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At least 1,531 records · Page 85Linked to original sources

USGS2014

Rapid mapping of ultrafine fault zone topography with structure from motion

Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from varying viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workflow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by existing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the first site, an ∼0.1 km 2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly >700 points/m 2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ∼50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (∼4 points/m 2 ) airborne LiDAR point cloud are mostly <3 cm. The second site spans an ∼1 km section of the 1992 Landers earthquake scarp. A colored point cloud of density mostly >530 points/m 2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ∼60 m above ground level. Closest point vertical distances to existing terrestrial LiDAR data of comparable density are mostly <6 cm. Each SfM survey took ∼2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earthquakes as well as rapid response mapping or long-term monitoring of faulted landscapes.

California↗

USGS2015

Geologic and structural controls on rupture zone fabric: A field-based study of the 2010 M w 7.2 El Mayor–Cucapah earthquake surface rupture

We systematically mapped (scales >1:500) the surface rupture of the 4 April 2010 Mw (moment magnitude) 7.2 El Mayor-Cucapah earthquake through the Sierra Cucapah (Baja California, northwestern Mexico) to understand how faults with similar structural and lithologic characteristics control rupture zone fabric, which is here defined by the thickness, distribution, and internal configuration of shearing in a rupture zone. Fault zone thickness and master fault dip are strongly correlated with many parameters of rupture zone fabric. Wider fault zones produce progressively wider rupture zones and both of these parameters increase systematically with decreasing dip of master faults, which varies from 20° to 90° in our dataset. Principal scarps that accommodate more than 90% of the total coseismic slip in a given transect are only observed in fault sections with narrow rupture zones (<25 m). As rupture zone thickness increases, the number of scarps in a given transect increases, and the scarp with the greatest relative amount of coseismic slip decreases. Rupture zones in previously undeformed alluvium become wider and have more complex arrangements of secondary fractures with oblique slip compared to those with pure normal dip-slip or pure strike-slip. Field relations and lidar (light detection and ranging) difference models show that as magnitude of coseismic slip increases from 0 to 60 cm, the links between kinematically distinct fracture sets increase systematically to the point of forming a throughgoing principal scarp. Our data indicate that secondary faults and penetrative off-fault strain continue to accommodate the oblique kinematics of coseismic slip after the formation of a thoroughgoing principal scarp. Among the widest rupture zones in the Sierra Cucapah are those developed above buried low angle faults due to the transfer of slip to widely distributed steeper faults, which are mechanically more favorably oriented. The results from this study show that the measureable parameters that define rupture zone fabric allow for testing hypotheses concerning the mechanics and propagation of earthquake ruptures, as well as for siting and designing facilities to be constructed in regions near active faults.

Baja California↗

USGS2015

Structural superposition in fault systems bounding Santa Clara Valley, California

Santa Clara Valley is bounded on the southwest and northeast by active strike-slip and reverse-oblique faults of the San Andreas fault system. On both sides of the valley, these faults are superposed on older normal and/or right-lateral normal oblique faults. The older faults comprised early components of the San Andreas fault system as it formed in the wake of the northward passage of the Mendocino Triple Junction. On the east side of the valley, the great majority of fault displacement was accommodated by the older faults, which were almost entirely abandoned when the presently active faults became active after ca. 2.5 Ma. On the west side of the valley, the older faults were abandoned earlier, before ca. 8 Ma and probably accumulated only a small amount, if any, of the total right-lateral offset accommodated by the fault zone as a whole. Apparent contradictions in observations of fault offset and the relation of the gravity field to the distribution of dense rocks at the surface are explained by recognition of superposed structures in the Santa Clara Valley region.

California↗

USGS2020

Three-dimensional shape and structure of the Susitna basin, south-central Alaska, from geophysical data

