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At least 109 records · Page 6Linked to original sources
USGS2008

Seawater osmium isotope evidence for a middle Miocene flood basalt event in ferromanganese crust records

Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10??Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10??Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12??Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the No??rdlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum. ?? 2008 Elsevier B.V.

Earth and Planetary Science Letters↗
USGS2003

Geologic Map of the Aino Planitia (V46) Quadrangle, Venus 1:5,000,000

The Aino Planitia quadrangle (V-46) extends from 25?-50? S. latitude, 60?-90? E. longitude. The quadrangle was mapped at 1:5,000,000 scale as part of the NASA Planetary Geologic Mapping Program. Aino Planitia is a lowland region in the southern hemisphere of Venus and is southwest of Thetis Regio in western Aphrodite Terra. It is dominated by low-lying plains units that are characterized by northeast-trending wrinkle ridges and numerous small volcanic edifices, including shields, domes, and cones. The quadrangle contains a major volcano, Kunapipi Mons, and portions of Juno Chasma. A northern extension of the Lada Terra highland is in the southwestern portion of the map. Eight coronae are mapped in the quadrangle, the largest of which is the 500-km-diameter Copia Corona. The region is dominated by plains that are interpreted to be of volcanic origin. Most of the plains units are composites of flow units of differing ages. The overall topography of V-46 consists of low-lying plains slightly below Mean Planetary Radius (MPR, 6051.84 km). The summit of Kunapipi Mons is the highest point in the quadrangle, at about 2.2 km above MPR; the lowest points in rifts and troughs are at about 1.7 km below MPR. The regions that are the roughest at Magellan radar wavelengths in the quadrangle occur along the rim of Copia Corona, with most regions being relatively smooth (roughness comparable to the average Venus surface. Emissivity values in the quadrangle vary from 0.82-0.90.

IMAP↗
USGS1979

Earthquake prediction research at the Seismological Laboratory, California Institute of Technology

The Seismological Laboratory at the California Institute of Techonology (Caltech) was founded in 1928 as a result of a study by the Carnegie Institue of Washington. The study was based primarily on a 1916 report by H. O. Wood which recommended that a network of seismic stations be established in southern California. In 1929, the Carnegie Advisory Committee sponsored a conference at Caltech involving world authorities in seismology (fig. 1). Shortly thereafter, Beno Gutenberg was appointed to work at the Seismological Laboratory, although it was not until 1947 that he was formally names as director. He was succeeded in 1957 by Frank Press (now the President's Science Advisor) and in 1967 by Don Anderson. Much of the present research at the laboratory involves disciplines that did not exist 20 years ago. They included studies of the free oscillations of the Earth after a great earthquake, studies of the properties of rocks and minerals at high temperatures and pressures, construction of synthetic seismograms, and planetary seismology. Nevertheless, basic earthquake-related information has always been of consuming interest to the public and the media in this part of California (fig. 2.). So it is not surprising that earthquake prediction continues to be a significant reserach program at the laboratory. Several of the current spectrum of projects related to prediction are discussed below.

Earthquake Information Bulletin (USGS)↗
USGS2005

HRSC on Mars Express: Photogrammetric and cartographic research

The High Resolution Stereo Camera (HRSC) on the European spacecraft Mars Express is the first camera on a planetary mission especially designed for photogrammetric and cartographic purposes. Since January 2004 the camera has been taking image data from the Martian surface, characterized by high-resolution, stereo capability and color. These data provide an enormous potential for the generation of 3D surface models, color orthoimages, topographic and thematic maps, and additional products. The image data acquired undergo calibration and systematic processing to orthoimages and 3D data products. Within the international HRSC Science Team the members of the Photogrammetric/Cartographic Working Group are concerned with further refinements in order to achieve highest quality data products. These activities comprise improvements of the exterior orientation of the camera, various approaches to enhance DTM quality, and the generation of maps in the standard scale of 1:200 000 and larger scales as well. The paper reports on these activities and the results achieved so far .

