Geology topics

Christopher B. DuRoss

Publications and source records attributed to Christopher B. DuRoss.

At least 19 recordsLinked to original sources

USGS2026

High‐resolution surface deformation and slip distribution observations for the 2023 Kahramanmaraş, Türkiye, earthquake sequence help constrain the rupture process

Splay, or branch, faults are a common geometric feature of earthquake surface ruptures and may provide constraints on the rupture behavior of an earthquake. The 2023 M w 7.8 Pazarcık and M w 7.5 Elbistan, Türkiye, earthquakes are examples of ruptures with multiple small splays, and the Pazarcık earthquake nucleated on a splay fault, the Narlı fault, before rupturing bilaterally on the East Anatolian fault (EAF). Here, we present 3‐m‐resolution surface displacement from subpixel correlation of Planet Dove optical images for the entirety of both ruptures with corresponding surface slip distributions. For a 30‐km‐long study region spanning the Narlı‐EAF intersection, we compare surface slip derived from five data sets with different resolutions (on‐the‐ground, WorldView, Planet Dove, Sentinel‐2, and Sentinel‐1) to elucidate complementary information. In addition, we integrate information from the surface expression of faulting with published dynamic rupture simulations and rupture process studies to constrain a rupture evolution for the Pazarcık earthquake that is consistent across data sets. This work highlights the complementary nature of disparate surface slip data sets and the role that high‐resolution surface displacement information, including from fault splays, can play in constraining nonunique rupture models and refining understanding of the earthquake rupture process.

Bulletin of the Seismological Society of America↗

USGS2026

The Great Salt Lake (Utah, USA) acoustic and sedimentary archive of Wasatch Front earthquakes

As the largest low-relief basin in the western United States, the Great Salt Lake offers an opportunity to explore acoustic and sedimentary archives of earthquake ruptures in a shallow terminal basin. Here, we use subbottom compressed high intensity radiated pulse (Chirp) profiles and sedimentary cores to address questions related to how Great Salt Lake sediments respond to surface rupture and earthquake shaking and whether the lake is sensitive to both Great Salt Lake fault (GSLF) and Wasatch fault zone (WFZ) earthquakes. Chirp profiles reveal laterally continuous seismic stratigraphy with vertically displaced strata, onlap surfaces, and growth stratigraphy produced by GSLF surface ruptures. We identify and date two ruptures on the Fremont Island section and three on the Antelope Island section; temporal overlap of these ruptures supports synchronous rupture of both sections. Combined with previous data, our results yield a record of four Holocene surface-rupturing (M W 6.9−7.3) earthquakes on the GSLF with a mean recurrence of ∼3.2 k.y. Sediment cores include ≤41-cm-thick, massive, homogeneous to normally graded disturbance beds that interrupt laminated bioclastic sediment. Disturbance bed correlations yield four lacustrine earthquake deposits since ca. 1.7 ka; the youngest possibly records the most recent GSLF surface rupture whereas older deposits were likely produced by WFZ earthquakes. Modeled historical earthquakes yield a Great Salt Lake sediment disturbance shaking threshold of MMI ∼VI, controlled in part by the lake-bottom expression of the GSLF scarp. Our integration of primary (fault-related) and secondary (shaking-related) earthquake evidence improves our understanding of sediment disturbance processes and the archival potential of low-relief lake basins.

Utah↗

USGS2026

Surface rupture and slip distribution of the 2025 Mw7.7 Mandalay earthquake and updated length scaling of supershear earthquakes

The 2025 M w 7.7 Mandalay, Burma (Myanmar), earthquake ruptured 475 km of the central Sagaing fault and is the longest continental strike-slip rupture on record. The observed rupture length is 1.6–4.7 times the value expected (100–300 km) from existing length-magnitude scaling relations for strike-slip earthquakes. The earthquake resulted from shallow dextral faulting and ruptured bilaterally with supershear speeds south of the epicenter, rupturing close to three major cities in Myanmar and exposing over six million people to violent or extreme shaking. We report on the surface rupture character, length, and slip distribution based on sub-pixel correlation of Sentinel-2 (10 m) and Planet Dove (3 m) optical images and visual analysis of SkySat and WorldView (0.3–0.5 m) optical images. The earthquake had moderate surface slip (average = 3.3 m, maximum = 5.6 m, 25–75% range = 3.0–4.0 m), narrow deformation zone width (1–10 pixels in sub-pixel correlation and up to 190 meters for the detailed surface rupture mapping), and simple fault geometry (no stepovers or large changes in strike, 87% of the rupture that was mapped in detail is single-stranded). We attribute the extreme length of the Mandalay earthquake to supershear rupture speed, simple fault geometry, narrow down-dip width, and moderate surface slip. Based on a compilation of 25 supershear strike-slip earthquakes ( M w 6.5–8.6; 1979–2025), we find that the rupture length of supershear earthquakes does not fit empirical scaling relationships for strike-slip earthquakes that predict length from magnitude. A length-magnitude scaling relationship based on supershear earthquakes has a best fit of log 10 (surface rupture length) = 0.89 M w – 4.44, indicating that supershear earthquakes tend to be longer than their subshear counterparts for any given magnitude and thus may expose a greater population to shaking.

