Earthquakes in Switzerland and surrounding regions during 1998

This report of the Swiss Seismological Service summarizes the seismic activ ity in Switzerland and surrounding regions during 1998. During this period, 226 earthquakes were detected and located in the region under consideratio n. In addition, 54 quarry blasts and 3 rock avalanches were identified. Wit h only 18 events with M-L greater than or equal to 2.5 and with only a sing le event reaching M-L = 3.6, the seismic activity in 1998 was below the ave rage over the last 24 years. As in the past, most of the earthquakes occurr ed in the Valais as well as in Graubunden and were restricted to the upper 15 km of the crust. Noteworthy are the two earthquake swarms near Walenstad t, SG, and Grimentz, VS, that together account for three of the five events with M-L > 3 and for about 20% of the total seismic activity observed in 1 998.