Steven N. Bacon

A 25,000-year record of earthquakes on the Owens Valley fault near Lone Pine, California: Implications for recurrence intervals, slip rates, and segmentation models

Seven trenches in eastern California across the Owens Valley fault near Lone Pine expose two episodes of faulting since early Holocene time in the form of ∼1 m throw in lacustrine beds with liquefaction that were buried and then faulted again ∼1 m by the M 7.5 to 7.75 A.D. 1872 Owens Valley earthquake. Geomorphic maps, applications of sequence stratigraphy, and analyses of radiocarbon from charcoal and tufa deposits indicate that the paleoearthquake, the penultimate event here, occurred between 10,200 ± 200 and 8800 ± 200 cal yr B.P. The cumulative vertical displacement from these last two earthquakes in three trenches averages 2.4 ± 0.3 m (2σ), and the penultimate event has slightly larger displacements. A synthesis of available data indicates that the antepenultimate event was probably as large and occurred between ca. 24,000 and 14,000 cal yr B.P. (2σ). Thus, the two interseismic intervals between the last three surface-faulting earthquakes on the southern Owens Valley fault are each ∼10,000 yr. This ∼25,000-year record indicates that the “two-event” normal-oblique slip rate on the Owens Valley fault near Lone Pine is 1.0 ± 0.5 m/k.y. This result is similar to that of several previous geological studies here, yet it is still slower than slip rates on the northern Owens Valley fault and several factors slower than contemporary geodetic measurements. This study attempts to account for different dating methods and interpretational uncertainties, to acknowledge how little is known about the slip history of the Owens Valley fault and adjacent faults, and to consider the role of segmentation, as well as splay and distributed faulting, in comparisons of displacement data among different sites along the entire ∼100 ± 10 km length of the Owens Valley fault.

Paleo-equilibrium line altitude estimates from late Quaternary glacial features in the inland Kaikoura Range, South Island, New Zealand

Abstract A reconnaissance investigation of glacial features in the Inland Kaikoura Range (IKR), South Island, New Zealand, confirms that over 30 km of the length of the range, with a maximum elevation of 2885 m, has been extensively glaciated in the past, in contrast to previous reports. Identified glacial features include cirques, lateral moraines, moraine fragments and associated features, and rock glaciers. Up to five glacial advances have been identified in any one catchment in the range, with the most complete sequence found in Branch Stream, which drains the steep southeastern flank of the highest portion of the range. The lateral moraines of Branch Stream are impressive; they range in elevation from c. 1700 to 1200 m, and, because of their large size and relatively good state of preservation, they are interpreted to be of late Otiran age. Glacial features that are less well preserved and more fragmentary are found at lower elevations in other catchments (e.g., Dart, Muzzle, and Bluff Streams), and are here inferred to be of early‐mid Otiran age. The lack of preservation of older glacial landforms is attributed to the steep, unstable terrain of the IKR generated by the relatively high uplift rate (c. 5 mm/ yr), and consequent high erosion rate in the range, which is located in the hanging wall of the active Clarence Fault. A sequence of paleo‐equilibrium line altitudes (paleo‐ELAs) for the past glaciers in the IKR have been derived using cirque floor elevations, accumulation‐area ratios (AARs) and interpolated estimates, and give snowline depressions below the present (2530 m) of 830 m for the early‐mid Otiran, 740 m for late Otiran, 575 m for final Otiran, 450 m for Late Glacial, 270 m for Neoglacial, and 150 m for the Little Ice Age. Because glacial features in the IKR have yet to be directly dated, these age estimates should be regarded as interpretive in nature and are based solely on relative size, elevation, sequence position, and degree of preservation. The paleo‐ELAs have been normalised to a southerly aspect using a correction established in the northern Southern Alps that has yet to be tested in the IKR. Correcting for accrued uplift over the past c. 18 000 yr conceivably provides an additional c. 90 m of depression, suggesting a total ELA depression of as much as c. 830 m during the late Otiran compared to modern climate. The paleo‐ELA depression estimates for the IKR appear to be similar to estimates calculated in other areas in the South and North Islands. Evidence of glacial features in the IKR, and the apparent similarity of ELA depressions in the range with that elsewhere in New Zealand, suggests that past climate fluctuations in the IKR have been, to at least some degree, “in harmony” with those throughout the remainder of the country.

Total suspended particulate matter emissions at high friction velocities from desert landforms

[1] Most wind erosion studies that characterize dust emission potential measure particulate matter smaller than 10 mm (PM10) for air quality purposes or atmospheric modeling. Because the PM10 size fraction is only a portion of the total range of fine‐grained particles potentially emitted from desert landforms, we modified the miniature Portable In Situ Wind Erosion Lab (PI‐SWERL) by adding a new instrument to measure total suspended particulate matter (TSP). The modified PI‐SWERL is capable of measuring TSP with diameters <500 mm emitted from highly erodible surfaces at friction velocities up to 1.28 m s −1 . Undisturbed and artificially disturbed surfaces of six common landforms in the Negev Desert of Israel were studied to evaluate the utility of TSP measurements. These landforms include alluvial fans and plains armored by desert pavements, loessial soils with silt‐rich surficial crusts, fluvial loess with biological crusts, and active sand dunes. The landforms differ in character and surface age, thereby exhibiting a wide range of surface covers, soil properties, and soil strengths. Our results indicate that the magnitude of TSP emission is primarily controlled by geomorphic setting and surface characteristics. TSP and PM10 concentrations measured from dust‐rich loessial soils were significantly correlated, and TSP emission was best predicted at all sites using PM10 content and bearing capacity. Our results demonstrate that further research is needed to determine correction factors for friction velocities related to erodible, anisotropic surface roughness elements and that the modified PI‐SWERL is a promising tool to quantify total potential emission flux from desert landforms.