Mandalay↗

USGS2025

A scientific vision and roadmap for earthquake rupture forecast developments, a USGS perspective

We articulate a scientific vision and roadmap for the development of improved Earthquake Rupture Forecast models, which are one of the two main modeling components used in modern seismic hazard and risk analysis. One primary future objective is to provide fully time-dependent models that include both elastic rebound and spatiotemporal clustering nationwide, which is particularly important for shorter-term hazard and risk considerations (e.g., earthquake insurance products). We also discuss the importance and perennial challenges associated with quantifying epistemic uncertainties, including those associated with deformation-model slip rates, un-quantified sampling errors with respect to off-fault seismicity, and any spatial covariances. The need for more physics-based approaches is also emphasized, as is the benefit of adding model valuation (quantifying usefulness) to our verification and validation protocols. Given the multidisciplinary and system-level nature of this activity, modular design is critical. Future updates will also draw from best-available science by both the United States Geological Survey and the external community. The primary goal of this paper is to highlight plans that guide research and facilitate community engagement with model development, especially with respect to lowering the entry barrier for early career scientists and engineers. The paper is written so readers can focus on the sections that interest them most (see table of contents), with the Introduction and Discussion providing a stand-alone overview and summary.

Bulletin of the Seismological Society of America↗

USGS2025

Evidence for nonlocal sediment transport on hillslopes from fault scarp morphology

Hillslope sediment transport processes such as bioturbation, rainsplash, and granular mechanics occur across the entire planet. Yet, it remains uncertain how these small-scale processes act together to shape landscapes. Longstanding hillslope diffusion theory posits that hillslope processes are spatially limited, whereas new concepts of nonlocal sediment transport argue otherwise. However, each theory produces subtly different, but distinct, predictions for the evolution of fault scarps. We use the topographic change of fault scarps to demonstrate that hillslope processes produce nonlocal sediment transport. Analysis of a global compilation of 340 dated single-earthquake scarp profiles reveals a statistically significant ( p < 0.05 ) relationship between scarp age and scarp asymmetry, here defined as the ratio of imaginary to real components of the Fourier transform of absolute slope. Numerical simulations show that nonlocal models predict this relationship, whereas hillslope diffusion models do not. To further investigate this result, we examined the depositional geometry of a well-exposed colluvial wedge along the Wasatch fault in central Utah, United States. Our quantitative comparison between the exposure and numerical simulations reveals better agreement with the nonlocal model. Nonlocal sediment transport theory appears to best capture the physics of how hillslope processes shape fault scarps, yet hillslope diffusion provides a useful approximation in many cases. As the processes that act on fault scarps are nearly identical to those acting on hillslopes, our results provide evidence supporting nonlocality as a generalized model of hillslope sediment transport.

Utah↗

USGS2024

Shallow lake, strong shake: Record of seismically triggered lacustrine sedimentation from the 1959 M7.3 Hebgen Lake earthquake within Henrys Lake, Idaho

We investigate a shallow lake basin for evidence of a large historic intraplate earthquake in western North America. Henrys Lake, Idaho is an atypical candidate for a lacustrine paleoseismic study given its shallow depth (~7 m) and low relief (≤2° slopes ). Here, we test the earthquake-recording capacity of this basin type by showing sedimentological evidence of the 1959 M7.3 Hebgen Lake earthquake within sediment cores, using anthropogenically produced 137 Cs activity to constrain timing. In addition to expanding the morphologic range of basins targeted for lacustrine paleoseismic studies, this work has implications for sediment response in dam-enhanced basins. Lack of sedimentological evidence for other earthquakes coupled with radiocarbon chronology reveals that the 1959 event is the only clearly recorded earthquake within Henrys Lake since the mid-Holocene. Henrys Lake offers a proxy for paleo-earthquake signatures within similar lacustrine environments and underscores the importance of further paleoseismic studies in the region.

