The greater part of curved ship-hull is consisted of assembly of thin shallow shells reinforced with stiffeners.
Static strength of shells and stiffened shells is analyzed by means of the finite strip method¹⁾ proposed by author in addition to the Fourier's analysis and the effects of stiffeners fitted for the purpose of stress reduction on shell plate are clarified. Therewith, the practical formulas for determining optimum stiffener for given shell are obtained.
As results of investigation on stiffened shells, it is found that the less stiffeness of shell itself, the more effective of stiffener for strength of shell structure for the case of fitting a few stiffners.

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Tsushima Island is covered largely by Tertiary Taishu Group consisting mainly of thick alternation of major amount of shale and thin sandstone beds, which shows abundant NE-SW trending folds throughout the island. The group is intruded by many igneous dikes and stocks having the same trend. To the west offshore of the island large N-S trending faults are recognized (after Tomita et al., 1974, 1975).
Based upon field data, the authors examined a distributional characteristics of wavelength, amplitude and plunge of the folds, and found the following facts; (1) the island can be divided into two tectonic provinces of a short-period folding province in the northwest and a long-period folding province in the southeast which are bounded by a NE-SW trending tectonic line. (2) the short-period folding province can be further divided into two tectonic units of a medium-period folding sub-province in the west and a long-period folding sub-province in the east which are bounded by a N-S trending tectonic line. (3) the first order trend surface of the folds in these three tectonic units have different dip and strike each other. Because any remarkable fault is never found along the boundaries among each unit, the tectonic lines must represent the axis of two different flexures of the Taishu Group.
Based upon these results, the authors reprocessed and reinterpreted the gravity data, and came to the conclusion that the NE-SW trending axis of the flexure reflects a step-like structure of high-density basement, which is inferred to consist of gneissose rocks or weak-metamorphosed Palaeozoic System, and the N-S trending axis of the other flexure corresponds to the axial zone of the basement flexure, a inclination of which is nearly horizontal in eastern side and about 20 degrees toward west in the western tectonic units.
The complicated fold system of the Taishu Group is an reflection of structural movement resulted from the older NE-SW folds and younger N-S flexures of the Taishu Group and the basement.

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An active fault that develops in a plain is often covered with a weak sand layer. The large-scale fault slip in a bedrock may spread to the surface and will frequently generate a fault rupture. Depending on the case, the fault slip occasionally appears on the surface as a fault flexure. This study identifies the reason for the formation of a fault flexure on the sand layer using numerical simulation. The simulation technique employs the constrained interpolation profile (CIP) method a new technique that overcomes the flaws such as numerical diffusion in the finite difference method. Furthermore, we study the influence of fault parameters on the configuration of the fault-related flexure. The experimental results indicate that the fault-related flexure is generated when a shear-zone migration occurs in the sand. We ascertain that the velocity of the shear-zone migration is proportional to the velocity of the fault slip. As a result, we conclude that this migration is probably one of causes of fault-related flexure generation at faulting. Therefore, we conclude that the velocity and acceleration of the fault slip affect the configuration of the fault-related flexure.

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The 2018 northern Osaka Prefecture earthquake (M_j 6.1) was caused by ruptures of blind strike-slip and reverse faults. The earthquake was moderate in size but caused severe damages to the northeastern part of the densely populated Osaka metropolitan area. The epicentral area is located at a junction of east-trending strike-slip faults and north-trending reverse faults. In order to better understand the geologic setting of the earthquake, we conducted an integrated analysis of published seismic reflection profiles and gravity basement structure map together with geomorphic and geologic data. We interpreted that the Arima-Takatsuki Tectonic Line fault zone extends about 9 km further to the east of the geomorphologically mapped surface trace. We also found that the Hirakata flexure extends northeast beneath the Yodo River as a southeast-dipping reverse fault. The area bounded by the Arima-Takatsuki Tectonic Line fault zone and northeast extension of the Hirakata flexure is a northeast-trending graben which we call here as the Yodogawa graben. The 2018 earthquake occurred beneath the graben but the ruptured faults do not offset gravity basement. The identification of the previously unknown active faults warrants further geological and geophysical studies of the faults in this highly urbanized area of the Osaka Plain.

