A new, simple and efficient algorithm is described which computes the probability of occurrence of at least (or exactly) k out of N events, given the individual event probabilities. A comparison is made with two previous methods. Computer program listings are given.

Topics: DTIC Archive, Wirth, Mark H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *PROBABILITY,...

An efficient contour-plotting routine is discussed which is based on a scanning algorithm of Cottafava and LeMoli and employs bi-linear interpolation. An auto-interpolation scheme is developed which automatically adjusts the number of interpolations in any data square to produce smooth line segments. A program listing and examples are given.

Topics: DTIC Archive, Wirth, Mark, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *COMPUTER PROGRAMS,...

Solutions of the ray propagation equation are obtained for various boundary conditions, assuming vertical incidence in plane, parallel, equal- travel-time layers. The solutions are examined in both the time and frequency domains and certain properties derived. A complete discussion of frequency- domain synthesis techniques is given in connection with a treatment of the absorption problem. FORTRAN programs are given which compute any of the solutions in either the frequency or time domains, with...

Topics: DTIC Archive, Wirth, Mark, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *EPICENTERS, *SEISMIC...

The results of a study of Ms vs mb characteristics of earthquakes in the Eastern Himalayan region are given in this report. It is shown that in this region some earthquakes occur which have Ms vs mb characteristics similar to explosions, exhibiting low surface wave magnitudes relative to body wave magnitudes, when seen at the reporting stations available to this study. The existence of these anomalous events in certain areas of the world can seriously decrease the effectiveness of the Ms vs mb...

Topics: DTIC Archive, Der, Zoltan A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *EARTHQUAKES,...

Joint Epicenter Determination (JED), a least squares method of estimating earthquake epicenters and station corrections, is shown to be unstable for some teleseismic nets in that estimated locations and station corrections change substantially when a few readings from a large set are omitted. Locations are also shown to change if different travel-time tables are used. The result is established both for a North American and a world-wide net, using an epicentral region ranging 30 degrees along...

Topics: DTIC Archive, Ahner, R O, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *EARTHQUAKES,...

The objective of the study was to determine whether source modeling could improve teleseismic event locations near island arc structures, using models defined by available information about the underthrusting plates of these regions. The authors describe a location method based on ray-tracing, using a crude source region plate model. In the case of the Aleutian-Alaskan region, this method predicts that all teleseismic locations should be shifted along the perpendicular to the Aleutian arc near...

Topics: DTIC Archive, Page, E A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

For seven earthquakes a comparison is made between the TFO long- period horizontal array and the sum of the horizontal strain and pendulum instruments at QCAZ. The performance of both systems was severely limited by noise of non-seismic origin. Within these limits the performance of the two systems is about equal. This report is preliminary in the sense that the installation of instruments at QCAZ was not complete at the time data was obtained. A lower level of non-seismic noise is to be...

Topics: DTIC Archive, Woolson, J R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

MILROW, the second United States underground nuclear explosion on Amchitka Island, was an order of magnitude larger than LONG SHOT, the first test there. Magnitude-yield scaling between the two for both surface waves and body waves followed theoretical predictions well and agreed with Nevada Test Site (NTS) scaling. A computed location of MILROW using LONG SHOT travel-time anomalies was only 1.2 km in error horizontally and 11.8 km vertically, a substantial improvement over a location using no...

Topics: DTIC Archive, Von Seggern, D H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *NUCLEAR...

Amplitudes of Rayleigh waves generated by some southern Nevada nuclear explosions and cavity collapses were analyzed. The Rayleigh amplitude radiation patterns for all the explosions and collapses investigated were found to be similar within the expected variation of 30% due to calibration and measurement errors. The primary factor affecting the Rayleigh amplitude radiation patterns of the explosions was found to be the effect of the earth structure along the travel paths from source to...

Topics: DTIC Archive, Masse, Robert P, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *NUCLEAR...

A method is proposed for whitening the spectra of teleseismic P waves to aid in the determination of event depths. The method uses a network of common recording stations, all of which must have recorded signals from a suite of closely-spaced events, e.g., a set of underground explosions. Individual spectra are whitened by removing a path-recording site response determined by averaging spectra from the suite of events as recorded at a single station. The whitened spectra from a single event are...

