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At least 361 records · Page 20Linked to original sources
USGS2016

Climate change implications for tropical islands: Interpolating and interpreting statistically downscaled GCM projections for management and planning

The potential ecological and economic effects of climate change for tropical islands were studied using output from 12 statistically downscaled general circulation models (GCMs) taking Puerto Rico as a test case. Two model selection/model averaging strategies were used: the average of all available GCMs and the average of the models that are able to reproduce the observed large-scale dynamics that control precipitation over the Caribbean. Five island-wide and multidecadal averages of daily precipitation and temperature were estimated by way of a climatology-informed interpolation of the site-specific downscaled climate model output. Annual cooling degree-days (CDD) were calculated as a proxy index for air-conditioning energy demand, and two measures of annual no-rainfall days were used as drought indices. Holdridge life zone classification was used to map the possible ecological effects of climate change. Precipitation is predicted to decline in both model ensembles, but the decrease was more severe in the “regionally consistent” models. The precipitation declines cause gradual and linear increases in drought intensity and extremes. The warming from the 1960–90 period to the 2071–99 period was 4.6°–9°C depending on the global emission scenarios and location. This warming may cause increases in CDD, and consequently increasing energy demands. Life zones may shift from wetter to drier zones with the possibility of losing most, if not all, of the subtropical rain forests and extinction risks to rain forest specialists or obligates.

Puerto Rico↗
USGS2024

Testing tree-ring cellulose δ18O with water isotopes for Holocene lake δ18O interpretations in the central Rocky Mountains USA

Stable isotopes of water preserved in geologic archives, primarily as oxygen (δ18O), have proven critical for documenting Earth’s climatic and hydrologic systems past and present. However, timescale differences of water isotope inputs to proxy systems and the signal embedded in long paleorecords often confound translation to observed hydroclimatic metrics. Here, a unique 20-year dataset of meteorology, hydrology, and the isotopic composition of weekly meteoric and surface water samples (δ18O, δ2 H) are combined with paleoclimate δ18O data from tree-ring cellulose and lake carbonate to better understand proxy signals of Upper Colorado river basin drought. Annual tree-ring cellulose δ18O from Picea engelmannii growing within a glacier-fed creek and a spring discharge area were used to derive annual source water δ18O using a cellulose source-water isotope model. Comparisons with the monitoring record indicates that tree-ring cellulose δ18O tracks variations in wet and dry hydroclimatic extremes. Source water isotopes are shown to reflect the hydroclimate of the current year and some number of previous years as an effective moisture-discharge proxy rather than a precipitation isotope proxy. Results contextualize Holocene lake carbonate δ18O data. The contemporary-to-paleo comparison identifies changes in seasonal precipitation extremes during recent millennia and several earlier arid and monsoon-dominated Holocene periods that exceed the arid maximum of the calibration period.

Colorado↗
USGS1989

Marine magnetic gradiometer: A tool for the seismic interpreter

The marine magnetometer has been used since the early '50s as an ancillary tool on vessels conducting regional and local seismic surveys. Emphasis on marine magnetic data by academia has led to major discoveries about the structure of the earth's crust, such as the association of shallow, crustal magnetic anomalies to seafloor spreading and long-wavelength anomalies to deep crustal origin. The same enthusiasm has not occurred in industry primarily because greater emphasis has been placed on multichannel seismic reflection data.

Geophysics↗
USGS1985

A nomogram for interpreting slope stability of fine-grained deposits in modern and ancient-marine environments.

Design of the nomogram is based on effective stress and combines consolidation theory as applicable to depositional environments with the infinite-slope model of slope-stability analysis. The link between the two combined theories is a term representing the effective overburden stress, which may be predicted from consolidation theory and a knowledge of sedimentation rate, time, and the coefficient of consolidation. In turn, if infinite-slope conditions are assumed to exist, the effective overburden stress can be used to derive a factor of safety against static slope failure by using the angle of internal friction and the slope angle. The nomogram applies to depostitional settings in which fine-grained sediment has accumulated at a relatively constant rate upon a base that is essentially impermeable. The model further assumes that the lateral extent of sediment affected by any mass movement will be great compared to its thickness and that no outside agents (e.g., cements, gas) are influencing the section. The nomogram is applicable to static conditions (inherent stability of the slope) and certain dynamic conditions (such as earthquakes). It may be used to investigate mass movements in the geologic past as well as those in modern environments.--Modified journal abstract.

