Possible Mechanisms for Generation of Anomalously High PGA During the 2011 Tohoku Earthquake

Possible Mechanisms for Generation of Anomalously High PGA During the 2011 Tohoku Earthquake Mechanisms are suggested that could explain anomalously high PGAs (peak ground accelerations) exceeding 1 g recorded during the 2011 Tohoku earthquake (M w = 9.0). In my previous research, I studied soil behavior during the Tohoku earthquake based on KiK-net vertical array records and revealed its ‘atypical’ pattern: instead of being reduced in the near-source zones as usually observed during strong earthquakes, shear moduli in soil layers increased, indicating soil hardening, and reached their maxima at the moments of the highest intensity of strong motion, then reduced. We could explain this assuming that the soils experienced some additional compression. The observed changes in the shapes of acceleration time histories with distance from the source, such as a decrease of the duration and an increase of the intensity of strong motion, indicate phenomena similar to overlapping of seismic waves and a shock wave generation, which led to the compression of soils. The phenomena reach their maximum in the vicinity of stations FKSH10, TCGH16, and IBRH11, where the highest PGAs were recorded; at larger epicentral distances, PGAs sharply fall. Thus, the occurrence of anomalously high PGAs on the surface can result from the combination of the overlapping of seismic waves at the bottoms of soil layers and their increased amplification by the pre-compressed soils. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Pure and Applied Geophysics Springer Journals

Possible Mechanisms for Generation of Anomalously High PGA During the 2011 Tohoku Earthquake

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Publisher
Springer International Publishing
Copyright
Copyright © 2017 by Springer International Publishing
Subject
Earth Sciences; Geophysics/Geodesy
ISSN
0033-4553
eISSN
1420-9136
D.O.I.
10.1007/s00024-017-1558-2
Publisher site
See Article on Publisher Site

Abstract

Mechanisms are suggested that could explain anomalously high PGAs (peak ground accelerations) exceeding 1 g recorded during the 2011 Tohoku earthquake (M w = 9.0). In my previous research, I studied soil behavior during the Tohoku earthquake based on KiK-net vertical array records and revealed its ‘atypical’ pattern: instead of being reduced in the near-source zones as usually observed during strong earthquakes, shear moduli in soil layers increased, indicating soil hardening, and reached their maxima at the moments of the highest intensity of strong motion, then reduced. We could explain this assuming that the soils experienced some additional compression. The observed changes in the shapes of acceleration time histories with distance from the source, such as a decrease of the duration and an increase of the intensity of strong motion, indicate phenomena similar to overlapping of seismic waves and a shock wave generation, which led to the compression of soils. The phenomena reach their maximum in the vicinity of stations FKSH10, TCGH16, and IBRH11, where the highest PGAs were recorded; at larger epicentral distances, PGAs sharply fall. Thus, the occurrence of anomalously high PGAs on the surface can result from the combination of the overlapping of seismic waves at the bottoms of soil layers and their increased amplification by the pre-compressed soils.

Journal

Pure and Applied GeophysicsSpringer Journals

Published: Apr 28, 2017

References

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