Low frequency electromagnetic signals from underground explosions: On-site inspections research progress report

Abstract

We are investigating the characteristics of extremely low frequency (ELF) electromagnetic pulse (EMW) phenomena from underground nuclear and chemical explosions and from surface chemical explosions as they may be applied in an On-Site Inspection (OSI) context under a Comprehensive Test-Ban Treaty (CTBT). The principal application of these phenomena is for discrimination among underground chemical explosions, underground nuclear explosions, and earthquakes. Underground chemical and nuclear explosions both generate low-frequency EMP signals (about 1 Hz) that are observable within several kilometers of ground zero. During this fiscal year we have been gathering data from explosions of opportunity to see if ELF EMP signals are observable from large ripple-fired blasts and from smaller dedicated explosions such as those occurring at the NTS. In addition, we are continuing to review data from the Henderson Mine deployment that took place during FY94 and data from previous underground nuclear tests including Hunter`s Trophy and past underground nuclear tests have been analyzed and we here make estimates of the properties of the EMP ftom underground nuclear ard chemical explosions, including detectability, dependence on yield, and dependence on distance from the source. Data from the Henderson Mine provide information about detection of EMP from typical moderate size underground chemical explosions in hard rock and problems related to detection of EMP in a mine environment located at high elevations. Data from the Carlin Mine site provide information about EMP from surface ripple-fired chemical explosions and detection in an open-pit mine environment. Data from the Kuchen experiment at NTS provide additional data about small underground chemical explosions in a setting similar to that for underground nuclear tests at the NTS.