Field exercise to test aftershock
equipment deployment is hosted
by the Government of Slovakia
A Directed Exercise is currently taking place in Slovakia. The exercise, which began on 4 October and will conclude on 8 October 2004, is designed to study how a seismic network can best be deployed to detect seismic aftershocks in the event of a suspected nuclear test explosion. Taking advantage of this activity, communication equipment and a geographical information system are also being tested in field conditions. The exercise is hosted by the Government of Slovakia, which has also hosted an earlier on-site inspection field experiment in 2001.
The current field exercise in Slovakia builds on the lessons of the 2001 experiment, and aims to accumulate measurements on the detection capability of passive seismic stations under field conditions. The findings will be incorporated into final recommendations on the deployment of seismic networks over an inspection area in the case of an on-site inspection. Aftershocks will be simulated by exploding small quantities of explosive (from 100 to 600 grammes) at a depth of approximately ten metres.
Seismic aftershocks occur following a larger event such as an earthquake or a nuclear explosion, and can be described as weak intensity replicas of the original shock. In the case of a nuclear explosion, aftershocks can be caused by the stress relaxation of the ground below the blast site, which will have been subjected to very high temperature and pressure. They may also be generated by the collapse of the roof of the cavity caused by an underground explosion. The frequency and magnitude of such aftershocks decreases very quickly with time, so that just a few weeks after a nuclear explosion has occurred only 'micro' or 'nanoaftershocks' may still be produced and recorded. It is therefore essential that aftershock detection equipment is deployed at the site as soon as possible after the initial explosion, and that the location and density of the deployment maximizes the potential of the equipment and the site.
The Government of Slovakia is providing a convenient location for the field exercise, and is also supporting the generation of the explosions for aftershocks simulation purposes. In addition equipment has been made available by two other Member States. Experts from a number of Member States are also participating in the experiment.