Photogrammetric Engineering and Remote Sensing↗
USGS2021

A geologic field guide to S P Mountain and its lava flow, San Francisco Volcanic Field, Arizona

Introduction We created this guide to introduce the user to the San Francisco Volcanic Field as a terrestrial analog site for planetary volcanic processes. For decades, the San Francisco Volcanic Field has been used to teach scientists to recognize the products of common types of volcanic eruptions and associated volcanic features. The volcanic processes and products observed in this volcanic field are like those observed on lunar and Martian surfaces. As a result, this region has been a favored location for training National Aeronautics and Space Administration astronauts and engineers since the Apollo missions. Though the San Francisco Volcanic Field has more than 600 volcanic vents and flows, this guide will focus on S P Mountain (known locally as S P Crater, located ~30 miles north of Flagstaff, Arizona), one of the best preserved and most accessible of the volcanic cones and lava flows. S P Mountain presents both major types of basaltic eruptions—explosive and effusive—as well as some commonly associated tectonic landforms. We assume that the user has a basic understanding of geologic concepts and terminology. For more specialized terminology, we include tables showing the classification scheme for lava compositions, styles of eruptions, and tephra sizes (tables 1, 2, and 3). If a further introduction or refresher in volcanological terminology is desired, we suggest reviewing such terms on the U.S. Geological Survey Volcano Science Center’s online glossary ( https://volcanoes.usgs.gov/vsc/glossary/ ). One term requires clarification at the start of this guide—the term cinder. The terms cinder and cinder cone are widely used to describe the material and edifice produced by lava fountains. However, the term comes from the mining and construction industries and has no clear or formal definition. The international committees in geology and volcanology have chosen the term tephra to be the general term to describe pyroclasts (material ejected through a volcanic explosion or from a volcanic vent). Therefore, in this guide, we use the term tephra rather than cinder. This guide is outlined as follows: A brief tour of volcanism across the solar system A brief geologic history of the Colorado Plateau and San Francisco Volcanic Field Background on distributed volcanism and S P Mountain Driving directions and field stops Questions for discussion Each field stop includes a brief description, learning goals, tasks, and a summary of key points. At the end of the field guide are discussion points and questions that will ask the user to consider what they have observed and learned and how such knowledge can be used to better our understanding of geologic processes on other planetary bodies. Upon the completion of this field guide, we expect the user to: Have a basic understanding of the volcanic processes relevant to S P Mountain and its lava flow. Be able to identify different volcanic textures that are associated with tephra cones. Be aware of the different observations one can make at different scales (for example, observing lava flow morphology from aerial or satellite imagery versus tephra characteristics in the field).

Arizona↗
USGS1986

Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain

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

Earth and Planetary Science Letters↗
USGS1993

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

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

Earth and Planetary Science Letters↗
USGS1998

The Meteoritical Bulletin, No. 82, 1998 July

Meteoritical Bulletin No. 82 lists information for 974 new meteorites, including 521 finds from Antarctica, 401 finds from the Sahara, 21 finds from the Nullarbor region of Australia, and 7 falls (Ban Rong Du, Burnwell, Fermo, Jalanash, Juancheng, Monahans (1998), and Silao). Many rare types of meteorites are reported: counting pairing groups as one, these include one CR chondrite, two CK chondrites, two CO chondrites, four CV chondrites, one CH chondrite or Bencubbin-like, six C2 (unclassified) chondrites, two EH chondrites, two EL chondrites, three R chondrites, thirty unequilibrated ordinary chondrites, one ungrouped chondrite, three eucrites, six howardites, one diogenite, eleven ureilites, nine iron meteorites, one mesosiderite, two brachinites, one lodranite, one winonaite, and two lunar meteorites (Dar al Gani 400 and EET 96008). All italicized abbreviations refer to addresses tabulated at the end of this document. ?? Meteoritical Society, 1998.

