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  • 1
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    The effect of shallow San Francisco Bay sediments on waveforms recorded during the MW 4.6 Bolinas, California, Earthquake (2003)
    In:  Bull. Seism. Soc. Am., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 93, no. 1, pp. 465-479, pp. 2122
    Details
    Publication Date: 2003
    Description: To investigate the effect of the shallow, low-velocity sediments on the seismic wave field in the northern San Francisco Bay, we modeled tangential component displacement seismograms recorded during the 18 August 1999 MW 4.6 Bolinas, California, earthquake. The modeling indicates that the velocity structure of Pleistocene horizons in the San Francisco Bay is important for simulations of weak ground motions for Bay Area earthquakes. Models including the Pleistocene sediments generate the 1-sec-period surface waves observed at several stations. Modeling of Treasure and Yerba Buena Island records requires structures approximately an order of magnitude higher in spatial resolution than the current 3D velocity models for the region. This pair of sites, located only 2 km apart in the bay, records a sixfold difference in peak ground acceleration during the Bolinas earthquake. Three transects are forward modeled using 1D frequency-wavenumber integration and 2D finite-difference methods. Generally the ground motions are characterized by a direct shear wave (S0), a midcrustal reflection (S1), a near-receiver multiple (S2), and surface waves. The direct S0 arrival at all six stations requires a faster model than GIL7, the model routinely used to estimate earthquake source parameters using the Berkeley Digital Seismic Network. In addition, the timing of S1 indicates the possibility of a dipping midcrustal interface. S2 can be matched with a single strong impedance contrast at 3 km depth. A thin (200-m) surface layer of weathered rock and sediments simulates the surface waves that follow S2 at the Richmond Field Station site. However, the surface waves at Treasure Island and the Berkeley sites are longer in duration and higher amplitude than at Richmond and require 2D structure. A simple shallow uniform basin model for the San Francisco Bay consisting of stiff sediments (shear-wave velocity, Vs = 400 m/sec; thickness ~100 m) over weathered rock (Vs = 1.5 km/sec) of the Franciscan assemblage produces surface waves in the 0.02-2 Hz passband at Treasure Island and the Berkeley sites.
    Keywords: Seismology ; Earthquake ; Site amplification ; Wave propagation ; Wave form analysis ; USA ; Two-dimensional ; Finite difference method ; Modelling ; Velocity depth profile ; Shear waves ; Surface waves ; Seismic networks ; Reflectivity ; noksp ; BSSA
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Site response at Yerba Buena Island, San Francisco Bay, California analyzed with weak motion recordings (2001)
    In:  Bollettino di Geofisica Teorica ed Applicata, Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 42, no. 3-4, pp. 219-243, pp. 2122
    Details
    Publication Date: 2001
    Keywords: Site amplification ; Earthquake engineering, engineering seismology ; USA
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Consistency of ground-motion estimates made using system identification (2000)
    In:  Bull. Seism. Soc. Am., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 90, no. 4, pp. 993-1009, pp. 2122
    Details
    Publication Date: 2000
    Keywords: Strong motions ; Earthquake engineering, engineering seismology ; Modelling ; BSSA
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Laboratory-developed Contact Models Controlling Instability on Frictional Faults (2015)
    Wiley
    Details
    Publication Date: 2015-05-02
    Description: Laboratory experiments were performed on a PMMA-PMMA frictional interface in a direct shear apparatus in order to gain understanding of fault dynamics leading to gross rupture. Actual asperity sizes and locations along the interface were characterized using a pressure sensitive film. Slow aseismic slip accumulated non-uniformly along the fault and showed dependency on the applied normal force – increased normal force resulted in higher slip gradients. The slow slip front propagated from the trailing (pushed) edge into a region of more densely distributed asperities at rates between 1 and 9.5 mm/s. Foreshocks were detected and displayed impulsive signals with source radii ranging between 0.21 and 1.09 mm; measurements made using the pressure sensitive film were between 0.05 and 1.2 mm. The spatio-temporal clustering of foreshocks and their relation to the elastodynamic energy released was dependent on the normal force. In the region where foreshocks occurred, qualitative optical measurements of the asperities along the interface were used to visualize dynamic changes occurring during the slow slip phase. To better understand the nucleation process a quasi-static asperity finite element (FE) model was developed, and focused in the region where foreshocks clustered. The FE model consisted of 172 asperities, located and sized based on pressure sensitive film measurements. The numerical model provides a plausible explanation as to why foreshocks cluster in space and observed a normal force dependency and lend credence to Ohnaka's nucleation model.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Micromechanics of asperity rupture during laboratory stick slip experiments (2011)
