Records of Local Earthquakes as a Basis for the Correct Estimation of Strong Ground Motion (the Area of the Second Severomuisk Tunnel)

Abstract

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 2005–2010 are studied (magnitudes Mb of ~4.2–5.5, hypocentral distances r of ~15–220 km). Stochastic-simulation methods are used to estimate the regional parameters of radiation and propagation of seismic waves in northeastern Buryatia: the stress parameter Δσ, 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: Δσ ≈ 100 bars; k ≈ 0.012 s; Q(f) as ~60 f1.05 for r of ~15–30 km, ~80 f1.0 for r of ~40–60 km, ~90 f0.9 for r of ~100–110 km, and ~150 f0.7 for r of ~160–220 km; geometris spreading as 1/r for r <50 km, 1/50 for 50 < r <150 km, and 1/r0.5 for r >150 km; and duration as 0 for 0 < r < 5 km, 0.222r for 5 < r < 50 km, and 10 + 0.015r for r > 50 km. These estimates can be used to predict ground motion parameters during future strong earthquakes in the region.