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At least 649 records · Page 36Linked to original sources

Absolute calibration accuracy of L4 TM and L5 TM sensor image pairs

The Landsat suite of satellites has collected the longest continuous archive of multispectral data of any land-observing space program. From the Landsat program's inception in 1972 to the present, the Earth science user community has benefited from a historical record of remotely sensed data. However, little attention has been paid to ensuring that the data are calibrated and comparable from mission to mission, Launched in 1982 and 1984 respectively, the Landsat 4 (L4) and Landsat 5 (L5) Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The approach involves comparing image statistics derived from large common areas observed eight days apart by the two sensors. The average percent differences in reflectance estimates obtained from the L4 TM agree with those from the L5 TM to within 15 percent. Additional work to characterize the absolute differences between the two sensors over the entire mission is in progress.

Conference Paper↗

Simple equations guide high-frequency surface-wave investigation techniques

We discuss five useful equations related to high-frequency surface-wave techniques and their implications in practice. These equations are theoretical results from published literature regarding source selection, data-acquisition parameters, resolution of a dispersion curve image in the frequency-velocity domain, and the cut-off frequency of high modes. The first equation suggests Rayleigh waves appear in the shortest offset when a source is located on the ground surface, which supports our observations that surface impact sources are the best source for surface-wave techniques. The second and third equations, based on the layered earth model, reveal a relationship between the optimal nearest offset in Rayleigh-wave data acquisition and seismic setting - the observed maximum and minimum phase velocities, and the maximum wavelength. Comparison among data acquired with different offsets at one test site confirms the better data were acquired with the suggested optimal nearest offset. The fourth equation illustrates that resolution of a dispersion curve image at a given frequency is directly proportional to the product of a length of a geophone array and the frequency. We used real-world data to verify the fourth equation. The last equation shows that the cut-off frequency of high modes of Love waves for a two-layer model is determined by shear-wave velocities and the thickness of the top layer. We applied this equation to Rayleigh waves and multi-layer models with the average velocity and obtained encouraging results. This equation not only endows with a criterion to distinguish high modes from numerical artifacts but also provides a straightforward means to resolve the depth to the half space of a layered earth model. ?? 2005 Elsevier Ltd. All rights reserved.

Soil Dynamics and Earthquake Engineering↗

U.S. Geological Survey climate and land use change science strategy—A framework for understanding and responding to global change

Executive Summary The U.S. Geological Survey (USGS), a nonregulatory Federal science agency with national scope and responsibilities, is uniquely positioned to serve the Nation’s needs in understanding and responding to global change, including changes in climate, water availability, sea level, land use and land cover, ecosystems, and global biogeochemical cycles. Global change is among the most challenging and formidable issues confronting our Nation and society. Scientists agree that global environmental changes during this century will have far-reaching societal implications (Intergovernmental Panel on Climate Change, 2007; U.S. Global Change Research Program, 2009). In the face of these challenges, the Nation can benefit greatly by using natural science information in decisionmaking. Since the passage of the U.S. Global Change Research Act of 1990, the USGS has made substantial scientific contributions to understanding the interactive living and nonliving components of the Earth system. USGS natural science activities have led to fundamental advances in observing and understanding climate and land-cover change and the effects these changes have on ecosystems, natural-resource availability, and societal sustainability. Most of these major advances were pursued in partnership with other organizations within and outside the Department of the Interior. The inherent value of partnerships with other U.S. Global Change Research Program agencies and natural-resource managers is emphasized in all aspects of the planning and implementation of this Science Strategy for the coming decade. Over the next 10 years, the USGS will make substantial contributions to understanding how Earth systems interact, respond to, and cause global change. The USGS will work with science partners, decisionmakers, and resource managers at local to international levels (including Native American tribes) to improve understanding of past and present change; develop relevant forecasts; and identify those lands, resources, and communities most vulnerable to global change processes. Science will play an essential role in helping communities and land and resource managers understand local to global implications, anticipate effects, prepare for changes, and reduce the risks associated with decisionmaking in a changing environment. USGS partners and stakeholders will benefit from the data, predictive models, and decision-support products and services resulting from the implementation of this strategy. This Science Strategy recognizes core USGS strengths that are applied to key societal problems. It establishes seven goals for USGS global change science and strategic actions that may be implemented in the short term (1–5 years) and the longer term (5–10 years) to improve our understanding of the following areas of inquiry: Rates, causes, and impacts of past global changes; The global carbon cycle; Biogeochemical cycles and their coupled interactions; Land-use and land-cover change rates, causes, and consequences; Droughts, floods, and water availability under changing land-use and climatic conditions; Coastal response to sea-level rise, climatic change, and human development; and Biological responses to global change. In addition to the seven thematic goals, we address the central role of monitoring in accordance with the USGS Science Strategy recommendation that global change research should rely on existing “…decades of observational data and long-term records to interpret consequences of climate variability and change to the Nation’s biological populations, ecosystems, and land and water resources” (U.S. Geological Survey, 2007, p. 19). We also briefly describe specific needs and opportunities for coordinating USGS global change science among USGS Mission Areas and address the need for a comprehensive and sustained communications strategy.

