Scarp Morphology Research Articles

Geomechanical Modeling of Ground Surface Deformation Associated with Thrust and Reverse-Fault Earthquakes: A Distinct Element Approach

ABSTRACTWe seek to improve our understanding of the physical processes that control the style, distribution, and intensity of ground surface ruptures on thrust and reverse faults during large earthquakes. Our study combines insights from coseismic ground surface ruptures in historic earthquakes and patterns of deformation in analog sandbox fault experiments to inform the development of a suite of geomechanical models based on the distinct element method (DEM). We explore how model parameters related to fault geometry and sediment properties control ground deformation characteristics such as scarp height, width, dip, and patterns of secondary folding and fracturing. DEM is well suited to this investigation because it can effectively model the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. Our results show that localized fault scarps are most prominent in cases with strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults. Based on insights from 45 experiments, the key parameters that influence scarp morphology include the amount of accumulated slip on a fault, the fault dip, and the sediment strength. We propose a fault scarp classification system that describes the general patterns of surface deformation observed in natural settings and reproduced in our models, including monoclinal, pressure ridge, and simple scarps. Each fault scarp type is often modified by hanging-wall collapse. These results can help to guide both deterministic and probabilistic assessment in fault displacement hazard analysis.

Revealing the hidden signature of fault slip history in the morphology of degrading scarps

Active faults accommodate tectonic plate motion through different slip modes, some stable and aseismic, others characterized by the occurrence of large earthquakes after long periods of inactivity. Although the slip mode estimation is of primary importance to improve seismic hazard assessment, this parameter inferred today from geodetic observations needs to be better constrained over many seismic cycles. From an analytical formulation developed for analyzing fault scarp formation and degradation in loosely consolidated material, we show that the final topographic shape generated by one earthquake rupture or by creep (i.e., continuous slip) deviates by as much as 10–20%, despite a similar cumulated slip and a constant diffusion coefficient. This result opens up the theoretical possibility of inverting, not only the cumulated slip or averaged slip rate, but also the number of earthquakes and their sizes from scarp morphologies. This approach is all the more relevant as the number of rupture events is limited. Estimating the fault slip history beyond a dozen earthquakes becomes very difficult as the effect of erosion on scarp morphology prevails. Our modeling also highlights the importance of trade-offs between fault slip history and diffusive processes. An identical topographic profile can be obtained either with a stable fault creep associated with rapid erosion, or a single earthquake rupture followed by slow erosion. These inferences, derived from the simplest possible diffusion model, are likely to be even more pronounced in nature.

Vessel Wake Impact Forces on Marsh Scarps

Priestas, A.M.; Styles, R., and Bain, R., 2023. Vessel wake impact forces on marsh scarps. Journal of Coastal Research, 39(2), 207–220. Charlotte (North Carolina), ISSN 0749-0208. A common morphological feature of high-energy coastal plain salt marshes is an erosive scarp separating the marsh platform from the abutting tidal flat. A noted deficiency in the understanding of scarp erosion is a lack of direct wave impact measurements to better constrain the physical processes driving material loss. To measure wave impact forces, load cells were embedded into a scarp face along the Intracoastal Waterway in northern Florida, which is frequented by shallow-draft vessels. The largest impact forces occurred when the mean water surface elevation was just below the midpoint of the scarp and decayed as the mean depth either increased or decreased. Early wave breaking around low tide reduced the direct impact on the scarp, whereas wave reflection around high tide reduced wave breaking and the associated maximum impact force. The sensitivity of impact force to tidal stage suggests that wave energetics (breaking vs. reflection) and scarp morphology (ramp vs. near-vertical surface) combine to produce a force pattern that favors maximum impact around midtide. Regression analysis indicated that the impact pressures were positively correlated with wave power and dynamic pressure, which are primary metrics used to model shoreline erosion. This study argues that the critical threshold for erosion may be refined by evaluating the relationship between impact pressures and marsh resistance, since wave exposure alone does not necessarily initiate erosion.

