Geology topics

Adam Schultz

Publications and source records attributed to Adam Schultz.

8 recordsLinked to original sources

USGS2026

The United States Magnetotelluric Array and the National Impedance Map

The United States Magnetotelluric Array (USMTArray) data set, collected in the years 2006–2024, consists of more than 1,700 long-period magnetotelluric stations covering the entirety of the contiguous United States on a quasi-regular 70 km grid. Funding across multiple federal agencies was critical to sustaining this effort to its completion. Important components of the project included active guidance and participation from the MT community, the open and timely availability of all data, and the application of consistent instrumentation and robust data processing. Together with parallel advancement in the development of publicly available three-dimensional (3D) inversion codes, the USMTArray has revitalized the US magnetotelluric community and increased the visibility of magnetotellurics within the Earth-science community. Taken as a whole, these data are visualized as the National Impedance Map, which, together with a 3D synthesis conductivity model of the nation, reveals the electrical architecture of the contiguous US. USMTArray data are used by researchers worldwide for fundamental and applied studies, including investigations of continental architecture and evolution, estimation of hazards to critical infrastructure due to geomagnetic storms, and assessment of the nation's undiscovered geothermal and mineral resources. We here review the history and development of the project, discuss the challenges and successes in its execution, present the National Impedance Map and synthesis conductivity model, and highlight the breadth of research stemming from this rich data set.

conterminous United States↗

USGS2025

The progression of basaltic–rhyolitic melt storage at Yellowstone Caldera

Yellowstone Caldera is one of the largest volcanic systems on Earth, hosting three major caldera-forming eruptions in the past two million years, interspersed with periods of less explosive, smaller-volume eruptions 1 . Caldera-forming eruptions at Yellowstone are sourced by rhyolitic melts stored within the mid- to upper crust. Seismic tomography studies have suggested that a broad region of rhyolitic melt extends beneath Yellowstone Caldera, with an estimated melt volume that is one to four times greater than the eruptive volume of the largest past caldera-forming eruption, and an estimated melt fraction of 6–28 per cent 2 , 3 , 4 , 5 . Seismic velocity is strongly influenced by temperature, pressure and melt; however, magnetotelluric data are primarily sensitive to the presence of melt, making these data ideal for constraining volcanic systems. Here we utilize magnetotelluric data to model the resistivity structure of Yellowstone Caldera’s crustal magma reservoir and constrain the region’s potential for producing major volcanic eruptions. We find that rhyolitic melts are stored in segregated regions beneath the caldera with low melt fractions, indicating that the reservoirs are not eruptible. Typically, these regions have melt volumes equivalent to small-volume post-caldera Yellowstone eruptions. The largest region of rhyolitic melt storage, concentrated beneath northeast Yellowstone Caldera, has a storage volume similar to the eruptive volume of Yellowstone’s smallest caldera-forming eruption. We identify regions of basalt migrating from the lower crust, merging with and supplying heat to the northeast region of rhyolitic melt storage. On the basis of our analysis, we suggest that the locus of future rhyolitic volcanism has shifted to northeast Yellowstone Caldera.

Idaho, Montana, Wyoming↗

USGS2023

Estimating geomagnetically induced currents in southern Brazil using 3-D Earth resistivity model

Geomagnetically induced currents (GICs) result from the interaction of the time variation of ground magnetic field during a geomagnetic disturbance with the Earth's deep electrical resistivity structure. In this study, we simulate induced GICs in a hypothetical representation of a low-latitude power transmission network located mainly over the large Paleozoic Paraná basin (PB) in southern Brazil. Two intense geomagnetic storms in June and December 2015 are chosen and geoelectric fields are calculated by convolving a three-dimensional (3-D) Earth resistivity model with recorded geomagnetic variations. The dB / dt proxy often used to characterize GIC activity fails during the June storm mainly due to the relationship of the instantaneous geoelectric field to previous magnetic field values. Precise resistances of network components are unknown, so assumptions are made for calculating GIC flows from the derived geoelectric field. The largest GICs are modeled in regions of low conductance in the 3-D resistivity model, concentrated in an isolated substation at the northern edge of the network and in a cluster of substations in its central part where the east-west (E-W) oriented transmission lines coincide with the orientation of the instantaneous geoelectric field. The maximum magnitude of the modeled GIC was obtained during the main phase of the June storm, modeled at a northern substation, while the lowest magnitudes were found over prominent crustal anomalies along the PB axis and bordering the continental margin. The simulation results will be used to prospect the optimal substations for installation of GIC monitoring equipment.

