022): 15669. http://dx.doi.org/10.3390/su142315669.
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The energy sources required for general development and maintenance cause environmental pollution due to the carbon emissions released into the atmosphere. For these reasons, countries have turned to renewable energy sources. Energy production methods also cause serious problems in terms of the health and safety of employees. This study aimed to create an occupational health and safety performance model in geothermal energy fields, which generate renewable energy sources, using multi-criteria decision-making methods. A two-stage model was created for OHS performance index measurement. In the first stage, a literature screening was performed, risk analysis criteria were examined, and performance measurement criteria were determined with geophysical engineers and OHS experts. Seven main criteria and forty-seven subcriteria were set. An analytical hierarchy process method (AHP) and a fuzzy analytical hierarchy process (F-AHP) using the main criteria and subcriteria were determined. In the second stage, exposure rates were obtained using the Promethee method in three geothermal wells. The risks in these three wells are listed according to their importance. A performance model was created. The Results section includes conclusions and suggestions. This study, by creating an OHS performance model, can be used by managers and OHS professionals working in geothermal energy production fields to solve problems.
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Musta, B., M. A. Asat, S. Y. Ling, and H. Saleh. "Geophysical Investigation and Geochemical Study of Sediment along the Coastal Area in Kota Belud Sabah, Malaysia." Journal of Physics: Conference Series 2165, no. 1 (January 1, 2022): 012046. http://dx.doi.org/10.1088/1742-6596/2165/1/012046.
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Abstract This article discusses the geophysical investigation of sediment and the status of heavy metals pollution in the coastal sediment from Usukan Beach, Kota Belud Sabah Malaysia. Study area is located at the northwest coast of Sabah which is bounded by the South China Sea and made up of Crocker Formation which age from Late Eocene to Early Miocene, Wariu Formation with Middle Miocene age and Quaternary Alluvium. This study using geoelectrical method namely electrical resistivity (IR) and induced polarization (IP) to measure the thickness of sediment and the parent rock lithology respectively. Whereas the heavy metal contents were measured using the Inductively Coupled Plasma-Optical Emission Spectrometry (ICP- OES). Three sets of subsurface cross-sections were conducted for the geophysical survey and covered the depth around 37 meters for all the survey line. The result of geophysical survey shows that the alluvium quaternary deposits in the low-lying flat area have a thickness up to 13 metres and overlie the mudstone dominated rock of the Crocker Formation. The geochemical analysis shows a decreasing ranking order of elemental concentrations Fe>Mn>Zn>Cu>Pb>Cr>As. The analyses show all elements are within the background values and acceptable standard limits of the Sediment Quality Guidelines (SQG) by USEPA for coastal sediments. The assessment of heavy metals revealed only minimal degree of pollution in the coastal sediments.
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Zhu, Gaohua, Hongfeng Yang, Jian Lin, and Qingyu You. "Determining the Orientation of Ocean-Bottom Seismometers on the Seafloor and Correcting for Polarity Flipping via Polarization Analysis and Waveform Modeling." Seismological Research Letters 91, no. 2A (February 12, 2020): 814–25. http://dx.doi.org/10.1785/0220190239.
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Abstract The erroneous flipping of polarity in seismic records of ocean-bottom seismometers (OBSs) could go unnoticed and undiagnosed because it is coupled with unknown horizontal orientation of OBS instruments on the seafloor. In this study, we present detailed approaches to first identify potential errors in the flipping polarity of individual OBS instruments, and then determine the correct orientation of OBS instruments on the seafloor. We first conduct a series of tests by artificially flipping the polarity of seismic records of the Global Seismographic Network stations to determine the effects on orientation estimates, utilizing polarization characteristics of teleseismic P and Rayleigh waves, respectively. The tests demonstrate that erroneous polarity reversal in seismic recording could cause false estimates and reverse radial (R) and tangential (T) components. We determine the sensor orientations through comparing the observed waveforms to the synthetic waveforms, which could solve the ambiguity of R and T directions caused by potential erroneous polarity reversal of OBS data. We then apply the approaches to an OBS data set collected in the southern Mariana subduction zone to obtain the correct orientation for 9 out of 12 OBS instruments.
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Bragato, Pier Luigi, Paolo Comelli, Angela Saraò, David Zuliani, Luca Moratto, Valerio Poggi, Giuliana Rossi, et al. "The OGS–Northeastern Italy Seismic and Deformation Network: Current Status and Outlook." Seismological Research Letters 92, no. 3 (March 10, 2021): 1704–16. http://dx.doi.org/10.1785/0220200372.
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Abstract In this article, we describe the infrastructure developed and managed by the Italian National Institute of Oceanography and Applied Geophysics – OGS for the seismological and geodetic monitoring of northeastern Italy. The infrastructure was constituted in response to the ML 6.4 Friuli destructive earthquake of 1976, with the main mandate of supporting civil protection emergency activities. The OGS monitoring infrastructure is presently composed of a seismometric and a strong-motion network, complemented by a number of Global Navigation Satellite Systems stations, each delivering observational data in real time, which are collected and processed by the headquarters of the Center for Seismological Research of OGS in Udine. The OGS networks operate in close cooperation with Italian and international networks from neighboring countries, within the framework of the agreements for real-time data exchange, to obtain improved rapid earthquake location and magnitude estimations. Information regarding seismic events is released to the public through a dedicated web portal and, since 2013, through social media. Aside from the standard monitoring activities (>30,000 events have been recorded since 1976), the OGS has progressively increased the number of services to the public and to the Civil Protection of the Friuli Venezia Giulia and Veneto regions. The high availability of good quality data has resulted in the enhancement of scientific products, including advanced seismological studies of the area, spanning broadly from seismic source characterization to engineering seismology. In the future, the OGS networks are expected to further contribute to the development of seismological research and monitoring infrastructures of the Central European region.
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Trobec, Ana, Martina Busetti, Fabrizio Zgur, Luca Baradello, Alberto Babich, Andrea Cova, Emiliano Gordini, et al. "Thickness of marine Holocene sediment in the Gulf of Trieste (northern Adriatic Sea)." Earth System Science Data 10, no. 2 (June 14, 2018): 1077–92. http://dx.doi.org/10.5194/essd-10-1077-2018.
