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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 289 records · Page 16Linked to original sources

USGS1998

Defining the southwestern end of the Blytheville Arch, northeastern Arkansas: Delimiting a seismic source zone in the New Madrid region

Vibroseis seismic-reflection profiles around the southwestern end of the Blytheville arch document the southwesternly extent of the arch and refine the length of a fault zone that coincides with the arch. The 74.3 km of newly interpreted profiles and previously described profiles form a network of lines across and around the southern end of the arch. The southwestern terminus of the arch is defined by the absence of significantly upwarped or extensively disrupted reflectors, which are diagnostic traits of the arch where it is well developed. The arch is 134 km long as documented here, which is only slightly longer than the length reported by previous studies. Differing opinions about the magnitude of the 1811-1812 New Madrid earthquakes could be partly explained by substantially longer seismic source zones, but this minor increase in source zone length does not reconcile the large differences in magnitude estimates of the events. If future earthquake ruptures associated with the arch are confined to areas of extensive deformation, then this well documented southwestern termination precludes a rupture substantially longer than ~134 km along the zone of seismicity that coincides with the axis of the Reelfoot rift.

Arkansas↗

USGS2004

Geotechnical characterization of TriNet sites: A status report

The TriNet project, launched in 1997, created an improved, real-time seismic monitoring network in Southern California. Planning of the network began in 1995 ( e.g. , Heaton et al. , 1996 ), building on the success of the earlier TERRAscope network, which included 24 digital broadband and strong-motion instruments throughout Southern California ( e.g. , Kanamori et al. , 1993 ). At the end of the five-year TriNet project the network comprised 150 real-time digital broadband stations and another 400 strong-motion sensors, 50 of which were also real-time. This network is now recording digital broadband data for Southern California earthquakes at an unprecedented rate, data that are already proving valuable for investigations of earthquake sources and regional wave propagation, as well as earthquake response. In this report we describe an ongoing effort aimed at a full geotechnical characterization of the newly installed TriNet sets. Shallow geologic structure is known to play a substantial role in controlling the ground motions recorded at any site. Documentation of amplified ground motion at soft-sediment sites can be found among even early macroseismic observations of strong ground motions ( e.g. , Drake, 1815 ). Seismic waves are also now known to be strongly affected by deep basin structure as well ( e.g. , Frankel et al. , 1991 ; Field, 2000 ; Joyner, 2000 ). It will be necessary to understand these effects to exploit fully the rich data set being recorded at TriNet sites. Clearly, the nature of site conditions and site response at the recording sites must be understood for studies focused on ground motions and hazard from future large earthquakes, but it is also necessary to understand these effects to conduct earthquake source studies of both large and small earthquakes. Our multifaceted site characterization project involves geological/geotechnical site investigations, database development, and investigation of empirical amplification factors determined from broadband and strong-motion data recorded to date. Our goal is to complete a first-order geologic site characterization by 2005 and then employ appropriate methods to obtain direct constraint on shallow shear-wave velocity structure at each site. In the latter effort we will endeavor to find the most accurate and cost-effective methods to quantify geotechnical parameters at sites that have ranges of geologic site conditions and cultural settings. Our long-term goal is to obtain direct estimates of the average shear-wave velocity in the upper 30 m, Vs30, at each site. If velocity information is available to greater depths, for example at sites characterized under the ROSRINE project ( http://geoinfo.usc.edu/rosrine/ ), this information will be included in the database as well. The original motivation for using Vs30 to characterize near-surface velocity was pragmatic, determined by such factors as the typical reach of a drill rig in a single day. The parameter has become the accepted standard with which many seismic recording sites are characterized, however. In a recent study using mainshock and aftershock recordings at sites in the Los Angeles region, Wald and Mori ( 2000 ) observed good correlation between Vs30 and amplification at 1-7 Hz, albeit with significant scatter. The purpose of this report is threefold. First, we describe our ongoing efforts and present site characterization results collected to date for 62 broadband and strong-motion stations in and around the greater Los Angeles metropolitan region. Second, we present preliminary results that illustrate how improved geologic site characterizations can improve the correlation between site conditions and site response. Finally, we invite feedback from the community to guide our future investigations, in particular with respect to our ongoing database development efforts.

