Improvements in Monitoring the CTBT in the Middle East by the Israel Seismic Network

Abstract : The Israel Seismic Network (ISN), operated by the Geophysical Institute of Israel, is continuously monitoring the seismicity of the Middle East, and in that capacity provides crucial information to the International Monitoring System (IMS) for monitoring the Comprehensive Nuclear Test Ban Treaty (CTBT). This report presents reliable seismic information, primarily obtained by the ISN, that improves event detection, location, and discrimination in the Middle East. For the sake of IMS calibrations, more accurate information is now available for 61 earthquakes (GT2-GT5) and 26 explosions (GT0), including five controlled quarry blasts, three large-scale Dead Sea underwater calibration tests, and three India and Pakistan nuclear tests recorded by Israeli IMS stations. Several M(sub L)>4 earthquakes from Lebanon and Cyprus were used to characterize different propagation paths. The highlight of this project was the detonation of a 5-ton explosion in the Dead Sea that was used in the process of travel time calibration of IMS stations in the Middle East and farther. The experiment provided important information that characterizes the phenomenology of underwater explosions. The authors estimated the threshold magnitudes of detection by the ISN system for different seismic zones in the Middle East and evaluated the efficiency of the detection methods: Johnson STA/LTA, Murdock & Hutt, and the Statistically Optimal Detector. Improvements in location were provided by the development of a new automatic location method (Pinsky 2000), which is based on a combination of the optimal statistical time series analysis and robust statistical phase identification. Spectral semblance and ratio discriminants applied to the India and Pakistan nuclear test recordings showed good performance. The same methods proved reliable for identifying the Dead Sea calibration explosions and the controlled industrial blasts at the Arad phosphate quarry in the Negev desert. (44 tables, 111 figures, 76 re7