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Abstract. We use various geophysical datasets (multibeam and singlebeam echosounder data, sub-bottom profiling Chirp and sonar data and very high-resolution boomer seismic data) along with published sedimentological data and depth data from nautical charts in order to create models of the depth of the seafloor and the base of Holocene marine sediment in the Gulf of Trieste. The two models are later used in order to calculate the thickness of marine Holocene sediment which has been depositing on the Late Pleistocene alluvial plain since the Holocene transgression in the Italian and Slovenian parts of the gulf. Thicker Holocene marine sedimentary sequences averaging at around 5 m are characteristic for the southeastern part of the gulf. In other parts of the gulf the Holocene marine sedimentary cover is very thin or even absent, except in close proximity to the shoreline and fluvial sediment sources, in the area of the Trezza Grande paleodelta and above topographic depressions of the Late Pleistocene base. The presented datasets available from the OGS SNAP data repository (http://doi.org/cpz2) represent a valuable reference for a wide variety of research disciplines dealing with the dynamic Earth system in the Gulf of Trieste and could be used as a valuable tool for designing sampling and geophysical campaigns in the studied area.
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Loviknes, Karina, Zeinab Jeddi, Lars Ottemöller, and Thibaut Barreyre. "When Clocks Are Not Working: OBS Time Correction." Seismological Research Letters 91, no. 4 (May 27, 2020): 2247–58. http://dx.doi.org/10.1785/0220190342.
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Abstract Ocean-bottom seismographs (OBSs) are used to obtain seismic recordings offshore and are an increasingly important tool for investigating the globe. However, because OBS data cannot be time stamped using Global Positioning System (GPS) during deployment, correction for drift of the internal clock is required. This time drift is typically derived by synchronizing the clock before and after deployment. Linear correction is then applied using the timing deviation between GPS and the instrument’s internal clock at recovery, that is, the skew measurement. If synchronization measurements are missing, ambient noise cross-correlation functions (CCFs) are commonly used for time correction. When investigating recordings from a small-scale OBS network located on the Mohn’s mid-ocean ridge, we observed a remaining drift on the skew-corrected data. After recalculating the drift of the raw data using CCFs, we found that the skew-based time correction was incorrect. This was also verified with the observation of teleseismic P-wave arrivals. We describe a method to obtain properly time-corrected data and discuss the OBS timing issues in detail. The results shown were obtained using a software package that we developed for this specific purpose and made available as open-source software. Although we cannot explain the technical reason for the failure of skew correction, this study shows that skew corrections should not be trusted alone, and OBS timing should always be verified by either ambient noise correlations or P-wave arrival times.
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Cunningham, John D., Don Chambers, Curtiss O. Davis, Andrew Gerber, Rosalind Helz, James P. McGuire, and William Pichel. "Ocean Observer Study: A Proposed National Asset to Augment the Future U.S. Operational Satellite System." Marine Technology Society Journal 37, no. 3 (September 1, 2003): 142–57. http://dx.doi.org/10.4031/002533203787537302.
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The next generation of U.S. polar orbiting environmental satellites, are now under development. These satellites, jointly developed by the Department of Defense (DoD), the Department of Commerce (DOC), and the National Aeronautics and Space Administration (NASA), will be known as the National Polar-orbiting Operational Environmental Satellite System (NPOESS). It is expected that the first of these satellites will be launched in 2010. NPOESS has been designed to meet the operational needs of the U.S. civilian meteorological, environmental, climatic, and space environmental remote sensing programs, and the Global Military Space and Geophysical Environmental remote sensing programs. This system, however, did not meet all the needs of the user community interested in operational oceanography (particularly in coastal regions). Beginning in the fall of 2000, the Integrated Program Office (IPO), a joint DoD, DOC, and NASA office responsible for the NPOESS development, initiated the Ocean Observer Study (OOS). The purpose of this study was to assess and recommend how best to measure the missing or inadequately sampled ocean parameters. This paper summarizes the ocean measurement requirements documented in the OOS, describes the national need to measure these parameters, and describes the satellite instrumentation required to make those measurements.
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Kowalska, Sylwia, Benedykt Kubik, Rafał Skupio, and Krzysztof Wolański. "Downhole Lithological Profile Reconstruction Based on Chemical Composition of Core Samples and Drill Cuttings Measured with Portable X-ray Fluorescence Spectrometer." Minerals 10, no. 12 (December 8, 2020): 1101. http://dx.doi.org/10.3390/min10121101.
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The reconstruction of a lithological profile based on geophysical logs of chemical composition provided by geochemical gamma-gamma well logging probes has been increasingly used for geophysical interpretation. A chemical profile, analogous to the measurements mentioned above, can be determined based on measurements made with a portable X-ray fluorescence spectrometer (pXRF). This paper presents a methodology for determining the mineral composition of drilled, clastic, as well as clay-rich rocks on the basis of both inexpensive and timesaving pXRF measurements as well as models combining the results of chemical composition analysis with results of mineral composition analysis (XRD). The results of chemical composition analysis obtained with a portable XRF spectrometer were calibrated based on a detailed analysis produced with ICP-OES and ICP-MS methods. A significant advantage of the proposed method is the possibility to apply it with regard to drill cuttings as well as archival cores. However, considerable discrepancies in the results obtained were identified while comparing the results of chemical composition analysed directly on the core and milled material. The analysed material comprised Carboniferous rocks derived from three boreholes located in Poland: Kobylin-1 as well as Biesiekierz-1 and -2. It was possible to directly compare the lithological profile obtained based on measurements taken on drill cuttings with the results of the lithological interpretation of a geochemical probe log.
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Eilon, Zachary C., James B. Gaherty, Lun Zhang, Joshua Russell, Sean McPeak, Joseph Phillips, Donald W. Forsyth, and Göran Ekström. "The Pacific OBS Research into Convecting Asthenosphere (ORCA) Experiment." Seismological Research Letters 93, no. 1 (October 20, 2021): 477–93. http://dx.doi.org/10.1785/0220210173.
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Abstract The Pacific ocean-bottom seismometer (OBS) Research into Convecting Asthenosphere (ORCA) experiment deployed two 30-station seismic arrays between 2018 and 2020—a US contribution to the international PacificArray project. The “Young ORCA” array deployed on ∼40 Ma central Pacific seafloor had a ∼68% data recovery rate, whereas the “Old ORCA” array deployed on ∼120 Ma southwest Pacific seafloor had a ∼80% recovery rate. We detail here the seismic data quality, spectral characteristics, and engineering challenges of this experiment. We provide information to assist users of this dataset, including OBS orientations and tables of daily data quality for all channels. Preliminary analysis illustrates the utility of these data for surface- and body-wave seismic imaging.
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Wehr, Richard, and Scott R. Saleska. "The long-solved problem of the best-fit straight line: application to isotopic mixing lines." Biogeosciences 14, no. 1 (January 3, 2017): 17–29. http://dx.doi.org/10.5194/bg-14-17-2017.
