A technique to determine systematic shifts in microseismic databases

Due to the complex nature of the seismic response to mining, geotechnical engineers often require back analysis to provide a base line against which to interpret future behaviour. This practice assumes, and is reliant on, the database being consistent in space and time. Few tools are available for geotechnical engineers dedicated to the task of quantifying the consistency of the seismic database, and to aid in identifying systematic inconsistencies in their databases. A methodical approach is also required to warn geotechnical engineers of unexpected systematic shifts in their database as soon as they arise so that timeous and appropriate action can be taken. The industry collectively also requires a systematic approach to quantify the consistency of seismic databases. A technique is proposed to adequately address these aims. The technique is fast and efficient and can be easily employed on any database. By continuously updating results, users would know within a few tens to hundreds of events when data shifts have occurred. This would allow for the effective management of these errors in the database. Application of the method on some current industry databases showed that the shifts are sufficiently significant to render the use of some widely used analysis techniques unreliable. It is shown that shifts in the data have a significant influence on the interpretation of the source parameters. Systematic errors are causing significant artefacts in seismic databases. Of the 20 databases investigated, 70% had one or more systematic shifts a year, and only one database showed no shifts at all. There is justified concern with respect to systematic inconsistencies in seismic databases in the industry. Such inconsistencies could lead to misinterpretation of seismic analysis results, which will have a carry-on effect on other parts of the operations.