Shimajiri Group equivalent sedimentary rocks dredged from sea knolls off Kume Island,central Ryukyus: Implications for timing and mode of rifting of the middle Okinawa Trough back-arc basin

The late Cenozoic geohistory of the Ryukyu arc is closely related to the rifting history of the Okinawa Trough. The submarine geology and stratigraphy of areas around Kume Island, which is situated near the eastern rifted margin of the middle Okinawa Trough, provide key constraints to understand the timing and mode of Okinawa Trough rifting. Here we report the lithology of sedimentary rocks dredged along slopes of ~1000-m-deep sea knolls located north and northwest off Kume Island, and their depositional ages determined by calcareous nannofossils and strontium (Sr) isotope analyses. Various types of sedimentary rocks, such as siltstone, very fine-grained sandstone, medium-grained sandstone, fossiliferous coarse-grained sandstone, and tuffaceous sandstone, were recovered at two dredge sites. These sedimentary rocks are lithologically similar to those in the Aka Formation and a part of the Maja Formation of the Shimajiri Group in nearby Kume Island. Calcareous nannofossils and Sr isotope analyses indicate their depositional ages from the early Pliocene to the early Pleistocene, which are generally consistent with those of the Aka Formation. The finding of the dredged rocks similar in lithology and ages to the Aka Formation indicates that marine deltaic area continued toward north and northwest from Kume Island during these periods. The presence of the Shimajiri Group equivalent sedimentary rocks at the dredge sites are likely related to the main rifting of the Okinawa Trough after ca. 2 Ma in the central Ryukyus.     

The effect of pyridine treatment on phase Q: Orgueil and Allende

Marrocchi et al. (2005) reported that low‐temperature fractions of heavy noble gases were largely removed upon pyridine treatment of the Orgueil CI meteorite. As pyridine is known to induce the swelling of the macromolecular network of organic matter, they concluded that the low‐temperature phase Q is macromolecular organic carbon. However, Busemann et al. (2008) showed that pyridine had no significant effect on the noble gas contents for other very primitive meteorites, such as CM and CR. Therefore, we prepared an HF–HCl residue and the pyridine‐treated residue of Orgueil, and re‐examined the results of Marrocchi et al. (2005) by analyzing all noble gases. We confirmed that heavy noble gases are surely removed by the pyridine treatment, but the degree of the loss of heavy noble gases is generally small, and is even smaller for the lighter noble gases. Furthermore, we could not observe the evidence of Xe isotopic ratios by removing only phase Q after the pyridine treatment. We further prepared the HF–HCl residue and the pyridine‐treated residue of the Allende CV3 meteorite and performed noble gas analyses. For Allende, there is no significant change in the elemental abundances after the pyridine treatment. These results suggest that only Orgueil is special, and it is likely that the gas loss of the Orgueil residue is due to the loss of some kind of organic matter that was formed and that adsorbed the fractionated Q and HL gases during the aqueous alteration within the parent body of Orgueil.     

Non‐linear‐Maxwell‐element‐type hysteretic control force

A simple non‐linear control law is proposed for reducing structural responses against seismic excitations. This law defines control force dynamics by one differential equation involving a non‐linear term that restrains the control force amplitude. If non‐linearity is neglected, the control force becomes the force in a Maxwell element, so it is called the non‐linear‐Maxwell‐element‐type (NMW) control force. The NMW control force vs. deformation relation plots hysteretic curves. The basic performance of an SDOF model with the NMW control force is examined for various conditions by numerical analyses. Furthermore, the control law is extended to fit an MDOF structural model, and an application example is shown. The computational results show that the NMW control force efficiently reduces structural responses. Copyright © 2000 John Wiley & Sons, Ltd.     

Hydraulic model tests for evaluating sediment control function with a grid-type Sabo dam in mountainous torrents

There are two kinds of Sabo dams in order to control sediment transport by debris flow and flash floods in mountainous area, which are closed and open-type＇s dams. In Japan, open-type＇s Sabo dams are constructed taking into account the continuity of sediment routing from upstream to downstream reach in a basin. A plan to construct a 20 m high grid-type Sabo dam which can capture a sediment volume of 400,000 m3 is proposed in the Amahata river basin in Japan. Hydraulic model tests are conducted to decide on the section for a dam （Section A, B） and the grid size such as clearance of vertical/horizontal bars for evaluating the plan. Several runs of flume tests are conducted and the sediment control function of the Sabo darn is discussed using several experimental data such as dimensionless sediment runoff rate from Sabo dam, temporal changes of bed profile and mean diameter and so on. It was found that sediment deposition in sediment storage area of Sabo dam was affected by curved channel, and that next the grid size of steel bars and thirdly the section of a dam was able to capture sediment in storage area of Sabo dam. Sediment was controlled well in the section B and in the grid size of 1.0×d95, and the problems related to sediment runoffafter sediment capturing in Sabo dam are pointed out.     

