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Summary. A new method of estimating the yields of events at a nuclear test site is introduced and tested against the Amchitka experience. The intercorrelation method is a relative waveform comparison technique, which involves convolution of the first few seconds of each short-period P-wave recorded at a given station for two events with estimates of the effective source function (including pP) for the other event. This procedure accounts for common path and receiver effects as well as differences in time functions and near-source surface interactions. If the source parameters for a master event are determined independently, the assumed source parameters for a second event can be adjusted to minimize the residual differences in the inter-correlated signal pairs for a large number of stations simultaneously. Yield estimates can then be made using empirical relations between the source parameters and yield. The source time function representation used is ?(t) =?{1 - exp(-Kt)[1 +Kt+ (Kt)2/2 -B(Kt)3]}.

We have simulated accelerograms from many of the strong motion stations close to the mainshock of the 1987 Whittier Narrows earthquake using a semi-empirical Green's function summation technique. This method allows gross aspects of the source rupture process to be treated deterministically using a kinematic model based on first motion studies, teleseismic modeling and the distribution of aftershocks. Stochastic aspects of the rupture process are then included to simulate irregularity in both rupture and slip velocity. Gross aspects of wave propagation are modeled using theoretical Green's functions calculated with generalized rays. Detailed aspects of the source radiation at high frequencies, as well as unmodeled propagational aspects such as scattering, are included empirically by using multiple recordings of a smaller Imperial Valley earthquake as empirical source functions. Our main objective is to see how well we can predict the peak ground accelerations, time histories and response spectra of ground motions of a moderate sized earthquake within the Los Angeles Basin having limited detailed source information. We find that the simulations predict the observations accurately enough to identify which phases and amplitudes in the observed data may be due to local site response rather than source or radiation effects. Comparisons between observed and simulated accelerograms for all the stations modeled are made using peak ground acceleration, and using time histories and response spectra for the stations that have been hand-digitized to date. The Bright Avenue Whittier station has the largest simulated peak acceleration, in agreement with the recorded peak acceleration data.

New short-period waveform data from the US-Soviet Joint Seismic Program (JSP) make possible investigations of Asian upper mantle structure. the goal of this paper is to explore the potential use of the newly available JSP data to gain a qualitative view of upper mantle structure beneath Asia, and to facilitate more detailed future detailed future upper mantle studies. In a reconnaissance approach, waveform upper mantle studies. In a reconnaissance approach, waveform predictions from upper mantle P-wave velocity models of previous studies are compared to the JSP data to investigate regional differences in the central Asian upper mantle. Data coverage brackets the upper mantle triplications with excellent multi-source-to-stations sections. the abundance of data for controlled source-receiver geometries and the impulsive nature of the arrivals enable us to stack seismograms to improve signal-to-noise ratio. Arrivals from the 400 and 670 km discontinuities are apparent in the data and are compared to predictions of the mantle models. the principal result is that, for the regions studied, paths through cratonic regions of Asia are compatible with shield-type models, while paths through highly deformed regions of Asia are compatible with models derived for tectonically active regions, suggesting large lateral variations beneath the Eurasian continent. Use of the JSP data in a comparative approach is fast and simple, and proves effective in obtaining a first-order understanding of the Asian upper mantle. This result also presents the potential for qualitative studies elsewhere with digital portable stations.

The generalized ray and reflectivity methods of waveform synthesis have been compared for realistic models of the upper mantle and of the oceanic crust. Both methods entail some approximations, but the one which requires the most careful testing is the truncation of the generalized ray sum. It has been shown in this study that for the types of time windows typically used in waveform modelling the generalized ray sum converges very rapidly to the reflectivity result. In most cases, it is only necessary to include the primary rays in the sum. Additional internal multiples are sometimes necessary if the model contains thin high gradient zones. The primary rays alone do not always correctly predict the amplitude decay of the supercritical reflection from the gradient. Multiples are also required to avoid long-period errors and truncation arrivals if very shallow travelling energy arrives within the time window of interest. It has also been shown that a number of fast approximate methods provide a very cost efficient alternative to the two more exact methods. The best approach to trial and error modelling studies appears to be to begin with a fast approximate method, to advance to generalized ray theory for the final iterations and to use reflectivity to test and to store the results.

