The newly formed Republic of Kazakhstan has declared itself to be a non-nuclear state and the US is providing technical and financial support to aid in the decommissioning of the test facilities (tunnels and boreholes) through the Defense Special Weapons Agency (DSWA). The decommissioning of a series of Balapan boreholes in the summer of 1997 provided the opportunity to perform the Source Depth of Burial Experiment. A map showing the location of the Balapan test site is shown in Figure 1.
The properties of geological materials change quickly near the earths surface and if effects of these materials allow us to discriminate between shallow (near-surface) and deep (1-km) explosions we may be able to develop techniques to discriminate between large industrial blasts and an underground nuclear test. We rarely observe large mine blasts deep in the earth because of the potential of irreversible damage to the mine infrastructure.
We are also interested in calibrating regional seismic stations. These stations include the Kazakhstan seismic network stations at Makanchi (MAK), Kurchatov (KUR) and Aktyubinsk (AKT). MAK has been designated a primary station of the International Monitoring System (IMS), while KUR and AKT have been designated auxiliary stations.
A final objective is to provide a model for cooperation amongst nations that can lead to calibration experiments for the benefit of all. Such work is formally encouraged as part of ground-based nuclear explosion monitoring (GNEM) under the heading of confidence building measures. Extensive world-wide calibration will be critical for monitoring small seismic events using regionally recorded data.
Recording seismic data close to the explosions is an important part of regional calibration. Although close-in data will not be available on a routine basis, what we learn about source details may be important to later studies based on regional data alone. Because the effects of attenuation or scattering (the path effect) will not be as apparent in the close-in records, they will help to separate out the effects of source and path in the regional data. For example, Xang et al. (1998) develop models of an induced mine collapse that are very different from accepted models using close-in data recorded at White Pine, Michigan. A second, and very important objective is to confirm the initiation time of the source in an independent manner. This will be critical to calibrating travel times to IMS stations for purposes of accurately locating events in this region. Thirdly, close-in stations may also record aftershocks which might be important indicators of source location and type in an On Site Inspection (OSI) situation (Phillips et al., 1997).
In the following, we will describe data collection procedures and present preliminary results from the near-source field deployment at Balapan. The explosions included a 5 ton proof of concept shot, a number of 50 to 100 kg Green's function shots and three, 25 ton, depth of burial shots, set at 50 m, 300 m and 550 m.