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The July 2019 Ridgecrest sequence was observed in exquisite detail by the National Science Foundation’s (NSF) Geodetic Facility for the Advancement of Geoscience (GAGE) Network of the Americas (NOTA), which has a dense array of continuously observing Global Navigation Satellite System (GNSS) stations and subarrays of strain and seismic borehole networks in southern California. Two hundred and eighteen GNSS and 10 borehole NOTA stations within 250 km of the epicentral area recorded the sequence. Special downloads of high-rate data from sites within a specified radius of each earthquake were initiated by the GAGE Facility for the time period of 1.5 days before and 1.5 days after each event to ensure transient deformation was captured at a high-temporal resolution. Rapid field deployments of temporary GNSS stations were carried out by UNAVCO in support of NSF-funded investigators and U.S. Geological Survey activities. The data recorded by the permanent network are available from the GAGE Facility’s Data Center at UNAVCO, data recorded at the temporary campaign sites will also be made available on completion of data collection. The OpenTopography project, of which UNAVCO is a partner, released a preliminary pre-event digital surface model of the area covering the Ridgecrest earthquake sequence to support the ongoing imaging efforts to measure the deformation from these events. In this article, we document the significant amount of detailed, open-access geodetic data available from GAGE to study this sequence and advance our understanding of earthquake processes, the geodynamics of the California eastern shear zone, and our capacity to respond to damaging earthquakes for research.

[1] The 1959 Mw 7.3 Hebgen Lake, MT, normal-faulting earthquake occurred in an extensional stress regime near the Yellowstone volcanic field. Time-dependent crustal deformation data following this major earthquake were acquired by precise trilateration and GPS surveys from 1973 to 2000 around the Hebgen Lake fault zone. Modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology, in which the lithosphere is stronger near the Hebgen Lake fault zone than in the vicinity of the Yellowstone volcano system. The models also imply that the lower crust is stronger than the upper mantle, in agreement with results from studies of postseismic and post-lake-filling relaxations (

The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ∼1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

[1] Studies in magma-tectonics point to a spatiotemporal correlation between earthquakes and volcanic eruptions. Here, we examine the correlation between two great Japanese earthquakes, the 1703 Mw 8.2 Genroku and 1707 Mw 8.7 Hoei, and Mt. Fuji's explosive (VEI 5) Hoei eruption, 49 days after the 1707 earthquake. We model the static stress changes and dilatational strain imparted on the Mt. Fuji magmatic system due to each earthquake to determine if these mechanisms enhanced the potential for eruption. Our results show that both earthquakes clamped the dike from 8 km to the surface and compressed magma chambers at 8 km and 20 km depths. The 1707 earthquake decreased the normal stress on the dike at 20 km, the proposed depth of a basaltic magma chamber, by 1.06 bars (0.106 MPa). We hypothesize that the stress change and strain generated by the 1707 earthquake triggered the eruption of Mt. Fuji by permitting opening of the dike and ascent of basaltic magma from 20 km into andesitic and dacitic magma chambers located at 8 km depth. The injection of basaltic magma into the more evolved magmatic system induced magma mixing and a Plinian eruption ensued.

[1] Geodetic measurements of Yellowstone ground deformation from 2006 to June 2010 reveal deceleration of the recent uplift of the Yellowstone caldera following an unprecedented period of uplift that began in 2004. In 2006–2008 uplift rates decreased from 7 to 5 cm/yr and 4 to 2 cm/yr in the northern and southwest caldera, respectively, and in 2009 rates further reduced to 2 cm/yr and 0.5 cm/yr in the same areas. Elastic-dislocation modeling of the deformation data robustly indicates an expanding sill at ∼7–10 km depth near the top of a seismically imaged, crystallizing magma reservoir, with a 60% decrease in the volumetric expansion rate between 2006 and 2009. Reduction of hydrothermal-volcanic recharge from beneath the northeast caldera and seismic moment release of the 2008 and 2010 large earthquake swarms are plausible mechanisms for decelerating the caldera uplift and may have influenced the change in recent caldera motion from uplift to subsidence.

