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At least 415 records · Page 23Linked to original sources
USGS2008

Hematite spherules at Meridiani: results from MI, Mini-TES, and Pancam

We report on observations of hematite‐bearing spherules at Meridiani Planum made using the Microscopic Imager (MI), Mini‐Thermal Emission Spectrometer (Mini‐TES), and Panoramic Camera (Pancam) instruments on the Mars Exploration Rover Opportunity. Spherules were observed on soil surfaces and in outcrop rocks, both on undisturbed surfaces and in abraded surfaces ground using the Rock Abrasion Tool (RAT). Spherule size and shape change little along the 850 m eastward traverse from Eagle Crater to Endurance Crater, but spherules decrease and then slightly increase in size along the 6 km traverse from Endurance south to Victoria Crater. Local populations range from submillimeters to several millimeters in diameter. An additional small diameter (100 μ m) size population is possible. An increase in irregular shapes is found near Victoria Crater. This, combined with the size decrease south of Endurance, suggests either a changing depositional environment, or variation in the duration and timing of diagenetic events. The dominant smaller size population observed early in the mission in aeolian areas and ripple crests is observed as the primary size population in abraded outcrop farther south. This suggests that successively younger beds are exposed at the surface along the southward traverse. Stratigraphically higher units removed by erosion could be recorded by the present surface lag deposit. Coordinated systematic observations are used to determine optical and infrared hematite indices of the surface soils in Pancam and Mini‐TES. In spite of the systematic variation seen in MI, both Pancam and Mini‐TES indices are highly variable based on the local surface, and neither show systematic trends south of Endurance. The lack of a 390 cm −1 feature in Mini‐TES spectra suggests concentric or radial interior structure within the spherules at scales too fine for MI to observe. Mini‐TES does not detect any silicate component in the spherules. A bound water component in soils or in exchange with the atmosphere is observed. These spherules have been previously interpreted as concretions formed within what were once water‐saturated, diagenetically altered “dirty evaporate” sandstone sediments. Our observations support this interpretation; however, no single terrestrial analog provides a model that can account for all attributes of the spherules on Mars.

Journal of Geophysical Research↗
USGS1976

Geology and Rb-Sr ages of reactivated Precambrian gneisses and granite in the Marenisco-Watersmeet area, northern Michigan

Rb-Sr dating of Precambrian W (lower Precambrian) gneisses and granitic rocks that form the cores of antiforms or domes mantled by metamorphosed Precambrian X (middle Precambrian) bedded rocks in the Marenisco-Watersmeet area, northern Michigan, shows that the rock systems have been disturbed to different degrees by complex tectonic and thermal events subsequent to primary crystallization. The disturbance is indicated by a lowering of the whole-rock Rb-Sr ages of many samples of gneiss from 2,600 m.y. or older to about 1,800 m.y. and by the scattering of data points, although some of the points can be fit to secondary isochrons; probably the major mechanism was redistribution of previously accumulated radiogenic Sr, which is indicated by the high initial 87 Sr/ 86 Sr of the resultant isochrons. The disturbance is interpreted as having resulted from internal cataclasis and recrystallization accompanied by metamorphic segregation and (or) partial melting during reactivation of the gneisses about 1,800 m.y. ago. Variations in the degree of reconstitution and mobility of individual bodies of basement rocks are indicated by differences in structural reconstitution of the basement rocks and in the metamorphic grade of the Precambrian X bedded rocks.

Michigan↗
USGS2005

Geochemistry and the understanding of ground-water systems

Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information, and calibrate ground-water flow models. Progress needs to be made in obtaining representative samples. Improvements are needed in the interpretation of the information obtained, and in the construction and interpretation of numerical models utilizing hydrochemical data. The best approach will ensure an optimized iterative process between field data collection and analysis, interpretation, and the application of forward, inverse, and statistical modeling tools. Advances are anticipated from microbiological investigations, the characterization of natural organics, isotopic fingerprinting, applications of dissolved gas measurements, and the fields of reaction kinetics and coupled processes. A thermodynamic perspective is offered that could facilitate the comparison and understanding of the multiple physical, chemical, and biological processes affecting ground-water systems.

