Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

Very large vertical surface acceleration of nearly four times gravity was measured at a strong motion observation station in Iwate Prefecture during the 2008 Iwate-Miyagi Inland, Japan, earthquake (Mw 6.9). The station is located about 3 km southwest of the epicenter and equipped with three-component accelerometers, installed at both the free surface and the bottom of a 260-m borehole. The wave form of the vertical acceleration shows a clearly asymmetric form with large amplitude in the upward direction. Aoi et al. (2008) reported and qualitatively explained the mechanism of this phenomenon by the analogy of bouncing a piece of matter on a trampoline, and thus they called it the “trampoline effect.” To simulate this recently discovered nonlinear behavior of the surface ground motion, numerical analysis with a finite-element method has been employed with parameters derived from the borehole data at the station. The analysis successfully simulates the asymmetric vertical motion. Results indicate that the asymmetric motion may be characterized by the existence of a lower bound of negative acceleration, which in most cases corresponds to the acceleration of gravity, and high positive pulses caused by the compression stress of the disturbed surface ground material.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Fifth Conference

Publisher

Missouri University of Science and Technology

Publication Date

5-24-2010

Document Version

Final Version

Rights

© 2010 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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May 24th, 12:00 AM May 29th, 12:00 AM

Numerical Analysis of Trampoline Effect in Extreme Ground Motion

San Diego, California

Very large vertical surface acceleration of nearly four times gravity was measured at a strong motion observation station in Iwate Prefecture during the 2008 Iwate-Miyagi Inland, Japan, earthquake (Mw 6.9). The station is located about 3 km southwest of the epicenter and equipped with three-component accelerometers, installed at both the free surface and the bottom of a 260-m borehole. The wave form of the vertical acceleration shows a clearly asymmetric form with large amplitude in the upward direction. Aoi et al. (2008) reported and qualitatively explained the mechanism of this phenomenon by the analogy of bouncing a piece of matter on a trampoline, and thus they called it the “trampoline effect.” To simulate this recently discovered nonlinear behavior of the surface ground motion, numerical analysis with a finite-element method has been employed with parameters derived from the borehole data at the station. The analysis successfully simulates the asymmetric vertical motion. Results indicate that the asymmetric motion may be characterized by the existence of a lower bound of negative acceleration, which in most cases corresponds to the acceleration of gravity, and high positive pulses caused by the compression stress of the disturbed surface ground material.