Semiannual Technical Summary, 1 October 1985-31 March 1986

• Main Author: Loughran, L. B.
• Other Authors: ROYAL NORWEGIAN COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH KJELLER
• Format: Text
• Language: English
• Published: 1986
• Subjects: Seismology; Seismic Detection and Detectors; *SEISMIC ARRAYS; *SEISMIC DETECTION; NETWORKS; LAYERS; ENERGY; SIGNAL TO NOISE RATIO; SEISMIC DATA; LOW VELOCITY; SPECTRA; NOISE; NORWAY; STRUCTURAL GEOLOGY; EARTH MANTLE; SEISMOGRAPHS; NORTHERN EUROPE; VELOCITY; DATA BASES; NORSAR(NORWEGIAN SEISMIC ARRAY); HFSE(HIGH FREQUENCY SEISMIC ELEMENT); FOREIGN REPORTS; Norway; Fennoscandia
• Online Access: http://www.dtic.mil/docs/citations/ADA221965; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA221965

This Semiannual Technical Summary describes the operation, maintenance and research activities at the Norwegian Seismic Array (NORSAR) for the period 1 October 1985 - 31 March 1986. About 100 regional events recorded by the High Frequency Seismic Element (HFSE) at NORSAR have been analyzed with respect to spectral characteristics of recorded phases. For epicentral distances within about 500 km, the Pn and Sn phases consistently show extremely strong high frequency energy. Thus, the SNR shows no drop with increasing frequency within the recorded bandwidth (up to 62.5 Hz). Around 400 km distance, where we have a particularly good data set, the Pg and Lg phases are dominant at low frequencies (1-5 Hz), whereas the Pn and Sn phases dominate the seismograms from 10-62.5 Hz). At distances from 500-1500 km, the signal spectra drop more rapidly than the noise spectra at high frequencies, but signal energy up to 20-30 Hz is still observable for many events of M sub L approx. = 3.0. A study has been undertaken to obtain a 3-D imaging of the upper mantle velocity structure beneath the southern part of Fennoscandia, on the basis of P-wave travel time residuals as observed across a local seismograph network in this region. Results are presented in the form of a map showing areas of high and low velocities in four layers, extending to 600 km depth.