DeLong S.B.,U.S. Geological Survey |
Hilley G.E.,Stanford University |
Prentice C.S.,U.S. Geological Survey |
Crosby C.J.,UNAVCO |
Yokelson I.N.,University of Arizona
Bulletin of the Geological Society of America | Year: 2017
Relative horizontal motion along strikeslip faults can build mountains when motion is oblique to the trend of the strike-slip boundary. The resulting contraction and uplift pose off-fault seismic hazards, which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges. Sparse geomorphic markers, topographic analyses, and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern San Andreas fault. Between Jenner and Mendocino, California, emergent marine terraces found southwest of the San Andreas fault record late Pleistocene uplift rates between 0.20 and 0.45 mm yr-1 along much of the coast. However, on the northeast side of the San Andreas fault, a zone of rapid uplift (0.6-1.0 mm yr-1) exists adjacent to the San Andreas fault, but rates decay northeastward as the coast becomes more distant from the San Andreas fault. A newly dated 4.5 Ma shallow-marine deposit located at ~500 m above sea level (masl) adjacent to the San Andreas fault is warped down to just 150 masl 15 km northeast of the San Andreas fault, and it is exposed at just 60-110 masl to the west of the fault. Landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of, and adjacent to, the San Andreas fault are 0.16-0.29 mm yr-1, but they are only 0.03-0.07 mm yr-1 west of the fault. Basin-average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock. Calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties. The lower-elevation areas of this landscape that show high channel steepness (and hence calibrated erosion rate) are distinct from higher-elevation areas with systematically lower channel steepness and denudation rates. These two areas do not appear to be coincident with lithologic contacts. Assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream-propagating kinematic wave that separates high and low channel steepness values, the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase. This analysis suggests that rock uplift rates along the coast changed from 0.3 to 0.75 mm yr-1 between 450 and 350 ka. This zone of recent, relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the Gualala block into the thinner, weaker oceanic crust left at the western margin of the North American plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary. The warped Pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses, and further indicate that the zone of rapid uplift may herald elevated off-fault seismic hazard if this uplift is created by periodic stick-slip motion on contractional structures. © 2016 Geological Society of America.
Tyler S.W.,University of Nevada, Reno |
Holland D.M.,Courant Institute of Mathematical Sciences |
Zagorodnov V.,Ohio State University |
Stern A.A.,Courant Institute of Mathematical Sciences |
And 5 more authors.
Journal of Glaciology | Year: 2013
Monitoring of ice-shelf and sub-ice-shelf ocean temperatures represents an important component in understanding ice-sheet stability. Continuous monitoring is challenging due to difficult surface access, difficulties in penetrating the ice shelf, and the need for long-term operation of nonrecoverable sensors. We aim to develop rapid lightweight drilling and near-continuous fiber-optic temperature-monitoring methods to meet these challenges. During November 2011, two instrumented moorings were installed within and below the McMurdo Ice Shelf (a sub-region of the Ross Ice Shelf, Antarctica) at Windless Bight. We used a combination of ice coring for the upper portion of each shelf borehole and hot-point drilling for penetration into the ocean. The boreholes provided temporary access to the ice-shelf cavity, into which distributed temperature sensing (DTS) fiber-optic cables and conventional pressure/temperature transducers were installed. The DTS moorings provided nearcontinuous (in time and depth) observations of ice and ocean temperatures to a depth of almost 800m beneath the ice-shelf surface. Data received document the presence of near-freezing water throughout the cavity from November through January, followed by an influx of warmer water reaching -150m beneath the ice-shelf base during February and March. The observations demonstrate prospects for achieving much higher spatial sampling of temperature than more conventional oceanographic moorings.
Smith M.K.,University of Maine, United States |
Vinson E.L.,University of Maine, United States |
Smith J.A.,UNAVCO |
Lewin J.D.,University of Maine, United States |
Stetzer M.R.,University of Maine, United States
CBE Life Sciences Education | Year: 2014
At the University of Maine, middle and high school science, technology, engineering, and mathematics (STEM) teachers observed 51 STEM courses across 13 different departments and collected information on the active-engagement nature of instruction. The results of these observations show that faculty members teaching STEM courses cannot simply be classified into two groups, traditional lecturers or instructors who teach in a highly interactive manner, but instead exhibit a continuum of instructional behaviors between these two classifications. In addition, the observation data reveal that student behavior differs greatly in classes with varied levels of lecture. Although faculty members who teach large-enrollment courses are more likely to lecture, we also identified instructors of several large courses using interactive teaching methods. Observed faculty members were also asked to complete a survey about how often they use specific teaching practices, and we find that faculty members are generally self-aware of their own practices. Taken together, these findings provide comprehensive information about the range of STEM teaching practices at a campus-wide level and how such information can be used to design targeted professional development for faculty. © 2014 M. K. Smith et al.
