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Geology 2022

Takaji Kokusho

Takaji Kokusho, Speaker at Geology Conference
Chuo University, Japan
Title : Energy Demand in Surface Soils for Earthquake Engineering based on Vertical Array Strong Motion Records


In earthquake engineering, acceleration has been playing a major role while wave energy has rarely been considered as a demand in design. In order to understand earthquake damage in terms of energy, the demand of wave energy in surface soils is studied here assuming one-dimensional SH-wave propagation, by using a number of vertical array records during 9 strong earthquakes in Japan in the last two decades. A drastic decreasing trend of the energy demand has been found in general with decreasing ground depth to be almost 1/10 from the bottom to the surface. A simple formula has also been developed to evaluate upward energy at a given soil from the bedrock using the corresponding S-wave impedance ratio. Incident energies extrapolated at seismological bedrocks using the depth-dependent variations have been found roughly compatible with a well-known empirical formula despite that individual fault mechanisms are utterly neglected. Also indicated quite unexpectedly is that the softer the surface soil is, the more the energy demand tends to decrease. However, it may not be contradictory with a widely accepted perception that softer soil sites tend to suffer heavier damage as far as geotechnical influence is concerned, because induced soil strain tends to be larger due to decreasing soil stiffness despite the decreasing trend of energy demand there.


Professor, Chuo University, Tokyo, Japan, until 2015, and Professor emeritus thereafter. PhD in 1982, MS & BS in 1969 &1967 from the University of Tokyo, and MS from Duke University USA in 1975. Major academic society activities; 5th Ishihara Lecturer on Earthquake Geotechnical Engineering, Christchurch (2015), Chairman of TC4 (Earthquake Geotechnical Engineering), ISSMGE (2005-2009), Chairman of Organizing Committee of IS-2009 Tokyo by TC4, ISSMGE (2009) . Publications in English (all CRC Press, London); Innovative Earthquake Soil Dynamics (2017): Performance-Based Design in Earthquake Geotechnical Engineering - from Case History to Practice- (2009). Earthquake Geotechnical Case Histories for Performance-Based Design: (2009). More than 100 reviewed English papers.

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