Circular↗

Cassini/VIMS observations of the moon

In this paper, we present preliminary scientific results obtained from the analysis of VIMS (Visible and Infrared Mapping Spectrometer) lunar images and spectra. These data were obtained during the Cassini Earth flyby in August 1999. Spectral ratios have been produced in order to derive lunar mineralogical maps. Some spectra observed at the north-east lunar limb, show few unusual absorption features located at 0.357, 0.430 and 0.452 ??m, the origin of which is presently unknown. ?? 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Advances in Space Research↗

Deglaciation, lake levels, and meltwater discharge in the Lake Michigan basin

The deglacial history of the Lake Michigan basin, including discharge and routing of meltwater, is complex because of the interaction among (1) glacial retreats and re-advances in the basin (2) the timing of occupation and the isostatic adjustment of lake outlets and (3) the depositional and erosional processes that left evidence of past lake levels. In the southern part of the basin, a restricted area little affected by differential isostasy, new studies of onshore and offshore areas allow refinement of a lake-level history that has evolved over 100 years. Important new data include the recognition of two periods of influx of meltwater from Lake Agassiz into the basin and details of the highstands gleaned from sedimentological evidence. Major disagreements still persist concerning the exact timing and lake-level changes associated with the Algonquin phase, approximately 11,000 BP. A wide variety of independent data suggests that the Lake Michigan Lobe was thin, unstable, and subject to rapid advances and retreats. Consequently, lake-level changes were commonly abrupt and stable shorelines were short-lived. The long-held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge-line discontinuity are becoming difficult to maintain. Numerical modeling of the ice-earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake-level gauges. New studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal Glenwood level. Finally, the Lake Michigan region as a whole appears to behave in a similar manner to other areas, both local (other Great Lakes) and regional (U.S. east coast), that have experienced major isostatic changes. Detailed sedimentological and dating studies of field sites and additional development of geophysical models offer hope for reconciling the field data with our understanding of earth rheology. ?? 1995.

Lake Michigan Basin↗

Geologic characteristics of sediment- and volcanic-hosted disseminated gold deposits - Search for an occurrence model

