Seismic velocities measured in three drill holes through a gas hydrate deposit on the Blake Ridge, offshore South Carolina, indicate that substantial free exists to at least 250 meters beneath bottom-simulating reflection (BSR). Both methane and exist even where clear BSR is absent. The low reflectance, or blanking, above caused by lithologic homogeneity of sediments rather than cementation. average saturation relatively (5 7 percent porosity), which suggests earlier global estimates...

We present results from a combined multichannel seismic reflection (MCS) and wideangle onshore/offshore experiment conducted in 1996 across the southeast Greenland continental margin. A new tomographic method is developed to jointly invert refraction travel times for two‐dimensional velocity structure. employ hybrid ray‐tracing scheme based on graph local ray‐bending refinement efficiently obtain an accurate forward solution, we smoothing optional damping constraints regularize iterative...

Bedrock weathering runs to the hills Fractures in bedrock drive breakdown of rock into soil. Soil makes observations processes challenging. St. Clair et al. combined a three-dimensional stress model with geophysical measurements show that erosion rates mirror changes topography (see Perspective by Anderson). Seismic reflection and electromagnetic profiles allowed mapping fracture density. The surface elevation thus provide way study critical zone between Science , this issue p. 534 ; see also 506

Abstract Details of Earth's shallow subsurface—a key component the critical zone (CZ)—are largely obscured because making direct observations with sufficient density to capture natural characteristic spatial variability in physical properties is difficult. Yet this inaccessible region CZ fundamental processes that support ecosystems, society, and environment. Geophysical methods provide a means for remotely examining form function over length scales span centimeters kilometers. Here we...

ABSTRACT The conversion of bedrock to regolith marks the inception critical zone processes, but factors that regulate it remain poorly understood. Although thickness and degree weathering are widely thought be important regulators development its water‐storage potential, functional relationships between properties processes generate documented. This is due in part fact difficult characterize by direct observations over broad scales needed for process‐based understanding zone. Here we use...

We present results of a seismic reflection and refraction investigation the Aleutian island arc, designed to test hypothesis that volcanic arcs constitute building blocks continental crust. The arc has requisite thickness (30 km) build crust, but it differs strongly from crust in its composition reflectivity structure. Seismic velocities compositions erupted lavas suggest mafic bulk composition, contrast andesitic continents. silicic upper reflective lower are characteristic conspicuously...

We present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between Labrador Current and North Atlantic Current. The show that distinct water masses can be mapped, their internal imaged, using low-frequency reflections sound speed contrasts at interfaces which temperature changes. warm/cold is characterized by east-dipping generated intrusions in uppermost 1000 meters ocean. Our results imply techniques...

Recent seismic results on the U.S. East Coast continental margin show that zone between rifted and normal oceanic crust consists of thick (up to 25 km), high velocity (ν p 7.2–7.3 km s −1 ) crust, interpreted as mafic igneous rocks emplaced during Triassic/Jurassic rifting. The total volume in this zone, which we call Margin Igneous Province (ECMIP), may be much 2.7 × 10 6 3 , placing ECMIP among world's large provinces. We constrain composition origin thick, by using a compilation...

The Cocos plate experiences extensional faulting as it bends into the Middle American Trench (MAT) west of Nicaragua, which may lead to hydration subducting mantle.To estimate along strike variations volatile input from subduction zone, we gathered marine seismic refraction data with R/V Marcus Langseth a 396 km long trench parallel transect offshore Nicaragua and Costa Rica.Our inversion crustal mantle phases shows two notable features in deep structure plate: (1) Normal oceanic crust 6...

Enhanced understanding of subsurface water storage will improve prediction future impacts climate change, including drought, forest mortality, wildland fire, and strained security. Previous research has examined the importance plant‐accessible in soil, but upland landscapes within Mediterranean climates, soil often accounts for only a fraction storage. We draw insights from previous case study Southern Sierra Critical Zone Observatory to define attributes storage; review observed patterns...