Idaho↗

USGS2024

Are field observations of surface rupture useful? An example from the 2023 Mw 7.8 Pazarcık, Turkey (Türkiye), earthquake

Field investigations have long been an important component of the scientific response to surface‐faulting earthquakes. However, in light of advances in remote data and models, the question arises whether field‐based observations of surface rupture remain useful for understanding rupture processes and seismic hazards. We approach this question using a field‐based study of the central 2023 M w 7.8 Pazarcık, Turkey (Türkiye), earthquake rupture, at the intersection of the east Anatolian fault (EAF) and Narlı fault. Our field observations include the surface rupture expression and extent of the central EAF and northernmost Narlı fault in generally forested and steep terrain and 68 measurements of left‐lateral surface displacement. These data improve our understanding of the Pazarcık rupture complexity, resolve the surface geometry of the Narlı fault–EAF connection, and exhibit a clear (>2 m) change in surface displacement across this intersection zone that confirms remote‐based coseismic slip models. Our study shows that focusing field efforts in areas of obscured or low‐resolution remote data can yield essential data for refining rupture extent, documenting perishable on‐fault displacement, and improving postearthquake situational awareness. A comparison of similarly large‐magnitude continental surface‐rupturing earthquakes indicates that displacement uncertainties relate to a complex set of factors, including measurement methods, rupture complexity, and displacement magnitude. Our study validates the need for postearthquake field observations, which, when driven by clear motivating questions and knowledge of methodological strengths and limitations, provide high‐resolution rupture data that complement remote‐based models.

Pazarcık↗

USGS2024

Geologic input databases for the 2025 Puerto Rico – U.S. Virgin Islands National Seismic Hazard Model update: Crustal faults component

The last National Seismic Hazard Model (NSHM) for Puerto Rico and the U.S. Virgin Islands (PRVI) was published in 2003. In advance of the 2025 PRVI NSHM update, we created three geologic input databases to summarize new onshore and offshore fault source information in the northern Caribbean region between 62°–70° W and 16°–21° N. These databases, of fault sections, fault‐zone polygons, and geologic estimates of fault activity (fault‐slip rate and earthquake recurrence intervals) at specific sites, document updates to fault parameters used in prior seismic hazard models in PRVI. Fault sources were reviewed from published studies since 2003, which document substantial changes to the understanding of fault location, geometry, or activity. New fault section sources were added for features that meet the criteria of (1) length ≥7 km, (2) unequivocal evidence of recurrent tectonic Quaternary activity, and (3) documentation that is publicly available in a peer‐reviewed source. In addition, we revised several broad areal sources, such as the Mona and Anegada extensional zones. The 2003 model included three fault sections and two fault‐zone polygons (areal sources). These databases include 35 fault sections, 6 fault‐zone polygons, and 51 earthquake geology sites. To characterize fault activity rates, slip‐rate bins were assigned based on landscape expression and paleoseismic trench observations for faults without published slip‐rate sites. Additional fault sources were evaluated but not included in these databases due to a lack of published information about fault location, geometry, or recurrent Quaternary activity. The PRVI NSHM 2025 geologic input databases describe crustal faulting; the geometries and coupling of Puerto Rico subduction zone and Muertos Trough models are considered in a separate database. Updates to the fault sections, fault‐zone polygons, and earthquake geology databases can help inform the location and recurrence rate of damaging earthquakes in the PRVI NSHM implementation.

Puerto Rico, U.S. Virgin Islands↗

USGS2024

Paleoseismology of the Sawtooth fault and implications for fault behavior in the epicentral region of the 2020 Mw 6.5 Stanley, Idaho, earthquake

The 2020 moment magnitude ( M w ⁠⁠ ) 6.5 Stanley, Idaho, earthquake raised questions about the history and extent of complex faulting in the northwestern Centennial Tectonic Belt (CTB) and its relation to the Sawtooth normal fault and Eocene Trans‐Challis fault system (TCFS). To explore faulting in this area, we excavated a paleoseismic trench across the Sawtooth fault along the western margin of the CTB, and compared an early Holocene (9.1 ± 2.1 ka, 1δ ⁠ ) rupture at the site with lacustrine paleoseismic data and fault mapping in the 2020 epicentral region. We find: (1) a history of partial to full rupture of the Sawtooth fault ( M w ⁠ 6.8–7.4), (2) that shorter ruptures ( M w ≤ ⁠⁠6.9 ) are likely along distributed and discontinuous faults in the epicentral region, (3) that this complex system that hosted the 2020 earthquake is not directly linked to the Sawtooth fault, (4) that the northeast‐trending TCFS likely plays a role in controlling fault length and rupture continuity for adjacent faults, and (5) that parts of the TCFS may facilitate displacement transfer between normal faults that accommodate crustal extension and rotation. Our results help unravel complex faulting in the CTB and imply that relict structures can help inform regional seismic hazard assessments.