Meteoritics and Planetary Science↗
USGS2003

Rivers, runoff, and reefs

The role of terrigenous sediment in controlling the occurrence of coral reef ecosystems is qualitatively understood and has been studied at local scales, but has not been systematically evaluated on a global-to-regional scale. Current concerns about degradation of reef environments and alteration of the hydrologic and sediment cycles place the issue at a focal point of multiple environmental concerns. We use a geospatial clustering of a coastal zone database of river and local runoff identified with 0.5?? grid cells to identify areas of high potential runoff effects, and combine this with a database of reported coral reef locations. Coastal cells with high runoff values are much less likely to contain reefs than low runoff cells and GIS buffer analysis demonstrates that this inhibition extends to offshore ocean cells as well. This analysis does not uniquely define the effects of sediment, since salinity, nutrients, and contaminants are potentially confounding variables also associated with runoff. However, sediment effects are likely to be a major factor and a basis is provided for extending the study to higher resolution with more specific variables. ?? 2003 Elsevier B.V. All rights reserved.

Global and Planetary Change↗
USGS2002

Mars Geodesy/Cartography Working Group recommendations on Mars cartographic constants and coordinate systems

NASA's Mars Geodesy/Cartography Working Group (MGCWG), established in 1998 and chaired since 2000 by one of us (TCD), consists of leading researchers in planetary geodesy and cartography at such diverse institutions as JPL, NASA Ames and Goddard Centers, Purdue and Ohio State Universities, Malin Space Science Systems, the German Center for Aerospace Research DLR, and the US Geological Survey, as well as representatives of the current and future Mars mission teams that are the customers for Mars maps. The purpose of the group is the coordinate the activities of the many agencies active in Mars geodesy and cartography in order to minimize redundant effort and ensure that the products needed by mission customers are generated. A specific objectives has been to avoid repeating the experience of the 1970s-80s, when competing researchers produced geodetic control solutions and maps of Mars that were mutually inconsistent. To this end, the MGCWG has recently assembled a set of preferred values for Mars cartographic constants, based on the best available data. These values have been transmitted to the International Astronomical Union and appear in the report of the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites as the officially recommended constants for Mars (Seidelmann et al., 2002). The MGCWG has also recommended to NASA that the USGS adopt the IAU-approved coordinate system of planetocentric latitude and east longitude for future maps of Mars, in the place of the (also IAU-approved) planetographic system with west longitude positive. This recommendation has recently been approved by NASA. In this paper we present the preferred values for Mars cartographic constants with discussion of the process by which they were derived, then discuss the rationale and implications of the use of east/planetocentric coordinates in future Mars maps.

Conference Paper↗
USGS1991

Major element, REE, and Pb, Nd and Sr isotopic geochemistry of Cenozoic volcanic rocks of eastern China: Implications for their origin from suboceanic-type mantle reservoirs

Major- and rare-earth-element (REE) concentrations and U Th Pb, Sm Nd, and Rb Sr isotope systematics are reported for Cenozoic volcanic rocks from northeastern and eastern China. These volcanic rocks, characteristically lacking the calc-alkaline suite of orogenic belts, were emplaced in a rift system which formed in response to the subduction of the western Pacific plate beneath the eastern Asiatic continental margin. The rocks sampled range from basanite and alkali olivine basalt, through olivine tholeiite and quartz tholeiite, to potassic basalts, alkali trachytes, pantellerite, and limburgite. These rock suites represent the volcanic centers of Datong, Hanobar, Kuandian, Changbaishan and Wudalianchi in northeastern China, and Mingxi in the Fujian Province of eastern China.

Earth and Planetary Science Letters↗
USGS1983

Fission track dating of kimberlitic zircons

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206 Pb and 238 U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0–1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ± 6.5 m.y.), Orapa (87.4 ± 5.7 and 92.4 ± 6.1 m.y.), Nzega (51.1 ± 3.8 m.y.), Koffiefontein (90.0 ± 8.2 m.y.), and Val do Queve (133.4 ± 11.5 m.y.). In addition we report the first radiometric ages (707.9 ± 59.6 and 705.5 ± 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption.