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In this paper, a method using finite strip method to calculate the natural vibration of the stiffened shell which is often seen in ship structure is proposed. The results by this method are compared with the experimental results and the results calculated by applying Rayleigh-Ritz method, and a good agreement can be seen between them in regard to the natural frequency. It is also found that the proposed method can calculate the more accurate stress distribution than the method applying Rayleigh-Ritz method.

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The Nara Basin, the eastern rim of which is bordered by N-S trending faults and flexures, is located in the central part of the Kinki Triangle.
The writers have investigated displaced topographies and deformed strata to understand the nature of neotectonics of the area. The findings are summarized as follows.
1) Several river terraces distribute widely along the eastern rim of the Nara Basin. They are classified into five according to their age: namely Kokuzoyama, Narasaka, Rokuyaon, Wani and Ichinomoto surfaces in descending order. The deposits of the Ichinomoto surface are dated 18, 410±920y.B.P. (GaK-9709) by ¹⁴C method.
2) Terraces have been deformed along the Tenri and Narasaka flexures. These flexures are surface expressions of the reverse faults in bed rocks. The average rate of the vertical component of the deformation is calculated 0.07-0.30m/10³y. for the Tenri flexure and 0.13-0.17m/10³y. for the Narasaka flexure.
3) The Tenri flexure occurred after the formation of the Kokuzoyama surface, and simultaneously the Sanbyaku fault, which borders the basin in the west and the mountains in the east, became inactive. This implies that the fault movement migrated from the mountain foot toward the basin in middle Pleistocene.

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Continuous observations of the earth tides with Verbaandert-Melchior pendulums at Akagane Observation Station was commenced in 1967. Hourly reading values of the records have been sent every three months to the International Centre of the Earth Tides at the Royal Observatory of Belgium. On the other hand, the data have beenn analyzed successively by means of Lecolazet's method in our observatory.
Tidal factors of four main waves were determined by the analysis, but they were very peculiar values in comparison with that of global values of 0.60.8. As shown in Table II, γ of the diurnal waves were larger than 1.0, on the contrary, that of the semidiurnal waves were too small. After detailed examinations it was considered to be affected mainly by the oceanic tides, because the observation station was located merely 50 kilometers distant from the pacific coast.
Attraction (A) of oceanic waters, the flexure (B) of the earth's crust due to the water and the potential variation (C) due to the earth's flexure were calculated using co-tidal maps under the following assumptions.
For the first approximation, the Boussinesq's formula for solving the deformation of the earth due to surface load was applied. Then, the total oceanic term was expressed as, A+B+C =(1+υ+ε)A. The value of v increases proportional to the depth, and it iss expressed as the hyperbolic function,
υ=C₂/γ+C₁,
where r denotes angle distance in degree between the observation station and the point mass. C₁ and C₂ depend on underground structure and distribution of the rigidity.
In this paper, the values of C₁, C₂ and ε are adopted as 12.6, 3.0 and 0.5 respectively, which were determined by Dr. Nishimura.
Consequently, the total oceanic term was expressed as follows,
A+B+C=(1+12.6/γ+3.0-0.5)·A.
The corrected values of ?A for M₂ wave became larger than that of previous values as shown in Table IV. The first approximation shows good result, and further investigations for local indirect effect of oceanic tides are now continued.

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京阪奈丘陵の大阪層群は全層厚300m以上であり, 層相によって下位より登美ヶ丘累層 (鹿畑礫層・東畑互層), 田辺累層 (水取礫層・柘榴互層), 精華累層, 招提累層に区分できる. 挾まれる火山灰層のうち, 下位より北谷, 東畑, 普賢寺, 同志社, 煤谷I, 煤谷II, ピンク, アズキ, 八町池, カスリの各火山灰層が, 海成粘土層はMa1, Ma2, Ma5, Ma6, Ma8層が, それぞれ鍵層として有効である. 本地域には, 大阪層群の標準層序のうち, 三ツ松火山灰層のやや下位よりMa8層のやや上位の層準が分布している. 本地域は大阪層群の地質構造によって, 普賢寺以南, 交野断層-長尾以北, 交野断層-長尾間の3地域に区分され, 交野断層-長尾は, 大阪層群の堆積盆地としての奈良盆地と大阪盆地を境する主要構造である.