We use gravity, magnetic, seismic reflection, well, and outcrop data to determine the three-dimensional shape and structural features of south-central Alaska’s Susitna basin. This basin is located within the Aleutian-Alaskan convergent margin region and is expected to show effects of regional subduction zone processes. Aeromagnetic data, when filtered to highlight anomalies associated with sources within the upper few kilometers, show numerous linear northeast-trending highs and some linear north-trending highs. Comparisons to seismic reflection and well data show that these highs correspond to areas where late Paleocene to early Eocene volcanic layers have been locally uplifted due to folding and/or faulting. The combined magnetic and seismic reflection data suggest that the linear highs represent northeast-trending folds and north-striking faults. Several lines of evidence suggest that the northeast-trending folds formed during the middle Eocene to early Miocene and may have continued to be active in the Pliocene. The north-striking faults, which in some areas appear to cut the northeast-trending folds, show evidence of Neogene and probable modern movement. Gravity data facilitate estimates of the shape and depth of the basin. This was accomplished by separating the observed gravity anomaly into two components—one representing low-density sedimentary fill within the basin and one representing density heterogeneities within the underlying crystalline basement. We then used the basin anomaly, seismic reflection data, and well data to estimate the depth of the basin. Together, the magnetic, gravity, and reflection seismic analyses reveal an asymmetric basin comprising sedimentary rock over 4 km thick with steep, fault-bounded sides to the southwest, west, and north and a mostly gentle rise toward the east. Relations to the broader tectonic regime are suggested by fold axis orientations within the Susitna basin and neighboring Cook Inlet basin, which are roughly parallel to the easternmost part of the Alaska-Aleutian trench and associated Wadati-Benioff zone as it trends from northeast to north-northeast to northeast. An alignment between forearc basin folds and the subduction zone trench has been observed at other convergent margins, attributed to strain partitioning generated by regional rheologic variations that are associated with the subducting plate and arc magmatism. The asymmetric shape of the basin, especially its gentle rise to the east, may reflect uplift associated with flat-slab subduction of the Yakutat microplate, consistent with previous work that suggested Yakutat influence on the nearby Talkeetna Mountains and western Alaska Range. Yakutat subduction may also have contributed to Neogene and later reverse slip along north-striking faults within the Susitna basin.

Alaska↗

USGS2013

A spatial age-structured model for describing sea lamprey ( Petromyzon marinus ) population dynamics

The control of invasive sea lampreys ( Petromyzon marinus ) presents large scale management challenges in the Laurentian Great Lakes. No modeling approach has been developed that describes spatial dynamics of lamprey populations. We developed and validated a spatial and age-structured model and applied it to a sea lamprey population in a large river in the Great Lakes basin. We considered 75 discrete spatial areas, included a stock-recruitment function, spatial recruitment patterns, natural mortality, chemical treatment mortality, and larval metamorphosis. Recruitment was variable, and an upstream shift in recruitment location was observed over time. From 1993–2011 recruitment, larval abundance, and the abundance of metamorphosing individuals decreased by 80, 84, and 86%, respectively. The model successfully identified areas of high larval abundance and showed that areas of low larval density contribute significantly to the population. Estimated treatment mortality was less than expected but had a large population-level impact. The results and general approach of this work have applications for sea lamprey control throughout the Great Lakes and for the restoration and conservation of native lamprey species globally.

Great Lakes↗

USGS2018

Evaluating trade-offs in bull trout reintroduction strategies using structured decision making

Structured decision making allows reintroduction decisions to be made despite uncertainty by linking reintroduction goals with alternative management actions through predictive models of ecological processes. We developed a decision model to evaluate the trade-offs between six bull trout ( Salvelinus confluentus ) reintroduction decisions with the goal of maximizing the number of adults in the recipient population without reducing the donor population to an unacceptable level. Sensitivity analyses suggested that the decision identity and outcome were most influenced by survival parameters that result in increased adult abundance in the recipient population, increased juvenile survival in the donor and recipient populations, adult fecundity rates, and sex ratio. The decision was least sensitive to survival parameters associated with the captive-reared population, the effect of naivety on released individuals, and juvenile carrying capacity of the reintroduced population. The model and sensitivity analyses can serve as the foundation for formal adaptive management and improved effectiveness, efficiency, and transparency of bull trout reintroduction decisions.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1994