California↗

USGS2008

Quantifying and Qualifying USGS ShakeMap Uncertainty

We describe algorithms for quantifying and qualifying uncertainties associated with USGS ShakeMap ground motions. The uncertainty values computed consist of latitude/longitude grid-based multiplicative factors that scale the standard deviation associated with the ground motion prediction equation (GMPE) used within the ShakeMap algorithm for estimating ground motions. The resulting grid-based 'uncertainty map' is essential for evaluation of losses derived using ShakeMaps as the hazard input. For ShakeMap, ground motion uncertainty at any point is dominated by two main factors: (i) the influence of any proximal ground motion observations, and (ii) the uncertainty of estimating ground motions from the GMPE, most notably, elevated uncertainty due to initial, unconstrained source rupture geometry. The uncertainty is highest for larger magnitude earthquakes when source finiteness is not yet constrained and, hence, the distance to rupture is also uncertain. In addition to a spatially-dependant, quantitative assessment, many users may prefer a simple, qualitative grading for the entire ShakeMap. We developed a grading scale that allows one to quickly gauge the appropriate level of confidence when using rapidly produced ShakeMaps as part of the post-earthquake decision-making process or for qualitative assessments of archived or historical earthquake ShakeMaps. We describe an uncertainty letter grading ('A' through 'F', for high to poor quality, respectively) based on the uncertainty map. A middle-range ('C') grade corresponds to a ShakeMap for a moderate-magnitude earthquake suitably represented with a point-source location. Lower grades 'D' and 'F' are assigned for larger events (M>6) where finite-source dimensions are not yet constrained. The addition of ground motion observations (or observed macroseismic intensities) reduces uncertainties over data-constrained portions of the map. Higher grades ('A' and 'B') correspond to ShakeMaps with constrained fault dimensions and numerous stations, depending on the density of station/data coverage. Due to these dependencies, the letter grade can change with subsequent ShakeMap revisions if more data are added or when finite-faulting dimensions are added. We emphasize that the greatest uncertainties are associated with unconstrained source dimensions for large earthquakes where the distance term in the GMPE is most uncertain; this uncertainty thus scales with magnitude (and consequently rupture dimension). Since this distance uncertainty produces potentially large uncertainties in ShakeMap ground-motion estimates, this factor dominates over compensating constraints for all but the most dense station distributions.

Open-File Report↗

USGS2010

Carbonate control of H 2 and CH 4 production in serpentinization systems at elevated P-Ts

Serpentinization of forsteritic olivine results in the inorganic synthesis of molecular hydrogen (H 2 ) in ultramafic hydrothermal systems (e.g., mid-ocean ridge and forearc environments). Inorganic carbon in those hydrothermal systems may react with H 2 to produce methane (CH 4 ) and other hydrocarbons or react with dissolved metal ions to form carbonate minerals. Here, we report serpentinization experiments at 200°C and 300 bar demonstrating Fe 2+ being incorporated into carbonates more rapidly than Fe 2+ oxidation (and concomitant H 2 formation) leading to diminished yields of H 2 and H 2 -dependent CH 4 . In addition, carbonate formation is temporally fast in carbonate oversaturated fluids. Our results demonstrate that carbonate chemistry ultimately modulates the abiotic synthesis of both H 2 and CH 4 in hydrothermal ultramafic systems and that ultramafic systems present great potential for CO 2 -mineral sequestration.

Geophysical Research Letters↗

USGS1967

Infection of the walleye, Stizostedion v. vitreum, of western Lake Erie with Bothriocephalus cuspidatus (Cooper)

In recent years appreciable changes have taken place in the biota and physiochemical conditions in Lake Erie. The accelerated eutrophication of the lake has been accompanied by the near disappearance of several fish species, e.g., blue pike (Stizostedion vitreum glaucum), lake herring (Coregonus artedi), lake trout (Salvelinus namaycush), sauger (Stizostedion canadense), and whitefish (Coregonus clupeaformis). Interest in the biology of the remaining species has increased as means have been sought to preserve their numbers in the lake. This report, which describes the caecal and intestinal parasites of the walleye, Stizostedion vitreum vitreum, is a contribution to the natural history of this fish in western Lake Erie. This study concerns: the type and degree of intestinal parasitic infestations in a single year class of walleyes during their first 3 years of life; seasonal changes in the incidence and maturity of the dominant parasite Bothriocephalus cuspidatus; and the effects of the infestations on the physical condition of the host.

