All issues
Volume 62, Issue 2+3
Displaying 1-6 of 6 articles from this issue
- |<
- <
- 1
- >
- >|
ARTICLES
-
Fuyuki HIROSE, Kenji MAEDA, Hiroyuki TAKAYAMA2009 Volume 62 Issue 2+3 Pages 67-84
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSLong-term slow slip events with the recurrence period of about 10-30 years have been observed beneath Lake Hamana in the Tokai district where historically great interplate earthquakes occurred repeatedly. We intend to simulate the recurrent slow slip events before the occurrence of cyclic great earthquakes using a three-dimensional earthquake cycle model based on the rate- and state-dependent friction law with heterogeneous friction parameters on the plate interface. In our model we can simulate recurring slow slip events with the period of about 30-40 years near beneath Lake Hamana, by applying small negative values to frictional parameter (a-b)and small values to characteristic distance L for the western region of the Tokai district, and large values to L for the regions off Tokai district where seismic structure surveys reveal the existence of a subducting ridge.View full abstractDownload PDF (2391K) -
Kazutomo TAKANO, Fumiaki KIMATA2009 Volume 62 Issue 2+3 Pages 85-96
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSThis study reexamines the ground deformation and fault slip model of the 1945 Mikawa earthquake (M =6.8), central Japan. We reevaluate two geodetic data sets from the years 1886/1887 and 1955/56 that were obtained from the Geographical Survey Institute; these data sets consist of displacements calculated from the net adjustment of triangulation surveys carried out before and after the Mikawa earthquake. We remove the interseismic deformation and coseismic deformation of the 1944 Tonankai earthquake from the two unique data sets used in our analysis. Maximum coseismic horizontal displacements of over 1.4 m were detected to the west of the Fukozu fault. We estimated the coseismic slip by analyzing our data set. The geometry of the fault planes was adopted from a recent seismicity study and from the surface earthquake fault of this area. The best fit to the data is obtained from two faults along the sections running north and south of the Fukozu and Yokosuka faults. The estimated uniform-slip elastic dislocation model consists of two adjacent planes. The fault also appeared to connect the sections running north and south of the Fukozu and Yokosuka faults. Because it can suitably explain the coseismic deformation due to two earthquake source faults, the earthquake source fault is not admitted under the section for the run. The mechanism is considered to be two reverse faults with right-lateral components. The estimated slips for the two source faults are 2.5 m and 1.4 m, respectively. The pressure axis is directed along NE-SW or E-W. The total seismic moment determined from this model is 1.6 × 1019 Nm, corresponding to Mw=6.7.View full abstractDownload PDF (2240K) -
Shigeyasu TONE, Takashi MIYATAKE, Kazuhito HIKIMA, Aitaro KATO2009 Volume 62 Issue 2+3 Pages 97-107
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSTo understand earthquake triggering, computation of Coulomb stress change (ΔCFF) associated with earthquake slip is a powerful tool. However, uniform half space is usually assumed in the computation, though highly heterogeneous crustal structures have been estimated in source regions. The purpose of this study is to evaluate the effect of heterogeneity on the calculation of static stress field. In order to calculate stress field from fault slip in a heterogeneous half space, we solve the equation of motion using 3D finite difference method in which the Lamé's constants vary with position. Since fault slip is represented by double couple force system, we apply equivalent body forces in our finite difference grids. First, we calculated stress and ΔCFF field for several simple 2D models to easily understand the effect of heterogeneous medium on ΔCFF field. For two-layered medium, stress is amplified on the region with larger elastic constants. The ratio of the stress amplification is less than the ratio of elastic constants between two layers, which is explained by interaction between two layers. For simplified basin structure and shallow thrust fault below, ΔCFF is larger near the basin and smaller in it than that of uniform structure. We also discuss the effect of heterogeneity near subducting plate on ΔCFF. We found that the subducting plate structure expands the area of positive ΔCFF in the region where outer rise earthquakes occur. Second, we apply the 3D calculation to the 2004 Chuetsu (mid-Niigata prefecture) earthquake (Mw 6.6) and four large aftershocks (MJMA >6). Hikima and Koketsu (2005) and Miyazawa et al. (2005) calculated distribution of ΔCFF for the homogeneous crustal structure and concluded that ΔCFF values just before each aftershock was positive at the hypocenters of the major aftershocks. However, since the structure is complex in the source region, it is important to consider the effect of heterogeneity. We used the fault models estimated by Hikima and Koketsu (2005) and the 3D structure model by Kato et al. (2006) in computation of ΔCFF. The results show that the large aftershocks occurred in the area with positive values of ΔCFF.View full abstractDownload PDF (1491K) -