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 We should understand the earthquake potential in and around Quaternary fault zones, in view of recent destructive inland earthquakes at previously unknown active fault zones in Japan. The Senpoku Plain and its surrounding areas are characterized by high seismic activity in northeast Japan, highlighted by four destructive earthquakes, M 6.8 in 2008, M 6.4 in 2003, M 6.5 in 1962, and M 7.0 in 1900, which occurred during the past 100 years, although few geomorphic features indicate active faulting. A comprehensive survey was conducted on the tectonic geomorphology in the area to understand the structural and geomorphic expression of the Ichinoseki–Ishikoshi Flexure Line (IIFL), which suggests Quaternary activity. Geological and geomorphical mapping shows that the IIFL is located between the Kitakami Lowland Fault Zone and the Senpoku Plain. The IIFL extends about 30 km from Isawa to Ishikoshi with a slightly sinuous trace. A high-resolution seismic reflection profile and a gravity profile define the subsurface geometry of the IIFL. The IIFL is interpreted to be a steeply west-dipping reverse fault. The Pliocene Kazawa and Yushima Formations typically dip 40° to 20°E along the IIFL, and are overlain by the Pleistocene Mataki Formation, which becomes thinner toward the fold axis of the IIFL, and their dips decrease progressively upward. This suggests that the Mataki Formation was deposited concurrently with fault activity of the IIFL. Fission-track dating of a tuff layer within the uppermost section of the Kazawa Formation indicates that active reverse faulting of the IIFL began at about 2 Ma. At least 280 m of the tectonic uplift is consumed by active faulting and the average uplift rates are estimated to be 0.14–0.08 mm/yr. Vertical separations of Hh surface are about 15 to 40 m. Heights of fold scarps on L1 surface are about 2 m. Their ages are determined to be 0.4–0.5 Ma for Hh and 24–12 ka for L1, respectively. Therefore, the Quaternary average uplift rates of the IIFL are estimated to be 0.03–0.17 mm/yr. Quaternary activity of the IIFL is weak, but there are differences in the magnitude of dissection in the Iwai Hills between the hanging-wall and the footwall of the IIFL.

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本研究では，都市圏活断層図(国土地理院)，長期評価(地震本部) から各種データを収集し，日本全国の帯上の土地利用について334 箇所を対象に調査を行った。帯の傾斜でみると，0◦ ≦ 傾斜< 5◦ では28% を占めていた住居・商業建築物が20◦ ≦ 傾斜< 25◦ では9% に減少し，0◦ ≦ 傾斜< 5◦ では11% に留まっていた森林が20◦ ≦ 傾斜< 25◦ では68% まで上昇するなど，傾斜の変化とともに土地利用の特徴にも変化が見られた。各地域における傾向を分析すると，北海道地方や東北地方，中部地方では他の地域に比べて農業などの第1次産業における生産量が大きいが，帯上の土地利用でも同様の傾向が出ており，それぞれ農業用地として37%，41%，43% が利用されていた。その一方で，関東地方や近畿地方などは人口が集中している都市を抱えていながら，住居・商業建築物や公共建築物などの人的利用が見込まれる施設の割合が59%，61% と非常に高くなっていた。政令指定都市に位置する帯に絞ってみると，帯上の土地の70% が人的利用の見込まれる施設に使用されていた。

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The terraces along the Hirose river well-develop especially in the Ayashi basin, and in the urban area of Sendai. They, however, often disappear in the gorge between the two areas mentioned above. These terraces have been studied by several researchers. The present writer tried the re-examination of terrace classification and correlation especially from the viewpoint of the influence of the crustal movement on the terrace surfaces.
In addition to the tephrochronological method, the thickness of the weathering crust of terrace gravels is used as an index for terrace classification and correlation, as proposed by Akojima et al. (1971).
The present writer's terrace classification and correlation is shown in Fig. 1. The writer found displacements of the terrace surfaces in the Ayashi basin and in Sendai which suggest the continuous crustal movements (Fig. 2). It is considered that these displacements are due to flexures with axes of N-S direction in the Tertiaries. Such crustal movements are more remarkable in the upper stream area, and seem to have been continuing with uniform velocity.

