Phelps works in the GMEG Science Center. He received a BA in geology from UC Berkeley and an MSc from the University of London, Birkbeck in geographic information science. He specializes in geologic mapping, gravity and magnetics, and spatial analysis. Presently his research is focused on using data science tools in 2D and 3D geologic mapping, and gravity and magnetic forward and inverse modeling.
Science and Products
Airborne magnetic and radiometric survey, Idaho Cobalt Belt, Central Idaho, 2021 - Magnetic and Radiometric Data
This publication provides digital flight line data for a high resolution magnetic and radiometric survey over an area of central Idaho, USA. The survey includes airborne geophysical data collected as part of the U.S. Geological Survey (USGS) Earth Mapping Resource Initiative (Earth MRI) effort (Day, 2019). Earth MRI is a cooperative effort between the USGS, the Association of American State Geolog
Uncrewed aerial system aeromagnetic test survey at the Boulder Magnetic Observatory
This data release contains two related datasets acquired for the uncrewed aerial system aeromagnetic test survey at the Boulder Magnetic Observatory. The first contains the raw magnetic data for the set of four test flights, and the second contains the compensated magnetic data for the same four flights. Details of the data are recorded in the metadata files associated with each dataset.
Geophysical datasets for the FORGE Fallon site
The datasets include geophysical and rock property measurements and models accompanying the FORGE Fallon Phase II study
Assessing reproducibility in sedimentary macroscopic charcoal count data
Current understanding of global late Quaternary fire history is largely drawn from sedimentary charcoal data. Since publication, CharAnalysis increasingly has been relied upon as a robust method for analyzing these data. However, several underlying assumptions of the algorithm have not been tested. This study uses replicated charcoal count data to examine the assumption of Poisson distribution and
Achieving sub-nanoTesla precision in multirotor UAV aeromagnetic surveys
An uncrewed aerial vehicle (UAV) multirotor aeromagnetic system using a 5-m sling load for a magnetic sensor system is described and characterized. Four magnetic surveys with identical flight lines were completed, at two nominal altitudes of 25 and 40 m. The surveys were used to assess the repeatability of data collected with the described UAV aeromagnetic system, and comparison with a ground surv
Exploring viable geologic interpretations of gravity models using distance-based global sensitivity analysis and kernel methods
We have explored ways to integrate alternative geologic interpretations into the modeling of gravity data. These methods are applied to the Vaca Fault east of Fairfield, California, USA, where the structure across the fault is in question, and the Vaca Fault is used as a case study to demonstrate the method. The Vaca Fault is modeled using gravity data collected along a 10 km line perpendicular to
A time-lapse gravity survey of the Coso geothermal field, China Lake Naval Air Weapons Station, California
We have conducted a gravity survey of the Coso geothermal field to continue the time-lapse gravity study of the area initiated in 1991. In this report, we outline a method of processing the gravity data that minimizes the random errors and instrument bias introduced into the data by the Scintrex CG-5 relative gravimeters that were used. After processing, the standard deviation of the data was esti
Analysis of the age and paleomagnetic orientation of the Broadwell Mesa Basalt, Bristol Mountains, CA
To add to the regional paleomagnetic data documenting block rotation in eastern California, we determined the age and paleomagnetic rotation of the Broadwell Mesa basalt, a basalt in the Bristol Mountains, CA as part of an effort to constrain the timing and rotation of blocks adjacent to the fault. The east-striking sinistral Broadwell Mesa fault cuts and separates the basalt into two outcrops. An
Active tectonics of the northern Mojave Desert: The 2017 Desert Symposium field trip road log
The 2017 Desert Symposium field trip will highlight recent work by the U.S. Geological Survey geologists and geophysicists, who have been mapping young sediment and geomorphology associated with active tectonic features in the least well-known part of the eastern California Shear Zone (ECSZ). This area, stretching from Barstow eastward in a giant arc to end near the Granite Mountains on the south
Forward modeling of gravity data using geostatistically generated subsurface density variations
Using geostatistical models of density variations in the subsurface, constrained by geologic data, forward models of gravity anomalies can be generated by discretizing the subsurface and calculating the cumulative effect of each cell (pixel). The results of such stochastically generated forward gravity anomalies can be compared with the observed gravity anomalies to find density models that match
The Pilot Valley shoreline: An early record of Lake Bonneville dynamics
The Pilot Valley shoreline is named for distinctive gravel beaches on the eastern, northern, and western sides of Pilot Valley playa, Utah. The shoreline has been identified across the Bonneville basin where it is characterized by one to three beach crests between ~ 1305 and 1309 m elevation, all overlain by deep-water marl of Lake Bonneville. It thus represents the lowest and earliest recognized
Geologic setting of the proposed West Flank Forge Site, California: Suitability for EGS research and development
The proposed West Flank FORGE site is within the China Lake Naval Air Weapons Station (NAWS), China Lake, CA. The West Flank is west of the Coso geothermal field, an area of China Lake NAWS dominated by the Quaternary Coso volcanic field largely comprised of rhyolite domes and their volcaniclastic and epiclastic horizons. The largest dome flow complex, Sugarloaf Mountain, marks the northwestern ma
Payload-directed control of geophysical magnetic surveys
No abstract available.
