Geology topics

Jaime Delano

Publications and source records attributed to Jaime Delano.

7 recordsLinked to original sources

USGS2022

The Pondosa fault zone: A distributed dextral-normal-oblique fault system in northeastern California, USA

The tectonic domains of Basin and Range extension, Cascadia subduction zone contraction, and Walker Lane dextral transtension converge in the Mushroom Rock region of northeastern California, USA. We combined analysis of high-resolution topographic data, bedrock mapping, 40 Ar/ 39 Ar geochronology, low-temperature thermochronology, and existing geologic and fault mapping to characterize an extensive dextral-normal-oblique fault system called the Pondosa fault zone. This fault zone extends north-northwest from the Pit River east of Soldier Mountain, California, into moderately high-relief volcanic topography as far north as the Bartle (California) townsite with normal and dextral offset apparent in geomorphology and fault exposures. New and existing 40 Ar/ 39 Ar and radiocarbon dating of offset lava flows provides ages of 12.4 ka to 9.6 Ma for late Cenozoic stratigraphic units. Scarp morphology and geomorphic expression indicate that the fault system was active in the late Pleistocene. The Pondosa fault zone may represent a dextral-oblique accommodation zone between north-south–oriented Basin and Range extensional fault systems and/or part of the Sierra Nevada–Oregon Coast block microplate boundary.

California↗

USGS2022

How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?

We excavated trenches at two paleoseismic sites bounding a trans-basin bedrock ridge (the Willow Creek Hills) along the northern Lost River fault zone to explore the uniqueness of the 1983 M w 6.9 Borah Peak earthquake compared to its prehistoric predecessors. At the Sheep Creek site on the southernmost Warm Springs section, two earthquakes occurred at 9.8−14.0 ka (95% confidence) and 6.5−7.1 ka; each had ∼1.9 m of vertical displacement. About 4 km to the southeast, across the Willow Creek Hills, two ruptures at the Arentson Gulch site on the northernmost Thousand Springs section occurred at 9.0−14.7 ka and 6.1−7.5 ka with ∼1.9 m of vertical displacement each. We synthesize these and previous paleoseismic results into a model of five postglacial (<15 ka) ruptures along a ∼65 km reach of the northern Lost River fault zone. Our results show that the Borah Peak earthquake (34 km; 0.9 m mean displacement) was unique compared to previous ruptures that had both longer and shorter rupture lengths (∼25−38 km), more displacement (mean of ∼1.3−1.4 m), and equal or greater magnitude ( M w 6.9−7.1) than that in the 1983 earthquake. These ruptures support a hypothesis of variable rupture length and displacement on the northern Lost River fault zone and show that predecessors to the 1983 rupture have passed unimpeded through the Willow Creek Hills. Our work demonstrates that normal faults are capable of producing variable spatial-temporal patterns of rupture that, together with comparisons of fault geometry and historical rupture length, improve our understanding of fault segmentation and help inform models of earthquake rupture probability.

Idaho↗

USGS2021

Quaternary reelfoot fault deformation in the Obion River Valley, Tennessee, USA

Blind reverse faults are challenging to detect, and earthquake records can be elusive because deep fault slip does not break the surface along readily recognized scarps. The blind Reelfoot fault in the New Madrid seismic zone in the central United States has been the subject of extensive prior investigation; however, the extent of slip at the southern portion of the fault remains unconstrained. In this study, we use lidar to map terraces and lacustrine landforms in the Obion River valley and investigate apparent broad folding resulting from slip on the buried Reelfoot fault. We compare remote surface mapping results with three auger boreholes in the ∼24 ka Finley terrace and interpret apparent warping as due to tectonic folding and not stratigraphic thickening. We combine our results with historical records of coseismic lake formation that indicate surface deformation dammed the Obion River in the 1812 CE earthquake. Older terraces (deposited at least 35–55 ka) record progressive fold scarps ≥1, ≥2, and ≥8 m high indicating a long record of earthquakes predating the existing paleoseismic record. Broad, distributed folding above the Reelfoot fault into the Obion River valley is consistent with a deep active fault tip along the southern reaches of the fault. Our analyses indicate the entire length of the fault (≥70 km) is capable of rupture and is more consistent with longer rupture scenarios.

