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Detection of localized small-scale heterogeneities in the Hanshin-Awaji region, Japan, by anomalous amplification of coda level

Kayoko Tsuruga, Kiyoshi Yomogida, Hisao Ito and Kin'ya Nishigami
Detection of localized small-scale heterogeneities in the Hanshin-Awaji region, Japan, by anomalous amplification of coda level
Bulletin of the Seismological Society of America (August 2003) 93 (4): 1516-1530

Abstract

We estimated the spatial distribution of small-scale heterogeneities in and around the Hanshin-Awaji region including the coseismic fault area of the 1995 Hyogo-ken Nanbu, Japan, earthquake, by using the amplification factor of the coda level as a measure of scattering strength. We analyzed 137 earthquakes recorded at 64 stations. Because the coda level is strongly affected by site amplification, the determination of the amplification factor of the coda level requires the following three major steps: (1) checking the stability of coda waves among different stations such as coda Q and lapse time, (2) estimating the site amplification of coda waves for events outside the fault region, and (3) taking the spectral ratio of coda waves for events inside the fault zone after correcting the site characteristics obtained in step 2. The coda decay rate, Qc (super -1) , is common among stations for each event. The site amplification factor at each site estimated from 25 events correlates with the surface geological setting. The most important result is that coda amplification anomalies exist as clusters along the coseismic fault area, depending on frequency: beneath Awaji Island in the range of 1-4 Hz and beneath the area southwest of Kobe, 8-16 Hz. These high coda levels imply that strong heterogeneities exist there. The scales of these heterogeneities are estimated to be about 0.2-1.4 and 0.06-0.18 km, corresponding to the observed dominant frequencies (1-4 and 8-16 Hz, respectively).


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 93
Serial Issue: 4
Title: Detection of localized small-scale heterogeneities in the Hanshin-Awaji region, Japan, by anomalous amplification of coda level
Affiliation: Japan Nuclear Cycle Development Institute, Tono Geoscience Center, Toki, Japan
Pages: 1516-1530
Published: 200308
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 36
Accession Number: 2003-083117
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N33°45'00" - N35°15'00", E134°00'00" - E136°10'00"
Secondary Affiliation: Hokkaido University, JPN, JapanGeological Survey of Japan, JPN, JapanKyoto University, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200324
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