Papers of the Michigan Academy of Science, Arts, a↗

USGS1986

Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain

Magnesioferrite grading toward magnetite has been identified as a very small but meaningful constituent of the basal iron-rich portion of the Cretaceous-Tertiary (K-T) boundary clay at the Barranco del Gredero section, Caravaca, Spain. This spinel-type phase and others of the spinel group, found in K-T boundary clays at many widely separated sites, have been proposed as representing unaltered remnants of ejecta deposited from an earth-girdling dust cloud formed from the impact of an asteroid or other large bolide at the end of the Cretaceous period. The magnesioferrite occurs as euhedral, frequently skeletal, micron-sized octahedral crystals. The magnesioferrite contains29 ± 11 ppb Ir, which accounts for only part of the Ir anomaly at this K-T boundary layer(52 ± 1 ppb Ir). Major element analyses of the magnesioferrite show variable compositions. Some minor solid solution exists toward hercynite-spinel and chromite-magnesiochromite. A trevorite-nichromite (NiFe 2 O 4 -NiCr 2 O 4 ) component is also present. The analyses are very similar to those reported for sites at Furlo and Petriccio, Umbria, Italy. On the basis of the morphology and general composition of the magnesioferrite grains, rapid crystallization at high temperature is indicated, most likely directly from a vapor phase and in an environment of moderate oxygen fugacity. Elemental similarity with metallic alloy injected into rocks beneath two known impact craters suggests that part of the magnesioferrite may be derived from the vaporized chondritic bolide itself, or from the mantle; there is no supporting evidence for its derivation from crustal target rocks.

Earth and Planetary Science Letters↗

USGS1993

Impact-shocked zircons: Discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

Textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously. However, planar deformation features (PDF) due to shock metamorphism are well documented in quartz and other mineral grains from these same environments. An etching technique was developed that allows SEM visualization of PDF and other probable shock-induced textural features, such as granular (polycrystalline) texture, in zircons from a variety of impact shock environments. These textural features in shocked zircons from K/T boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the UPb isotopic system.

Earth and Planetary Science Letters↗

USGS2016

Quaternary geologic map of the Wolf Point 1° × 2° quadrangle, Montana and North Dakota

The Wolf Point quadrangle encompasses approximately 16,084 km 2 (6,210 mi 2 ). The northern boundary is the Montana/Saskatchewan (U.S.-Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes the Peerless Plateau and Flaxville Plain. The primary river is the Missouri River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (for example, ground-moraine deposits, end-moraine deposits, and stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 23 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or agronomy. Rather, it is a generalized map of soils recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. The surficial deposits are glacial, ice-contact, glaciofluvial, alluvial, lacustrine, eolian, colluvial, and mass-movement deposits. Till of late Wisconsin age is represented by three map units. Till of Illinoian age also is mapped. Till deposited during pre-Illinoian glaciations is not mapped, but is widespread in the subsurface. Linear ice-molded landforms (primarily drumlins), shown by symbol, indicate directions of ice flow during late Wisconsin and Illinoian glaciations. The Quaternary geologic map of the Wolf Point quadrangle, northeastern Montana and North Dakota, was prepared to provide a database for compilation of a Quaternary geologic map of the Regina 4° × 6° quadrangle, United States and Canada, at scale 1:1,000,000, for the U.S. Geological Survey Quaternary Geologic Atlas of the United States map series. This map was compiled from data from many sources, at several different map scales. That information was generalized and simplified, and then transferred to a base map at 1:250,000 scale to serve as the base for final reduction to 1:1,000,000, the nominal reading scale of maps in the Quaternary Geologic Atlas of the United States map series. This map is the generalized and simplified 1:250,000 scale compilation. Letter symbols for the map units are those used for the same units in the Quaternary Geologic Atlas of the United States map series. The map summarizes new, and selected published and unpublished, geologic information for public use and for use by Federal, State, and local governmental agencies for land use planning, including assessment of natural resources, natural hazards, recreation potential, and land use management. It also is a base from which a variety of maps relating to earth surface processes and Quaternary geologic history can be derived.

Montana, North Dakota↗

USGS2013

Plasticity of parental care under the risk of predation: how much should parents reduce care?