A new method of estimating the yields of events at a nuclear test site is introduced and tested against the Amchitka experience. The intercorrelation method is a relative waveform comparison technique, which involves convolution of the first few seconds of each short-period P-wave recorded at a given station for two events with estimates of the effective source function (including pP) for the other event. This procedure accounts for common path and receiver effects as well as differences in time functions and near-source surface interactions. If the source parameters for a master event are determined independently, the assumed source parameters for a second event can be adjusted to minimize the residual differences in the intercorrelated signal pairs for a large number of stations simultaneously. Yield estimates can then be made using empirical relations between the source parameters and yield. The source time function representation used is ψ(t)=ψ{1 − exp(−Kt)[1 +Kt+ (Kt)2/2 −B(Kt)3]}. Due to the narrowband character of short-period P-waves and the possibility of yield dependence of overshoot of the source spectrum (controlled by B), it is generally not possible to resolve uniquely the static source strength, ψ∞. However; for fixed values of B, an alternate parameter, ψ′∞, can be determined, which gives the correct source strength in the period range of the signals. For the Amchitka events ψ′∞ is found to have a simple power law relation with yield. With B=1, intercorrelation of MILROW with CANNIKIN gives a ψ′∞ of 4.0 ± 0.6 × 1011 cm3 for CANNIKIN, compared with 4.5±0.5 × 1011 cm3 determined from near-field data. Intercorrelations of MILROW and CANNIKIN with LONGSHOT give consistent ψ′∞ values of 2.0 ± 0.3 × 1010cm3 for LONGSHOT. In all cases the pP lag times and amplitudes obtained in the procedure are consistent with previous determinations. The effects of underparameterization of the effective source functions are investigated and found not to bias the ψ′∞ determinations strongly. The use of complete waveform information is shown to have several advantages over standard amplitude comparisons for estimating yield.

A measurement of the relative frequency content of ScP and ScS phases from deep earthquakes provides a simple indication of the average value for Q in the mantle. When the ScP converts to the compressional mode at the core-mantle boundary it begins to attenuate at a slower rate than the ScS. Assuming that the core reflections are frequency-independent, the spectral ratio of the two phases provides a measure of the spectral ratio of the P and S attenuation operators. The average value of mantle Q can be inferred from this information if it is assumed that negligible losses occur in pure compression. Both rays travel downward through the anomalous source region as S. Q is measured on the upward leg of the raypath well away from the subduction zone. The two raypaths diverge somewhat in the lower mantle, so they sample different portions of the core-mantle boundary. They converge closely again in the upper mantle, however, where most attenuation takes place. Clear ScP-ScS observations have been collected from the short period records at 25 WWSSN stations in a variety of tectonic regimes. The relative waveshapes have been analysed in terms of a standard linear solid Q operator. The low-frequency level of Q was set to be consistent with Q measurements from multiple ScS phases. The parameter controlling the increase of Q at high frequency, τm has been determined by minimizing a quantitative measure of fit between ScP waveforms filtered with standard linear solid Q operators and observed ScS waveforms. The frequency band of the observations is from about 0.5 to 1.5 Hz. The observations constrain τm to be between 0.0 and 0.2s. This implies that the rapid increase of Q with frequency does not occur until frequency exceeds 1 Hz. Good quality ScP-ScS pairs appear to be much more common in the WWSSN record library than good quality ScS–ScSm, pairs. As more ScP-ScS data are analysed, we should, therefore, be able to constrain the average mantle Q better in the ScP-ScS frequency band than in the multiple ScS band. No clear correlation exists between the ScP–ScSQ measurements and the tectonic regime of the recording sites. ScS phases are not more strongly attenuated with respect to ScP at oceanic island sites than at stable continent sites. This is interpreted to mean that other types of lateral variation often overwhelm the attenuation bias patterns induced by surface tectonics. These other lateral variations could be anelastic (deep seated low Q zones) or elastic (lateral velocity variations which focus or defocus seismic waves).

The relative size of 15 underground nuclear explosions at the Novaya Zemlya test site is determined by applying a relative waveform analysis called intercorrelation to 566 teleseismic short-period P-waves. The waveforms are corrected for the effects of pP interference and yield scaling of the explosion source functions so that signals from different events recorded at the same station can be analytically compared. For events within a single test site, this procedure accounts for common path and receiver effects. Relative explosion source strengths in the 0.5-2.0 Hz frequency band determined by intercorrelation are consistent with the results of conventional mb analysis. Absolute yield estimates from both intercorrelation and mb analyses have much greater uncertainty due to unknown baselines. The yield estimates for the 15 events range from 36 to 3886 kt, assuming that t*α= 0.5 s and that yield scaling relations for the Amchitka test site are appropriate for Novaya Zemlya. The pP delay times obtained from intercorrelation of Novaya Zemlya events are similar to the delay times for Amchitka events with equivalent yields, consistent with both being hardrock sites. The analytical waveform comparisons also provide criteria for identifying anomalous events. The Novaya Zemlya test site has two subsites separated by about 300 km. One of the 11 events in the Northern subsite and one of the four events in the Southern sub-site have anomalous waveforms. A waveform modelling study indicates that the anomalous Southern event was a double explosion. Northern and Southern Novaya Zemlya have different waveform and amplitude patterns, apparently caused by different focusing and defocusing of seismic energy by laterally varying structure near the sources.