Abstract
The KiK-net is a vertical array system and seismic motions are recorded at the ground surface and in the borehole. With the peak acceleration of 24.5m/s2 at AKTH04 (EW) and 38.7m/s2 at IWTH25 (UD) during the Iwate-Miyagi Nairiku earthquake in 2008, the occurrence mechanism of large accelerations is investigated by the non-stationary Fourier spectra and the double integrated displacement profile. From the difference in the occurrence time, the frequency and the amplitude of dominant components between the surface and the borehole, it is clear that the amplification in the surface soil caused the large acceleration at the surface. In the deformation process of the surface soil, the whipping mode is picked up at AKTH04. The relative displacement profile between the surface and the borehole is analyzed by the phase curves. The orbit at AKTH04 is identified by the sinusoidal waves of the sway, up-down and rocking modes. It can be concluded that the large accelerations at AKTH04 may be due to an irregular local mode caused by the collision between the base-mat and surrounding soil. From the orbit at IWTH25, the vertical pulse can be regarded as “an induced vertical motion” due to the collision between the base-mat of an observation house and the soil beneath it.
Highlights
After the Hyogoken-Nanbu earthquake in 1995, the importance of seismic records was re-recognized for mitigation of seismic hazard, and the Strong-motion Seismograph Networks (K-NET, KiK-net) were established by the National Research Institute for Earth Science Disaster Prevention (NIED, 2016) in 1996
During the Iwate–Miyagi Nairiku earthquake in 2008, large accelerations were measured at the KiK-net stations, i.e., 38.9 m/ s2 in IWTH25 (UD) and 24.5 m/s2 in AKTH04 (EW)
The occurrence mechanisms of such large acceleration have been explained by using several analytical results, such as the non-stationary Fourier spectra and the double integrated displacement profiles
Summary
The property of dominant components was analyzed as follows: (1) At the surface at AKTH04, the peak maximum amplitude occurred in the EW component at the frequency of 3.3 Hz (2) At the surface at IWTH25, the peak maximum amplitude occurred in the UD component at the frequency of 10.9 Hz with the amplitude of 4.89 m/s2, and the average value is 2.80 m/s2.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