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

Abstract 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, 40Ar/39Ar 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 40Ar/39Ar 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.

Constraining Paleoseismicity of the Wulashan Piedmont Fault on the Northern Margin of the Ordos Block From Fault Scarp Morphology

Fault scarps preserve important information about past earthquakes on a fault, and thus can be applied to investigate the fault slip histories and rupture patterns. In this study, the morphology of fault scarps was used to constrain the paleoseismicity of the Wulashan Piedmont Fault located on the northern margin of the Ordos Block based on high-resolution LiDAR topography. We constructed the vertical displacement distribution of the fault through measuring the heights of a large number of scarp profiles extracted on different geomorphic surfaces along the fault. Through statistical analysis of the dense collection of vertical displacement dataset, a total of seven paleoseismic events were identified which followed a characteristic slip pattern with an average slip of ∼1.0 m. We further detected slope breaks in the fault scarp morphology to quantify the number of paleoearthquakes that occurred on the scarps, and discriminated at least five individual surface-breaking events. Both the number and slip of paleoearthquakes recognized from the morphology of fault scarps were in good agreement with previous paleoseismic trenching records. Based on the empirical scaling relationship between moment magnitude and rupture parameters, a moment magnitude ofMw6.7–7.5 was determined for the paleoearthquakes occurred on the fault. With the fault slip rate derived by previous studies, we estimated an average recurrence interval of 1.3–1.8 kyr for the paleoseismic events, which is very close to the elapsed time since the most recent earthquake, indicating a high potential seismic hazard on the Wulashan Piedmont Fault.

Structural and biological analysis of faults in basalts in Sheepshead Mountains, Oregon as an Earth analogue to Mars

Endoliths and chasmoendoliths, organisms that live in rock fractures, rely on connected open spaces in rocks for fluid and nutrient circulation on Earth and perhaps other planetary bodies. These life forms are not visible from orbit or easily detectable by rover cameras, but the fracture networks and scarp morphologies associated with fracture networks are measurable. We conducted a field analogue study of 92 normal fault scarps in the Sheepshead Mountains, Oregon to examine the correlation between scarp morphology and vegetation growth in the Steens Basalt of the Columbia River Flood Basalts. While vegetation is not expected on Mars or other bodies, the fracture networks that sustain vegetation are the same that would support and protect endoliths. Structural variables measured in the field are: percent of fault scarp that is fault surface and talus surface, scale of columnar jointing, consistency in location of columns, talus size and sorting, fault lengths, distance to hot springs and playa lakes, and strike and dips of fault surfaces, talus surfaces, and flow bedding. Infrared spectra of fault scarps were measured using a handheld multispectral camera and Normalized Difference Vegetation Index (NDVI) were calculated from these images in ArcGIS™. Statistical analysis of the scarp morphologic parameters indicate that interconnectedness of fractures is key for elevated NDVI and is represented by a range of parameters including bedding strike, talus sorting, and proximity to playas. Results support a model for ideal slopes to investigate for preserved biological activity on Mars.

Особенности вертикальных смещений вдоль Дельтового разлома при Цаганском землетрясении 1862 г. на Байкале

Based on the ground penetrating radar, geological and morphostructural data, the particularities of single-event vertical displacements in Holocene sediments of various competencies along the land and underwater segments of the Delta fault activated on January 12, 1862 during the M ~ 7.5 Tsagan earthquake (southeastern side of the Baikal rift.). It is shown that the slip determined from the scarp morphology and the position of the main rupture in the section reflects the total displacement value, which is the sum of the brittle and plastic deformational components. The presence of water-saturated poorly consolidated sediments in the geological section increases the contribution of the plastic component. In this case, the width of the rupture zone increases. Despite the fact that the northeastern segment of the Delta Fault was submerged in the water of Proval Bay, the largest seismotectonic displacements occurred between the villages of Kudara and Sherashevo and on the outskirts of the village Dubinino in the land southwestern part of the structure, where the total displacement was 9,59 and 9,28 m, respectively. No such depths were recorded in Proval Bay after the earthquake. Along the Delta Fault under water, seismotectonic displacements were relatively small with a rather significant contribution of the plastic component from 26 to 53 %. This slip was a trigger for the seismic- gravity subsidence of the bay and sediment compaction, which continues to this day, judging by its almost unchanged depth since 1862 and the proximity of numerous seismic events, including the last Мs = 5.4 09.12.2020 earthquake happened on December 9, 2020 and strongly felt in Irkutsk.

