Towards a physical understanding of the m b :M s Event Screening Criterion Neil D. Selby UK NDC 01 British Crown Owned Copyright/MOD Page 1
Introduction Event Screening is the rejection of H0 at a given significance level, where the null hypothesis, H 0, is that seismic (hydroacoustic, infrasound) signals are from a single explosion source. mb :Ms is one of the four experimental provisional event screening criteria in use at the International Data Centre. mb :Ms is based on teleseismic body-wave magnitude m b and surface wave magnitude Ms. Improving our understanding of the physical basis of mb :Ms may enable us to enhance screening performance. 01 British Crown Owned Copyright/MOD Page
Introduction Body-waves travel through the interior of the Earth, while surface waves are guided by the surface of the Earth. The basis of the mb :Ms criterion is that, in general, explosions generate smaller surface waves than earthquakes with the same body-wave magnitude. 01 British Crown Owned Copyright/MOD Page
Body waves and surface waves 01 British Crown Owned Copyright/MOD Page
The m b :M s plot Earthquakes: from IDC REB for 00. surface wave magnitude, M s REB Events 00 China 9081 China 9008 Pakistan 9808 India: mb from Bowers et al. 00; Ms from Douglas et al 00. Pakistan: mb and Ms from Bowers et al. 00. China: mb from pidc REB; Ms from Bonner et al. 00. China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page
Original IDC Experimental Screening Line Screening line: Fisk et al 00. Earthquakes: from IDC REB for 00. surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line China 9081 China 9008 Pakistan 9808 India: mb from Bowers et al. 00; Ms from Douglas et al 00. Pakistan: mb and Ms from Bowers et al. 00. China: mb from pidc REB; Ms from Bonner et al. 00. China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page
DPRK 00 DPRK 00: UK NDC mb =.9, Ms =.8. (REB: m b =.1). surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line China 9081 China 9008 Pakistan 9808 Screening line: Fisk et al 00. Earthquakes: from IDC REB for 00. India: mb from Bowers et al. 00; Ms from Douglas et al 00. Pakistan: mb and Ms from Bowers et al. 00. China: mb from pidc REB; Ms from Bonner et al. 00. DPRK 01009 China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page
DPRK 009 DPRK 009: UK NDC mb =., Ms =.. (REB: m b =., Ms =.). surface wave magnitude, M s DPRK 090 REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line China 9081 China 9008 Pakistan 9808 DPRK 00: UK NDC mb =.9, Ms =.8. (REB: m b =.1). Screening line: Fisk et al 00. DPRK 01009 China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 8
01 Experimental Screening Line Screening line: Selby et al. 01. DPRK 009: UK NDC mb =., Ms =.. (REB: m b =., Ms =.). surface wave magnitude, M s DPRK 090 REB Events 00 M s = m b 0. IDC Experimental Screening Line China 9081 China 9008 Pakistan 9808 DPRK 00: UK NDC mb =.9, Ms =.8. (REB: m b =.1). DPRK 01009 China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 9
DPRK 01 DPRK 01: UK NDC mb =.0, Ms =.9. (REB: m b =.9, Ms =.9). Screening line: Selby et al. 01. surface wave magnitude, M s REB Events 00 DPRK 101 DPRK 090 M s = m b 0. IDC Experimental Screening Line China 9081 China 9008 Pakistan 9808 DPRK 009: UK NDC mb =., Ms =.. (REB: m b =., Ms =.). DPRK 00: UK NDC mb =.9, Ms =.8. (REB: m b =.1). DPRK 01009 China 909 India 98011 body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 10
NTS explosions Explosion magnitudes from Selby et al. (01). surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line NTS Explosions body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 11
East Kazakhstan explosions Explosion magnitudes from Selby et al. (01). surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line East Kazakh Explosions NTS Explosions body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 1
Novaya Zemlya explosions Explosion magnitudes from Selby et al. (01). surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line East Kazakh Novaya Zemlya NTS body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 1
Lop Nor explosions Explosion magnitudes from Selby et al. (01). surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line East Kazakh Novaya Zemlya Lop Nor NTS body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 1
FSU PNEs surface wave magnitude, M s REB Events 00 M s = 1.m b.0 Original IDC Experimental Screening Line East Kazakh PNEs Novaya Zemlya Lop Nor Peaceful Nuclear Explosions in the Former Soviet Union. Explosion magnitudes from Selby et al. (01). NTS body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 1
