EFFECT OF GROUND MOTION PARAMETERS ON THE SEISMIC VERTICAL-TO-HORIZONTAL ACCELERATION RATIOS

Recent studies clearly show the necessity of including the vertical component of earthquake ground motions in the seismic analysis and design of structures. This study investigates the effects of earthquake magnitude (M_w), epicentral distance (R_epi), and soil condition according to the average shear wave velocity (V_s30) on both the vertical-to-horizontal (V/H) spectral accelerations (SA) and peak ground accelerations (PGA) in the Eastern Canada region. To this end, 248 sets of records were selected from 67 earthquakes that occurred in the studied seismic region, with a magnitude (M_w) of 3.0 and above, an epicentral distance (R_epi) of less than 150 km, and different site soil conditions. In all cases, the computed average trendlines of PGA and SA ratios were found to be higher than the empirical ratio of 2/3 recommended in the current NBC edition. Moreover, a significant increase in the PGA ratios was observed with larger earthquake magnitude (M_w), reduced distance from the epicentre (R_epi), and smaller shear wave velocity (V_s30). Likewise, notable impacts of earthquake magnitude and soil condition on the V/H SA ratios were observed. In this regard, the average V/H SA ratio increased for periods up to 2.0 sec for larger earthquake magnitudes, and the ratio increased at soil conditions with smaller shear wave velocity (V_s30) for periods less than 0.5 sec. Finally, no correlation between the epicentral distance and the SA ratios was concluded.