The First Version of the A max  ( M W  , R) Relationship for Kamchatka

Abstract

To estimate for the first time the typical relation between peak acceleration A max , moment magnitude M W and hypocentral distance R for Kamchatka, 101 analog strong motion records for 1969-1993 were employed as the initial data set. Records of acceleration and velocity meters were obtained at 15 rock to medium-ground Kamchatkan sites from 33 earthquakes with M W =4.5 -7.8, at R =30-250 km. A max values were determined from ''true'' acceleration time histories calculated by spectral deconvolution of digitized records. The maximum value over the two horizontal components was used as the A max value in the further analysis. With the scarce data available, there were no chances to determine reliably the whole A max (M W , R) average surface; thus the shape of this trend surface was determined on a theoretical basis and only the level was fitted to the data. The theoretical model employed included: (1) source spectrum: according to the Brune's spectral model; (2) point-source attenuation: as 1/R plus loss specified by Q(f) =250 f 0.8 ; (3) finite-source correction for a disc-shaped incoherent source, its size depending on M W ; (4) accelerogram duration: including source-dependent and distance-dependent terms; (5) A max value: based on random process representation. Distance trends calculated with this model agree with the empirical ones of FUKUSHIMA and TANAKA (1990). To calculate the absolute level for these trends, observed A max (M W , R) values were reduced to M W =8, R =100 km using the theoretical trends as reference. The median of the reduced values, A max (8, 100), equal to 188 gal. was taken as the absolute reference level for the relation we sought. Note that in the process of data analysis we were forced to entirely reject relatively abundant data of two particular stations because of their prominent local amplification (×5.5) or deamplification (×0.45).

Preliminary Model for Scaling of Fourier Spectra of Strong Ground Motion Recorded on Kamchatka

“…Among processed records we have a few supporting each of these two ideas. The individual spectral anomalies of KRI and PET stations are consistent with earlier results from small earthquake amplitude data (FEDOTOV, 1972;ZOBIN et al, 1993) and A max data (GUSEV et al, 1997a). 5.…”

“…4). No significant anomaly has been found for KBG in terms of peak acceleration amplitude: in GUSEV et al (1997a) we found that A max data for KBG do not differ from other medium-ground (or rock ground) Average Fourier spectrum at R= 80 km and M W =7.15 (M jma =7), rock ground, for Kamchatka (this work) compared to similar spectra calculation from regression formulas for Japan (KAMIYAMA and MATSUKAWA, 1990) and California (ATKINSON and SILVA, 1997). Also given is the expected Kamchatka spectrum from GUSEV (1990), adjusted to M W =7.15.…”

“…The described reduction technique is in fact the particular version of the multiple-use procedure of GUSEV and PETUKHIN (1996). Recently the latter was applied to peak acceleration data (GUSEV et al, 1997a) and yielded attenuation relations that compare quite well with empirical trends of FUKUSHIMA and TANAKA (1990) based on a considerably larger volume of data.…”

“…To avoid this, we seek site corrections only for the three stations that have abundant records; incidentally, they are also characterized by clear site anomalies. This decision is based on our previous analysis of peak accelerations (GUSEV et al, 1997a) and on a preliminary analysis of Fourier spectra (GUSEV et al, 1997b). These two studies have revealed prominent individual station anomalies for the three stations, whereas two of these stations supplied most of the volume of medium-ground data.…”

“…The initial data that we use here are the same set of digitized and processed records as in (GUSEV et al, 1997a) …”