Evidence for erosion and deposition by the 2011 Tohoku-oki tsunami on the nearshore shelf of Sendai Bay,Japan     

Shuro?YoshikawaEmail author  Toshiya?Kanamatsu  Kazuhisa?Goto  Izumi?Sakamoto  Masatoshi?Yagi  Mikio?Fujimaki  Riichirou?Imura  Kenji?Nemoto  Hide?Sakaguchi 《Geo-Marine Letters》2015,35(4):315-328

Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces.  相似文献   

A gravity survey on Volcano Huzi,Japan by means of a Worden gravimeter     

Yokoyama  Izumi  Tajima  Hirokazu 《Pure and Applied Geophysics》1960,45(1):1-12

Summary Observations and reductions of the gravimeter survey on Volcano Huzi are fully described. The survey was accompanied by various inevitable difficulties but the accuracy of calculating the Bouguer anomalies is kept high enough to bear volcanological discussion. The results are rather suggestive to the theory of caldera-formation. Comparison with the gravity anomaly on the volcanic islands in the middle of the ocean is also made.  相似文献   

Role of Time-Delay Concept in Understanding Mechanism of Total Solar Irradiance Variation and its Effect on the Climate of the Earth     

Hirokazu Yoshimura 《Solar physics》1998,177(1-2):329-342

A time-delay concept is described to play a vital role in a hypothesis of the mechanism of the solar total irradiance variation driven by time variation of the thermal structure of the solar convection zone, with time scales on the order of 10 to 10000 years. The hypothesis is formulated on an empirical basis from an analysis of the observed data of the magnetic field of the Sun and of the global land-air temperature anomalies of the Earth, with the assumption that the land area of the Earth can be a good recorder of the solar total irradiance variation in the past. As a result of the assumption within the context of the present hypothesis, it was found that the solar total irradiance increase and the global warming of the Earth from the early 20th century to the present time could be caused by release of heat stored in the solar convection zone in the Maunder Minimum of the 17th century.  相似文献   

High-Speed Data Acquisition System Messia for Subaru     

Maki Sekiguchi  Hidehiko Nakaya  Hirokazu Kataza  Satoshi Miyazaki 《Experimental Astronomy》1998,8(1):51-58

We have developed a high-speed data acquisition system, Messia-III (Modularized Extensible SyStem for Image Acquisition) for Subaru, Japanese 8.2m telescope. Messia has a direct 1-Gbps link to a host UNIX workstation. Messia is a VMEbus-based system but it does not have local OS nor CPU's in order to minimize software development and maintenance.  相似文献   

Optimum Design of Resilient Sliding Isolation System for Seismic Protection of Equipments     

Hirokazu Iemura  Touraj Taghikhany  Sarvesh K. Jain 《Bulletin of Earthquake Engineering》2007,5(1):85-103

Seismic isolation is one of the effective methods to protect equipments. It helps to keep seismic response accelerations in equipment below its allowable limits. Among different types of isolation systems, the combination of restoring spring and slider, also called as resilient sliding isolation (RSI) system, is the one which has been effectively used for protection of equipment. Principal design parameters for this type of isolation system are period of system (stiffness of spring) and friction coefficient of slider. There may be number of combinations of these design parameters which can enable the isolated equipment to remain functional during and after the predicted seismic event. The optimum design of RSI system can be considered as the one which maintains the response acceleration in the equipment below its allowable limit and at the same time keeps the relative displacement between floor and the equipment to the minimum. This study deals with optimum design of resilient sliding system. First the RSI system is modeled analytically by (i) precise and (ii) simplified SDOF models. The accuracy of the model is then validated by shaking table tests. The validated simplified SDOF model is then used to determine optimum design parameters for different levels of allowable accelerations. Results show that the optimum period decreases and the optimum friction coefficient increases with higher allowable acceleration.  相似文献   

On the characteristics of the basic framework of solar active regions and the magnetohydrodynamical structure of the convection zone     

