The figure below shows monitoring results for the day of the nuclear test (9 October 2006). In this figure we have used only those of our selected stations that were operational at the IDC during that day (i.e. without KSRS). The continuous detection threshold traces for three-station P wave detection (red) are close to magnitude 4.0 or slightly below, except for occasional increases during the nuclear test (at 01.35) and during some interfering events later in the day. The monitoring thresholds (blue) average about magnitude 3.0. The individual station P-thresholds (black) are also shown.
Operational IMS network, North Korean test site.
Monitoring results for 9 Oct 2006 (day 282).
The next figure shows a one-day plot of detection traces (red) and monitoring traces (blue) for 15 November 2006, when a large earthquake occurred in the Kurile Islands. The top panel uses the IMS network (including KSRS) and the middle panel shows the effect of adding the MDJ station. We find that the current IMS primary network, supplemented with MDJ, has a typical “threshold monitoring capability” of between mb 2.1 and 2.3 for the North Korean test site. For comparison, the three-station network detection threshold is found to be typically one magnitude higher than these numbers. Note that the bottom right panel shows that using only the three “best” stations KSRS, MDJ and MJAR provides a capability which approaches that of the full network.
Monitoring results for 15 Nov 2006 (day 319).
It is important to be aware that the main purpose of the threshold monitoring method is to draw attention to any time instance when a given threshold is exceeded. This will enable the analyst to focus efforts on those events that are truly of interest in a monitoring situation. The analyst will then apply other, traditional analysis tools in detecting, locating and characterizing the source of the disturbance. Thus, the threshold monitoring method is a supplement to, and not a replacement of, traditional methods.
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