Correction to: Microtremor array method using spatial autocorrelation analysis of Rayleigh-wave data     

Hayashi  Koichi  Asten  Michael W.  Stephenson  William J.  Cornou  Cécile  Hobiger  Manuel  Pilz  Marco  Yamanaka  Hiroaki 《Journal of Seismology》2022,26(4):629-629

Journal of Seismology -  相似文献   

Microtremor array method using spatial autocorrelation analysis of Rayleigh-wave data     

Hayashi  Koichi  Asten  Michael W.  Stephenson  William J.  Cornou  Cécile  Hobiger  Manuel  Pilz  Marco  Yamanaka  Hiroaki 《Journal of Seismology》2022,26(4):601-627

Journal of Seismology - Microtremor array measurements, and passive surface wave methods in general, have been increasingly used to non-invasively estimate shear-wave velocity structures for...  相似文献   

Statistical features of foreshocks in comparison with other earthquake clusters   总被引：2，自引：0，他引：2  

Yosihiko Ogata  Tokuji Utsu  Koichi Katsura 《Geophysical Journal International》1995,121(1):233-254

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Geochemical characteristics of Carboniferous greenstones in the Inner Zone of Southwest Japan   总被引：3，自引：0，他引：3  

Sakae Sano  Yasutaka Hayasaka and  Koichi Tazaki 《Island Arc》2000,9(1):81-96

Abstract Greenstones, representing remnants of paleo-oceanic crust, occur in Permian and Jurassic accretionary complexes of the Inner Zone in the Southwestern Japan arc. The formation age of most of the greenstones is early Carboniferous, based on fossil ages for overlying limestones and Sm-Nd isotope ages of the greenstones themselves. The geochemistry of such greenstones is similar to those of present-day oceanic islands. Greenstones of the Permian accretionary complex (Akiyoshi belt) are alkalic and tholeiitic in composition. Some alkali basalts show peculiar features from an EM-1 mantle source, such as the Gough Island and Tristan da Chunha basalts in the South Atlantic. Greenstones of the Jurassic accretionary complex (Tamba belt) are also alkali and tholeiitic basalts with both basalt types in the northern part of the Tamba belt coming from strongly depleted characters similar to a mid-ocean ridge basalt source mantle. The variable geochemistry of the oceanic basalts is explained by hypothesis on existence of a Carboniferous mantle plume below the spreading ridge which divides the Farallon and Izanagi plates. The Akiyoshi belt seamounts and/or oceanic islands of the Farallon plate and Tamba belt seamounts and/or oceanic islands of the Izanagi plate formed simultaneously by the upwelling of the thermal plume. Some part of the Akiyoshi belt basalts originated locally from an EM-1 mantle source, while basalts from the northern parts of the Tamba belt have a normal-type mid-ocean ridge basalt (N-MORB) source component. Existence of an N-MORB signature is consistent with the presence of a spreading center in a Carboniferous 'Pacific Ocean' that caused separation of the Farallon and Izanagi plates. Disparity in accretion ages of the basaltic rocks in the Permian and Jurassic may have been caused by differences in the relative motion of the two plates.  相似文献   

On measuring settlement by magnetic method at any depth     

Keiichiro Taniguchi  Harushige Kusumi  Tateshi Sakamoto  Koichi Kimura 《Marine Georesources & Geotechnology》2013,31(1):81-98

Abstract

When artificial islands are constructed, they are subject to surface subsidence, which is the resultant sum of the consolidation strata, many of which seem differ in character. When these strata are soft and thick, or heavily loaded, it becomes very difficult to estimate how much settlement will eventually take place, and over how long a period. For the estimate to be accurate, the settlement characteristics of each layer must first be determined.

For this purpose, the authors have investigated a new method of measuring settlement, based on two unique principles. One principle is the application of a permanent magnet as an indicator of settlement, and the other is the exploitation of semiconductor, magneto‐resistance elements for detecting the magnetic fields. In advance of the observation, the magnets are forced into the earth, being pushed out through the bore‐hole casing by the oil jack at suitable depths and intervals. The small‐sized magneto‐resistance element is essential to the practicality and efficiency of this method.