    Wiley
    Details
    Publication Date: 2011-06-28
    Description: Acoustic emissions and tremor-like signals are widely recorded in laboratory experiments. We are able to isolate the physical origins of these signals using high resolution nanoseismic analysis. The use of a picometer-sensitive, wide-band sensor array permits us to determine force-time functions and focal mechanisms for discrete events found amid the “noise” of friction, similar to how low frequency earthquakes are found buried within tremor. We interpret these localized events to be the rupture of μm-sized contacts, known as asperities. We performed stick-slip experiments on plastic/plastic and rock/rock interfaces and found a systematic difference between the nano earthquakes: the rock interface produces very rapid (
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Sensor placement strategies for SWE estimation in the american river basin (2013)
    Wiley
    Details
    Publication Date: 2013-01-17
    Description: An 11-year dataset of spatially distributed snow water equivalent (SWE) was used to inform a quantitative, near-optimal sensor placement methodology for real-time SWE estimation in the American River basin of California. Rank-based clustering was compared to geographically based clustering (sub-basin delineation) to determine the existence of stationary covariance structures within the overall SWE dataset. The historical SWE data, at 500 x 500 m resolution, were split into eight years of training and three years of validation data. Within each cluster, a quantitative sensor-placement algorithm, based on maximizing the metric of Mutual Information, was implemented and compared to random placement. Gaussian Process models were then built from validation data points selected by the algorithm to evaluate the efficacy of each placement approach. Rank based clusters remained stable inter-annually, suggesting that rankings of pixel-by-pixel SWE exhibit stationary features that can be exploited by a sensor-placement algorithm, yielding a 200 mm average root mean square error (RMSE) for twenty randomly selected sensing locations. This outperformed geographic and basin-wide placement approaches, which generated 460 mm and 290 mm RMSE, respectively. Mutual Information- based sampling provided the best placement strategy, improving RMSE between 0 and 100 mm compared to random placements. Increasing the number of rank-based clusters consistently lowered average RMSE from 400 mm for one cluster to 175 mm for eight clusters, for twenty total sensors placed. To optimize sensor placement we recommend a strategy that couples rank-based clustering with Mutual Information -based sampling design.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Design and performance of a wireless sensor network for catchment-scale snow and soil moisture measurements (2012)
    Wiley
    Details
    Publication Date: 2012-09-12
    Description: A wireless sensor network (WSN) was deployed as part of a water balance instrument cluster across a forested 1 km2 headwater catchment in the southern Sierra Nevada of California. The network, which integrates readings from over 300 sensors, provides spatially representative measurements of snow depth, solar radiation, relative humidity, soil moisture, and matric potential. The ability of this densely instrumented watershed to capture catchment-scale snow depth and soil moisture distributions is investigated through comparison with three comprehensive gridded surveys and 1 day of detailed lidar snow data. Statistical analysis shows that the network effectively characterized catchment-wide distributions of snow depth, while offering a cost-effective, reliable, and energy-efficient means for collecting distributed data in real time. A temporal analysis of snow depth variability reveals that canopy cover is the major explanatory variable of snow depth and that under-canopy measurements persistently show higher variability compared to those in open terrain. An analysis of soil moisture shows lower variability at deeper soil depth and a correlation between mean soil moisture and variability for shallow soils. A three-phase design procedure was used to optimize the WSN deployment. First, as off-the-shelf performance of current WSN platforms for large-scale, long-term deployments cannot be guaranteed, statistics from a prototype deployment were analyzed. Two indicators of network performance, the packet delivery ratio and received signal strength indicator, showed that for our site conditions, a conservative 50 m node-to-node spacing would ensure low-power, reliable, and robust network communications. Second, results from the prototype were used to refine hardware specifications and to guide the layout of the full 57-node wireless network. Of these nodes, 23 were used actively for sensing, while the remaining 34 nodes were used as signal repeaters to ensure proper spatial radio coverage and robust network operations. Further analysis of network statistics is conducted during the third, operational, phase to validate system performance.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Technical report: The design and evaluation of a basin-scale wireless sensor network for mountain hydrology (2017)
