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Publications (10)0 Total impact

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    ABSTRACT: In Osaka, Uemachi Fault is one of the famous active faults. It across the center of Osaka and lies in N-S direction mainly and is more than 40 km in length. Pliocene to Quaternary sediment "Osaka Group" and terrace sediment are found to be deposited in the Osaka Plain and Holocene marine clay layers (Ma13) are covered these plains in order to sea level change. These sediment are very thick layers over 1000m therefore, fault structure are appeared as flexure zone (only vending the strata) and hidden the fault displacement around the surface. The up side on the fault (east side) is modified by erosion and urban development however, many seismic reflection surveys information the fault trace line on a piecemeal basis. One of the subway construction project across the fault, are carried out the many borehole drilling survey around the fault. It is the good case to understand the subsurface structure around fault. GI database collects more than 40,000 boreholes and includes both geological information and soil properties around Osaka by the Geo-database Information Committee of Kansai Area. In this study, we try to show the flexure zone around central Osaka area and decided the site of borehole drilling site and carried out the survey in order to decide the displacement rate of Uemachi fault. About 2500 borehole data exist in the fault area and made many section using GI base. Sakuragawa flexure and Suminoe flexure are considered the secondary fault of Uemachi fault system. These are NE-SW trend and only several km lengths. GI database show the Sakuragawa flexure wind in the plain. We carried out the drilling the borehole and sampling the core samples in the Sakuragawa flexure zone. About 120m deep core sample were analyzed by tephrochronological method, and correlated around borehole data. Ma5, Ma6 and Ma8 marine clay layers are correlated. The result of compare with the neighbor area, the average displacement speed indicates more active the Sakuragawa flexure rather than Uemachi fault zone.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: The Osaka basin surrounded by the Rokko and Ikoma Ranges is one of the typical Quaternary sedimentary basins in Japan. The Osaka basin has been filled by the Pleistocene Osaka group and the later sediments. Several large cities and metropolitan areas, such as Osaka and Kobe are located in the Osaka basin. The basin is surrounded by E-W trending strike slip faults and N-S trending reverse faults. The N-S trending 42-km-long Uemachi faults traverse in the central part of the Osaka city. The Uemachi faults have been investigated for countermeasures against earthquake disaster. It is important to reveal the detailed fault parameters, such as length, dip and recurrence interval, so on for strong ground motion simulation and disaster prevention. For strong ground motion simulation, the fault model of the Uemachi faults consist of the two parts, the north and south parts, because of the no basement displacement in the central part of the faults. The Ministry of Education, Culture, Sports, Science and Technology started the project to survey of the Uemachi faults. The Disaster Prevention Institute of Kyoto University is carried out various surveys from 2009 to 2012 for 3 years. The result of the last year revealed the higher fault activity of the branch fault than main faults in the central part (see poster of "Subsurface Flexure of Uemachi Fault, Japan" by Kitada et al., in this meeting). Kusumoto et al. (2001) reported that surrounding faults enable to form the similar basement relief without the Uemachi faults model based on a dislocation model. We performed various parameter studies for dislocation model and gravity changes based on simplified faults model, which were designed based on the distribution of the real faults. The model was consisted 7 faults including the Uemachi faults. The dislocation and gravity change were calculated based on the Okada et al. (1985) and Okubo et al. (1993) respectively. The results show the similar basement displacement pattern to the Kusumoto et al. (2001) and no characteristic gravity change pattern. The Quantitative estimation is further problem.
    AGU Fall Meeting Abstracts. 12/2011;
  • N. Inoue, N. Kitada, K. Takemura
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    ABSTRACT: In Japan, recent damaging earthquakes did not occurred along obvious active faults in Japan. It is imperative that developing a new method to extract concealed earthquake source faults. The detailed gravity anomaly distribution was published from several gravity databases in Japan. The gravity anomaly indicates the subsurface density distribution. We have investigated the validity of gravity data to extract the information of earthquake source faults. We investigated the relationship between faults and gravity anomaly. Steep gradient zones of short wavelength components of gravity anomaly surrounded several source faults. However, in gravity data process, there are several uncertainty parameters to obtain some depth information. Velocity model and density model of Japan have been constructed for strong ground simulation from various institutes and organizations, and are available to the public. In this study, the three-dimensional density structure was estimated around the earthquake source fault applying a conjugate gradient (CG) method and velocity model. The separation of gravity components was carried out constructed density models from velocity models. Long wavelength component of gravity anomaly was removed by velocity model below 30km. Initial density models around source faults were constructed from velocity model. The inverted subsurface density distributions indicated that large asperity areas corresponded to high-density areas.