Berglund H.T.,UNAVCO |
Blume F.,UNAVCO |
Geophysical Research Letters | Year: 2015
We use a shake table capable of large (7G) three-dimensional accelerations with large payloads to simulate ground motion reconstructed from acceleration data collected during the February 2010 Mw=8.8 Maule, Chile, earthquake. The tracking performance of five modern geodetic GNSS receiver and antenna combinations was investigated while undergoing simulated seismic shaking at three two levels of amplification. Individual system performance was characterized by the number of tracked GNSS observations. The L1 and L2 GPS signal tracking was significantly impacted for the majority of the receiver models during simulations with maximum accelerations of 4G, and the tracking performance for all of the tested receiver types was significantly impaired during the 7G simulations. Results show improved tracking when only the antenna was shaken suggesting that vibration-induced oscillator phase noise may contribute significantly to tracking degradation during shaking. Key Points Previous experiments ignored receiver response to vibration We find that receivers are sensitive to vibration The tracking performance of receivers is not consistent between make ©2015. American Geophysical Union. All Rights Reserved.
King M.A.,Northumbria University |
Bevis M.,Ohio State University |
Wilson T.,Ohio State University |
Johns B.,UNAVCO |
Journal of Geodesy | Year: 2012
We examine the electromagnetic coupling of a GPS antenna-monument pair in terms of its simulated affect on long GPS coordinate time series. We focus on the Earth and Polar Observing System (POLENET) monument design widely deployed in Antarctica and Greenland in projects interested particularly in vertical velocities. We base our tests on an absolute robot calibration that included the top ~0.15 m of the monument and use simulations to assess its effect on site coordinate time series at eight representative POLENET sites in Antarctica over the period 2000.0-2011.0. We show that the neglect of this calibration would introduce mean coordinate bias, and most importantly for velocity estimation, coordinate noise which is highly sensitive to observation geometry and hence site location and observation period. Considering only sub-periods longer than 2.5 years, we show vertical site velocities may be biased by up to ±0.4 mm/year, and biases up to 0.2 mm/year may persist for observation spans of 8 years. Changing between uniform and elevation-dependent observation weighting alters the time series but does not remove the velocity biases, nor does ambiguity fixing. The effect on the horizontal coordinates is negligible. The ambiguities fixed series spectra show noise between flicker and random walk with near-white noise at the highest frequencies, with mean spectral indices (frequencies <20 cycles per year) of approximately -1.3 (uniform weighting) and -1.4 (elevation-dependent weighting). While the results are likely highly monument specific, they highlight the importance of accounting for monument effects when analysing vertical coordinate time series and velocities for the highest precision and accuracy geophysical studies. © 2011 Springer-Verlag.
Fritz H.M.,Georgia Institute of Technology |
Phillips D.A.,UNAVCO |
Okayasu A.,Tokyo University of Marine Science and Technology |
Shimozono T.,Tokyo University of Marine Science and Technology |
And 6 more authors.
Geophysical Research Letters | Year: 2012
On March 11, 2011, a magnitude M w 9.0 earthquake occurred off the coast of Japan's Tohoku region causing catastrophic damage and loss of life. The tsunami flow velocity analysis focused on two survivor videos recorded from building rooftops at Kesennuma Bay along Japan's Sanriku coast. A terrestrial laser scanner was deployed at the locations of the tsunami eyewitness video recordings. The tsunami current velocities through the Kesennuma Bay are determined in a four step process. The LiDAR point clouds are used to calibrate the camera fields of view in real world coordinates. The motion of the camera during recordings was determined. The video images were rectified with direct linear transformation. Finally a cross-correlation based particle image velocimetry analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields. The measured maximum tsunami height of 9 m in the Kesennuma Bay narrows were followed by maximum tsunami outflow currents of 11 m/s less than 10 minutes later. © 2012 by the American Geophysical Union.
