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At least 1,549 records · Page 86Linked to original sources

USGS2011

Global climate change implications for coastal and offshore oil and gas development

The discussion and debate about climate change and oil and gas resource development has generally focused on how fossil fuel use affects the Earth's climate. This paper explores how the changing climate is likely to affect oil and gas operations in low-lying coastal areas and the outer continental shelf. Oil and gas production in these regions comprises a large sector of the economies of many energy producing nations. Six key climate change drivers in coastal and marine regions are characterized with respect to oil and gas development: changes in carbon dioxide levels and ocean acidity, air and water temperature, precipitation patterns, the rate of sea level rise, storm intensity, and wave regime. These key drivers have the potential to independently and cumulatively affect coastal and offshore oil and gas exploration, production, and transportation, and several impacts of climate change have already been observed in North America.

Energy Policy↗

USGS2016

Geologic and geochemical results from boreholes drilled in Yellowstone National Park, Wyoming, 2007 and 2008

Between 2007 and 2008, seven Earthscope Plate Boundary Observatory (PBO) boreholes ranging in depth from about 200 to 800 feet deep were drilled in and adjacent to the Yellowstone caldera in Yellowstone National Park, for the purpose of installing volcano monitoring instrumentation. Five of the seven boreholes were equipped with strainmeters, downhole seismometers, and tiltmeters. Data collected during drilling included field observations of drill cuttings, stratigraphy within the boreholes, water temperature, and water and drill cuttings samples from selected depths. Six of the seven boreholes encountered rhyolite lavas and tuffs. The rhyolite lavas compose the Canyon flow, the Gardner River flow, the Gibbon River flow, the Hayden Valley flow, the Nez Perce Creek flow, and the West Thumb flow. Boreholes also penetrated a vertical sequence through the Lava Creek Tuff and the Tuff of Bluff Point. In addition, one borehole drilled through a Swan Lake Flat Basalt sequence and terminated in a rhyolite lava flow. After drilling the seven PBO boreholes, cuttings were examined and selected for preparation of grain mounts, thin sections, and geochemical analysis. Major ions and trace elements (including rare earth elements) of selected cuttings were determined by x-ray fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS); the ICP-MS provided more precise trace-element analysis than XRF. A preliminary interpretation of the results of geochemical analyses generally shows a correlation between borehole cuttings and previously mapped geology. The geochemical data and borehole stratigraphy presented in this report provide a foundation for future petrologic, geochemical, and geophysical studies.

Wyoming↗

USGS2008

In situ Raman spectroscopic investigation of the structure of subduction-zone fluids

In situ Raman spectra of synthetic subduction-zone fluids (KAlSi3O8-H2O system) were measured to 900?? and 2.3 GPa using a hydrothermal diamond-anvil cell. The structures of aqueous fluid and hydrous melt become closer when conditions approach the second critical endpoint. Almost no three-dimensional network was observed in the supercritical fluid above 2 GPa although a large amount of silicate component is dissolved, suggesting that the physical and chemical properties of these phases change drastically at around the second critical endpoint. Our experimental results indicate that the fluids released from a subducting slab change from aqueous fluid to supercritical fluid with increasing depth under the volcanic arcs. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2009

Tracking magma volume recovery at Okmok Volcano using GPS and an unscented kalman filter

Changes beneath a volcano can be observed through position changes in a GPS network, but distinguishing the source of site motion is not always straightforward. The records of continuous GPS sites provide a favorable data set for tracking magma migration. Dense campaign observations usually provide a better spatial picture of the overall deformation field, at the expense of an episodic temporal record. Combining these observations provides the best of both worlds. A Kalman filter provides a means for integrating discrete and continuous measurements and for interpreting subtle signals. The unscented Kalman filter (UKF) is a nonlinear method for time‐dependent observations. We demonstrate the application of this technique to deformation data by applying it to GPS data collected at Okmok volcano. Seven years of GPS observations at Okmok are analyzed using a Mogi source model and the UKF. The deformation source at Okmok is relatively stable at 2.5 km depth below sea level, located beneath the center of the caldera, which means the surface deformation is caused by changes in the strength of the source. During the 7 years of GPS observations more than 0.5 m of uplift has occurred, a majority of that during the time period January 2003 to July 2004. The total volume recovery at Okmok since the last eruption in 1997 is ∼60–80%. The UKF allows us to solve simultaneously for the time‐dependence of the source strength and for the location without a priori information about the source. 2009 by the American Geophysical Union.

