Frequency‐dependent regional wave attenuation is estimated for continental paths to the NORESS array in Norway. Regional Lg and Pn spectra from 186 events at ranges between 200 and 1400 km and local magnitudes between 1.1 and 4.8 are inverted for both seismic moment and apparent attenuation. The Lg spectra were inverted between 1 and 7 Hz, and the Pn spectra were inverted between 1 and 15 Hz. The method uses both the spectral and spatial decay of observed signal amplitudes to separate source and path contributions. The assumptions include the geometric spreading rate and the source spectrum to be uniquely defined by its long‐period level. Most events considered have local magnitudes less than 3.0, so the source corner frequencies are near or beyond the upper limit of the inverted bandwidth. The Q results, particularly for Lg, are therefore not very sensitive to the details of our source parameterization. The inversion parameters are source moment (for each event), a constant relating corner frequency and moment for the entire data set, and two parameters describing a power law frequency dependence of Q in the region. For fixed source and spreading assumptions the inversion defines clear trade‐offs among model parameters. These trade‐offs are resolved by adding the constraint that the separately derived source parameters for Lg and Pn are consistent. The “preferred” estimates for the apparent attenuation are QLg(f) = 560f0.26 and QPn(f) = 325f0.48. These Q values correspond to assumed geometric spreading rates of r−0.5 for Lg and r−1.3 for Pn. For fixed Lg spreading, the Pn spreading rate is constrained by requiring that the relative Lg amplitude for earthquakes and explosions of the same moment be consistent with well‐supported results from previous empirical studies. The relationship between the inverted seismic moment values and local magnitude is generally consistent with values from near‐field studies. Since magnitude does not enter the inversion, this result lends considerable support to the derived Q models. Whatever the physical interpretation of the results, they certainly provide an accurate parameterization of observed amplitude spectra in this region. This is valuable for representing wave propagation in the region, and it provides important data for assessing the event monitoring capabilities of small regional networks.

A model for the attenuation of high-frequency (0.5-8 Hz) P-waves is developed for teleseismic paths from eastern Kazakhstan t o five seismic arrays. Four are the UKAEA arrays in Scotland (EKA), Canada (YKA), India (GBA) and Australia (WRA) and the attenuation effects on these paths were studied in an earlier paper (Bache, Marshall & Bache). Here we add the path t o NORSAR (southern Norway) and extend the analysis by introducing explicit corrections for the source spectrum. The events are underground explosions at the Soviet Semipalatinsk test site and the source corrections are based on the Mueller & Murphy model which is normalized t o US experience. Averaging spectra from many array elements and many explosions leads t o smooth spectra that essentially display the effects of attenuation on each path. There are three major features. First, from 0.5 t o 3 Hz the attenuation effects are nearly the same for all five paths and indicate strong frequency dependence in Q. Second, from 3 to 8 Hz the four UKAEA paths are nearly the same, but the NORSAR path is quite different in that the sourcecorrected spectrum is nearly flat. This means that the path-average Q is nearly proportional to frequency in this band. Finally, above 7-8 Hz some additional attenuation effects are seen in the NORSAR data. Thus, for this teleseismic P-wave path the maximum signal/noise occurs a t 7 or 8 Hz. The attenuation effects from 0.5 t o 8 Hz can be represented with absorption band models. For the paths t o the UKAEA arrays the preferred model has to* (travel time/Q at long periods) about 0.6 s and 7, about 0.5 s. Superimposed on this is a frequency-independent tf of about 0.1 s. This dominates the high-frequency ( f > 3 Hz) attenuation and appears t o represent attenuation primarily by scattering. For the NORSAR path a single absorption band (t,* -5 0.7, 7 , = 0.045) is adequate for the 0.5-7 Hz band. We have no explanation for why this path is so different, but it appears to be associated with some difference in the contribution of scattering t o the attenuation of the initial P-wave.

Boiling AFB, 20332 .-16. ISTSBUTION 57A TEMEN r0t ths Repor) Approved for public release; distribution ,nlimit ed. 17 :ISTRIBuTION STATEMENT (o tie abstract entered Sl atock 20. it different Irom Report) 18. SUPPLEMENTARY NOTES t9. KEY NORCS ,Continue on reverse s@ e '1 necessary and ,denrtv by block number) Lg, synthetic seismograms, nuclear explosion detection, earthquake simulation 20. ABS RACT Confln.e on r.ers. side it. nece85erv end idoneifv by Odock n-mbe, This report summarizes three research efforts performed during the past fiscal year. The firstthese efforts is a study of the theoret,.al behavior of the region-I seismic phase Lg in various tectonic provinces. Synthetic seismograms are used to determine the sensitivity of Lg to source and medium properties. The primary issues addressed concern the relationship of regional Lg characteristics to the crustal attenuation properties, the comparison of Lg in many crustal structures and the source depth dependence of Lg..... * , DO , 2 ,. 1473 EZTON 00' NOV S5 S OBSOLE E Unclassified SEC-jRITY LASSIV A10ATION :V '-iS ; ,AGE I Oare ter";