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Abstract. It has been almost 50 years since York published an exact and general solution for the best-fit straight line to independent points with normally distributed errors in both x and y. York's solution is highly cited in the geophysical literature but almost unknown outside of it, so that there has been no ebb in the tide of books and papers wrestling with the problem. Much of the post-1969 literature on straight-line fitting has sown confusion not merely by its content but by its very existence. The optimal least-squares fit is already known; the problem is already solved. Here we introduce the non-specialist reader to York's solution and demonstrate its application in the interesting case of the isotopic mixing line, an analytical tool widely used to determine the isotopic signature of trace gas sources for the study of biogeochemical cycles. The most commonly known linear regression methods – ordinary least-squares regression (OLS), geometric mean regression (GMR), and orthogonal distance regression (ODR) – have each been recommended as the best method for fitting isotopic mixing lines. In fact, OLS, GMR, and ODR are all special cases of York's solution that are valid only under particular measurement conditions, and those conditions do not hold in general for isotopic mixing lines. Using Monte Carlo simulations, we quantify the biases in OLS, GMR, and ODR under various conditions and show that York's general – and convenient – solution is always the least biased.
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Walter, Jacob I., Paul Ogwari, Andrew Thiel, Fernando Ferrer, Isaac Woelfel, Jefferson C. Chang, Amberlee P. Darold, and Austin A. Holland. "The Oklahoma Geological Survey Statewide Seismic Network." Seismological Research Letters 91, no. 2A (November 13, 2019): 611–21. http://dx.doi.org/10.1785/0220190211.
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Abstract The Oklahoma Geological Survey (OGS) monitors seismicity throughout the state of Oklahoma utilizing permanent and temporary seismometers installed by OGS and other agencies, while producing a real-time earthquake catalog. The OGS seismic network was recently added to the Advanced National Seismic System (ANSS) as a self-supporting regional seismic network, and earthquake locations and magnitudes are automatically reported through U.S. Geological Survey and are part of the ANSS Comprehensive Earthquake Catalog. In Oklahoma, before 2009, background seismicity rates were about 2 M 3.0+ earthquakes per year, which increased to 579 and 903 M 3.0+ earthquakes in 2014 and 2015, respectively. After seismicity peaked, the rate fell to 624, 304, and 194 M 3.0+ earthquakes in 2016, 2017, and 2018, respectively. The catalog is complete down to M 2.2 from mid-2014 to present, despite the significant workload for a primarily state-funded regional network. That astonishing uptick in seismicity has been largely attributed to wastewater injection practices. The OGS provides the Oklahoma Corporation Commission, the agency responsible for regulating oil and gas activities within the state, with technical guidance and earthquake products that inform their “traffic-light” mitigation protocol and other mitigating actions. We have initiated a citizen-scientist-driven, educational seismometer program by installing Raspberry Shake geophones throughout the state at local schools, museums, libraries, and state parks. The seismic hazard of the state portends a continued need for expansion and densification of seismic monitoring throughout Oklahoma.
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Dash, Ranjan, George Spence, Roy Hyndman, Sergio Grion, Yi Wang, and Shuki Ronen. "Wide-area imaging from OBS multiples." GEOPHYSICS 74, no. 6 (November 2009): Q41—Q47. http://dx.doi.org/10.1190/1.3223623.
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The subseafloor structure offshore western Canada was imaged using first-order water-layer multiples from ocean-bottom seismometer (OBS) data and the results were compared to conventional imaging using primary reflections. This multiple-migration (mirror-imaging) method uses the downgoing pressure wavefield just above the seafloor, which is devoid of any primary reflections but consists of receiver-side ghosts of these primary reflections. The mirror-imaging method employs a primaries-only Kirchhoff prestack depth migration algorithm to image the receiver ghosts. The additional travel path of the multiples through the water layer is accounted for by a simple manipulation of the velocity model and processing datum: the receivers lie not on the seabed but on a sea surface twice as high as the true water column. Migration results show that the multiple-migrated image provides a much broader illumination of the subsurface than is possible for conventional imaging using the primaries, especially for the very shallow reflections and sparse OBS spacing. The resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer (single-channel) reflection data.
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Stähler, Simon C., Mechita C. Schmidt‐Aursch, Gerrit Hein, and Robert Mars. "A Self‐Noise Model for the German DEPAS OBS Pool." Seismological Research Letters 89, no. 5 (August 1, 2018): 1838–45. http://dx.doi.org/10.1785/0220180056.
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Jeddi, Zeinab, Lars Ottemöller, Mathilde B. Sørensen, Sara Rezaei, Steven J. Gibbons, Marte L. Strømme, Peter H. Voss, and Trine Dahl-Jensen. "Improved Seismic Monitoring with OBS Deployment in the Arctic: A Pilot Study from Offshore Western Svalbard." Seismological Research Letters 92, no. 5 (March 31, 2021): 2705–17. http://dx.doi.org/10.1785/0220200471.
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Abstract The mid-ocean ridge system is the main source of earthquakes within the Arctic region. The earthquakes are recorded on the permanent land-based stations in the region, although, smaller earthquakes remain undetected. In this study, we make use of three Ocean Bottom Seismographs (OBSs) that were deployed offshore western Svalbard, along the spreading ridges. The OBS arrival times were used to relocate the regional seismicity, using a Bayesian approach, which resulted in a significant improvement with tighter clustering around the spreading ridge. We also extended the regional magnitude scales for the northern Atlantic region for OBSs, by computing site correction terms. Besides location and magnitude improvement, the OBS network was able to detect hundreds of earthquakes, mostly with magnitude below Mw 3, including a swarm activity at the Molloy Deep. Our offshore observations provide further evidence of a low-velocity anomaly offshore Svalbard, at the northern tip of Knipovich ridge that was previously seen in full-waveform inversion. We conclude that even a single permanent OBS near the ridge would make a significant difference to earthquake catalogs and their interpretation.
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Tian, Hongying, Xiran Xu, Hongbao Chen, Rui Huang, Shiyan Zhang, and Jiali Luo. "Analysis of the Anomalous Signals near the Tropopause before the Overshooting Convective System Onset over the Tibetan Plateau." Advances in Meteorology 2020 (September 17, 2020): 1–13. http://dx.doi.org/10.1155/2020/8823446.
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This study investigates the anomalous signals near the tropopause before the overshooting convective system (OCS) onset over the Tibetan Plateau (TP). It is found that the tropopause height is stable at the maximum height for the 7th day and the 5th day before the OCS onset. It then decreases significantly one day before and on the day of the OCS onset. The upward motion in the troposphere is the strongest for the 5th day before the OCS onset. From one day before and after the OCS onset, there are strong ascending motions at 500–300 hPa but weak descending motions near the tropopause. It is proposed that the descending of the tropopause height on the day of the OCS onset is caused by frequent tropopause fold events over the eastern TP associated with frequent cold trough intrusion from the north and the southeastward movement of upper-level westerly jet stream. The decrease of the tropopause height is accompanied by the intrusion of stratospheric air with higher potential vorticity (PV). Positive potential vorticity anomalies on 350 K isentropic surface can be noted in the region where the tropopause height decreases one day before and on the day of the OCS onset. With the deepening of the tropopause fold on the day of the OCS onset, there is not only downward motion near the tropopause in the area behind of the fold but also upward motion in the troposphere beneath the folding region. In addition, the upward displacement of isentropic surfaces leads to an upper-level cold pool, which causes a reduction in static stability beneath the PV anomaly on the day of the OCS onset. The upper-level PV anomalies and their associated strong instability in the middle troposphere can trigger convective activities by the release of potential instability on the day of the OCS onset. The overshooting convection is more likely to occur due to lower tropopause height, although upward motion in the troposphere is not the strongest.