Deep structure beneath Lake Ontario: Crustal-scale Grenville subdivisions

Lake Ontario marine seismic data reveal major Grenville crustal subdivisions beneath central and southern Lake Ontario separated by interpreted shear zones that extend to the lower crust. A shear zone bounded transition between the Elzevir and Frontenac terranes exposed north of Lake Ontario is linked to a seismically defined shear zone beneath central Lake Ontario by prominent aeromagnetic and gravity anomalies, easterly dipping wide-angle reflections, and fractures in Paleozoic strata. We suggest the central Lake Ontario zone represents crustal-scale deformation along an Elzevir–Frontenac boundary zone that extends from outcrop to the south shore of Lake Ontario.Seismic images from Lake Ontario and the exposed western Central Metasedimentary Belt are dominated by crustal-scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east-dipping linear reflections. The images show that zones analogous to the interpreted Grenville Front Tectonic Zone are also present within the Central Metasedimentary Belt and support models of northwest-directed crustal shortening for Grenvillian deep crustal deformation beneath most of southeastern Ontario.A Precambrian basement high, the Iroquoian high, is defined by a thinning of generally horizontal Paleozoic strata over a crestal area above the basement shear zone beneath central Lake Ontario. The Iroquoian high helps explain the peninsular extension into Lake Ontario forming Prince Edward County, the occurrence of Precambrian inlier outcrops in Prince Edward County, and Paleozoic fractures forming the Clarendon–Linden structure in New York.

Lake Ontario↗

USGS2008

Landscape-scale evaluation of genetic structure among barrier-isolated populations of coastal cutthroat trout, Oncorhynchus clarkii clarkii

Relationships among landscape structure, stochastic disturbance, and genetic diversity were assessed by examining interactions between watershed-scale environmental factors and genetic diversity of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in 27 barrier-isolated watersheds from western Oregon, USA. Headwater populations of coastal cutthroat trout were genetically differentiated (mean FST = 0.33) using data from seven microsatellite loci (2232 individuals), but intrapopulation microsatellite genetic diversity (mean number of alleles per locus = 5, mean He = 0.60) was only moderate. Genetic diversity of coastal cutthroat trout was greater (P = 0.02) in the Coast Range ecoregion (mean alleles = 47) than in the Cascades ecoregion (mean alleles = 30), and differences coincided with indices of regional within-watershed complexity and connectivity. Furthermore, regional patterns of diversity evident from isolation-by-distance plots suggested that retention of within-population genetic diversity in the Coast Range ecoregion is higher than that in the Cascades, where genetic drift is the dominant factor influencing genetic patterns. Thus, it appears that physical landscape features have influenced genetic patterns in these populations isolated from short-term immigration. ?? 2008 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1997

Population structure and the evolution of sexual size dimorphism and sex ratios in an insular population of Florida box turtles ( Terrapene carolina bauri )

Hypotheses in the chelonian literature suggest that in species with sexual size dimorphism, the smaller sex will mature at a smaller size and a younger age than the larger sex, sex ratios should be biased in favor of the earlier maturing sex, and deviations from a 1:1 sex ratio result from maturation of the smaller sex at a younger age. I tested these hypotheses using data collected from 1991 to 1995 on an insular (Egmont Key) population of Florida box turtles, Terrapene carolina bauri. Contrary to predictions, the earlier maturing sex (males) grew to larger sizes than the late maturing sex. Males were significantly larger than females in mean carapace length but not mean body mass. Sex ratios were not balanced, favoring the earlier maturing sex (1.6 males:1 female), but the sex-ratio imbalance did not result from faster maturation of the smaller sex. The imbalance in the sex ratio in Egmont Key's box turtles is not the result of sampling biases; it may result from nest placement. Size-class structure and sex ratios can provide valuable insights into the status and trends of populations of long-lived turtles.

Canadian Journal of Zoology↗

USGS2015

Evaluation of vector coastline features extracted from 'structure from motion'-derived elevation data

For extensive and remote coastlines, the absence of high-quality elevation models—for example, those produced with lidar—leaves some coastal populations lacking one of the essential elements for mapping shoreline positions or flood extents. Here, we compare seven different elevation products in a lowlying area in western Alaska to establish their appropriateness for coastal mapping applications that require the delineation of elevation-based vectors. We further investigate the effective use of a Structure from Motion (SfM)-derived surface model (vertical RMSE<20 cm) by generating a tidal datum-based shoreline and an inundation extent map for a 2011 flood event. Our results suggest that SfM-derived elevation products can yield elevation-based vector features that have horizontal positional uncertainties comparable to those derived from other techniques. We also provide a rule-of-thumb equation to aid in the selection of minimum elevation model specifications based on terrain slope, vertical uncertainties, and desired horizontal accuracy.