Tennessee↗

USGS2021

Quick and dirty (and accurate) 3-D paleoseismic trench models using coded scale bars

Structure‐from‐motion (SfM) modeling has dramatically increased the speed of generating geometrically accurate orthophoto mosaics of paleoseismic trenches, but some aspects of this technique remain time and labor intensive. Model accuracy relies on control points to establish scale, reduce distortion, and orient 3D models. Traditional SfM methods use total station or Global Navigation Satellite System (GNSS) surveys to constrain models, but collecting control points along a vertical trench wall is often inhibited by poor line of sight to the survey sensor or limited sky view and requires many hours in the field and office. We used physical scale bars printed with coded targets to constrain SfM models of a dusty, 46‐m‐long trench excavation across the Teton fault (Wyoming, U.S.A.). We present a workflow for generating quick and accurate 3D SfM models and orthophoto mosaics and compare the effectiveness of using scale bar, GNSS, and total‐station control in the models. Our results show that the scale bar model deviates from total station survey points by an average of 3.1 cm (maximum of 5.3 cm). In addition, the scale‐bar model only deviates an average of 1.7 cm (maximum 3.5 cm) when compared to the best model alternative, the SfM model controlled by the total station survey. Scale bars eliminate several hours needed to collect and incorporate control points from total station or GNSS surveys and significantly simplify the workflow, at the cost of slightly increased 3D model and orthophoto mosaic error. Our results further suggest that trench models can be constrained with at least four physical scale bars, but using five to six physical scale bars provides redundant control for field deployment and model optimization. The scale bar method for paleoseismic trenches proves to be portable and fast, minimizes the need for specialized survey equipment, and maintains model accuracy needed for mapping trench walls.

Seismological Research Letters↗

USGS2020

Seismic reflection imaging of the low-angle Panamint normal fault system, eastern California

Shallowly dipping (<30°) low‐angle normal faults (LANFs) have been documented globally; however, examples of active LANFs in continental settings are limited. The western margin of the Panamint Range in eastern California is defined by a LANF that dips west beneath Panamint Valley and has evidence of Quaternary motion. In addition, high‐angle dextral‐oblique normal faults displace middle to late Quaternary alluvial fans near the range front. To image shallow (<1 km depth), crosscutting relationships between the low‐ and high‐angle faults along the range front, we acquired two high‐resolution P wave seismic reflection profiles. The northern, 4.6‐km‐long profile crosses the 2‐km‐wide Wildrose graben and the southern, 0.8‐km‐long profile extends onto the Panamint Valley playa, ~7.5 km S of Ballarat, CA. The profile across the Wildrose graben reveals a robust, low‐angle reflector interpreted to represent the LANF separating Plio‐Pleistocene alluvial fanglomerate and Proterozoic metasedimentary deposits. High‐angle faults interpreted in the seismic profile correspond to fault scarps on Quaternary alluvial fan surfaces. Interpretation of the reflection data suggests that the high‐angle faults vertically displace the LANF up to 80 m within the Wildrose graben. Similarly, the profile south of Ballarat reveals a low‐angle reflector, which appears both rotated and displaced up to 260 m by high‐angle faults. These results suggest that near the Panamint range front, the high‐angle faults are the dominant active structures. We conclude that at least at shallow (<1 km) depths, the LANF we imaged is not active today.