Hydrogeology Journal↗
USGS2015

Heat flux from magmatic hydrothermal systems related to availability of fluid recharge

Magmatic hydrothermal systems are of increasing interest as a renewable energy source. Surface heat flux indicates system resource potential, and can be inferred from soil CO 2 flux measurements and fumarole gas chemistry. Here we compile and reanalyze results from previous CO 2 flux surveys worldwide to compare heat flux from a variety of magma-hydrothermal areas. We infer that availability of water to recharge magmatic hydrothermal systems is correlated with heat flux. Recharge availability is in turn governed by permeability, structure, lithology, rainfall, topography, and perhaps unsurprisingly, proximity to a large supply of water such as the ocean. The relationship between recharge and heat flux interpreted by this study is consistent with recent numerical modeling that relates hydrothermal system heat output to rainfall catchment area. This result highlights the importance of recharge as a consideration when evaluating hydrothermal systems for electricity generation, and the utility of CO 2 flux as a resource evaluation tool.

Journal of Volcanology and Geothermal Research↗
USGS2019

The Miocene Atastra Creek sinter (Bodie Hills volcanic field, California and Nevada): 4D evolution of a geomorphically intact siliceous hot spring deposit

The Atastra Creek siliceous hot spring deposit, or sinter, occurs in the Paramount-Bald Peak alteration zone, due north of the Bodie precious metals mining district in the Miocene Bodie Hills volcanic field, California and Nevada, U.S.A. Distinctive features include its geomorphically intact geyser vent mounds, the presence of growth-fault-stepped sinter terraces that developed westward along a NNW trending fault, and atypical Hg, Sb and As concentrations. High-temperature (>75 °C), subaerial, proximal apron sinter occurs in two settings – (1) radiating botryoidal geyserite in vent mounds and (2) bedded geyserite (columnar, nodular, size-sorted geyser eggs) intercalated with mid- to low-temperature (<60 °C), middle to distal apron terrace sinter. The active geyser vent mounds migrated from south to north across the apron terrace through time. A newly recognized, visually striking type of sinter – termed silica infiltrate herein – formed directly beneath the subaerial geyserite deposits. It is characterized by mainly parallel, thin, irregular beds of white silica with narrow borders of dark blue-gray silica, as well as swirly to globular white silica, all chaotically linked together by silica ‘necks’ and ‘bridges’. The silica infiltrate permeates the pre-existing sinter, and is interpreted to represent super-heated fluid injections into the immediately overlying geyser vent mounds and pools. The adjacent sinter sheets preserve fluid-flow directions of warm-water channels that traversed the discharge apron, including microbial streamer fabric and wavy laminated sinter with flattened bubbles. More distal sinter textures are recorded by rimmed terracettes with mammillated and palisade microbial fabrics and rare, warm pool-related stromatolites. However, plants are absent, probably due to the high metalloids, in particular As. Post-depositional events include an inferred hydrothermal eruption breccia and an interpreted drop in the water table accompanied by incursion of steam acid condensate, as evidenced by pervasive hydrothermal alteration of the Atastra Creek deposits. Hence, the well-exposed sedimentary facies distributions, well-preserved geomorphology, and stratigraphic and structural relationships together allow an unusually complete, paleoenvironmental reconstruction of the Atastra Creek paleohydrothermal deposit.

