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TitreReport on Cruise 2010007PGC, C.C.G. Vessel John P. Tully, 30 June - 10 July 2010, SeaJade-I Seafloor Earthquake Array - Japan Canada Cascadia Experiment, Ocean bottom seismometer recovery, methane gas-plume acoustic imaging, and CTD-water sampling program
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AuteurRiedel, M; Côté, M M; Neelands, P J; Obana, K; Wania, R; Price, A; Taylor, S
SourceCommission géologique du Canada, Dossier public 7557, 2014, 85 pages, https://doi.org/10.4095/295545
Année2014
ÉditeurRessources naturelles Canada
Documentdossier public
Lang.anglais
DOIhttps://doi.org/10.4095/295545
Medianumérique; en ligne
Référence reliéeCette publication est reliée les publications suivantes
Formatspdf
ProvinceRégion extracotière de l'ouest
Lat/Long OENS-128.5000 -126.0000 49.6667 44.9167
Sujetslevés géophysiques; secousses séismiques; études séismiques; magnitudes des séismes; epicentres; répliques sismiques; interpretations sismiques; sismicité; sismographes; réseau sismique; séismologie; ondes sismiques; gaz; bulles de gaz; levés acoustiques; levés acoustiques marins; analyses de l'eau; géophysique
Illustrationslocation maps; tables; photographs; profiles; logs
Consultation
Endroit
 
Bibliothèque de Ressources naturelles Canada - Ottawa (Sciences de la Terre)
 
ProgrammeOuest du Canada, risque géoscience, Géoscience pour la sécurité publique
Diffusé2014 12 04
Résumé(Sommaire disponible en anglais seulement)
1.1 Objectives
This expedition 2010007 is the second cruise of a major international collaboration of NRCan ("Public Safety Geoscience" (PSG) Program) with Japan (JAMSTEC) and the Woods Hole Oceanographic Institution (WHOI). The main objective of this collaboration is to acquire passive seismic data using Ocean Bottom Seismometers (OBS) for earthquake studies. The OBS monitoring will provide direct information on seismic activity beneath the continental slope and further offshore which cannot be provided by land-based seismic networks and therefore will fill a critical knowledge gap. The filling of this knowledge gap is essential to the assessment of earthquake hazard due to the Cascadia subduction fault, an important output of the "Targeted Hazard Assessment in Western Canada" project under the PSG program.
In total, 33 OBSs were deployed during the cruise 2010005-PGC (SeaJade-I) from June 30 to July 10, 2010. The objective of cruise 2010007 was to collect back these OBS.
Secondary objectives of the expedition included acoustic imaging of known methane vent sites (plumes). This imaging was combined with conducting casts using a Conductivity-Temperature-Depth (CTD) measurement-unit attached to a 24-Niskin-bottle rosette for water-sampling. The water-sampling was conducted to measure the concentration of dissolved methane in the water. The analyses of the water samples are carried out in collaboration with Prof. Dr. Michael Whiticar from the School of Earth and Ocean Sciences, University of Victoria.
1.2 Accomplishments and Results
Despite extreme weather conditions due to a storm at the beginning of the cruise forcing a major shutdown of all operations for 60 hours (2.5 days) from Friday evening, September 24th to Monday morning, September 27th the OBS were all, except one, recovered. OBS Station 11 did not respond to the acoustic release commands, and the station was abandoned after 4 hours of trials to recover the system.
All 32 OBS were physically (from the outside) in good shape, all transponders and light-strobes worked making the identification of floating instrument and recovery relatively simple, despite, in part, heavy seas. All OBS were brought back to the Pacific Geoscience Centre (PGC), where the glass spheres were opened and all data recovered. Copies of the data set were distributed to the different scientific parties involved.
Due to the weather interruption, only 3.5 days remained in the program to complete the acoustic imaging and water-sampling program. In total, 84 lines were acquired over seven (7) plume locations (2 grids at Bullseye Vent, 2 grids at Spinnaker Vent, 2 grids at Amnesiac Vent, and 2 cross-lines at Barkley Canyon). Out of these lines seven (7) locations for CTD casts and water-sampling were chosen. Onboard analyses of some samples showed overall very small amounts of dissolved methane (not exceeding 20 n-moles/l). However, sufficient volumes of gas were collected allowing for post-cruise analyses including isotope measurements at all seven vent locations.
Résumé(Résumé en langage clair et simple, non publié)
Ce dossier public de la Commission géologique du Canada présente un résumé des activités menées au cours de la phase de récupération de l'expédition SeaJade (Seafloor Earthquake Array Japan Cascadia Experiment). Un résumé de la phase de déploiement se trouve dans le dossier public 7558. Le principal objectif de l'expédition était de récupérer les 35 sismomètres de fond marin déployés trois mois plus tôt pour surveiller l'activité sismique au large des côtes de l'île de Vancouver. La surveillance au moyen de ces sismomètres a permis d'obtenir des renseignements directs sur l'activité sismique sous le talus continental et encore plus au large, renseignements que ne peuvent fournir les réseaux de sismomètres terrestres. Il est essentiel de combler cette lacune de nos connaissances pour bien évaluer le risque que la faille de subduction Cascadia cause un tremblement de terre. Les objectifs secondaires de l'expédition incluent l'imagerie acoustique des sites d'exhalaison du méthane et le prélèvement d'échantillons d'eau. Ces prélèvements permettront de mesurer la teneur en méthane dissous dans l'eau au-dessus de ces sites d'exhalaison.
GEOSCAN ID295545