Abstract

F-k analyses of NORESS array recordings of teleseismic events have indicated a prominent secondary source about 25 to 30 km southwest of the array, in the region of Lake Mjosa with large topographical relief. Residual seismograms derived by subtracting the beamed record from each array channel are used to investigate the effects of this scatterer on the regional phases Pn, Pg, and Lg from several events at regional distances. The beamed record for each regional phase is obtained by incorporating steering delays based on the known azimuth and phase velocity from the f-k analysis of raw data. Both explosion and earthquake sources along several different azimuths to NORESS provide evidence for scattered arrivals Pn-to-Rg, Pg-to-Rg, and Lg-to-Rg, originating from the same region of Lake Mjosa. These scattered arrivals are observed with remarkable clarity and closeness to the expected arrival times and are rich in low frequencies, as expected for Rg. Their presence in various regional phases indicates that near-receiver scattering plays an important role in the composition of regional phases.

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