Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration     

Takeshi Ohmura  Takeo Moriya  Chengshi Piao  Takaya Iwasaki  Toshikastu Yoshi  Shin'ichi Sakai  Tetsuya Takeda  Kaoru Miyashita  Humihito Yamazaki  Kiyoshi Ito  Akira Yamazaki  Yoji Shimada  Katsuya Tashiro  Hiroki Miyamachi 《Island Arc》2001,10(3-4):215-227

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.  相似文献   

Effect of earthquake ground motions on fragility curves of highway bridge piers based on numerical simulation     

Kazi R. Karim  Fumio Yamazaki 《地震工程与结构动力学》2001,30(12):1839-1856

Fragility curves express the probability of structural damage due to earthquakes as a function of ground motion indices, e.g., PGA, PGV. Based on the actual damage data of highway bridges from the 1995 Hyogoken‐Nanbu (Kobe) earthquake, a set of empirical fragility curves was constructed. However, the type of structure, structural performance (static and dynamic) and variation of input ground motion were not considered to construct the empirical fragility curves. In this study, an analytical approach was adopted to construct fragility curves for highway bridge piers of specific bridges. A typical bridge structure was considered and its piers were designed according to the seismic design codes in Japan. Using the strong motion records from Japan and the United States, non‐linear dynamic response analyses were performed, and the damage indices for the bridge piers were obtained. Using the damage indices and ground motion indices, fragility curves for the bridge piers were constructed assuming a lognormal distribution. The analytical fragility curves were compared with the empirical ones. The proposed approach may be used in constructing the fragility curves for highway bridge structures. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Comparison of observed and theoretically calculated seiches of Heda Bay,Japan     

Taku Tada  Yoshinobu Tsuji  Masahito Tsukamoto  Yoshikazu Ueno  Masayuki Kawashima  Takashi Egawa  Yasuhiro Yamazaki 《Pure and Applied Geophysics》1992,138(2):309-322

We carried out observations of sea-level fluctuations simultaneously at three stations on the coast of Heda Bay, Honshu, Japan, using supersonic-type water level gauges controlled by a personal computer. Analyses of the obtained data showed predominant spectral peaks at periods of 7.6, 2.0 and 1.3 minutes for all three stations. Comparison of the observed data with numerically calculated normal oscillation modes of the bay indicates that these three spectral peaks correspond to the theoretical first, third and seventh normal modes of the basin respectively, judging from the results of cross-spectral analyses. The reason for the absence of the remaining normal modes, especially of the second or the lateral first mode of the basin, is briefly considered.  相似文献   

Soil amplification based on seismometer array and microtremor observations in Chiba,Japan     

Lin Lu  Fumio Yamazaki  Tsuneo Katayama 《地震工程与结构动力学》1992,21(2):95-108

Soil amplification characteristics of earthquake ground motion were investigated in terms of peak ground acceleration and transfer function based on the Chiba array observation records. The amplification of peak ground acceleration occurred mostly at the top soft layer and was similar for the three components. The effects of non-linear response of soil deposits on the transfer function were examined. Transfer functions calculated by ensemble average were close for the two horizontal components while those obtained from a smoothing operation were generally different. Both the transfer functions from the ensemble average and the smoothing operation underestimated the gain factor around the natural frequencies. A two-step smoothing procedure was proposed and a rotary spectrum was used to improve the estimation of the transfer function. Microtremors were observed at the locations of the boreholes where seismometers are buried. The power spectrum and spatial coherency of the microtremors were compared with those of the earthquake ground motion. Emphasis was placed on the wavetypes which dominated the peaks in the power spectra.  相似文献   

Orientation error estimation of buried seismographs in array observation     

Fumio Yamazaki  Lin Lu  Tsuneo Katayama 《地震工程与结构动力学》1992,21(8):679-694

Array observation is an efficient tool to investigate various characteristics of earthquake ground motion. However, seismographs used in arrays may involve unexpected errors in their orientations. Methods of orientation error estimation were developed in three-dimensional space by comparing recorded ground motions at a reference point with those at a checking point. A maximum cross-correlation method and a maximum coherence method were proposed and their accuracy was demonstrated. The earthquake ground motions recorded in the Chiba array and in two other arrays were used in numerical examples. Non-trivial orientation errors were detected for all these arrays. The cross-correlation coefficients and the coherence values between two points increased significantly by correcting the estimated orientation errors.  相似文献   

Thermal diffusivity of lunar rocks under atmospheric and vacuum conditions     

Naoyuki Fujii  Masahiro Osako 《Earth and Planetary Science Letters》1973,18(1):65-71

Thermal diffusivity, k, of three lunar rocks (10049 and 10069; Type A, Apollo 11 and 14311; Apollo 14) and a terrestrial basalt (alkaline olivine basalt, Oki-do?go, Japan) was measured under one atmosphere and in vacuum conditions (10^?3 ～ 10^?5 mmHg) in the temperature range from 85 to 850°K. The semi-empirical curve of k =A + B/T +CT³ is fitted to the data in each condition. The porosity of rocks strongly affects the thermal diffusivity at low temperature ( T ? 500°K) in vacuum condition. At 150°K, thermal diffusivity of lunar rocks with porosity of 5.5% (10049) and 11% (10069) at one atmosphere is about 1.7 and 3.2 times of that in vacuum, respectively. The difference between the values at one atmosphere and those in vacuum decreases as the temperature increases. Measurements of k should be made at gas pressures at least lower than 10^?3 mmHg to estimate the value under lunar surface conditions.  相似文献   

