Local attenuation in western Nagano, central Japan, estimated from seismograms recorded in three boreholes

Abstract

[1] Seismic attenuation parameters three borehole stations in Western Nagano, Central Japan. Based on the difference in attenuation between combinations of two boreholes, the local attenuation (QP−1) is 1.23 × 10−3 s in the frequency range of 80 to 250 Hz. Obtained QP−1 is consistent with the trend estimated by grid search with the assumption of the ω2 source model. Even though the boreholes are located on the fracture area of the 1984 Nagano-Ken-Seibu Earthquake, the estimated QP−1 is low. The result is not completely consistent with a previous study, and a result of QS−1 obtained from the twofold spectral ratio, but the difference can be interpreted as the difference of frequency ranges. The differences of station corrections of attenuation between boreholes are much smaller than the difference between borehole and surface, and the result shows the advantage of borehole seismometers.