Regional monitoring of explosions: Single-array case study of the Kovdor mine, NW Russia

Introduction

In many regions, the majority of observed seismic signals are the result of mining activity. One such region is the Kola Peninsula in north-western Russia where explosions are routinely carried out at many mines located within several clusters. In the context of monitoring nuclear explosions, it is important to be able to identify such events and associate them with a specific source. An automated monitoring system which can attribute events to activities at a given mine with a high level of confidence can free analyst resources to examine events which cannot, with confidence, be ascribed to a known source.

In the monitoring context, situations will arise where a suspicious event is only detected by a single seismic array. It is therefore essential to quantify the accuracy with which such events can be located.

The ARCES regional array in northern Norway is approximately 300 km from the Kovdor open cast mine in Russia, for which origin times of explosions have been obtained. Using this Ground Truth information, we have analysed signals recorded at ARCES which are known to result from Kovdor events. For each of the phases Pn, Sn, and Lg resulting from such an event, arrival times are determined by autoregressive methods and, using fk-analysis in fixed frequency bands, apparent velocity and backazimuth are determined within appropriate time windows relative to the first P-arrival.

These results from confirmed events have been applied to a new automatic monitoring process which scans ARCES detections for potential Kovdor events. Detections are sought which correspond to P-arrivals from Kovdor events; if newly determined velocity and azimuth values fall within ranges consistent with the set of known events, the detection is considered to be a likely candidate. Secondary phases are sought for all such P-detections and the determined velocity, azimuth and onset times are compared with those from the confirmed events.

By clicking on the year in the menu, you may can choose any day and view all of the ARCES detections which were considered possible P-arrivals. This displays all of the calculated arrival times and fk-analysis results. Values in white on a red background are those which were not consistent with Kovdor events. For events where the redetermination of the Pn phase was consistent with a Kovdor event, a summary sheet can be obtained by clicking on the P-arrival time.