Topics: DTIC Archive, Cohen, T J, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

In estimating signals as P-waves, without regard to distinguishing the P-waves in ambient noise from those which are added by a teleseismic signal, the comparative performance of a thirteen element small aperture horizontal array and a seven element vertical array favors the vertical array. Analysis of the variance of the residual noise under the estimate of signal on the vertical array results in a signal estimation error which is 31 db down on the vertical array estimate of signal, and 15 db...

Topics: DTIC Archive, Sax, R L, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *UNDERGROUND EXPLOSIONS,...

It is shown that an F detector reduces the number of beams in velocity space over which a search must be made before declaring a short period seismic array detection, that its main detection lobe is satisfactorily wide for practical purposes, and that simple F detection is poor at detecting mixed signals. Design considerations are given for selection of particular detection algorithms for different sizes and types of arrays.

Topics: DTIC Archive, Blandford, Robert R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

P and PKP coda characteristics are determined for earthquakes from 15 seismic regions as recorded at 17 World Wide Standard Seismograph Stations (WWSSS). In determining the coda characteristics for an event, amplitude measurements, scaled relative to the largest excursion in the coda, are made in successive time windows, and the coda envelope obtained by connecting successive observations. The individual coda, average coda, and standard deviations about the average coda as a function of time...

Topics: DTIC Archive, Cohen, T J, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *UNDERGROUND EXPLOSIONS,...

Short-period beams were formed for twenty-four events recorded at both the LASA and TFO arrays. The mean RMS noise in the frequency range 0.4-3.0 Hz for the LASA beams was 0.16 millimicron, and for the TFO beams 0.13 millimicron. Noise reduction by beam formation in the range 0.4-3.0 Hz varied from 17 to 23 db for LASA, from 12 to 18 db for the 37-sensor TFO array, and from 6 to 14 db for the 19-sensor TFO subarray. Averaging over several source regions in the distance range 25 degrees delta90...

Topics: DTIC Archive, Mecklenburg, Herman J, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB,...

A seismic location study has been conducted in a continental region, Central Alaska, to verify the general applicability of the travel-time anomaly technique. First, using local stations and estimating event depths by observing pP, a set of earthquakes in the Central Alaska region was located with residual travel time errors attributable to reading error. The distribution of anomalies for teleseismic stations indicates that the Central Alaska region is composed of three subregion between which...

Topics: DTIC Archive, Chiburis, E F, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *EARTHQUAKES,...

An extension is made of linear discriminant analysis to the case where multiple station observations are available for each event. Multivariate regression is used to estimate the mean vectors and covariance matrix in the multiple station discriminant function. The same stations need not be observed for all events as a separate discriminant vector is derived for each station observation and only the discriminant functions available for each event are added. The identification curves for this...

Topics: DTIC Archive, Shumway, R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

An analysis of 418 small-event (m sub b or = 5.8) seismograms recorded at 17 world-wide stations, and of 148 large-event (m sub b, M sub s (NOS), or m sub b from Pasadena or Berkeley or = 7.0) seismograms recorded at 8 worldwide stations and TFO indicates that coda shape is primarily a function of the arrival times and relative amplitudes of significant secondary arrivals. However, for times greater than 10 to 20 seconds into the coda, large-event codas are approximately 0.14 m sub b units...

Topics: DTIC Archive, Sweetser, E I, Cohen, T J, Tillman, M F, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA...

The theoretical amplitude ratio of shear waves to compressional waves is computed using point double-couple representations of earthquakes. These ratios are compared to earthquake data from the LRSM and VELA observatory network. The earthquake data on shear-to-compressional ratios from this network is directly compared to that from NTS underground nuclear explosions. The shear-to-compressional ratio in the teleseismic distance range is found to be significantly greater for earthquakes than...

Topics: DTIC Archive, von Seggern, D H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

Comparisons are made of Rayleigh wave spectra for Nevada Test Site explosions and Nevada earthquakes and for a limited number of teleseismic explosions and earthquakes recorded in North America. For a given combination of source and receiver location, the explosions consistently exhibit the same spectral shape over a significant range of magnitudes while spectral shapes for earthquakes commonly vary in a manner that appears independent of magnitude, with some earthquake shapes closely matching...

Topics: DTIC Archive, Alexander, S S, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *RAYLEIGH WAVES,...