Hirokazu Yoshimura 《Solar physics》1973,33(1):131-143

The characteristics of the basic framework of structure and development of solar active regions are interpreted as good indicators of the magnetohydrodynamical structure of the convection zone, the magnetic field lines of which are twisted and are made wave-like by the action of the very large scale non-axisymmetric convection, called here the global convection. The characteristics discussed in this paper are: (i) the preponderance of preceding spots of bipolar sunspot groups in strength and life time relative to the following spots of the groups, (ii) the tilt of bipolar axes of the sunspot groups to the local parallels of latitude, (iii) the forward inclination of normal axes of sunspots inferred from the east-west asymmetry of the appearance and total area of sunspots, (iv) the faster rotation of sunspots than the averaged fluid rotation, and (v) the association of the characteristics of an active region with the presence of an older active region in its vicinity and with the relative disposition of the two active regions.  相似文献   

Estimation of property loss and business interruption loss caused by storm surge inundation due to climate change: a case of Typhoon Vera revisit     

Jiang  Xinyu  Mori  Nobuhito  Tatano  Hirokazu  Yang  Lijiao  Shibutani  Yoko 《Natural Hazards》2015,84(1):35-49

This paper estimates property loss and business interruption loss under scenarios of storm surge inundation to explore the economic impact of climate change on Ise Bay, Japan. Scenarios-based analyses are conducted with respect to Typhoon Vera, which caused the most severe storm surge in the recorded history of Japan in 1959. Four different hazard scenarios are chosen from a series of typhoon storm surge inundation simulations: Typhoon Vera’s landfall with respect to the condition of the past seawall; Typhoon Vera’s landfall with respect to the condition of the current seawall; intensifying Typhoon Vera, but retaining its original tracks; and intensifying Typhoon Vera, but choosing the worst tracks from various possible typhoon tracks. Our economic loss estimation takes advantage of fine geographical scale census and economic census data that enable us to understand the spatial distribution of property loss and business interruption loss as well as identify the most potentially affected areas and business sectors on a sub-city scale. By comparing the property loss and business interruption loss caused by different hazard scenarios, the effect of different seawalls is evaluated and the economic impact of future climate change is estimated. The results indicate that although the current seawall can considerably reduce the scale of losses, climate change can cause Ise Bay to experience more serious storm surge inundation. Moreover, the resulting economic losses would increase significantly owing to a combination of climate change and the worst track scenario. It is, therefore, necessary to consider more countermeasures to adapt to climate change in this area.

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Frequency–Magnitude Distribution of −3.7 ≤ M W  ≤ 1 Mining-Induced Earthquakes Around a Mining Front and b Value Invariance with Post-Blast Time     

Makoto Naoi  Masao Nakatani  Shigeki Horiuchi  Yasuo Yabe  Joachim Philipp  Thabang Kgarume  Gilbert Morema  Sifiso Khambule  Thabang Masakale  Luiz Ribeiro  Koji Miyakawa  Atsushi Watanabe  Kenshiro Otsuki  Hirokazu Moriya  Osamu Murakami  Hironori Kawakata  Nana Yoshimitsu  Anthony Ward  Ray Durrheim  Hiroshi Ogasawara 《Pure and Applied Geophysics》2014,171(10):2665-2684

We investigated frequency-magnitude distribution (FMD) of acoustic emissions (AE) occurring near an active mining front in a South African gold mine, using a catalog developed from an AE network, which is capable of detecting AEs down to M _W  ?5. When records of blasts were removed, FMDs of AEs obeyed a Gutenberg?Richter law with similar b values, not depending on post-blasting time from the initial 1-min interval through more than 30 h. This result denies a suggestion in a previous study (Richardson and Jordan Bull Seismol Soc Am, 92:1766–1782, 2002) that new fractures generated by blasting disturb the size distribution of background events, which they interpreted as slip events on existing weak planes. Our AE catalog showed that the GR law with b ～ 1.2 was valid between M _W  ?3.7 and 0 for AEs around the mining front. Further, using the mine’s seismic catalog, which covers a longer time period of the same area, we could extend the validity range of the GR law with the same b value up to M _W 1.  相似文献   