Non-planarity, scale-dependent roughness and kinematic properties of the Pidima active normal fault scarp (Messinia, Greece) using high-resolution terrestrial LiDAR data

Terrestrial LiDAR (TLS), photogrammetric and field data were collected during the years 2014, 2015 and 2017, at a 20-m long limestone scarp locality along the N–S striking, 70° west-dipping, active Pidima fault (Messinia, SW Peloponnese, Greece). This locality presents an artificially exhumed portion of an active fault plane, thus providing a unique opportunity to study kinematics and limestone scarp morphology (including its curvature and roughness). The survey of 2015 offered a high-density point cloud of the fault scarp with 6-mm working resolution, creating a very close to real life representation 3D model. We found that scarp geometry is non-planar with increasing convexity up-dip and increasing northwesterly dip-directions from north towards south, along strike. Non-planarity is also recorded from the morphological data along strike with the appearance of several, slip-parallel troughs and ridges with a mean distance (half-wavelength) of 0.75 m. The fault-plane roughness (absolute values) is scale dependent. The roughness configuration attains a slip-parallel pattern for observation scales above 1-cm. At observations scales less than 1-cm a slip-normal pattern is weakly visible. The obtained TLS results agree with field data (manual compass measurements) and macroscopic observations. We infer an earthquake magnitude of 6.2 ± 0.2 for the last event along the Pidima fault based on the measured thickness of the smooth stripe that was imaged by t-LiDAR along the non-exhumed surface of the scarp.

Assessment of a seismo-neotectonic origin for the New Liskeard–Thornloe scarp, Timiskaming graben, northeastern Ontario

To test an inference that the New Liskeard–Thornloe scarp (NLTS), Timiskaming graben, Ontario, is a deglacial–postglacial seismo-neotectonic fault, we collected shallow geophysical data along lines 7.2, 0.28, and 0.52 km long, located on three roads crossing the middle portion of the scarp. Data revealed a valley subsurface composed of bedrock (seismic unit a), glaciolacustrine–lacustrine deposits (units b to f), mass movement deposits (units ls 1 to ls 3), wave-worked sediments, mass wasting deposits and (or) artificial fill (unit g), and a minor occurrence of roadfill (unit h). The bedrock surface exhibits only minor undulations in the area underlying the scarp, indicating that the scarp morphology is unrelated to the underlying bedrock topography. Parallel reflectors in glaciolacustrine seismic units b and c conformably overlie the minor bedrock undulations and there is an absence of disturbed or offset zones within the reflectors underlying the scarp. This lack of disturbance or offset provides strong evidence that the scarp is not the product of deglacial–postglacial seismo-neotectonic faulting. The erosive truncation of glaciolacustrine seismic units d and e indicate that the scarp is an erosive feature cut into the glaciolacustrine deposits. It is likely a bluff formed by shoreline erosion, as is consistent with a geomorphic setting previously inundated by a large glacial lake and subsequent recessional lake stages. The non-fault origin for the NLTS limits the northern extent of the hypothesized Timiskaming East Shore Fault to within the Lake Timiskaming basin and, hence, constrains estimates of maximum rupture length.