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Shiraishi, Kazuya, Gou Fujie, Takeshi Sato, Susumu Abe, Eiichi Asakawa, and Shuichi Kodaira. "Interferometric OBS imaging for wide-angle seismic data." GEOPHYSICS 82, no. 5 (September 1, 2017): Q39—Q51. http://dx.doi.org/10.1190/geo2016-0482.1.
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Marine wide-angle seismic data obtained using air guns and ocean-bottom seismographs (OBSs) are effective for determining large-scale subseafloor seismic velocities, but they are ineffective for imaging details of shallow seismic reflection structures because of poor illumination. Surface-related multiple reflections offer the potential to enlarge the OBS data illumination area. We have developed a new seismic imaging method for OBS surveys applying seismic interferometry, a technique that uses surface-related multiples similarly to mirror imaging. Seismic interferometry can use higher order multiple reflections than mirror imaging, which mainly uses first-order multiple reflections. A salient advantage of interferometric OBS imaging over mirror imaging is that it requires only single-component data, whereas mirror imaging requires vertical geophone and hydrophone components to separate upgoing and downgoing wavefields. We applied interferometric OBS imaging to actual 175 km long wide-angle OBS data acquired in the Nankai Trough subduction zone. We obtained clear continuous reflection images in the deep and shallow parts including the seafloor from the OBS data acquired with large spacing. Deconvolution interferometry is more suitable than correlation interferometry to improve spatial resolution because of the effects of spectral division when applied to common receiver gathers. We examined the imaging result dependence on data acquisition and processing parameters considering the data quality and target depth. An air-gun-to-OBS distance of up to 50 km and a record length of 80 s were necessary for better imaging. In addition, our decimation tests confirmed that denser OBS spacing yielded better quality and higher resolution images. Understanding crosstalk effects due to the acquisition setting will be useful to optimize methods for eliminating them. Interferometric OBS imaging merged with conventional primary reflection imaging is a powerful method for revealing crustal structures.
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Lontsi, Agostiny Marrios, Anastasiia Shynkarenko, Katrina Kremer, Manuel Hobiger, Paolo Bergamo, Stefano C. Fabbri, Flavio S. Anselmetti, and Donat Fäh. "A Robust Workflow for Acquiring and Preprocessing Ambient Vibration Data from Small Aperture Ocean Bottom Seismometer Arrays to Extract Scholte and Love Waves Phase-Velocity Dispersion Curves." Pure and Applied Geophysics 179, no. 1 (December 14, 2021): 105–23. http://dx.doi.org/10.1007/s00024-021-02923-8.
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AbstractThe phase-velocity dispersion curve (DC) is an important characteristic of the propagation of surface waves in sedimentary environments. Although the procedure for DC estimation in onshore environments using ambient vibration recordings is well established, the DC estimation in offshore environments using Ocean Bottom Seismometers (OBS) array recordings of ambient vibrations presents three additional challenges: (1) the localization of sensors, (2) the orientation of the OBS horizontal components, and (3) the clock error. Here, we address these challenges in an inherent preprocessing workflow to ultimately extract the Love and Scholte wave DC from small aperture OBS array measurements performed between 2018 and 2020 in Lake Lucerne (Switzerland). The arrays have a maximum aperture of 679 m and a maximum deployment water depth of 81 m. The challenges related to the OBS location on the lake floor are addressed by combining the multibeam bathymetry map and the backscatter image for the investigated site with the differential GPS coordinates of the OBS at recovery. The OBS measurements are complemented by airgun surveys. Airgun data are first used to estimate the misorientation of the horizontal components of the OBS and second to estimate the clock error. To assess the robustness of the preprocessing workflow, we use two array processing methods, namely the three-component high-resolution frequency-wavenumber and the interferometric multichannel analysis of surface waves, to estimate the dispersion characteristics of the propagating Scholte and Love waves for one of the OBS array sites. The results show the effectiveness of the preprocessing workflow. We observe the phase-velocity dispersion curve branches in the frequency range between 1.2 and 3.2 Hz for both array processing techniques.
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Essing, David, Vera Schlindwein, Mechita C. Schmidt-Aursch, Celine Hadziioannou, and Simon C. Stähler. "Characteristics of Current-Induced Harmonic Tremor Signals in Ocean-Bottom Seismometer Records." Seismological Research Letters 92, no. 5 (April 28, 2021): 3100–3112. http://dx.doi.org/10.1785/0220200397.
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Abstract Long-lasting harmonic tremor signals are frequently observed in spectrograms of seismological data. Natural sources, such as volcanoes and icebergs, or artificial sources, such as ships and helicopters, produce very similar harmonic tremor episodes. Ocean-bottom seismometer (OBS) records may additionally be contaminated by tremor induced by ocean-bottom currents acting on the OBS structure. This harmonic tremor noise may severely hinder earthquake detection and can be misinterpreted as volcanic tremor. In a 160-km-long network of 27 OBSs deployed for 1 yr along the Knipovich ridge in the Greenland Sea, harmonic tremor was widely observed away from natural sources such as volcanoes. Based on this network, we present a systematic analysis of the characteristics of hydrodynamically induced harmonic tremor in OBS records to make it distinguishable from natural tremor sources and reveal its generation processes. We apply an algorithm that detects harmonic tremor and extracts time series of its fundamental frequency and spectral amplitude. Tremor episodes typically occur twice per day, starting with fundamental frequencies of 0.5–1.0 Hz, and show three distinct stages that are characterized by frequency-gliding, mode-locking, and large spectral amplitudes, respectively. We propose that ocean-bottom currents larger than ∼5 cm/s cause rhythmical Karman vortex shedding around protruding structures of the OBS and excite eigenvibrations. Head-buoy strumming is the most likely source of the dominant tremor signal, whereas a distinctly different tremor signal with a fundamental frequency ∼6 Hz may be related to eigenvibrations of the radio antenna. Ocean-bottom current velocities reconstructed from the fundamental tremor frequency and from cross correlation of tremor time series between stations match observed average current velocities of 14–20 cm/s in this region. The tremor signal periodicity shows the same tidal constituents as the forcing ocean-bottom currents, which is a further evidence of the hydrodynamic nature of the tremor.
