Sources and depositional processes of tsunami deposits: Analysis using foraminiferal tests and hydrodynamic verification     

Jun‐Ichi Uchida  Osamu Fujiwara  Shiro Hasegawa  Takanobu Kamataki 《Island Arc》2010,19(3):427-442

Foraminiferal tests are commonly found in tsunami deposits and provide evidence of transport of sea floor sediments, sometimes from source areas more than 100 m deep and several kilometers away. These data contribute to estimates of the physical properties of tsunami waves, such as their amplitude and period. The tractive force of tsunami waves is inversely proportional to the water depth at sediment source areas, whereas the horizontal sediment transport distance by tsunami waves is proportional to the wave period and amplitude. We derived formulas for the amplitudes and periods of tsunami waves as functions of water depth at the sediment source area and sediment transport distance based on foraminiferal assemblages in tsunami deposits. We applied these formulas to derive wave amplitudes and periods from data on tsunami deposits in previous studies. For some examples, estimated wave parameters were reasonable matches for the actual tsunamis, although other cases had improbably large values. Such inconsistencies probably reflect: (i) local amplification of tsunami waves by submarine topography, such as submarine canyons; and (ii) errors in estimated water depth at the sediment source area and sediment transport distance, which mainly derive from insufficient identification of foraminiferal tests.  相似文献   

Thematic Section: Bridging the gap separating geological studies and disaster mitigation countermeasures for earthquakes and tsunami
Preface     

Kazuhisa Goto  Osamu Fujiwara  Shigehiro Fujino 《Island Arc》2010,19(3):371-373

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Geological records of storms,tsunamis and other extreme events          下载免费PDF全文

Shigehiro Fujino  Kazuhisa Goto  David Tappin  Osamu Fujiwra 《Island Arc》2016,25(5):303-304

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Geodynamic evolution of a forearc rift in the southernmost Mariana Arc     

Julia M. Ribeiro  Robert J. Stern  Fernando Martinez  Osamu Ishizuka  Susan G. Merle  Katherine Kelley  Elizabeth Y. Anthony  Minghua Ren  Yasuhiko Ohara  Mark Reagan  Guillaume Girard  Sherman Bloomer 《Island Arc》2013,22(4):453-476

The southernmost Mariana forearc stretched to accommodate opening of the Mariana Trough backarc basin in late Neogene time, erupting basalts at 3.7–2.7 Ma that are now exposed in the Southeast Mariana Forearc Rift (SEMFR). Today, SEMFR is a broad zone of extension that formed on hydrated, forearc lithosphere and overlies the shallow subducting slab (slab depth ≤ 30–50 km). It comprises NW–SE trending subparallel deeps, 3–16 km wide, that can be traced ≥ ∼30 km from the trench almost to the backarc spreading center, the Malaguana‐Gadao Ridge (MGR). While forearcs are usually underlain by serpentinized harzburgites too cold to melt, SEMFR crust is mostly composed of Pliocene, low‐K basaltic to basaltic andesite lavas that are compositionally similar to arc lavas and backarc basin (BAB) lavas, and thus defines a forearc region that recently witnessed abundant igneous activity in the form of seafloor spreading. SEMFR igneous rocks have low Na₈, Ti₈, and Fe₈, consistent with extensive melting, at ∼23 ± 6.6 km depth and 1239 ± 40°C, by adiabatic decompression of depleted asthenospheric mantle metasomatized by slab‐derived fluids. Stretching of pre‐existing forearc lithosphere allowed BAB‐like mantle to flow along the SEMFR and melt, forming new oceanic crust. Melts interacted with pre‐existing forearc lithosphere during ascent. The SEMFR is no longer magmatically active and post‐magmatic tectonic activity dominates the rift.  相似文献   

Integrated magnetobiochronology of the Pliocene–Pleistocene Miyazaki succession,southern Kyushu,southwest Japan: Implications for an Early Pleistocene hiatus and defining the base of the Gelasian (P/P boundary type section) in Japan     

Motoyoshi Oda  Shun Chiyonobu  Masayuki Torii  Takashi Otomo  Jumpei Morimoto  Yuri Satou  Hiroshi Ishikawa  Matsuaki Ashikawa  Osamu Tominaga 《Journal of Asian Earth Sciences》2011,40(1):84-97

An integrated magnetobiochronology of the Miyazaki Pliocene–Pleistocene succession in the Miyazaki area, southwest Japan, was established using planktic foraminiferal and calcareous nannofossil biostratigraphy together with paleomagnetic data. The upper Miyazaki succession in the northern Miyazaki region can be divided into the Takanabe, Hisamine (redefined), and Higoyashiki (new) Formations, in ascending order. A depositional hiatus between the Hisamine Formation and the Takanabe and/or older formations was also identified based on integrated magnetobiostratigraphy from five sections including the Nagatani River (NGT) section through the uppermost Miyazaki succession. The hiatus, herein called the Hisamine unconformity, is equivalent to the Kurotaki unconformity between the Miura and Kazusa groups of the Boso Peninsula in central Japan. The depositional hiatus recognised in the lower Pleistocene of Pacific coastal areas in southwestern and central Japan may have resulted from tectonic activity associated with a change in the subduction direction of the Philippine Sea plate, which commenced prior to ca. 2.2 Ma. The youngest unit just below the hiatus is the upper part of the Takanabe Formation in the NGT section. The NGT section represents the continuous Late Pliocene to earliest Pleistocene sequence including the Gauss/Matuyama boundary and is here proposed as the type section for the Pliocene/Pleistocene boundary in Japan, which the IUGS ratified as the base of the Gelasian in 2009.  相似文献   

