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USGS2012

Casual instrument corrections for short-period and broadband seismometers

Of all the filters applied to recordings of seismic waves, which include source, path, and site effects, the one we know most precisely is the instrument filter. Therefore, it behooves seismologists to accurately remove the effect of the instrument from raw seismograms. Applying instrument corrections allows analysis of the seismogram in terms of physical units (e.g., displacement or particle velocity of the Earth’s surface) instead of the output of the instrument (e.g., digital counts). The instrument correction can be considered the most fundamental processing step in seismology since it relates the raw data to an observable quantity of interest to seismologists. Complicating matters is the fact that, in practice, the term “instrument correction” refers to more than simply the seismometer. The instrument correction compensates for the complete recording system including the seismometer, telemetry, digitizer, and any anti‐alias filters. Knowledge of all these components is necessary to perform an accurate instrument correction. The subject of instrument corrections has been covered extensively in the literature (Seidl, 1980; Scherbaum, 1996). However, the prospect of applying instrument corrections still evokes angst among many seismologists—the authors of this paper included. There may be several reasons for this. For instance, the seminal paper by Seidl (1980) exists in a journal that is not currently available in electronic format and cannot be accessed online. Also, a standard method for applying instrument corrections involves the programs TRANSFER and EVALRESP in the Seismic Analysis Code (SAC) package (Goldstein et al. , 2003). The exact mathematical methods implemented in these codes are not thoroughly described in the documentation accompanying SAC.

Seismological Research Letters↗

USGS2024

Getting to the surface of the problem: A dynamic rupture benchmark for shallowly dipping faults near Earth’s surface

The Statewide California Earthquake Center (SCEC) Dynamic Rupture Group workshop “Getting to the Surface of the Problem: A Dynamic Rupture Benchmark for Shallowly-Dipping Faults Near Earth’s Surface” was convened virtually, in an online meeting on November 4, 2024. 52 people participated, including two who sent pre-recorded lightning talks earlier, but were unable to join us that day due to the international time-zone difference. One-half of our participants were students or postdocs, and the group included scientists from 11 countries (USA, Canada, China, Czech Republic, France, Germany, Iceland, Japan, New Zealand, Saudi Arabia, Switzerland).

Final Report↗

USGS2005

The life cycle of a mineral deposit: a teacher's guide for hands-on mineral education activities

This teacher's guide defines what a mineral deposit is and how a mineral deposit is identified and measured, how the mineral resources are extracted, and how the mining site is reclaimed; how minerals and mineral resources are processed; and how we use mineral resources in our every day lives. Included are 10 activitybased learning exercises that educate students on basic geologic concepts; the processes of finding, identifying, and extracting the resources from a mineral deposit; and the uses of minerals. The guide is intended for K through 12 Earth science teachers and students and is designed to meet the National Science Content Standards as defined by the National Research Council (1996). To assist in the understanding of some of the geology and mineral terms, see the Glossary (appendix 1) and Minerals and Their Uses (appendix 2). The process of finding or exploring for a mineral deposit, extracting or mining the resource, recovering the resource, also known as beneficiation, and reclaiming the land mined can be described as the “life cycle” of a mineral deposit. The complete process is time consuming and expensive, requiring the use of modern technology and equipment, and may take many years to complete. Sometimes one entity or company completes the entire process from discovery to reclamation, but often it requires multiple groups with specialized experience working together. Mineral deposits are the source of many important commodities, such as copper and gold, used by our society, but it is important to realize that mineral deposits are a nonrenewable resource. Once mined, they are exhausted, and another source must be found. New mineral deposits are being continuously created by the Earth but may take millions of years to form. Mineral deposits differ from renewable resources, such as agricultural and timber products, which may be replenished within a few months to several years.