All Explosion magnitudes from Selby et al. (01). surface wave magnitude, M s REB Events 00 DPRK 101 DPRK 090 M s = m b 0. IDC Experimental Screening Line East Kazakh PNEs Novaya Zemlya Lop Nor DPRK 01009 NTS body wave magnitude, m b 01 British Crown Owned Copyright/MOD Page 1
Magnitude yield relationships m b m b = 0.log 10 Y + NTS FSU PNEs Kazakhstan Explosion magnitudes from Selby et al. (01). NTS yields from Springer et al. (00). Nominal magnitude yield relationships. 0 1 log 10 Y M s = log 10Y + M s 0 1 log 10 Y 01 British Crown Owned Copyright/MOD Page 1
Magnitude yield relationships m b m b = 0.log 10 Y + NTS FSU PNEs Kazakhstan Explosion magnitudes from Selby et al. (01). NTS yields from Springer et al. (00). PNE yields from Sultanov et al. (1999). Nominal magnitude yield relationships. 0 1 log 10 Y M s = log 10Y + M s Both mb and Ms higher for PNEs than NTS explosions of same yield. 0 1 log 10 Y 01 British Crown Owned Copyright/MOD Page 18
Magnitude yield relationships m b m b = 0.log 10 Y + 0 1 log 10 Y NTS FSU PNEs Kazakhstan Explosion magnitudes from Selby et al. (01). NTS yields from Springer et al. (00). PNE yields from Sultanov et al. (1999). Magnitude yield relationships: Mueller & Murphy (191) model suggests mb -yield and Ms-yield relationships should have the same slope. This does not seem to be the case for NTS. M s = log 10Y + M s 0 1 log 10 Y Both mb and Ms higher for PNEs than NTS explosions of same yield. For Kazakhstan, mb higher than NTS but Ms similar. Higher mb usually attributed to difference in t. 01 British Crown Owned Copyright/MOD Page 19
Yield and depth...0.0 log 10 h. log 10 h..0.0 1. 0 1 log 10 Y 1. 0 1 log 10 Y NTS explosions (blue) mostly at scaled depth, FSU PNEs (red) deeper, with no obvious relationship between depth and yield. If m b and Ms scale differently with depth, could this, together with differences in t, explain the difference in m b - and Ms-yield relationships between NTS and the PNEs? 01 British Crown Owned Copyright/MOD Page 0
Earthquake mb Ms regional variability. I I I I 0.0 0. 0. 0. 0.8 REB magnitudes 010 Nb 10, Ns 10. Depth, h = 0.0. mb Ms plotted at event epicentre. 1.0 mb Ms 01 British Crown Owned Copyright/MOD Page 1
M s path effects Selby et al. 00. -0. 0.0 0. δγ 01 British Crown Owned Copyright/MOD Page
Questions Is the variation in m b -yield between NTS, Kazakhstan and the PNEs due to t? If so, what is the correct value of t for DPRK? Are the differences in M s -yield between NTS/Kazakhstan and the FSU PNEs due to the depth of burial? Is the difference in the m b -yield and M s -yield relationships for NTS due to the scaled depth of burial? What is the appropriate depth / depth-scaling for DPRK? Can the variability of earthquake m b :M s values be reduced by cleverer measurements of m b and M s? 01 British Crown Owned Copyright/MOD Page
References Bonner J.L., Russell D.R., Harkrider D.G., Reiter D.T., and Herrmann R.B., 00. Development of a time-domain, variable-period surface-wave magnitude measurement procedure for application at regional and teleseismic distances, part II: application and Ms-m b performance. Bull. seism. Soc. Am. 9, 8 9. Bowers, D., Douglas, A., Selby, N.D., Marshall, P.D., Porter, D., and Wallis, N. J., 00. Seismological identification of the 1998 May 8 Pakistan nuclear test. Geophys. J. Int., 10, 1-11. Douglas A., Selby N.D., and Bowers D., 00. Seismic magnitude and yield for the Indian nuclear test of 11 May 1998. Current Science 8, 989-9. Fisk, M., D. Jepsen and J.R. Murphy, 00. Experimental seismic event-screening criteria at the Prototype International Data Centre, Pure Appl. Geophys., 19, 8-888. Selby, N.D., D. Bowers, P.D. Marshall and N.D. Selby, 00. Empirical path and station corrections for surface-wave magnitude, Ms, using a global network. Geophys. J. Int., 1, 9-90. Selby, N.D., P.D. Marshall, and D. Bowers, 01. mb :Ms event screening revisited. Bull. seism. Soc. Am., 10, 88-9. Springer, D.L., G.A. Pawloski, J.L. Ricca, R.F. Rohrer, and D.K. Smith, 00. Seismic source summary for all U.S. below-surface nuclear explosions. Bull. seism. Soc. Am., 9, 180-180. Sultanov, D. D., J.R. Murphy, and Kh. D. Rubinstein, 1999. A seismic source summary for Soviet peaceful nuclear explosions. Bull. seism. Soc. Amer., 89, 0-. 01 British Crown Owned Copyright/MOD Page