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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 169 (1993), S. 317-323 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Few data exist on the elemental composition of the human body during infancy. The scarcity of the data is due, in part, to the destructive nature of total body analyses normally required for the classical chemical approach. To help determine such data for infants, we have developed a neutron activation facility for nondestructive postmortem analyses. The system consists of a multisource241AmBe irradiator and a multidetector NaI(T1) whole body counter. The total body contents of K, Ca, P, Na and Cl are determined. Postmortem examinations have been performed in twelve infant cadavers. These results are compared with those of the reference fetus.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1993-03-01
    Print ISSN: 0236-5731
    Electronic ISSN: 1588-2780
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Springer
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  • 3
    Publication Date: 2016-08-05
    Description: We develop an automated strategy for discriminating deep microseismic events from shallow ones on the basis of the waveforms recorded on a limited number of surface receivers. Machine-learning techniques are employed to explore the relationship between event hypocentres and seismic features of the recorded signals in time, frequency and time–frequency domains. We applied the technique to 440 microearthquakes –1.7 〈  M w  〈 1.29, induced by an underground cavern collapse in the Napoleonville Salt Dome in Bayou Corne, Louisiana. Forty different seismic attributes of whole seismograms including degree of polarization and spectral attributes were measured. A selected set of features was then used to train the system to discriminate between deep and shallow events based on the knowledge gained from existing patterns. The cross-validation test showed that events with depth shallower than 250 m can be discriminated from events with hypocentral depth between 1000 and 2000 m with 88 per cent and 90.7 per cent accuracy using logistic regression and artificial neural network models, respectively. Similar results were obtained using single station seismograms. The results show that the spectral features have the highest correlation to source depth. Spectral centroids and 2-D cross-correlations in the time–frequency domain are two new seismic features used in this study that showed to be promising measures for seismic event classification. The used machine-learning techniques have application for efficient automatic classification of low energy signals recorded at one or more seismic stations.
    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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  • 4
    Publication Date: 2016-07-26
    Description: A 1D normal moveout (NMO)-corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary P - and S -wave coda and on Sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure (~5 km) in the upper Mississippi embayment. Acoustic well log data were used to constrain the P -wave velocity in the upper 5 km. Events at close distances and with clear P and S arrivals were selected to ensure reliable NMO correction for reflections and transmissions. The observed reflections and transmissions are important controlling factors on modeling waveforms. We analyzed local earthquake data recorded at all broadband and one short-period station of the Cooperative New Madrid Seismic Network. Despite polarity differences among P , S , and Sp waveforms, consistent reflectors in the sedimentary section can be imaged across the three wave types. Correlation with a basement-penetrating well indicates that reflectors at the base of the Upper Cretaceous–Holocene Mississippi Embayment Supergroup, the base of the Cambrian–Ordovician Knox Group, and the high-velocity lower Upper Cambrian Bonneterre Formation are shown in pseudoprofiles among stations in the upper Mississippi embayment. Our study finds that a one-layer homogeneous velocity model of sediments in the ranges of 1.95–2.42 km/s for V P and 0.60–0.73 km/s for V S overlying a half-space of Paleozoic rocks with velocities in the ranges of 6.0–6.2 km/s for V P and 3.26–3.6 km/s for V S can represent shallow crustal structure in the upper Mississippi embayment. Differential times of P – PpPhp and S – SsShs appear linearly proportional to sediment thicknesses, which best fits a one-layer sediment structure with average V P 2.042±0.041 km/s and V S 0.709±0.051 km/s, in the least-squares sense predicted by the wave propagation effects. Online Material: Figures illustrating seismograms, process procedure, imaged reflectors, and resolved velocity structure for six broadband stations and one short-period station.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2016-07-26
    Description: We introduce a nondiagonal seismic denoising method based on the continuous wavelet transform with hybrid block thresholding (BT). Parameters for the BT step are adaptively adjusted to the inferred signal property by minimizing the unbiased risk estimate of Stein (1980) . The efficiency of the denoising for seismic data has been improved by adapting the wavelet thresholding and adding a preprocessing step based on a higher-order statistical analysis and a postprocessing step based on Wiener filtering. Application of the proposed method on synthetic and real seismic data shows the effectiveness of the method for denoising and improving the signal-to-noise ratio of local microseismic, regional, and ocean bottom seismic data.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 6
    Publication Date: 2015-05-05
    Description: Seismic waveforms from the Eastern Tennessee Seismic Network are corrected to the nominal Wood–Anderson (WA) torsion seismometer to obtain a total of 11,905 maximum trace amplitudes from 690 events seen on 50 different horizontal components to determine a local magnitude scale for the Eastern Tennessee Seismic Zone (ETSZ). We use the following distance-correction function –log 10 ( A 0 )=0.538( r /17)–0.0002516( r –17)+2.0, in which A 0 is the maximum amplitude measured in millimeters and r is the hypocentral distance measured in kilometers; this better agrees with reported moment magnitudes for larger events in the ETSZ. Using the normal 100 km distance for M L normalization severely overestimates M L , and we therefore chose to adopt the 17 km normalization technique. The –log 10 ( A 0 ) is very flat at distances 〉200 km, suggesting unusually low distance attenuation at local and near-regional distances from the ETSZ. The WA response reported by the International Association of Seismology and Physics of the Earth’s Interior to the nominal response shows no significant difference in the distance-dependent factor for the log A 0 term, although the revised response consistently yields M L values that are 0.1 lower than those found using the nominal response. The b -values for the currently reported duration magnitude are lower than the b -values obtained using the newly calculated M L scale. The relationship between M L and M D can be expressed as M L =0.68093 M D +0.64603. The catalog of events used in this study is complete for M L 〉1.3.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 7