The current expansion of resource information, particularly on "disseminated" gold, and the improved technologies now available for resource investigations should place us in an enhanced position for developing a better predictive methodology for meeting one of the important responsibilities of the U.S. Geological Survey-to examine and assess the mineral resources of the geologic terranes composing the public (and privately owned) lands of the United States. The first step is systematic organization of these data. Geologic-occurrence models are an effective systematic method by which to organize large amounts of resource information into a logical sequence facilitating its use more effectively in meeting several industry and Survey objectives, which include the exploration for resources and the assessment of resource potential for land-use decisions. Such models also provide a scientific basis for metallogenesis research, which considers the observable features or attributes of ore occurrence and their "fit" into the Earth's resource puzzle. The use of models in making resource assessments/appraisals was addressed by Shawe (1981), who reported the results of a workshop on methods for resource appraisal of Wilderness and Conterminous United States Mineral Appraisal Program (CUSMAP; 1:250,000-scale quadrangles) areas. The Survey's main objective in the 1982 workshop was to evaluate the status of knowledge about disseminated or very fine grained gold deposits and, if possible, to develop an occurrence model(s). This report on the workshop proceedings has three main objectives: (1) Education through the publication of a summary review and presentation of new thinking and observations about the scientific bases for those geologic processes and environments that foster disseminated gold-ore formation; (2) systematic organization of available geologic, geochemical, and geophysical information for a range of typical disseminated gold deposits (including recognition of gaps in those data); and (3) assessment of current understanding (as presented in objective 2) toward formulating an empirical ore-occurrence model for this type of deposit. As such, this volume represents a preliminary first step at classification and provides a source of pertinent background information. Readers of this volume will soon discover, however, that full agreement has not yet been achieved in the interpretation of some of the geologic evidence. The resulting variations in tentative occurrence models for these controversial deposits ultimately will be resolved by filling the gaps in information that have already been identified. Thus, this volume does not report a U.S. Geological Survey consensus; the conclusions expressed in each chapter represent the particular interpretations of the various workshop participants.

Arizona, California, Idaho, Nevada, Utah↗

Possible solar noble-gas component in Hawaiian basalts

The noble-gas elemental and isotopic composition in the Earth is significantly different from that of the present atmosphere, and provides an important clue to the origin and history of the Earth and its atmosphere. Possible candidates for the noble-gas composition of the primordial Earth include a solar-like component, a planetary-like component (as observed in primitive meteorites) and a component similar in composition to the present atmosphere. In an attempt to identify the contributions of such components, we have measured isotope ratios of helium and neon in fresh basaltic glasses dredged from Loihi seamount and the East Rift Zone of Kilauea 1–3 . We find a systematic enrichment in 20 Ne and 21 Ne relative to 22 Ne, compared with atmospheric neon. The helium and neon isotope signatures observed in our samples can be explained by mixing of solar, present atmospheric, radiogenic and nucleogenic components. These data suggest that the noble-gas isotopic composition of the mantle source of the Hawaiian plume is different from that of the present atmosphere, and that it includes a significant solar-like component. We infer that this component was acquired during the formation of the Earth.

Hawaii↗

Quantifying uncertainty for remote spectroscopy of surface composition

Remote surface measurements by imaging spectrometers play an important role in planetary and Earth science. To make these measurements, investigators calibrate instrument data to absolute units, invert physical models to estimate atmospheric effects, and then determine surface properties from the spectral reflectance. This study quantifies the uncertainty in this process. Global missions demand predictive uncertainty models that can estimate future errors for varied environments and observing conditions. Here we validate uncertainty predictions with remote surface composition retrievals and in situ measurements in a field analogue of Earth and planetary exploration. We consider rover transects at Cuprite, Nevada, and remote observations by NASA's Next- Generation Airborne Visible Infrared Imaging Spectrometer (AVIRIS-NG). We show that accounting for input uncertainties can benefit mineral detection methods such as constrained spectrum fitting. This suggests that operational uncertainty estimates could improve future NASA missions like the Earth Mineral dust source InvesTigation (EMIT) and the Lunar Trailblazer mission, as well as NASA's Decadal Surface Biology and Geology (SBG) Investigation.