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Park, Joseph, Jamie MacMahan, William V. Sweet, and Kevin Kotun. "Continuous seiche in bays and harbors." Ocean Science 12, no. 2 (March 7, 2016): 355–68. http://dx.doi.org/10.5194/os-12-355-2016.
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Abstract. Seiches are often considered a transitory phenomenon wherein large amplitude water level oscillations are excited by a geophysical event, eventually dissipating some time after the event. However, continuous small-amplitude seiches have been recognized which raises a question regarding the origin of continuous forcing. We examine six bays around the Pacific where continuous seiches are evident and, based on spectral, modal, and kinematic analysis, suggest that tidally forced shelf resonances are a primary driver of continuous seiches.
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Bromirski, P. D., L. N. Frazer, and F. K. Duennebier. "Sediment shear Q from airgun OBS data." Geophysical Journal International 110, no. 3 (September 1992): 465–85. http://dx.doi.org/10.1111/j.1365-246x.1992.tb02086.x.
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Carrière, Olivier, and Peter Gerstoft. "Deep-water subsurface imaging using OBS interferometry." GEOPHYSICS 78, no. 2 (March 1, 2013): Q15—Q24. http://dx.doi.org/10.1190/geo2012-0241.1.
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Seismic interferometry processing is applied to an active seismic survey collected on ocean bottom seismometers (OBS) deployed at 900-m water depth over a carbonate/hydrates mound in the Gulf of Mexico. Common midpoint processing and stacking of the extracted Green’s function gives the subsurface PP reflectivity, with a horizontal resolution of half the receiver spacing. The obtained seismic section is comparable to classical upgoing/downgoing wavefield decomposition and deconvolution applied on a common receiver gather. Seismic interferometry does not require precise knowledge of source geometry or shooting times, but more accurate results are obtained when including this information for segmenting the signals before the crosscorrelations, especially when signals from distant surveys are present in the data. Reflectivity estimates can be obtained with the crosscorrelation of pressure or vertical particle velocity signals, but the pressure data gives the best resolution due to the wider frequency bandwidth and the reduced amount of noise bursts.
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Bragato, P. L., D. Pesaresi, A. Saraò, P. Di Bartolomeo, and G. Durì. "OGS improvements in the year 2011 in running the Northeastern Italy Seismic Network." Advances in Geosciences 34 (April 30, 2013): 5–8. http://dx.doi.org/10.5194/adgeo-34-5-2013.
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Abstract. The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS (Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake of magnitude Mw = 6.4 occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the Northeastern Italy Seismic Network: it currently consists of 12 very sensitive broad band and 21 simpler short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data centre in Udine. Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of 93 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of Northeastern Italy, as shown in Fig. 1 (Bragato et al., 2011; Saraò et al., 2010). Since 2002 OGS-CRS is using the Antelope software suite as the main tool for collecting, analyzing, archiving and exchanging seismic data, initially in the framework of the EU Interreg IIIA project "Trans-national seismological networks in the South-Eastern Alps" (Bragato et al., 2010; Pesaresi et al., 2008). SeisComP is also used as a real time data exchange server tool. In order to improve the seismological monitoring of the Northeastern Italy area, at OGS-CRS we tuned existing programs and created ad hoc ones like: a customized web server named PickServer to manually relocate earthquakes, a script for automatic moment tensor determination, scripts for web publishing of earthquake parametric data, waveforms, state of health parameters and shaking maps, noise characterization by means of automatic spectra analysis, and last but not least scripts for email/SMS/fax alerting. A new OGS-CRS real time seismological website (http://rts.crs.inogs.it/) has also been operative since several years.
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Lewis Williams, Elizabeth. "Creating poetry from the BAS archives: Commentary on, and extracts from, a new poetic sequence, “Met Obs”." Polar Record 55, no. 5 (September 2019): 341–46. http://dx.doi.org/10.1017/s0032247419000512.
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AbstractThe Antarctic Treaty of 1959, which dedicates the continent to peace and international scientific cooperation in the face of rising east–west tensions, is informed in part by a shared scientific imaginary created by the UK and other nations which maintained scientific bases in Antarctica at the time. In this article, the poet offers works extracted from her longer sequence “Met Obs,” based on meteorological reports and journals from the UK station at Port Lockroy written in advance of the 1957–1958 International Geophysical Year (IGY). The poems engage with the work and circumstances which helped foster such an imaginary, as well as with the nexus of Antarctic “values” endorsed by the Treaty, and the later Madrid Protocol. The commentary further contextualises these literary responses in terms of the attitudes of the men working there as well as the “wilderness and aesthetic values” recognised by the later Protocol on Environmental Protection. The world of the poems may belong to 1950s Antarctica, but their observations reach beyond that experience, making a case for the continued relevance of Treaty values, and for the importance of artistic, as well as scientific, responses to the environment in a world under threat from accelerating climate change and competition for resources.
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Pesaresi, D., M. Romanelli, C. Barnaba, P. L. Bragato, and G. Durì. "OGS improvements in 2012 in running the North-eastern Italy Seismic Network: the Ferrara VBB borehole seismic station." Advances in Geosciences 36 (July 22, 2014): 61–67. http://dx.doi.org/10.5194/adgeo-36-61-2014.
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Abstract. The Centro di Ricerche Sismologiche (CRS, Seismological Research Centre) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake of magnitude M=6.4 occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the North-eastern Italy Seismic Network: it currently consists of 17 very sensitive broad band and 18 simpler short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data centre in Udine. Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of about 100 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of North-eastern Italy. The south-western edge of the OGS seismic network (Fig. 1) stands on the Po alluvial basin: earthquake localization and characterization in this area is affected by the presence of soft alluvial deposits. OGS ha already experience in running a local seismic network in high noise conditions making use of borehole installations in the case of the micro-seismicity monitoring of a local gas storage site for a private company. Following the ML = 5.9 earthquake that struck the Emilia region around Ferrara in Northern Italy on 20 May 2012 at 02:03:53 UTC, a cooperation of Istituto Nazionale di Geofisica e Vulcanologia, OGS, the Comune di Ferrara and the University of Ferrara lead to the reinstallation of a previously existing very broad band (VBB) borehole seismic station in Ferrara. The aim of the OGS intervention was on one hand to extend its real time seismic monitoring capabilities toward South-West, including Ferrara and its surroundings, and on the other hand to evaluate the seismic response at the site. We will describe improvements in running the North-eastern Italy Seismic Network, including details of the Ferrara VBB borehole station configuration and installation, with first results.
