QR- Factors in the Crystalline Uppermost Crust in Finland from Rayleigh Surface Waves

• Main Authors: M. Grad, W. Czuba, U. Luosto, M. Zuchniak
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1998
• Subjects: Key words; Q; Rayleigh waves; Upper Crust; Finland; Fennoscandian
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.520.2007; http://www.geophysica.fi/pdf/geophysica_1998_34_3_115_grad.pdf

During the period 1981-1993 five deep seismic sounding profiles were performed in Finland as an international co-operation to study the crustal structure of the Fennoscandian Shield. Apart from P-and S-waves, well developed Rayleigh surface waves (R-waves) with periods of 0.5-1.0 s were recorded from all the shot points on profiles SVEKA'81, BALTIC, POLAR, SVEKA'91 and FENNIA. In the seismic record sections, filtered in the frequency band 0.5-2.5 Hz, the R-waves were clearly observed up to distances of about 300 km. Short-period recordings from permanent seismograph stations on Finnish territory were used to study the relationship between the amplitude and charge size of the shot points. Amplitudes of R-waves corrected for charge size were used to study QR quality factor of the rocks below the Earth's surface, especially in the uppermost 4 or 5 kilometres. The quality factor QR varies in the uppermost 1 km on average from 30 for Archean basement in the northern and eastern Finland to 60 for the Proterozoic Svecokarelides in Central and Southern Finland. For depths of 1 to 4 km quality factor QR has larger value for both tectonic units being about 130 and 250, respectively.