Remote Sensing of Environment↗

Assessment of Mars Pathfinder landing site predictions

Remote sensing data at scales of kilometers and an Earth analog were used to accurately predict the characteristics of the Mars Pathfinder landing site at a scale of meters. The surface surrounding the Mars Pathfinder lander in Ares Vallis appears consistent with orbital interpretations, namely, that it would be a rocky plain composed of materials deposited by catastrophic floods. The surface and observed maximum clast size appears similar to predictions based on an analogous surface of the Ephrata Fan in the Channeled Scabland of Washington state. The elevation of the site measured by relatively small footprint delay-Doppler radar is within 100 m of that determined by two-way ranging and Doppler tracking of the spacecraft. The nearly equal elevations of the Mars Pathfinder and Viking Lander 1 sites allowed a prediction of the atmospheric conditions with altitude (pressure, temperature, and winds) that were well within the entry, descent, and landing design margins. High-resolution (~38 m/pixel) Viking Orbiter 1 images showed a sparsely cratered surface with small knobs with relatively low slopes, consistent with observations of these features from the lander. Measured rock abundance is within 10% of that expected from Viking orbiter thermal observations and models. The fractional area covered by large, potentially hazardous rocks observed is similar to that estimated from model rock distributions based on data from the Viking landing sites, Earth analog sites, and total rock abundance. The bulk and fine-component thermal inertias measured from orbit are similar to those calculated from the observed rock size-frequency distribution. A simple radar echo model based on the reflectivity of the soil (estimated from its bulk density), and the measured fraction of area covered by rocks was used to approximate the quasi-specular and diffuse components of the Earth-based radar echos. Color and albedo orbiter data were used to predict the relatively dust free or unweathered surface around the Pathfinder lander compared to the Viking landing sites. Comparisons with the experiences of selecting the Viking landing sites demonstrate the enormous benefit the Viking data and its analyses and models had on the successful predictions of the Pathfinder site. The Pathfinder experience demonstrates that, in certain locations, geologic processes observed in orbiter data can be used to infer surface characteristics where those processes dominate over other processes affecting the Martian surface layer. Copyright 1999 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

Capacity assessment for Earth Monitoring, Analysis, and Prediction (EarthMAP) and future integrated monitoring and predictive science at the U.S. Geological Survey