The report summarizes the work done by the SDL during the period January through March 1972, and primarily concerns the seismic research activities related to the detection and identification of nuclear explosions and earthquakes. The report also contains brief discussions of the support tasks and data services which were performed for other government contractors and for participants in the VELA-UNIFORM and PRIME ARGUS projects.

Topics: DTIC Archive, Hartenberger, R A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *UNDERGROUND...

The report summarizes the work done by the SDL during the period April through June 1973, and primarily concerns the seismic research activities related to the detection and identification of nuclear explosions and earthquakes. The report also contains brief discussions of the support tasks and data services which were performed for other government contractors and for participants in the VELA-UNIFORM and PRIME ARGUS projects.

Topics: DTIC Archive, Blandford, Robert R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

Analysis of seismic signals recorded on both the standard long period and the wide band long period seismograph systems at TFO revealed that these systems yield equivalent information concerning long period energy in the signals. The Rayleigh wave energy at periods greater than sixty seconds was determined to originate almost entirely from events with epicenters near oceanic trenches or orceanic ridges.

Topics: DTIC Archive, Masse, R P, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

RULISON was an underground nuclear explosion detonated to stimulate gas production as part of the PLOWSHARE program. The RULISON device was detonated at 21:00:00.1Z on 10 September 1969. It was detonated in Western Colorado, which represented a new source region, and was emplaced at a depth nearly double that of previous American explosions. Analysis includes a study of seismograms from 18 LRSM, 2 VELA observatories, LASA and 8 WWSS stations. Proposed identification criteria, developed most...

Topics: DTIC Archive, Lambert, D G, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *NUCLEAR EXPLOSIONS,...

We present a method for predicting the noise reduction by simple beamforming of an array. The method gives an accurate estimate of the known capabilities of LASA, and is applied to the design of possible new arrays. The method requires field measurement of noise and signal correlations as a function of distance.

Topics: DTIC Archive, Blandford, R R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The intermediate period strain-pendulum combination at HNME is very effective in reducing 4-8 second microseisms and enhancing body phases. The spectra and the relative excitation of intermediate period P and S waves show good potential as discriminants between earthquakes and explosions. If, however, discrimination can be made using 1 and 20 second information, then standard instruments have a lower threshold. The spectral behavior of body and surface waves is sensitive to the local structure,...

Topics: DTIC Archive, Der, Zoltan A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

A method of relative location for explosions using Rayleigh waves is developed and tested. It involves cross correlating a wavetrain with a previously recorded signal from the same source region and determining a relative 'travel-time' from the peak in the cross correlation trace. Locations are fairly accurate, but do not compare with the precision obtained with body waves and relative travel-time corrections. A number of causes of errors are discussed, and it is estimated that a sophisticated...

Topics: DTIC Archive, Von Seggern, D H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

A method of relative magnitude determination using all available data for a limited source area is proposed. The attenuation factor B, event terms F(j), and station terms C(i) for the linear model X(ij) = C(i) + F(j) + H - BR(ij) are solved simultaneously by an interative least-squares procedure; here X(ij) is the logarithm of the amplitude and R(ij) is the logarithm of the distance. The method is analogous to joint epicenter determination, and so is termed 'joint magnitude determination'...

Topics: DTIC Archive, Von Seggern, D H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *UNDERGROUND...

Earlier theoretical work on automatic detection by an array or a network of arrays is extended to include the case where the signal amplitude varies log-normally between sensors or arrays. It was found that a 'multi-array' detector which detects on the sum of the subsystem detector outputs is substantially superior to a 'voting' detector. This result is in agreement with the few available empirical data. It is recommended that the multi-array detector be further evaluated using empirical data...

Topics: DTIC Archive, Blandford, R R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The theory of automatic detection at a seismic array by means of an F statistic is extended to a network of such arrays. The arrays may have equal or different expected signal-to-noise ratios. Two techniques are discussed: the composite F detector in which a vote is taken among the arrays; a multi-array F detector in which the original data from the independent arrays are combined to form one F statistic.

Topics: DTIC Archive, Wirth, M H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

The report investigates the effect of realistic propagation paths on the visual and spectral amplitudes of fundamental mode Rayleigh waves. It shows that the Harkrider amplitude response factor of a layered media should relate directly to a station correction; it varies by a factor of nearly three between oceanic and continental sites. Attenuation due to effective Q losses may cause scatter, of over one-half magnitude unit, in teleseismic amplitudes but is unimportant at regional distances....