Alaska↗

USGS2015

Indium: bringing liquid-crystal displays into focus

Introduction Indium is rare in the Earth’s crust. The continental crust contains an average of about 50 parts per billion of indium, whereas the oceanic crust contains about 72 parts per billion, which is similar to meteoritic abundances and comparable to the crustal abundance of silver. Indium minerals are rare in nature and only 12 indium minerals are known. In its elemental form, indium is a soft, lustrous, silver-white metal with a low melting point relative to other metals. It is ductile and malleable, even at temperatures approaching absolute zero, making it ideal for cryogenic applications. Indium was discovered in the mid-1800s by two German chemists who were investigating zinc ores from Freiberg, Saxony. They named it after the distinctive indigo-blue color observed in its emission spectrum. For years indium remained only a scientific curiosity and early applications of indium were few, but included manufacturing of light-emitting diodes and coatings for bearings used in aircraft engines. Indium-bearing nuclear control rods became more widely used in the 1970s, and today the major application of indium is in manufacturing liquid-crystal displays. Compared to more abundant industrial metals such as lead and zinc, information about the behavior and toxicity of indium in the environment is limited. However, many indium compounds have been proven to be toxic to animals.

Fact Sheet↗

USGS2022

Thermophysical and compositional properties of paleobedforms on Mars

Bedforms on Earth and Mars are often preserved in the rock record in the form of sedimentary rock with distinct cross-bedding. On rare occasions, the full-surface geometry of a bedform can be preserved through burial and lithification. These features, known as paleobedforms, are found in a variety of geographic locations on Mars. Evidence in the morphology of paleobedforms, such as the retention of impact craters and steep erosional scarps, suggests that these features are well-lithified and capable of withstanding prolonged weathering and erosion. Here, we present results from thermophysical and compositional analyses on a subset of the best preserved paleobedform candidate fields on Mars. Thermophysical modeling elucidates the changes these bedforms underwent from their unconsolidated, particulate nature to their currently observed properties. Certain paleobedforms have elevated thermal inertias (e.g., ∼300–500 J·m −2 ·s −1/2 ·K −1 ) when compared with modern bedforms (∼250 J·m −2 ·s −1/2 ·K −1 ), and modeling indicates that they have cement volumes of 0.8%–1.5% even as high as 30%. However, most paleobedform candidates have unexpectedly low thermal inertia when compared with modern dunes. Additionally, compositional analyses reveal a range of spectral characteristics within paleobedforms (e.g., primary and secondary alteration products). These features add to the already existing class of Martian surfaces in which thermal inertia does not seem to correspond to erodibility, cohesion, or mechanical strength. Studying paleobedforms with both raised and nonraised thermal inertia has provided new insights into lithification on Mars and constrained the environmental conditions leading to the formation of these enigmatic features.

Journal of Geophysical Research - Planets↗

USGS2023

Forecasts of polar bear (Ursus maritimus) land use in the southern Beaufort and Chukchi Seas, 2040–65

