start-ver=1.4
cd-journal=joma
no-vol=31
cd-vols=
no-issue=1
article-no=
start-page=1
end-page=15
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2025
dt-pub=20250331
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Improved sedimentary layer model including the accretionary prism in the fore-arc region of the Ryukyu arc, Japan
kn-title=南西諸島の前弧域における付加体を含む堆積層のモデル化
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=　We combine the recent seismic reflection profiles to construct a new seismic velocity model of the sedimentary layer incorporating the accretionary prism along the Ryukyu trench. In constructing the new model, we refer to the zoning (ZONE1 to ZONE4) identified by Okamura et al. (2017, Tectonophys.). The construction process consists of the following steps: First, we digitize either unconformities or VP=4 to 5 km/s lines as the seismic basement, whichever is more clearly identifiable. Second, the digitized thickness data of the sedimentary layer from the reflection profiles are geometrically modeled and interpolated to make the three-dimensional structure model. Finally, we supplement the external region of the constructed 3-D sedimentary model using the J-SHIS model provided by the NIED to complete the velocity structure model in the entire Ryukyu arc. The main features of our model are as follows: In ZONE1, off Ishigaki-jima island, the thick sedimentary layer extends about 50 km wide from the Ryukyu trench. In ZONE2, off Miyako-jima island, the thinner layer compared to the other zones is found near the trench, with a thin sedimentary terrace covering the area behind it. In ZONE3, off Okinawa-jima island, the sedimentary layer deepens as it approaches the trench. In ZONE4, off Tokara islands, the deepest layer among all zones is identified. We then conduct 3-D finite-difference simulations of seismic wave propagation using the new and the previous models to confirm the improvement of the new model. In the simulations, the effects of the accretionary prism along the Ryukyu trench on the seismic wave propagation are clearly identified.
en-copyright=
kn-copyright=

en-aut-name=KOMATSUMasanao
en-aut-sei=KOMATSU
en-aut-mei=Masanao
kn-aut-name=小松正直
kn-aut-sei=小松
kn-aut-mei=正直
aut-affil-num=1
ORCID=

en-aut-name=URAKAMISohei
en-aut-sei=URAKAMI
en-aut-mei=Sohei
kn-aut-name=浦上想平
kn-aut-sei=浦上
kn-aut-mei=想平
aut-affil-num=2
ORCID=

en-aut-name=OKAMOTOTaro
en-aut-sei=OKAMOTO
en-aut-mei=Taro
kn-aut-name=岡元太郎
kn-aut-sei=岡元
kn-aut-mei=太郎
aut-affil-num=3
ORCID=

en-aut-name=TAKENAKAHiroshi
en-aut-sei=TAKENAKA
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=4
ORCID=

affil-num=1
en-affil=Okayama Gakuin University
kn-affil=岡山学院大学

affil-num=2
en-affil=Formerly Department of Earth Sciences, Okayama University
kn-affil=元・岡山大学大学院自然科学研究科

affil-num=3
en-affil=Department of Earth and Planetary Sciences, School of Science, Institute of Science Tokyo
kn-affil=東京科学大学理学院地球惑星科学系

affil-num=4
en-affil=Department of Earth Sciences, Okayama University
kn-affil=岡山大学学術研究院環境生命自然科学学域
en-keyword=Sedimentary layer model
kn-keyword=Sedimentary layer model
en-keyword=Accretionary prism
kn-keyword=Accretionary prism
en-keyword=Ryukyu arc
kn-keyword=Ryukyu arc
END

start-ver=1.4
cd-journal=joma
no-vol=30
cd-vols=
no-issue=1
article-no=
start-page=13
end-page=20
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2024
dt-pub=20240331
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Microtremor exploration in Tsushima Campus, Okayama University
kn-title=岡山大学津島キャンパスおける微動探査
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=　In this report, microtremor array observations were conducted in the Tsushima Campus of Okayama University, and the subsurface velocity structure was estimated from the analysis of the records. The results indicate that a five-layer S-wave velocity structure from the surface to the seismic basement equivalent layer with thicknesses of 8, 24, 80 and 180 m and velocities of 150, 450, 1100, 1700 and 3200 m/s, respectively, is reasonable. This model explains to some extent the observed phase velocity and H/V spectral ratios. It is also consistent with the surface borehole results. Furthermore, the areal characteristics of the H/V spectral ratios were also presented, allowing us to estimate the trend of the ground structure in shallow areas.
en-copyright=
kn-copyright=