Topics: DTIC Archive, Von Seggern, David H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

A detailed analysis of the surface wave radiation from two underground explosions (BILBY and SHOAL) and an earthquake (near Fallon, Nevada) whose epicenter is only 60 km from SHOAL indicates that: at long periods the surface wave radiation from the earthquake can be explained by a pure quadrupole (double-couple) source, but a higher frequencies the radiation pattern shows asymmetries which suggest effects due to rupture propagation which require higher-order multipole terms in the source...

Topics: DTIC Archive, Lambert, D G, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

A technique to process array data has been developed to determine when a second signal is hidden in the coda of a primary signal; and to estimate the waveform of the two signals. The effectiveness of the mixed-signal processor has been demonstrated by operating on various possible mixed signals formed from recordings of earthquakes at Tonga in the South Pacific and at the Fox Islands in the Aleutians. For small arrays the processor is found to be substantially superior to simple beamforming....

Topics: DTIC Archive, Shumway, R H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The report summarizes the work done by the SDL during the period April - June 1970, and is primarily concerned with seismic research activities related to the detection and identification of nuclear explosions and earthquake phenomena. Also discussed are the support tasks and data services performed for other government contractors and participants in the VELA-Uniform and PRIME ARGUS projects.

Topics: DTIC Archive, Hartenberger, Royal A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB,...

The report summarizes the work done by the SDL during the period October through December 1971, and primarily concerns the seismic research activities related to the detection and identification of nuclear explosions and earthquakes. The report also contains brief discussions of the support tasks and data services which were performed for other government contractors and for participants in the VELA-UNIFORM and PRIME ARGUS projects.

Topics: DTIC Archive, Hartenberger, Royal A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB,...

Two suites of events, one in the Tonga Islands, and the other in the Hindu Kush, were match filtered to determine relative enhancement in signal-to- noise ratio achieved by various procedures. It was found that match-filter S/N enhancement depends very little on the proximity of the reference event used as a match filter for distances as great as 600 km. For both regions, one event with high S/N ratio performed as well as many closer events in match filtering. Pre-whitening the real signals...

Topics: DTIC Archive, Von Seggern, David H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The report summarizes the work done by the SDL during the period July - September 1970 and is primarily concerned with seismic research activities related to the detection and identification of nuclear explosions and earthquake phenomena. Also discussed are the support tasks and data services performed for other government contractors and participants in the VELA-Uniform and PRIME ARGUS projects.

Topics: DTIC Archive, Hartenberger, Royal A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB,...

The object of this study was to determine the characteristics of signals and noise as recorded at the Alaska Long Period Array (ALPA), and to evaluate the performance of signal processing techniques using data from this array. Only a partial array of five to eight sites was available for analysis. Results are discussed.

Topics: DTIC Archive, Clark, D M, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

The precision with which the focal depth may be determined using Love/Rayleigh wave spectral ratios depends on the accuracy of the models for Earth structure and for source mechanism used in the focal depth calculations. Estimates of the precision of the focal depth determination are obtained using the partial derivatives of Love/Rayleigh spectral ratios with respect to the parameters: focal depth, shear velocity, dip angle, and slip angle. It was found that errors due to imprecise knowledge of...

Topics: DTIC Archive, Masse, R P, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

A comparison has been made of the coda attenuation capabilities of the beam and mixed-signal processor using 7- and 19-element TFO subarrays. The major source region was taken as Semipalatinsk (96 degrees distance from TFO), while the interfering signals from various earthquakes were time-shifted to simulate arrivals from various azimuths at 60 degrees distance. Conclusion are discussed.

Topics: DTIC Archive, Cohen, T J, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

Analog analysis techniques have been applied to the long-period (peak response at 25 seconds period) strain and pendulum system at QCAZ (Queen Creek, Arizona). The purpose is to determine the effectiveness period P wave and Rayleigh wave signals from earthquakes. The long-period pendulum instruments at QCAZ are used as a standard for comparison. Outputs of the strain and pendulum seismographs are combined using an analog computer. The resultant output is then compared for a sample of forty-four...

Topics: DTIC Archive, Woolson, J R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The theory of generalized linear filtering (Oppenheim, 1966, 1969) is applied to the problem of averaging the transfer functions between a seismic source and seismic recording stations on a continental-sized array. To provide synthetic data for a test of the processor, a simple source signal is passed through nine different random perturbations of a velocity-depth structure yielding nine different synthetic seismograms. Two nuclear explosions (LONGSHOT and MILROW) and an Andreanoff Islands...