Executive Summary Managers of our Nation’s resources face unprecedented challenges driven by the convergence of increasing, competing societal demands and a changing climate that affects the stability, vulnerability, and predictability of those resources. To help meet these challenges, the scientific community must take advantage of all available technologies, data, and integrative Earth systems modeling capacity to better inform resource and risk management decisions. This is the overarching goal of the U.S. Geological Survey (USGS) Earth Monitoring, Analysis, and Prediction (EarthMAP) vision: “By 2030, the USGS will deliver well integrated observations and predictions of the future state of natural systems—water, ecosystems, energy, minerals, hazards—at regional and national scales, working primarily with federal, state, and academic partners to develop and operate the capability” (U.S. Geological Survey, 2021). Providing more integrated Earth systems science and actionable information to decision makers, stakeholders, and the public requires a better understanding of the depth and distribution of existing capacity (capabilities, tools, and techniques) across the Bureau. Identifying existing capacity is also a critical first step toward gap analysis and targeted investments to increase capacity over time. The USGS formed a Capacity Assessment Team (CAT) and charged it with (1) conducting a Request for Information (RFI) to identify existing USGS expertise and activities supportive of integrated and predictive science to inform decision making, (2) developing a strategy and proof-of-concept for a continuously updated capacity assessment capability, and (3) identifying lessons learned to inform development of best practices for future capacity assessment efforts. The RFI took the form of a survey, with content guided by the science and technology needs identified in a USGS report titled “Grand Challenges for Integrated U.S. Geological Survey Science—A Workshop Report” (Jenni and others, 2017). The 44-question survey provided respondents the ability to rate their level of experience with a suite of priority disciplines, analysis and modeling approaches, technologies, and stakeholder engagement strategies and to enter optional narrative text for supporting context. An introductory portion focused on general science capacity assessment, followed by three sections targeting capabilities related to the foundational components of EarthMAP: (1) data and information integration, (2) integrated predictive science, and (3) actionable information. The survey results provided a high-level snapshot of USGS capacity in the targeted areas. Respondents (1,035 individuals) represented approximately 13 percent of the USGS across all mission areas and regions. Seventy-four percent of the respondents held a science-focused position title and the remainder had position titles in information technology, computer science, management, administrative, or other (contractors, volunteers, emeritus, and unknown). To provide greater insight into respondent capabilities and activities, information from the U.S. Department of the Interior and USGS enterprise information systems were used to further characterize topical expertise and organizational associations of survey respondents. To address the ongoing need to assess the Bureau’s capacity to address integrated predictive science priorities, the CAT developed a software-based proof-of-concept called the Integrated Science Assessment Information Database (iSAID) for assembling various information sources together toward making the full extent of USGS capabilities and scientific assets available for routine capacity assessment. This proof-of-concept is intended to serve as a catalyst for further development. The process of implementing the EarthMAP capacity assessment survey, analyzing survey responses, and developing the proof-of-concept resulted in lessons learned, findings, and recommendations. Example scenarios throughout the report demonstrate how capacity assessment data can inform science planning. Three overarching findings and recommendations are: (1) Finding: Capacity is limited in some critical disciplines, skills, and technology applications, but “sufficient” depends on the question and the need relative to availability at a given point in time. Recommendation: Develop an on-demand capacity assessment framework that enables rapid identification and evaluation of existing and available expertise to support decision needs as they arise. (2) Finding: Institutional barriers and lack of awareness constrain the ability of USGS staff to adopt new technologies, collaborate across administrative boundaries, and deliver actionable information to stakeholders in a timely manner. However, these barriers are not universally experienced. Recommendation: Pursue more targeted inquiries to clarify which institutional barriers are obstructing the adoption of new technologies and approaches or the sharing of expertise and equipment across organizational and regional boundaries. These inquiries should inform USGS leadership, mission areas, and regions whether policies can be revised or whether a lack of understanding is creating perceived obstacles. Highlight cases when staff have successfully adopted new technologies and approaches to advance EarthMAP priorities and provide actionable information in a timely manner to spread awareness of how perceived obstacles can be navigated and overcome when appropriate. (3) Finding: Examples of people and projects integrating across disciplines and scales and applying advanced approaches to meet complex stakeholder needs exist. Such examples provide transfer value across the spectrum from approach to decision making. Many projects, already underway, appear to meet elements of the EarthMAP vision, and the USGS has people who can provide leadership in multiple types of specific integrated science efforts. Recommendation: Use these findings as a starting point for near-term strategic planning for integrated science. Highlight, incentivize, and build on existing interdisciplinary predictive science and information delivery activities across the USGS to advance toward further realization of an EarthMAP capacity. The CAT efforts to develop and assess existing USGS capacity to advance the EarthMAP vision revealed a fundamental challenge for not only this effort but any effort to assess existing capacity: A considerable amount of thought, time, and effort is required to survey and assess capabilities and tools available to support a given need, yet best results are still likely to provide an incomplete assessment. To better meet the frequent need to assess capabilities, tools, products, and projects that address an expressed strategic priority, the CAT proposes the concept of an on-demand capacity assessment framework supported by a software package that dynamically pulls and integrates information from existing USGS information systems and public domain registries. Although existing USGS enterprise information systems currently lack the structure, cross-system consistency, interoperability, and stability to support a continuously updated capacity assessment capability, we identify reasonable near-term steps to improve the utility of information gathered on expertise and project capacity and to improve the consistency and completeness of information and the ability of USGS systems to share that information. The ability to search and characterize this information will make future assessments of capacity faster, more complete, more efficient, and more targeted. This approach would grow the Bureau’s capacity knowledge over time, iteratively improving the ability to access, leverage, and synthesize existing capabilities and assets as well as identify and fill critical gaps. The greatest promise for developing integrated science could lie in linking across existing projects and expertise to create a multi-project capacity for addressing large, complex environmental issues.