en-aut-name=YAMADANobuyuki
en-aut-sei=YAMADA
en-aut-mei=Nobuyuki
kn-aut-name=山田伸之
kn-aut-sei=山田
kn-aut-mei=伸之
aut-affil-num=1
ORCID=

en-aut-name=TAKENAKAHiroshi
en-aut-sei=TAKENAKA
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=2
ORCID=

affil-num=1
en-affil=Faculty of Science and Technology, Kochi University
kn-affil=高知大学理工学部地球環境防災学科

affil-num=2
en-affil=Department of Earth Sciences, Okayama University
kn-affil=岡山大学学術研究院環境生命自然科学学域
en-keyword=Okayama
kn-keyword=Okayama
en-keyword=Microtremor array exploration
kn-keyword=Microtremor array exploration
en-keyword=S-wave velocity
kn-keyword=S-wave velocity
en-keyword=H/V spectral ratio
kn-keyword=H/V spectral ratio
END

start-ver=1.4
cd-journal=joma
no-vol=27
cd-vols=
no-issue=1
article-no=
start-page=39
end-page=50
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2021
dt-pub=20210331
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Estimation of displacement waveforms by baseline correction of near-fault acceleration records of the 2016 Kumamoto earthquake with median filter
kn-title=メジアンフィルターを用いた2016年熊本地震の断層近傍における加速度記録の基線補正と変位波形の推定
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The 2016 Kumamoto earthquake sequence occurred on April 14 (MJMA 6.5) and April 16 (MJMA 7.3). Seismic intensity of 7 on the Japan Meteorological Agency (JMA) scale was observed in Mashiki Town, Kumamoto Prefecture for the both events and in Nishihara Village, Kumamoto Prefecture for the April-16 event. We estimate the displacement waveforms from these acceleration records. Since the acceleration seismograms include the long-period noise due to tilting of the ground and instrumental effects, the baseline corrections are required to derive the accurate velocity and displacement waveforms. We apply a median filter to the velocity waveforms to identify the linear trends on them due to the steplike noise on the acceleration records, and determine the time at which baseline shifts take place and the step value of each shift for the baseline correction through trial and error. Our baseline correction can successfully reconstruct the velocity and displacement waveforms from the acceleration records. The displacement waveforms show the static components consistent with the geodetic data.
en-copyright=
kn-copyright=

en-aut-name=WatanabeTomotsugu
en-aut-sei=Watanabe
en-aut-mei=Tomotsugu
kn-aut-name=渡邉禎貢
kn-aut-sei=渡邉
kn-aut-mei=禎貢
aut-affil-num=1
ORCID=

en-aut-name=KomatsuMasanao
en-aut-sei=Komatsu
en-aut-mei=Masanao
kn-aut-name=小松正直
kn-aut-sei=小松
kn-aut-mei=正直
aut-affil-num=2
ORCID=

en-aut-name=TakenakaHiroshi
en-aut-sei=Takenaka
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科

affil-num=2
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科

affil-num=3
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科
en-keyword=2016 Kumamoto earthquake
kn-keyword=2016 Kumamoto earthquake
en-keyword=baseline correction
kn-keyword=baseline correction
en-keyword=median filter
kn-keyword=median filter
en-keyword=displacement
kn-keyword=displacement
END

start-ver=1.4
cd-journal=joma
no-vol=27
cd-vols=
no-issue=1
article-no=
start-page=29
end-page=38
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2021
dt-pub=20210331
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Synthetic nearfield seismograms at a subsurface position in a horizontally layered half-space
kn-title=水平成層構造における地中の近地理論地震記象
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=We extend the computational code of Takenaka and Sasatani (2000) for synthetic nearfield seismograms for horizontally layered elastic media, based on the reflection/transmission matrices and the discrete wavenumber summation method, to calculate seismic motion and its spatial derivatives at a subsurface position in the attenuative media. In this paper we describe the theory of this extension and show some numerical examples to verify the extended code.
en-copyright=
kn-copyright=

en-aut-name=TakenakaHiroshi
en-aut-sei=Takenaka
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=1
ORCID=

