William Charles Hammond

On 9 December 2024, at 3:08 p.m. local time, the Mw 5.7 Parker Butte earthquake occurred about 24 km north-northeast of Yerington, Nevada. From 1 December 2024 to 10 May 2025, we cataloged 1301 earthquakes, including seven events ML>3.5. We use high-precision earthquake relocation, Interferometric Synthetic Aperture Radar (InSAR) data, Global Positioning System (GPS) data, and strong-motion data to explore the tectonic context and spatiotemporal evolution of this sequence. The high-precision relocations of the sequence reveal a main cluster of earthquakes that form a planar feature which can be fit with a plane striking N62°E and dipping 85° SE. Events that are not in the main cluster are primarily 5–10 km to the southeast and are more scattered, but some smaller linear clusters can be identified. We used InSAR and GPS data to model fault geometry and slip. From this analysis, we found that the ground deformation can be fit with a single fault 12 km long × 8 km wide with a strike of N61.5°E ± 1.0°, dipping 73° ± 1.5° southeast and slip up to ∼50 cm, concentrated between depths of 2.5 and 7 km, consistent with an Mw 5.7 rupture. However, a better fit is found by adding a second fault plane. The second fault strikes N24.5°W and was detected as a displacement discontinuity in descending InSAR scenes, correlating to minor surface fracturing observed in the field, but had low aftershock activity. The GPS observations of interseismic deformation before the event show similar directions of principal strain accumulation and strain release in the mainshock moment tensor. Ground-motion measurements from the mainshock strong-motion data are generally in agreement with existing active crustal ground-motion models for the western United States. The sequence provided a valuable dataset for examining faulting rupture patterns in the Walker Lane Shear Zone.

Models of active deformation of the Earth's crust are predominantly represented with dislocations having a downdip continuation into the lower crust, where the fault slips continuously. This model predicts surface strain accumulation concentrated near the fault during the interseismic period. In an alternative model, faults do not extend beneath the elastic portion of the crust and are accompanied by a wide zone of distributed shear underneath, predicting a more constant strain rate lacking concentrations at the faults. We use high‐precision GPS data collected across the northern and central Walker Lane, USA— a region of complex faulting near the western edge of the Basin and Range Province to evaluate which model is appropriate. Despite the existence of dense continuous and semi‐continuous geodetic networks that have been surveyed for ∼20 years, the horizontal velocities reveal no evidence of localized strain accumulation across the fault surface expressions. Instead, deformation within the Walker Lane is uniformly linear, suggesting that the surface deformation reflects distributed shear within the ductile crust rather than focused deformation at faults. This suggests no downdip extension of the faults below the seismogenic layer. The shear zone is 172 ± 6 km wide in the northernmost Walker Lane narrowing to 116 ± 4 km in the central Walker Lane. The total velocity budget across the shear zone is 7.2 ± 0.1 mm/yr in the north, increasing to 10.1 ± 0.1 mm/yr in the central Walker Lane. We conclude that assuming the presence of lower crustal dislocations when estimating geodetic faults slip rates may be inappropriate.

The Walker Lane (WL) in the western Great Basin (GB) is an active plate boundary system accommodating 10%–20% of the relative tectonic motion between the Pacific and North American plates. Its neotectonic framework is structurally complex, having hundreds of faults with various strikes, rakes, and crustal blocks with vertical axis rotation. Faults slip rates are key parameters needed to quantify seismic hazard in such tectonically active plate boundaries but modeling them in complex areas like the WL and GB is challenging. We present a new modeling strategy for estimating fault slip rates in complex zones of active crustal deformation using data from GPS networks. The technique does not rely on prior estimates of slip rates from geologic studies, and only uses data on the surface trace location, dip, and rake. The iterative framework generates large numbers of block models algorithmically from the fault database to obtain many estimates of slip rates for each fault. This reduces bias from subjective choices about how discontinuous faults connect and interact to accommodate strain. Each model iteration differs slightly in block boundary configuration, but all models honor geodetic and fault data, regularization, and are kinematically self‐consistent. The approach provides several advantages over bespoke models, including insensitivity to outlier data, realistic uncertainties, explicit mapping of off‐fault deformation, and slip rates that are more objective and independent of geologic slip rates. Comparisons to the U.S. National Seismic Hazard Model indicate that ∼80% of our geodetic slip rates agree with their geologic slip rates to within uncertainties.

1. We estimate Walker Lane fault slip rates using a dense filtered and gridded geodetic velocity field and a robust multi-block model approach 2. The geodetic slip rates are independent of geologic slip rates, but 80% agree with them to within uncertainties 3. The method images off-fault deformation and vertical axis rotations providing more insight into how crustal motion drives earthquakes Hammond et al., 2023

