The Relationship between Ground Motion Intensity in Zones of Strong Earthquakes and Soil Conditions: Large Dataset-Based Analysis

Abstract—The relationship between seismic intensity of ground shaking and soil conditions is analyzed using a large set of records obtained in the zones of strong earthquakes by KiK-net vertical arrays (Japan). The observed seismic intensity is compared in pairs of stations with different V_S30 soil characteristics, equidistant from the epicenter. In total, more than 1300 station pairs for 45 seismic events analyzed. For most pairs (more than 970), an inverse dependence of measured intensity on V_S30 is obtained (i.e., the necessary condition for applicability of seismic rigidity method (SRM) is fulfilled). However, for more than 350 pairs, the measured intensity was higher at the stations installed on denser soils. A probable cause is that nonlinear behavior of soft soils under strong motions and the resonance effects in the ground layers were neglected when using SRM. Besides, a large scatter is revealed in experimental estimates of seismic intensity as function of V_S30 at a fixed earthquake magnitude and hypocentral distance. The seismic intensity estimates from the Blake–Shebalin equations with coefficients for Kamchatka and the Kuril Islands proved to be inconsistent with observational data, which indicates rather low accuracy of intensity prediction based on soil conditions and the Blake–Shebalin equation. Improving outdated approaches in building codes has been a pressing issue for many years.