[1] Yellowstone National Park experienced an unusual earthquake swarm in December–January, 2008–2009 that included rapid northward migration of the activity at 1 km per day and shallowing of the maximum focal depths from 12 to 2 km beneath northern Yellowstone Lake. The swarm consisted of 811 earthquakes, 0.5 < MW < 4.1, aligned on a N–S 12-km-long vertical plane of hypocenters. The largest earthquake of the swarm had a 50% tensile crack-opening source determined by a full waveform inversion that we interpret as a magmatic expansion component. In addition, GPS data revealed E–W crustal extension coincident with the swarm. Modeling of GPS and seismic data is consistent with E–W opening of ∼10 cm on a N–S striking vertical dike. Our interpretation is that the swarm was induced by magmatic fluid migration or propagation of a poroelastic stress pulse along a pre-existing fracture zone.

SUMMARY We apply a viscoelastic cycle model to a compilation of GPS velocity fields in order to address the kinematics of deformation in the northwestern United States. A viscoelastic cycle model accounts for time-dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field. Building on the approach taken in Pollitz et al., we construct a deformation model for the entire western United States—based on combined fault slip and distributed deformation—and focus on the implications for the Mendocino triple junction (MTJ), Cascadia megathrust, and western Washington. We find significant partitioning between strike-slip and dip-slip motion near the MTJ as the tectonic environment shifts from northwest-directed shear along the San Andreas fault system to east–west convergence along the Juan de Fuca Plate. By better accounting for the budget of aseismic and seismic slip along the Cascadia subduction interface in conjunction with an assumed rheology, we revise a previous model of slip for the M∼ 9 1700 Cascadia earthquake. In western Washington, we infer slip rates on a number of strike-slip and dip-slip faults that accommodate northward convergence of the Oregon Coast block and northwestward convergence of the Juan de Fuca Plate. Lateral variations in first order mechanical properties (e.g. mantle viscosity, vertically averaged rigidity) explain, to a large extent, crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure. Our analysis also shows that present crustal deformation measurements, particularly with the addition of the Plate Boundary Observatory, can constrain such lateral variations.

[1] Contemporary deformation of the Yellowstone hot spot and surrounding western United States is analyzed using tectonic microplate modeling, employing constraints from GPS observations corrected for postseismic deformation of M7+ earthquakes, fault slip rates, and earthquake focal mechanisms. We focus primarily on the kinematics of the Yellowstone hot spot and the eastern Snake River Plain volcanic field (ESRP), and secondarily on Basin-Range and Columbia Plateau provinces. Our results reveal southwest motion of the Yellowstone Plateau, excluding localized volcanic deformation, at 0.9 ± 0.1 mm/a that decreases to 0.8 ± 0.1 mm/a in the ESRP block. The southwest to west motion of the Yellowstone-ESRP introduces shear in the northern Rocky Mountain block, which is translating east at 0.78 ± 0.08 mm/a. There is

Integration of geophysical and geological data show that the Yellowstone hotspot resulted from a mantle plume interacting with the overriding North America plate, a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16-17 Ma, 700-km-long Yellowstone-Snake River Plain (YSRP) silicic volcanic system. Accessibility of the YSRP allowed large-scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements. Seismic tomography reveals a crustal magma reservoir of 8% to 15% melt, 6 km to 16 km deep, beneath the Yellowstone caldera. An upper-mantle low-P-wave-velocity body extends vertically from 80 km to 250 km beneath Yellowstone, but the anomalous body tilts 60 °WNW and extends to 660 km depth into the mantle transition zone. We interpret this conduit-shaped low-velocity body as a plume of up to - 3.5% Vp and - 5.5% Vs perturbation that corresponds to a 1-2% partial melt. Models of whole mantle convection reveal eastward upper-mantle flow beneath Yellowstone at relatively high rates of 5 cm/yr that deflects the ascending plume into its west-tilted geometry. A geodynamic model of the Yellowstone plume constrained by Vp and Vs velocities and attenuation parameters suggests low excess temperatures of up to 120 K, corresponding to a maximum 2.5% melt, and a small buoyancy flux of 0.25 Mg/s, i.e., properties of a cool, weak plume. The buoyancy flux is many times smaller than for oceanic plumes, nonetheless, plume buoyancy has produced a ~ 400-km-wide, ~ 500-m-high topographic swell centered on the Yellowstone Plateau. Contemporary deformation derived from GPS measurements reveals SW extension of 2-3 mm/yr across the Yellowstone Plateau, one-fourth of the total Basin-Range opening rate, which we consider to be part of Basin-Range intraplate extension. Locally, decadal episodes of subsidence and uplift, averaging ~ 2 cm/yr, characterize the 80-year Yellowstone caldera monitored history and are modeled as hydrothermal-magmatic sources. Moreover a recent episode, 2004-2009, of accelerated uplift of the Yellowstone caldera at rates up to 7 cm/yr has been modeled as resulting from magmatic recharge of a 10-km-deep sill at the top of the crustal magma reservoir. Regionally, gravitational potential energy of the Yellowstone swell drives the lithosphere southwest and “downhill” from the Yellowstone Plateau 400 km where it coalesces with Basin-Range province-wide westward extension. Based on the geometry and its assumed 660 km depth, we extrapolate the plume source southwest to its original location at 17 Ma and 600 km southwest and 200 km north of the YSRP. Importantly, this location is beneath the southern part of the Columbia Plateau flood basalt field of the same age and implies that the Yellowstone mantle plume may be the common source for both of these large volcanic fields. Our time-progression model suggests that the original plume head rose vertically behind the Juan de Fuca plate, but at ~ 12 Ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler, thicker continental lithosphere, becoming entrained in eastward upper-mantle flow. These results reveal that Yellowstone plume-plate processes have had a profound effect on Late Cenozoic geologic evolution and topography of a large part of the western U.S.