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Taburet, Guillaume, Antonio Sanchez-Roman, Maxime Ballarotta, Marie-Isabelle Pujol, Jean-François Legeais, Florent Fournier, Yannice Faugere, and Gerald Dibarboure. "DUACS DT2018: 25 years of reprocessed sea level altimetry products." Ocean Science 15, no. 5 (September 12, 2019): 1207–24. http://dx.doi.org/10.5194/os-15-1207-2019.
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Abstract. For more than 20 years, the multi-satellite Data Unification and Altimeter Combination System (DUACS) has been providing near-real-time (NRT) and delayed-time (DT) altimetry products. DUACS datasets range from along-track measurements to multi-mission sea level anomaly (SLA) and absolute dynamic topography (ADT) maps. The DUACS DT2018 ensemble of products is the most recent and major release. For this, 25 years of altimeter data have been reprocessed and are available through the Copernicus Marine Environment Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S). Several changes were implemented in DT2018 processing in order to improve the product quality. New altimetry standards and geophysical corrections were used, data selection was refined and optimal interpolation (OI) parameters were reviewed for global and regional map generation. This paper describes the extensive assessment of DT2018 reprocessing. The error budget associated with DT2018 products at global and regional scales was defined and improvements on the previous version were quantified (DT2014; Pujol et al., 2016). DT2018 mesoscale errors were estimated using independent and in situ measurements. They have been reduced by nearly 3 % to 4 % for global and regional products compared to DT2014. This reduction is even greater in coastal areas (up to 10 %) where it is directly linked to the geophysical corrections applied to DT2018 processing. The conclusions are very similar concerning geostrophic currents, for which error was globally reduced by around 5 % and as much as 10 % in coastal areas.
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Wei, XiaoZhuo, Yang Shen, Jacqueline Caplan-Auerbach, and Julia K. Morgan. "An OBS Array to Investigate Offshore Seismicity during the 2018 Kīlauea Eruption." Seismological Research Letters 92, no. 1 (November 11, 2020): 603–12. http://dx.doi.org/10.1785/0220200206.
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Abstract On 3 May 2018, Kīlauea Volcano, one of the most active volcanoes in the world, entered a new eruptive phase because of a dike intrusion in the East Rift zone. One day later, an Mw 6.9 earthquake, which was likely trigged by the dike intrusion, occurred in the submarine south flank of Kīlauea Volcano. In mid-July, an ocean-bottom seismometer (OBS) array consisting of 12 stations was deployed on the submarine south flank of Kīlauea Volcano to monitor the aftershocks and lava–water interaction near the ocean entry. Eleven OBSs were recovered in mid-September. Preliminary evaluation of the data reveals a large number of seismic and acoustic events, which provide a valuable dataset for understanding flank deformation and stability as well as lava–water interaction. Here, we introduce this dataset and document notable instrument malfunctions along with some initial seismic and acoustic observations.
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Belviso, Sauveur, Ba Cuong Nguyen, and Patrick Allard. "Estimate of carbonyl sulfide (OCS) volcanic source strength deduced from OCS/CO2 ratios in volcanic gases." Geophysical Research Letters 13, no. 2 (February 1986): 133–36. http://dx.doi.org/10.1029/gl013i002p00133.
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Zheng, Hong, Jianke Fan, Dapeng Zhao, Cuilin Li, Dongdong Dong, Guangxu Zhang, and Xiujuan Wang. "A new method to estimate ocean-bottom-seismometer orientation using teleseismic receiver functions." Geophysical Journal International 221, no. 2 (January 24, 2020): 893–904. http://dx.doi.org/10.1093/gji/ggaa041.
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SUMMARY The orientation of an ocean-bottom-seismometer (OBS) is a critical parameter for analysing three-component seismograms, but it is difficult to estimate because of the uncontrollable OBS posture after its deployment. In this study, we develop a new and effective method to estimate the OBS orientation by fitting the amplitude of direct P wave of teleseismic receiver functions. The reliability of this method is verified using synthetic data and observed waveforms recorded at land seismic stations in Shandong Province, China. Our extensive synthetic tests show that our new method is little affected by a thin sedimentary layer that has a low S-wave velocity. The orientations of OBS stations that we deployed in the Yap subduction zone in the Western Pacific Ocean are estimated and corrected using our new method. After the correction, the direct P waves of teleseismic receiver functions show very good consistency. The effects of white and coloured noise in different levels, epicentral distance and backazimuth are also investigated, and the results show that these factors have small effects on the new method. We also examine the effect of sensor tilting on estimation of the OBS orientation, and find that a tilting correction should be made before the misorientation correction. We compare the OBS orientations determined with the new method and other methods and find that they are generally consistent with each other. We also discuss advantages and shortcomings of various methods, and think that our new method is more robust than the existing methods.
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Avansi, Guilherme Daniel, Célio Maschio, and Denis José Schiozer. "Simultaneous History-Matching Approach by Use of Reservoir-Characterization and Reservoir-Simulation Studies." SPE Reservoir Evaluation & Engineering 19, no. 04 (June 14, 2016): 694–712. http://dx.doi.org/10.2118/179740-pa.
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Summary Reservoir characterization is the key to success in history matching and production forecasting. Thus, numerical simulation becomes a powerful tool to achieve a reliable model by quantifying the effect of uncertainties in field development and management planning, calibrating a model with history data, and forecasting field production. History matching is integrated into several areas, such as geology (geological characterization and petrophysical attributes), geophysics (4D-seismic data), statistical approaches (Bayesian theory and Markov field), and computer science (evolutionary algorithms). Although most integrated-history-matching studies use a unique objective function (OF), this is not enough. History matching by simultaneous calibrations of different OFs is necessary because all OFs must be within the acceptance range as well as maintain the consistency of generated geological models during reservoir characterization. The main goal of this work is to integrate history matching and reservoir characterization, applying a simultaneous calibration of different OFs in a history-matching procedure, and keeping the geological consistency in an adjustment approach to reliably forecast production. We also integrate virtual wells and geostatistical methods into the reservoir characterization to ensure realistic geomodels, avoiding the geological discontinuities, to match the reservoir numerical model. The proposed methodology comprises a geostatistical method to model the spatial reservoir-property distribution on the basis of the well-log data; numerical simulation; and adjusting conditional realizations (models) on the basis of geological modeling (variogram model, vertical-proportion curve, and regularized well-log data). In addition, reservoir uncertainties are included, simultaneously adjusting different OFs to evaluate the history-matching process and virtual wells to perturb geological continuities. This methodology effectively preserves the consistency of geological models during the history-matching process. We also simultaneously combine different OFs to calibrate and validate the models with well-production data. Reliable numerical and geological models are used in forecasting production under uncertainties to validate the integrated procedure.
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KHOSRAVI, YOUNES, HASAN LASHKARI, and HOSEIN ASAKEREH. "Spatial variability of water vapour in south and southwest of Iran." MAUSAM 68, no. 1 (November 30, 2021): 9–22. http://dx.doi.org/10.54302/mausam.v68i1.405.