    Publication Date: 2013-10-25
    Description: The spatial variation of seismic b -value is mapped for the New Madrid seismic zone using local earthquakes occurring between 1995 and 2013. A region of high b -value at about 1.8 is found in the northern part of the Reelfoot fault. By performing probability tests and following different procedures to obtain the result, we show the anomalously high b -value is not a processing artifact and is statistically significant. We attribute the b -value anomaly to creep behavior on the northern segment of the Reelfoot fault. Creep behavior is suggested by the recently discovered possible tremor and by the presence of quartz-rich rock as indicated by low V P / V S ratios detected in a local earthquake tomography study. Because quartz is a weak mineral, ductile, creeping behavior could be facilitated at depth resulting in generation of earthquakes in the shallower, brittle crust. To the south of the Reelfoot fault, the b -value is about 1.2. The character of seismic activity along the Reelfoot fault clearly changes from north to south indicating a change in the physical state of the fault zone.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 8
    Publication Date: 2014-10-04
    Description: Design of large-aperture broadband arrays and array stacking of waveforms for receiver function studies critically depend on the coherence of waveforms across an array. The coherence of teleseismic P and S waves in the 0.05–1.6 Hz frequency band has been examined using high signal-to-noise teleseisms recorded by the USArray Transportable Array. Instrument-corrected, time-windowed, and rotated P and S waves were filtered in five, single-octave frequency bands and then correlated to determine coherence in each band. The normalized correlation coefficient is used as a measure of relative coherence and plotted as a function of interstation distance, which is used as a proxy for horizontal wavelength. Up to ~100,000 unique station correlation pairs can be found for vertical component P and transverse component S . Coherence of teleseismic P waves across the USArray is seen to be uniformly high in the frequency band between 0.05 and 0.4 Hz, with average correlation coefficients of 0.8 or greater for over 10 horizontal wavelengths. P -wave coherence degrades at higher frequency, although coherence is still higher than 0.6 for lower mantle propagation paths. S -wave coherence is relatively less robust but is greater than 0.8 for the 0.05–0.2 Hz frequency band, again for lower mantle propagation paths. Average coherence drops for both P and S waves for frequency bands greater than 0.2 Hz at station distances influenced by wave propagation through the upper mantle. This characteristic of wave propagation in the Earth can be used to design high-resolution broadband phased arrays for detailed studies of large earthquake sources and Earth structure and increases confidence in using vertical stacks of P waves as effective source functions in regional receiver function analysis.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 9
    Publication Date: 2014-10-04
    Description: A phased array of 19 broadband seismometers was deployed from November 2009 to September 2011 in an effort to detect nonvolcanic tremor or tectonic tremor associated with the Reelfoot fault, northern Tennessee. An autodetection algorithm using broadband frequency–wavenumber analysis was used to search for the recurrence of signals first reported during an active source experiment in 2006. The original signals appeared as short duration, impulsive arrivals with a high phase velocity ranging from 3 to 25 km/s. We have identified thousands of similar signals on the 2-year long array data. Two distinct detection peaks are observed with event azimuths from the west and northeast. The detections are most similar to the events seen in 2006 and are inferred to come from very small ( M L ~–1) microearthquakes that occur in the shallow basement on faults adjacent to the Reelfoot fault. These include detections with coherent S -wave energy that reinforce the interpretation of very small local and regional events. Other signals detected show distinct changes in slowness and azimuth as a function of time. These events were interpreted as atmospheric acoustic sources. The high-frequency content and impulsive arrivals of the nonacoustic arrivals are not consistent with tectonic tremor as seen in other parts of the world but do indicate seismic activity in the crust near the Reelfoot thrust fault that was previously unknown.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2014-10-04
    Description: The horizontal-to-vertical (H/V) technique by Nakamura (1989) was applied to data from 30 new field stations and 64 other broadband temporary and permanent seismic stations within the Mississippi Embayment of the central United States to develop a 3D model of unconsolidated sediment shear-wave velocity structure. Using the Dart (1992) map of sediment thickness as a basis, two self-consistent models of average shear-wave velocity versus sediment thickness were developed by utilizing the theoretical linear relationship between the frequency of the H/V peak and shear-wave velocity. One model was based on the observation that the H/V peak period T p (s) versus sediment thickness h (m) was seen to be approximately linear with the relationship T p =0.003266 h +1.084. The second model was developed by considering peak frequency f p versus sediment thickness parameterized to follow ln f p =8.325 x 10 –7 h 2 –0.00232 h –0.01796. Overall, the models show low-average shear-wave velocity near the edge of the Mississippi Embayment with velocities increasing with increasing sediment thickness, consistent with increased sediment compaction. These models will be useful in studies of site resonance and amplification for earthquake-shaking hazards and for wave propagation computations for the region.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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