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1. High-resolution structure-from-motion models of hydrothermal sites in the Central Nevada Seismic Belt: applications in tectonic, climate, and hydrothermal investigations

   Callahan, O. A. ( February 2023 , Proceedings 48th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California.)

   ABSTRACT Hot spring travertine and sinter deposits record discharge from hydrothermal systems through evolving hydrothermal, hydrologic, and tectonic regimes. The location and volume of the largest deposits may reflect persistent or particularly robust periods of hydrothermal flow. As part of a broader investigation into the chemical evolution of travertine deposits, we used unoccupied aerial vehicles (UAVs) coupled with high-precision GPS surveys to collect and assemble orthorectified photomosaics and high-resolution digital elevation models (DEMs) using structure-from-motion (SfM) software for eight sites in the northern Central Nevada Seismic Belt. These sites range from large, intrabasin travertine mounds to travertine and sinter deposits offset by Quaternary faults. Some highlights of the research made possible by the acquisition of these topographic datasets include: 1) geomorphic evidence that hydrothermal flow at Hyder Hot Springs has persisted since at least the last highstand of glacial Lake Dixie, 2) documenting the impact of hot spring sinter and hydrothermal alteration on the preservation and morphology of Quaternary fault scarp profiles, 3) mapping the extent of a large extinct travertine deposit in the Stillwater Range, and 4) constraints on the offset of hot spring deposits affected by Quaternary faulting at Kyle Hot Springs. Areas between 0.51 – 1.23 km^2more »(126-303 acres) were easily acquired with less than half a day of surveying and flying, and models capable of producing orthorectified photomosaics and DEMs with average resolution of 2.5 cm/pixel and 9.7 cm/pixel, respectively, were built on a desktop computer with 1-10 days of processing time. In desert landscapes, the resolution of the resulting DEMs approaches that of bare earth LiDAR datasets at a fraction of the cost, with little to no special permitting in most cases, and with limited preplanning. The imagery and models described herein are freely available from the NSF-EAR-funded data facility OpenTopography (https://portal.opentopography.org/datasets) for use in commercial, academic, and educational applications with proper attribution.« less
2. Finite Slip Models of the 2019 Ridgecrest Earthquake Sequence Constrained by Space Geodetic Data and Aftershock Locations

   https://doi.org/10.1785/0120200060  

   Jin, Zeyu ; Fialko, Yuri ( June 2020 , Bulletin of the Seismological Society of America)

   ABSTRACT The July 2019 Ridgecrest, California, earthquake sequence involved two large events—the M 6.4 foreshock and the M 7.1 mainshock that ruptured a system of intersecting strike-slip faults. We present analysis of space geodetic observations including Synthetic Aperture Radar and Global Navigation Satellite System data, geological field mapping, and seismicity to constrain the subsurface rupture geometry and slip distribution. The data render a complex pattern of faulting with a number of subparallel as well as cross-cutting fault strands that exhibit variations in both strike and dip angles, including a “flower structure” formed by shallow splay faults. Slip inversions are performed using both homogeneous and layered elastic half-space models informed by the local seismic tomography data. The inferred slip distribution suggests a moderate amount of the shallow coseismic slip deficit. The peak moment release occurred in the depth interval of 3–4 km, consistent with results from previous studies of major strike-slip earthquakes, and the depth distribution of seismicity in California. We use the derived slip models to investigate stress transfer and possible triggering relationships between the M 7.1 mainshock and the M 6.4 foreshock, as well as other moderate events that occurred in the vicinity of the M 7.1 hypocenter. Triggering is discouraged for the average strikemore »of the M 7.1 rupture (320°) but encouraged for the initial orientation of the mainshock rupture suggested by the first-motion data (340°). This lends support to a scenario according to which the earthquake rupture nucleated on a small fault that was more optimally oriented with respect to the regional stress and subsequently propagated along the less-favorably oriented pre-existing faults, possibly facilitated by dynamic weakening. The nucleation site of the mainshock experienced positive dynamic Coulomb stress changes that are much larger than the static stress changes, yet the former failed to initiate rupture.« less
3. Rupture Process of the 2019 Ridgecrest, California Mw 6.4 Foreshock and Mw 7.1 Earthquake Constrained by Seismic and Geodetic Data

   https://doi.org/10.1785/0120200108  

   Wang, Kang ; Dreger, Douglas S. ; Tinti, Elisa ; Bürgmann, Roland ; Taira, Taka’aki ( July 2020 , Bulletin of the Seismological Society of America)