General Information Product↗

USGS2013

The stability of sulfate and hydrated sulfate minerals near ambient conditions and their significance in environmental and planetary sciences

Sulfate and hydrated sulfate minerals are abundant and ubiquitous on the surface of the Earth and also on other planets and their satellites. The humidity-buffer technique has been applied to study the stability of some of these minerals at 0.1 MPa in terms of temperature-relative humidity space on the basis of hydration-dehydration reversal experiments. Updated phase relations in the binary system MgSO 4 -H 2 O are presented, as an example, to show how reliable thermodynamic data for these minerals could be obtained based on these experimental results and thermodynamic principles. This approach has been applied to sulfate and hydrated sulfate minerals of other metals, including Fe (both ferrous and ferric), Zn, Ni, Co, Cd, and Cu. Metal-sulfate salts play important roles in the cycling of metals and sulfate in terrestrial systems, and the number of phases extends well beyond the simple sulfate salts that have thus far been investigated experimentally. The oxidation of sulfide minerals, particularly pyrite, is a common process that initiates the formation of efflorescent metal-sulfate minerals. Also, the overall abundance of iron-bearing sulfate salts in nature reflects the fact that the weathering of pyrite or pyrrhotite is the ultimate source for many of these phases. Many aspects of their environmental significance are reviewed, particularly in acute effects to aquatic ecosystems related to the dissolution of sulfate salts during rain storms or snow-melt events. Hydrous Mg, Ca, and Fe sulfates were identified on Mars, with wide distribution and very large quantities at many locations, on the basis of spectroscopic observations from orbital remote sensing and surface explorations by rovers. However, many of these findings do not reveal the detailed information on the degree of hydration that is essential for rigorous interpretation of the hydrologic history of Mars. Laboratory experiments on stability fields, reactions pathways, and reaction rates of hydrous sulfates likely to be found on Mars enhance our understanding of the degrees of hydration of various sulfates that should currently exist on Mars at various seasons and locations and during various atmospheric pressure and obliquity periods. Two sets of systematic experiments were described; one on hydrous Mg sulfates and the other on hydrous Fe 3+ sulfates. Also, their implications to Mars sulfates mineralogy were discussed.

Journal of Asian Earth Sciences↗

USGS1951

Geologic history of sea water: An attempt to state the problem

Paleontology and biochemistry together may yield fairly definite information, eventually, about the paleochemistry of sea water and atmosphere. Several less conclusive lines of evidence now available suggest that the composition of both sea water and atmosphere may have varied somewhat during the past; but the geologic record indicates that these variations have probably been within relatively narrow limits. A primary problem is how conditions could have remained so nearly constant for so long. It is clear, even from inadequate data on the quantities and compositions of ancient sediments, that the more volatile materials—H 2 O, CO 2 , Cl, N, and S— are much too abundant in the present atmosphere, hydrosphere, and biosphere and in ancient sediments to be explained, like the commoner rock-forming oxides, as the products of rock weathering alone. If the earth were once entirely gaseous or molten, these “excess” volatiles may be residual from a primitive atmosphere. But if so, certain corollaries should follow about the quantity of water dissolved in the molten earth and the expected chemical effects of a highly acid, primitive ocean. These corollaries appear to be contradicted by the geologic record, and doubt is therefore cast on this hypothesis of a dense primitive atmosphere. It seems more probable that only a small fraction of the total “excess” volatiles was ever present at one time in the early atmosphere and ocean. Carbon plays a significant part in the chemistry of sea water and in the realm of living matter. The amount now buried as carbonates and organic carbon in sedimentary rocks is about 600 times as great as that in today's atmosphere, hydrosphere, and biosphere. If only 1/100 of this buried carbon were suddenly added to the present atmosphere and ocean, many species of marine organisms would probably be exterminated. Furthermore, unless CO 2 is being added continuously to the atmosphere-ocean system from some source other than rock weathering, the present rate of its subtraction by sedimentation would, in only a few million years, cause brucite to take the place of calcite as a common marine sediment. Apparently, the geologic record shows no evidence of such simultaneous extinctions of many species nor such deposits of brucite. Evidently the amount of CO 2 in the atmosphere and ocean has remained relatively constant throughout much of the geologic past. This calls for some source of gradual and continuous supply, over and above that from rock weathering and from the metamorphism of older sedimentary rocks. A clue to this source is afforded by the relative amounts of the different “excess” volatiles. These are similar to the relative amounts of the same materials in gases escaping from volcanoes, fumaroles, and hot springs and in gases occluded in igneous rocks. Conceivably, therefore, the hydrosphere and atmosphere may have come almost entirely from such plutonic gases. During the crystallization of magmas, volatiles such as H 2 O and CO 2 accumulate in the remaining melt and are largely expelled as part of the final fractions. Volcanic eruptions and lava flows have brought volatiles to the earth's surface throughout the geologic past; but intrusive rocks are probably a much more adequate source of the constituents of the atmosphere and hydrosphere. Judged by the thermal springs of the United States, hot springs (carrying only 1 per cent or less of juvenile matter) may be the principal channels by which the “excess” volatiles have escaped from cooling magmas below. This mechanism fails to account for a continuous supply of volatiles unless it also provides for a continuous generation of new, volatile-rich magmas. Possibly such local magmas form by a continuous process of selective fusion of subcrustal rocks, to a depth of several hundred kilometers below the more mobile areas of the crust. This would imply that the volume of the ocean has grown with time. On this point, geologic evidence permits differences of interpretation; the record admittedly does not prove, but it seems consistent with, an increasing growth of the continental masses and a progressive sinking of oceanic basins. Perhaps something like the following mechanism could account for a continuous escape of volatiles to the earth's surface and a relatively uniform composition of sea water through much of geologic time: (1) selective fusion of lower-melting fractions from deep-seated, nearly anhydrous rocks beneath the unstable continental margins and geosynclines; (2) rise of these selected fractions (as granitic and hydrous magmas) and their slow crystallization nearer the surface; (3) essentially continuous isostatic readjustment between the differentiating continental masses and adjacent ocean basins; and (4) renewed erosion and sedimentation, with resulting instability of continental margins and mountainous areas and a new round of selective fusion below.