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We have examined the surface geology and tectonic landforms of the Hoshiyama Hills and its surrounding areas in the Fujikawa-kako Fault Zone (FKFZ), central Japan. The FKFZ is generally regarded as a collision zone between the Honshu Arc, mainly composed of the pre-Neogene accretionary and the Neogene collisional complexes of South Fossa Magna region, and the Neogene Izu-Bonin Volcanic Arc on the Philippine Sea Plate. This zone is believed to be the most active and dangerous area of Japan in association with violent earthquakes. One of the keys to understand the activities of this zone since the Pleistocene is to reveal the geologic structures of the Hills, as well as the characteristics of the Omiya and Iriyamase Faults along the northeastern and southeastern margin of this Hills, respectively. Our surface geological survey reveals that the upper Lower-lower Middle Pleistocene Ihara Group, main constituent of the basement of the Hoshiyama Hills, has complicated structures including several-hundreds meters scale steeply-dipping beds without distinctive preferred orientations. The structures also include chevron-shaped anticlines and flat synclines, suggesting that the E-W horizontal shortening due to fault-related foldings was the main cause of their formations. The flexure-landform associated with the Omiya Fault clearly suggests that the Fault, previously believed to be a high-angled normal fault dipping toward NE, is a reverse fault dipping toward SW. However, the landform around the Iriyamase Fault, also believed to be a NW dipping reverse fault, show no evidence of its existence. Finally, we have summarized the tectonic and volcanic events in and around the FKFZ since about 1 Ma. These results suggest that the Quaternary tectonics and seismic activities of the FKFZ should be necessary to re-evaluate based not only on the surface geological and landform data but also on the subsurface geological structures now being poorly known.

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The 2011 off the Pacific coast of Tohoku Earthquake generated huge tsunami waves causing severe damage to coastal areas throughout the Tohoku region. Tsunami waves also affected the seafloor and biological conditions in coastal areas. This research project (Tohoku Ecosystem-Associated Marine Sciences, TEAMS) supported by Japan Ministry of Education, Culture, Sports, Science and Technology has been conducted to analyze changes in marine ecosystems in areas off the Tohoku coast after the earthquake. Bathymetric data accumulated using acoustic instruments not only provide a distribution of sea debris and existing artificial fish reefs; they also provide basic information related to the various scientific uses of the project results. Several research efforts were undertaken in and around Otsuchi Bay before the earthquake. This area is regarded as an important area for this project. We conducted detailed bathymetric and subbottom profiling surveys off Otsuchi Bay. The results obtained from the surveys indicate the existence of a narrow channel extending west‒east in our observation area. Sub-bottom profiling data show that the channel structure is very shallow: less than 2 m. This channel only erodes the uppermost layer (Unit 1). Therefore, these results imply that this channel structure was formed in newer geological time. Unit 1 covers the lower layer (Unit 2) with disconformity. Therefore, unit 1 probably formed after Unit 2 was eroded at the time of marine regression. Unit 1 becomes thinner toward offshore. It became difficult to recognize Unit 1 at 140‒150 m depth around 8 km west of Line A. Unit 2 exists throughout Line A. This difference might be attributable to their different distances from the shoreline, which supplies sediment, or to different sea floor inclination angles. Moreover, a buried flexural structure was detected clearly at the lower portion of Unit 1 and Unit 2 around 2.7 km from the north of Line B. However the seafloor is almost flat. Therefore, we concluded that the flexural structure was formed during the formation of Unit 1. These flexure structures imply the existence of a deeper buried fault structure. Therefore, studying not only the lineament of bathymetry but also the sub-seafloor sedimental structure is important.

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