Features of soil behavior in the near-fault zones during the 2011 Tohoku mega-thrust earthquake Mw 9

Olga V Pavlenko

doi:10.1038/s41598-020-65629-2

Abstract

Soil behavior is studied during the Tohoku earthquake, where abnormally high accelerations > 1 g were recorded. Based on vertical array records, models of soil behavior are constructed at 28 sites in northern Honshu (Tohoku region). They are compared with previously studied models of soil behavior in southern Tohoku and Kanto regions, where shock waves were identified as possible causes of the recorded high accelerations. Shear moduli did not reduce during strong motion at many sites, and the behavior of softer and denser soils was similar to a large extent. The nonlinearity of soil response during the Tohoku earthquake was weaker than that observed earlier during the 1995 Kobe and 2000 Tottori earthquakes (Mw ~6.7–6.8). Instead, a widespread soil hardening was found, most expressed at stations recorded the highest PGAs. To explain the observed features of soil behavior, two possible mechanisms are suggested, such as, 1) shock wave fronts generated by rupture propagation along the fault plane induce soil hardening and high PGAs; 2) soil compaction and hardening is a soil response to long-lasting dynamic loadings during the earthquake. Most likely we may expect similar effects of soil hardening and generation of high PGAs during other mega-thrust earthquakes in future.

Highlights

Soil behavior is studied during the Tohoku earthquake, where abnormally high accelerations > 1 g were recorded
Based on the records of KiK-net vertical arrays, in[2], models of soil behavior during the Tohoku earthquake were constructed for southern Tohoku and Kanto regions, where abnormally high accelerations were recorded, i.e., vertical distributions of stresses and strains induced in soil layers during the strong motion were estimated
We found useful to identify such sites and discuss the features of soil behavior during the Tohoku earthquake at sites with softer and denser soils, as was done for KiK-net sites in southern Tohoku and Kanto regions[2]

Summary

Introduction

Soil behavior is studied during the Tohoku earthquake, where abnormally high accelerations > 1 g were recorded. Based on the records of KiK-net vertical arrays, in[2], models of soil behavior during the Tohoku earthquake were constructed for southern Tohoku and Kanto regions (to the south of FKSH17, 37.66 N parallel, Fig. 1), where abnormally high accelerations were recorded, i.e., vertical distributions of stresses and strains induced in soil layers during the strong motion were estimated.

Results

Conclusion