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  • 1
    Publication Date: 2015-12-18
    Description: This paper describes a generalization of the iterative deconvolution method commonly used as a component of passive array wavefield imaging. We show that the iterative method should be thought of as a sparse output deconvolution method with the number of terms retained dependent on the convergence criteria. The generalized method we introduce uses an inverse operator to shape the assumed wavelet to a peaked function at zero lag. We show that the conventional method is equivalent to using a damped least-squares spiking filter with extremely large damping and proper scaling. In that case, the inverse operator used in the generalized method reduces to the cross-correlation operator. The theoretical insight of realizing the output is a sparse series provides a basis for the second important addition of the generalized method—an output shaping wavelet. A constant output shaping wavelet is a critical component in scattered wave imaging to avoid mixing data of variable bandwidth. We demonstrate the new approach can improve resolution by using an inverse operator tuned to maximize resolution. We also show that the signal-to-noise ratio of the result can be improved by applying a different convergence criterion than the standard method, which measures the energy left after each iteration. The efficacy of the approach was evaluated with synthetic experiment in various signal and noise conditions. We further validated the approach with real data from the USArray. We compared our results with data from the EarthScope Automated Receiver Survey and found that our results show modest improvements in consistency measured by correlation coefficients with station stacks and a reduced number of outliers.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
    Publication Date: 2015-01-29
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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  • 3
    Publication Date: 2014-12-03
    Description: We use broadband seismic data acquired by the St. Elias Erosion/Tectonics Project (STEEP) and the Alaska Earthquake Information Center to image the geometry of the subducting Yakutat Block in southeast Alaska. We combine results for both P- and S-wave receiver functions. P-wave to S-wave data were imaged with a fully three-dimensional wavefield imaging method centered on the STEEP region. The S-wave to P-wave data were imaged using a simpler common conversion point stacking method at two scales: a regional scale covering all of southeast Alaska and a smaller scale identical to the P-wave data. Our data confirm that the southeastern Alaska subduction zone extends from the eastern end of the Aleutian Trench an additional 300 km to the Fairweather–Queen Charlotte fault system. We also locate the boundary between the Yakutat Block and North American Plate. We find direct evidence that the subducted Yakutat Block and Pacific plate slabs are continuous and that Yakutat Block subduction extends from Prince William Sound to the east at least as far as Icy Bay. The dip angle of the slab ranges from 11° to 16° with a gradual increase from west to east across this region. Our data show a clear separation between the subducted Yakutat Block and the North American Plate under the Alaska Range, suggesting that deformation along the Denali fault and interior Alaska is not the product of coupling between North America and the subducted Yakutat Block. This dip angle also places the subducted Yakutat Block at the proper depth to produce arc magmatism found in the Wrangell volcanic field. Modeling the geometry of the system suggests that sedimentary cover is being stripped at the western side of the Yakutat Block and the lower crust of the Yakutat Block is involved in the subduction. The system transitions from a single dipping megathrust on the western side of the Yakutat Block to intense shortening in the vicinity of Mount Saint Elias, where we suggest that the lower crust is likely undergoing ductile deformation and has thickened more than 60 km under the Peninsular terrane.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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  • 4
    Publication Date: 2016-10-08
    Description: We introduce a new semiautomated quality control (QC) method for teleseismic P -wave receiver functions consisting of 13 editing procedures. These procedures are categorized into three groups based on (1) deconvolution attributes, (2) characteristics of each receiver function, and (3) the statistical attributes of a station gather. We evaluated the efficacy of individual procedure and combination of multiple procedures by applying them to receiver functions estimated from the EarthScope Ozark–Illinois–Indiana–Kentucky experiment for the Illinois basin area, and 10 years of USArray Transportable Array data for the contiguous United States. The method developed in this study significantly improves the efficiency and accuracy of receiver function QC. Our approach has three useful properties: (1) unlike a manual editing method, our approach produces reproducible results defined by a finite set of tunable parameters; (2) it provides an effective and efficient tool for processing large datasets containing millions of receiver functions; (3) the QC procedures are less dependent on phase similarities comparing to the automated scheme used by the EarthScope Automated Receiver Survey while producing comparable common conversion point stacking images.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2014-01-03
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 6
    Publication Date: 2014-05-29
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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  • 7
    Publication Date: 2017-04-12