    Wiley
    Details
    Publication Date: 2017-04-27
    Description: A network of sensors for spatially representative water-balance measurements was developed and deployed across the 2000 km 2 snow-dominated portion of the upper American River basin, primarily to measure changes in snowpack and soil-water storage, air temperature and humidity. This wireless sensor network (WSN) consists of 14 sensor clusters, each with 10 measurement nodes that were strategically placed within a 1­km 2 area, across different elevations, aspects, slopes and canopy covers. Compared to existing operational sensor installations, the WSN reduces hydrologic uncertainty in at least three ways. First, redundant measurements improved estimation of lapse rates for air and dew-point temperature. Second, distributed measurements captured local variability and constrained uncertainty in air and dew-point temperature, snow accumulation and derived hydrologic attributes important for modeling and prediction. Third, the distributed relative-humidity measurements offer a unique capability to monitor upper-basin patterns in dew-point temperature and characterize elevation gradient of water vapor-pressure deficit across steep, variable topography. Network statistics during the first year of operation demonstrated that the WSN was robust for cold, wet and windy conditions in the basin. The electronic technology used in the WSN reduced adverse effects, such as high current consumption, multipath signal fading and clock drift, seen in previous remote WSNs.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Sensors, Vol. 12, Pages 16194-16210: TDMA-Based Dual-Mode Communication for Mobile Wireless Sensor Networks (2012)
    MDPI Publishing
    In: Sensors
    Details
    Publication Date: 2012-12-04
    Description: Small highly mobile robots, and in particular micro air vehicles (MAVs), are well suited to the task of exploring unknown indoor environments such as buildings and caves. Such a task imposes a number of requirements on the underlying communication infrastructure, with differing goals during various stages of the mission. This work addresses those requirements with a hybrid communications infrastructure consisting of a stationary mesh network along with the mobile nodes. The combined network operates in two independent modes, coupling a highly efficient, low duty cycle, low throughput mode for routing and persistent sensing with a burst mode for high data rate communication. By strategically distributing available frequency channels between the mobile agents and the stationary nodes, the overall network provides reliable long-term communication paths while maximizing data throughput when needed.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI Publishing
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  • 10
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    Design and performance of a wireless sensor network for catchment-scale snow and soil moisture measurements (2013)
    Wiley
    Details
    Publication Date: 2013-01-03
    Description: [1]  A wireless sensor network (WSN) was deployed as part of a water balance instrument cluster across a forested 1 km 2 headwater catchment in the southern Sierra Nevada of California. The network, which integrates readings from over 300 sensors, provides spatially representative measurements of snow depth, solar radiation, relative humidity, soil moisture, and matric potential. The ability of this densely instrumented watershed to capture catchment-scale snow depth and soil moisture distributions is investigated through comparison with three comprehensive gridded surveys and 1 day of detailed lidar snow data. Statistical analysis shows that the network effectively characterized catchment-wide distributions of snow depth, while offering a cost-effective, reliable, and energy-efficient means for collecting distributed data in real time. A temporal analysis of snow depth variability reveals that canopy cover is the major explanatory variable of snow depth and that under-canopy measurements persistently show higher variability compared to those in open terrain. An analysis of soil moisture shows lower variability at deeper soil depth and a correlation between mean soil moisture and variability for shallow soils. A three-phase design procedure was used to optimize the WSN deployment. First, as off-the-shelf performance of current WSN platforms for large-scale, long-term deployments cannot be guaranteed, statistics from a prototype deployment were analyzed. Two indicators of network performance, the packet delivery ratio and received signal strength indicator, showed that for our site conditions, a conservative 50 m node-to-node spacing would ensure low-power, reliable, and robust network communications. Second, results from the prototype were used to refine hardware specifications and to guide the layout of the full 57-node wireless network. Of these nodes, 23 were used actively for sensing, while the remaining 34 nodes were used as signal repeaters to ensure proper spatial radio coverage and robust network operations. Further analysis of network statistics is conducted during the third, operational, phase to validate system performance.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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