Complex Holocene Fault Ruptures on the Warm Springs Valley Fault in the Northern Walker Lane, Nevada–Northern California

ABSTRACT The Warm Spring Valley fault is a right-lateral strike-slip fault situated in the northern Walker Lane—a region of distributed deformation that accommodates ~15% of the dextral shear between the North American and the Pacific plates. We assess the Holocene slip history through new mapping for the entire fault and a paleoseismic trenching investigation for the northern section of the fault. The fault is expressed in Holocene deposits for a minimum of 80 km and upward of 96 km, encompassing a wide deformation zone (~0.5–2 km) characterized by short discontinuous fault scarps in young alluvial deposits, stepping and anastomosing fault strands, pop-up features, linear drainages, and sag ponds. Trenching on the northern section of the fault reveals evidence for at least two and possibly three surface-rupturing events since 15.8 ± 1.3 ka, matching the timing of the Seehoo highstand of Lake Lahontan. Earthquakes are broadly constrained between 16.4 and 9.2 ka, a possible event between 9.0 and 6.4 ka, and an event between 3.5 and 0.1 ka, determined based on stratigraphic relationships and radiocarbon and optically stimulated luminescence geochronology. The ages of all three earthquakes provide a recurrence interval of ~5.5 ± 1.6 ka for the fault. The earthquake timing overlaps with trenching results from the southern section of the fault, suggesting that full-length fault ruptures generating Mw 7.3–7.4 earthquakes are possible. Post-Lake Lahontan sand dunes are faulted in the Honey Lake basin along with pluvial lake deposits next to Honey Lake, providing supportive evidence for one or multiple Holocene earthquakes. Faults range in orientation from 270° to 360° and match the orientations of shears in clay model experiments suggesting that fault ruptures on the Warm Springs Valley fault are complex, similar to complex historical earthquakes, and consistent with youthful fault development in the northern Walker Lane.

DIG: A New Project to De-risk Ireland’s Geothermal Energy Potential

<p>Potential deep (greater > 400 m) geothermal resources, within low to medium temperature settings remain poorly understood and largely untapped in Europe. DIG (De-risking Ireland’s Geothermal Potential) is a new academic project started in 2020, which aims to develop a better understanding of Ireland’s (all-island) low-enthalpy geothermal energy potential through the gathering, modelling and interpretation of geophysical, geological, and geochemical data.</p><p>The overarching research objectives, are to (i) determine the regional geothermal gradient with uncertainty estimates across Ireland using new and existing geophysical and geochemical-petrophysical data, (ii) investigate the thermochemical crustal structure and secondary fracture porosity in Devonian/Carboniferous siliciclastic and carbonate lithologies using wide-angle seismic, gravity and available geochemical data, and (iii) identify and assess the available low-enthalpy geothermal resources at reservoir scale within the Upper Devonian Munster Basin, i.e. the Mallow warm springs region, using electromagnetic and passive seismic methods, constrained by structural geological mapping results. A new hydrochemistry programme to characterise deep reservoir water composition will add further constraints.</p><p>In the island-scale strand of the project, we are using Rayleigh and Love surface waves in order to determine the seismic-velocity and thermal structure of the lithosphere, with crustal geometry. Together with the legacy surface heat flow, gravity, and newly available long-period MT data, this will place bounds on the shape of regional geotherms. Radiogenic heat production and thermal conductivity measurements for Irish rocks will be incorporated into an integrated geophysical-petrological model, within a scheme able to provide critical temperature uncertainties. Regional-scale research will exploit legacy wide-angle seismic data across the Laurentian and Avalonian geological terranes. Geochemical and petrophysical databases will guide in-house Bayesian inversion tools, to estimate probabilities on model outcomes.</p><p>Local-scale research will derive subsurface electrical conductivity and velocity images from electromagnetic and passive seismic surveys from the northern margin of the Munster Basin, where the thermal waters tend to have a distinctive chemical fingerprint and a meteoric origin based on available geochemical and isotopic compositions. This local focus aims to directly image fault conduits and fluid aquifer sources at depth, within a convective/conductive region associated with warm springs. This will determine the scale of the geothermal anomaly and hence will evaluate the potential for local- and industrial-scale space heating in the survey locality.</p><p>This presentation will give an overview of this new research project and will deliver preliminary multi-parameter crustal models produced by the thermodynamic inversions that fit the surface-wave and surface elevation data. The project is funded by the Sustainable Energy Authority of Ireland under the SEAI Research, Development & Demonstration Funding Programme 2019 (grant number 19/RDD/522) and by the Geological Survey Ireland.</p>

Impact of Heavy-rail-based Rapid Transit on House Prices: Evidence from the Fremont, CA, Warm Springs BART Extension Project

This study estimates households’ willingness to pay for single-family houses and condominiums/townhouses located within 2 miles of Warm Springs (WS) BART Station in Fremont, CA. The study finds that, compared to the houses sold in the control distance band (2–5 miles away), an average-priced single-family house within 2 miles of the WS BART Station was higher in price by 9 to 15 percent. The total property value increment for the single-family houses is large enough to fund the $802 million Warm Springs BART Extension Project cost five times over.

Variable normal-fault rupture behavior, northern Lost River fault zone, Idaho, USA

The 1983 Mw 6.9 Borah Peak earthquake generated ∼36 km of surface rupture along the Thousand Springs and Warm Springs sections of the Lost River fault zone (LRFZ, Idaho, USA). Although the rupture is a well-studied example of multisegment surface faulting, ambiguity remains regarding the degree to which a bedrock ridge and branch fault at the Willow Creek Hills influenced rupture progress. To explore the 1983 rupture in the context of the structural complexity, we reconstruct the spatial distribution of surface displacements for the northern 16 km of the 1983 rupture and prehistoric ruptures in the same reach of the LRFZ using 252 vertical-separation measurements made from high-resolution (5–10-cm-pixel) digital surface models. Our results suggest the 1983 Warm Springs rupture had an average vertical displacement of ∼0.3–0.4 m and released ∼6% of the seismic moment estimated for the Borah Peak earthquake and <12% of the moment accumulated on the Warm Springs section since its last prehistoric earthquake. The 1983 Warm Springs rupture is best described as the moderate-displacement continuation of primary rupture from the Thousand Springs section into and through a zone of structural complexity. Historical and prehistoric displacements show that the Willow Creek Hills have impeded some, but not all ruptures. We speculate that rupture termination or penetration is controlled by the history of LRFZ moment release, displacement, and rupture direction. Our results inform the interpretation of paleoseismic data from near zones of normal-fault structural complexity and demonstrate that these zones may modulate rather than impede rupture displacement.