gravmagsubs: Gravitational and magnetic attraction of 3-D vertical rectangular prisms
gravmagsubs is a software package for the R language that provides tools for forward modeling gravity and magnetic anomalies from 3-D right rectangular prisms. The gravity anomaly is defined as the vertical component of gravitational acceleration, while the magnetic anomaly includes the effects of both induced and remanent magnetization. The package can model the total anomaly from a collection
Science and Products
- Data
Airborne magnetic and radiometric survey, Idaho Cobalt Belt, Central Idaho, 2021 - Magnetic and Radiometric Data
This publication provides digital flight line data for a high resolution magnetic and radiometric survey over an area of central Idaho, USA. The survey includes airborne geophysical data collected as part of the U.S. Geological Survey (USGS) Earth Mapping Resource Initiative (Earth MRI) effort (Day, 2019). Earth MRI is a cooperative effort between the USGS, the Association of American State GeologUncrewed aerial system aeromagnetic test survey at the Boulder Magnetic Observatory
This data release contains two related datasets acquired for the uncrewed aerial system aeromagnetic test survey at the Boulder Magnetic Observatory. The first contains the raw magnetic data for the set of four test flights, and the second contains the compensated magnetic data for the same four flights. Details of the data are recorded in the metadata files associated with each dataset.Geophysical datasets for the FORGE Fallon site
The datasets include geophysical and rock property measurements and models accompanying the FORGE Fallon Phase II study - Multimedia
No results found.
- Publications
Assessing reproducibility in sedimentary macroscopic charcoal count data
Current understanding of global late Quaternary fire history is largely drawn from sedimentary charcoal data. Since publication, CharAnalysis increasingly has been relied upon as a robust method for analyzing these data. However, several underlying assumptions of the algorithm have not been tested. This study uses replicated charcoal count data to examine the assumption of Poisson distribution andAchieving sub-nanoTesla precision in multirotor UAV aeromagnetic surveys
An uncrewed aerial vehicle (UAV) multirotor aeromagnetic system using a 5-m sling load for a magnetic sensor system is described and characterized. Four magnetic surveys with identical flight lines were completed, at two nominal altitudes of 25 and 40 m. The surveys were used to assess the repeatability of data collected with the described UAV aeromagnetic system, and comparison with a ground survExploring viable geologic interpretations of gravity models using distance-based global sensitivity analysis and kernel methods
We have explored ways to integrate alternative geologic interpretations into the modeling of gravity data. These methods are applied to the Vaca Fault east of Fairfield, California, USA, where the structure across the fault is in question, and the Vaca Fault is used as a case study to demonstrate the method. The Vaca Fault is modeled using gravity data collected along a 10 km line perpendicular toA time-lapse gravity survey of the Coso geothermal field, China Lake Naval Air Weapons Station, California
We have conducted a gravity survey of the Coso geothermal field to continue the time-lapse gravity study of the area initiated in 1991. In this report, we outline a method of processing the gravity data that minimizes the random errors and instrument bias introduced into the data by the Scintrex CG-5 relative gravimeters that were used. After processing, the standard deviation of the data was estiAnalysis of the age and paleomagnetic orientation of the Broadwell Mesa Basalt, Bristol Mountains, CA
To add to the regional paleomagnetic data documenting block rotation in eastern California, we determined the age and paleomagnetic rotation of the Broadwell Mesa basalt, a basalt in the Bristol Mountains, CA as part of an effort to constrain the timing and rotation of blocks adjacent to the fault. The east-striking sinistral Broadwell Mesa fault cuts and separates the basalt into two outcrops. AnActive tectonics of the northern Mojave Desert: The 2017 Desert Symposium field trip road log
The 2017 Desert Symposium field trip will highlight recent work by the U.S. Geological Survey geologists and geophysicists, who have been mapping young sediment and geomorphology associated with active tectonic features in the least well-known part of the eastern California Shear Zone (ECSZ). This area, stretching from Barstow eastward in a giant arc to end near the Granite Mountains on the southForward modeling of gravity data using geostatistically generated subsurface density variations
Using geostatistical models of density variations in the subsurface, constrained by geologic data, forward models of gravity anomalies can be generated by discretizing the subsurface and calculating the cumulative effect of each cell (pixel). The results of such stochastically generated forward gravity anomalies can be compared with the observed gravity anomalies to find density models that matchThe Pilot Valley shoreline: An early record of Lake Bonneville dynamics
The Pilot Valley shoreline is named for distinctive gravel beaches on the eastern, northern, and western sides of Pilot Valley playa, Utah. The shoreline has been identified across the Bonneville basin where it is characterized by one to three beach crests between ~ 1305 and 1309 m elevation, all overlain by deep-water marl of Lake Bonneville. It thus represents the lowest and earliest recognizedGeologic setting of the proposed West Flank Forge Site, California: Suitability for EGS research and development
The proposed West Flank FORGE site is within the China Lake Naval Air Weapons Station (NAWS), China Lake, CA. The West Flank is west of the Coso geothermal field, an area of China Lake NAWS dominated by the Quaternary Coso volcanic field largely comprised of rhyolite domes and their volcaniclastic and epiclastic horizons. The largest dome flow complex, Sugarloaf Mountain, marks the northwestern maPayload-directed control of geophysical magnetic surveys
No abstract available. - Software
gravmagsubs: Gravitational and magnetic attraction of 3-D vertical rectangular prisms
gravmagsubs is a software package for the R language that provides tools for forward modeling gravity and magnetic anomalies from 3-D right rectangular prisms. The gravity anomaly is defined as the vertical component of gravitational acceleration, while the magnetic anomaly includes the effects of both induced and remanent magnetization. The package can model the total anomaly from a collection - News