   ABSTRACT The 2019 Ridgecrest earthquake sequence culminated in the largest seismic event in California since the 1999 Mw 7.1 Hector Mine earthquake. Here, we combine geodetic and seismic data to study the rupture process of both the 4 July Mw 6.4 foreshock and the 6 July Mw 7.1 mainshock. The results show that the Mw 6.4 foreshock rupture started on a northwest-striking right-lateral fault, and then continued on a southwest-striking fault with mainly left-lateral slip. Although most moment release during the Mw 6.4 foreshock was along the southwest-striking fault, slip on the northwest-striking fault seems to have played a more important role in triggering the Mw 7.1 mainshock that happened ∼34  hr later. Rupture of the Mw 7.1 mainshock was characterized by dominantly right-lateral slip on a series of overall northwest-striking fault strands, including the one that had already been activated during the nucleation of the Mw 6.4 foreshock. The maximum slip of the 2019 Ridgecrest earthquake was ∼5  m, located at a depth range of 3–8 km near the Mw 7.1 epicenter, corresponding to a shallow slip deficit of ∼20%–30%. Both the foreshock and mainshock had a relatively low-rupture velocity of ∼2  km/s, which is possibly related to the geometric complexity and immaturity of the eastern California shear zone faults. The 2019more »Ridgecrest earthquake produced significant stress perturbations on nearby fault networks, especially along the Garlock fault segment immediately southwest of the 2019 Ridgecrest rupture, in which the coulomb stress increase was up to ∼0.5  MPa. Despite the good coverage of both geodetic and seismic observations, published coseismic slip models of the 2019 Ridgecrest earthquake sequence show large variations, which highlight the uncertainty of routinely performed earthquake rupture inversions and their interpretation for underlying rupture processes.« less
4. Seismic and Geodetic Analysis of Rupture Characteristics of the 2020 Mw 6.5 Monte Cristo Range, Nevada, Earthquake

   https://doi.org/10.1785/0120200327  

   Liu, Chengli ; Lay, Thorne ; Pollitz, Fred F. ; Xu, Jiao ; Xiong, Xiong ( July 2021 , Bulletin of the Seismological Society of America)

   ABSTRACT The largest earthquake since 1954 to strike the state of Nevada, United States, ruptured on 15 May 2020 along the Monte Cristo range of west-central Nevada. The Mw 6.5 event involved predominantly left-lateral strike-slip faulting with minor normal components on three aligned east–west-trending faults that vary in strike by 23°. The kinematic rupture process is determined by joint inversion of Global Navigation Satellite Systems displacements, Interferometric Synthetic Aperture Radar (InSAR) data, regional strong motions, and teleseismic P and SH waves, with the three-fault geometry being constrained by InSAR surface deformation observations, surface ruptures, and relocated aftershock distributions. The average rupture velocity is 1.5  km/s, with a peak slip of ∼1.6  m and a ∼20  s rupture duration. The seismic moment is 6.9×1018  N·m. Complex surface deformation is observed near the fault junction, with a deep near-vertical fault and a southeast-dipping fault at shallow depth on the western segment, along which normal-faulting aftershocks are observed. There is a shallow slip deficit in the Nevada ruptures, probably due to the immature fault system. The causative faults had not been previously identified and are located near the transition from the Walker Lane belt to the Basin and Range province. The east–west geometry of the system is consistentmore »with the eastward extension of the Mina Deflection of the Walker Lane north of the White Mountains.« less
5. Shallow Megathrust Rupture during the 10 February 2021 Mw 7.7 Southeast Loyalty Islands earthquake sequence

   https://doi.org/10.1785/0320210035  

   Ye, L. ( January 2021 , The Seismic record)

   Koper, Keith (Ed.)

   On 10 February 2021, an MW 7.7 thrust earthquake ruptured the megathrust along the southeast Loyalty Islands within the strong bend in the plate boundary between the Australian plate and the North Fiji Basin. The mainshock involved rupture with ~50 s duration, with pure thrust slip concentrated in an east-west trending slip patch with up to 4.2 m of slip extending from 10 to 25 km depth. Slip at depths <10 km depth is negligible on the curved fault surface, which conforms to the SLAB2 interface model. Static stress drop estimates are ~5.5 MPa, and the radiated energy is 2.38 x 1015 J, with moment-scaled value of 5.7 x 10-6. The relatively shallow rupture from 10-25 km was moderately efficient in generating tsunami, with waves amplitudes up to 20 cm recorded in New Caledonia, New Zealand, Kermadec, and Fiji. Numerous M5+ normal-faulting aftershocks occur south of the trench, indicating effective stress change transfer from the megathrust to the bending flange of Australian plate that is negotiating the bend in the trench. Highly productive sequences involving paired thrust and normal faulting have occurred repeatedly westward along the northwest-trending portion of the Loyalty Islands region, also indicating unusually efficient stress communication.