Geological Society of America Bulletin↗

USGS1995

A mass proportion method for calculating melting reactions and application to melting of model upper mantle lherzolite

We present a method for calculating quantitative melting reactions in systems with multiple solid solutions that accounts for changes in the mass proportions of phases between two points at different temperatures along a melting curve. This method can be applied to any data set that defines the phase proportions along a melting curve. The method yields the net change in mass proportion of all phases for the chosen melting interval, and gives an average reaction for the melting path. Instantaneous melting reactions can be approximated closely by choosing sufficiently small melting intervals. As an application of the method, reactions for melting of model upper mantle peridotite are calculated using data from the system CaO-MgO-Al 2 O 3 -SiO 2 -Na 2 O (CMASN) over the pressure interval 0.7 – 3.5 GPa. Throughout almost this entire pressure range, melting of model lherzolite involves the crystallization of one or more solid phases, and is analogous to melting at a peritectic invariant point. In addition, we show that melting reactions for small melting intervals (< 5%) along the solidus of mantle peridotite are significantly different from those calculated for large melting intervals. For large melting intervals (> 10%), reaction stoichiometries calculated in CMASN are usually in good agreement with those available for melting of natural peridotite. The coefficients of melting reactions calculated from this method can be used in equations that describe the behavior of trace elements during melting. We compare results from near-fractional melting models using (1) melting reactions and rock modes from CMASN, and (2) constant reactions representative of those used in the literature. In modeling trace element abundances in melt, significant differences arise for some elements at low degrees of melting (< 10%). In modeling element abundances in the residue, differences increase with increase in degree of melting. Reactions calculated along the model lherzolite solidus in CMASN are the only ones available at present for small degrees of melting so we recommend them for accurate trace element modeling of natural lherzolite.

