Why People Cannot Keep Standing under Strong Earthquake

(Aging Effect to Human Postural Control in Quiet Standing)

Abstract

By modelling human posture in quiet standing as an inverted pendulum and its control from the central nervous system as piecewise sampled-data control, we discuss the aging effect to its stability control under seismic acceleration with different intensity. In the model, aging parameters, such as muscular strength, reaction time and sensing errors, are easy to be quantified. We simulated healthy people’s falling down under the acceleration of earthquake according to seismic intensity scale of Japan meteorological agency. The maximum muscular torque at the ankle strongly affects quiet standing posture and 40% its reduction induces frequent falling down. Although degradation of reaction time doesn’t so much influence to the stability control, it becomes important after increasing the error of postural angle.