We have added some new event filter options to General Analysis related to ‘background’ activity. ‘Background’ events are generally defined as having low variability in space and time. The new background filters aim to identify events that are clustered in space and time and the user can either display the ‘clustered’ or the ‘background’ component of seismicity.
There are three ways of classifying clustered events; by time-of-day, by proximity to blasts and significant events, and by a stochastic declustering procedure. Stochastic declustering will be explained in a separate blog post.
With the time-of-day filter, you can specify up to five periods of the day, to define increased activity around shift change/blasting times. Times are entered in hours, e.g. 5:30pm = 17.5. Events within these periods will not be shown by default but you can toggle/invert the time-of-day filter to only show events inside the time-of-day periods (and hide events outside).
With the short-term responses filter, you can define a time period and spherical radius around blasts and significant events to filter out events. Use the normal blast filter to control which blasts are considered. Significant events are considered if they are within the current base filter, and above the specified magnitude. Note that the significant event itself is not filtered out (it is treated as a background event, not a clustered event). Just like the time-of-day filter, you can toggle/invert the filter to only show the responses, and hide events outside the response windows.
The last filter option is an automatic classification system for separating background and clustered events. You can toggle between each component of seismicity defined from stochastic declustering. Watch out for the next blog post if you are interested in the details of how this method works.
This is a new addition to the General Analysis application. Find the panel under ‘Event Filters / Background Activity’. If you don’t see this option, you need a root upgrade. Get in touch with support to arrange an upgrade by emailing email@example.com.