Journal of Sedimentary Petrology↗
USGS2011

Cold-water coral distributions in the Drake Passage area from towed camera observations - Initial interpretations

Seamounts are unique deep-sea features that create habitats thought to have high levels of endemic fauna, productive fisheries and benthic communities vulnerable to anthropogenic impacts. Many seamounts are isolated features, occurring in the high seas, where access is limited and thus biological data scarce. There are numerous seamounts within the Drake Passage (Southern Ocean), yet high winds, frequent storms and strong currents make seafloor sampling particularly difficult. As a result, few attempts to collect biological data have been made, leading to a paucity of information on benthic habitats or fauna in this area, particularly those on primarily hard-bottom seamounts and ridges. During a research cruise in 2008 six locations were examined (two on the Antarctic margin, one on the Shackleton Fracture Zone, and three on seamounts within the Drake Passage), using a towed camera with onboard instruments to measure conductivity, temperature, depth and turbidity. Dominant fauna and bottom type were categorized from 200 randomized photos from each location. Cold-water corals were present in high numbers in habitats both on the Antarctic margin and on the current swept seamounts of the Drake Passage, though the diversity of orders varied. Though the Scleractinia (hard corals) were abundant on the sedimented margin, they were poorly represented in the primarily hard-bottom areas of the central Drake Passage. The two seamount sites and the Shackleton Fracture Zone showed high numbers of stylasterid (lace) and alcyonacean (soft) corals, as well as large numbers of sponges. Though data are preliminary, the geological and environmental variability (particularly in temperature) between sample sites may be influencing cold-water coral biogeography in this region. Each area observed also showed little similarity in faunal diversity with other sites examined for this study within all phyla counted. This manuscript highlights how little is understood of these isolated features, particularly in Polar regions.

PLoS ONE↗
USGS2014

Persistence of DNA in carcasses, slime and avian feces may affect interpretation of environmental DNA data

The prevention of non-indigenous aquatic invasive species spreading into new areas is a goal of many resource managers. New techniques have been developed to survey for species that are difficult to capture with conventional gears that involve the detection of their DNA in water samples (eDNA). This technique is currently used to track the invasion of bigheaded carps (silver carp and bighead carp; Hypophthalmichthys molitrix and H. nobilis ) in the Chicago Area Waterway System and Upper Mississippi River. In both systems DNA has been detected from silver carp without the capture of a live fish, which has led to some uncertainty about the source of the DNA. The potential contribution to eDNA by vectors and fomites has not been explored. Because barges move from areas with a high abundance of bigheaded carps to areas monitored for the potential presence of silver carp, we used juvenile silver carp to simulate the barge transport of dead bigheaded carp carcasses, slime residue, and predator feces to determine the potential of these sources to supply DNA to uninhabited waters where it could be detected and misinterpreted as indicative of the presence of live bigheaded carp. Our results indicate that all three vectors are feasible sources of detectable eDNA for at least one month after their deposition. This suggests that current monitoring programs must consider alternative vectors of DNA in the environment and consider alternative strategies to minimize the detection of DNA not directly released from live bigheaded carps.

