Over the next four years, in cooperation with Center GEON (Moscow, Russia) the University of Wyoming will obtain, preprocess, and transfer to IRIS a series of unique long-range Deep Seismic Sounding (DSS) profiles. These datasets will include nine major DSS projects using 22 Peaceful Nuclear Explosions (PNEs), several hundred of chemical explosions, and recordings of natural seismicity in Northern Eurasia (see map). This project is jointly supported by the Defense Threat Reduction Agency (DTRA01-01-C-0081; 75% of funding) and NSF (EAR-0092744; 25%). The data from project QUARTZ have already been transferred to IRIS.
The profiles were recorded between the early 1970’s and late 80’s using ~400 three-component analogue instruments, with recordings of 2-4 PNEs and several dozens of chemical explosions (per profile) at the same locations. Long listening times (up to ~600 sec after the first arrivals) allowed recording of the secondary phases (S, Lg). The energies of the PNE sources (magnitudes >5) were sufficient for reliable recordings beyond 3000 km; including several reflections from the core-mantle boundary.
DSS PNE data have been widely recognized as an unparalleled source of seismic information about the detailed structure of the upper mantle down to 400-800 km depth and even to the Earth’s core. DSS data present an unparalleled source of such information that is practically impossible to obtain by other means. The core PNE data sets of the DSS program cover an intermediate distance range between 0 – 3200 km, bridging the gap between the conventional controlled-source and earthquake seismology. The dense, linear systems of PNEs and chemical explosions allow obtaining unusually detailed models of the crust and uppermost mantle along over 4000-km long geotraverses. Numerous publications (principally by the Russians, the University of Wyoming, Potsdam/Karlsruhe, and Copenhagen groups) have presented velocity, reflectivity, attenuation, scattering, and receiver function models inspired by these profiles. The digitized DSS recordings and models of the upper mantle could provide ideal reference and calibration data sets for the detailed structure of the upper mantle targeted by the initiative of USArray.
by Igor Morozov (University of Wyoming)