F-K Analysis of Array and Single-Station Data to Identify Sources of Near-Receiver and Near-Source Scattering

摘要

F-k analyses of short-period recordings of both U.S. and Soviet undergroundnuclear explosions at the Eskdalemuir (EKA), Scotland array indicate arrivals from a local source about 15 km due northwest of the array. Use of residual seismograms derived by subtracting the beamed record from each array channel confirmed the presence of the same scatterer. The secondary seismic source appears to be short-period surface waves due to the scattering of incident P waves at a nearby deep valley known as Moffat Water, in agreement with Key's (1967) earlier results. Similar analyses of the NORESS (Norway) array data from U.S. and Soviet nuclear shots also indicate secondary arrivals suggesting a local near-surface scatterer about 25-30 km south-west of the array, in the region of Lake Mjosa. Thus, short-aperture array data can be useful in identifying and locating sources of near-receiver scattering. F-k analyses of short-period recordings of both explosion and earthquake sources at the high-frequency NORESS array indicate secondary arrivals from a near-receiver source about 25-30 km southwest of the array. F-k power difference plots, obtained by subtracting (after normalization) the f-k power versus slowness estimates for the initial P window from those for the later windows, provided nearly identical results. The secondary seismic source appears to be short-period surface waves, Rg, generated by the scattering of incident P waves in the region of Lake Mjosa, 27 km SW of NORESS, where there is about 1 km of relief from the bottom of the lake to the top of an adjacent hill.