Space Weather↗

USGS2022

Fluid transport and storage in the Cascadia forearc influenced by overriding plate lithology

Subduction of hydrated oceanic lithosphere can carry water deep into the Earth, with consequences for a range of tectonic and magmatic processes. Most of the fluid is released in the forearc where it plays a critical role in controlling the mechanical properties and seismic behaviour of the subduction megathrust. Here we present results from three-dimensional inversions of data from nearly 400 long-period magnetotelluric sites, including 64 offshore, to provide insights into the distribution of fluids in the forearc of the Cascadia subduction zone. We constrain the geometry of the electrically resistive Siletz terrane, a thickened section of oceanic crust accreted to North America in the Eocene, and the conductive accretionary complex underthrust along the margin. We find that fluids accumulate over timescales exceeding 1 My above the plate in metasedimentary units, while the mafic rocks of Siletzia remain dry. Fluid concentrations tend to peak at slab depths of 17.5 and 30 km, suggesting control by metamorphic processes, but also concentrate around the edges of Siletzia, suggesting that this mafic block is impermeable, with dehydration fluids escaping up-dip along the megathrust. Our results demonstrate that the lithology of the overriding crust can play a critical role in controlling fluid transport in a subduction zone.

British Columbia, California, Oregon, Washington↗

USGS2018

Crustal inheritance and a top-down control on arc magmatism at Mount St Helens

In a subduction zone, the volcanic arc marks the location where magma, generated via flux melting in the mantle wedge, migrates through the crust and erupts. While the location of deep magma broadly defines the arc position, here we argue that crustal structures, identified in geophysical data from the Washington Cascades magmatic arc, are equally important in controlling magma ascent and defining the spatial distribution and compositional variability of erupted material. As imaged by a three-dimensional resistivity model, a broad lower-crustal mush zone containing 3–10% interconnected melt underlies this segment of the arc, interpreted to episodically feed upper-crustal magmatic systems and drive eruptions. Mount St Helens is fed by melt channelled around a mid-Tertiary batholith also imaged in the resistivity model and supported by potential–field data. Regionally, volcanism and seismicity are almost exclusive of the batholith, while at Mount St Helens, along its margin, the ascent of viscous felsic melt is enabled by deep-seated metasedimentary rocks. Both the anomalous forearc location and composition of St Helens magmas are products of this zone of localized extension along the batholith margin. This work is a compelling example of inherited structural control on local stress state and magmatism.

Washington↗

USGS2017

Geomagnetically induced currents: Science, engineering, and applications readiness

This paper is the primary deliverable of the very first NASA Living With a Star Institute Working Group, Geomagnetically Induced Currents (GIC) Working Group. The paper provides a broad overview of the current status and future challenges pertaining to the science, engineering, and applications of the GIC problem. Science is understood here as the basic space and Earth sciences research that allows improved understanding and physics-based modeling of the physical processes behind GIC. Engineering, in turn, is understood here as the “impact” aspect of GIC. Applications are understood as the models, tools, and activities that can provide actionable information to entities such as power systems operators for mitigating the effects of GIC and government agencies for managing any potential consequences from GIC impact to critical infrastructure. Applications can be considered the ultimate goal of our GIC work. In assessing the status of the field, we quantify the readiness of various applications in the mitigation context. We use the Applications Readiness Level (ARL) concept to carry out the quantification.

Space Weather↗

USGS2017

Down to Earth with an electric hazard from space

In reaching across traditional disciplinary boundaries, solid-Earth geophysicists and space physicists are forging new collaborations to map magnetic-storm hazards for electric-power grids. Future progress in evaluation storm time geoelectric hazards will come primarily through monitoring, surveys, and modeling of related data.

Space Weather↗

USGS2001

GEODE (Geo-Data Explorer) - A U.S. Geological Survey Application for Data Retrieval, Display, and Analysis through the Internet

GEODE (Geo-Data Explorer) is a free service offered by the U.S. Geological Survey (USGS) on the Internet at http://geode.usgs.gov (fig. 1). It provides digital geographically referenced data to the desktop computers of any user, including policymakers, land and resource managers, educators, industries, and private citizens. The ultimate goal of GEODE is to provide diverse users a gateway (data portal) that will supply real-time data and analysis over the Internet without the need for special hardware, software, and training.

Fact Sheet↗