The predominant approach for modeling faults in the Earth’s crust represents them as elastic dislocations, extending downdip into the lower crust, where the faults slip continuously. The resulting surface deformation features strain accumulation concentrated across locked faults during the interseismic period. An alternative model proposes faults confined to the elastic crust, with surface deformation driven by a wide zone of distributed shear underneath. Using high-precision GPS data, we analyze deformation profiles across the Walker Lane (WL), USA. The WL is a transtensional region of complex faulting, which delineates the western edge of the Basin and Range province and accommodates a significant portion of the Pacific-North American plate boundary deformation budget. Despite a dense geodetic network surveyed collectively for nearly 20 years, horizontal velocities reveal no evidence of localized strain rate accumulation across fault surface expressions. Instead, deformation within the shear zone is uniformly linear, suggesting that the surface velocities reflect distributed shear within the ductile crust rather than discrete fault deformation. This implies no downdip fault extension below the seismogenic layer. The shear zone, bound by the Sierra Nevada crest in the west, is 172±6 km wide in the northernmost WL narrowing to 116±4 km in the central WL. This study’s conclusion challenges the assumption of the presence of dislocations in the lower crust when estimating geodetic slip rates, suggesting that slip rates are instead controlled by the fault’s position and orientation within the shear zone. This has important implications for quantifying seismic hazards in regions with complex fault systems.

We review five deformation models generated for the 2023 update to the U.S. National Seismic Hazard Model (NSHM), which provide input fault-slip rates that drive the rate of earthquake moment release. Four of the deformation models use the Global Positioning System-derived surface velocity field and geologic slip-rate data to derive slip-rate estimates (Evans, Pollitz, Shen-Bird, and Zeng), and one model uses geologic data (the “geologic model”). The correlation between the geologic model preferred slip rates and geodetically derived slip rates is high for the Pollitz, Zeng, and Shen-Bird models, and the median of all slip-rate models has correlation coefficient of 0.88. The median geodetic model slip rates are systematically lower than the preferred geologic model rates for faults with slip rates exceeding 10 mm/yr and systematically higher on faults with slip rates less than 0.1 mm/yr. Geodetically derived slip rates tend to the low end of the geologic model range along sections of the San Andreas fault and the Garlock fault, whereas they tend to be higher across north coast California faults. The total on-fault moment rates agree well across models with all rates within 18% of the median. Estimated off-fault strain rate orientations and styles vary considerably across models and off-fault moment rates vary more than on-fault moment rates. Path integrals across the western U.S. accounting for fault-slip rate and off-fault deformation are generally consistent with Pacific-North America plate motion with the median deformation rates recovering about 98% of the plate motion with about 20% of the total plate motion accommodated by off-fault strain rate. The geologic model, which has no off-fault deformation, accounts for about 82% of plate motion with fault slip. Finally, we make a recommendation for relative weighting of the models for the NSHM as well as several recommendations for future NSHM deformation model development.

We investigate the present‐day strike‐slip faulting and intracontinental deformation of North China using horizontal GPS velocities and a block modeling strategy. The data demonstrate that the fault slip rates and block rotations in North China can be better constrained using GPS velocities where the influence of groundwater extraction has been reduced by applying median spatial filtering of the velocity field. The modeled senses of motion and slip rates on active faults are generally in good agreement with the geological estimates. The left‐lateral slip rate along the boundary fault of Weihe Graben is apparently lower than the differential motion between the South China Block and Ordos Block. The missing left‐lateral slip is accommodated by the counterclockwise rotation of the Ordos Block. The sinistral slip rate along the eastern segment of the Altyn Tagh‐Haiyuan‐Qinling fault system decreases eastward from ∼1.0 to ∼0 mm/yr, much slower than that expected in the fast eastward extrusion hypothesis. We interpret the systematic counterclockwise rotation of blocks and left/right‐lateral faulting in North China to be driven both by the left‐lateral shear between the South China Block to the south and Yinshan‐Yanshan Block to the north and a push from the Tibetan Plateau on the southwestern margin of the Ordos Block.

We developed a high-quality global integrated water vapour (IWV) dataset from 12 552 ground-based global positioning system (GPS) stations in 2020. It consists of 5 min GPS IWV estimates with a total number of 1 093 591 492 data points. The completeness rates of the IWV estimates are higher than 95 % at 7253 (58 %) stations. The dataset is an enhanced version of the existing operational GPS IWV dataset provided by the Nevada Geodetic Laboratory (NGL). The enhancement is reached by employing accurate meteorological information from the fifth generation of European ReAnalysis (ERA5) for the GPS IWV retrieval with a significantly higher spatiotemporal resolution. A dedicated data screening algorithm is also implemented. The GPS IWV dataset has a good agreement with in situ radiosonde observations at 182 collocated stations worldwide. The IWV biases are within ±3.0 kg m⁻² with a mean absolute bias (MAB) value of 0.69 kg m⁻². The standard deviations (SD) of IWV differences are no larger than 3.4 kg m⁻². In addition, the enhanced IWV product shows substantial improvements compared to NGL's operational version, and it is thus recommended for high-accuracy applications, such as research of extreme weather events and diurnal variations of IWV and intercomparisons with other IWV retrieval techniques. Taking the radiosonde-derived IWV as reference, the MAB and SD of IWV differences are reduced by 19.5 % and 6.2 % on average, respectively. The number of unrealistic negative GPS IWV estimates is also substantially reduced by 92.4 % owing to the accurate zenith hydrostatic delay (ZHD) derived by ERA5. The dataset is available at https://doi.org/10.5281/zenodo.6973528 (Yuan et al., 2022).