Source parameters of two M_L ∼ 5 earthquakes near Anza, California, and a comparison with an Imperial Valley aftershock

Strong-motion records were used to determine the seismic moments, source dimensions, and stress drops for two earthquakes near the proposed Anza seismic gap (Thatcher et al., 1975) along the San Jacinto fault: the 25 February 1980 (M_L 5.5) event and the shock of 15 June 1982 (M_L 4.8). Seismic moments determined for the two events were 2.5 × 10^(23) and 1.1 × 10^(23) dyne cm, respectively. The source radii were estimated from the displacement pulse widths using the source model of Madariaga (1976). Static stress drops for the 1980 and 1982 earthquakes were calculated as 110 and 100 bars, respectively. Stress drops determined from the rms accelerations using the method of Hanks and McGuire (1981) were 220 bars for the 1980 earthquake and 180 bars for the 1982 event. The long-period seismic moments for these events, derived from regional recordings of 30- to 40-sec Love waves, were a factor of two to three greater than the moments estimated from the strong-motion records. As a comparison to the Anza events, source parameters were also determined from strong-motion records for an immediate aftershock (M_L 5.0) of the 1979 Imperial Valley earthquake. The seismic moment of this aftershock was calculated as 4.2 × 10^(23) dyne-cm, and its static stress drop was 130 bars. Static stress drops calculated from the displacement pulse shapes for the three events studied in this paper, as well as for an aftershock of the Oroville earthquake reported by Fletcher et al. (1980), exhibit a relatively narrow range between about 100 and 180 bars. This result indicates that the stress drops of the two main shocks near Anza were not unusually high, relative to those of certain aftershocks in other tectonic settings in California

Finite Difference Simulations of Seismic Scattering: Implications for the Propagation of Short-Period Seismic Waves in the Crust and Models of Crustal Heterogeneity

Synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two-dimensional media with random spatial variations in seismic velocity. The results of this study provide important insights about the propagation of short-period ( 5), the self-similar medium is characterized by a scattering Q that is constant with frequency, whereas theory predicts that the apparent Q in an exponential medium is proportional to frequency. These alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal Q at frequencies greater than about 1 Hz, assuming that scattering is responsible for most of the attenuation at these frequencies. Measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation (scattering Q ≤ 200). In these cases, Q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission Q of the medium. The cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium. The self-similar random medium proposed here for the crust produces waveform variations at high frequencies (15–30 Hz) similar to those reported for actual small-scale seismic arrays with apertures of hundreds of meters

A finite-difference simulation of wave propagation in two-dimensional random media

A finite-difference algorithm is used to generate synthetic seismograms for waves propagating through two-dimensional random media. The media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle. The finite-difference technique retains all multiply scattered and diffracted waves, and also accounts for transmission losses. The synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering. For a medium with a white wavenumber spectrum of velocity fluctuations, the coda is higher frequency than the initial pulse. The apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength. The spectra of the coda generally increase in frequency as the scatterers decrease in size. Examples demonstrate how scattering can produce spectra with broad peaks and sharp fall-offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

Homeroom Guidance Activities For May Goodrell Junior High School, Des Moines, Iowa

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A headspace solid-phase microextraction method of use in monitoring hexanal and pentane during storage: Application to liquid infant foods and powdered infant formulas

The determination of two secondary lipid oxidation compounds (hexanal and pentane) in liquid infant foods using a headspace solid-phase microextraction gas chromatographic (HS-SPME-GC) method has been developed and validated. The HS-SPME analytical conditions (fibre position, equilibration and sampling times) were selected. The analytical parameters of the method (linearity: hexanal from 2.48 to 84.78 ng/g, pentane from 6.21 to 79.55 ng/g; precision: hexanal 2.87%, pentane 2.343.46%; recovery: hexanal 106.60%, pentane 95.39%; detection limit: hexanal 3.63 ng and pentane 4.2 ng) demonstrate the usefulness of the method. Once optimized, the method was applied to liquid infant foods based on milk and cereals, and to powdered adapted and follow-up milk-based infant formulas (IF), stored for four and seven months. In all cases the hexanal content was higher in IF than in milk-cereal based infant foods. No pentane was found in IF

Monolingual and crosslingual comparison of tandem features derived from articulatory and phone MLPs

In recent years, the features derived from posteriors of a multilayer perceptron (MLP), known as tandem features, have proven to be very effective for automatic speech recognition. Most tandem features to date have relied on MLPs trained for phone classification. We recently showed on a relatively small data set that MLPs trained for articulatory feature classification can be equally effective. In this paper, we provide a similar comparison using MLPs trained on a much larger data set - 2000 hours of English conversational telephone speech. We also explore how portable phone- and articulatory feature- based tandem features are in an entirely different language - Mandarin - without any retraining. We find that while phone-based features perform slightly better in the matched-language condition, they perform significantly better in the cross-language condition. Yet, in the cross-language condition, neither approach is as effective as the tandem features extracted from an MLP trained on a relatively small amount of in-domain data. Beyond feature concatenation, we also explore novel observation modelling schemes that allow for greater flexibility in combining the tandem and standard features at hidden Markov model (HMM) outputs