    Description: Across much of North America, the contact between Precambrian basement and Paleozoic strata is the Great Unconformity, a surface that represents a 〉0.4 b.y.-long hiatus. A digital elevation model (DEM) of this surface visually highlights regional-scale variability in the character of basement topography across the United States cratonic platform. Specifically, it delineates Phanerozoic tectonic domains, each characterized by a distinct structural wavelength (horizontal distance between adjacent highs) and/or structural amplitude (vertical distance between adjacent lows and highs). The largest domain, the Midcontinent domain, includes long-wavelength epeirogenic basins and domes, as well as fault-controlled steps. The pronounced change in land-surface elevation at the Rocky Mountain Front coincides with the western edge of the Midcontinent domain on the basement DEM. In the Rocky Mountain and Colorado Plateau domains, west of the Rocky Mountain Front, structural wavelength is significantly shorter and structural amplitude significantly higher than in the Midcontinent domain. The Bordering Basins domain outlines the southern and eastern edges of the Midcontinent domain. As emphasized by the basement DEM, several kilometers of structural relief occur across the boundary between these two domains, even though this boundary does not stand out on ground-surface topography. A plot of epicenters on the basement DEM supports models associating intraplate seismicity with the Midcontinent domain edge. Notably, certain changes in crustal thickness also coincide with distinct changes in basement depth.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 8
    Publication Date: 2017-02-24
    Description: P -wave travel-time residuals from USArray helped improve the scale and consistency with which the mantle beneath North America is resolved. Beginning in 2008, we published a series of P -wave velocity models based on a global ray theoretical inversion of USArray and global catalog data. Here, we present the final model update, MITP_USA_2016MAY, which includes the complete set of travel-time residuals from USArray Transportable Array (TA) in the contiguous United States. In this model, the area of high resolution extends to the eastern margin of the continent, allowing us to better estimate the location and extent of slow features in Central Virginia and New England. An increasing number of data from the TA in Alaska also allows us to recover the structure of subducting Pacific plate and Yakutat terrane. In addition to highlighting new features in the final model, we visualize and discuss the improvements to the model due to the addition of USArray data through time.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 9
    Publication Date: 2013-11-22
    Description: The objective of this paper is to provide a better understanding of the relationship between the microseismicity, active tectonics, and crustal structures in the southwest Yukon Territory, Canada, in order to improve seismic-hazard assessments in this region. We utilize data from a new dense seismic array that was deployed in the southwest Yukon in the summer of 2010. Data from the new seismic array significantly improve the magnitude completeness level in the region from M L  3.0 to 1.0. We analyze 980 events ranging in magnitudes from M L  0.2 to 4.7, at depths from 0 to 35 km. Relocation analysis using the progressive multiple event location shows that seismicity is concentrated in four main areas: (1) Yakutat block northern boundary–Fairweather fault, (2) Duke River fault, (3) southern Denali fault, and (4) a previously unrecognized northeast trending cluster that may highlight a previously unknown active fault. This cluster may contribute to stress and strain transfer inland from the Yakutat block region.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2013-02-15
    Description: We develop a generic method to appraise the reliability of wavefield imaging methods and use it to validate some novel observations on the 410-km discontinuity. The core concept of the error appraisal method is to produce a simulated data set that replicates the geometry of the real data. Here we implemented two simulation methods: (1) flat layer primary P to S conversions, and (2) a point source scattering model for P to S conversion data based on the Born approximation and ray theory propagators. We show how the approach can be extended for any simulation algorithm. We apply this new approach to appraise recent results using a 3-D, three-component P to S conversion imaging method applied to data collected by the USArray. Multiple metrics show that the amplitude of P to S converted energy scattered from the 410-km discontinuity varies by 18 dB with a systematically lower amplitude in an irregular band running from Idaho through northern Arizona. In addition, we observe strong lateral changes in the ratio of amplitudes recovered on the radial versus the transverse component. We compute point resolution functions and a checkerboard test to demonstrate we can reliably recover relative amplitudes with a lateral scale of the order of 200 km and a vertical scale of approximately 10 km. Irregular coverage locally distorts the amplitudes recovered in the checkerboard, but a 156 km scale checkerboard pattern is recovered. Flat layer simulations show we can recover relative amplitudes to within a range of 1 dB and the reconstructed transverse to radial amplitude is everywhere less than 0.1. A model with north–south oriented ridges with a 3° wavelength and 12.5 km amplitude shows of the order of ±6 dB amplitude variations and small, but clear correlation of the transverse/radial amplitude ratio topography in the model. Finally, we model the 410-km discontinuity as a rough surface characterized by variations in amplitude and depth derived from the USArray data. The rough surface model recovers the scale of the observed amplitude variations, but does not explain the observed large variations in transverse component amplitudes imaged by the USArray data. The results indicate the 410-km discontinuity is definitely not a single interface separating isotropic media. We argue that it is likely better viewed as a rough surface with a structural fabric that creates anisotropic behaviour in some places.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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