Teleseismic Signals Calculated for Underground, Underwater, and Atmospheric Explosions

Carpenter, E. W.

doi:10.1190/1.1439854

Cited by 69 publications

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“…The synthetics were computed using generalized ray theory and the Cagniard-de Hoop method [Heimberger, 1983]. To account for extra attenuation in the inner core, a t• operator [Futterman, 1962;Carpenter, 1967] (t* = J q-1 dt along the ray) is applied to the DF branch. Table 1 summarizes some useful parameters of DF ray paths in the inner core.…”

Section: Introductionmentioning

confidence: 99%

Depth dependence of anisotropy of Earth's inner core

Song¹,

Helmberger²

1995

J. Geophys. Res.

135

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Abstract.Both body wave (PKP) travel times (Creager, 1992;Song and Heimberger, 1993a; McSweeney and Creager, 1993;Shearer, 1994) and fits to the splitting of core modes (Tromp, 1993) show general agreement that the top 300 km of inner core is very anisotropic. The anisotropy displays axial symmetry around the Earth's spin axis, with the polar direction 3% faster than the equatorial direction. One key problem now is the depth dependence of the inner core anisotropy. Here we extend our polar path studies to include both long-period and short-period modeling for the PKP phases at ranges 120° to 173°. Arrivals from the top of the inner core (PKIKP) and reflections from the inner core boundary (PKiKP) can be observed distinctly in short-period records at ranges 130° to 140° and as waveform distortions in the long-period records at ranges 130° to 146°. These waveforms provide a new set of data for examining the topmost 150 km of the inner core, which is not well sampled by the previous body wave travel times. Record sections of waves traversing the inner core nearly parallel to the Earth's spin axis (polar paths) from three events, two beneath the South Sandwich Islands and one along the Macquarie Ridge, recorded at World Wide Standardized Seismograph Network, Canadian Network, and Long Range Seismic Measurements stations are analyzed. Our results suggest that the top 150 km of the inner core is only weakly anisotropic (less than 1% ), with strong evidence indicating that the top 60 km is not anisotropic at all.

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Section: Introductionmentioning

confidence: 99%

Depth dependence of anisotropy of Earth's inner core

Song¹,

Helmberger²

1995

J. Geophys. Res.

135

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“…However, there also seems to be an affect of source layering which results in explosions in alluvium generating very low surface wave amplitudes. A check with point sources which removes any effects of differences in source spectra suggests that Comparison of the absolute amplitudes of the body waves given in Table 2 and body wave magnitudes given in Table 4 with the amplitude-yield predictions (for the direct P ) of Carpenter (1967) shows that there is good agreement for all media except granite. Nevertheless the amplitudes predicted in this paper should be greater than those of Carpenter (1967) because we have included the effects on the direct P of the reflection from the free surface (which interferes constructively for the models described here).…”

Section: R D T S and Discussion (A) The Earth Modelsmentioning

confidence: 86%

“…A check with point sources which removes any effects of differences in source spectra suggests that Comparison of the absolute amplitudes of the body waves given in Table 2 and body wave magnitudes given in Table 4 with the amplitude-yield predictions (for the direct P ) of Carpenter (1967) shows that there is good agreement for all media except granite. Nevertheless the amplitudes predicted in this paper should be greater than those of Carpenter (1967) because we have included the effects on the direct P of the reflection from the free surface (which interferes constructively for the models described here). Carpenter (1966a) does predict a P amplitude for one model that includes the effects of the surface reflection: this is for a 40 kt explosion in granite and the model is almost identical to that used for Fig.…”

Section: R D T S and Discussion (A) The Earth Modelsmentioning

confidence: 86%

A Quantitative Evaluation of Seismic Signals at Teleseismic Distances--III Computed P and Rayleigh Wave Seismograms

