Microearthquakes and seismotectonic analysis for a nuclear plant area in southeastern Finland

Microearthquake observations are used to study the local seismicity and seismotectonics in the Precambrian Rapakivi Granite, in the Loviisa area, SE Fi around the nuclear power plant in Loviisa, is limited to a radius of 100 km. The results from a local microearthquake network in the Loviisa area showed that, during 6 years of measuring there were 29 micro- and ultra-microearth 0.1–1.2) in the area. The events identify active faults in the area. The estimated value of the peak slip is an important parameter connecting microearthquakes to geodynamical processes. The peak slip gives an approximat and aseismic movement on a certain fault and thus an indication of ongoing tectonic processes. The movements on the active fault may continue for thous Source parameters were computed for a simple circular source model, giving peak slips less than 0.25 mm, stress drop values less than 2 × 10 5N/m 2 and source radii generally less than 50 m. The earthquakes occurred at depths of less than 5 km.