HYDGAS - Quantification of gas hydrates and gas in the sediment of the Cascadia accretionary wedge using seismic methods = Seismische Quantifizierung von Gashydraten im Sediment der Cascadia-Subduktionszone : FS SONNE FAHRTBERICHT SO-150 / CRUISE REPORT SO-150, 17.09.2000 - 27.10.2000.

Klaeschen, Dirk, Kopf, Achim, Arsenault, Matthew and Bialas, Jörg, eds. (2001) HYDGAS - Quantification of gas hydrates and gas in the sediment of the Cascadia accretionary wedge using seismic methods = Seismische Quantifizierung von Gashydraten im Sediment der Cascadia-Subduktionszone : FS SONNE FAHRTBERICHT SO-150 / CRUISE REPORT SO-150, 17.09.2000 - 27.10.2000. . GEOMAR Research Center for Marine Geosciences Christian-Albrechts-University in Kiel, Kiel, 245 pp. DOI 10.3289/CR_SO_150.

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Supplementary data:

Abstract

The circulation of gases and aqueous fluids, as well as the abundance of gas hydrates in
convergent margin scenarios, play a significant role in global mass balances. Hence, the study of
these processes with various techniques has become a major objective in geosciences research
during the previous decade. The main focus of the research expedition HYDGAS during cruise
Sonne SO-150 was the qualification and quantification of massive gas hydrates in the sediment
using seismic methods. Gas hydrates, or clathrates, are ice-like crystals of gases (predominantly
methane) and water, which occur in various forms in subseafloor sediments. According to global
estimates, the carbon fixed in such gas hydrates exceeds by far the amount of presently
discovered oil and gas occurrences. Thus, gas hydrate research is of both scientific, economic, and
environmental importance.
The continental margin off Oregon, where the Juan de Fuca Plate is subducted beneath the North
American continental plate, is a well studied area which is characterized by its wealth of clathrates
and hydrate-related deposits. Within the accumulated sediment of the upper subduction zone, the
so called Cascadia accretionary prism, massive gashydrates and associated chemical anomalies
(brines), their chemical oxidization products (authigenic carbonate), and typical fauna
assemblages related to methane-rich fluids have been previously reported. Apart from shedding
more light on the principal understanding of gas hydrate environments, the main aim of the
HYDGAS expedition is an estimate of gas hydrate quantities, their potential economic relevance in
the future, and the risk of environmental hazards (submarine slides, release of greenhouse gases
into the atmosphere) from gas hydrate dissociation.

During cruise Sonne SO-150 , improved geophysical methods were used to identify and quantify
the spatial variation of gas hydrates across Hydrate Ridge. Narrowly spaced receivers on the
seafloor (approximately 200 m apart), shallow and deep towed systems, and a broad range of
source frequencies (5 Hz to 2 kHz) were used to guarantee pristine data quality. Here, special
attention will be given to parameters which will assist in gas hydrate identification and
quantification. The new geophysical data will be compared and calibrated using the results from
direct measurements on recovered core as well as along the borehole wall (downhole logging) at
ODP Site 892. Calibration of the geophysical information will allow us to optimize data processing
and interpretation. The results from cruise Sonne SO-150 will significantly broaden the
understanding of seismic signals in hydrate-bearing sediments, and thus will add a quantitative
component to the overall gas hydrate research.
Five receiver assemblages in three locations, at Site 892 (ODP Leg 146) and at two future ODP
drillsites (ODP Leg 204, scheduled for autumn 2002), provided a wealth of data from 5 different
sources used. During intervals of data retrieval and OBH/OBS refitting, a total of 1490 km of
seismic reflection profiles were acquired using five different source (broad frequency range) and
three different streamer (surface and deep tow) configurations. The narrowly spaced grid of
seismic reflexion and Parasound lines permits us to tie in the results from the receiver experiments
for quantitative estimates.

Document Type: Report (Cruise Report)
Keywords: RV Sonne ; Cruise report ; SO150 ; HYDGAS
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Open Access Journal?: Yes
DOI etc.: 10.3289/CR_SO_150
Projects: HYDGAS
Expeditions/Models/Experiments:
Date Deposited: 09 Dec 2014 08:18
Last Modified: 09 Dec 2014 08:32
URI: http://oceanrep.geomar.de/id/eprint/26358

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