Douglas¹,

Hudson²,

Blamey³

1972

Geophysical Journal International

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Body (P) and Rayleigh wave seismograms are computed for explosions and earthquakes using the expressions developed by Hudson; many of the features of observed seismograms are noted. For the earthquake source models used average Rayleigh wave magnitudes relative to P wave magnitudes are larger than for the explosion source models. This is true even for point sources; increasing the dimensions of the earthquake source only accentuates this difference in the relative excitation of Rayleigh waves. However the relative amplitudes are strongly dependent on the orientation of the observer relative to the fault plane of the earthquake owing to the radiation pattern of the P and Rayleigh waves. Where the observer is at an anti-node of the P radiation the relative amplitudes of the Rayleigh waves are not significantly greater than for explosions. A detailed study of observed P and Rayleigh amplitudes is now needed to see if the same effects of the P radiation pattern can also explain the observed differences in the relative excitation of P and Rayleigh waves by earthquakes and explosions.

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“…The first attempts at modelling explosion seismograms were to predict the amplitude of P (and hence m b ) and thus the m b /yield relationship (Carpenter and Thirlaway 1966;Carpenter 1966aCarpenter , 1967. To predict m b /yield at teleseismic distances it was assumed that t*&1 s. As Fig.…”

Section: Using Seismogram Modelling To Understand Discriminationmentioning

confidence: 99%

Forensic seismology revisited

Douglas

2007

Surv Geophys

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The first technical discussions, held in 1958, on methods of verifying compliance with a treaty banning nuclear explosions, concluded that a monitoring system could be set up to detect and identify such explosions anywhere except underground: the difficulty with underground explosions was that there would be some earthquakes that could not be distinguished from an explosion. The development of adequate ways of discriminating between earthquakes and underground explosions proved to be difficult so that only in 1996 was a Comprehensive Nuclear Test Ban Treaty (CTBT) finally negotiated. Some of the important improvements in the detection and identification of underground teststhat is in forensic seismology-have been made by the UK through a research group at the Atomic Weapons Establishment (AWE). The paper describes some of the advances made in identification since 1958, particularly by the AWE Group, and the main features of the International Monitoring System (IMS), being set up to verify the Test Ban.Once the Treaty enters into force, then should a suspicious disturbance be detected the State under suspicion of testing will have to demonstrate that the disturbance was not a test. If this cannot be done satisfactorily the Treaty has provisions for on-site inspections (OSIs): for a suspicious seismic disturbance for example, an international team of inspectors will search the area around the estimated epicentre of the disturbance for evidence that a nuclear test really took place.Early observations made at epicentral distances out to 2,000 km from the Nevada Test Site showed that there is little to distinguish explosion seismograms from those of nearby earthquakes: for both source types the short-period (SP: *1 Hz) seismograms are complex showing multiple arrivals. At long range, say 3,000-10,000 km, loosely called teleseismic distances, the AWE Group noted that SP P waves-the most widely and well-recorded waves from underground explosions-were in contrast simple, comprising one or two cycles of large amplitude followed by a low-amplitude coda. Earthquake signals on the other hand were often complex with numerous arrivals of similar amplitude spread over 35 s or more. It therefore appeared that earthquakes could be recognised on complexity.Later however, complex explosion signals were observed which reduced the apparent effectiveness of complexity as a criterion for identifying earthquakes. Nevertheless, the AWE Group concluded that for many paths to teleseismic distances, Earth is transparent for P signals and this provides a window through which source differences will be most clearly seen. Much of the research by the Group has focused on understanding the influence of source type on P seismograms recorded at teleseismic distances. Consequently the paper concentrates on teleseismic methods of distinguishing between explosions and earthquakes.One of the most robust criteria for discriminating between earthquakes and explosions is the m b : M s criterion which compares the amplitudes of the SP P waves as measured ...

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Teleseismic Signals Calculated for Underground, Underwater, and Atmospheric Explosions

Cited by 69 publications

References 0 publications

Depth dependence of anisotropy of Earth's inner core

Depth dependence of anisotropy of Earth's inner core

A Quantitative Evaluation of Seismic Signals at Teleseismic Distances--III Computed P and Rayleigh Wave Seismograms

Forensic seismology revisited

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