PLoS ONE↗
USGS2017

Interpreting surveys to estimate the size of the monarch butterfly population: Pitfalls and prospects

To assess the change in the size of the eastern North American monarch butterfly summer population, studies have used long-term data sets of counts of adult butterflies or eggs per milkweed stem. Despite the observed decline in the monarch population as measured at overwintering sites in Mexico, these studies found no decline in summer counts in the Midwest, the core of the summer breeding range, leading to a suggestion that the cause of the monarch population decline is not the loss of Midwest agricultural milkweeds but increased mortality during the fall migration. Using these counts to estimate population size, however, does not account for the shift of monarch activity from agricultural fields to non-agricultural sites over the past 20 years, as a result of the loss of agricultural milkweeds due to the near-ubiquitous use of glyphosate herbicides. We present the counter-hypotheses that the proportion of the monarch population present in non-agricultural habitats, where counts are made, has increased and that counts reflect both population size and the proportion of the population observed. We use data on the historical change in the proportion of milkweeds, and thus monarch activity, in agricultural fields and non-agricultural habitats to show why using counts can produce misleading conclusions about population size. We then separate out the shifting proportion effect from the counts to estimate the population size and show that these corrected summer monarch counts show a decline over time and are correlated with the size of the overwintering population. In addition, we present evidence against the hypothesis of increased mortality during migration. The milkweed limitation hypothesis for monarch decline remains supported and conservation efforts focusing on adding milkweeds to the landscape in the summer breeding region have a sound scientific basis.

PLoS ONE↗
USGS2003

Intraplate triggered earthquakes: Observations and interpretation

We present evidence that at least two of the three 1811-1812 New Madrid, central United States, mainshocks and the 1886 Charleston, South Carolina, earthquake triggered earthquakes at regional distances. In addition to previously published evidence for triggered earthquakes in the northern Kentucky/southern Ohio region in 1812, we present evidence suggesting that triggered events might have occurred in the Wabash Valley, to the south of the New Madrid Seismic Zone, and near Charleston, South Carolina. We also discuss evidence that earthquakes might have been triggered in northern Kentucky within seconds of the passage of surface waves from the 23 January 1812 New Madrid mainshock. After the 1886 Charleston earthquake, accounts suggest that triggered events occurred near Moodus, Connecticut, and in southern Indiana. Notwithstanding the uncertainty associated with analysis of historical accounts, there is evidence that at least three out of the four known Mw 7 earthquakes in the central and eastern United States seem to have triggered earthquakes at distances beyond the typically assumed aftershock zone of 1-2 mainshock fault lengths. We explore the possibility that remotely triggered earthquakes might be common in low-strain-rate regions. We suggest that in a low-strain-rate environment, permanent, nonelastic deformation might play a more important role in stress accumulation than it does in interplate crust. Using a simple model incorporating elastic and anelastic strain release, we show that, for realistic parameter values, faults in intraplate crust remain close to their failure stress for a longer part of the earthquake cycle than do faults in high-strain-rate regions. Our results further suggest that remotely triggered earthquakes occur preferentially in regions of recent and/or future seismic activity, which suggests that faults are at a critical stress state in only some areas. Remotely triggered earthquakes may thus serve as beacons that identify regions of long-lived stress concentration.

South Carolina↗
USGS2004

Surface rupture on the Denali fault interpreted from tree damage during the 1912 Delta River Mw 7.2–7.4 earthquake: Implications for the 2002 Denali fault earthquake slip distribution

During the 3 November 2002 Denali fault earthquake, surface rupture propagated through a small, old-growth forest in the Delta River valley and damaged many trees growing on the fault. Damage was principally the result of fault offset of tree roots and tilting of trees. Some trees were split by surface faults that intersected the base of their trunks or large taproots. A few trees appear to have been damaged by strong shaking. Many of the older trees damaged in 2002 were deformed and scarred. Some of these scarred trees exhibit past damage indicative of surface faulting and have abrupt changes in their annual ring patterns that coincide with the past damage. Annual ring counts from several of these older scarred trees indicate the damage was caused by surface rupture on the Denali fault in 1912. The only earthquake of sufficient magnitude that fits the requirements for timing and general location as recorded by the damaged trees is a widely felt Ms 7.2-7.4 earthquake on 6 July 1912 informally referred to as the 1912 Delta River earthquake. Seismologic data and intensity distribution for the 1912 Delta River earthquake indicate that its epicenter was within 60-90 km of the Delta River and that rupture probably propagated toward the west. Inferred fault length, displacement, and rupture direction suggest the 1912 rupture was probably largely coincident with the western, lower slip section of the 2002 rupture.