Abstract As bedrock weathers to regolith – defined here as weathered rock, saprolite, and soil porosity grows, guides fluid flow, liberates nutrients from minerals. Though vital terrestrial life, the processes that transform into are poorly understood, especially in deep regolith, where direct observations difficult. A 65-m-deep borehole Calhoun Critical Zone Observatory, South Carolina, provides unusual access a complete weathering profile an Appalachian granitoid. Co-located geophysical...

Abstract Observing the critical zone (CZ) below top few meters of readily excavated soil is challenging yet crucial to understanding Earth surface processes. Near‐surface geophysical methods can overcome this challenge by imaging CZ in three dimensions (3‐D) over hundreds meters, thus revealing lateral heterogeneity subsurface properties across scales relevant hillslope erosion, weathering, and biogeochemical cycling. We imaged under a soil‐mantled ridge developed granitic terrain Laramie...

We conducted a seismic refraction experiment across Flemish Cap and into the deep basin east of Newfoundland, Canada, developed velocity model for crust mantle from forward inverse modeling data 25 ocean bottom seismometers dense air gun shots. The continental at is 30 km thick divided three layers with P wave velocities 6.0–6.7 km/s. Across southeast margin, thins over 90‐km‐wide zone to only 1.2 km. ocean‐continent boundary near base marked by fault between thinned 3‐km‐thick 4.7–7.0 km/s...

Seismic reflection and refraction data from the SE Greenland margin provide a detailed view of volcanic rifted Archean continental crust to near‐to‐average oceanic over spatial scale 400 km. The SIGMA III transect, located ∼600 km south Greenland‐Iceland Ridge presumed track Iceland hot spot, shows that continent‐ocean transition is abrupt only small amount crustal thinning occurred prior final breakup. Initially, 18.3 thick accreted productivity decreased through time until steady state...

We present a new quantitative framework to understand the process of mantle melting based on velocity structure igneous crust. Our approach focuses lower crustal section, which is expected be least affected by porosity and seawater alteration, especially for thick methodology thus best constraining origin large provinces. First, relation between bulk parameters established basis data from experiments. Second, we show how can used place bounds range velocity, despite ambiguity in emplacement...

Research Article| April 01, 2002 Migration of methane gas through the hydrate stability zone in a low-flux province Andrew R. Gorman; Gorman 1Department Geology and Geophysics, University Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar W. Steven Holbrook; Holbrook Matthew J. Hornbach; Hornbach Kara L. Hackwith; Hackwith Dan Lizarralde; Lizarralde 2School Earth Atmospheric Sciences, Georgia Institute Technology, Atlanta, 30332, Ingo Pecher...

We present the results of a combined multichannel seismic reflection (MCS) and wide‐angle, ocean bottom profile collected in 1988 across Carolina Trough on U.S. Atlantic continental margin. Inversion vertical‐incidence wide‐angle travel time data has produced velocity model entire crust continent‐ocean transition. The margin consists three structural elements: (1) rifted crust, comprising 1–4 km post‐rift sedimentary rocks overlying 30–34 thick subsedimentary (2) transitional 70‐ to...

Research Article| January 01, 2004 Continental breakup and the onset of ultraslow seafloor spreading off Flemish Cap on Newfoundland rifted margin John R. Hopper; Hopper 1Danish Lithosphere Center, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark Search for other works by this author on: GSW Google Scholar Thomas Funck; Funck Brian E. Tucholke; Tucholke 2Department Geology Geophysics, Woods Hole Oceanographic Institution, Hole, Massachusetts 02543, USA Hans Christian Larsen; Larsen 3Danish...

Internal waves affect many important dynamical processes in the ocean, but situ observations of internal are infrequent and spatially sparse. Here we show that remote sensing by marine seismic reflection methods can provide quantitative information on wave energy its spatial variability at high lateral resolution full ocean depth over large volumes ocean. Seismic images Norwegian Sea water column reflections capture snapshots finestructure displacements due to waves. Horizontal number...