Geology topics

William C. Hammond

Publications and source records attributed to William C. Hammond.

5 recordsLinked to original sources

USGS2020

Rupture process of the M6.5 Stanley, Idaho, earthquake inferred from seismic waveform and geodetic data

The 2020 M 6.5 Stanley, Idaho, earthquake produced rupture in the north of the active Sawtooth fault in the northern basin and range at depth, without any observable surface rupture. Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data yield several millimeters of static offsets out to ∼100 km from the rupture and up to ∼0.1 m of near‐field crustal deformation. We combine the GPS and InSAR data with long‐period regional seismic waveforms to derive models of kinematic slip and afterslip. We find that the coseismic rupture is complex, likely involving up to 2 m combined left‐lateral strike slip and normal slip on a previously unidentified ∼south‐southeast‐striking fault. This slip is predominantly left‐lateral strike slip, different from the dominant east‐northeast–west‐northwest normal faulting of the region. At least one ∼northeast‐trending fault, likely associated with the Trans‐Challis fault system, is inferred to have accommodated a few decimeters of right‐lateral afterslip, consistent with vigorous aftershock activity at depth along northeast‐trending lineations.

Idaho↗

USGS2019

Regional Global Navigation Satellite System networks for crustal deformation monitoring

Regional networks of Global Navigation Satellite System (GNSS) stations cover seismically and volcanically active areas throughout the United States. Data from these networks have been used to produce high‐precision, three‐component velocity fields covering broad geographic regions as well as position time series that track time‐varying crustal deformation. This information has contributed to assessing interseismic strain accumulation and related seismic hazard, revealed previously unknown occurrences of aseismic fault slip, constrained coseismic slip estimates, and enabled monitoring of volcanic unrest and postseismic deformation. In addition, real‐time GNSS data are now widely available. Such observations proved invaluable for tracking the rapidly evolving eruption of Kīlauea in 2018. Real‐time earthquake source modeling using GNSS data is being incorporated into tsunami warning systems, and a vigorous research effort is focused on quantifying the contribution that real‐time GNSS can make to improve earthquake early warnings as part of the Advanced National Seismic System ShakeAlert system. Real‐time GNSS data can also aid in the tracking of ionospheric disturbances and precipitable water vapor for weather forecasting. Although regional GNSS and seismic networks generally have been established independently, their spatial footprints often overlap, and in some cases the same institution operates both types of networks. Further integration of GNSS and seismic networks would promote joint use of the two data types to better characterize earthquake sources and ground motion as well as offer opportunities for more efficient network operations. Looking ahead, upgrading network stations to leverage new GNSS technology could enable more precise positioning and robust real‐time operations. New computational approaches such as machine learning have the potential to enable full utilization of the large amounts of data generated by continuous GNSS networks. Development of seafloor Global Positioning System‐acoustic networks would provide unique information for fundamental and applied research on subduction zone seismic hazard and, potentially, monitoring.

Seismological Research Letters↗

USGS2014

Geodesy- and geology-based slip-rate models for the Western United States (excluding California) national seismic hazard maps

The 2014 National Seismic Hazard Maps for the conterminous United States incorporate additional uncertainty in fault slip-rate parameter that controls the earthquake-activity rates than was applied in previous versions of the hazard maps. This additional uncertainty is accounted for by new geodesy- and geology-based slip-rate models for the Western United States. Models that were considered include an updated geologic model based on expert opinion and four combined inversion models informed by both geologic and geodetic input. The two block models considered indicate significantly higher slip rates than the expert opinion and the two fault-based combined inversion models. For the hazard maps, we apply 20 percent weight with equal weighting for the two fault-based models. Off-fault geodetic-based models were not considered in this version of the maps. Resulting changes to the hazard maps are generally less than 0.05 g (acceleration of gravity). Future research will improve the maps and interpret differences between the new models.

Arizona;Colorado;Idaho;Montana;New Mexico;Nevada;O↗

USGS2011

Global Positioning System constraints on crustal deformation before and during the 21 February 2008 Wells, Nevada M6.0 earthquake

Using Global Positioning System (GPS) data from permanent sites and U.S. Geological Survey (USGS) campaign data we have estimated co-seismic displacements and secular background crustal deformation patterns associated with the 21 February 2008 Wells Nevada earthquake. Estimated displacements at nearby permanent GPS sites ELKO (84 km distant) and GOSH (81 km distant) are 1.0±0.2 mm and 1.1±0.3 mm, respectively. The magnitude and direction are in agreement with those predicted from a rupture model based on InSAR measurements of the near-field co-seismic surface displacement. Analysis of long GPS time series (>10 years) from the permanent sites within 250 km of the epicenter indicate the eastern Nevada Basin and Range undergoes steady tectonic transtension with rates on the order of 1 mm/year over approximately 250 km. The azimuth of maximum horizontal crustal extension is consistent with the azimuth of the Wells earthquake co-seismic slip vector. The orientation of crustal shear is consistent with deformation associated with Pacific/North America plate boundary relative motion seen elsewhere in the Basin and Range. In response to the event, we deployed a new GPS site with the capability to telemeter high rate, low latency data that will in the future allow for rapid estimation of surface displacement should aftershocks or postseismic deformations occur. We estimated co-seismic displacements using campaign GPS data collected before and after the event, however in most cases their uncertainties were larger than the offsets. Better precision in co-seismic displacement could have been achieved for the campaign sites if they had been surveyed more times or over a longer interval to better estimate their pre-event velocity.

Nevada↗

USGS2010

Evaluation of geodetic and geologic datasets in the Northern Walker Lane-Summary and recommendations of the Workshop

The Northern Walker Lane comprises a complex network of active faults in northwestern Nevada and northeastern California bound on the west by the Sierra Nevada and on the east by the extensional Basin and Range Province. Because deformation is distributed across sets of discontinuous faults, it is particularly challenging to integrate geologic and geodetic data in the NWL to assess the region's seismic hazard. Recent GPS measurements show that roughly one centimeter per year of relative displacement is accumulating across a zone about 100 km wide at the latitude of Reno, Nevada, but it is not clear where or how much of this strain might ultimately be released in damaging earthquakes. Despite decades of work in the region, the sum of documented late Pleistocene to recent slip rates is distinctly less than the GPS-measured relative displacement.

California;Nevada↗