RECORDS OF LOCAL EARTHQUAKES AS A BASIS FOR THE CORRECT ESTIMATION OF STRONG GROUND MOTION (the area of the second Severomuisk tunnel)
O.V. Pavlenko
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
Keywords: Stochastic simulation, stress parameter, quality factor, geometric spreading, local site amplification, duration of strong ground motion, soil response, local earthquakes
Abstract
To obtain realistic and correct estimates of strong ground motion in the area of construction of the second Severomuisk tunnel, the records of local earthquakes obtained by the Severomuisk seismic station (SVKR) in 20052010 are studied (magnitudes M_{b} of ~4.25.5, hypocentral distances r of ~15220 km). Stochasticsimulation methods are used to estimate the regional parameters of radiation and propagation of seismic waves in northeastern Buryatia: the stress parameter Ds, shapes of source spectra, wave attenuation at high frequencies (k), parameters defining the shape and duration of the acceleration time history, etc. Beforehand, the duration of strong motion as a function of the hypocentral distance was evaluated from the records; the local site amplification A ( f ) was estimated based on the velocity structure of the region; and the envelope method was applied to estimate the quality function Q ( f ). The following data were obtained: Ds ≈ 100 bars; k ≈ 0.012 s; Q ( f ) as ~ 60 f ^{1.05} for r of ~1530 km, ~ 80 f ^{1.0} for r of ~4060 km, ~ 90 f ^{0.9} for r of ~100110 km, and ~ 150 f ^{0.7} for r of ~160220 km; geometric spreading as 1/ r for r < 50 km, 1/50 for 50 < r < 150 km, and 1/ r ^{0.5} for r > 150 km; and duration as 0 for 0 < r < 5 km, 0.222 r for 5 < r < 50 km, and 10 + 0.015 r for r > 50 km. These estimates can be used to predict ground motion parameters during future strong earthquakes in the region.