California↗

USGS2020

Post-glacial Mw 7.0-7.5 earthquakes on the North Olympic fault zone, Washington

Holocene crustal faulting in the northern Olympic Peninsula of Washington State manifests in a zone of west‐northwest‐striking crustal faults herein named the North Olympic fault zone, which extends for ∼ 80    km "> ∼ 80 km ∼80 km along strike and includes the Lake Creek–Boundary Creek fault to the east and the Sadie Creek fault and newly discovered scarps to the west. This study focuses on the Sadie Creek fault, which extends for > 14    km "> > 14 km >14 km west‐northwest from Lake Crescent. Airborne light detection and ranging (lidar) imagery reveals the trace of the Sadie Creek fault and offset postglacial landforms showing a history of Holocene surface‐rupturing earthquakes dominated by dextral displacement along a steeply dipping fault zone. Paleoseismic trenches at two sites on the Sadie Creek fault reveal till and outwash overlain by progressively buried forest and wetland soils developed on scarp‐derived colluvial wedges. Trench exposures of complex faulting with subhorizontal slickenlines indicate dextral displacement with lesser dip slip. Correlation of broadly constrained time intervals for earthquakes at the Sadie Creek sites and those to the east along the Lake Creek–Boundary Creek fault is consistent with rupture of much of the length of the North Olympic fault zone three to four times: at about 11, 7, 3, and 1 ka, with a shorter rupture at about 8.5 ka. Dated ruptures from trenches only partially coincide with coseismic landslides and megaturbidites in Lake Crescent, indicating that some earthquakes did not trigger megaturbidites, and some turbidites were unrelated to local fault rupture. Landform mapping suggests single‐event dextral displacement of 4 ± 1    m "> 4 ± 1 m 4±1 m on the Sadie Creek fault. Inferred maximum rupture length and single‐event slip imply earthquake magnitudes M w "> M w Mw 7.0–7.5. Dextral slip rates of 1.3 – 2.3    mm / yr "> 1.3 – 2.3 mm / yr 1.3–2.3 mm/yr and the ∼ 11 , 000    yr "> ∼ 11 , 000 yr ∼11,000 yr slip history suggest that the North Olympic fault zone is a prominent contributor to permanent strain in the northern Cascadia fore‐arc.

Washington↗

USGS2020

Surface displacement distributions for the July 2019 Ridgecrest, California earthquake ruptures

Surface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left‐lateral and northeast‐striking rupture in the M w "> M w 6.4 foreshock and dominantly right‐lateral and northwest‐striking rupture in the M w "> M w 7.1 mainshock. We present > 650 "> > 650 field‐based, surface‐displacement observations for these ruptures and synthesize our results into cumulative along‐strike displacement distributions. Using these data, we calculate displacement gradients and compare our results with historical strike‐slip ruptures in the eastern California shear zone. For the M w "> M w 6.4 rupture, we report 96 displacements measured along 18 km of northeast‐striking rupture. Cumulative displacement curves for the rupture yield a mean left‐lateral displacement of 0.3–0.5 m and maximum of 0.7–1.6 m. Net mean vertical displacement based on the difference of down‐to‐the‐west (DTW) and down‐to‐the‐east (DTE) displacement curves is close to zero (0.02 m DTW). The M w "> M w 6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the M w "> M w 7.1 rupture. The M w "> M w 7.1 rupture is northwest‐striking and 50 km long based on 576 field measurements. Displacement curves indicate a mean right‐lateral displacement of 1.2–1.7 m and a maximum of 4.3–7.0 m. Net vertical displacement in the rupture averages 0.3 m DTW. The M w "> M w 7.1 displacement distributions demonstrate that maximum displacement occurred along a 12‐km‐long portion of the fault near the M w "> M w 7.1 epicenter, releasing 66% of the geologically based seismic moment along 24% of the total rupture length. Using our displacement distributions, we calculate kilometer‐scale displacement gradients for the M w "> M w 7.1 rupture. The steepest gradients ( ⁠ ∼ 1 – 3    m / km "> ∼ 1 – 3 m / km ⁠ ) flank the 12‐km‐long region of maximum displacement. In contrast, gradients for the 1992 M w "> M w 7.3 Landers and 1999 M w "> M w 7.1 Hector Mine earthquakes are < 0.6    m / km "> < 0.6 m / km . Our displacement distributions are important for understanding the influence of cross‐fault rupture on M w "> M w 6.4 and 7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.

California↗