3-D internal architecture of methane hydrate-bearing turbidite channels in the eastern Nankai Trough, Japan     

Satoshi Noguchi  Naoyuki Shimoda  Osamu Takano  Nobutaka Oikawa  Takao Inamori  Tatsuo Saeki  Tetsuya Fujii 《Marine and Petroleum Geology》2011,28(10):1817-1828

The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels.  相似文献   

莱芜市独路石墨矿矿床地质特征及矿床成因     

李雷  赵体群  周广海  李世达  柳清丽  王强  张相峰  李鹏辉  蒋波  沙启文 《山东地质》2013,(10):27-30

独路石墨矿位于泰山一沂山断隆泰山凸起东端,矿床赋存于新太古代泰山岩群雁翎关组之中。矿床内发育6个石墨矿体,呈层状、似层状产出。矿石类型主要为含石墨黑云变粒岩型,石墨矿石属鳞片状晶质石墨矿,石墨矿物片径细小。矿石样品固定碳含量一般为6％～8％,在省内属较高品位。原岩为富含有机质的杂砂岩——沉积凝灰岩,经中低压变质相系变质作用形成石墨矿,属沉积变质成因。找矿标志明显,外围及深部找矿前景良好。独路石墨矿的发现填补了鲁西地区石墨矿空白。  相似文献   

近百年中国、北半球和南半球气温内在结构比较（I）   总被引：3，自引：0，他引：3  

刘式达  陈炯  刘式适 《应用气象学报》1999,10(Z1)

气温气候资料是一个含有月、年、十年、百年等时间尺度的分形客体．大尺度上是冷暖之分,而每个冷（或暖）又分为较小尺度上的冷暖,形成层次结构．利用它的子波变换的尺度α－时间位置ｔ０表述,可以构造出分段线性一维映射动力系统,这个映射表征气候的层次结构,反映气候变化的突变点时间位置的规律和标度不变性．文中讨论了构造一维动力映射的基本原理,并以中国气温为例进行了验证．  相似文献   

近百年中国、北半球和南半球气温内在结构比较(Ⅱ)   总被引：2，自引：0，他引：2  

陈炯  刘式达  刘式适 《应用气象学报》1999,(Z1)

气温序列的变化不仅包含月、季、年、百年等不同的时间尺度,而且具有一定的局域性,全球、南半球、北半球和中国的气温变化各不相同．文中利用子波变换极大值线表征的突变点来构造一维映射动力系统的基本原理,研究中国、北半球和南半球气温的异同,从而映证了气候变化的局域性  相似文献   

Effects of fluid displacement pattern on complex electrical impedance in Berea sandstone over frequency range 104–106 Hz          下载免费PDF全文

Yi Zhang  Hyuck Park  Osamu Nishizawa  Tamotsu Kiyama  Yu Liu  Kwangseok Chae  Ziqiu Xue 《Geophysical Prospecting》2017,65(4):1053-1070

To better understand the effect of fluid distribution on the electric response of rocks saturated with oil and brine, we conducted experimental studies on the complex electrical impedance in a Berea sandstone, together with in situ acquisitions of oil distribution images employing a high‐resolution medical X‐ray computed tomography. We performed two tests of brine displacement by oil under high (10 MPa) and low (5 MPa) pressures, which were accompanied by fingering and stable displacement patterns, respectively. The measured complex impedance data were fitted to the Cole model to obtain the resistance, capacitance, peak frequency of the imaginary impedance, and the exponent α of the rock–fluid system. With increasing oil saturation, the resistance showed an increasing trend, whereas the other three parameters decreased. The fingering displacement exhibited lower resistance and capacitance than the stable displacement. The analysis of the resistance changes using a simple parallel connection model indicates that there are more components of residual brine in parallel connections in the fingering pattern than in the stable displacement pattern at the same saturation. We also interpreted the normalised changes in the capacitance (or apparent dielectric constant) with respect to the oil saturation via an analysis of the shape factor of fluid distribution based on the Maxwell–Wagner–Brugermann–Hanai model. The changes in the shape factor suggest that the pinch‐off of the brine in parallel connection by the oil is a dominant mechanism reducing the capacitance. In the stable displacement, most of the connections in the brine phase are immediately pinched off by oil displacement front at a local oil saturation of 65%. Conversely, in the fingering displacement, there is a transition from the bulk or layered brine to the pinched‐off at a local oil saturation below 60%. The analyses indicate that the difference in the fluid distribution under different fluid conditions is responsible for the non‐Archie behaviour.  相似文献