Ultra High Resolution 3D Seismic Surveying of Active Hydrate Ridge Vents to Complement Proposed CORKing

智力上的优点。该项目将获得新的超高分辨率三维地震数据立方体跨越小区域周围的三个不同的活跃甲烷排放系统沿着俄勒冈州边缘。最近在海伯利斯海岭进行的204航次ODP钻井发现了一个动态天然气喷口系统，其中游离气要么通过连续的垂直裂缝沿沿着快速的直接路线运移，要么通过可渗透的水平地层浊积砂和垂直裂缝沿更曲折的路线运移。目前还不清楚天然气如何通过水合物稳定带（GHSZ）迁移到海脊海底，特别是流体流动是否主要受结构或地层的限制。此外，天然气在海底水合物区的排放是常见的，但神秘的。要到达海底喷口，游离气体必须通过GHSZ迁移，但GHSZ中的游离气体应该是不稳定的，形成水合物并变得不流动。这些神秘的气体喷口系统，如海伯利脊和其他地方的结构，机制和时间演化，知之甚少。在204航次期间，最近的三维地震反射测量和钻探揭示了一个主要的自由气体管道，该管道通往海布里海岭南部的山顶。浊积岩层位，层位A，提供了一个管道的南部峰会下40米的GHSZ基地和150米以下的海底（mbsf）的游离气。现有的三维地震反射数据揭示了层位A的几何形状和反射特性的细节，但它们很少揭示从层位A通过GHSZ到海底的最有趣的间隔中的游离气迁移。第204航段的结果表明，目前地震数据的有限分辨率（~ 5 m）显然不足以探测高含水率层（~ 1-2 m厚）或探测可能通过水力连接层位A的主要气源与海底的小规模断层。支持者将应用一种新颖的低成本超高分辨率三维地震成像技术，该技术将提供两个额外的更高分辨率尺度，并在俄勒冈州边缘喷口处产生流体管道的戏剧性图像。具体地说，他们将在三个地点收集两个三维地震数据集：海伯利斯海岭南部，北方海伯利斯海岭和东南丘陵。这两项调查将利用高频气枪和啁啾源，将提供关于浅喷口管道、地层管道、小规模断层、水合物层以及由于喷口下游离气体和水合物积聚而引起的异常反射率的最佳图像。这些数据将揭示有关喷口管道空间和可能的时间演变的新细节，并为潜在的IODP钻探（625-Full）的规划、选址和解释结果提供关键细节，该钻探计划安装CORK以测量和监测喷口特性在南部水化物岭就地。更广泛的影响。这项工作将建立在现有的ODP第146和204航段钻井工作的基础上，以调查海桑岭，并补充IODP后续钻井（625-Full）。该钻井旨在在多个地点安装软木塞，并调查排气系统的时空变化，该系统通过GHSZ将甲烷输送到海桑海岭南部的顶峰，并进入当地的海底化学合成群落。这项工作将直接支持IODP初始科学计划中概述的了解甲烷水合物系统的广泛目标（甲烷既是温室气体，也是一种巨大的潜在能源），并为未来钻探和软木塞的选址和解释结果提供更广泛的背景。这项工作将促进与英国南安普顿国家海洋学中心的合作，并促进低成本高分辨率三维地震采集设施的实施和开发，作为对研究船Langseth上更深穿透三维地震设施的补充。研究生支持将提供航海经验和教育发展的机会。

Intellectual merit. The project will acquire new ultra-high-resolution 3D seismic data cubesacross small areas around three different active methane venting systems along the Oregonmargin. Recent ODP drilling on Hydrate Ridge during Leg 204 discovered a dynamic gas ventsystem in which free gas either migrates along fast direct routes through continuous verticalfractures or through more tortuous routes through permeable horizontal stratigraphic turbiditesands and vertical fractures. It is fundamentally unclear how gas migrates through the gashydrate stability zone (GHSZ) to the seafloor at Hydrate Ridge, and, in particular, whetherfluid flow is constrained primarily by structure or stratigraphy. Furthermore, gas venting at theseafloor in hydrate regions is common but enigmatic. To reach the seafloor vents, free gas mustmigrate through the GHSZ, yet free gas in the GHSZ should be unstable, form hydrate andbecome immobile. The structures, mechanisms, and temporal evolution of these enigmatic gasvent systems, such as Hydrate Ridge and elsewhere, are poorly known. A recent 3D seismicreflection survey and drilling during Leg 204 revealed a major free gas conduit leading to thesummit of southern Hydrate Ridge. A turbidite horizon, Horizon A, provides a conduit for freegas at the southern summit 40 m beneath the base of the GHSZ and 150 m below seafloor(mbsf). The existing 3D seismic reflection data reveal details about the geometry and reflectionproperties of Horizon A, yet they reveal very little about free gas migration in the mostintriguing interval, from Horizon A through the GHSZ to the seafloor. Leg 204 results revealthat the limited resolution of current seismic data (~ 5 m) is clearly inadequate for imaginghydrate layers (which are ~ 1-2 m thick) or detecting small-scale faults that may hydraulicallyconnect the primary gas source at Horizon A to the seafloor. The proponents will apply a noveland low-cost ultra-high resolution 3D seismic imaging technique that will provide twoadditional higher scales of resolution and produced dramatic images of fluid conduits at theOregon margin vents. Specifically, they will collect two 3D seismic datasets at each ofthree sites; southern Hydrate Ridge, northern Hydrate Ridge, and SE Knolls. The two surveys,which will utilize high frequency air-gun and chirp sources, will provide the best possibleimages of shallow vent conduits, stratigraphic conduits, small-scale faults, hydrate layers, andanomalous reflectivity due to free gas and hydrate accumulations beneath the vents. These data will reveal new details about the spatial and possibly temporal evolution of vent conduits, and provide critical details for planning, siting, and interpreting the results of potential IODP drilling (625-Full), which plans to install CORKs to measure and monitor vent properties in situ at southern Hydrate Ridge.Broader impacts. The work will build on the existing ODP Legs 146 and 204 drilling efforts to investigate Hydrate Ridge and to complement IODP follow-up drilling (625-Full). The drilling is designed to install CORKs at multiple sites and investigate temporal and spatial variability in a venting system that feeds methane up through the GHSZ to the summit of southern Hydrate Ridge and into the local seafloor chemosynthetic communities. This work will directly support the broad goals of understanding methane hydrate systems as outlined in the IODP Initial Science Plan (methane is both a greenhouse gas and a large potential energy resource), and provide a broader context for siting and interpreting the results of the future drilling and CORKing. The work will foster collaboration with the National Oceanography Centre, Southampton, UK, and promote the implementation and development of a low-cost high-resolution 3D seismic acquisition facility, as a complement to deeper penetration 3D seismic facilities on the R/V Langseth. Graduate student support will provide an opportunity for sea-going experience and educational development.