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In this study two regression models, ordinary least square and geographically weighted regression as widely applied techniques, were used in modeling the regression relationships between water vapour and related geographic features, i.e., longitude, latitude, elevation, slope and aspect. Accordingly, the water vapour data in south and southwest of Iran were collected in pixels in the time interval 1981-2010. According to the general OLS regression, the relationship between WV and latitude, elevation and aspect were reverse and with longitude and slope were positive. Analyzing the relationship between geographic features and WV by GWR model determined that greatest coefficients of explanatory variables were in longitude, latitude, slope, aspect and elevation, respectively. Regarding to the model performance, GWR showed an improvement over OLS in estimating the WV and provided more realistic and useful results. So that the R2, Adjusted R2 and AICc for GWR were 0.967, 0.968 and 9329.38, respectively while these factors for OLS were 0.8478, 0.8475 and 14559.04.
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Zeng, Qicheng, and Robert L. Nowack. "Analysis of Local Seismic Events near a Large-N Array for Moho Reflections." Seismological Research Letters 92, no. 1 (October 28, 2020): 408–20. http://dx.doi.org/10.1785/0220200087.
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Abstract Local seismic events recorded by the large-N Incorporated Research Institutions for Seismology Community Wavefield Experiment in Oklahoma are used to estimate Moho reflections near the array. For events within 50 km of the center of the array, normal moveout corrections and receiver stacking are applied to identify the PmP and SmS Moho reflections on the vertical and transverse components. Corrections for the reported focal depths are applied to a uniform event depth. To stack signals from multiple events, further static corrections of the envelopes of the Moho reflected arrivals from the individual event stacks are applied. The multiple-event stacks are then used to estimate the pre-critical PmP and SmS arrivals, and an average Poisson’s ratio of 1.77±0.02 was found for the crust near the array. Using a modified Oklahoma Geological Survey (OGS) velocity model with this Poisson’s ratio, the time-to-depth converted PmP and SmS arrivals resulted in a Moho depth of 41±0.6 km. The modeling of wide-angle Moho reflections for selected events at epicenter-to-station distances of 90–135 km provides additional constraints, and assuming the modified OGS model, a Moho depth of 40±1 km was inferred. The difference between the pre-critical and wide-angle Moho estimates could result from some lateral variability between the array and the wide-angle events. However, both estimates are slightly shallower than the original OGS model Moho depth of 42 km, and this could also result from a somewhat faster lower crust. This study shows that local seismic events, including induced events, can be utilized to estimate properties and structure of the crust, which, in turn, can be used to better understand the tectonics of a given region. The recording of local seismicity on large-N arrays provides increased lateral phase coherence for the better identification of precritical and wide-angle reflected arrivals.
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Barcheck, Grace, Geoffrey A. Abers, Aubreya N. Adams, Anne Bécel, John Collins, James B. Gaherty, Peter J. Haeussler, et al. "The Alaska Amphibious Community Seismic Experiment." Seismological Research Letters 91, no. 6 (August 19, 2020): 3054–63. http://dx.doi.org/10.1785/0220200189.
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Abstract The Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline-crossing passive- and active-source seismic experiment that took place from May 2018 through August 2019 along an ∼700 km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were deployed onshore, and 75 were deployed offshore in Ocean Bottom Seismometer (OBS) packages. Additional strong-motion instruments were also deployed at six onshore seismic sites. Offshore OBS stretched from the outer rise across the trench to the shelf. OBSs in shallow water (<262 m depth) were deployed with a trawl-resistant shield, and deeper OBSs were unshielded. Additionally, a number of OBS-mounted strong-motion instruments, differential and absolute pressure gauges, hydrophones, and temperature and salinity sensors were deployed. OBSs were deployed on two cruises of the R/V Sikuliaq in May and July 2018 and retrieved on two cruises aboard the R/V Sikuliaq and R/V Langseth in August–September 2019. A complementary 398-instrument nodal seismometer array was deployed on Kodiak Island for four weeks in May–June 2019, and an active-source seismic survey on the R/V Langseth was arranged in June 2019 to shoot into the AACSE broadband network and the nodes. Additional underway data from cruises include seafloor bathymetry and sub-bottom profiles, with extra data collected near the rupture zone of the 2018 Mw 7.9 offshore-Kodiak earthquake. The AACSE network was deployed simultaneously with the EarthScope Transportable Array (TA) in Alaska, effectively densifying and extending the TA offshore in the region of the Alaska Peninsula. AACSE is a community experiment, and all data were made available publicly as soon as feasible in appropriate repositories.
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Nakagawa, Seiji, and Thomas M. Daley. "Modeling wave generation by borehole orbital vibrator source." GEOPHYSICS 71, no. 1 (January 2006): F1—F11. http://dx.doi.org/10.1190/1.2168008.
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An orbital vibrator source (OVS), a fluid-coupled shear-wave source, has many properties useful for crosswell, single-well, and borehole-to-surface imaging of both P- (compressional) and S- (shear) wave velocities of reservoir rocks. To this day, however, only a limited number of quantitative models have been developed to explain its properties. In this article, we develop both 2D and 3D models of an OVS, allowing us to examine source characteristics such as radiation patterns, frequency dependence of wave amplitudes, and guided-wave generation. These models are developed in the frequency-wavenumber domain using the partial wave expansion of the wavefield within and outside the borehole. The models predict many unique characteristics of an OVS, including formation-property-dependent vibrator amplitudes, uniform isotropic S-wave radiation pattern, and small tube-wave generation.
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Laeter, J. R. De, and K. J. R. Rosman. "Deficiencies in the classical model ofs-process nucleosynthesis." Meteoritics & Planetary Science 34, no. 5 (September 1999): 717–21. http://dx.doi.org/10.1111/j.1945-5100.1999.tb01383.x.
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Zhu, Gaohua, Hongfeng Yang, Jian Lin, Zhiyuan Zhou, Min Xu, Jinlong Sun, and Kuiyuan Wan. "Along-strike variation in slab geometry at the southern Mariana subduction zone revealed by seismicity through ocean bottom seismic experiments." Geophysical Journal International 218, no. 3 (June 10, 2019): 2122–35. http://dx.doi.org/10.1093/gji/ggz272.
