Masata Sugito

Time-dependent ground motion amplification characteristics at reclaimed land after the 1995 Hyogoken Nambu Earthquake

Two sets of borehole array records obtained from the Great Hanshin Earthquake, as well as its fore and after shocks, are investigated. One of the stations is located at Port Island in Kobe City, where severe liquefaction occurred and the records from the main event include the typical phenomena of liquefaction. The other station is located at Rokko Island in Kobe City, where the liquefaction phenomenon was not predominant as it was at Port Island. The non-linear ground motion amplification, depending on the level of input ground motion as well as its spectral characteristics, is carefully investigated. Two numerical techniques for seismic response ground analysis are applied for these stations: one is the frequency-dependent equivalent linearization technique for frequency domain analysis, and the other is the effective stress-based liquefaction analysis. The discussion is focused on the amplification characteristics of these two reclaimed lands, depending on their reclamation history. The time-dependent amplification ratio for peak ground motion and spectral contents is demonstrated, caused by the recovery of soil rigidity due to the decrease in excess pore water pressure after the main event.

On the precursors to the 2011 Tohoku earthquake: crustal movements and electromagnetic signatures

We compare the precursory behaviour of crustal movements with electromagnetic signatures for the 2011 off the Pacific Coast of Tohoku earthquake. First, we present the Global Positioning System (GPS) data on the co-seismic variations and pre-seismic precursors (medium-term, short-term and imminent precursors). Then, we will review recently published results on electromagnetic precursors, including mainly short-term subionospheric very low frequency (VLF)/LF propagation anomaly, ultralow frequency (ULF) magnetic field depression and ULF/extremely low frequency (ELF) atmospheric radiation. Finally, we examine the relationship between the crustal movements and electromagnetic phenomena. We conclude that at least short-term electromagnetic precursors are closely correlated in time with the corresponding crustal movements. This seems to provide evidence on the link between lithospheric and electromagnetic processes. Some discussions will be given on the possible mechanism of this link.

Analysis of strong motion records from the South Hyogo earthquake of January 17, 1995

Abstract Strong motion records from the South Hyogo earthquake of January 17, 1995, are overviewed. The discussion is focused on (1) the characteristic of near field records including the predominant direction of motion versus the fault strike and their spectral characteristic, and (2) the orientation error of seismometers and ground motion amplification at borehole array stations. Two numerical techniques for seismic response analysis of ground are applied for the array stations. The one is the frequency-dependent equi-linearized technique for the frequency domain analysis, and the other is the effective stress-based liquefaction analysis method. The numerical calculations are compared with the records at four borehole array stations.

Seismic Reliability Analysis of Existing Structures Based on Fuzzy Probability

This paper provides a reliability analysis of existing bridge structures for earthquake loads. Using a fuzzy graph and fuzzy relation, an attempt is made to consider the effect of structural deterioration in the evaluation of structural reliability. The analysis method gives the final result in the form of fuzzy probability, which can provide more information to the reliability analysis of the structure in future. Several numerical examples are presented to demonstrate the applicability of the method proposed here.

Chapter 2 Analysis of strong motion records from the Southern Hyogo earthquake of January 17, 19951

Abstract Strong motion records from the Southern Hyogo earthquake of January 17, 1995, are overviewed. The discussion is focused on (1) the characteristic of near field records including the predominant direction of motion versus the fault strike and their spectral characteristic, and (2) the orientation error of seismometers and ground motion amplification at borehole array stations. Two numerical techniques for seismic response analysis of ground are applied for the array stations. The one is the frequency-dependent equi-linearized technique for the frequency domain analysis, and the other is the effective stress-based liquefaction analysis method. The numerical calculations are compared with the records at four borehole array stations.