CFD flow dynamics over model scarps and slopes

ABSTRACT Knowledge of wind flow over dune scarps and, as scarps fill, their subsequent various slopes, is important for understanding sediment transport pathways from beach to dunes. In this study, flow over scarps (also termed forward-facing steps) is reviewed, and the flow over a vertical scarp (90°) and three slopes of 45°, 24°, and 14°, all 2 m in height, is examined via CFD modelling. The flow over three 90° scarps, with heights of 1 m, 2 m and 4 m, and over a 2-m high vertical (90°) scarp for three oblique incident winds is studied. The extent of wind flow deceleration and separation becomes smaller with decreased slope, with maximum flow separation and reverse vortex development occurring on the vertical scarp. The extent of crest wind flow separation is greatest for the scarp and considerably less for the 45° slope. As scarp height increases, so too does the spatial extent of turbulent wind flow, wind speed, and extent of the flow separation region. As incident wind direction became more oblique over a vertical scarp, less deceleration occurs, and helicoidal vortices replace roller vortices. Our results demonstrate how scarp morphology and wind direction are likely to influence transport pathways.

A semi-automated algorithm to quantify scarp morphology (SPARTA): application to normal faults in southern Malawi

Abstract. Along-strike variation in scarp morphology reflects differences in a fault's geomorphic and structural development and can thus indicate fault rupture history and mechanical segmentation. Parameters that define scarp morphology (height, width, slope) are typically measured or calculated manually. The time-consuming manual approach reduces the density and objectivity of measurements and can lead to oversight of small-scale morphological variations that occur at a resolution impractical to capture. Furthermore, inconsistencies in the manual approach may also lead to unknown discrepancies and uncertainties between, and also within, individual fault scarp studies. Here, we aim to improve the efficiency, transparency and uniformity of calculating scarp morphological parameters by developing a semi-automated Scarp PARameTer Algorithm (SPARTA). We compare our findings against a traditional, manual analysis and assess the performance of the algorithm using a range of digital elevation model (DEM) resolutions. We then apply our new algorithm to a 12 m resolution TanDEM-X DEM for four southern Malawi fault scarps, located at the southern end of the East African Rift system: the Bilila–Mtakataka fault (BMF) and three previously unreported scarps – Thyolo, Muona and Malombe. All but Muona exhibit first-order structural segmentation at their surface. By using a 5 m resolution DEM derived from high-resolution (50 cm pixel−1) Pleiades stereo-satellite imagery for the Bilila–Mtakataka fault scarp, we quantify secondary structural segmentation. Our scarp height calculations from all four fault scarps suggest that if each scarp was formed by a single, complete rupture, the slip–length ratio for each earthquake exceeds the maximum typical value observed in historical normal faulting earthquakes around the world. The high slip–length ratios therefore imply that the Malawi fault scarps likely formed in multiple earthquakes. The scarp height distribution implies the structural segments of both the BMF and Thyolo fault have merged via rupture of discrete faults (hard links) through several earthquake cycles, and the segments of the Malombe fault have connected via distributed deformation zones (soft links). For all faults studied here, the length of earthquake ruptures may therefore exceed the length of each segment. Thus, our findings shed new light on the seismic hazard in southern Malawi, indicating evidence for a number of large (Mw 7–8) prehistoric earthquakes, as well as providing a new semi-automated methodology (SPARTA) for calculating scarp morphological parameters, which can be used on other fault scarps to infer structural development.

Investigating paleoseismicity using fault scarp morphology of the Dushanzi Reverse Fault in the northern Tian Shan, China

This study uses the morphology of fault scarps to study the paleoseismic history of the Dushanzi Reverse Fault (DRF) in the northern Tian Shan region, China. Using high-resolution LiDAR DEMs to create a large number of scarp profiles, we detected slope breaks in the fault scarp morphology to quantify the number of paleoearthquakes that occurred on the scarps and obtained the along-strike scarp height distribution to determine the cumulative and single-event vertical displacements. Our results revealed four surface-rupturing events with similar co-seismic vertical displacements of ~1.4 m via the statistical analysis of displacement datasets and slope breaks, which were in agreement with the findings from paleoseismic trenching. We then assessed the paleomagnitudes using the empirical scaling relationships between moment magnitude and rupture parameters and the recurrence interval for surface-rupturing events using the formation ages of the displaced terrace surfaces. The results indicate that the possible magnitudes range from Mw 6.5 to 6.7, even reaching Mw ~7.2 in the case of a multi-fault rupture of the entire anticline-fault belt, with an average recurrence interval of ~2.4–3.0 ka. This study also demonstrates the importance of using high-resolution topographic data in paleoseismic investigations, which enables the determination of fine-scale tectono-geomorphic interpretations and detailed offset measurements over large regions along the fault.

