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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 1,153 records · Page 64Linked to original sources
USGS2007

Temporal variability of submarine groundwater discharge: Assessments via radon and seep meters, the southern carmel coast, Israel

Seep meter data from Dor Bay, Israel, showed a steady decrease in submarine groundwater discharge (SGD) rates between March and July 2006 (averages of 34, 10.4 and 1.5 cm d-1 in March, May and July, respectively), while estimates based on radon time series showed remarkably uniform averages (8 cm d-1). The May seep meter data show a rough positive correlation with sea level, unlike the negative correlation shown by the Rn-calculated rates. Smaller-size meters, deployed in July adjacent to the regular-size ones, showed significantly higher rates (10 cm d-1), which negatively correlated with salinity. It is suggested that the decreased rates documented by the seep meters are the result of an increased shallow seawater recharge in the bay (due to decreasing hydraulic gradients). This is not captured by the radon, since recharging water is radon-poor. The positive correlation of discharge with sea level is due to increased seawater recycling in times of high sea stand. Copyright ?? 2007 IAHS Press.

Conference Paper↗
USGS2009

NOAA/West coast and Alaska Tsunami warning center Atlantic Ocean response criteria

West Coast/Alaska Tsunami Warning Center (WCATWC) response criteria for earthquakesoccurring in the Atlantic and Caribbean basins are presented. Initial warning center decisions are based on an earthquake's location, magnitude, depth, distance from coastal locations, and precomputed threat estimates based on tsunami models computed from similar events. The new criteria will help limit the geographical extent of warnings and advisories to threatened regions, and complement the new operational tsunami product suite. Criteria are set for tsunamis generated by earthquakes, which are by far the main cause of tsunami generation (either directly through sea floor displacement or indirectly by triggering of sub-sea landslides).The new criteria require development of a threat data base which sets warning or advisory zones based on location, magnitude, and pre-computed tsunami models. The models determine coastal tsunami amplitudes based on likely tsunami source parameters for a given event. Based on the computed amplitude, warning and advisory zones are pre-set.

Science of Tsunami Hazards↗
USGS2011

Zircon U-Pb age of the Pescadero felsite: A late Cretaceous igneous event in the forearc, west-central California Coast Ranges

Downstream grain-size fining in stratigraphy is driven primarily by selective deposition of sediment, and the long-term efficiency of this process is determined by: (1) the magnitude and characteristics of the input sediment supply; (2) the spatial distribution of subsidence rate, which creates accommodation for sediment preservation; and (3) the dynamics of sediment transport and deposition. A key challenge is to determine how these first two factors control the caliber and spatial distribution of deposits over time scales of 10 4 –10 6 yr without incorporating sediment transport details that are largely unknowable for time-averaged stratigraphy in the geological past. We address this using grain-size data collected from fluvial conglomerates in the Eocene Pobla Basin, Spanish Pyrenees, a synorogenic basin where the timing of sediment deposition is well-constrained; the sediment budget is closed; and good exposure enables time lines within stratigraphy to be picked out unambiguously. For successive stratigraphic horizons, downstream trends in grain size and composition are derived for basin-filling sediment-routing systems with length scales of 6 and 40 km, respectively. Our data show that the rate of grain-size fining varies over time and with system length and can be linked to changes in source area. These results are contrasted with grain-size data from the Antist Group, a 60-km-long Oligocene system that mantles the Southern Pyrenees, where very slow rates of grain-size fining on the wedge top of this fold-and-thrust belt are observed. We apply a self-similarity–based selective deposition model to quantify the competing controls of tectonic subsidence and sediment supply on derived grain-size trends, and model results are compared with independent constraints on the Eocene–Oligocene evolution of the Pyrenees. Our results suggest that it is now possible to invert time-averaged grain-size trends in stratigraphy to gain quantitative information on the geological boundary conditions governing the evolution of sedimentary basins.

Geological Society of America Bulletin↗
USGS2013

Appendix D: Use of wave scenarios to assess potential submerged oil mat (SOM) formation along the coast of Florida and Alabama

During the Deepwater Horizon oil spill, oil in the surf zone mixed with sediment in the surf zone to form heavier-than-water sediment oil agglomerates of various size, ranging from small (cm-scale) pieces (surface residual balls, SRBs) to large mats (100-m scale, surface residue mats, SR mats). Once SR mats formed in the nearshore or in the intertidal zone, they may have become buried by sand moving onshore or alongshore. To assist in locating possible sites of buried oil, wave scenarios previously developed by the U.S. Geological Survey (USGS) were used to determine the depths at which surface oil had the potential to mix with suspended sediment. For sediment to mix with floating oil and form an agglomerate of sufficient density to sink to the seafloor, either the water must be very shallow (e.g., within the swash zone) or sediment must be suspended to the water surface in sufficient concentrations to create a denser-than-sea water agglomerate. The focus of this study is to analyze suspended sediment mixing with surface oil in depths beyond the swash zone, in order to define the seaward limit of mat formation. A theoretical investigation of sediment dynamics in the nearshore zone revealed that non-breaking waves do not suspend enough sediment to the surface to form sinking sand/oil agglomerates. For this study, it was assumed that the cross-shore distribution of potential agglomerate formation is associated with the primary breaker line, and the presence of plunging breakers, over the time frame of oiling. The potential locations of submerged oil mats (SOMs) are sites where (1) possible agglomerate formation occurred, where (2) sediment accreted post-oiling and buried the SOM, and where (3) the bathymetry has not subsequently eroded to re-expose any mat that may have formed at that site. To facilitate identification of these locations, the range of water level variation over the time frame of oiling was also prescribed, which combined with the wave-breaking depth analysis and pre-oiling bathymetry would identify the potential geographic locations of SOMs.

Operational Science Advisory Team Report↗