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体，覆盖俄勒冈边缘三个不同的活跃甲烷排放系统周围的小区域。最近在204标段水合物山脊进行的ODP型钻探发现了一个动态的气体喷口系统，在该系统中，游离气体要么通过连续的垂直裂缝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体和垂直裂缝沿着更曲折的路线运移。目前尚不清楚天然气如何通过天然气水合物稳定带(GHSZ)运移到水合物海脊的海底，尤其是流体流动是否主要受构造或地层的限制。此外，在水合物区域的这些地下水位中，天然气的排放是常见的，但却是谜。为了到达海底喷口，游离气必须通过GHSZ迁移，但GHSZ中的游离气应该是不稳定的，形成水合物并变得不能移动。这些神秘的气体喷发系统的结构、机制和时间演化，如水合物岭和其他地方，人们知之甚少。最近在204航段进行的三维地震反射调查和钻探发现了一条通往南水合物山脊的主要游离气管道。浊积地平线，地平线A，为南部山顶GHSZ底部下40米和海底下150米处的自由气体提供了一条管道。现有的三维地震反射数据揭示了地平线A的几何结构和反射性质的细节，但它们很少揭示最有趣的区间内的自由气体迁移，从地平线A通过GHSZ到海底。LEG 204结果表明，当前地震数据的有限分辨率(~5m)显然不足以成像水合物层(~1-2m厚)或探测可能在水力上将A层的初级气源连接到海底的小规模断层。支持者将应用一种新的、低成本的超高分辨率3D地震成像技术，该技术将提供另外两种更高分辨率的分辨率，并在俄勒冈州边缘喷口产生引人注目的流体管道图像。具体地说，他们将在三个地点分别收集两个3D地震数据集：南部水合物山脊、北部水合物山脊和东南部诺尔斯。这两次调查将利用高频气枪和啁啾源，将提供浅层喷口管道、地层管道、小规模断层、水合物层以及因喷口下方聚集的游离气和水合物而产生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时间演变的新细节，并为规划、选址和解释潜在的IODP钻探(625-Full)的结果提供关键细节，该钻探计划安装软木塞，以现场测量和监测南部水合物山脊的喷口特性。这项工作将建立在现有的ODP146和204段钻探工作的基础上，以调查水合物岭，并补充IODP后续钻探(625-Full)。钻探的目的是在多个地点安装软木塞，并调查通风系统中的时间和空间变异性，该系统将甲烷通过GHSZ向上输送到南部水合物岭的山顶，并进入当地的海底化学合成社区。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(甲烷既是一种温室气体，也是一种巨大的潜在能源)，并为确定和解释未来钻探和软木封堵的结果提供更广泛的背景。这项工作将促进与英国南安普敦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R/V朗塞特更深入渗透的三维地震设施的补充。研究生支持将提供一个出海体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.