THE FIRST VERSION OF THE A(MAX)(M(W),R) RELATIONSHIP FOR KAMCHATKA

To estimate for the first time the typical relation between peak accel eration A(max), moment magnitude M(W), and hypocentral distance R for Kamchatka, 101 analog strong motion records for 1969-1993 were employe d as the initial data set. Records of acceleration and velocity meters were obtained at 15 rock to medium-ground Kamchatkan sites from 33 ea rthquakes with M(W) = 4.5-7.8, at R = 30-250 km. A(max) values were de termined from ''true'' acceleration time histories calculated by spect ral deconvolution of digitized records. The maximum value over the two horizontal components was used as the A(max), value in the further an alysis. With the scarce data available, there were no chances to deter mine reliably the whole A(max)(M(W), R) average surface; thus the shap e of this trend surface was determined on a theoretical basis and only the level was fitted to the data. The theoretical model employed incl uded: (1) source spectrum: according to the Prune'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 sourc e, its size depending on M(W); (4) accelerogram duration: including so urce-dependent and distance-dependent terms; (5) A(max) value: based o n 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 t rends 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 re lation we sought. Note that in the process of data analysis we were fo rced to entirely reject relatively abundant data of two particular sta tions because of their prominent local amplification (x 5.5) or deampl ification (x 0.45).