Jones L.K.,New Mexico Institute of Mining and Technology |
Kyle P.R.,New Mexico Institute of Mining and Technology |
Oppenheimer C.,University of Cambridge |
Frechette J.D.,University of New Mexico |
Journal of Volcanology and Geothermal Research | Year: 2015
A Terrestrial Laser Scanning (TLS) instrument was used to image the topography of the Main Crater at Erebus volcano each December in 2008, 2009, and 2010. Our high-spatial resolution TLS scans provide unique insights into annual and decadal scale geomorphic evolution of the summit area when integrated with comparable data collected by an airborne instrument in 2001. We observe both a pattern of subsidence within the Inner Crater of the volcano and an ~. 3. m per-year drop in the lava lake level over the same time period that are suggestive of decreasing overpressure in an underlying magma reservoir. We also scanned the active phonolite lava lake hosted within the Inner Crater, and recorded rapid cyclic fluctuations in the level of the lake. These were sporadically interrupted by minor explosions by bursting gas bubbles at the lake surface. The TLS data permit calculation of lake level rise and fall speeds and associated rates of volumetric change within the lake. These new observations, when considered with prior determinations of rates of lake surface motion and gas output, are indicative of unsteady magma flow in the conduit and its associated variability in gas volume fraction. © 2015 Elsevier B.V.
Luttrell K.,U.S. Geological Survey |
Mencin D.,UNAVCO |
Francis O.,University of Luxembourg |
Hurwitz S.,U.S. Geological Survey
Geophysical Research Letters | Year: 2013
Seiche waves in Yellowstone Lake with a ~78-minute period and heights <10 cm act as a load on the solid earth observed by borehole strainmeters with subnanostrain sensitivity throughout the Yellowstone Caldera. The far-field strain induced by the load of the seiche waves calculated with a homogeneous elastic model representing the upper crust is more than an order of magnitude smaller than the measured strain amplitude ~30 km from the lake shore. By contrast, the observed far field strain amplitudes are consistent with the seiche load on a two-layered viscoelastic model representing an elastic upper crust overlying a partially molten body deeper than 3-6 km with Maxwell viscosity less than 1011 Pa s. These strain observations and models provide independent evidence for the presence of partially molten material in the upper crust, consistent with seismic tomography studies that inferred 10%-30% melt fraction in the upper crust. Key Points Strain induced by seiche waves in Yellowstone Lake is observed 30 km away Observed strainfield requires some support from an upper crustal magma reservoir Top of shallowest upper crustal partial melt is at 3 - 6 km depth ©2013. American Geophysical Union. All Rights Reserved.
Wang G.,University of Houston |
Joyce J.,University of Puerto Rico at Mayaguez |
Phillips D.,UNAVCO |
Shrestha R.,University of Houston |
Carter W.,University of Houston
Landslides | Year: 2013
Light detection and ranging (LIDAR) is a remote sensing technique that uses light, often using pulses from a laser to measure the distance to a target. Both terrestrial- and airborne-based LIDAR techniques have been frequently used to map landslides. Airborne LIDAR has the advantage of identifying large scarps of landslides covered by tree canopies and is widely applied in identifying historical and current active landslides hidden in forested areas. However, because landslides naturally have relatively small vertical surface deformation in the foot area, it is practically difficult to identify the margins of landslide foot area with the limited spatial resolution (few decimeters) of airborne LIDAR. Alternatively, ground-based LIDAR can achieve resolution of several centimeters and also has the advantages of being portable, repeatable, and less costly. Thus, ground-based LIDAR can be used to identify small deformations in landslide foot areas by differencing repeated terrestrial laser scanning surveys. This study demonstrates a method of identifying the superficial boundaries as well as the bottom boundary (sliding plane) of an active landslide in National Rainforest Park, Puerto Rico, USA, using the combination of ground-based and airborne LIDAR data. The method of combining terrestrial and airborne LIDAR data can be used to study landslides in other regions. This study also indicates that intensity and density of laser point clouds are remarkably useful in identifying superficial boundaries of landslides. © 2013 Springer-Verlag Berlin Heidelberg.
Williams K.,UNAVCO |
Olsen M.J.,Oregon State University |
Roe G.V.,MPN Components |
Glennie C.,University of Houston
Remote Sensing | Year: 2013
A thorough review of available literature was conducted to inform of advancements in mobile LIDAR technology, techniques, and current and emerging applications in transportation. The literature review touches briefly on the basics of LIDAR technology followed by a more in depth description of current mobile LIDAR trends, including system components and software. An overview of existing quality control procedures used to verify the accuracy of the collected data is presented. A collection of case studies provides a clear description of the advantages of mobile LIDAR, including an increase in safety and efficiency. The final sections of the review identify current challenges the industry is facing, the guidelines that currently exist, and what else is needed to streamline the adoption of mobile LIDAR by transportation agencies. Unfortunately, many of these guidelines do not cover the specific challenges and concerns of mobile LIDAR use as many have been developed for airborne LIDAR acquisition and processing. From this review, there is a lot of discussion on "what" is being done in practice, but not a lot on "how" and "how well" it is being done. A willingness to share information going forward will be important for the successful use of mobile LIDAR. © 2013 by the authors; licensee MDPI, Basel, Switzerland.