en-aut-name=WatanabeTomotsugu
en-aut-sei=Watanabe
en-aut-mei=Tomotsugu
kn-aut-name=渡邉禎貢
kn-aut-sei=渡邉
kn-aut-mei=禎貢
aut-affil-num=2
ORCID=

affil-num=1
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科

affil-num=2
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科
en-keyword=synthetic seismogram
kn-keyword=synthetic seismogram
en-keyword=reflectivity method
kn-keyword=reflectivity method
en-keyword=layered half-space
kn-keyword=layered half-space
END

start-ver=1.4
cd-journal=joma
no-vol=26
cd-vols=
no-issue=1
article-no=
start-page=1
end-page=17
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2019
dt-pub=20191227
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Computation of non-linear site response by the time-domain finite-difference method
kn-title=時間領域差分法による表層地盤の非線形応答の計算
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract= We have developed a time-domain staggered-grid finite-difference code for modeling non-linear response of a one-dimensionally inhomogeneous subsurface structure to a SH plane-wave incidence. It employs the velocity-stress formulation of elastodynamic equation for the linear part, and adopts a elastoplastic rheology model for the non-linear relation between the stress and strain. In this paper, we apply this code to four constitutive models from linear-elastic to nonlinear: (1) linear elastic model, (2) linear viscoelastic model, (3) elastoplastic model, and (4) viscoelastoplastic model, which simulate shallow sand and clay structures and are vibrated by a vertically incident SH plane-wave of Ricker wavelet, to compare the linear and the non-linear soil behaviors including low strains damping (viscoelastic effect) and/or hysteretic attenuation (non-linear effect). We also apply it to a local strong-motion record of the 2000 Western-Tottori earthquake (MW6.8). We then simulate characteristics of non-linear site response such as reduction of the spectral amplitude in the high frequency band and shift of the peak frequencies to lower frequencies.
en-copyright=
kn-copyright=

en-aut-name=TORIGOEYusuke
en-aut-sei=TORIGOE
en-aut-mei=Yusuke
kn-aut-name=鳥越友輔
kn-aut-sei=鳥越
kn-aut-mei=友輔
aut-affil-num=1
ORCID=

en-aut-name=KOMATSUMasanao
en-aut-sei=KOMATSU
en-aut-mei=Masanao
kn-aut-name=小松正直
kn-aut-sei=小松
kn-aut-mei=正直
aut-affil-num=2
ORCID=

en-aut-name=TAKENAKAHiroshi
en-aut-sei=TAKENAKA
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Department of Earth Sciences, Faculty of Science, Okayama University
kn-affil=岡山大学理学部地球科学科

affil-num=2
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科

affil-num=3
en-affil=Graduate School of Natural Science and Technology, Okayama University
kn-affil=岡山大学大学院自然科学研究科
en-keyword=finite-difference method
kn-keyword=finite-difference method
en-keyword=non-linear site response
kn-keyword=non-linear site response
en-keyword=strong motion
kn-keyword=strong motion
END

start-ver=1.4
cd-journal=joma
no-vol=22
cd-vols=
no-issue=1
article-no=
start-page=9
end-page=23
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2015
dt-pub=20151227
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Application of simulated annealing to focal mechanism determination
kn-title=焼きなまし法による初動発震機構解の決定
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=Simulated annealing (SA) is known as one of the efficient methods for global optimization. It allows for getting an optimal solution by jumping out of local minimum. In this paper, we apply the simulated annealing to determination of focal mechanism solution. To investigate the feasibility of the application, we determine focal mechanism solution of the 14 March 2014 Iyo-Nada intermediatedepth earthquake. The computation of SA method is then 1278 times faster than that of the grid search method.
en-copyright=
kn-copyright=

en-aut-name=KomatsuMasanao
en-aut-sei=Komatsu
en-aut-mei=Masanao
kn-aut-name=小松正直
kn-aut-sei=小松
kn-aut-mei=正直
aut-affil-num=1
ORCID=

en-aut-name=TakenakaHiroshi
en-aut-sei=Takenaka
en-aut-mei=Hiroshi
kn-aut-name=竹中博士
kn-aut-sei=竹中
kn-aut-mei=博士
aut-affil-num=2
ORCID=

affil-num=1
en-affil=
kn-affil=岡山大学大学院自然科学研究科

affil-num=2
en-affil=
kn-affil=岡山大学大学院自然科学研究科
en-keyword=focal mechanism solution
kn-keyword=focal mechanism solution
END