Idaho↗

USGS2023

The 2023 US 50-State National Seismic Hazard Model: Overview and implications

The US National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications (defined for return periods greater than ∼475 or less than ∼10,000 years). Changes in 2023 time-independent seismic hazard (both increases and decreases compared to previous NSHMs) are substantial because the new model considers more data and updated earthquake rupture forecasts and ground-motion components. In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs. The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures. Seismic hazard calculations yield hazard curves at hundreds of thousands of sites, ground-motion maps, uniform-hazard response spectra, and disaggregations developed for pseudo-spectral accelerations at 21 oscillator periods and two peak parameters, Modified Mercalli Intensity, and 8 site classes required by building codes and other public policy applications. Tests show the new model is consistent with past ShakeMap intensity observations. Sensitivity and uncertainty assessments ensure resulting ground motions are compatible with known hazard information and highlight the range and causes of variability in ground motions. We produce several impact products including building seismic design criteria, intensity maps, planning scenarios, and engineering risk assessments showing the potential physical and social impacts. These applications provide a basis for assessing, planning, and mitigating the effects of future earthquakes.

Earthquake Spectra↗

USGS2023

The USGS 2023 Conterminous U.S. time‐independent earthquake rupture forecast

We present the 2023 U.S. Geological Survey time‐independent earthquake rupture forecast for the conterminous United States, which gives authoritative estimates of the magnitude, location, and time‐averaged frequency of potentially damaging earthquakes throughout the region. In addition to updating virtually all model components, a major focus has been to provide a better representation of epistemic uncertainties. For example, we have improved the representation of multifault ruptures, both in terms of allowing more and less fault connectivity than in the previous models, and in sweeping over a broader range of viable models. An unprecedented level of diagnostic information has been provided for assessing the model, and the development was overseen by a 19‐member participatory review panel. Although we believe the new model embodies significant improvements and represents the best available science, we also discuss potential model limitations, including the applicability of logic tree branch weights with respect different types of hazard and risk metrics. Future improvements are also discussed, with deformation model enhancements being particularly worthy of pursuit, as well as better representation of sampling errors in the gridded seismicity components. We also plan to add time‐dependent components, and assess implications with a wider range of hazard and risk metrics.

Bulletin of the Seismological Society of America↗

USGS2023

Rapid surface rupture mapping from satellite data: The 2023 Kahramanmaraş, Turkey (Türkiye), earthquake sequence

The 6 February 2023 Kahramanmaraş, Turkey (Türkiye), earthquake sequence produced > 500 km of surface rupture primarily on the left‐lateral East Anatolian (~345 km) and Çardak (~175 km) faults. Constraining the length and magnitude of surface displacement on the causative faults is critical for loss estimates, recovery efforts, rapid identification of impacted infrastructure, and fault displacement hazard analysis. To support these efforts, we rapidly mapped the surface rupture from satellite data with support from remote sensing and field teams, and released the results to the public in near‐real time. Detailed surface rupture mapping commenced on 7 February and continued as high‐resolution (< 1.0 m/pixel) optical images from WorldView satellites (2023 Maxar) became available. We interpreted the initial simplified rupture trace from subpixel offset fields derived from Advanced Land Observation Satellite2 and Sentinel‐1A synthetic aperture radar image pairs available on 8 and 10 February, respectively. The mapping was released publicly on 10 February, with frequent updates, and published in final form four months postearthquake ( Reitman, Briggs, et al. , 2023 ). This publicly available, rapid mapping helped guide fieldwork and constrained U.S. Geological Survey finite‐fault and loss estimate models, as well as stress change estimates and dynamic rupture models.