Earth and Planetary Science Letters↗

USGS2008

Probabilistic seismic hazard in the San Francisco Bay area based on a simplified viscoelastic cycle model of fault interactions

We construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time-dependent interseismic strain accumulation, coseismic strain release, and viscoelastic relaxation of the substrate beneath the seismogenic crust. For a given fault system, time-averaged stress changes at any point (not on a fault) are constrained to zero; that is, kinematic consistency is enforced for the fault system. The dates of last rupture, mean recurrence times, and the slip distributions of the (assumed) repeating ruptures are key inputs into the viscoelastic cycle model. This simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis (PSHA). Stress evolution is combined with a Coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures. In our PSHA we consider uncertainties in a four-dimensional parameter space: the rupture peridocities, slip distributions, time of last earthquake (for prehistoric ruptures) and Coulomb failure stress thresholds. We apply this methodology to the San Francisco Bay region using a recently determined fault chronology of area faults. Assuming single-segment rupture scenarios, we find that fature rupture probabilities of area faults in the coming decades are the highest for the southern Hayward, Rodgers Creek, and northern Calaveras faults. This conclusion is qualitatively similar to that of Working Group on California Earthquake Probabilities, but the probabilities derived here are significantly higher. Given that fault rupture probabilities are highly model-dependent, no single model should be used to assess to time-dependent rupture probabilities. We suggest that several models, including the present one, be used in a comprehensive PSHA methodology, as was done by Working Group on California Earthquake Probabilities.

Journal of Geophysical Research B: Solid Earth↗

USGS2024

How to select an objective function using information theory

In machine learning or scientific computing, model performance is measured with an objective function. But why choose one objective over another? According to the information-theoretic paradigm, the “best” objective function is whichever minimizes information loss. To evaluate different objectives, transform them into likelihoods. The ratios of these likelihoods represent how strongly we should prefer one objective versus another, and the log of that ratio represents the relative information loss (or gain) from one objective to another. In plain terms, minimizing information loss is equivalent to minimizing uncertainty, as well as maximizing probability and general utility. We argue that this paradigm is well-suited to models that have many uses and no definite utility like the complex Earth system models used to understand the effects of climate change. Furthermore, the benefits of “maximizing information and general utility” extend beyond model accuracy to other important considerations including how efficiently the model calibrates, how well it generalizes, and how well it compresses data.

Water Resources Research↗

USGS1998

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

From 1986 to 1997, the Pu'u 'O'o-Kupaianaha eruption of Kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10–12 km from vents on the volcano's east rift zone to the ocean. Within a kilometer of the vent, tubes were as much as 20 m high and 10–25 m wide. On steep slopes (4–10°) a little farther away from the vent, some tubes formed by roofing over of lava channels. Lava streams were typically 1–2 m deep flowing within a tube that here was typically 5 m high and 3 m wide. On the coastal plain (<1°), tubes within inflated sheet flows were completely filled, typically 1–2 m high, and several tens of meters wide. Tubes develop as a flow's crust grows on the top, bottom, and sides of the tubes, restricting the size of the fluid core. The tubes start out with nearly elliptical cross-sectional shapes, many times wider than high. Broad, flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts. Temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting. Sometimes, the tubes began downcutting. Progressive downcutting was frequently observed through skylights; a rate of 10 cm/d was measured at one skylight for nearly 2 months.

Journal of Geophysical Research B: Solid Earth↗

USGS2010

Initial Results from a Study of Climatic Changes and the Effect on Wild Sheep Habitat in Selected Study Areas of Alaska