Journal of Volcanology and Geothermal Research↗
USGS2003

Deformation of the Long Valley Caldera, California: Inferences from measurements from 1988 to 2001

Two periods of volcanic unrest occurred between 1989 and 1998 in the Long Valley Caldera, eastern California. Numerous earthquakes were recorded, and these periods of unrest were documented with high-precision geodetic measurements. The first round of unrest started rapidly in late 1989 and slowly decreased in rate through the early 1990s. For this interval there are both leveling and two-color electronic distance meter (EDM) measurements. The second round of unrest started slowly in mid-1997, climaxed in late 1997, and rapidly returned to quiescence by mid-1998. Deformation was recorded by both the two-color EDM and continuous GPS. Both episodes require inflation at 6-7 km beneath the resurgent dome, and both episodes had roughly 0.1 m extension across the resurgent dome. In addition, the data presented here suggest that there is a deeper, 10-20 km, inflation source beneath the south moat of the caldera. For both episodes, the better-resolved inflation beneath the resurgent dome is a near-vertical, prolate spheroid rather than an isotropic source, which suggests that magma came up through vertical cracks. However, the modeling suggests that the location changed with the depth from 6.0 to 6.7 km for the later episode. In contrast to the earlier episode, the 1997-1998 episode has additional deformation in the south moat, where the simplest model is that of a right-lateral slip on a steeply dipping plane that is defined by the location of earthquakes in the south moat. Models of the time-dependent behavior suggest that slip on this fault occurred from late November through December 1997, corresponding to the time of greatest moment release by the earthquake swarm in the south moat. Confounding the interpretation of these data is an active geothermal field near the center of the EDM network and adjacent to the south moat and resurgent dome. Additional modeling of leveling and EDM data within the geothermal field during a period of low rate of inflation of the dome suggests some methods of adjustments to the EDM data during the inflation episodes. ?? 2003 Elsevier B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗
USGS1999

P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography

We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and velocity problems. In the upper 7 km of the resulting model there is good correlation between velocity anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-velocity trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate ( M 6.5–7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A ∼10 km-wide low-velocity anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic velocity pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics.

Journal of Geophysical Research B: Solid Earth↗
USGS2019

Ar-Ar age constraints on the timing of Havre Trough opening and magmatism

The age and style of opening of the Havre Trough back-arc system is uncertain due to a lack of geochronologic constraints for the region. 40 Ar/ 39 Ar dating of 19 volcanic rocks from across the southern Havre Trough and Kermadec Arc was conducted in three laboratories to provide age constraints on the system. The results are integrated and interpreted as suggesting that this subduction system is young (<2 Ma) and coeval with opening of the continental Taupo Volcanic Zone of New Zealand. Arc magmatism was broadly concurrent across the breadth of the Havre Trough.

Kermadec Arc–Havre Trough↗
USGS2021

Unmixing multiple metamorphic muscovite age populations with powder X-ray diffraction and 40Ar/39Ar analysis

A combination of modal estimates from powder X-ray diffraction (XRD) experiments and argon isotopic data shows that muscovite 40 Ar/ 39 Ar total gas age correlates with muscovite composition near the retrograde Bald Mountain shear zone (BMSZ) in Claremont, New Hampshire, and that the shear zone was active at ∼245 Ma. Petrologic study demonstrates that chemical disequilibrium is preserved in muscovite grains in these samples. The recognition of this preservation is critical to the interpretation of the 40 Ar/ 39 Ar step-heating experiments, which never produce age plateaus and yield spectra with steps that range in age by ∼20 Ma. Petrographic, compositional, and crystallographic data all indicate that the age spectra reflect dissolution of metastable Na-rich muscovite and precipitation of stable Na-poor muscovite associated with deformation in the BMSZ.Comparison of whole rock and muscovite concentrate XRD patterns from individual samples demonstrates that the mineral separation process can fractionate these muscovite populations. Therefore, four muscovite concentrates of varying magnetic susceptibility were prepared from a single hand sample, analyzed by XRD, and dated. These four splits define a mixing line that resolves end-member ages of 244.5 ± 4.2 Ma and 302.5 ± 12.5 Ma (1σ). Although the ages are imprecise, the petrologically supported conclusion that these schists preserve two discrete ages is distinct from an interpretation that the spectra reflect cooling through closure at ∼270 Ma, as might be concluded in the absence of petrologic characterization. The XRD results also demonstrate that, even well above anchizone conditions, petrologic information relevant to 40 Ar/ 39 Ar dating is observable in subtle variations in the crystallography of muscovite grains.