This report provides analysis to extend the 2040 forecasts of polar bear ( Ursus maritimus ) land use for the southern Beaufort and Chukchi Sea populations presented in a recent publication (Rode and others, 2022) through the year 2065. To inform long-term polar bear management considerations, we provide point-estimate forecasts and 95-percent prediction intervals of the proportion of polar bear populations summering onshore for 21 days or more (≥) and their duration onshore every 5 years from 2040 to 2065. Because sea-ice projections based on earth system models show greater divergence with emission scenarios after 2040, we have provided forecasts for three greenhouse gas emission scenarios, SSP1-2.6, SSP2-4.5 and SSP5-8.5, compared to the two emission scenarios used in Rode and others (2022). Our forecasting methods estimated that 61–97 percent of polar bears in the southern Beaufort Sea and 80–100 percent of polar bears in the Chukchi Sea populations may summer onshore for ≥21 days by 2065. Forecasts of mean duration onshore were 105–158 days for polar bears in the southern Beaufort Sea and 111–178 days in the Chukchi Sea populations by 2065. Sea ice conditions projected to occur by 2065 could alter the current patterns of bear behavior from what has been observed over the past 30 years. As a result, these extended projections are associated with a higher degree of uncertainty than estimates through 2040, especially under the SSP5-8.5 scenario.

Open-File Report↗

USGS2010

Geodetic evidence for en echelon dike emplacement and concurrent slow slip during the June 2007 intrusion and eruption at Kilauea volcano, Hawaii

A series of complex events at Kīlauea Volcano, Hawaii, 17 June to 19 June 2007, began with an intrusion in the upper east rift zone (ERZ) and culminated with a small eruption (1500 m 3 ). Surface deformation due to the intrusion was recorded in unprecedented detail by Global Positioning System (GPS) and tilt networks as well as interferometric synthetic aperture radar (InSAR) data acquired by the ENVISAT and ALOS satellites. A joint nonlinear inversion of GPS, tilt, and InSAR data yields a deflationary source beneath the summit caldera and an ENE-striking uniform-opening dislocation with ~2 m opening, a dip of ∼80° to the south, and extending from the surface to ~2 km depth. This simple model reasonably fits the overall pattern of deformation but significantly misfits data near the western end of an inferred dike-like source. Three more complex dike models are tested that allow for distributed opening including (1) a dike that follows the surface trace of the active rift zone, (2) a dike that follows the symmetry axis of InSAR deformation, and (3) two en echelon dike segments beneath mapped surface cracks and newly formed steaming areas. The en echelon dike model best fits near-field GPS and tilt data. Maximum opening of 2.4 m occurred on the eastern segment beneath the eruptive vent. Although this model represents the best fit to the ERZ data, it still fails to explain data from a coastal tiltmeter and GPS sites on Kīlauea's southwestern flank. The southwest flank GPS sites and the coastal tiltmeter exhibit deformation consistent with observations of previous slow slip events beneath Kīlauea's south flank, but inconsistent with observations of previous intrusions. Slow slip events at Kīlauea and elsewhere are thought to occur in a transition zone between locked and stably sliding zones of a fault. An inversion including slip on a basal decollement improves fit to these data and suggests a maximum of ~15 cm of seaward fault motion, comparable to previous slow-slip events.

Hawai'i↗

USGS2022

Magnetotelluric investigations of the Kīlauea Volcano, Hawaii

In 2002 and 2003 a collaborative effort was undertaken between Lawrence Berkeley National Laboratory, Sandia National Laboratories, the U.S. Geological Survey (USGS) Menlo Park, the USGS Hawaiian Volcano Observatory, and Electromagnetic Instruments Inc. to study the Kīlauea volcano in Hawaii using the magnetotelluric (MT) technique. The work was motivated by a desire to improve understanding of the magma reservoirs and conduits within Kīlauea and the East and Southwest Rift zones, which has implications for understanding Kīlauea's plumbing system. An improved understanding of the rift zones has implications in understanding large-scale landslides that are generated in the Hilina Slump, which produce significant impacts on coastal communities. Up to eight stations operated simultaneously, with multiple remote reference sites, and data were processed using multi-station robust processing techniques. In total, data were acquired at 70 sites over the Southwest and East rift zones. Good to excellent quality data were obtained even in the harshest conditions, such as those encountered on the fresh lava flows of the East Rift Zone, where electrical contact resistances are on the order of 100 kΩ. A three-dimensional (3D) MT model study was done to guide interpretation of the observed MT measurements. Synthetic modeling demonstrates that conductive bodies in the upper 3 km can be spatially resolved where MT station sampling is good. Resistivity anomalies in the 3D inversions have a high degree of spatial correlation with previously published seismic velocity anomalies beneath Kīlauea. Melt fractions between 0.096 and 0.117 are calculated for the Kīlauea and Puʻuʻōʻō low resistivity anomalies, respectively.