Topics: DTIC Archive, Lintz, P R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL STATIONS,...

The report summarizes the work done by the SDL during the period July through September 1972, and primarily concerns the seismic research activities related to the detection and identification of nuclear explosions and earthquakes. The report also contains brief discussions of the support tasks and data services which were performed for other government contractors and for participants in the VELA-UNIFORM and PRIME ARGUS projects.

Topics: DTIC Archive, Blandford, Robert R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

A study was made of a set of well-recorded Aleutian Islands earthquakes and the nuclear explosion LONG SHOT. Whereas past studies of travel- time anomalies and location errors have been based on seismic signals from explosions, the main object of the current study has been to extend our working principles to seismic data from earthquakes. Using a selected teleseismic station network, travel-time anomalies were computed and various techniques applied to achieve location consistency across the...

Topics: DTIC Archive, Chiburis, E F, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *UNDERGROUND...

The authors have tested several methods of analyzing short-period seismic records to detect multiple events. The data were from a pair of chemical explosions at a dam site near Alma Ata, recorded at the Mould Bay, Canada, seismic observatory. The methods evaluated included visual analysis of array beams, multichannel matched filtering, autocorrelation analysis, and cepstral analysis. For matched filtering the seismogram waveforms were used from a seismic event which occurred reasonably close to...

Topics: DTIC Archive, Flinn, E A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC WAVES,...

The report summarizes the work done by the SDL during the period January through March 1973, and primarily concerns the seismic research activities related to the detection and identification of nuclear explosions and earthquakes. The report also contains brief discussions of the support tasks and data services which were performed for other government contractors and for participants in the VELA-UNIFORM and PRIME ARGUS projects.

Topics: DTIC Archive, Blandford, Robert R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The model of Haskell for explosion source time functions and spectra fails to satisfy data in the short-period band recorded teleismically from the three Amchitka Island underground nuclear tests: LONG SHOT, MILROW and CANNIKAN. A more recent model due to Mueller and Murphy satisfies the data quite well. The difference in the two models is basically in the falloff at high frequencies. A simple revision of Haskell's model produces waveforms and spectra nearly identical to ones from Mueller and...

Topics: DTIC Archive, Von Seggern, D H, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *NUCLEAR...

Long period signals and noise recorded at the seismic arrays UBO, TFO and LASA were analyzed to provide information useful to signal detection efforts and to evaluate the performance of simple long-period beams formed with these arrays. The analysis included the computation of group velocity dispersion for fundamental mode Rayleigh waves generated by seismic events recorded at these arrays, and the calculation of noise reducing properties of beamforming each of the three arrays for a set of...

Topics: DTIC Archive, Masse, Robert P, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *NOISE,...

A location study is made of 28 large underground explosions detonated in the northern area of the Nevada Test Site (NTS). Recording networks were comprised of between 9 and 49 teleseismic stations having two- to three-quadrant distributions. Errors of locations obtained without applying travel-time anomalies (relative residuals), and with depths restrained to the known values, average about 7 km but are as large as 20 km. With anomalies, the errors are consistently 2.5-3.0 km. The size of the...

Topics: DTIC Archive, Chiburis, E F, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

The on-line operation of a Fisher detector has been evaluated at the Tonto Forest Observatory short-period seismic array. Using 31 seismometers and one fixed threshold, the 90 percent incremental detection threshold on the Kuril Islands beam, centered at delta = 70 degrees, is mb = 4.15 plus or minus .05; with an experimentally determined false alarm rate of 0.17 per day. This compares favorably with the capabilities of a human operator. Storms in the Kurils significantly affect the...

Topics: DTIC Archive, Blandford, R R, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMOLOGICAL...

Investigation of regional phase amplitudes at a large number of LRSM sites showed a pronounced increase of Pn, Pg, and Lg amplitudes at sedimentary structures relative to hard rock. In the early part of the coda and the main part of the wavetrain for Lg, lower order modes generated by mode conversion at local inhomogeneities must be present to explain the site variations and the coherence structure of Lg. A modification of Aki's scattering theory is presented to explain such observations....

Topics: DTIC Archive, Der,Zoltan A, TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA LAB, *SEISMIC DETECTION,...