A model for the attenuation of high-frequency (1-8 Hz) P waves is developed for paths from eastern Kazakhstan to arrays in Scotland (EKA), Canada (YKA), India (GBA), and Australia (WRA). The attenuation model includes contributions from both intrinsic absorption and scattering. Distinction between the two is especially important for forward modeling because the dispersion is quite different. However, no satisfactory complex operator for representing the scattering attenuation appears to be available at present. Attenuation consistent with an absorption band model dominates at low frequencies and is strongly dependent on frequency in this band. Attenuation that appears to be due to scattering has an important effect above 2.5 Hz and dominates at high frequency. It can be represented by a constant effective Q-x, or by Q-• • f The details of the best fitting model depend on which of these is chosen and on the value of to* (travel time/Q ratio at long period) which is poorly constrained by these data. The general conclusion is that the intrinsic attenuation can be represented by an absorption band model with 0.04 _• z,• _• 0.1, while 0.5 _• to* -• 1.0. Superimposed on this is scattering attenuation, which can be represented by a constant t* of about 0.1 s or by t* = Af, with A about 0.01. Some differences are seen among the four paths, with the greatest attenuation in the 1-3 Hz band seen at YKA and the least at EKA. Above 3 Hz the attenuation effects are essentially identical for all four paths. mori and Anderson, 1977] provides a good theoretical framework for interpreting attenuation data and is now used in most studies of frequency dependent attenuation. However, this model does not represent the effects of scattering which can be an important cause for amplitude attenuation at high frequencies. Thus the nature of the attenuation mechanism is an impoi'tant issue in the short-period band.The objective of this study is to determine the attenuation of teleseismic P waves in the 1-8 Hz band for several paths for which particularly good data are available. The technique is to analyze the spectra of very short time windows chosen to isolate the first-arriving P wave pulse. The attenuation effects of interest are those which influence the amplitude of this pulse and therefore rnb. The attenuation determined this way is not necessarily the same as that determined from a longer window including much of the P coda.The main reason the frequency dependence near 1 Hz remains so poorly understood is that adequate data are difficult to obtain. The illuminating characteristics are obscured by noise and by complexity caused by path effects. Also, there is a strong trade-off between source and attenuation effects, since most of the events that provide the best data have corner frequencies near 1 Hz. In this study these deficiencies are largely overcome by using recordings of Soviet Eastern Kazakhstan explosions from four arrays designed by the United Kingdom Atomic Energy Authority and operated by organizations in Scotland, Canada...

A B S T R A C TA continuum theory with microstructure for wave propagation in laminated composites, proposed in a previous work concerning normal propagation, is extended herein to the case of propagation parallel to the laminates.Model construction is based upon an asymptotic scheme in which dominant signal wavelengths are assumed large compared to typical composite microdimensions. A hierarchy of models is defined by the order of truncation of the obtained asymptotic sequence. To estimate accuracy, the phase velocity spectrum is investigated. As in the previous case, retention of all terms in the asymptotic sequence is found to yield the exact spectrum of Rytov. Spectral collation of the lowest order dispersive theory with exact first mode data gives excellent agreement.Based upon asymptotic expansions, a simplified first-order theory is also developed. Transient pulse data obtained from the latter exhibits good correlation with experimental results. In addition, representative calculations of microcomponent velocity distributions and interface shear stress are carried out using the simplified theory. Z U S A M M E N F A S S U N GEine Kontinuumtheorie mit Mikrostruktur fiir die Wellenfortschreitung in lamellierten zusammengesetzten Materialien wird erweitert fiir den Fall einer Wellenfortschreitung parallel zu den Lamellen. Eine solche Kontinuumtheorie war in eine friiheren Arbeit fiir Ausbreitung senkrecht zu den Lamellen vorgeschlagen worden.Der Bau des Models ist begriindet auf einen asymptotischen Schema, in welchem vorherrschende Signalwellenlangen als gross verglichen mit der typischen Mikrodimension der Lamellen angenommen wird. Eine Hierarchic yon Modellen wurde nach der Ordnung der Abschneidung der erhaltenen asymptotischen Reihe definiert. Urn Genaugkeit abzusch~itzen, wird das Phasengeschwindigkeitsspektrum untersucht. Genau wie im vorhergehenden Falle, fanden wir, dass das Beibehalten alle Terme in der asymptotischen Reihe das exakte Spektrum von Rytov liefert. Die spektrale Zuordnung der niedersten Ordnung Dispersionstheorie zu den exakten ersten Modusdaten zeigt eine ausgezeichnete Obereinstimmung.Ebenfalls wurde eine vereinfachte erste Ordnung Theorie entwickelt, welche auf einer asymtotischen Erweiterung beruht. Die Durchgangspulsdaten, welche yon den letzteren erhalten wurden, zeigen eine gute Korrelation zu deft experimentellen Ergebnissen. Weiterhin werden mit Itilfe der vereinfachten Theorie einige re-pr~isentative Berechnungen der Geschwindigkeitsverteilungen der Mikrokomponenten und der Schubspannung in der Zwischenschicht durchgefiihrt.