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

The yield threshold at which a fully decoupled explosion can be identified has been a recurring issue in the debate on whether the Comprehensive Nucle ar Test Ban (CTB) can be adequately verified. Here, we assess this yield th reshold for the Novaya Zemlya (NZ) and Kola Peninsula regions by analysing seismograms from six small body wave magnitude (m(b) less than or equal to 3.5) seismic disturbances recorded at regional distances (1050 < <Delta> < 1300 km) by the seismometer array at Spitsbergen (SPITS). Multiple filter a nalysis of the seismograms shows clear high-frequency P-n (f <greater than or equal to> 14 Hz), except from a calibration explosion on the Kola Penins ula. From four of the disturbances studied we observe clear high-frequency S-n; the explosion showed no clear high-frequency S-n and the data from the remaining disturbance was potentially contaminated by a data glitch. Frequ ency-domain analysis indicates that the P-n and S-n attenuation across the Barents Sea is similar to that observed across stable tectonic regions (shi elds). We define a spectral magnitude for the 2.5-3.5 Hz passband that is t ied to teleseismic m(b) from NZ explosions; the six disturbances considered have 2.3 less than or equal to m(b) less than or equal to 3.5. Three-compo nent data are available from SPITS for four of the disturbances considered (including the explosion). From the explosion the S/P ratios on the vertica l (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 co mponent from the remaining three disturbances are less than unity, but the ratios on the R and T components are significantly greater than unity. We a rgue 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 i n the Kola Peninsula and NZ regions. The temporal variation of seismic nois e, 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 wit h m(b) greater than or equal to 2.8. We suggest that m(b) = 4.25 +/- b log( 10)W, where W is the explosive yield in kilotons (kt), with b = 0.75 for W greater than or equal to 1, and b = 1.0 for W < 1, is suitable for conserva tively estimating the yield threshold of a potential violation of the CTB i n the NZ region. From this we infer that a 35 ton fully coupled explosion i n the NZ region is likely to be identified as suspicious under the CTB usin g the three-component S/P criterion. Simulations show that the low-frequenc y decoupling factor (DF) for a fully decoupled nuclear explosion in hard ro ck 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 conser vatism likely to be employed by a potential violator and uncertainties in t he DFs for nuclear explosions in hard rock cavities, together with data fro m stations other than SPITS within 2000 km of the NZ region, suggest that t he yield at which a potential violator of the CTB could confidently escape detection (using decoupling) in the NZ region is in reality probably less t han 0.5 kt.