Open-File Report↗

Streamflow and surface-water presence data availability across the conterminous United States: A review for headwater systems

Water is essential for life on Earth, supporting ecosystems, human health, and economic activities. Hydrology relies on observational data, and this paper discusses regional and national datasets for the conterminous United States (CONUS) publicly available as of 2023, focusing on headwaters, defined as first- and second-order streams at 1:24000 scale. It identifies 72 primary and secondary datasets and 11 repositories and argues how better integration and accessibility of hydrological data can improve research. The paper distinguishes between datasets where streamflow was the primary data collection objective and those where it was secondary. This distinction highlights opportunities to consider data from efforts peripheral to hydrology but is still useful for understanding hydrologic conditions. The analysis reveals that out of about 118 000 active and inactive stream observation sites, about 6.6% and 25% are located on first- and second-order streams, respectively. This indicates a substantial data gap for headwater systems, which account for over 77% of stream length in CONUS. Federal agencies manage 72% of hydrologic monitoring sites across all stream orders, but only 34% of these are in headwater systems. Academic institutions operate about 2% of sites, with almost half (48%) in headwater systems, focusing on ecosystem research. State agencies also operate about 2% of sites, primarily on larger systems, with 19% on headwaters. Additionally, 23% of sites are managed by multiple agencies. Spatial patterns further reveal pronounced disparities among physiographic regions. Eastern and coastal provinces show relatively dense monitoring, while central and western regions show sparse coverage. These gaps reflect historical priorities, logistical constraints, funding limitations, and the high cost of continuous instrumentation. To address biases in monitoring networks, data collection could be enhanced with low-cost monitoring, community science, and remote sensing technologies. This study also notes the benefits of long-term monitoring and prioritizing retention of streamgages with longer records.

conterminous United States↗

Emplacement and differentiation of the york haven diabase sheet, Pennsylvania

Many of the high-Ti quartz-normative tholeiitic intrusive sheets in the early Mesozoic rift basins of the Eastern USA exhibit lateral differentiation from mafic cumulate units, through diabase, to relatively evolved iron-rich rock types. We have investigated a representative example in detail, the York Haven sheet in the Gettysburg basin of south-central Pennsylvania. It ranges in thickness from 330 m to 675 m, and we have sampled it from base to top along four separate stratigraphic sections evenly spaced over the extent of the intrusion. The easternmost section (York Haven) is entirely basaltic bronzite cumulate (average 15 vol. % bronzite), whereas the westernmost (Reesers Summit) consists of diabase and low-MgO diabase with a middle to upper 'sandwich zone' of ferrogabbro. The intervening sections feature rock types transitional between the two end-member sequences. Chemically, the rock series shows a gradual east to west depletion of compatible elements (Mg, Ca, Ni, and Cr), and enrichment of incompatible elements [Ti, Fe, Na, K, P, Cu, Zr, Th, Ta, Hf, Sb, Cs, As, platinum group elements (PGEs), and rare earth elements (REEs)].We suggest two main processes for the trends observed in the York Haven sheet. First, flow differentiation during ascent and lateral injection of the parental magma produced a tongue of basaltic bronzite cumulate that thins from southeast to northwest and passes laterally into diabase, and, at the distal end of the intrusion, into low-MgO diabase. Then, in the latter stages of crystallization, densitydriven hydrothermal fluids transported incompatible elements westward, into structurally higher parts of the intrusion. Reaction of this residual aqueous fluid with partly crystallized low-MgO diabase produced a zone of ferrogabbro rich in hydrothermal replacement products (e.g., Cl-amphibole, biotite, ferrohypersthene, and skeletal ilmenite) and precipitates (e.g., quartz, fayalite, Cl-apatite, sulfides, and PGE minerals). © 1993 Oxford University Press.