Coronal general magnetic field evolution as a new parameter of the solar cycle     

Hirokazu Yoshimura 《Solar physics》1977,52(1):41-52

The magnetic field lines of the corona associated with the solar-cycle surface general magnetic field are calculated by a potential-field approximation to study the solar-cycle evolution of the geometry of the coronal field. The surface field evolution used here is the radial field evolution, predicted by a model of the solar cycle driven by the dynamo action of the global convection, and justified observationally using Mount Wilson magnetic synoptic chart data. The evolution of the calculated coronal general field is now good for comparison with observations and shows the following. (i) The field of the polar and high-altitude corona has dipolar structure in almost all phases of the solar cycle except in a short time interval around maximum phase despite the quadrupolar structure of the general magnetic field at the surface; quadrupolar field forms loop-like structure in the lower corona. The almost-dipolar structure of the polar and high-latitude corona and the loop formation of the equatorial lower corona explain the appearance of the undisturbed minimum corona observed at eclipses. (ii) The polar field lines are directed almost radially at the minimum phase, which should be responsible for polar plumes. The field lines slowly open up to participate in the loop-like structure of the equatorial lower corona, and rapidly change their structure and polarity at the maximum phase, to resume the almost radial configuration slowly, (iii) During the rapidly changing maximum phase, the field lines do not penetrate deep into the interplanetary space resulting in the absence of polar plumes and the appearance of the circular corona- the maximum corona. In this phase, the coronal field should not be approximated by a dipole field. The surface field evolution which can explain such behaviors of the corona is characteristic of the solar-cycle process dominated by the latitudinal gradient of the differential rotation. If the radial gradient dominated in the subsurface process, the coronal evolution would look quite different and would show latitudinal propagation of enhancement of activity. Although nonaxisymmetric features should be superposed on the axisymmetric general field to express the real corona, the general field can be a basic coronal field in studying long-term interaction between the convection zone and the interstellar space especially in studying the magnetic braking of the solar rotation.  相似文献   

The secular modulation of solar rotation from 1943 to 1992 and its time-delayed correlation with the 55-year grand cycle of the 11-year solar cycle     

Hirokazu Yoshimura  Maspul Aini Kambry 《Solar physics》1993,148(1):11-26

We devised a new method, which we call the running-segment method, to achieve high-resolution time series of indices of solar rotation for determining the latitude dependence of the differential rotation by a least-squares fitting of the daily translation of positions of sunspot groups during a fixed time segment of 11 years. The segment is moved by an amount of one year to determine the differential profile of the next point of time. Time of the determined rotation data is defined by an arithmetic mean of the beginning and ending years of the segment. The rotation underwent an acceleration from 1948 to 1974 and a deceleration from 1974 to 1987. We found that the time profile of the indexM, the angular momentum surface layer density defined by integration of the angular momentum volume density over the whole surface, follows almost exactly the time profile of the 11-year running mean of the yearly mean of the sunspot relative number with a delay time of about 20 years. The acceleration (deceleration) phase corresponds to the ascending (descending) phase of amplitude of the 11-year solar cycle of cycle 16 (19) to cycle 19 (20) with a delay time of about 20 years. The cycles 15–20 correspond to the 55-year grand cycle V of the 11-year cycle. The delay time of about 20 years agrees well with the delay time predicted by a nonlinear dynamo theory of the solar cycle for driving the 55-year modulation of the 11-year solar cycle. The agreement suggests that the Lorentz force of the magnetic field of the solar cycle during grand cycle V drives the solar rotation modulation from 1948 to 1987 and that the force needed about 20 years to modify the rotation during 1943–1992.  相似文献