Holocene and Latest Pleistocene Oblique Dextral Faulting on the Southern Inyo Mountains Fault, Owens Lake Basin, California

The Inyo Mountains fault (imf) is a more or less continuous range-front fault system, with discontinuous late Quaternary activity, at the western base of the Inyo Mountains in Owens Valley, California. The southern section of the imf trends ∼N20°–40° W for at least 12 km at the base of and within the range front near Keeler in Owens Lake basin. The southern imf cuts across a relict early Pliocene alluvial fan complex, which has formed shutter ridges and northeast-facing scarps, and which has dextrally offset, well-developed drainages indicating long-term activity. Numerous fault scarps along the mapped trace are northeast-facing, mountain-side down, and developed in both bedrock and younger alluvium, indicating latest Quaternary activity. Latest Quaternary multiple- and single-event scarps that cut alluvium range in height from 0.5 to 3.0 m. The penultimate event on the southern imf is bracketed between 13,310 and 10,590 cal years b.p., based on radiocarbon dates from faulted alluvium and fissure-fill stratigraphy exposed in a natural wash cut. Evidence of the most recent event is found at many sites along the mapped fault, and, in particular, is seen in an ∼0.5-m northeast-facing scarp and several right-stepping en echelon ∼0.5-m-deep depressions that pond fine sediment on a younger than 13,310 cal years b.p. alluvial fan. A channel that crosses transverse to this scarp is dextrally offset 2.3 ± 0.8 m, providing a poorly constrained oblique slip rate of 0.1–0.3 m/k.y. The identified tectonic geomorphology and sense of displacement demonstrate that the southern imf accommodates predominately dextral slip and should be integrated into kinematic fault models of strain distribution in Owens Valley.

Predictive Soil Maps Based on Geomorphic Mapping, Remote Sensing, and Soil Databases in the Desert Southwest

We present an expert based system to rapidly predict the shallow soil attributes that control dust emissions in the arid southwest U.S. Our system’s framework integrates geomorphic mapping, remote sensing, and the assignment of soil properties to geomorphic map units using a soil database within a geographic information systems (GIS) framework. This expert based system is based on soil state factor-forming model parameters that include: (1) climate data, (2) landform, (3) parent material, and (4) soil age. The four soil-forming data layers are integrated together to query the soil database. To validate the accuracy of the expert based model and resultant predictive soil map, a blind test was performed at Cadiz Valley in the Mojave Desert, California. The desert terrain in Cadiz Valley consists of alluvial fans, fan remnants, sand dunes, and playa features. The test began with three users independently mapping an area of over 335 km2 using 1:40,000-scale base maps to rapidly create geomorphic and age class layers, and then integrating these with climate and parent material layers. The results of the four data layers were then queried in the soil data base and soil attributes assigned to map unit layers. The soil-forming model presented here is geomorphic-based, and considers soil age as a significant factor in accurately predicting soil conditions in hyper arid to mildly arid regions. This work comprises a successful first step in the development of an expert-based system to map shallow soil conditions in support of dust emission models in remote desert regions.

Integrated Terrain Forecasting for Military Operations in Deserts: Geologic Basis for Rapid Predictive Mapping of Soils and Terrain Features

During the past three decades, the U.S. armed forces have been called on repeatedly to operate in the deserts of the Middle East and southwest Asia. Avoiding locations susceptible to extreme dust emissions and other terrain-related hazards requires the ability to predict soil and terrain conditions, often from limited information and under dynamic environmental conditions. This paper reports the approach used to develop an integrated, predictive tool for forecasting terrain conditions to support military operations in desert environments at strategic, operational, and tactical scales. The technical approach relies on the systematic integration of desert landform parameters in geomorphic models for predicting terrain conditions. This integrated effort is performed in a geographic information system (GIS) framework using expert-based analysis of airborne and spaceborne imagery to identify terrain elements. Advances in earth science research have established that unique, predictable relations exist among landscape position, soils, vegetation, and geology. Furthermore, new instrumentation allows the collection of a wide range of environmental information to characterize surface and subsurface conditions. By integrating models and methods from geomorphology, soil science, climatology, and atmospheric science with remote sensing and other technologies, a predictive model can be developed to support military operations.