On-going orogeny in the outer-arc of the Timor–Tanimbar region, eastern Indonesia     

Yoshiyuki Kaneko  Shigenori Maruyama  Ade Kadarusman  Tsutomu Ota  Masahiro Ishikawa  Tatsuki Tsujimori  Akira Ishikawa  Kazuaki Okamoto   《Gondwana Research》2007,11(1-2):218

The Timor–Tanimbar islands of eastern Indonesia form a non-volcanic arc in front of a 7 km deep fore-arc basin that separates it from a volcanic inner arc. The Timor–Tanimbar Islands expose one of the youngest high P/T metamorphic belts in the world, providing us with an excellent opportunity to study the inception of orogenic processes, undisturbed by later tectonic events.Structural and petrological studies of the high P/T metamorphic belt show that both deformation and metamorphic grade increase towards the centre of the 1 km thick crystalline belt. Kinematic indicators exhibit top-to-the-north sense of shear along the subhorizontal upper boundaries and top-to-the-south sense in the bottom boundaries of the high P/T metamorphic belt. Overall configuration suggests that the high P/T metamorphic rocks extruded as a thin sheet into a space between overlying ophiolites and underlying continental shelf sediments. Petrological study further illustrates that the central crystalline unit underwent a Barrovian-type overprint of the original high P/T metamorphic assemblages during wedge extrusion, and the metamorphic grade ranged from pumpellyite-actinolite to upper amphibolite facies.Quaternary uplift, marked by elevation of recent reefs, was estimated to be about 1260 m in Timor in the west and decreases toward Tanimbar in the east. In contrast, radiometric ages for the high P/T metamorphic rocks suggest that the exhumation of the high P/T metamorphic belt started in western Timor in Late Miocene time and migrated toward the east. Thus, the tectonic evolution of this region is diachronous and youngs to the east. We conclude that the deep-seated high P/T metamorphic belt extrudes into shallow crustal levels as a first step, followed by doming at a later stage. The so-called ‘mountain building’ process is restricted to the second stage. We attribute this Quaternary rapid uplift to rebound of the subducting Australian continental crust beneath Timor after it achieved positive buoyancy, due to break-off of the oceanic slab fringing the continental crust. In contrast, Tanimbar in the east has not yet been affected by later doming. A wide spectrum of processes, starting from extrusion of the high P/T metamorphic rocks and ending with the later doming due to slab break-off, can be observed in the Timor–Tanimbar region.  相似文献   

Preparation of Two New GSJ Geochemical Reference Materials: Basalt JB-1b and Coal Fly Ash JCFA-1   总被引：1，自引：0，他引：1  

Shigeru Terashima  Masahiro Taniguchi  Masumi Mikoshiba  Noboru Imai 《Geostandards and Geoanalytical Research》1998,22(1):113-117

  相似文献   

Air-sea interaction studies at the station occupied by R/V Sirius     

Nandamundi Jagan Rao  A. S. Mascarenhas  Y. Yamazaki 《Boundary-Layer Meteorology》1980,19(3):387-391

The transfer formulas are used to compute hourly values of sensible and latent heat exchanges for the period July 29 to July 31, 1974. Also, values of eddy shearing stress at the sea surface, Bowen's ratio and dissipation of kinetic energy are computed. The data used cover part of the GATE period for station 20 occupied by the Brazilian Naval Ship R/V Sirius in the Equatorial Atlantic (0730 N 4000 W). The variations in the computed values are studied in relation to rainfall and the synoptic situation.  相似文献   

Growth of ringwoodite reaction rims from MgSiO3 perovskite and periclase at 22.5 GPa and 1,800 °C     

Akira Shimojuku  Asmaa Boujibar  Daisuke Yamazaki  Takashi Yoshino  Naotaka Tomioka  Junshan Xu 《Physics and Chemistry of Minerals》2014,41(7):555-567

The growth rate of ringwoodite reaction rims between MgSiO₃ perovskite and periclase was investigated at 22.5 GPa and 1,800 °C for 1–24 h using the Kawai-type high-pressure apparatus. The reaction was likely to proceed by a diffusion-controlled mechanism in which the dominant diffusion mechanism was grain-boundary diffusion. The reaction constant (the width of the ringwoodite reaction rim squared divided by time) determined from these experiments was between 1.3 × 10^?15 and 5.6 × 10^?15 m²/s. A Pt inert marker experiment indicated that the MgO component migrated faster than the SiO₂ component in ringwoodite. Thus, either Mg or O having the slower diffusion rate controlled the reaction. Because previous diffusion studies have shown that diffusion rates of O are slower than those of Mg, O would be a rate-controlling element for ringwoodite formation from MgSiO₃ perovskite and periclase. The growth rate appeared to be too fast to explain the observed topographic rise (~10 km) inside mantle plumes at the 660-km discontinuity.  相似文献