Predation can be an important agent of natural selection shaping parental care behaviours, and can also favour behavioural plasticity. Parent birds often decrease the rate that they visit the nest to provision offspring when perceived risk is high. Yet, the plasticity of such responses may differ among species as a function of either their relative risk of predation, or the mean rate of provisioning. Here, we report parental provisioning responses to experimental increases in the perceived risk of predation. We tested responses of 10 species of bird in north temperate Arizona and subtropical Argentina that differed in their ambient risk of predation. All species decreased provisioning rates in response to the nest predator but not to a control. However, provisioning rates decreased more in species that had greater ambient risk of predation on natural nests. These results support theoretical predictions that the extent of plasticity of a trait that is sensitive to nest predation risk should vary among species in accordance with predation risk.

Biology Letters↗

USGS2003

Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada

Northern Nevada is one of the world's foremost regions of gold production. The Humboldt River Basin (HRB) covers 43,500 km2 in northern Nevada (Crompton, 1995), and it is home to approximately 18 active gold and silver mines (Driesner and Coyner, 2001) among at least 55 significant metallic mineral deposits (Long and others, 1998). Many of the gold mines are along the Carlin trend in the east-central portion of the HRB, and together they have produced 50 million ounces of gold from 1962 (when the Carlin mine first opened) through April 2002 (Nevada Mining Association, 2002). Mining is not new to the region, however. Beginning in 1849, mining has taken place in numerous districts that cover 39 percent of the land area in the HRB (Tingley, 1998). In addition to gold and silver, As, Ba, Cu, Fe, Hg, Li, Mn, Mo, Pb, S, Sb, V, W, Zn, and industrial commodities such as barite, limestone, fluorite, sand and gravel, gypsum, gemstones, pumice, zeolites, and building stone, have been extracted from the HRB (McFaul and others, 2000). All papers within this series of investigations can be found as lettered chapters of USGS Bulletin 2210, Geoenvironmental Investigations of the Humboldt River Basin, Northern Nevada. Each chapter is available separately online. The data and software utilized in this product (Chapter F) permit the user to view and analyze the geographic relationships among chemistry of stream sediments and surface waters, geology, and various cartographic base information such as but not limited to cities, county boundaries, and land ownership. Data for this product were compiled and or produced as part of a mineral and environmental assessment of the Humboldt River basin conducted by the U.S. Geological Survey between 1995 - 2000.

Bulletin↗

USGS2010

Global climate changes recorded in coastal wetland sediments: Empirical observations linked to theoretical predictions

Whether coastal areas are experiencing, and responding to, an accelerated rate of global sea-level rise (GSLR) is critically important for the ∼2 billion people living near Earth's oceans. Accretion rates from a suite of physiographically diverse coastal wetlands surrounding Long Island, NY accelerated during the 20th century at 2.3 ± 0.2 × 10 −2 mm yr −2 , which is comparable to reported rates of GSLR acceleration and global temperature changes. Wetlands varied in tidal range, salinity and geomorphic setting, and were located in embayments with limited human impacts in a region with limited and constant rates of subsidence. From geochronologies with temporal resolutions of 2–5 yr, we constructed new composite histories of sediment accretion and mineral deposition. Wetland dynamics are consistent with predictions from sedimentology and a numerical model of ecogeomorphic response, suggesting that these systems, and likely others worldwide, are responding to accelerated GSLR and related climatic changes.

New York↗

USGS2007

Assessing methane release from the colossal Storegga submarine landslide

Marine slope failure involving methane-gas-hydrate-bearing sediments is one mechanism for releasing enormous quantities of methane to the ocean and atmosphere. The Storegga Slide, on the Norwegian margin, is the largest known Holocene-aged continental margin slope failure complex and is believed to have occurred in sediments that may have initially contained gas hydrate. Here, we report pore water sulfate gradient measurements that are used as a proxy for the relative amounts of methane that exist in continental margin sediments associated with the colossal Storegga Slide. These measurements suggest that a considerable inventory of methane occurs in sediments adjacent to, and unaffected by, the Storegga Slide events, but indicate that methane is notably absent from sediments on the sole of the slide and distal deposits created by the slide events. Either methane was lost during previous Pleistocene failure events or was never present in significant concentrations within the sediments that failed.