New Hampshire↗
USGS1977

Effect of initial radioactive-daughter disequilibrium on U-Pb isotope apparent ages of young minerals

Most calculations of U-Pb isotope apparent ages are made by use of equations that assume initial secular equilibrium of the uranium decay-chains. The possible error in calculated Pb/U isotope ratios arising from this assumption (especially for ores of sandstone uranium deposits) can be over 10 percent at 1 million years and exceed analytical error even at a 30 m.y. apparent age. Use of the more general equations (adapted from the Bateman equations) is desirable for calculation and interpretation of U-Pb isotope apparent ages of both open and closed systems in the range of 2 to 20 m.y. and is essential for apparent ages less than about 2 m^y. For very young sandstone uranium deposits, a significant uncertainty in the 208 Pb/ 238 U systematics may still persist owing to the uncertainty in the initial value of 234 U/ 238 U.

Journal of Research of the U.S. Geological Survey↗
USGS1985

Stratigraphic and interregional changes in Pennsylvanian coal-swamp vegetation: Environmental inferences

Quantitative analysis of Pennsylvanian coal-swamp vegetation provides a means of inferring organization and structure of communities. Distribution of these communities further provides inferences about environmental factors, including paleoclimate. Our observations are based on in situ, structurally preserved peat deposits in coal-ball concretions from 32 coal seams in the eastern one-half of the United States and from several seams in western Europe and on spore assemblages from more than 150 seams. There were three times of particularly significant and nearly synchronous vegetational changes in the Midcontinent and Appalachian coal regions during the Pennsylvanian Period. Each was different in kind and magnitude. The first marked changes occurred during the early part of the Middle Pennsylvanian with the fluctuating decline in the high level of lycopod dominance. The abundance of cordaites increased. There was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity. Changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree-fern spores. The next significant time of change was during the middle part of the Middle Pennsylvanian, representing both a culmination of earlier trends and expansions of cordaites in the Midcontinent where there was a maximum change in species without net loss of diversity. Tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the Atokan-Desmoinesian transition of the Midcontinent. The third and sharpest break occurred near the Middle—Late Pennsylvanian boundary when extinctionsof the dominant, coal-swamp lycopods allowed development of tree-fern dominance. The Late Pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the Middle Pennsylvanian swamps. Paralleling the changes in floras through the Pennsylvanian are changes in preservational aspects of the peat. These include a decline in shoot/root ratios from approximately 1 to < 1 during the first time of vegetational changes and a rise in this ratio during the second; there was a parallel rise and fall in fusain abundance and a rise in wood/periderm ratios. The stratigraphic distribution of identified coal resources in the United States is interpreted as largely dependent on net changes in relative wetness of Pennsylvanian coal swamps, a pattern of drying during the first period of vegetational change, followed by a concomitant increase in continuous wet climate with brackish influence in the Midcontinent during the second; this was followed by a time of extreme moisture stress bringing on the third, and most severe, vegetational change.

International Journal of Coal Geology↗
USGS1980

Circular current loops, magnetic dipoles and spherical harmonic analysis.