Earth and Planetary Science Letters↗
USGS2012

Geologic map of the Hecate Chasma quadrangle (V-28), Venus

The Hecate Chasma quadrangle (V–28) extends from lat 0° to 25° N. and from long 240° E. to 270° E. The quadrangle was mapped at 1:5,000,000 scale as part of the National Aeronautics and Space Administration (NASA) Planetary Geologic Mapping Program. Hecate Chasma is an extensive rift system consisting of multiple branches that lies in the lowland region of Hinemoa Planitia in the northern hemisphere of Venus. Here, we use the term “rift” and “chasma” (plural “chasmata”) to designate the trough and fracture zones that make up the Hecate system. Lineaments within the Hecate rift system that define Hecate, Zverine, and Hanwi Chasmata are mapped in red for emphasis. The system consists of several rifts and fracture belts, low-lying plains units, coronae and numerous small volcanic edifices including shields, domes and cones. The three branches of the Hecate rift system in this quadrangle are Hecate Chasma (centered at lat 18.2° N., long 254.3° E.), Zverine Chasma (centered at lat 18.5° N., long 271° E.), and Hanwi Chasma (centered at lat 10.5° N., long 247° E.). The quadrangle also contains many intermediate to large volcanoes, including Polik-mana Mons and Nazit Mons. Eighteen coronae are located in the quadrangle, the largest of which is the 525 km across Taranga Corona, along with fourteen impact craters. Corona maximum widths are measured to the outer edge of the annulus. Lineaments that form the corona annulus are mapped in green for emphasis. The overall topography of V–28 consists of plains located slightly below mean planetary radius (MPR, 6051.84). The lowest regions are found in the rift trough (3.3 m below MPR), and the highest along the rift rim (4.3 km above MPR). The regions that are the roughest at Magellan radar wavelengths in the quadrangle occur along Hecate Chasma (root mean square [rms] slopes >10°), with most regions being relatively smooth (roughnesses comparable to the average Venus surface value of 2.84°). Emissivity values in the quadrangle are typical of most venusian plains regions, with a range in values for the quadrangle of 0.68–0.91. The highest emissivity values in the quadrangle lie at the highest elevations in the quadrangle (corona rims and interiors).

Scientific Investigations Map↗
USGS1989

Review of magnetic and electric field effects near active faults and volcanoes in the U.S.A.