Late Quaternary tectonic activity and shortening rate of the Beiluntai fault zone in the South Tianshan, Xinjiang, NW China

The Beiluntai fault is a Holocene active fault and is the boundary fault between the South Tianshan and Tarim Basin. Since the Late Quaternary, the continuous activities of the Beiluntai fault have caused dislocation, deformation, and fold uplift of multi-phase alluvial geomorphologic surfaces. Using a high-precision differential global positioning system, we measured the fault scarp morphology of multi-phase geomorphologic surfaces in the Akeaiken and Zhuanchang sections of the Beiluntai fault. Via large-scale active fault mapping, we found that the Akeaiken section is dominated by thrusting, while the Zhuanchang section is dominated by fold uplift. We obtained the ages of the different phases of the geomorphologic surfaces (Fan4, Fan3b, Fan3c, and Fan2) using the optically stimulated luminescence dating method. We found that since the formation of the Fan4 geomorphologic surface, the crustal shortening rate (approximately 2.4 mm/a) of the Akeaiken section has remained basically constant. However, the crustal shortening rate of the Zhuanchang section in the south–north direction (1.43–1.81 mm/a) during the Late Quaternary was significantly less than that in the Akeaiken section, suggesting that the crustal shortening rate in the south–north direction of the Beiluntai fault zone decreases from west to east. A comprehensive comparison of the South Tianshan piedmont thrust-and-fold belt system also showed that the crustal shortening rate decreases from west to east.

Geomorphological and structural patterns of the scarp‑related steep dry valleys in limestone ridges: A case study from South Carpathians, Romania

Scarp retreat is a common natural process which drives the evolution of landscape in monoclinal or horizontally bedded structures. The NW‑facing, retreating limestone slope of the Vânturarița‑Buila Massif, a mountain ridge in the South Carpathians, is incised by steep dry valleys (SDVs), parallel to each other and perpendicular to the ridge crest. We performed morphometric and structural analyses on these features in order to estimate the geomorphic control on the scarp retrogressive evolution and their relations to tectonics. Longitudinal profiles display most of their relevant morphometry. Average slope commonly ranges between 35° and 50°, often exceeding 60° on certain segments. Lengths reflect the variability of exposed caprock thickness, and changes in slope show the structural control of bedding on scarp morphology. Spatial distribution and development of the steep dry valleys, as well as the scarp retreat process, is controlled by tectonic lineaments. We performed a comparative orientation analysis on fractures of extensional origin, dextral strike‑slip faults, major faults, and steep dry valleys. Results show preferred orientations on the NW‑SE and NE‑SW. Variability in size and morphology of the amphitheater‑shaped scarp sectors depends on the exposed caprock thickness. Speleothems formed in crevice‑type caves and unearthed by scarp retreat were found along some of the steep dry valleys. This study shows that combined geomorphological and structural analysis of steep dry valleys from alpine limestone ridges can provide valuable information on the evolution and morphology of the retreating scarp they develop on.

Observations on normal-fault scarp morphology and fault system evolution of the Bishop Tuff in the Volcanic Tableland, Owens Valley, California, U.S.A.