Conference Paper↗

USGS2002

Structure and flow-induced variability of the subtidal salinity field in northern San Francisco Bay

The structure of the salinity field in northern San Francisco Bay and how it is affected by freshwater flow are discussed. Two datasets are examined: the first is 23 years of daily salinity data taken by the U.S. Bureau of Reclamation along the axis of northern San Francisco Bay; the second is a set of salinity transects taken by the U.S. Geological Survey between 1988 and 1993. Central to this paper is a measure of salinity intrusion, X 2 : the distance from the Golden Gate Bridge to where the bottom salinity is 2 psu. Using X 2 to scale distance, the authors find that for most flow conditions, the mean salinity distribution of the estuary is nearly self-similar with a salinity gradient in the center 70% of the region between the Golden Gate and X 2 that is proportional to X −1 2 . Analysis of covariability of Q and X 2 showed a characteristic timescale of adjustment of the salinity field of approximately 2 weeks. The steady-state response deduced from the X 2 time series implies that X 2 is proportional to riverflow to the 1/7 power. This relation, which differs from the standard 1/3 power dependence that is derived theoretically assuming constant exchange coefficients, shows that the upstream salt flux associated with gravitational circulation is more sensitive to the longitudinal salinity gradient than theory supposes. This is attributed to the strengthening of stratification caused by the stronger longitudinal salinity gradient that accompanies larger river flows.

California↗

USGS2014

Structural equation models of VMT growth in US urbanised areas.

Vehicle miles travelled (VMT) is a primary performance indicator for land use and transportation, bringing with it both positive and negative externalities. This study updates and refines previous work on VMT in urbanised areas, using recent data, additional metrics and structural equation modelling (SEM). In a cross-sectional model for 2010, population, income and freeway capacity are positively related to VMT, while gasoline prices, development density and transit service levels are negatively related. Findings of the cross-sectional model are generally confirmed in a more tightly controlled longitudinal study of changes in VMT between 2000 and 2010, the first model of its kind. The cross-sectional and longitudinal models together, plus the transportation literature generally, give us a basis for generalising across studies to arrive at elasticity values of VMT with respect to different urban variables.

Urban Studies↗

USGS2021

Preliminary assessment of carbon and nitrogen sequestration potential of wildfire-derived sediments stored by erosion control structures in forest ecosystems, southwest USA

The role of pyrogenic carbon (PyC) in the global carbon cycle is still incompletely characterized. Much work has been done to characterize PyC on landforms and in soils where it originates or in “terminal” reservoirs such as marine sediments. Less is known about intermediate reservoirs such as streams and rivers, and few studies have characterized hillslope and in-stream erosion control structures (ECS) designed to capture soils and sediments destabilized by wildfire. In this preliminary study, organic carbon (OC), total nitrogen (N), and stable isotope parameters, δ 13 C and δ 15 N, were compared to assess opportunities for carbon and nitrogen sequestration in postwildfire sediments (fluvents) deposited upgradient of ECS in ephemeral- and intermittent-stream channels. The variability of OC, N, δ 13 C, and δ 15 N were analyzed in conjunction with fire history, age of captured sediments, topographic position, and land cover. Comparison of samples in 2 watersheds indicates higher OC and N in ECS with more recently captured sediments located downstream of areas with higher burn severity. This is likely a consequence of (1) higher burn severity causing greater runoff, erosion, and transport of OC (organic matter) to ECS and (2) greater cumulative loss of OC and N in older sediments stored behind older ECS. In addition, C/N, δ 13 C, and δ 15 N results suggest that organic matter in sediments stored at older ECS are enriched in microbially processed biomass relative to those at newer ECS. We conservatively estimated the potential mean annual capture of OC by ECS, using values from the watershed with lower levels of OC, to be 3 to 4 metric tons, with a total potential storage of 293 to 368 metric tons in a watershed of 7.7 km 2 and total area of 2000 ECS estimated at 2.6 ha (203-255 metric tons/ha). We extrapolated the OC results to the regional level (southwest USA) to estimate the potential for carbon sequestration using these practices. We estimated a potential of 0.01 Pg, which is significant in terms of ecosystem services and regional efforts to promote carbon storage.