Pennsylvania↗

Track of the Yellowstone hotspot: Young and ongoing geologic processes from the Snake River Plain to the Yellowstone Plateau and Tetons

This field trip highlights various stages in the evolution of the Snake River Plain–Yellowstone Plateau bimodal volcanic province, and associated faulting and uplift, also known as the track of the Yellowstone hotspot. The 16 Ma Yellowstone hotspot track is one of the few places on Earth where time-transgressive processes on continental crust can be observed in the volcanic and tectonic (faulting and uplift) record at the rate and direction predicted by plate motion. Recent interest in young and possible renewed volcanism at Yellowstone along with new discoveries and synthesis of previous studies, i.e., tomographic, deformation, bathymetric, and seismic surveys, provide a framework of evidence of plate motion over a mantle plume. This 3-day trip is organized to present an overview into volcanism and tectonism in this dynamically active region. Field trip stops will include the young basaltic Craters of the Moon, exposures of 12–4 Ma rhyolites and edges of their associated collapsed calderas on the Snake River Plain, and exposures of faults which show an age progression similar to the volcanic fields. An essential stop is Yellowstone National Park, where the last major caldera-forming event occurred 640,000 years ago and now is host to the world's largest concentration of hydrothermal features (>10,000 hot springs and geysers). This trip presents a quick, intensive overview into volcanism and tectonism in this dynamically active region. Field stops are directly linked to conceptual models related to hotspot passage through this volcano-tectonic province. Features that may reflect a tilted thermal mantle plume suggested in recent tomographic studies will be examined. The drive home will pass through Grand Teton National Park, where the Teton Range is currently rising in response to the passage of the North American plate over the Yellowstone hotspot.

Idaho, Wyoming↗

Sedimentary basin effects in Seattle, Washington: Ground-motion observations and 3D simulations

Seismograms of local earthquakes recorded in Seattle exhibit surface waves in the Seattle basin and basin-edge focusing of S waves. Spectral ratios of Swaves and later arrivals at 1 Hz for stiff-soil sites in the Seattle basin show a dependence on the direction to the earthquake, with earthquakes to the south and southwest producing higher average amplification. Earthquakes to the southwest typically produce larger basin surface waves relative to S waves than earthquakes to the north and northwest, probably because of the velocity contrast across the Seattle fault along the southern margin of the Seattle basin. S to P conversions are observed for some events and are likely converted at the bottom of the Seattle basin. We model five earthquakes, including the M 6.8 Nisqually earthquake, using 3D finite-difference simulations accurate up to 1 Hz. The simulations reproduce the observed dependence of amplification on the direction to the earthquake. The simulations generally match the timing and character of basin surface waves observed for many events. The 3D simulation for the Nisqually earth-quake produces focusing of S waves along the southern margin of the Seattle basin near the area in west Seattle that experienced increased chimney damage from the earthquake, similar to the results of the higher-frequency 2D simulation reported by Stephenson et al. (2006). Waveforms from the 3D simulations show reasonable agreement with the data at low frequencies (0.2-0.4 Hz) for the Nisqually earthquake and an M 4.8 deep earthquake west of Seattle.

Bulletin of the Seismological Society of America↗

Fractionation of metal stable isotopes by higher plants

Higher plants induce chemical reactions in the rhizosphere, facilitating metal uptake by roots. Fractionation of the isotopes in nutrients such as calcium, iron, magnesium, and zinc produces a stable isotope composition in the plants that generally differs from that of the growth medium. Isotope fractionation also occurs during transport of the metals within most plants, but its extent depends on plant species and on the metal, in particular, on the metal's redox state and what ligand it is bound to. The metal stable isotope variations observed in plants create an isotope signature of life at the Earth's surface, contributing substantially to our understanding of metal cycling processes in the environment and in individual organisms.

