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Analysis of regional events recorded at NORESS

DEPARTMENT OF GEOSCIENCES THE PENNSYLVANIA STATE UNIVERSITY, UNIVERSITY PARK, PENNSYLVANIA 16802

Abstract

Events recorded by NORESS are analyzed to determine the velocities and times of coherent crustal phases to be used in accurate locations and determination of crustal structure. The events straddle two azimuthal directions, and range in distance from 50 to 300 km, thus sampling two cross-sections of the crust and upper mantle: one in the Caledonides to the northwest of NORESS and the other to the south along the eastern rim of the Oslo Graben. f-k analysis is used to search for coherent phases in the data. All vertical channels are then stacked with the appropriate time delays calculated from the phase velocities and azimuths obtained for the coherent arrivals. Finally, a composite seismogram is made for each event by piecing together time sections from the stacks, where each time piece represents a coherent arrival. All detectable coherent phases are enhanced in the composite seismograms, and on closer inspection it is possible to improve some of the locations from the NORESS Bulletin. This causes a number of events to group together to the same location. Travel-time curves are constructed from plane-layered homogeneous models to match travel times and phase velocities in the composite seismograms.