3-D Seismic Imaging of an Active Margin Hydrate System - Oregon Continental Margin

99-06990 Trehu99-07205 Bang推荐的项目是对俄勒冈州近海大陆边缘卡斯卡迪亚增生杂岩上水合物山脊9 x 4公里区域进行高分辨率三维海洋地震勘探。这项调查将使用海底地震仪(OBS)来优化地震信号的记录，并将重点放在绘制这一高流体通量区域的吸积沉积物中天然气水合物的存在图。其他目标包括：确定天然气水合物的稳定性条件；估计天然气水合物和游离气的体积，将游离气困在与天然气水合物存在有关的海底模拟反射体(BSR)之下；确定流体流动的路径及其在天然气水合物形成中的重要性；以及与卡斯卡迪亚边缘天然气水合物存在有关的斜坡稳定性(或不稳定性)。这项研究要检验的具体假设包括：1)明亮的地层反射是否代表集中流体流动的发育区；2)研究区背斜内先前多通道工作中的双BSR成像是否代表了水合物对褶皱的不稳定；3)折射波到达的层析反演能成像存在游离气的次BSR体积；以及4)水合物和游离气的存在是否影响力学性质，从而影响斜坡稳定性和增长复合体的形态。这项工作将为拟议的水合物山脊大洋钻探计划钻探(ODP Proposal 546-Full)提供3维地层和构造背景，该计划旨在“证实”与天然气水合物形成和稳定性有关的因素。

99-06990 Trehu99-07205 BangsRecommended project is for a high-resolution, 3-D marine seismic survey of a 9 x 4 km area on the crest of Hydrate Ridge, on the Cascadia accretionary complex of the offshore Oregon continental margin. The survey will use ocean bottom seismometers (OBS's) to optimize recording of the seismic signals, and will focus on mapping the presence of gas hydrate within the accretionary sediments in this region of high fluid flux. Other goals center on defining the gas hydrate stability conditions; estimation of gas hydrate and free gas volumes, with the free gas trapped beneath bottom simulating reflectors (BSR's) associated with gas hydrate presence; defining pathways of fluid flux and their importance in gas hydrate formation; and slope stability (or instability) related to gas hydrate presence on the Cascadia margin. Specific hypotheses to be tested by the research include: 1) do bright stratigraphic reflections represent developing zones of focused fluid flow; 2) does a double BSR imaged in previous multichannel work within an anticline in the study region represent destabilization of hydrate in response to folding; 3) can tomographic inversion of refracted arrivals image the sub-BSR volume in which free gas is present; and 4) does the presence of hydrate and free gas affect the mechanical properties and thus slope stability and morphology of accretionary complexes. This work will provide the 3-dimensional stratigraphic and structural context for the proposed Ocean Drilling Program drilling (ODP proposal 546-Full) on Hydrate Ridge, which is designed to "ground truth" the factors related to gas hydrate formation and stability.***