Elements↗

Landscape change associated with the upper Scenic Drive landslide, La Honda, California, January 10–June 28, 2017

La Honda, California, is a small town in unincorporated San Mateo County, located on the west edge of the San Francisco Peninsula in the Santa Cruz Mountains, between San Francisco and San Jose. The Scenic Drive area of La Honda has experienced several past episodes of landslide motion, which were documented in 1998, 2005, and 2006. This report documents the movement of the upper Scenic Drive landslide that occurred between January 10 and June 28, 2017. Our mapping provides a snapshot of the 2017 upper Scenic Drive landslide, as imaged from high-resolution terrestrial laser scanner (TLS) survey data (also referred to as terrestrial lidar) that we collected January 27–28, 2017; we mapped the landforms associated with the 2017 upper Scenic Drive landslide motion using a bare-earth TLS shaded-relief base map, in addition to field observations. Our mapping is supplemented by photographs of the mapped landforms, which were taken between January 11 and 31, 2017; these photographs illustrate the development of selected landslide features. The purpose of this report is to make available the maps constructed from three-dimensional TLS data and the photographs that show the landslide morphology of the 2017 upper Scenic Drive landslide. The scope of this report is limited to the motion of the upper Scenic Drive landslide that occurred between January 10 and June 28, 2017.

California↗

Geologic field-trip guide to the volcanic and hydrothermal landscape of the Yellowstone Plateau

Yellowstone National Park, a nearly 9,000 km 2 (~3,468 mi 2 ) area, was preserved in 1872 as the world’s first national park for its unique, extraordinary, and magnificent natural features. Rimmed by a crescent of older mountainous terrain, Yellowstone National Park has at its core the Quaternary Yellowstone Plateau, an undulating landscape shaped by forces of late Cenozoic explosive and effusive volcanism, on-going tectonism, glaciation, and hydrothermal activity. The Yellowstone Caldera is the centerpiece of the Yellowstone Plateau. The Yellowstone Plateau lies at the most northeastern front of the 17-Ma Yellowstone hot spot track, one of the few places on Earth where time-transgressive processes on continental crust can be observed in the volcanic and tectonic (faulting and uplift) record at the rate and direction predicted by plate motion. Over six days, this field trip presents an intensive overview into volcanism, tectonism, and hydrothermal activity on the Yellowstone Plateau (fig. 1). Field stops are linked directly to conceptual models related to monitoring of the various volcanic, geochemical, hydrothermal, and tectonic aspects of the greater Yellowstone system. Recent interest in young and possible future volcanism at Yellowstone as well as new discoveries and synthesis of previous studies, (for example, tomographic, deformation, gas, aeromagnetic, bathymetric, and seismic surveys), provide a framework in which to discuss volcanic, hydrothermal, and seismic activity in this dynamic region.

Yellowstone Plateau↗

GRACE and GRACE Follow-On gravity observations of intermediate-depth earthquakes contrasted with those of shallow events

Earthquakes involve mass redistribution within the solid Earth and the ocean, and as a result, perturb the Earth's gravitational field. For most of the shallow (<60 km) earthquakes with M w > 8.0, the GRACE satellite gravity measurements suggest considerable volumetric disturbance of rocks. At a spatial scale of hundreds of km, the effect of volumetric change exceeds gravity change by vertical deformation; for example, negative gravity anomalies associated with volumetric expansion are characteristic patterns after shallow thrust events. In this study, however, we report contrasting observations of gravity change from two intermediate-depth (100–150 km) earthquakes of 2016 & 2017 Mw 8.0 (two combined) Papua New Guinea thrust faulting events and 2019 Mw 8.0 Peru normal faulting and highlight the importance of compressibility in earthquake deformation. The combined 2016/17 thrust events resulted in a positive gravity anomaly of 5–6 microGal around the epicenter, while the 2019 normal faulting produced a negative gravity anomaly of 3–4 microGal. Our modeling found that these gravity changes are manifestation of vertical deformation with limited volumetric change, distinct from gravity changes after the shallow earthquakes. The stronger resistance of rocks to volume change at intermediate-depth results in largely incompressible deformation and thus in a gravity change dominated by vertical deformation. In addition, malleable rocks under high pressure and temperature at depth facilitated substantial afterslip and/or fast viscoelastic relaxation causing additional vertical deformation and gravity change equivalent to the coseismic change. For the Papua New Guinea events, this means that postseismic relaxation enhanced coseismic uplift and relative sea level decrease.

Journal of Geophysical Research: Solid Earth↗