Kahramanmaraş↗

USGS2023

Rapid characterization of the February 2023 Kahramanmaraş, Turkey, earthquake sequence

The 6 February 2023 M w "> M w 7.8 Pazarcık and subsequent M w "> M w 7.5 Elbistan earthquakes generated strong ground shaking that resulted in catastrophic human and economic loss across south‐central Türkiye and northwest Syria. The rapid characterization of the earthquakes, including their location, size, fault geometries, and slip kinematics, is critical to estimate the impact of significant seismic events. The U.S. Geological Survey National Earthquake Information Center (NEIC) provides real‐time monitoring of earthquakes globally, including rapid source characterization and impact estimates. Here, we describe the seismic characterization products generated and made available by the NEIC over the two weeks following the start of the earthquake sequence in southeast Türkiye, their evolution, and how they inform our understanding of regional seismotectonics and hazards. The kinematics of rupture for the two earthquakes was complex, involving multiple fault segments. Therefore, incorporating observations from rupture mapping was critical for characterizing these events. Dense local datasets facilitated robust source characterization and impact assessment once these observations were obtained and converted to NEIC product input formats. We discuss how we may improve the timeliness of NEIC products for rapid assessment of future seismic hazards, particularly in the case of complex ruptures.

The Seismic Record↗

USGS2022

Revised earthquake geology inputs for the central and eastern United States and southeast Canada for the 2023 National Seismic Hazard Model

It has been nearly a decade since updates to seismic and fault sources in the central and eastern United States (CEUS) were last assessed for the 2012 Central and Eastern United States Seismic Source Characterization for nuclear facilities (CEUS-SSCn) and 2014 United States Geological Survey National Seismic Hazard Model (NSHM) for the conterminous U.S. In advance of the 2023 NSHM update, we created 3 related geospatial databases to summarize and characterize new fault source information for the CEUS. These include fault section, fault-zone polygon, and earthquake geology (fault slip rate, earthquake recurrence intervals) databases which document updates to fault parameters used in prior seismic hazard models in this region. The 2012 CEUS-SSCn and 2014 NSHM fault models served as a foundation, as we revised and added fault sources where new published studies documented significant changes to our understanding of fault location, geometry, or activity. We added 9 new fault sections that meet the criteria of (1) a length ≥7 km, (2) evidence of recurrent Quaternary tectonic activity, and (3) documentation that is publicly available in a peer-reviewed source. The prior CEUS models only included 6 fault sections (sources) and 10 fault-zone polygons (previously called repeating large magnitude earthquake (RLME) polygons). The revised databases include 15 fault sections and 10 fault zone polygons. Updates to the faults constitute a 150% increase in fault sections, but no change in the number of fault-zone polygons, although some fault-zone polygons differ from RLME polygons used in prior models. No faults were removed from past models. Several seismic zones and suspected faults were evaluated but not included in this update due to a lack of information about fault location, geometry, or recurrent Quaternary activity. These updates to the fault sections, fault-zone polygons, and earthquake geology databases will inform fault geometry and activity rates of CEUS sources during the 2023 NSHM implementation.

Seismological Research Letters↗

USGS2022

Paleoseismic investigation of the Taylorsville fault at the Airport East site, West Valley fault zone, Salt Lake County, Utah

The West Valley fault zone (WVFZ) and Salt Lake City segment (SLCS) of the Wasatch fault zone comprise Holoceneactive normal faults that bound an intrabasin graben in northern Salt Lake Valley, Utah. Both fault zones have evidence of recurrent Holocene surface-faulting earthquakes. A topic of recent research is the seismogenic relation of the antithetic (subsidiary) WVFZ to the Wasatch fault zone—specifically, to what degree are WVFZ earthquakes independent of slip on the SLCS, or other adjacent segments, of the Wasatch fault zone. To improve paleoseismic data for the WVFZ and better understand the seismogenic relation between the WVFZ and Wasatch fault zone, we conducted a fault-trench investigation at the Airport East site, developed new earthquake recurrence and fault sliprate estimates for the WVFZ, and compared WVFZ earthquake timing data with data from the Wasatch fault zone. The Airport East site is near the northern end of the easternmost traces of the WVFZ, collectively referred to as the Taylorsville fault. At this site, we excavated two parallel trenches across a small (~0.5-m high) east-facing fault scarp. Shallow groundwater severely limited trench depth, and we were able to expose deposits only as old as mid-Holocene. However, the late Holocene section contained evidence for three surfacefaulting earthquakes on the Taylorsville fault, as well as earthquake-related deformation (liquefaction and folding) from a fourth earthquake that was likely sourced elsewhere. Based on OxCal modeling of radiocarbon and optically stimulated luminescence ages, the most recent earthquake, AE1, occurred at 0.4 ± 0.2 ka (mean modeled time ± 2σ), earthquake AE2 occurred at 0.6 ± 0.2 ka, and earthquake AE3 occurred at 2.0 ± 0.3 ka. Timing data from the Airport East site indicate the liquefaction and folding event (LE1) occurred at 5.1 ± 0.3 ka. Net vertical displacement across the fault is 0.6–1.1 m, and calculations of mean per-event displacement range from 0.20 to 0.37 m. Inter-event recurrence intervals for the Taylorsville fault at the Airport East site vary from 200 to 1400 yr, and the mean late Holocene (post-2 ka) recurrence interval is 800 yr. Paleoseismic (closed-interval) slip rates range from 0.23 to 1.4 mm/yr, and geologic (open-interval) slip rates range from 0.1–0.2 mm/yr over the past ~5000 yr to 0.2–0.4 mm/yr over the past ~2500 yr. Combining our new Airport East data with previous paleoseismic data for the WVFZ shows that during individual late Holocene earthquakes, surface faulting has occurred on either the Taylorsville or Granger fault, but not both faults at the same time (at least not on the parts of the faults that have been trenched). However, five mid- to late Holocene WVFZ earthquakes have mean modeled times that are either very similar or identical to mean modeled times of SLCS and Weber-segment earthquakes, and temporal correlations of two additional late Pleistocene WVFZ earthquakes with SLCS earthquakes cannot be ruled out. When comparing the earthquake chronologies of the WVFZ and Wasatch fault zone, our new data lend support to the idea that, more often than not, some part of the WVFZ moves in response to, and possibly synchronously with, slip on the Wasatch fault zone.

