Long-Periods Ground Motion Characteristics in Niigata-Ken Chuetsu Area, Japan, Estimated From Acceleration Data of Teleseismic Event


Abstract eng:
In the Niigata-ken Chuetsu area, Japan, there are thick sedimentary layers and long-period ground motions have been observed frequently when large earthquake occurred. There is a high density seismic observation network (AN-net) consisting of 40 stations for studying seismicity in this area. The array size is about 40 km in east-west direction and about 60km in north-south direction. We studied the long-period ground motion characteristics using acceleration data of this array during the 2015 Gorkha, Nepal, earthquake. We detected the low-frequency signals from this teleseismic event in noisy acceleration waveforms and the dominant frequencies of signals were between 0.02 and 0.1 Hz. In such low frequency, the spatial variation of amplitude was recognized in the array area. To emphasize the dominant frequency components, velocity waveforms were made from acceleration waveforms by numerical integration with low-cut filter of 0.02 Hz. Many seismic phases (ex. P-wave, S-wave, Love waves and Rayleigh waves) were clearly recognized in the velocity traces and show the significant characteristics. About the body wave part, the waveforms at the stations in the hill and mountain area were very simple but the large later arrivals were recognized at stations in the plain area. These later arrivals were assumed to be excited by the deep sediment structure in the plain area. About the surface wave part, many wave packets with low frequency were passing through AN-net from the west to the east and the apparent frequency of the wave packets become higher as arrival order of the wave packets. We also confirmed this dispersion characteristics after multiple filtering analysis of the surface wave part data. Next, we estimated the phase velocities and propagation directions of surface waves after the frequency-wavenumber spectrum analysis. The back azimuths were almost between 260 and 280 degree measured clockwise from the north in frequency between 0.02 and 0.1 Hz for both Love and Rayleigh waves. It means that surface waves propagated from the epicenter direction. The estimated phase velocity did not show clear dispersion and did not fit the phase velocity calculated from the existing 1-D velocity model. The sub-surface velocity structure of this area are varied in short distance. The complex velocity structure makes wave propagation complicated. To estimate the phase velocity correctly, it is necessary to use a small array dependent on the local variance of velocity structure.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 3630.:
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