Climate change theorists have projected striking changes in local weather on earth due to increases in temperature. These predicted changes may cause melting glaciers and ice caps, rising sea levels, increasing desertification and other environmental changes which seem likely to affect presumed indicator species as harbingers of more significant changes. Wild sheep, even though they are one of the more successful mammalian taxa since Pleistocene times, exhibit a suite of adaptations to glacier driven environments which may be presumed to render them sensitive to environmental changes. The authors began investigation with these assumptions by comparing changes, as determined by satellite imagery, in glacier extent in our study areas in Denali National Park, Alaska, during the last 30 years. Our findings showed the extent of glacial retreat in Alaska during this time period was approximately 40-50 percent as measured by ablation zone and retreat of terminal moraines. During the first half of this 30-year period, Dall sheep (Ovis dalli dalli) populations were stable at historically recorded highs. In the early to mid-1990s, Dall sheep populations in Alaska declined from an historical estimated high of 75,000 sheep to the presently estimated 40-50,000. The declines seemed to be weather related, on the basis of the presumption that lamb survival rates are primarily weather-mediated in Alaska. Changes in local weather appear, at this point, to be correlated with oscillation in the Pacific Current in the Northern Pacific ocean. Of course, changes in local weather affect forage abundance and quality seasonally. In investigating a possible linkage of weather to seasonal forage abundance and quality, we also investigated changes in snow and ice extent and distribution, as well as increased water runoff associated with permafrost and depleted glaciers. Databases were assembled from a wide variety of remotely sensed satellite data, ground-based observations, and historical data bases relating to Dall sheep habitats in selected study areas. Alaska's sheep habitats are typified by long, narrow bands of mountainous uplifts generally arrayed west-to-east, and perpendicular to prevailing south-to-north weather-front movements. Classic Dall sheep habitat occurs on snow-shadowed slopes within these narrow mountainous habitats. On the basis of these data, we offer an explanatory hypothesis relating Dall sheep welfare to weather and climate-influenced nutrition and a monitoring scheme, which should produce data sufficient to test the robustness of this hypothesis. If correlated with population changes, the methods used in our comparative observations may provide long-term monitoring tools for wildlife managers and be applicable in other widely-dispersed wild sheep habitats. If no significant correlations emerge from our modeling exercises, the notion that wild sheep are a sufficiently sensitive species to be seen as an indicator species will have to be reexamined.

Open-File Report↗

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

Satellite-derived aerosol radiative forcing from the 2004 British Columbia wildfires

The British Columbia wildfires of 2004 was one of the largest wildfire events in the last ten years in Canada. Both the shortwave and longwave smoke aerosol radiative forcing at the top-of-atmosphere (TOA) are investigated using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) instruments. Relationships between the radiative forcing fluxes (??F) and wildfire aerosol optical thickness (AOT) at 0.55 ??m (??0.55) are deduced for both noontime instantaneous forcing and diurnally averaged forcing. The noontime averaged instantaneous shortwave and longwave smoke aerosol radiative forcing at the TOA are 45.8??27.5 W m-2 and -12.6??6.9 W m-2, respectively for a selected study area between 62??N and 68??N in latitude and 125??W and 145??W in longitude over three mainly clear-sky days (23-25 June). The derived diurnally averaged smoke aerosol shortwave radiative forcing is 19.9??12.1 W m-2 for a mean ??0.55 of 1.88??0.71 over the same time period. The derived ??F-?? relationship can be implemented in the radiation scheme used in regional climate models to assess the effect of wildfire aerosols.

Atmosphere - Ocean↗

USGS2022

A global catalog of calibrated earthquake locations

We produced a globally distributed catalog of earthquakes and nuclear explosions with calibrated hypocenters, referred to as the Global Catalog of Calibrated Earthquake Locations (GCCEL). This dataset currently contains 18,782 events in 289 clusters with >3.2 million arrival times observed at 19,258 stations. The term “calibrated” refers to the property that the hypocenters are minimally biased by unknown Earth structure. In addition, we calculate uncertainties using empirically determined variability of the arrival‐time data itself, specific to each calibrated cluster of hypocenters. Outliers in the arrival‐time dataset are removed based on measured variability of the data. In each cluster, we estimate the empirically determined uncertainty for each set of station‐phase arrival times. We use a version of the hypocentroidal decomposition multiple event relocation algorithm specifically adapted for calibrated relocations of clusters of seismic events. Most clusters are calibrated by fitting the subset of direct crustal first arrivals ( Pg and Sg ) with a locally appropriate travel‐time model to estimate the cluster hypocentroid. A few clusters are calibrated by aligning the pattern of relative locations in space and time with one or more events for which a ground‐truth hypocenter is available from an independent source with known uncertainty, such as a nuclear explosion. Epicentral uncertainties in GCCEL typically range from 1 to 5 km with a 90% confidence interval. Most events have depth constraint from one or more sources, usually with an uncertainty of ≤5 km. GCCEL is a significant resource for research at local, regional, and global scales because it provides minimally biased absolute hypocenters, meaningful associated error estimates, and curated arrival times as a reference dataset that can be used as prior constraints in the development of new regional, national, and global earthquake catalogs; validation of new location techniques; and the generation of advanced Earth models.