Alaska↗
USGS2019

Comment on “Interpretation of Kappa and fmax filters as source effect”, by Igor A. Beresnev

Beresnev (2019) advocates the use of an earthquake slip function that produces an ω-2.5 high-frequency falloff of Fourier displacement spectra in the far field, where ω denotes the angular frequency. He argues that the observed high-frequency decay of earthquake spectra can be adequately modeled by this ω-2.5 falloff, without needing to include high frequency attenuation at shallow depth under the site, commonly characterized as fmax or kappa. In his abstract, Beresnev (2019) describes source models with falloffs intermediate between ω-2 and ω-3 as “providing natural high-cut filtering exclusively as a source effect.” In many studies to date, observed spectra are modeled using an ω-2 source spectrum combined with attenuation along the propagation path, including strong attenuation at shallow depths (< 1 km) beneath a site. It is not clear whether Beresnev (2019) is claiming that path effects (including site attenuation) are unimportant to ground motions or if he is proposing a simple, pragmatic method to fit the high-frequency decay of earthquake spectra.

Bulletin of the Seismological Society of America↗
USGS2021

Seismotectonic analysis of the 2019–2020 Puerto Rico sequence: The value of absolute earthquake relocations in improved interpretations of active tectonics

We present a new catalog of calibrated earthquake relocations from the 2019–2020 Puerto Rico earthquake sequence related to the 7 January 2020 M w 6.4 earthquake that occurred offshore of southwest Puerto Rico at a depth of 15.9 km. Utilizing these relocated earthquakes and associated moment tensor solutions, we can delineate several distinct fault systems that were activated during the sequence and show that the M w 6.4 mainshock may have resulted from positive changes in Coulomb stress from earlier events. Seismicity and mechanisms define (1) a west–southwest (∼260°) zone of seismicity comprised of largely sinistral strike‐slip and oblique‐slip earthquakes that mostly occurs later in the sequence and to the west of the mainshock, (2) an area of extensional faulting that includes the mainshock and occurs largely within the mainshock’s rupture area, and (3) an north–northeast (∼30°)‐striking zone of seismicity, consisting primarily of dextral strike‐slip events that occurs before and following the mainshock and generally above (shallower than) the normal‐faulting events. These linear features intersect within the M w 6.4 mainshock’s fault plane in southwest Puerto Rico. In addition, we show that earthquake relocations for M 4+ normal‐faulting events, when traced along their fault planes, daylight along east–west‐trending bathymetric features offshore of southwest Puerto Rico. Correlation of these normal‐faulting events with bathymetric features suggests an active fault system that may be a contributor to previously uncharacterized seismic hazards in southwest Puerto Rico.

Puerto Rico↗
USGS1992

Structure of the Reelfoot rift as interpreted from 2-D magnetotelluric models

The results of magnetotelluric (MT) surveys reveal structures associated with the Reelfoot rift, including an axial high-resistivity structure that may be related to intrusions in the central part of the rift or to a previously unrecognized horst. The axis of this resistivity high generally follows the central part of the Reelfoot rift, but its orientation is offset several degrees from the enigmatic Blytheville arch. The MT structural high follows the main part of a northeast-trending seismicity belt, but in the New Madrid, Missouri area electrical structures are more complicated. In this northern part of the study area, the strike of resistivity structures determined from the MT data indicate a nearly north-south direction, rather than the N45°E direction indicated for most of the data. If the axial high-resistivity structure represents a horst, then it may form an interior divide between thick shale basins. Faults bounding the proposed horst may be a controlling factor for the northeast trending seismic zone.