Hawai'i↗

USGS1999

Petrology and geochemistry of late-stage intrusions of the A-type, mid-Proterozoic Pikes Peak batholith (Central Colorado, USA): Implications for petrogenetic models

The ~1.08 Ga anorogenic, A-type Pikes Peak batholith (Front Range, central Colorado) is dominated by coarse-grained, biotite ?? amphibole syenogranites and minor monzogranites, collectively referred to as Pikes Peak granite (PPG). The batholith is also host to numerous small, late-stage plutons that have been subdivided into two groups (e.g. Wobus, 1976. Studies in Colorado Field Geology, Colorado School of Mines Professional Contributions, Colorado): (1) a sodic series (SiO2= ~44-78 wt%; K/Na=0.32-1.36) composed of gabbro, diabase, syenite/quartz syenite and fayalite and sodic amphibole granite; and (2) a potassic series (SiO2= ~ 70-77 wt%; K/Na=0.95-2.05), composed of biotite granite and minor quartz monzonite. Differences in major and trace element and Nd isotopic characteristics for the two series indicate different petrogenetic histories. Potassic granites of the late-stage intrusions appear to represent crustal anatectic melts derived from tonalite sources, based on comparison of their major element compositions with experimental melt products. In addition, Nd isotopic characteristics of the potassic granites [??(Nd)(1.08 Ga) = -0.2 to -2.7] overlap with those for tonalites/granodiorites [ca 1.7 Ga Boulder Creek intrusions; ??(Nd)(1.08 Ga) = -2.4 to -3.6] exposed in the region. Some of the partial melts evolved by fractionation dominated by feldspar. The late-stage potassic granites share geochemical characteristics with most of the PPG, which is also interpreted to have an anatectic origin involving tonalitic crust. The origin of monzogranites associated with the PPG remains unclear, but mixing between granitic and mafic or intermediate magmas is a possibility. Syenites and granites of the sodic series cannot be explained as crustal melts, but are interpreted as fractionation products of mantle-derived mafic magmas with minor crustal input. High temperature and low oxygen fugacity estimates (e.g. Frost et al., 1988. American Mineralogist 73, 727-740) support a basalt fractionation origin, as do ??(Nd) values for sodic granitoids [??(Nd)(1.08 Ga) = +2.2 to -0.7], which are higher than ??(Nd) values for Colorado crust at 1.08 Ga (ca -1.0 to -4.0). Enrichments in incompatible elements (e.g. rare earth elements, Rb, Y) and depletions in compatible elements (e.g. Cr, Sr, Ba) in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation. Accessory mineral fractionation, release of fluorine-rich volatiles and/or removal of pegmatitic fluids could have modified abundances of Ce, Nb, Zr and Y in some sodic granitoid magmas. Gabbros and mafic dikes associated with the sodic granitoids have ??(Nd)(1.08 Ga) of -3.0 to +3.5, which are lower than depleted mantle at 1.08 Ga, and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction-related processes. However, it is difficult to characterize the mantle component in these magmas, because assimilation of crust during magma ascent could also result in their observed geochemical features. The Pikes Peak batholith is composed of at least two petrogenetically different granite types, both of which exhibit geochemical characteristics typical of A-type granites. Models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central Colorado at ~ 1.1 Ga.

