衆議院予算委員会(2018年1月29日)において，

文部科学大臣が「文部科学省の中に外部からの入試ミスに対応する専用の窓口を設ける」と発言したとの新聞記事を読んだ．「個別の大学の個々の入試問題の正解を文部省が決める」

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A seismic reflection exploration was conducted in the eastern part of the Arima-Takatsuki Tectonic Line (ATL), Kinki district, central Japan. A survey line with 2700m length was spread across the extension of the ATL that strikes from west to east on the northern border of the Osaka plain. The main aim of this survey is to investigate subsurface structure up to the depth of 1km, which possibly reveals buried faults along the ATL.
A weight-dropping type wave generator was used as a source apparatus. Through data processing by the CMP profiling method, following results were obtained:
(1) The depth of the basement rock is about 150m near the Otokoyama hill (northern section) and about 350m on the Osaka plain side (southern section). There is a large-scale buried fault zone below the survey line. The main fault along the ATL seems to extend eastward to the southern part of the Otokoyama hill beyond the survey location.
(2) Two flexures are discerned in this buried fault zone and they form a graben structure. This structure probably is the topographic expression of ATL (see text for detail).
(3) The movement producing the southern flexure is presumed to have begun after sedimentation of the 50m depth layer in the Osaka plain, based on parallel dipping of each layer at the depth.
(4) The rate of vertical movement mentioned above is estimated to be equal to or greater than those of B class active faults, based on the difference of the basement depths across the southern fault.

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The Great Kanto earthquake, 1923, triggered a catastrophic debris flow which devastated the village of Nebukawa with a loss of 300 to 400 lives. The buried area at Nebukawa is determined by synthesizing eyewitness accounts, photographs, the character of surface soils, etc. The moment of rushing at Nebukawa is estimated at about 5 minutes after the mainshock onset from the eyewitness accounts and aftershock records. The temporal change in topography in the mountain region is investigated by comparing topography maps prior and after the earthquake, and a probable source of the debris flow is assumed at a large depressed area, Obora about 4km upstream Nebukawa. The grain-size distributions of the debris-flow deposits and those of mountain soils are also consistent with this assumption.

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In a southeastern part of Kyoto basin, we observed the reflected waves from the basement some hundred meter deep by using air gun as a source and signal-enhancement technique by stacking. Both the velocity up to and the depth of the basement were greater than those previously given by KITSUNEZAKI et al. (1971). It is useful to use reflected waves for exploring sharp boundary, such as a basement, because it is relatively easy to observe them at far distances where surface waves are not disturbing. Synthetic seismograms also support the prospect to detect reflected phases from a sharp boundary.

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The Obaku fault is an active fault bounding the south-eastern edge of the Kyoto Basin. The location and underground structure of the fault has been investigated by means of electric-resistivity survey (ρ_a-ρ_u method), borings and trench excavation. The findings are discussed by comparing existing information on the fault obtained by seismic surveys, observation of microtremors and γ-ray measurements with observation of outcrops made in a construction-work area near the investigated site. This study reveals that the electrical method is effective for detecting discontinuities at shallow depths, and also other geophysical methods have their merits at various stages of investigations of active faults.

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Seismic reflection survey was conducted in Yokooji, the middle of the Kyoto basin in 1992. The reason why this site was chosen is that this is just the place where UEMURA and NAKATSUKA (1992) inferred a buried fault (named Yokooji fault) from wells' data. According to them, there is a systematic sudden change in depth of the lower sand and gravel layer which is widely spread at the depth of about 10m in the middle of the Kyoto basin. They have suggested that its change was caused by a buried fault running from east to west, which is likely a sub-fault of the Arima-Takatsuki tectonic line.
Though no topographical feature is found in this area, such a buried fault can have a high activity when the movement has begun in the recent past. From the disaster prevention point of view, it is hence important to investigate the subsurface structure of the possible fault to determine its activity even in the middle of a basin. It also can provide some information of the basin's growth history which leads to a better understanding of the Quaternary tectonics.
An air gun was used as a sourse apparatus. Through the data-processing for the CDP profiling, geological information of the site was obtained as follows:
(1) A velocity model up to the basement is obtained. The depth of the basement is estimated as 400-500m.
(2) A few reflections from interfaces in the Osaka group (unconsolidated sediments above the basement) are discerned. The key layer (Ma3) at 200m-300m below the ground surface is found to be consistent with the result of existing boring surveys. Considering Ma3 is 0.9 million years old, it is estimated that the middle of the Kyoto basin has been subsiding at the rate of 0.2m-0.3m/1000 years.
(3) From the revealed shape of the interfaces in the Osaka group, neither a large fault nor a large fold is found at the very position where UEMURA and NAKATSUKA (1992) suggested a buried fault.

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Seismic reflection survey was conducted in Fushimi-Momoyama, Kyoto in November 1990. A linear array was spread across the extension of the Momoyama fault, which strikes from north to south at the eastern edge of the Kyoto basin. The length of the survey line was 1200m. A main aim of this survey was to investigate subsurface structure up to the depth of about 1km which possibly reveals the activity of the growth history of the Momoyama hill as well as the Momoyama fault. Seismic reflection survey is capable of imaging sedimentary layers because of its relatively short wavelength. A hydraulic weight dropping machine named “Yuatsu impactor” was used as a source apparatus. Through the data-processing by the CDP method and reverse time migration, the following results mainly were obtained.
(1) The basement and some sedimentary layers were identified. They are bent beneath the surveyline and their maximum dip is about 20 degrees to the west. The depth of the basement is about 300m beneath the Momoyama hill (east side) and about 600m in the Kyoto basin (west side).
(2) From the change of the dip in each layer, we found that the movement forming the Momoyama hill began less than 0.9 million years ago. Additionally, from the depth difference of each layer, the relative velocity of faulting since then is estimated at about 0.2m per 1 thousand years. This indicates that the activity of this movement is B class as noted in “Active Faults in Japan” (1991).