    AGU Fall Meeting Abstracts. 12/2010;
  • N. Kitada, N. Inoue, K. Takemura
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    ABSTRACT: Concepts of setting source fault parameters from active faults are discussed for predictions of strong ground motion. Estimation of ground motion plays important rule for the prevention of earthquake hazards. From recent developments in waveform inversion analysis of source fault rupture processes through large earthquakes, it is found that strong ground motion is strongly affected by fault geometry and slip heterogeneity. At the prediction of strong ground motions for scenario earthquakes by active faults, the initial parameters of source faults, such as fault length, direction and dip are thus necessary to be determined. However, the study about relation between source fault and surface rupture, source fault length are certainly longer than surface ruptures (Kitada et al, 2004) and it is difficult to estimate exactly source fault length from the information around surface fault. In case of estimate the source fault, it might be better using spatial underground structure and its information such as gravity. Inoue et al (2007) discussed the relation between source fault and gravity data and suggest the short wave length component of bouguer anomaly have the possibility to show the distribution of density around seismogenic zone. In this study, we consider the length of source fault for scenario earthquake by distribution of the short wave length component of bouguer anomaly. The short wave length component of bouguer anomaly shows the relative high density area and low density area. These areas indicate the same tectonic block. Source fault are distributed not only on the boundary of these block but also in the same tectonic block. Therefore, the source fault seems to be difficult to continue over the other block.
    AGU Fall Meeting Abstracts. 12/2008;
  • N. Inoue, N. Kitada, K. Takemura
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    ABSTRACT: Osaka sedimentary basin in the southwest Japan, includes Osaka Bay and Osaka Plain. Several urban areas are situated around the bay. The basin is surrounded by many active faults. Detailed underground structure plays important role to seismic hazard for urban areas. The basin consists of granitic basement and overlaying thick unconsolidated sediment called as the 'Osaka Group'. Several marine clay layers of the Osaka Group are key layer for stratigraphy and are useful for interpretation of seismic profiles in the basin because marine clay layer is continuous and indicate wide distribution. The bottom of marine clay layer is confirmed clearly in the seismic profile due to high acoustic impedance between clay and coarse sediments. Many detail geological and geophysical information have been accumulated as the results of various survey after the 1995 Kobe Earthquake. These survey revealed underground structure and stratigraphy of Osaka Group of northwestern part of the basin. On the contrary, there are few subsurface information in the southeastern part of the basin. Several survey for estimation of seismic hazard, were carried out in the southeastern part of the basin. In the view point of the stratigraphy, Kansai International Airport (KIX) plays significant role. New second runway was opened at 2nd Aug. 2007. Before constructing the KIX airport, many geological and geophysical surveys have been performed. Accumulated data are basic information of stratigraphy and sedimentary environment in the southern part of the basin. Gravity and tremor surveys were carried out to estimate underground structure beneath the second runway before opening the runway. Deep borehole to basement is drilling in the second runway. The information derived by this borehole provides remarkable information. Recent deep borehole information will modify previous results. Thus, we summarized previous study to compare new results. In this study, we summarized information derived form geophysical surveys. The basement configuration were inferred form compiled result of gravity, tremor and seismic surveys. The seismic profiles around KIX were attempted to re-interpretation. In the poster, we will discuss characteristic of the local sub-basin with the basement configuration and interoperated seismic profiles.
    AGU Fall Meeting Abstracts. 12/2007;
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    ABSTRACT: Tectonic sedimentary basin in Osaka is formed by the activation of fault system with E-W trending fault (MTL and AL) and N-S trending fault (Ikoma fault and Osaka wan fault). This sedimentary basin during Quaternary time is aligned in the central part of Japan (Takemura, 1985). In this basin, thick sedimentary sequences deposited and these are including marine clay deposit. These marine clay deposit are formed at least 15 layers. The stratigraphy of the Osaka Group in the hill areas was summarized on the basis of intercalation of marine clay bed and volcanic ash layers. The stratigraphy of submarine strata at Kansai International Airport is summarized based on correlation of four 400m deep cores obtained during 1994 and 1995, and previous results published by Nakaseko et. al., (1984). In 2007, deep borehole core drilling was carried out at Kansai Airport again. It over 1200m depth and this drilling point is most near central axis in Osaka sedimentary basin. In this study, we are analysis by micropaleontological, tephrochronological and magnetostratigraphical method, and correlated around borehole data. The sequences are called upper group (Kukojima) and lower group (Sennanoki) (Nakaseko et al., 1984). These Kukojima and Sennanoki formations are include marine deposit. In this study, we can analysis deeper part formation and it appeared that deeper deposits are formed in the lake. It means these are non-marine deposit not include marine clay and seems to big lake because of main grain size are silt and sand. In this poster, we would like to show the stratigraphy at center of Osaka basin and its characteristics.