Synchronized measurements of geomagnetic field have been recorded along 800 km of the San Andreas fault and in the Long Valley caldera since 1974, and during eruptions on Mount St. Helens since 1980. For shorter periods of time, continuous measurements of geoelectric field measurements have been made on Mount St. Helens and near the San Andreas fault where moderate seismicity and fault slip frequently occurs. Significant tectonic and volcanic events for which nearby magnetic and electric field data have been obtained include: (1) two moderate earthquakes (ML > 5.8) for which magnetometers were close enough to expect observable signals (about three source lengths), (2) one moderate earthquake (MS 7.3) for which magnetometers were installed as massive fluid outflow occurred during the post-seismic phase, (3) numerous fault creep events and moderate seismicity, (4) a major explosive volcanic eruption and numerous minor extrusive eruptions, and (5) an episode of aseismic uplift. For one of the two earthquakes with ML > 5.8, seismomagnetic effects of -1.3 and -0.3 nT were observed. For this event, magnetometers were optimally located near the epicenter and the observations obtained are consistent with simple seismomagnetic models of the event. Similar models for the other event indicate that the expected seismomagnetic effects are below the signal resolution of the nearest magnetometer. Precursive tectonomagnetic effects were recorded on two independent instruments at distances of 30 and 50 km from a ML 5.2 earthquake. Longer-term changes were recorded in one region in southern California where a moderate ML 5.9 earthquake has since occurred. Surface observations of fault creep events have no associated magnetic or electrical signature above the present measurement precision (0.25 nT and 0.01%, respectively) and are consistent with near-surface fault failure models of these events. Longer-term creep is sometimes associated with corresponding longer-term magnetic field perturbations. Correlated changes in gravity, magnetic field, areal strain, and uplift occurred during episodes of aseismic deformation in southern California primarily between 1979 and 1983. Because the relationships between these parameters agrees with those calculated from simple deformation and tectonomagnetic models, the preferred explanation appeals to short-term strain episodes independently detected in each data set. An unknown source of meteorologically generated noise in the strain, gravity, and uplift data and an unknown, but correlated, disturbance in the absolute magnetic data might also explain the data. No clear observations of seismoelectric or tectonoelectric effects have yet been reported. The eruption of Mount St. Helens generated large oscillatory fields and 9 ?? 2 nT offset on the only surviving magnetometer. A large-scale traveling magnetic disturbance passed through the San Andreas array from 1 to 2 h after the eruption. Subsequent extrusive eruptions generated small precursory magnetic changes in some cases. These data are consistent with a simple volcanomagnetic model, magneto-gas dynamic effects, and a blast excited traveling ionospheric disturbance. Traveling ionospheric disturbances (TIDs), also generated by earthquake-related atmospheric pressure waves, may explain many electromagnetic disturbances apparently associated with earthquakes. Local near-fault magnetic field transients rarely exceed a few nT at periods of a few minutes and longer. ?? 1989.

Physics of the Earth and Planetary Interiors↗
USGS2021

Science and technology requirements to explore caves in our Solar System

We are in the incipient phase of exploring the subterranean realm of our Solar System. Planetary caves research offers interdisciplinary, cross-planetary body investigations spanning geology, climatology, astrobiology, robotics, and human use. Caves are of great importance in advancing our understanding of planetary processes and the search for life beyond Earth. Given these advances, a diverse and interdisciplinary community of planetary caves researchers has emerged. Their activities have been partially documented by a series of workshops and conferences over the last thirteen years (Titus & Boston, 2012; Wynne et al, 2016; Titus et al., 2020, submitted). These meetings brought together scientists and engineers from around the world to discuss both science needs (i.e., geology, habitability, and astrobiology), as well as engineering challenges (e.g., mobility, navigation, and communications) for cave research on other planetary bodies. It was determined at the last planetary caves conference that a goals and/or roadmap document, like those of the Assessment and Advisory Groups, was needed. This white paper is our initial conception of such an effort.

Bulletin of the AAS↗
USGS2002

A bibliography of terrain modeling (geomorphometry), the quantitative representation of topography: Supplement 4.0