[1] Geodetic observations, comprising Interferometric Synthetic Aperture Radar (InSAR), Global Positioning System (GPS), and precision leveling measurements, are used to infer volume change in the subsurface associated with the dynamics of the Yellowstone volcanic system. We focus primarily on the Yellowstone Caldera and its related magmatic, hydrothermal, and fault systems. It appears that known faults play a significant role in controlling crustal volume increases and decreases due to the migration of volcanic and hydrothermal fluids. For example, over 5 cm of subsidence from 1992 to 1995 is associated with source volume changes 6–10 km beneath the NW-trending Elephant Back fault zone and a north-trending fault cutting across the caldera. Furthermore, we are able to image an episode of fluid intrusion near the northern edge of the caldera. The intrusion is elongated in the north-south direction and is parallel to the north-trending volume decrease. The primary intrusion and related hydrothermal activity occurred between 1996 and 2000, though the volume changes appear to have continued, shallowed, and changed shape between 2000 and 2002. There is evidence that the intrusive activity influenced extensional faults to the north of the caldera.

[1] The Yellowstone–Snake River Plain tectonomagmatic province resulted from Late Tertiary volcanism in western North America, producing three large, caldera-forming eruptions at the Yellowstone Plateau in the last 2 Myr. To understand the kinematics and geodynamics of this volcanic system, the University of Utah conducted seven GPS campaigns at 140 sites between 1987 and 2003 and installed a network of 15 permanent stations. GPS deployments focused on the Yellowstone caldera, the Hebgen Lake and Teton faults, and the eastern Snake River Plain. The GPS data revealed periods of uplift and subsidence of the Yellowstone caldera at rates up to 15 mm/yr. From 1987 to 1995, the caldera subsided and contracted, implying volume loss. From 1995 to 2000, deformation shifted to inflation and extension northwest of the caldera. From 2000 to 2003, uplift continued to the northwest while caldera subsidence was renewed. The GPS observations also revealed extension across the Hebgen Lake fault and fault-normal contraction across the Teton fault. Deformation rates of the Yellowstone caldera and Hebgen Lake fault were converted to equivalent total moment rates, which exceeded historic seismic moment release and late Quaternary fault slip-derived moment release by an order of magnitude. The Yellowstone caldera deformation trends were superimposed on regional southwest extension of the Yellowstone Plateau at up to 4.3 ± 0.2 mm/yr, while the eastern Snake River Plain moved southwest as a slower rate at 2.1 ± 0.2 mm/yr. This southwest extension of the Yellowstone–Snake River Plain system merged into east-west extension of the Basin-Range province.

Recent earthquake activity in the Jackson Hole area, particularly the 2010 Gros Ventre sequence, has focused on possible regional ground deformation that may be related to the earthquakes (Farrell et al., 2010). The University of Utah has an established network of field GPS benchmarks that was last surveyed in 2003 and has now been resurveyed in 2010 (Figure 1). The campaign GPS measurements supplement the permanent regional GPS network and provide detailed information on temporal and spatial deformation in and around Grand Teton National Park.