Geophysical Research Letters↗

USGS2026

Digitizer Suite: The Albuquerque Seismological Laboratory Digitizer Testing Suite

Laboratory testing of digitizers and seismometers helps ensure that prior to deployment the instrumentation can produce high quality data and is operating within specifications. In this work we detail the software package called: the Albuquerque Seismological Laboratory (ASL) Digitizer Test Suite. This Java software package provides several algorithms to verify various performance parameters of digitizers commonly used for recording analog seismic instruments. The goal of these tests is not to be exhaustive, but to identify common failures that could compromise the integrity of seismic data being recorded on the digitizer. For example, Sandia National Laboratories (e.g., Slad and Merchant, 2018) routinely do comprehensive testing of digitizers for various monitoring missions. While these tests reports are valuable for comprehensively characterizing a recording system, it would be resource intensive to conduct such tests on every seismic recorder used in a network. We focus on tests that include ways to estimate the sensitivity, timing, self-noise, and clip-level of the digitizer, as well as the fidelity of the signal being recorded. The software is publicly available and provides a way for the community to verify the integrity of a digitizer using a minimum amount of outside equipment.

Seismological Research Letters↗

USGS2026

Vessel surveys for marine birds in the Gulf of America (Gulf of Mexico): Protocol manual (2017–2025)

This manual provides contextual background and detailed instructions for survey procedures that were used to collect, enter, archive, and analyze digitally-entered field data collected for marine birds during three large-vessel survey projects in the northern Gulf of America (also Gulf of Mexico, hereafter “Gulf”). Projects using this protocol included the Gulf of Mexico Marine Assessment Program for Protected Species (GoMMAPPS: 2017-2018), the Vessel Surveys for Abundance and Distribution of Marine Mammals and Seabirds (VSAD: 2023-2024), and certain repositioning legs of the Atlantic Marine Assessment Program for Protected Species (AMAPPS: 2021, 2023). Based substantially on Ballance and Force (2011), the protocol used in the Gulf is based on a standardized 300 m wide strip transect using software architecture available in program SeeBird (v.4.3.7), a data collection program developed by Robert Holland at the National Oceanic and Atmospheric Administration (NOAA) Southwest Fisheries Science Center, La Jolla, CA. Survey protocols relied on the digital entering of standardized metadata linked to sightings of seabirds (e.g., species, number, location, distance bin, association[s], behavior, flight direction, flight height, angle from ship, age, sex, plumage, and optional comments) as well as other protected species. SeeBird has additional modules that may be used to input data on mixed-species seabird flocks and flying fish (only the latter was used in the Gulf). SeeBird includes “user-driven” commands issued through the keyboard, touch screen, and/or mouse, many of which are aided by drop-down menus that prompt the user options that are available for input. In addition, the program features “event–driven” inputs updated at intervals selected by the user, and that also record exact time and location of such edits. We describe how SeeBird was adapted in the Gulf both to run directly via serial connections from the ship’s navigation system and to operate independently from the ship through a satellite-derived GPS feed. This user manual also gives information about: procedures used to document flying fish abundance on Gulf surveys; how to use the Beaufort scale for standardizing wind force and sea state environmental conditions; how to make and use a hand-held rangefinder for delimiting strip transect bin distances; additional functionalities in SeeBird for which user guides are not available; file-naming, file-archiving, and file location conventions used on Gulf marine bird surveys; protocols used in the Gulf for describing relative abundance of the macro-alga Sargassum as an environmental covariate; the standardized four-letter taxa codes (summarized in a SpeciesCode.txt file) used in the Gulf for denoting species, other taxonomic, and event categories as inputs to SeeBird; an Excel example spreadsheet that has successfully imported SeeBird’s ASCII text file; procedural steps to import, edit, and archive into Excel ASCII text files from SeeBird; initialization instructions for starting up program SeeBird on a Panasonic ToughBook™ that relies on integrated, satellite-derived GPS, and for writing “S” (seabirds + other taxa) and “E” (flying fish) ASCII files to a folder or subfolder other than the default root location on the laptop that contains program SeeBird; how to trouble-shoot miscellaneous start-up problems with program SeeBird; how to add new four-letter codes (into a SpeciesCode.txt file) when additional taxa or objects of interest are encountered. The primary objective of this manual is to archive a permanent, replicable history of survey methodology to facilitate continuity with comparable future projects that may be conducted in the Gulf. A secondary objective is to describe why and how program SeeBird was applied and adapted specifically for operating in Gulf survey conditions. As of late 2025, user guides for software program SeeBird were no longer readily accessible, so this manual serves also to address that gap.