Spherical harmonic analysis (SHA) is the most used method of describing the Earth's magnetic field, even though spherical harmonic coefficients (SHC) almost completely defy interpretation in terms of real sources. Some moderately successful efforts have been made to represent the field in terms of dipoles placed in the core in an effort to have the model come closer to representing real sources. Dipole sources are only a first approximation to the real sources which are thought to be a very complicated network of electrical currents in the core of the Earth. -Author

Journal of Geomagnetism & Geoelectricity↗
USGS1998

Trilobites from Lower Mississippian starved basin facies of the southern United States

A distinctive trilobite fauna occurs within condensed stratigraphic sections of the Lower Mississippian (Tournaisian) Chappel Limestone of the Llano region of Texas, the Welden Limestone of Oklahoma, and the Chouteau Limestone of Union County, Illinois. The seven species comprising this fauna are interpreted to have inhabited sediment-starved basinal environments. The starved-basin facies existed in the south-central United States throughout the Tournaisian (Kinderhookian to Osagean). Two species from this fauna, Australosutura llanoensis, and Carbonocoryphe planucauda, are new. The remaining five species, Griffithidella doris (Hall), Griffithidella alternata (Girty), Carbonocoryphe depressa (Girty), Thigiffides roundyi (Girty), and Pudoproetus chappelensis (Hessler), are restricted to starved-basin facies.

Journal of Paleontology↗
USGS1996

Proceedings of the ocean drilling program: New Jersey continental slope and rise

The Scientific Results volumes of the Proceedings of the Ocean Drilling Program contain specialty papers presenting the results of extensive research in various aspects of scientific ocean drilling. The authors of the papers published in this volume have enabled future investigators to gain ready access to the results of their research, and I acknowledge their contributions with thanks. Each paper submitted to a Scientific Results volume undergoes rigorous peer review by at least two specialists in the author's research field. A paper typically goes through at least one revision cycle before being accepted for publication. We seek to maintain a peer-review system comparable to those of the most highly regarded journals in the geological sciences. Each Scientific Results volume has an Editorial Review Board that is responsible for obtaining peer reviews of papers submitted to the volume. This board usually is made up of the two co-chief scientists for the cruise, the ODP staff scientist for the cruise, and one external specialist who is familiar with the geology of the area investigated. In addition, the volume has an ODP staff editor who assists with manuscripts that require English-language attention and who coordinates volume assembly. Scientific Results volumes may also contain short reports of useful data that are not ready for final interpretation. Papers of this type, which may be found together in a section in the back of the volume, are called Data Reports and include no interpretation of results. Data Report papers are read carefully by at least one specialist to make sure they are well organized, comprehensive, and discuss the techniques or procedures thoroughly. To acknowledge the contributions made by this volume's Editorial Review Board, the Board members are designated Editors of the volume and are so listed on the title page. Reviewers of manuscripts for this volume, whose efforts are so essential to the success of the publication, are listed in the front of the book, without attribution to a particular manuscript. On behalf of the Ocean Drilling Program, I extend sincere appreciation to members of the Editorial Review Boards and to the reviewers for giving their generous contribution of time and effort, which ensures that only papers of high scientific quality are published in the Proceedings .

Book↗
USGS2016

Evidence for nonuniform permafrost degradation after fire in boreal landscapes

Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. We present a combination of multiscale remote sensing, geophysical, and field observations that reveal details of both near-surface (<1 m) and deeper (>1 m) impacts of fire on permafrost. Along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska, subsurface electrical resistivity and nuclear magnetic resonance data indicate locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be most vulnerable to future change, and also areas where permafrost has thawed. High-resolution geophysical data corroborate remote sensing interpretations of near-surface permafrost and also add new high-fidelity details of spatial heterogeneity that extend from the shallow subsurface to depths of about 10 m. Results show that postfire impacts on permafrost can be variable and depend on multiple factors such as fire severity, soil texture, soil moisture, and time since fire.