Damping identification of a full‐scale passively controlled five‐story steel building structure

A series of large‐scale dynamic tests was conducted on a passively controlled five‐story steel building on the E‐Defense shaking table facility in Japan to accumulate knowledge of realistic seismic behavior of passively controlled structures. The specimen was tested by repeatedly inserting and replacing each of four damper types, that is, the buckling restrained braces, viscous dampers, oil dampers, and viscoelastic dampers. Finally, the bare steel moment frame was tested after removing all dampers. A variety of excitations was applied to the specimen, including white noise, various levels of seismic motion, and shaker excitation. System identification was implemented to extract dynamic properties of the specimen from the recorded floor acceleration data. Damping characteristics of the specimen were identified. In addition, simplified estimations of the supplemental damping ratios provided by added dampers were presented to provide insight into understanding the damping characteristics of the specimen. It is shown that damping ratios for the specimen equipped with velocity‐dependent dampers decreased obviously with the increasing order of modes, exhibiting frequency dependency. Damping ratios for the specimen equipped with oil and viscoelastic dampers remained constant regardless of vibration amplitudes, whereas those for the specimen equipped with viscous dampers increased obviously with an increase in vibration amplitudes because of the viscosity nonlinearity of the dampers. In very small‐amplitude vibrations, viscous and oil dampers provided much lower supplemental damping than the standard, whereas viscoelastic dampers could be very efficient. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamics of pounding when two buildings collide

A formulation and solution of the multiple-degree-of-freedom equations of motion for pounding between two multistorey buildings are presented. Pounding occurs at rigid horizontal diaphragms in each building. The theory is implemented into a microcomputer program and sample earthquake analyses involving pounding between 15-storey and 8-storey buildings are performed. The influence of building separation, relative mass, and contact location properties are assessed. Conclusions are drawn regarding response behaviour trends that are relevant to other actual pounding situations.     

Seismic-response-controlled structure with active mass driver system. Part 1: Design

An Active Mass Driver (AMD) system is proposed to suppress actively the response of a building to irregular external excitations such as earthquakes and typhoons. This system has been introduced to an actual ten-storey office building for the first time in the world. The system controls the motions of a structure by means of an external energy supply. It consists of an auxiliary mass installed in a building and an actuator that operates the mass and produces a control force which counters disturbances to the building. The design method of the AMD system, including the location of the installation and the capacity and stability of the system, is proposed. Simplification of the control algorithm is also described.     

Interrelationships Between Topography,Quaternary Vertical Displacement,Active Faults and Short-term Horizontal Crustal Strain in Honshu,Japan

Regional and local characteristics of active fault patterns and elevation variation throughout Honshu, Japan are characterized in terms of their fractal dimensions; this allows variation in these complex variables to be compared directly to the scalar properties of net Quaternary vertical displacement, elevation and 10- and 110-year horizontal strains. The comparisons reveal that, throughout Honshu as a whole, there is significant correlation (r=0.75) between Quaternary vertical displacement, elevation, and its fractal properties. There is poor correlation, however, of elevation and its fractal properties to horizontal crustal strain, and also between Quaternary vertical displacement and horizontal crustal strain. A slight negative correlation is observed between the fractal properties of the active fault system and horizontal crustal strain measured over 10- and 110-year time periods (–0.43 and –0.26, respectively). The correlation between the 10-year (1985–1994) and 110-year (1883–1994) area strains, 0.48, reveals the occurrence of considerable change in the distribution of regional strain over these short time frames. Local computations of the correlation between data sets made for overlapping 160 km length windows of data spaced every 20 km along analysis lines reveal internal fluctuations in the correlation between variables. The local correlation between Quaternary vertical displacement and elevation is highest through central Japan and the Kinki Triangle. There is weak negative correlation between area strain and fractal dimensions of the active fault network. The local correlation between the fractal dimensions of active faults and horizontal area strain over the recent 10-year time period averages about –0.6 through central Japan in an area that extends across the Kinki Triangle through the northern part of central Honshu and northeast across the Itoigawa Shizuoka Tectonic Line. In general, regions of greatest complexity in the active fault network are associated with persistent negative area or compressional strain. Sparsely faulted areas in general coincide with areas of positive or roughly zero area strain. The presence of negative correlation through central Japan and the Kinki Triangle area in the recent 10-year period results from a decrease of area strain within an increasingly complex active fault system that reaches maximum negative values concentrated in the Kinki Triangle during the 1985–1994 time period.     

Variation of dissolved organic matter and fluorescence characteristics before,during and after phytoplankton bloom

The variation of dissolved organic matter (DOM) and fluorescence characteristics during the phytoplankton bloom were investigated in Yashima Bay, at the eastern part of the Seto Inland Sea, Japan. We found significant accumulations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chromophoric dissolved organic matter (CDOM) fluorescence, and UV₂₆₀ during the phytoplankton bloom period in 2005, although lower accumulations of DOC and DON and only increases of CDOM fluorescence were observed during the bloom period in 2006. Little or no correlation between DOM and phytoplankton abundance might be due to the composition of DOM, which is a complex mixture of organic materials. The 3D-EEM results revealed that the DOM produced around the phytoplankton bloom period contained tyrosine, tryptophan, and humic-like substances. Our results showed that the occurrence of phytoplankton bloom contributed to the production of DOM in coastal water but the DOM accumulation depended on the type of phytoplankton bloom, the phytoplankton species in particular. From our results, we concluded that phytoplankton have a great role in the dynamics of DOM as a producer in a coastal environment.