Source Parameters of Major Earthquakes Near Kiruna, Northern Sweden, Deduced from Synthetic Seismogram Computation

摘要

The earthquakes that have occurred around Kiruna in northern Sweden have been studied in detail in order to determine their source characteristics and to understand the pattern of seismic acticity in the region. All earthquakes with magnitude greater than 3.0 (M/sub L/) that occurred during the period between 1967 and 1985 in the region bounded by 66.5 degrees - 69 degrees N and 19 degrees - 25 degrees E are studied. Relocated epicenters of the events exhibit a cluster of events in a direction NE - SW at at the western side of the region close to Kiruna, Though, the focal depths of the events are not very well constrained, the relocation results suggest that the events in this cluster might have occurred at focal depths between 15 and 25 km. At the easstern side of the region, the epicenters are roughly aligned along an elongated area trending NNW - SSE. The focal depths of the events in this area tend to be shallow and are probably in the upper crust at the depths range from 5 to 16 km. The earthquakes studied show nearly constant source radii of about 0.4 - 0.6 km over the seismic moment range 10/sup 20/ to 10/sup 21/ dyne-cm. Consequently, the events studied are characterized by a steadily incresing stress drop relative to increasing seismic moment. The source mechanisms obtained for the two largest earthquakes suggest that the mechanisms are dominated by the normal faultings on the near-vertical fault planes trending N - S to NE - SW. (With 26 refs.). (Atomindex citation 20:041080)