Alaska↗
USGS2018

Mass addition at Mount St. Helens, Washington, inferred from repeated gravity surveys

Measurements of subtle changes in the Earth’s gravityfield can provideinformation on the addition/loss of mass (e.g., magma or aqueousfluids) beneath a volcano. In this study, wemeasured gravity at Mount St. Helens from 2010 to 2016 to investigate possible mass changes followingthe 2004–2008 dome-forming eruption. The raw gravity measurements were corrected for changes in themass and shape of Crater Glacier and for deformation of the volcanic edifice to obtain residual gravity values.We found positive residual gravity changes that we interpret as evidence for partial recharge of the magmareservoir that fed the 2004–2008 eruption and/or for accumulation of groundwater in one or more shallowaquifers. Most of the gravity signal can be explained by groundwater accumulation; magma recharge is notrequired. However, there is additional evidence for at least partial recharge from seismic, deformation, andgeochemical observations

Washington↗
USGS2022

Rock alteration mapping in and around fossil shallow intrusions at Mt. Ruapehu New Zealand with laboratory and aerial hyperspectral imaging

Diagnostic absorption features in hyperspectral data can be used to identify a specific mineral or mineral associations. However, it is unknown how accurate hyperspectral mapping can be for identifying alteration mineral compositions at the resolution required to describe structures such as fossil intrusions, or whether it can accurately quantify the alteration present. This study compared petrographic observation with visible, near-infrared (VNIR), and shortwave infrared (SWIR) hyperspectral remote sensing at laboratory- (centimetre-scale) and aerial- (metre-scale) scales to characterise the abundance of surface hydrothermal rock alteration in and around a shallow fossil intrusion on Pinnacle Ridge, Mt. Ruapehu, New Zealand. We classified a high-resolution aerial hyperspectral image to develop a new surface alteration map using Spectral Angle Mapper (SAM) algorithm. The petrographic thin-section and the laboratory and aerial hyperspectral imaging revealed a spectrum of hydrous alteration phases as indicated by the presence of an absorption feature at 2207 nm. Moderate correlation exists between the depth of the absorption feature at 2207 nm and the point counting-derived alteration percent values, indicating reliability of laboratory-based hyperspectral analytical methods. In contrast, aerial hyperspectral data failed to provide any clear correlations to field-mapped alteration using a band-depth approach, and we interpret this due to ‘oversampling’ of surface (supergene) alteration, spectral mixing, and sensor limitations (e.g., bandwidth, signal-to-noise ratio). The hyperspectral image-derived alteration map, created using supervised image classification, can loosely be translated to a geotechnical map where porosity and permeability play a major role in localizing hydrothermal fluid flow and the formation of alteration mineral associations.

Mt. Ruapehu↗
USGS1996

Inelastic models of lithospheric stress - I. Theory and application to outer-rise plate deformation

Outer-rise stress distributions determined in the manner that mechanical engineers evaluate inelastic stress distributions within conventional materials are contrasted with those predicted using simple elastic-plate models that are frequently encountered in studies of outer-rise seismicity. This comparison indicates that the latter are inherently inappropriate for studies of intraplate earthquakes, which are a direct manifestation of lithospheric inelasticity. We demonstrate that the common practice of truncating elastically superimposed stress profiles so that they are not permitted to exceed laboratory-based estimates of lithospheric yield strength will result in an accurate characterization of lithospheric stress only under relatively restrictive circumstances. In contrast to elastic-plate models, which predict that lithospheric stress distributions depend exclusively upon the current load, inelastic plate models predict that stress distributions are also significantly influenced by the plate-loading history, and, in many cases, this influence is the dominant factor in determining the style of potential seismicity (e.g. thrust versus normal faulting). Numerous ‘intuitive’ interpretations of outer-rise earthquakes have been founded upon the implicit assumption that a unique relationship exists between a specified combination of plate curvature and in-plane force, and the resulting lithospheric stress distribution. We demonstrate that the profound influence of deformation history often invalidates such interpretations. Finally, we examine the reliability of ‘yield envelope’ representations of lithospheric strength that are constructed on the basis of empirically determined frictional sliding relationships and silicate plastic-flow laws. Although representations of this nature underestimate the strength of some major interplate faults, such as the San Andreas, they appear to represent a reliable characterization of the strength of intraplate oceanic lithosphere.

Geophysical Journal International↗