Terrain modeling, the practice of ground-surface quantification, is an amalgam of Earth science, mathematics, engineering, and computer science. The discipline is known variously as geomorphometry (or simply morphometry), terrain analysis, and quantitative geomorphology. It continues to grow through myriad applications to hydrology, geohazards mapping, tectonics, sea-floor and planetary exploration, and other fields. Dating nominally to the co-founders of academic geography, Alexander von Humboldt (1808, 1817) and Carl Ritter (1826, 1828), the field was revolutionized late in the 20th Century by the computer manipulation of spatial arrays of terrain heights, or digital elevation models (DEMs), which can quantify and portray ground-surface form over large areas (Maune, 2001). Morphometric procedures are implemented routinely by commercial geographic information systems (GIS) as well as specialized software (Harvey and Eash, 1996; Köthe and others, 1996; ESRI, 1997; Drzewiecki et al., 1999; Dikau and Saurer, 1999; Djokic and Maidment, 2000; Wilson and Gallant, 2000; Breuer, 2001; Guth, 2001; Eastman, 2002). The new Earth Surface edition of the Journal of Geophysical Research, specializing in surficial processes, is the latest of many publication venues for terrain modeling. This is the fourth update of a bibliography and introduction to terrain modeling (Pike, 1993, 1995, 1996, 1999) designed to collect the diverse, scattered literature on surface measurement as a resource for the research community. The use of DEMs in science and technology continues to accelerate and diversify (Pike, 2000a). New work appears so frequently that a sampling must suffice to represent the vast literature. This report adds 1636 entries to the 4374 in the four earlier publications1. Forty-eight additional entries correct dead Internet links and other errors found in the prior listings. Chronicling the history of terrain modeling, many entries in this report predate the 1999 supplement. Coverage is representative from about 1800 through early–mid 2002. Papers increasingly are published exclusively or in duplicate on the Internet's World Wide Web; the dates given here for Web addresses (URLs) that lack a print publication indicate a Web site's last update or my last access of it. The bibliography is arranged alphabetically and thus is not readily summarized. This introduction cites about 500 entries, a third of them grouped under 24 morphometric topics, as a guide to the listing's contents. Continuing the practice of previous bibliographies in the series to provide more information on a few applications (see summary of past topics in Pike, 2000a), this report elaborates further on topographic data, putative new parameters, tectonic geomorphology/neo-orometry, biogeography, ice-cap morphometry, results from the Mars Global DEM, landslide-hazard mapping, terrain modeling as physics, Hack's law, and broad-scale computer visualization. The literature of some of these subjects is large, and none of the summaries is intended to more than introduce the topic and comment on some of the current contributions of terrain modeling. Closing the essay is a discussion of pre-1900 papers that trace the evolution of ridge-line and watercourse quantification by descriptive geometry, as well as comments on some new books and an on-line bulletin board.

Open-File Report↗
USGS2018

The 1952 Kern County, California earthquake: A case study of issues in the analysis of historical intensity data for estimation of source parameters

Seismic intensity data based on first-hand accounts of shaking give valuable insight into historical and early instrumental earthquakes. Comparing an observed intensity distribution to intensity-prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes. Magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available. However, the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties. In this paper, we illustrate these challenges and possible solutions using the 1952 Kern County, California, earthquake as a case study. Published estimates of its magnitude vary from M W 7.2–7.5, making it possibly the second largest in California during the 20th century. We considered over 1100 first-hand reports of shaking, supplemented with other data, and inferred the magnitude in several ways using intensity prediction equations, yielding a preferred intensity magnitude M I 7.2 ± 0.2, where the uncertainty reflects our judgement. The revised intensity distribution reveals stronger shaking on the hanging wall, south of the surface expression of the White Wolf fault, than on the footwall. Characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region. Such reinterpreted intensities for historic earthquakes, combined with U.S. Geological Survey (USGS) Did You Feel It? data for more recent events, can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed.

California↗
USGS2025

Triple-oxygen isotopic evidence of prolonged direct bioleaching of pyrite with O2

Sulfate is often touted as containing atmospheric oxygen whose isotopic signature can constrain redox, environmental conditions, and biological activity. Yet, the amount and isotopic fractionation associated with air-O 2 incorporation during sulfate formation is still debated, making its verification difficult. In this study, we identify a distinct, microbially dominated environment with the potential to preserve maximum signals of air-O 2 in sulfate. We report triple-oxygen isotope data for sulfate produced from pyrite oxidation in microbial and abiotic experiments, and from natural dissolved sulfate from the Rio Tinto, Spain, an acid mine drainage site. The oxygen isotope systematics of sulfate in these environments define a unique kinetic isotope effect associated with initial stage pyrite oxidation by Acidithiobacillus ferrooxidans that preserves >80 % oxygen from air-O 2 in sulfate. Unlike experiments, which evolve toward water-oxygen dominated sulfate on short time scales, Rio Tinto, Spain hosts a microbe rich environment with distinct geochemistry that maintains high O 2 -oxygen in sulfate. Therefore, in addition to containing isotopic records from water and air, sulfates can also contain a biosignature that is promising for understanding conditions on Mars and early Earth.

Earth and Planetary Science Letters↗