Arkansas, Kentucky, Missouri, Tennessee↗
USGS1963

Studies of fluid inclusions; [Part] 2, Freezing data and their interpretation

Aqueous and non-aqueous inclusions in 84 samples of various minerals from a wide range of geologic environments were studied with the freezing stage in order to gain an insight into the range of concentrations and compositions of fluid inclusions . Inclusions in most Mississippi Valley-type ore minerals contain highly concentrated saline solutions, showing freezing temperatures between -23.4° and -10.5° C; minerals from ore deposits of more typically hydrothermal affiliations mainly show temperatures of -9.4° to nearly 0° C; and inclusions in quartz crystals from sedimentary, metamorphic, and igneous rock environments show a wide range of freezing temperatures. Inclusions in pegmatite minerals in particular vary over a wide range, from the most concentrated solutions found in any inclusion (> 40% salts) to fairly dilute solutions (< 5% salts). Most inclusions in quartz from Swiss Alpine-type veins, and from Brazilian quartz veins and pegmatites, show freezing temperatures in the range -8.5° to - 2 .5°, and considerable free C02. Other geologic environments sampled include Colombian emerald, pegmatitic topaz and fluorite, the Triassic traprock zeolite assemblage, and sedimentary halite beds. Not all the phenomena exhibited by inclusions at low temperature are completely understood at present but several crystalline hydrate phases, such as NaCl-2H,0 and CO,-5%H,0 (structural formula 8C02-46H20), are shown to be stable in inclusions of appropriate composition even at temperatures above 0° C, and probably exist in the inclusions in natural rocks in polar regions. More significantly, the formation and recognition of such phases aid in establishing the gross composition of individual inclusions far too small for chemical analysis. The data obtained are useful in a variety of ways, such as: discriminating among gas, liquid, and supercritical fluid , and among liquid water, liquid oil, and liquid C02 in inclusions ; improving precision of the pressure corrections applied to inclusion filling temperature determinations; proving the general lack of leakage into or out of inclusions ; estimating the minimum pressure at the time of deposition of certain samples; verifying the lack of extraneous solid crystallization nuclei in the inclusions and hence their formation from exceedingly quiet, clean solutions; determining the total equivalent NaCl concentrations and some information concerning the composition of the fluids from which ores have formed; and determining changes in the composition of the fluids bathing a single crystal during its growth, and at certain times throughout its history.

Economic Geology↗
USGS2002

Interpretation of K-Ar dates of illitic clays from sedimentary rocks aided by modeling

K-Ar dates of illitic clays from sedimentary rocks may contain "mixed ages," i.e., may have ages that are intermediate between the ages of end-member events. Two phenomena that may cause mixed ages are: (1) long-lasting reaction during the burial illitization of smectite: and (2) physical mixing of detrital and diagenetic components. The first phenomenon was investigated by simulation of illitization reactions using a nucleation and growth mechanism. These calculations indicate that values for mixed ages are related to burial history: for an equivalent length of reaction time, fast burial followed by slow burial produces much older mixed ages than slow burial followed by fast. The type of reaction that occurred in a rock can be determined from the distribution of ages with respect to the thickness of illite crystals. Dating of artificial mixtures confirms a non-linear relation between mixed ages and the proportions of the components. Vertical variation of K-Ar age dates from Gulf Coast shales can be modeled by assuming diagenetic illitization that overprints a subtle vertical trend (presumably of sedimentary origin) in detrital mineral content.

American Mineralogist↗
USGS2006

Are subcutaneous transmitters better than intracoelomic? The relevance of reporting methodology to interpreting results

Biologists rely on published scientific papers to increase their knowledge and to guide their future work. Papers comparing techniques can be especially influential when several options exist for accomplishing a task. In this paper, I use a recent publication comparing the effects on birds of several methods for attaching or implanting radio transmitters to illustrate the need for clear and accurate reporting of the techniques used. Because of deficiencies in methodology , in stating methodology , and in following cited methodology I argue that the conclusions drawn by the authors are not supportable.

Wildlife Society Bulletin↗
USGS1997

Alternative interpretations of oil spill data

In his article "Oil, Seabirds, and Science" (BioScience 46: 587-597), John Wiens attempted to review Exxon Valdez oil spill (EVOS) damage assessment studies and the politics of EVOS science in one stroke. In my opinion, neither purpose was particularly well served.

Alaska↗