Mapping of normal faults cutting the Bishop Tuff in the Volcanic Tableland, northern Owens Valley, California, using side-looking airborne radar data, low-altitude aerial photographs, airborne light detection and ranging (LiDAR) data, and standard field mapping yields insights into fault scarp development, fault system evolution, and timing. Fault zones are characterized by multiple linked fault segments, tilting of the welded ignimbrite surface, dilation of polygonal cooling joints, and toppling of joint-bounded blocks. Maximum fault zone width is governed by ( i ) lateral spacing of cooperating fault segments and ( ii ) widths of fault tip monoclines. Large-displacement faults interact over larger rock volumes than small-displacement faults and generate larger relay ramps, which, when breached, form the widest portions of fault zones. Locally intense faulting within a breached relay ramp results from a combination of distributed east-west extension, and within-ramp bending and stretching to accommodate displacement gradients on bounding faults. One prominent fluvial channel is offset by both east- and west-dipping normal faults such that the channel is no longer in an active flowing configuration, indicating that channel incision began before development of significant fault-related geomorphic features. The channel thalweg is “hanging” with respect to modern (Q1) and previous (Q2) Owens River terraces, is incised through the pre-Tahoe age terrace level (Q4, 131–463 ka), and is at grade with the Tahoe age (Q3, 53–119 ka) terrace. Differential incision across fault scarps implies that the channel remained active during some of the faulting history, but it was abandoned between Q2 and Q3 time, while faulting continues to the present day.

Investigating multiple fault rupture at the Salar del Carmen segment of the Atacama Fault System (northern Chile): Fault scarp morphology and knickpoint analysis

This study presents a new geomorphological approach to investigate the past activity and potential seismic hazard of upper crustal faults at the Salar del Carmen segment of the Atacama Fault System in the northern Chile forearc. Our contribution is based on the analysis of a large set of topographic profiles and allows extrapolating fault analysis from a few selected locations to distances of kilometers along strike of the fault. We detected subtle changes in the fault scarp geometry which may represent the number of paleoearthquakes experienced by the structure and extracted the cumulative and last incremental displacement along strike of the investigated scarps. We also tested the potential of knickpoints in channels crossing the fault scarps as markers for repeated fault rupture and proxies for seismic displacement. The number of paleoearthquakes derived from our analysis is 2–3, well in agreement with recent paleoseismological investigations, which suggest 2–3 earthquakes (Mw = 6.5–6.7) at the studied segments. Knickpoints record the number of events for about 55% of the analyzed profile pairs. Only few knickpoints represent the full seismic displacement, while most retain only a fraction of the displacement. The along-strike displacement distributions suggest fault growth from the center toward the tips and linkage of individual ruptures. Our approach also improves the estimation of paleomagnitudes in case of multiple fault rupture by allowing to quantify the last increment of displacement separately. Paleomagnitudes calculated from total segment length and the last increment of displacement (Mw = 6.5–7.1) are in agreement with paleoseismological results.

Geophysical and Geomorphological Analysis of the Teton Fault, Wyoming

This investigation applied geophysical and geomorphological analyses of the Teton Fault to assess its geometry, history, and influences on landscape evolution. This project builds on results from a preceding geophysical study completed one year ago (Thackray et al. 2014), a recent study of fault scarp morphology (Thackray and Staley, in review), and years of previous studies of the fault by many practitioners.

Deciphering cumulative fault slip vectors from fold scarps: Relationships between long‐term and coseismic deformations in central Western Taiwan

AbstractWe document the 30 ka cumulative slip history and long‐term slip vector azimuth on the northern Chelungpu fault based on a series of fault‐bend folded alluvial terraces and draw quantitative relationships between geological structure, deformation observed from the geomorphology, and coseismic displacements during the 1999Mw = 7.6 Chi‐Chi earthquake. In our study area, three main terrace levels show progressive folding by kink band migration in relation to the underlying fault geometry, forming a main N‐S fold scarp up to ~193 m high and secondary E‐W scarps. Detailed analysis using 5 m resolution digital elevation model allows us to characterize the scarp morphology and quantify the deformation parameters, namely, terrace heights, fold scarp relief, and fold limb width and slope angle. The 3‐D deformation of the highest terrace, dated by optically stimulated luminescence at 30.2 ± 4.0 ka, enables to simultaneously determine amplitude and azimuth of the long‐term slip vector based on scarp relief. The long‐term slip vector, oriented N338° ± 6°, is found to parallel the Chi‐Chi coseismic displacements in this area. Cumulative slip and dating results yield a constant slip rate of 17.7 ± 2.2 mm/a in the direction N338° ± 6°. Late Quaternary shortening rates observed at four sites vary along strike in a similar way to Chi‐Chi coseismic displacements. Together with the collinearity of long‐term and coseismic slip vectors at our study site, this suggests that Chi‐Chi earthquake is a characteristic earthquake for the Chelungpu thrust with recurrence interval ~470 years. We also discuss implications for the regional and long‐term distribution of shortening in the central Western Foothills.

