Discrimination of Earthquakes and Explosions at Regional Distances Using Complexity

Blanford, Robert R.

doi:10.21236/ada267638

Cited by 9 publications

(7 citation statements)

References 20 publications

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“…8) appears to be negative (dilatational), which is inconsistent with an explosive source. Further, the impulsive nature of S n at SPITS and AMD is similar to that on synthetic seismograms generated for earthquake sources (Blandford, 1993). Thus, we conclude that the 16 August 1997 disturbance was neither an underwater nor a wellcontained underground explosion.…”

Section: Three-component Seismograms At Spits and Kevsupporting

confidence: 55%

“…Baumgardt and Der (1998) further argued that the high-frequency L g observed from underwater explosions in the Baltic Sea can be explained by low attenuation due to thin sediment and granitic basement in this region. Blandford (1993) generated synthetic seismograms for earthquakes and underground explosions for the Fennoscandian region and showed that, whereas S n and L g from wellcontained explosions tend to be emergent in nature, S n from earthquakes tends to be impulsive. Blandford (1993) demonstrated that although some earthquake mechanisms produce vertical-component S/P ratios that are explosion-like, the S/P ratio on the tangential component from such mechanisms is usually earthquakelike.…”

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

“…Blandford (1993) generated synthetic seismograms for earthquakes and underground explosions for the Fennoscandian region and showed that, whereas S n and L g from wellcontained explosions tend to be emergent in nature, S n from earthquakes tends to be impulsive. Blandford (1993) demonstrated that although some earthquake mechanisms produce vertical-component S/P ratios that are explosion-like, the S/P ratio on the tangential component from such mechanisms is usually earthquakelike. The study of Blandford (1993) emphasized the potential of three-component observations for effective regional discrimination.…”

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

“…Blandford (1993) demonstrated that although some earthquake mechanisms produce vertical-component S/P ratios that are explosion-like, the S/P ratio on the tangential component from such mechanisms is usually earthquakelike. The study of Blandford (1993) emphasized the potential of three-component observations for effective regional discrimination.…”

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

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Was the 16 August 1997 Seismic Disturbance near Novaya Zemlya an Earthquake?

Bowers¹

2002

Bulletin of the Seismological Society of America

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The Reviewed Event Bulletin for 16 August 1997, produced by the prototype International Data Center (pIDC), reported a small seismic disturbance in the vicinity of the northern Russian test site at Novaya Zemlya (at about 02:11 UTC). Initial reports suggested that this disturbance was caused by a small nuclear explosion, whereas others identify the source as an earthquake using vertical-component S/P ratios. However, other authors show evidence that questions the validity of the S/P method for this region and conclude that the disturbance cannot be positively identified as an earthquake using seismological evidence. The apparent attenuation from the 16 August 1997 disturbance to SPITS (Spitsbergen, distance D ‫ס‬ 1280 km, azimuth ‫ס‬ 317Њ) is reported to be weak. Similar low attenuation is suggested from high-frequency observations at KEV (Kevo, Finland, D ‫ס‬ 1130 km, azimuth ‫ס‬ 268Њ). Thus, high-frequency P and S waves propagate efficiently across the Barents Sea, leading to the possibility that the radiation pattern of the source may be inferred. We show, using a grid-search method, that the high-frequency SV/SH amplitude ratios observed at SPITS and KEV (measured from the complex envelopes of the freesurface corrected three-component seismograms), combined with simple P n signals (with positive first motion) at HFS (Hagfors, Sweden) and NORES (Norway), are consistent with a double-couple source, with a range of orientations. We compute synthetic seismograms for one such double-couple source oriented at r ‫ס‬ 255Њ, d ‫ס‬ 115Њ, w ‫ס‬ 120Њ (similar to that reported for the 1 August 1986 Kara Sea earthquake). The synthetic P n seismograms at HFS and NORES and the relative SV/SH amplitudes of the synthetic S n seismograms at KEV and SPITS match those observed reasonably well. Our model also predicts (1) weak P n at NRI (Norilsk, Russia), suggesting that the emergent P n onset and low signal-to-noise ratio observed is related to the focal mechanism, and (2) the negative P first motion and large SH/SV ratio observed at AMD (Amderma, D ‫ס‬ 360 km, azimuth ‫ס‬ 152Њ). Thus, we conclude that the 16 August 1997 seismic disturbance was an earthquake beneath the Kara Sea and that identification is possible using only data that would normally be available to the pIDC (assuming KEV can be used as an alternative for the nearby station ARCES, which was not working at the time of the disturbance).

