Extreme Accelerations During Earthquakes Caused by Elastic Flapping Effect

Hiroyuki Goto,Len Damiano,Yoshihiro Kaneko,Hamish Avery,John Young

doi:10.1038/s41598-018-37716-y

Hiroyuki Goto, Len Damiano + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-37716-y

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Journal: Scientific Reports	Publication Date: Feb 4, 2019
Citations: 17	License type: open-access

Affiliation: Kyoto University, GNS Science

Abstract

Accurate recording of large, earthquake-induced ground shaking is critical for our understanding of earthquake physics as well as seismic hazard assessment. Extremely large accelerations with the peak value of 3.2 times the gravity acceleration were recorded at seismic station WTMC located in northern South Island of New Zealand during the recent magnitude 7.8 Kaikoura earthquake. However, the mechanisms responsible for the generation of such large accelerations are not well understood. Here we use numerical simulations to examine a range of physical models that can reproduce the observed characteristics of the acceleration record. We find that the record of the asymmetric, vertical accelerations, also observed during a magnitude 6.3 earthquake, can be explained by a flapping effect, that is, the local, elastic bouncing of a foundation slab on which the sensor is installed. Our results suggest that the extremely large accelerations recorded at seismic station WTMC do not reflect the actual ground shaking, but were caused by a local, system response around the sensor. Our finding has important implications for both the evaluation of future seismic hazard based on the waveform records of the Kaikoura earthquake and the installation methodology of strong-motion seismometers in all earthquake prone countries.

Highlights

The 13th November 2016 Mw7.8 Kaikoura earthquake resulted in high ground motion records at several seismic stations spanning more than 6000 km[2] of northern South Island of New Zealand[13]
We aim to reproduce the characteristics of the acceleration data at seismic station WTMC using finite-element modeling of dynamic interactions between the concrete foundation slab and underlying soil (Methods)
The elastic bouncing of the slab, which we refer to as a flapping effect, is induced by vertical motion through a system with variation in the horizontal direction, e.g., the foundation slab sitting on an irregular surface

Summary

Introduction

The 13th November 2016 Mw7.8 Kaikoura earthquake resulted in high ground motion records at several seismic stations spanning more than 6000 km[2] of northern South Island of New Zealand[13]. An anomalously large peak acceleration of 3.23 g in the vector sum of three components was recorded at seismic station WTMC (S42.6211°, E173.0535°), which is located in Waiau, Northern Canterbury in the vicinity of faults that ruptured during the earthquake (Fig. 1)[13,14,15]. Large upward accelerations are accompanied by high-frequency oscillations (80–85 Hz) in the horizontal components (Fig. 2). The rocking effect is characterized by upward accelerations induced by large horizontal motion when the structural basement underneath the seismic sensor impacts on the ground surface[20]. Vertically eccentric structures needed to induce the rocking effect were not found at station WTMC (see Fig. 1) Another mechanism must be responsible for the origin of the extremely large AsVA

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