Utah↗

USGS2022

Mid- to late Quaternary geomorphic and paleoseismic event history, Cheraw fault, southeastern Colorado

Despite its subdued expression and isolated location within the Great Plains of southeastern Colorado, the 80 km long Cheraw fault may be one of the most active faults in North America east of the Rocky Mountains. We present geomorphic analyses, geochronology, and paleoseismic trenching data to (1) document the rupture history of the ∼45 km long southwestern section of the Cheraw fault over the past ∼19 ka, and (2) evaluate slip rate changes for the entire fault over the past ∼200 ka. Results from new trenches excavated at the Old Ranch site show evidence of four surface rupture events since ∼19 ka, each with an average vertical displacement of 0.75 ± 0.15 m. An additional event is likely only slightly older than ∼19 ka. Evidence for relatively small displacements at and near the Old Ranch site indicates that most of these earthquakes were magnitude ( M ) 7 or less and likely did not rupture the full length of the Cheraw fault. Since ∼19 ka, the average slip rate is ∼0.16 ± 0.3 mm/yr near the Old Ranch site with an average interevent time of 3–5 ka. New geochronologic data for mid‐ to late‐Quaternary geomorphic surfaces cut by the Cheraw fault imply rapid incision by local Arkansas River tributaries from ∼145 to ∼100 ka. Maximum vertical offsets of 7–9 m for these surfaces indicate that from ∼19 to >200 ka the average slip rate was no greater than ∼0.03 mm/yr. The accelerated slip rate since ∼19 ka indicates a possible response to rapid erosional unloading and/or a limited late Cenozoic, <40 ka, paleoseismic history for the Cheraw fault.

Colorado↗

USGS2022

A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy

The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. To explore theoretical colluvial wedge evolution, we develop a cellular automata model driven by the production and disturbance (e.g., bioturbative reworking) of mobile regolith and fault-scarp collapse. We consider both 90 and 60 ∘ dipping faults and allow the colluvial wedges to develop over 2000 model years. By tracking sediment transport time, velocity, and provenance, we classify cells into analogs for the debris and wash sedimentary facies commonly described in paleoseismic studies. High values of mobile regolith production and disturbance rates produce relatively larger and more wash-facies-dominated wedges, whereas lower values produced relatively smaller, debris-facies-dominated wedges. Higher lateral collapse rates lead to more debris facies relative to wash facies. Many of the modeled colluvial wedges fully developed within 2000 model years after the earthquake, with many being much faster when process rates are high. Finally, for scenarios with the same amount of vertical displacement, differently sized colluvial wedges developed depending on the rates of geomorphic processes and fault dip. A change in these variables, say by environmental change such as precipitation rates, could theoretically result in different colluvial wedge facies assemblages for the same characteristic earthquake rupture scenario. Finally, the stochastic nature of collapse events, when coupled with high disturbance, illustrates that multiple phases of colluvial deposition are theoretically possible for a single earthquake event.

Earth Surface Dynamics↗

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↗