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Section: Three-component Seismograms At Spits and Kevsupporting

confidence: 55%

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

Section: Three-component Seismograms At Spits and Kevmentioning

confidence: 99%

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Was the 16 August 1997 Seismic Disturbance near Novaya Zemlya an Earthquake?

Bowers¹

2002

Bulletin of the Seismological Society of America

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“…Such discrimination studies using S/P from SPITS would require at least one calibration explosion in the NZ region. However, an analysis of synthetic seismograms by Blandford (1993), generated for the Fennoscandian region, shows large S/P ratios on the R and T components from earthquake sources when S/P on the Z ‐component is small (explosion‐like).…”

Section: Three‐component Spits Seismogramsmentioning

confidence: 99%

The level of deterrence provided by data from the SPITS seismometer array to possible violations of the Comprehensive Test Ban in the Novaya Zemlya region

Bowers¹,

Marshall²,

Douglas³

2001

Geophysical Journal International

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SUMMARY The yield threshold at which a fully decoupled explosion can be identified has been a recurring issue in the debate on whether the Comprehensive Nuclear Test Ban (CTB) can be adequately verified. Here, we assess this yield threshold for the Novaya Zemlya (NZ) and Kola Peninsula regions by analysing seismograms from six small body wave magnitude (mb≤3.5) seismic disturbances recorded at regional distances (1050<Δ<1300 km) by the seismometer array at Spitsbergen (SPITS). Multiple filter analysis of the seismograms shows clear high‐frequency Pn (f≥14 Hz), except from a calibration explosion on the Kola Peninsula. From four of the disturbances studied we observe clear high‐frequency Sn; the explosion showed no clear high‐frequency Sn and the data from the remaining disturbance was potentially contaminated by a data glitch. Frequency‐domain analysis indicates that the Pn and Sn attenuation across the Barents Sea is similar to that observed across stable tectonic regions (shields). We define a spectral magnitude for the 2.5–3.5 Hz passband that is tied to teleseismic mb from NZ explosions; the six disturbances considered have 2.3≤mb≤3.5. Three‐component data are available from SPITS for four of the disturbances considered (including the explosion). From the explosion the S/P ratios on the vertical (Z), radial (R) and tangential (T) components (in the 3.0–6.0 Hz passband) are all less than unity. The S/P ratios for the same passband on the Z component from the remaining three disturbances are less than unity, but the ratios on the R and T components are significantly greater than unity. We argue that S/P ratios (3.0–6.0 Hz passband) of less than unity on all of the Z, R and T components at SPITS may indicate a potential treaty violation in the Kola Peninsula and NZ regions. The temporal variation of seismic noise, in the 3.0–6.0 Hz passband, at SPITS suggests that our three‐component S/P criterion will be effective 95 per cent of the time for disturbances with mb≥2.8. We suggest that mb=4.25+b log10W, where W is the explosive yield in kilotons (kt), with b=0.75 for W≥1, and b=1.0 for W<1, is suitable for conservatively estimating the yield threshold of a potential violation of the CTB in the NZ region. From this we infer that a 35 ton fully coupled explosion in the NZ region is likely to be identified as suspicious under the CTB using the three‐component S/P criterion. Simulations show that the low‐frequency decoupling factor (DF) for a fully decoupled nuclear explosion in hard rock is about 40, suggesting that such an explosion with a yield of 1.6 kt in the NZ region is likely to be identified using data from SPITS. The conservatism likely to be employed by a potential violator and uncertainties in the DFs for nuclear explosions in hard rock cavities, together with data from stations other than SPITS within 2000 km of the NZ region, suggest that the yield at which a potential violator of the CTB could confidently escape detection (using decoupling) in the NZ region is in reality probably less than 0.5 kt.

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Regional Seismic Event Discrimination

Blandford¹

1996

Monitoring a Comprehensive Test Ban Treaty

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Discrimination of Earthquakes and Explosions at Regional Distances Using Complexity

Cited by 9 publications

References 20 publications

Was the 16 August 1997 Seismic Disturbance near Novaya Zemlya an Earthquake?

Was the 16 August 1997 Seismic Disturbance near Novaya Zemlya an Earthquake?

The level of deterrence provided by data from the SPITS seismometer array to possible violations of the Comprehensive Test Ban in the Novaya Zemlya region

Regional Seismic Event Discrimination

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