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This study is intended to clarify the mechanism of earthquake damage to embankments and slopes. Mechanisms, including 1) sliding of a mass, 2) collapse of an embankment, 3) failure of a slope of cohesive and of non-cohesive materials, 4) fissures on an embankment, 5) settlement of an embankment and 6) phenomena related to liquefaction of soil, are studied referring to examples of actual damage of the type. Sliding of a mass can most appropriately be explained by the block sliding theory by NEWMARK. The collapse of an embankment may also be explained by the theory with a little modification in the assumption for mechanical properties of soils. The mechanism of failure of a cohesive material is essentially the same as that of 1) or 2); that of a slope of a cohesionless material is, however, different and is correlated with the acceleration of the ground motion. The fissures on an embankment can be divided into three groups which are connected with either sliding or displacement of a part adjacent to the slope of the embankment or a local subsidence of the embankment. The settlement of an embankment occurs in regions of earthquake intensity of higher half of IV to V in the J. M. A. scale. In case of liquefaction of soils, flow of materials of an embankment as a liquid or subsidence due to decrease in volume of an embankment or an underlying layer may occur.
One of the most important factors which may influence the damage is the unbalance of acting forces due to the gravity, and the resistance to failure decreases noticeably with increase in inclination of the slope of an embankment or a cutting. The change in mechanical properties of soils during vibration or failure is another important factor for the damage and it should be taken, in general, into consideration to understand the damage. The number of effective pulses for damage is also important in estimating the extent of the damage. The number is estimated in the paper as 7-40 or moreover based on considerations on the mechanism of the damage or seismograms of destructive earthquakes.

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Shallow subsurface structure around Hino River in the south-east shore of Lake Biwa was investigated by means of seismic reflection survey. The target area on the western margin of a seismic quiescent zone between the lake and the Suzuka range includes a belt of steep gradient of Bouguer anomaly which inclines west.
Survey lines were designed, one on the east and another on the west of Hino River, in order to determine the subsurface structure beneath the steep gradient belt of gravity. Time sections were constructed by the Common Depth Point (CDP) method and followed by the frequency-wavenumber (F-K) migration to discuss the subsurface structure in detail.
In the time sections of two survey lines, a horizon “A”, which is smoothly continuous, and another horizon “B”, which is inclined to south-west are recognized. The “A” horizon is considered to be a reflective plane in the Biwako-group, Quaternary deposits, by referring to the deep drilling log available in the neighborhood of the survey line. The “B” horizon is inferred to be an uncomformity boundary between the Biwako-group and the basement rocks because no continuous reflector can be found thereunder. Since the “B” horizon exibits a buried valley in the center of the western survey line and an south-westward inclination through the eastern survey line, this structure may be a remnant channel which used to run SE to NW during the erosive period of this area.
It is noticeable that the “A” horizon shows onlap boundary relation against “B” horizon in the center of the eastern survey line. This suggests that this area turned into subsidence after the erosive period.
No active faults were found above the “B” horizon through this survey. Hence low seismicity around the target area is likely inherent in character.

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We develop a method to determine the boundary shape of basin structures using seismograms observed on the surface through a waveform inversion scheme. Our method is based on the fact that seismic waves observed at stations on the surface are affected not only by the local structure beneath the observation point but also by the whole basin structure. This fact suggests a possibility to determine the boundary shape by using the seismic records at only a few surface stations. This paper examines numerically how to determine the boundary shape from observed records on the surface in the case of the two dimensional SH problem. For simplicity, we parameterize only the boundary shape, i. e. the thickness variation of the sedimental layer. This inversion is performed iteratively since the problem we deal with is a non-linear inverse problem. When an appropriate model is given, we can evaluate the boundary shape accurately even though the waveform data at only a few surface stations are given.

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The scattering and attenuation properties of S-coda waves are investigated by analyzing seismic waves recorded during the off Ito earthquake swarm in 1989. First, on the basis of the analysis of tripartite array data, it is shown that coda waves of 3 earthquakes are propagated from all directions and their apparent velocities are estimated. Next, the values of Q^-1 of coda waves, Q_C^-1, are estimated in six frequency bands from 1.0 to 32.0Hz for two lapse time windows by using the single backscattering model. By fitting Q_C^-1 from the long lapse time window to the power law frequency dependence, Q_C^-1∝fⁿ, the power n is estimated as -0.81 for the band covering 1.0 to 16.0Hz. The values of Q_C^-1 for the two lapse time windows are compared in four frequency bands from 2.0 to 16.0Hz. While a good agreement is obtained in the 2.0Hz band, discrepancy is large in the 16.0Hz band. In addition, apparent velocities of coda waves are obtained within ±0.5km/s of the phase velocities of Rayleigh waves predicted for the subsurface structure over the frequency range from 2.0 to 4.0Hz. These results suggest that coda waves at around 2.0Hz contain backscattering surface waves and that the values of Q_C^-1 reflect the attenuation properties in the shallow crust exclusively. On the other hand, for frequencies higher than 4.0Hz a decrease of the values of Q_C^-1 with lapse time may be attributed to a decrease of Q^-1 with depth. We compare Q_C^-1 for earthquakes recorded before and after the two major events in the swarm, the July 9 Ito-Oki earthquake (M5.5) and the July 13 volcanic eruption. No appreciable temporal change of Q_C^-1 is found associated with these events. The heterogeneity size or the maximum crack length is estimated to be longer than 0.6km from the frequency at which Q_C^-1 takes the peak value.

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