Precambrian Research↗

USGS2016

Coseismic slip and early afterslip of the 2015 Illapel, Chile, earthquake: Implications for frictional heterogeneity and coastal uplift

Great subduction earthquakes are thought to rupture portions of the megathrust, where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, postseismic afterslip is assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, coseismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. Here we use interferometric synthetic aperture radar and Global Position System observations to map the distribution of coseismic slip of the 2015 M w 8.3 Illapel, Chile, earthquake and afterslip within the first 38 days following the earthquake. We find that afterslip overlaps the coseismic slip area and propagates along-strike into regions of both high and moderate interseismic coupling. The significance of these observations, however, is tempered by the limited resolution of geodetic inversions for both slip and coupling. Additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip, and both contribute to net uplift of the Chilean Coastal Cordillera. A simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations. Instead, stress heterogeneities, either preexisting or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. We also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones.

Journal of Geophysical Research B: Solid Earth↗

USGS2011

Tsunami inundation and sediment transport in a sediment-limited embayment on American Samoa

Field observations and numerical simulations are used to explore tsunami inundation and sediment transport in an embayment (Fagafue Bay) on the north side of Tutuila, American Samoa during the 29 September 2009 South Pacific tsunami. Field observations of the nearshore bathymetry and topography, tsunami flow depth and sediment deposition, and extent of movable sandy sediment remaining on the beach were collected during two field surveys approximately two and five weeks after the tsunami. Onshore measurements of flow depth at forty-eight locations indicate the wave inundated almost 250. m onshore with a depth exceeding 7. m locally. The tsunami deposited patchy areas of sediment up to 0.2. m thick interspersed with a thin dusting (< 0.01 m) of sandy sediment throughout most of the inundated area. A numerical simulation based on the best available topography and bathymetry and a simplified offshore wave forcing is calibrated with the onshore flow observations. The calibrated model is used to simulate tsunami-induced sediment transport within and onshore of both the actual embayment and several idealized embayments. The simulations show that the onshore deposition of sediment can be affected by more than 50% by both the amount of sediment available for transport and the steepness of the onshore topography, suggesting these effects may need to be considered when interpreting tsunami deposits.

Earth-Science Reviews↗

USGS1999

Stress transfer by the 1988-1989 M=5.3 and 5.4 Lake Elsman foreshocks to the Loma Prieta fault: Unclamping at the site of peak mainshock slip

We study the stress transferred by the June 27, 1988, M = 5.3 and August 8, 1989, M = 5.4 Lake Elsman earthquakes, the largest events to strike within 15 km of the future Loma Prieta rupture zone during 74 years before the 1989 M = 6.9 Loma Prieta earthquake. We find that the first Lake Elsman event brought the rupture plane of the second event 0.3–1.6 bars (0.03–0.16 MPa) closer to Coulomb failure but that the Lake Elsman events did not bring the future Loma Prieta hypocentral zone closer to failure. Instead, the Lake Elsman earthquakes are calculated to have reduced the normal stress on (or “undamped”) the Loma Prieta rupture surface by 0.5–1.0 bar (0.05–0.10 MPa) at the site where the greatest slip subsequently occurred in the Loma Prieta earthquake. This association between the sites of peak unclamping and slip suggests that the Lake Elsman events did indeed influence the Loma Prieta rupture process. Unclamping the fault would have locally lowered the resistance to sliding. Such an effect could have been enhanced if the lowered normal stress permitted fluid infusion into the undamped part of the fault. Although less well recorded, the M L = 5.0 1964 and M L = 5.3 1967 Corralitos events struck within 10 km of the southwest end of the future Loma Prieta rupture. No similar relationship between the normal stress change and subsequent Loma Prieta slip is observed, although the high-slip patch southwest of the Loma Prieta epicenter corresponds roughly to the site of calculated Coulomb stress increase for a low coefficient of friction. The Lake Elsman-Loma Prieta result is similar to that for the 1987 M = 6.2 Elmore Ranch and M = 6.7 Superstition Hills earthquakes, suggesting that foreshocks might influence the distribution of mainshock slip rather than the site of mainshock nucleation.

