PARAMETERIZED SEISMIC SOURCE DISCRIMINATION IN ASEISMIC REGIONS

Abstract

In the monitoring of local seismicity the occurrence of many explosions poses two types of severe practical problems: (1) Such recordings add significantly to the analyst's workload, and (2) in extreme cases they pollute the seismicity database to the extent of rendering it useless for scientific studies. In some countries only felt earthquakes are included in the seismicity listings, but the problem remains, since both earthquakes and explosions are and will be recorded by local stations. These events will therefore enter the network data center processing system and thus be subject to further analysis. Most of the events detected by seismological observatories in Scandinavia are man-made seismic events such as quarry blasts, mining explosions, and other types of chemical explosions. Hence the distinction between earthquakes and explosions is an important part of the daily work in seismological observatories in many regions like Fennoscandia. The seismological discrimination problem stems from nuclear disarmament negotiations made under UN auspices in Geneva, which commenced in 1958. In September 1995 the UN General Assembly signed the CTBT treaty, and the corresponding global monitoring system became operational in 2001 with an International Data Centre (IDC; UN/CTBTO) located in Vienna, Austria (Husebye and Dainty, 1995; http://www.ctbto.org). In Fennoscandia CTBT-discrimination research approaches have not been very successful in solving local seismicity problems of the type mentioned above partly due to a general lack of reliable ground-truth (GT) events. For example, earthquake occurrence is relatively frequent in southern and western Norway, with two to five earthquakes typically felt annually, while only two mines are in operation in this region (Titania and Olivin). On the other hand, irregular explosion activities are occasionally high, stemming from quarries, major construction work, and underwater harbor operations. In northern Fennoscandia, including Kola, there are many mines (Tarvainen and Husebye, 1993) and the …