    AGU Fall Meeting Abstracts. 12/2007;
  • N. Inoue, N. Kitada, K. Takemura
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    ABSTRACT: In Japan, a dense seismograph network and developments of data analysis and inversion theory of strong ground motion reproduce strong motion records with high precision. Government and municipalities require estimation of strong ground motion for disaster prevention planning. The estimation of strong ground motion requires to be assumed subjacent source fault with high precision. Active fault information play important role for assuming the source fault. However, recent earthquakes occurred in Japan, such as 2000 Tottori earthquake, did not accompany earthquake faults on the surface. These earthquakes were difficult to estimate subjacent source fault from active fault information. Thus, other information also needs to be assumed subjacent source fault of earthquake without surface rupture. The geological survey of Japan has published gravity database. The database includes the Bouguer anomaly data covering over Japan with 1km grid. Many previous studies discussed the relationship between the Bouguer anomaly and active faults. According to the previous studies, major active faults were along steep gradient zones of gravity anomaly. In the poster, we will present characteristics of the Bouguer anomaly around subjacent source faults in Japan. Subjacent source faults without surface ruptures were surrounded by steep zones of gravity anomaly. Thus, there is a possibility to determinate length of the subjacent source fault from the gravity anomaly. The Bouguer anomaly consists of various depth density sources. In order to analyze subsurface structure, such as surface fault structure, long wavelength of the gravity anomaly is removed as regional trend. We will also discuss the frequency characteristics of the gravity anomaly around subjacent source faults.
    AGU Fall Meeting Abstracts. 12/2006;
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    ABSTRACT: Concepts of setting source fault parameters from surface rupture due to active faults are discussed for predictions of strong ground motion. Estimation of ground motion plays important rule for the prevention of earthquake hazards. From recent developments in waveform inversion analysis of fault rupture processes through large earthquakes, it is found that strong ground motion is strongly affected by fault geometry and slip heterogeneity. At the prediction of strong ground motions for scenario earthquakes by active faults, the initial parameters of source faults, such as fault length, direction and dip are thus necessary to be determined. Among the parameters used for strong ground motion simulation, fault length and dip are derived from information related to active faults. Because these parameters take significant effect on the simulation, much care is required for geological investigation to construct source fault model. Kitada et al (2003) discuss about the relation between source fault and earthquake fault and indicate the possibility to determine the asperity area from surface ruptures. However, we have to determine these parameters using active fault not to earthquake fault. We first studied correlation between earthquake faults and subjacent source faults, such as basic geological estimation of the source fault derived from earthquake fault and active fault. We collected information of earthquake faults (length, dip, displacement and morphology), active faults (distribution around the earthquake faults) and results of waveform inversions (source fault length, dip and distribution of asperities) in large earthquakes. The next studied, we consider the micro tectonic area using geophysical data such as gravity, and estimate source fault. The result of this study, shallow asperity is well correlation to steep gradient zone of gravity anomaly.
    AGU Fall Meeting Abstracts. 12/2006;
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    ABSTRACT: Lake Biwa is the largest freshwater lake in Japan, measuring 22.6 km side by 68 km long and having a maximum depth of 104 m. The lake has a long history from the early Pliocene based on the geological survey and paleogeographical study of lake sediments around Lake Biwa (Kobiwako Group). The sediments revealed the paleoenvironmental change and tectonic events at the convergent margin of the Eurasian plate since early Pliocene times. Deep drillings were carried out 1970's and 1980's in and around present Lake Biwa. These studies showed that the present Lake Biwa Basin bears a sedimentary sequence of about 900 m thickness, which were deposited in lacustrine or fluvial environments. Recently obtained fission-track age of tephra layer at deeper part in the present lake shows the continuous sedimentation of whole lake basin during Quaternary. After correlation of three deep core samples in lake basin and on land by tephrochronological method, we can figure out the paleotopography of the initiation of present Lake Biwa basin using seismic reflection records. Correlation of sequence in lake basin with that on land by precise tephrochronology and sedimentary sequence also shows the sedimentary reply at lake basin and shore to major glacial - interglacial cycles.
    AGU Fall Meeting Abstracts. 12/2005;
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    ABSTRACT: Concepts of setting source fault parameters from surface rupture due to active faults are discussed for predictions of strong ground motion. Estimation of ground motion plays important rule for the prevention of earthquake hazards. From recent developments in waveform inversion analysis of fault rupture processes through large earthquakes, it is found that strong ground motion is strongly affected by fault geometry and slip heterogeneity. At the prediction of strong ground motions for scenario earthquakes by active faults, the initial parameters of source faults, such as fault length, direction and dip are thus necessary to be determined. Among the parameters used for strong ground motion simulation, fault length and dip are derived from information related to surface fault ruptures. Because these parameters take significant effect on the simulation, much care is required for geological investigation to construct source fault model. On the other hand, the development of study on surface faulting (rupture), recurrent interval and probability of occurrence are estimated from assessment of surface rupture. Surface fault morphology provides fault length, its segmentation, displacement, direction and dip. However, relationship between the parameters of the surface rapture and those of the subjacent source fault is still a problem. We first studied correlation between surface faults and subjacent source faults, such as basic geological estimation of the source fault derived from surface fault ruptures. We collected information of surface ruptures (length, dip, displacement and morphology) and results of waveform inversions (source fault length, dip and distribution of asperities) in twelve large earthquakes. They are being carefully investigated from the view point of geology and seismology. The relation among the intended parameters shall be presented in our poster.
    AGU Fall Meeting Abstracts. 12/2004;