Regional Distribution of Salt-Rich Dust Across Southwest Asia Based on Predictive Soil-Geomorphic Mapping Techniques

Understanding the source regions of soluble salt-rich dust is critical for military operations, monitoring potential environmental health impacts to military personnel, and for mitigating abrasion and corrosion to military materiel operating in desert regions. Arid regions are characterized by saline soils which are formed by a lack of precipitation and influenced by surrounding and underlying geology, among other factors. The dust content in soils and surface sediments in southwest Asia is commonly associated with specific landforms. This paper uses a soil-geomorphic conceptual model that integrates geographic datasets of Landsat imagery, soil and landforms, precipitation data, and geologic maps to produce derivative map-based predictions of the spatial distribution and content of salt-rich dust-sized particle in soils and surface sediments in the region. The derivative map is based on three regional dust and salt content maps and the assignment of a five-fold rating class and numerical factor value system to individual map polygons [e.g., Very High (5), High (4), Moderate (3), Low (2), Very Low (1)]. The three regional maps include: (1) dust content based on the identification of distinct landform assemblages from 15-m resolution compressed LANDSAT TM+ imagery at a scale of 1:750,000, (2) salt content developed from 1 km2-resolution mean annual precipitation data, and (3) geologic-based salt content developed from published geologic maps. This study presents an initial step towards the prediction of salt-rich dust sources at regional scales that is aimed to provide information to planning military operations and for mitigating the hazards of dust on military personnel and equipment operating in desert regions. The approach used to predict dust and salt sources could also be used to refine atmospheric dust loading models that require knowledge of the spatial distribution of geomorphic-based input parameters.

Military Test Site Characterization and Training Future Officers—An Integrated Terrain Analysis Approach

U.S. military equipment has become more sensitive to environmental conditions than ever before, especially with increasing application of sophisticated microprocessors, wireless connectively, and sensors commonly employed on highly maneuverable armored vehicles. Increasing development of military technology requires considerably more comprehensive information about the extreme testing environment (i.e., natural environmental test sites) than was required nearly a half century ago. An all-encompassing research, development, and testing program for current and new designs of tracked and wheeled military vehicles, the primary means of transport for U.S. ground forces, depends on the use of an extensive network of vehicle mobility and durability (i.e., endurance) test courses located in a variety of temperate, tropical, desert, and cold region environments. Most of these test courses consist of unimproved, dirt or gravel roads, primarily developed on the native soil and landscape. Although several of these test courses have been in use for nearly 50 years, many of their geotechnical attributes have not been characterized. In support primarily of the Army’s Test and Evaluation Command (ATEC) mission, the Department of Geography and Environmental Engineering (GEnE) from the United States Military Academy (USMA) at West Point and the Desert Research Institute (DRI) characterized numerous test courses at various geographic locations. Since 2007, multiple teams from West Point, primarily consisting of Cadets with supervising officers, have worked in collaboration with DRI to characterize geotechnical attributes of soils along test courses in desert, arctic, temperate and tropical landscapes. These data collection activities also support the Army in providing future officers with field training associated with sample collection and data management. The characterization activities focused on making geotechnical measurements, sampling soils, collecting imagery, generating map data, and developing geospatial databases. This effort also included the preparation of databases of in situ geotechnical properties along test courses at representative locations to a depth of ~ 0.3 m (1 ft) that included the measurements of: soil stiffness and modulus, penetration and shear resistance, bulk density, and particle size distribution. These new data sets will assist the Department of Defense (DoD) and the Department of the Army (DA) in maintaining a varied and detailed inventory of characterized soil-landform assemblages in different fundamental environments from various test sites throughout the U.S. and abroad. In addition, the data collected and the information compiled through these site studies will also benefit the DoD community that tests emerging technologies for the detection and defeat of Improvised Explosive Devices (IEDs), which require significant understanding of the natural variability of both physical and chemical soil attributes.

Parent Material Mapping of Geologic Surfaces Using ASTER in Support of Integrated Terrain Forecasting for Military Operations

Predicting soil physical and chemical properties for military operations requires knowledge of the geologic and lithologic component of the soil parent material. Geologic maps, a traditional source of geologic information, are often limited in coverage or inadequate for determining the basic characteristics of a soil parent material. We describe an approach for the rapid development of geologic surface maps that identify the lithologic composition of soil parent material generated from ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) data. Generated maps of parent material, in turn, provide key input parameters for a comprehensive terrain predictive model that forecasts key soil and surface cover characteristics in support of military operations. Parent material maps are generated using a multilayer approach where calibrated image data are mapped into lithologic units that best identify soil parent material and corresponding landform units (i.e. bedrock, fan, playa, dune, etc.). A unique and critical aspect of our approach is that expert-based analysis of spectral and geospatial information can produce a geologic map, covering 1000–5000 km2 of terrain, of soil parent material and surface cover in as little time as nine staff-hours. The approach was developed with a guiding principle that terrain predictions in military operations must be rapidly developed for areas where available ground information is limited. Results indicate that it is possible to quickly produce a realistic map of soil parent material using ASTER data without any additional geologic information or data. Results also indicate that analysts developing parent material maps require expert knowledge in both spectral analysis of remotely sensed data and the geologic and geomorphic processes that form desert landforms.