Registrations of seismic events by station VRAC in the period from 2011 to 2022 in comparison to global sesimicity
Vol.30,No.1-2(2023)
Broadband seismic station VRAC (Vranov u Brna), operated by IPE (Institute of physics of the Earth, Masaryk University) is one of certified stations of the IMS CTBTO (International Monitoring System of the Comprehensive Nuclear-Test_Ban Treaty Organization). That is why its capability to record the signal of distant seismic events is very important. This article try to show, for which seismically active regions in the world the usage of station VRAC for global seismic monitoring could be suitable. For this purpose the distribution of events registered by station VRAC in the period 2011 – 2022 was compared with global seismicity characteristics evaluated on the base of the REB bulletins (Reviewed Event Bulletin) of the CTBTO.
In the period 2011 – 2022, station VRAC registered 81110 seismic events, 60120 are events with known location (calculated in the IPE or adopted from another seismological institutes), and the epicentral distance from the station VRAC exceeds 3° for 24314 of them. During same period IMS located 440787 seismic events listed in the REB bulletins, data of station VRAC were used for evaluation of 21453 of these events.
The poor detection of seismic events by station VRAC was observed not only in the case of regions towards which the station VRAC is situated in the seismic shadow zone but also for regions in the distances from 90° to 103° from the station. It means less registrations of events from the seismically active regions of Sumatra, Philippines or Central America. The worse detectability of events in distances from 90° to 103° was expected, but not to that extent.
On the contrary, as a result of the caustic zone of PKP wave the number of registrations, including moderate or light seismic events, strongly increases, in the case of station VRAC. So the events from the southern part of New Hebrides Trench or from the Samoa region are well registered by station VRAC.
seismic monitoring; teleseismic events; station VRAC; detection capability; global seismicity
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