Holocene scarp on the Sawtooth fault, central Idaho, USA, documented through lidar topographic analysis

High-resolution lidar data reveal a prominent latest Pleistocene–Holocene scarp on the Sawtooth fault (central Idaho, United States). The fault scarp marks 55–65 km of the range front, and may comprise two segments. The scarp is 4–9 m high in latest Pleistocene glacial landforms (11–14 ka) and 2–3 m high in Holocene alluvial landforms, implying 2–3 postglacial rupture events. Patterns of fault scarp continuity, coupled with existing gravity data, suggest that active faulting may have migrated northward during Pleistocene time. Detailed comparisons of raw lidar digital elevation models (DEMs), bare-earth lidar DEMs, and field surveys indicate that the bare-earth lidar data document the fault scarp morphology accurately and allow for detailed fault analysis where field evaluation is difficult. The documentation of Holocene motion on the Sawtooth fault demonstrates that ENE-directed extension extends across central Idaho, and that the fault contributes to seismic hazards.

Spatial patterns of geomorphic surface features and fault morphology based on diffusion equation modeling of the Kumroch Fault Kamchatka Peninsula, Russia

Remote sensing data sets are widely used for evaluation of surface manifestations in active tectonic areas. This study utilizes ASTER GDEM and Landsat ETM+data sets with Google Earth images draped over terrain models. This study evaluates the surrounding surface geomorphology of the study area with these data sets and the morphology of the Kumroch Fault using diffusion modeling to estimate diffusion constants (κ), as well as to estimate slip-rates by means of real ground data measured across fault scarps by Kozhurin et al. (2006). The study area is located southeast of the Bezymianny Volcano within the Central Kamchatka Depression. It is part of the Kumroch Fault Zone. The area contains numerous geomorphic features indicative of active deformation, such as fault scarps, ponds, offset streams, and glacier moraines.The ASTER GDEM and Landsat ETM+data together with Google Earth imagery were used to create accurate geomorphic maps of specific sites within the study area along the western flank of the East Kamchatka Range. Previous studies have estimated the time elapsed since slip initiation of the faulted surface on the Kumroch Fault and the slip-rate by dividing the offset of moraines by the age of the ruptured surface. Slip-rates along the Kumroch Fault vary from 2.0mm/yr–2.5mm/yr, determined from previous 14C studies with time frames of 11.5ka to 14ka. Other slip-rates for the Kumroch Fault were determined from previous studies through tephra and stratigraphic chronology. These produced rates of 0.6mm/yr, with time frames of 3.2ka–10.5ka. Models of the evolution of fault scarp morphology provide the amount of time elapsed since slip initiated on a faults surface. They may therefore provide more accurate estimates of slip-rate than those calculated by dividing scarp offset by the age of the ruptured surface. Profile modeling of scarps collected by Kozhurin et al. (2006) show that the scarps were formed by several events distributed over time. They were evaluated using a constant slip-rate (CSR) solution which yields a value A/κ (1/2 slip rate/diffusivity). Time elapsed since slip initiated on the fault is determined by establishing a value for κ and measuring total scarp offset. For this study, CSR nonlinear modeling assisted in estimates of κ which along the Kumroch Fault range from 8m2/ka to 14m2/ka. Slip-rates have been estimated to range from 0.6mm/yr to 1.0mm/yr since 3.4ka–3.7ka. This method provides a quick and inexpensive way to gather data for a regional tectonic study and establish estimated rates of tectonic activity.