Nobuyuki YAMADA, Hiroaki YAMANAKA, Kentaro MOTOKI2009 Volume 62 Issue 2+3 Pages 109-120
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSWe investigate the shallow subsurface S-wave velocity structure across the Kego fault at the area of Tenjin in Chuo Ward, Fukuoka, Japan. We observed microtremors for several minutes by small arrays consisting of 7 sensors at 8 sites using wireless LAN data loggers. These sites were situated at the same locations of observation sites by Yamanaka et al. (2005) for aftershocks of the 2005 north-west off Fukuoka prefecture MJ 7.0 earthquake and with K-NET station FKO006. The micro-tremor array data were processed to obtain Rayleigh wave phase velocities in the period range of 0.04-0.4 s by SPAC analysis. Then the 1D S-wave velocity structures having three layers with a Vs of about 130-170 m/s, 220-260 m/s and 800 m/s are estimated from hybrid inversions at each site. The depth to the top of the layer of Vs 800 m/s is only 5 m at the site west of the Kego fault, while the depth is 25-40 m at the sites east of the fault. The layer with a Vs of 800 m/s has a steep slope with a thickness difference of about 20 m at the fault. These 1D velocity structure models show amplifica-tions characterized by dominant peaks in period range of longer than 0.2 s. However, the distribution of the AVS30s for the profiles shows no correlation to those of the ratios of PGA and PGV and the difference of seismic intensity. This indicates the limit of understanding only by 1D structure model and necessity of the consideration of 2D or 3D subsurface structure. The profile for FKO006 at site 08 is different from previous study, which has a deeper depth of the top of the engineering bedrock in our model. These results must be included to explain the observed strong ground motion records of the 2005 earthquake around the central Fukuoka area in short period range.View full abstractDownload PDF (6308K) -
Kimiyuki ASANO, Tomotaka IWATA, Asako IWAKI, Masayuki KURIYAMA, Wataru ...2009 Volume 62 Issue 2+3 Pages 121-135
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSDuring the 2007 Noto Hanto earthquake, a K-NET station ISK005, which is located in Anamizu town and approximately 19 km far from the epicenter, recorded the ground velocity larger than 100 cm/s. A set of observational study is carried out to investigate spatial variation of ground motion amplification characteristics in Anamizu town. Firstly, the spatial variation of the amplification was observed by aftershock observations along a temporary linear seismic array across Anamizu town. In the center of the town, the spectral amplification factor is 10 to 20 between 1 Hz and 2 Hz with respect to the rock site. Then, dense single-station microtremor observations were carried out at 147 sites with average spacing of 100 m in Anamizu town to see the spatial variation in thickness of low-velocity layers. The peak frequency of the microtremor H/V spectral ratio varies from 0.8 to 2.0 Hz in the town. The velocity structure model of shallow portion in Anamizu town is estimated from the mircrotremor H/V spectral ratios. The thickness of low-velocity layers (VS =70 to 100 m/s) changes along the Omata and the Manai rivers. Finally, a three-dimensional ground motion simulation is conducted using the obtained velocity structure model in order to see relationship between shallow sedimentary layers and ground motion amplification in Anamizu town. The peak velocity in the frequency range below 2.5 Hz is three or four times larger in the area around ISK005, where the thickness of low-velocity layers is approximately 10 to 25 m, than that in the rock side. It could be concluded that the ground motion amplification characteristics in the frequency range between 1 Hz and 2 Hz is mainly controlled by the existence of such low-velocity sedimentary layers.View full abstractDownload PDF (2037K)
ERRATA
-
Yosuke YAMAMOTO, Hiroshi TAKENAKA2009 Volume 62 Issue 2+3 Pages 137-138
Published: December 25, 2009
Released on J-STAGE: March 26, 2012
JOURNAL FREE ACCESSDownload PDF (67K)
- |<
- <
- 1
- >
- >|