Seismological Research Letters↗

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↗

USGS1968

Geology of the Great Smoky Mountains National Park, Tennessee and North Carolina

The boundary between Tennessee and North Carolina is delimited for about 50 miles in midlength by the crests of the Great Smoky Mountains, which include some of the highest summits in the southeastern United States, and which culminate in Clingmans Dome (alt 6,642 ft). Ramifying spurs and foothills descend northwestward from the State line divide toward the Appalachian Valley in Tennessee, as well as southeastward toward the less regularly disposed mountains of the main part of the Blue Ridge in North Carolina. All the Great Smoky Mountains are heavily forested, the higher summits being covered by spruce and fir, and the lower slopes, by a great variety of hardwoods. Much of this forested mountain wilderness has been set aside for public benefit and enjoyment as Great Smoky Mountains National Park. For most visitors to Great Smoky Mountains National Park, prime attractions are its noble forests, its open coves set gemlike amongst them, the animals of the forests and coves, and the relics of the mountaineers who have made their homes there. Only now and then, when the visitor's trail through the forest must circuit a rough ledge of rock, can he realize that the forest and the soil on which it grows are a mere veneer—a thin cover over the ancient rocks of the mountains. In the Yosemite, the Grand Canyon, and most of our other national parks in the West, the situation is very different; there, the impact of the bedrock of the parks is overwhelming in relation to the plants and animals that live on the bedrock. The terrain of the Great Smoky Mountains, their soils, unconsolidated deposits, and details of slope sculpture tell a geologic story of the last few million years of earth history, a story dominated by the drastic fluctuations of the ice-age climate. Although the mountains themselves were not covered with glacial ice, the climate at this latitude approached glacial conditions, and the mountaintops were occasionally above tree line. Deposits of debris that resulted from the associated accelerated erosion of the hillsides during glacial intervals and the deeply weathered soils produced during the episodes of warm and humid interglacial climate are evident at many places. These climatic oscillations also controlled the flora and fauna. The complex process of adjustment of plants and animals to the prevailing climate is one of the factors that has produced their present great diversity. This latest phase of the geologic history is not further treated in this publication. Maps showing the younger deposits and interpretations based on them are included in the several recent U.S. Geological Survey Professional Papers referred to below. Our concern in this text and its accompanying map (pl. 1) is with the bedrock geology of the Great Smoky Mountains and their surroundings, and with the story of far earlier times in earth history—when there were no Great Smoky Mountains, and when the geography and the landscape were very different from those today. Because of the forest cover and the scantiness of rock outcrops, the bedrock geology of the Great Smoky Mountains is not easy to decipher, and this difficulty is compounded by the enigmatic nature of most of the rocks themselves. It thus has come about that knowledge of the geology of the mountains has lagged behind that in surrounding regions. Following pioneer investigations of Safford (1869) and of Keith (1895, 1896), little further geologic study of the mountains was made until after World War II. The present text and map summarize the results of the more recent investigations, details of which are given at much greater length in a set of U.S. Geological Survey Professional Papers (Hamilton, 1961; Hadley and Goldsmith, 1963; King, 1964; Neuman and Nelson, 1965).