Journal of Geophysical Research B: Solid Earth↗

USGS2020

Twelve-year dynamics and rainfall thresholds for alternating creep and rapid movement of the Hooskanaden landslide from integrating InSAR, pixel offset tracking, and borehole and hydrological measurements

The Hooskanaden landslide is a large (~600 m wide × 1,300 m long), deep (~30 – 45 m) slide located in southwestern Oregon. Since 1958, it has had five moderate/major movements that catastrophically damaged the intersecting U.S. Highway 101, along with persistent slow wet‐season movements and a long‐term accelerating trend due to coastal erosion. Multiple remote sensing approaches, borehole measurements, and hydrological observations have been integrated to interpret the motion behaviors of the slide. Pixel offset tracking of both Sentinel‐1 and Sentinel‐2 images was carried out to reconstruct the 3‐D displacement field of the 2019 major event, and the results agree well with field measurements. A 12‐year displacement history of the landslide from 2007 to 2019 has been retrieved by incorporating offsets from Light Detection and Ranging (LiDAR) digital elevation model (DEM) gradients and Interferometric Synthetic Aperture Radar (InSAR) processing of ALOS and Sentinel‐1 images. Comparisons with daily/hourly ground precipitation reveal that the motion dynamics are predominantly controlled by intensity and temporal pattern of rainfall. A new empirical threefold rainfall threshold was therefore proposed to forecast the dates for the moderate/major movements. This threshold relies upon antecedent water‐year and previous 3‐day and daily precipitation and was able to represent observed movement periods well. Adaptation of our threshold methodology could prove useful for other large, deep landslides for which temporal forecasting has long been generally intractable. The averaged characteristic hydraulic conductivity and diffusivity were estimated as 6.6 × 10 −6 m/s and 6.6 × 10 −4 m 2 /s, respectively, based on the time lags between rainfall pulses and slide accelerations. Hydrologic modeling using these parameters helps to explain the ability of the new rainfall threshold.

Oregon↗

USGS2012

Stratigraphic contrasts and tectonic relationships between Carboniferous successions in the Trans-Alaska Crustal Transect corridor and adjacent areas, northern Alaska

The Carboniferous succession along the Trans-Alaska Crustal Transect (TACT) corridor in the Atigun Gorge area of the central Brooks Range consists of the Kayak Shale (Kinderhookian) and the Lisburne Group (Kinderhookian through Chesterian). The Kayak Shale is at least 210 m thick; it is chiefly black, noncalcareous shale with several limestone beds of pelmatozoan-bryozoan packstone and formed in an open-marine setting. The Lisburne Group is a carbonate rock succession about 650 m thick and consists mainly of skeletal packstone, wackestone, and milestone which contain locally abundant calcispheres, ostracodes, algae, and sponge spicules; it accumulated largely in a shallow water platform environment with restricted circulation. This restriction was probably produced by a coeval belt of skeletal sand shoals recognized 70 km to the west in the Shainin Lake area. Significant and apparently abrupt shifts in the age and lithofacies of Carboniferous strata occur across the central and eastern Brooks Range. These shifts are most marked in a zone roughly coincident with what is interpreted by many workers to be the leading edge of the Endicott Mountains allochthon. Notable lithologie contrasts are also observed, however, between sections in the northern and southern parts of the Endicott Mountains allochthon. This suggests that considerable tectonic shortening has taken place within the allochthon, as well as between it and parautochthonous rocks to the northeast. The Carboniferous section near Mount Doonerak is more similar in age and lithofacies to coeval sections in the central Brooks Range that are considered allochthonous than to parautochthonous sections to the northeast.

