Shock wave as possible mechanism for the generation of abnormally high accelerations during the M = 9.0 Tohoku earthquake on march 11, 2011

Abstract

This study proposes a mechanism for the generation of anomalously high accelerations (over 1g, maximum up to approximately 3g) recorded during the 2011 Tōhoku earthquake (Mw = 9.0). Soil behavior in the fault zones of the earthquake is examined based on the records of vertical groups, and the earthquakes “atypical” model is determined: shear moduli increased during strong motions, which are indicative of soil strengthening, and then decreased. That which can be explained by an assumption of soils being subjected to some additional impact. Accelerogram curves show a decrease in the duration and an increase in the intensity of strong motions with distance from the earthquake source, which may be indicative of superposition of seismic waves and generation of shock waves by a rapidly moving source — the tip of the fracture in the earthquake source.