North Carolina, Tennessee↗

USGS1998

From polar wander to dynamic planet: A tribute to Keith Runcorn

The evolution of Keith Runcorn's ideas from the static, elastic Earth of Jeffreys to a dynamic, convecting planet are presented based on discussions as his colleague over 25 years from 1963 to his retirement in 1988. Keith reached the concept of a dynamic planet by way of polar wander and continental drift using palaeomagnetism with great zeal. It took some time for Keith to convince himself of the reality of continental drift. Once convinced, he became an evangelist converting others and enthusiastically pursuing possible mechanisms for explaining it, homing in on mantle convection. To establish the nature and history of mantle convection his interests ranged from the world rift system and satellite gravity anomalies to the radiometric age peaks. A great step forward occurred when we realised that a region of uprising convection was not necessary under all the rifts as had been commonly advocated in the 1960s and that the mid-Atlantic, African and Indian Ocean rifts could be equally well explained by one large region of upwelling mantle convection. It was also realised that the plate convergence zones (island arcs, trenches and deep focus earthquakes) were much better correlated with the satellite gravity anomalies and it was much easier to locate the possible regions of downwelling mantle convection. Now, seismic tomography helps to establish the nature of mantle convection and it appears that relations among the Earth's surface features, the geoid anomalies and peturbations of mantle seismic velocities are near to being established. In the next few years a far better and accurate picture of the geometry of mantle convection so enthusiastically advocated by Keith Runcorn is likely to be seen.

Physics and Chemistry of the Earth↗

USGS1980

Grooved terrain on Ganymede

The icy crust of Ganymede comprises bright and dark areas. Investigation of Voyager 1 and 2 images has shown that bright terrain is grooved and separates dark polygons of cratered terrain. The grooved terrain contains alternating ridges and grooves in straight and curvilinear sets, which are locally interrupted by smooth patches and swaths. Cratered terrain, where 'it occurs in small wedges and slivers, has a pervasive grain of narrowly spaced furrows, and thus is transitional to grooved terrain. An analysis of the morphology of terrain types, and of superposition and cross-cutting relations, suggests that grooved terrain grew at the expense of cratered terrain, that tracts of cratered terrain were converted into grooved terrain in situ , and that vertical tectonism and shear movements dominated in the restructuring of Ganymede's surface. It is postulated that during a period in the planet's history when the lithosphere was thin, upwelling convection currents caused incipient rifting accompanied by intensive normal faulting; where rifting went to completion, crustal segments separated, locally spread apart, and sheared past one another. In places subduction and compression may have occurred, but the evidence is inconclusive. Thus, the grooved terrain on Ganymede may record an early phase of ice-plate tectonics that caused rifting and drifting of the icy lithosphere, but, unlike silicate plate tectonics on Earth, may have resulted in only minor vertical turnover.

Icarus↗

USGS1970

Water as an urban resource and nuisance

Generally, when people speak of water as a resource, they are considering its good aspects and recognizing that it is essential for life and living. Sometimes or at some places or to some people, the same water may be annoying or unpleasant and thus a nuisance-for example, rain at a picnic, snow at any time except Christmas Eve, ground water in a basement, floodwater inundating personal property, and any water after it has been polluted by somebody else. For purposes of this circular, water as a resource will be defined more broadly and as a nuisance more narrowly. Water is part of the natural resource base including all aspects of the land, the air, and the water that must be considered in planning if an environment suitable for the well-being of all life is to be maintained. A nuisance, private or public, is a cause of annoyance, inconvenience, or injury that is an invasion or disturbance of the rights of some particular person or of members of a community, and it is punishable under the laws or customs accepted by the community. An activity harmful to mankind but widely practiced by the general public may be condoned by human laws and thus not be defined legally as a nuisance; the punishment for this activity is deterioration of the natural environment until it becomes unsuitable for living. The water resource, which is widely and irregularly distributed on earth, is available to man for such enjoyment and development and use as he sees fit, some use being essential to his existence. Natural variations in the quantity and quality of water are inevitable and, if they cause annoyance or injury to someone, are accepted as one of the hardships that this planet imposes upon its inhabitants; such variations are recognized as "acts of God." However, if any man or society is partly responsible for these variations, which may cause such annoyance or injury, and may become a nuisance (an invasion or disturbance of the rights of others) such a man or society may perhaps be subject to injunctions and damage suits. Legal disputes over water as a nuisance are generally deeply involved with problems of the respective rights of plaintiff and defendant. These respective rights vary among the States.

Circular↗