Northern Gulf of America↗

USGS1948

Ground water in the Blanchard area, McClain County, Oklahoma

A letter from Lloyd L. Bowser, City Clerk, dated January 8, 1948, in behalf of the town council and Mayor Walter Casey, indicates that a serious shortage of water is faced by the town of Blanchard, McClain County, Oklahoma. The town is near the eastern boundary of Grady County, where an investigation of the ground-water resources is being made by the Oklahoma Geological Survey in cooperation with the U.S. Geological Survey as part of a State-wide investigation. Information obtained thus far may aid the town by showing where additional ground water for municipal supply may be sought.

Oklahoma↗

USGS2010

A new methodology for the quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding (MBES)

In order to investigate the interactions between turbulence and suspended sediment transport in natural aqueous environments, we ideally require a technique that allows simultaneous measurement of fluid velocity and sediment concentration for the whole flow field. Here, we report on development of a methodology using the water column acoustic backscatter signal from a multibeam echo sounder to simultaneously quantify flow velocities and sediment concentrations. The application of this new technique is illustrated with reference to flow over the leeside of an alluvial sand dune, which allows, for the first time in a field study, quantitative visualization of large-scale, whole flow field, turbulent coherent flow structures associated with the dune leeside that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows.

Geophysical Research Letters↗

USGS2023

Establishing an in vitro model to assess the toxicity of 6PPD-quinone and other tire wear transformation products

The tire wear transformation product 6PPD-quinone (6PPDQ) has been implicated as the causative factor for broad scale mortality events for coho salmon in the Pacific Northwest. Highly variable sensitivity to 6PPDQ in closely related salmonids complicates efforts to evaluate the broader toxicological impacts to aquatic ecosystems. Our goals were to (1) validate the large range of in vivo species sensitivities reported for coho, Chinook, and sockeye salmon and (2) develop an in vitro platform for assessing 6PPDQ toxicity. In vivo studies confirmed the acute sensitivity of juvenile coho (12 h LC 50 = 80.4 ng/L) and demonstrated that sockeye salmon were not vulnerable to mortality. Chinook salmon were sensitive to 6PPDQ mortality at initial concentrations >25 μg/L, ∼10-fold greater than reported environmental measurements. In vitro , the coho salmon cell line CSE-119 was acutely sensitive to 6PPDQ (metabolic EC 50 = 7.9 μg/L, cytotoxicity EC 50 = 6.1 μg/L). Analogous Chinook (CHSE-214) and sockeye salmon (SSE-5) cell lines were nonresponsive in both assays, and rainbow trout RTG-2 cells began showing metabolic effects at 68 μg/L (EC 5 ). Recreation of species-specific 6PPDQ sensitivity in vitro implicates conserved modes of action in CSE-119 that could be utilized for mechanistic studies of 6PPDQ toxicity and screening of other PPD transformation products.

Environmental Science and Technology Letters↗

USGS2018

Karachi tides during the 1945 Makran tsunami

This paper extends and detides a Karachi tide-gauge record as an observational basis for assessing Indian Ocean tsunami risk. The extended marigram encompasses the time of the great 1945 Makran earthquake of early November 28, local time, and of the ensuing tsunami, which continued into November 29. The marigram was published previously as a 9-h excerpt that begins 1 h after the earthquake. The full marigram presented here covers most of 17 days from November 15 to December 1. Gaps include a tsunami-induced outage that may help explain why the highest water level gauged is 1 m below the maximum water level reported nearby. The detiding method computes a reference tidal curve that disregards all observations from November 28 and 29. For those 2 days, the reference tide is guided by Admiralty tide tables and, secondarily, by high waters and low waters gauged before and after. As in previous estimates, the detided tsunami crests about 0.5 m above ambient tide, but now with the possibility that the gauge failed to record a higher wave. Anomalies described for the first time include an early one that likely resulted from a recognized problem with the Karachi tide station, but which might instead represent an earthquake precursor.

Karachi↗