Arizona↗

USGS1962

Limiting parameters in the magnetic interpretation of a geologic structure

A prominent aeromagnetic anomaly in Randolph County, Indiana, suggests the existence of a dikelike structure within the Precambrian basement rocks. Because of the ambiguity inherent in magnetic interpretation , a unique solution for the parameters involved (depth of burial, geometric configuration, and magnetic susceptibility of the mass producing the anomaly) is impossible. However, if one of the parameters is known it is sometimes possible to indicate a range of plausible values for each of the remaining parameters . The depth to the surface of the Precambrian rocks in Randolph County is known from drill-hole data to be about 3,000 ft. As the depth of burial is known, limits need be set only on the thickness, angle of dip, and susceptibility contrast of the assumed dike. These limits are determined by a graphical method. Theoretical anomalies over the postulated dike are computed for different dike thicknesses, angles of dip, and susceptibility contrasts. The computed profiles are then fitted to an observed magnetic profile flown at right angles to the trend of the feature. Numerical values for the "goodness of fit" are calculated by using the statistical method of sums of squares. Two plots, one of the index of goodness of fit and the other of susceptibility as functions of dip angle and dike thickness, are made to show graphically the interdependence of the variables and the plausible range of each. The contoured plots of the goodness of fit and the susceptibility contrast show that the range of best fit is between dip angles of 30 and 60 degrees and dike thickness of 1,000 to over 4,000 ft. The contoured plot of the susceptibility contrast, translated into percentage of magnetite, shows this parameter to be independent of the dip angle, varying only with thickness.

Indiana↗

USGS1940

Additional evidence on the relation of temperature to structure in the Salt Creek Oil field, Natrona County, Wyoming

Observations of bottom hole temperatures in approximately 100 deep wells in the Salt Creek field have been made during the past few years by the Stanolind Oil and Gas Company. These recent observations confirm and extend in a remarkable manner the results obtained in the summers of 1922 and 1923 when it was found from temperature surveys in 21 wells that the temperatures over a considerable portion of the field were definitely related to the structure.

Wyoming↗

USGS2010

Estimating structural dip from gravity and magnetic profile data

The anomalies of ideal sources, dipping magnetic contacts and dipping density sheets, provide the theoretical basis for estimating structural dip from gravity and magnetic profile data. The dip is always related to the local phase angle of a complex analytic signal evaluated directly over the source. For magnetic sheets, the complex analytic signal is constructed from the anomaly and its Hilbert transform. For magnetic contacts or density sheets, it is constructed from the first‐order horizontal and vertical derivatives of the anomaly. Dip estimation is implemented as an integral part of source‐location algorithms. The analytic signal and local wavenumber methods require interpolation of the local phase from sampled anomaly or derivative values. In the case of extended Euler deconvolution and multiple‐source Werner deconvolution the dip is derived as part of the least squares solution.

Conference Paper↗

USGS2018

Hydrogeophysics at societally relevant scales: Airborne electromagnetic applications and model structural uncertainty quantification

There is a critical and growing need for information about subsurface geological properties and processes over sufficiently large areas that can inform key scientific and societal studies. Airborne geophysical methods fill a unique role in Earth observation because of their ability to detect deep subsurface properties at regional scales and with high spatial resolution that cannot be achieved with groundbased measurements. Airborne electromagnetics, or AEM, is one technique that is rapidly emerging as a foundational tool for geological mapping, with widespread application to studies of water and mineral resources, geologic hazards, infrastructure, the cryosphere, and the environment. Applications of AEM are growing worldwide, with rapid developments in instrumentation and data analysis software. In this study, we summarize several recent hydrogeophysical applications of AEM, including examples drawn from a recent survey in the Mississippi Alluvial Plain (MAP). In addition, we discuss developments in computational methods for geophysical and geological model structural uncertainty quantification using AEM data, and how these results are used in a sequential hydrogeophysical approach to characterize hydrologic parameters and prediction uncertainty.

Conference Paper↗

USGS2017

Effects of deep basins on structural collapse during large subduction earthquakes

Deep sedimentary basins are known to increase the intensity of ground motions, but this effect is implicitly considered in seismic hazard maps used in U.S. building codes. The basin amplification of ground motions from subduction earthquakes is particularly important in the Pacific Northwest, where the hazard at long periods is dominated by such earthquakes. This paper evaluates the effects of basins on spectral accelerations, ground-motion duration, spectral shape, and structural collapse using subduction earthquake recordings from basins in Japan that have similar depths as the Puget Lowland basin. For three of the Japanese basins and the Puget Lowland basin, the spectral accelerations were amplified by a factor of 2 to 4 for periods above 2.0 s. The long-duration subduction earthquakes and the effects of basins on spectral shape combined, lower the spectral accelerations at collapse for a set of building archetypes relative to other ground motions. For the hypothetical case in which these motions represent the entire hazard, the archetypes would need to increase up to 3.3 times its strength to compensate for these effects.

Earthquake Spectra↗