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SUMMARYWe have conducted the first passive Ocean Bottom Seismograph (OBS) experiment near the Challenger Deep at the southernmost Mariana subduction zone by deploying and recovering an array of 6 broad-band OBSs during December 2016–June 2017. The obtained passive-source seismic records provide the first-ever near-field seismic observations in the southernmost Mariana subduction zone. We first correct clock errors of the OBS recordings based on both teleseismic waveforms and ambient noise cross-correlation. We then perform matched filter earthquake detection using 53 template events in the catalogue of the US Geological Survey and find >7000 local earthquakes during the 6-month OBS deployment period. Results of the two independent approaches show that the maximum clock drifting was ∼2 s on one instrument (OBS PA01), while the rest of OBS waveforms had negligible time drifting. After timing correction, we locate the detected earthquakes using a newly refined local velocity model that was derived from a companion active source experiment in the same region. In total, 2004 earthquakes are located with relatively high resolution. Furthermore, we calibrate the magnitudes of the detected earthquakes by measuring the relative amplitudes to their nearest relocated templates on all OBSs and acquire a high-resolution local earthquake catalogue. The magnitudes of earthquakes in our new catalogue range from 1.1 to 5.6. The earthquakes span over the Southwest Mariana rift, the megathrust interface, forearc and outer-rise regions. While most earthquakes are shallow, depths of the slab earthquakes increase from ∼100 to ∼240 km from west to east towards Guam. We also delineate the subducting interface from seismicity distribution and find an increasing trend in dip angles from west to east. The observed along-strike variation in slab dip angles and its downdip extents provide new constraints on geodynamic processes of the southernmost Mariana subduction zone.
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Teng, Ta-Liang, and Min Hsu. "A seismic telemetry system of large dynamic range." Bulletin of the Seismological Society of America 76, no. 5 (October 1, 1986): 1461–71. http://dx.doi.org/10.1785/bssa0760051461.
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Abstract An optimum telemetry system (OTS) has been developed that can be plugged directly into the front-end electronics of a field seismic station to enable large dynamic range (120 dB) data transmission, 60 dB resolution, and three-component seismic recording. This new system is designed to be accommodated within a conventional single ±125-Hz transmission channel. With CMOS microprocessors and a minimum of 64 kB memory, the OTS buffer stores 3.5 min of data for one channel or 1 min of data for three channels at 128 sps. The buffer storage can easily be expanded by an order of magnitude without significant increase in cost, but the present buffer size is sufficient for regional seismic networks of coverage less than 500 km in size; i.e., enough preevent memory is allowed for event trigger and gain-ranging operations. There is no sacrifice on timing accuracy, and to apply corrections to the travel-time delays is simple as the delays are exactly known. To guarantee the 60 dB resolution in a ±125-Hz FM transmission band, a new digital voltage-controlled oscillator has been designed for the OTS which keys the FM center frequency accurate to 0.1 per cent and practically eliminates the drift of the voltage-controlled oscillator center frequency. The OTS offers a practical solution to the severe signal-clipping problem that has plagued many high-performance telemetered seismic networks.
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Ikelle, Luc T., Lasse Amundsen, and Seung Yoo. "An optimization of the inverse scattering multiple attenuation method for OBS and VC data." GEOPHYSICS 67, no. 4 (July 2002): 1293–303. http://dx.doi.org/10.1190/1.1500392.
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The inverse scattering multiple attenuation (ISMA) algorithm for ocean‐bottom seismic (OBS) data can be formulated in the form of a series expansion for each of the four components of OBS data. Besides the actual data, which constitute the first term of the series, each of the other terms is computed as a multidimensional convolution of OBS data with streamer data, and aims at removing one specific order of multiples. If the streamer data do not contain free‐surface multiples, we found that the computation of only the second term of the series is needed to predict and remove all orders of multiples, whatever the water depth. As the computation of the various terms of the series is the most expensive part of ISMA, this result can produce significant savings in computation time, even in data storage, as we no longer need to store the various terms of the series. For example, if the streamer data contained free‐surface multiples, OBS seismic data of 6‐s duration, corresponding to a geological model of the subsurface with 250‐m water depth, require the computation of five terms of the series for each of the four components of OBS data. With the new implementation, in which the streamer data do not contain free‐surface multiples, we need the computation of only one term of the series for each component of the OBS data. The saving in CPU time for this particular case is at least fourfold. The estimation of the inverse source signature, which is an essential part of ISMA, also benefits from the reduction of the number of terms needed for the demultiple to two because it becomes a linear inverse problem instead of a nonlinear one. Assuming that the removal of multiple events produces a significant reduction in the energy of the data, the optimization of this problem leads to a stable, noniterative analytic solution. We have also adapted these results to the implementation of ISMA for vertical‐cable (VC) data. This implementation is similar to that for OBS data. The key difference is that the basic model in VC imaging assumes that data consist of receiver ghosts of primaries instead of the primaries themselves. We have used the following property to achieve this goal. The combination of VC data with surface seismic data, which do not contain free‐surface multiples, allows us to predict free‐surface multiples and receiver ghosts as well as the receiver ghosts of primary reflections. However, if the direct wave arrivals are removed from the VC data, this combination will not predict the receiver ghosts of primary reflections. The difference between these two predictions produces data containing only receiver ghosts of primaries.
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Barison, Erika, Giuseppe Brancatelli, Rinaldo Nicolich, Flavio Accaino, Michela Giustiniani, and Umberta Tinivella. "Wave equation datuming applied to marine OBS data and to land high resolution seismic profiling." Journal of Applied Geophysics 73, no. 3 (March 2011): 267–77. http://dx.doi.org/10.1016/j.jappgeo.2011.01.009.
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Kovachev, S. A., I. P. Kuzin, and S. L. Soloviev. "Microseismicity of the frontal Hellenic arc according to OBS observations." Tectonophysics 201, no. 3-4 (January 1992): 317–27. http://dx.doi.org/10.1016/0040-1951(92)90239-3.
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Marullo, S., B. Buongiorno Nardelli, M. Guarracino, and R. Santoleri. "Observing the Mediterranean Sea from space: 21 years of Pathfinder-AVHRR sea surface temperatures (1985 to 2005): re-analysis and validation." Ocean Science 3, no. 2 (May 30, 2007): 299–310. http://dx.doi.org/10.5194/os-3-299-2007.
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Abstract. The time series of satellite infrared AVHRR data from 1985 to 2005 has been used to produce a daily series of optimally interpolated SST maps over the regular grid of the operational MFSTEP OGCM model of the Mediterranean basin. A complete validation of this OISST (Optimally Interpolated Sea Surface Temperature) product with in situ measurements has been performed in order to exclude any possibility of spurious trends due to instrumental calibration errors/shifts or algorithms malfunctioning related to local geophysical factors. The validation showed that satellite OISST is able to reproduce in situ measurements with a mean bias of less than 0.1 K and RMSE of about 0.5 K and that errors do not drift with time or with the percent interpolation error.
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Wang, Xiangchun, Rongyi Qian, and Changliang Xia. "PS-wave processing and S-wave velocity inversion of OBS data from Northern South China Sea." Journal of Applied Geophysics 100 (January 2014): 58–65. http://dx.doi.org/10.1016/j.jappgeo.2013.11.002.
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