Journal of Geophysical Research B: Solid Earth↗

USGS1969

Rheology of basalt in the melting range

Experimental data have been obtained for viscosities of tholeiite melts at temperatures from 1300 to 1120 °Cat 1 atm, using a concentric cylinder viscometer. The apparent viscosity increases more than two orders of magnitude between 1200 and 1120 °C (0–25 per cent crystallization) for shear rates of about 10 sec -1 and even more for lower shear rates. Non-Newtonian behaviour of ‘pseudo-plastic type’ becomes extremely pronounced at temperatures below about 1130 °C. At these temperatures, differences of less than 5 °C can produce changes in apparent viscosity amounting to orders of magnitude. These observations have led to the conclusion that the heat of deformation must itself influence rheological behaviour in the melting range. An equation for thermal energy balances and their rates of change is constructed and placed in a non-dimensional form that has been given published solutions by I. J. Gruntfest (1963) relating the shear stress, rate of strain, and temperature through the temperature dependence of viscosity. The results show that in an adiabatic system the heating rate increases with time so that the temperature eventually runs out of bounds, a process termed ‘thermal feedback’ by Gruntfest. A hypothesis of shear melting is derived on the basis of a simplified viscosity function extrapolated to the solidus temperature. The hypothesis is applied to magma generation in the earth on the basis of dimensional arguments. It is also suggested that thermal instabilities give rise to a sort of viscous failure responsible for deep-focus earthquakes, and that the two phenomena have the same cause relating ultimately to a gravitational energy source.

Journal of Petrology↗

USGS2007

Dynamic triggering

A growing body of evidence demonstrates that dynamic stresses propagating as seismic waves from large earthquakes are capable of triggering additional earthquakes ranging from aftershocks in the near-field (within one or two source dimensions of the mainshock epicenter) to remotely triggered earthquakes at distances exceeding 10 000 km. Most of the triggered earthquakes are small (generally M ≤ 3) except within the near field, where dynamic stresses may trigger slip on subadjacent fault segments leading to complex rupture comprising of several large earthquakes of comparable magnitude. Crustal surface waves with periods of 15–30 s and peak dynamic stresses greater than ∼0.01 MPa seem to be most efficient in triggering remote seismicity. Current models for dynamic triggering fall under two broad groups: one appealing to Coulomb failure with various friction laws, and the other appealing to the activation of crustal fluids either hydrous or magmatic. No single model appears capable of accounting for the wide variation observed in the nature of triggered activity. Spatial sampling of dynamic triggering on a global scale is still woefully inadequate because of the limited distribution of adequate seismic networks. From the limited data currently available, it appears that extensional stress regimes hosting geothermal and volcanic activity are more susceptible to remote dynamic triggering than compressional stress regimes, although remote triggering is not limited to extensional regimes. Instances of remote triggering in the few areas with continuous, high-resolution deformation instrumentation (all volcanic or geothermal areas) include distinctive deformation transients, suggesting that the locally triggered seismicity in these areas may be a secondary response to a more fundamental aseismic process that likely involves some form of fluid transport or phase change. Recent evidence for triggering by solid Earth tides and ocean loading in convergent plate margins provides a low-frequency, low-amplitude reference point for the spectrum of stresses capable of dynamic triggering. Remaining challenges include establishing better sampling of the distribution of triggered seismicity and better constraints on physical models for the triggering process.

Book chapter↗

USGS2014

Advances in a distributed approach for ocean model data interoperability

An infrastructure for earth science data is emerging across the globe based on common data models and web services. As we evolve from custom file formats and web sites to standards-based web services and tools, data is becoming easier to distribute, find and retrieve, leaving more time for science. We describe recent advances that make it easier for ocean model providers to share their data, and for users to search, access, analyze and visualize ocean data using MATLAB® and Python®. These include a technique for modelers to create aggregated, Climate and Forecast (CF) metadata convention datasets from collections of non-standard Network Common Data Form (NetCDF) output files, the capability to remotely access data from CF-1.6-compliant NetCDF files using the Open Geospatial Consortium (OGC) Sensor Observation Service (SOS), a metadata standard for unstructured grid model output (UGRID), and tools that utilize both CF and UGRID standards to allow interoperable data search, browse and access. We use examples from the U.S. Integrated Ocean Observing System (IOOS®) Coastal and Ocean Modeling Testbed, a project in which modelers using both structured and unstructured grid model output needed to share their results, to compare their results with other models, and to compare models with observed data. The same techniques used here for ocean modeling output can be applied to atmospheric and climate model output, remote sensing data, digital terrain and bathymetric data.

Journal of Marine Science and Engineering↗