In this study, the principles of this method, measuring procedure, the special characteristics and potential of this system, and the results of field trials are described.  相似文献   

Stochastic control of a micro-dam irrigation scheme for dry season farming   总被引：1，自引：1，他引：0  

Koichi Unami  Macarius Yangyuoru  Abul Hasan Md. Badiul Alam  Gordana Kranjac-Berisavljevic 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):77-89

Micro-dams are expected to be feasible options for water resources development in semi-arid regions such as the Guinea savanna agro-ecological zone of West Africa. An optimal water management strategy in a micro-dam irrigation scheme supplying water from an existing reservoir to a potential command area is discussed in this paper based on the framework of stochastic control. Water intake facilities are assumed to consist of photovoltaic pumping system units and hoses. The knowledge of current states of the storage volume of the reservoir and the soil moisture in the command area is fed-back to the intake flow rate. A system of two stochastic differential equations is proposed as a model for the dynamics of the micro-dam irrigation scheme, so that temporally backward solution of the Hamilton–Jacobi–Bellman equation determines an optimal control, which represents the optimal water management strategy. A computational procedure using the finite element method is successfully implemented to provide comprehensive information on the optimal control. The results indicate that the water initially stored in the reservoir can support full irrigation for about 80 days under the optimal water management strategy, which is predominantly based on the demand-side principle. However, the volatility of the soil moisture in the command area must be reasonably small.  相似文献   

Another sea area separated from the Panthalassic Ocean in the Norian,the Late Triassic: The lowest Sr isotopic composition of the Ishimaki limestone in central Japan     

Kazuhiro Suzuki  Yoshihiro Asahara  Koichi Mimura  Tsuyoshi Tanaka 《Chemie der Erde / Geochemistry》2012,72(1):77-84

Mt. Ishimaki is the Jurassic accretionary complex of the Chichibu Belt in Toyohashi City, near Nagoya in central Japan. The Ishimaki limestone is thought to be seamount-type limestone. The P₁ elements of the conodonts Norigondolella navicula and Ancyrogondolella quadrata found in the limestone indicate it is of Norian age. The Sr isotopic compositions of 45 Ishimaki limestone samples ranged from 0.7055 to 0.7077. Eighteen of these samples had lower Sr isotopic compositions than the lowest Sr isotopic composition (0.7068) of seawater throughout the Phanerozoic. The Sr isotopic compositions in the limestone block are generally lower at the base of the block and higher at the top. The present Sr isotopic compositions of the Ishimaki limestone are unlikely to have been reduced by post-depositional alteration because most of the limestone samples had a low amount of Mn (<300 ppm) or high Sr/Mn ratios (>2) and the conodont elements had low (1–2) CAI (conodont alteration index) values. Additionally, there was little acid-insoluble residue. Thus, the low Sr isotopic compositions are thought to represent the strontium of the past ambient seawater. The low Sr isotopic compositions are in complete disagreement with the generally recognised range of seawater Sr isotopic compositions in the Norian stage of the Late Triassic (0.7075–0.7078) because the depositional environment of the Ishimaki limestone was closed or semi-closed from the Panthalassic Ocean. Therefore, the Sr isotopic composition of the limestone differs from that of the Panthalassic seawater. The low Sr isotopic compositions were probably affected by Sr inflows from mafic oceanic crust by hydrothermal fluid circulation or from hinterlands surrounded by mafic rocks by river water circulation.  相似文献   

Confirmation of Dropstones in the Dingjiazhai Formation of the Gondwana-Derived Baoshan Block, West Yunnan     

Ken-ichiro Hisada  Katsumi Ueno  Tetsuo Sugimaya  Koichi Nagai  Xiang-dong Wang 《Gondwana Research》2001,4(4):630-631

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Paleoenvironmental interpretations of Quaternary reef deposits based on comparisons of 10 selected modern and fossil larger foraminifera from the Ryukyu Islands, Japan     

Kazuhiko  Fujita  Hiroaki  Shimoji  Koichi  Nagai 《Island Arc》2006,15(4):420-436

Abstract A new method for reconstructing depositional environments of larger foraminifera‐bearing limestones is proposed. First, depth and spatial distributions of empty tests of 10 foraminiferal taxa in a 1–2 mm size fraction were examined using 32 surface sediment samples collected from depths shallower than 200 m, located to the west of Miyako Island, Ryukyu Islands, northwest Pacific. Distributional ranges of empty tests in the 1–2 mm size fraction appear to be more limited than those including other size fractions in previous reports, partly because larger empty tests of each taxon are less easily transported than smaller ones. Multivariate analyses (Q‐mode cluster analysis and non‐metric multidimensional scaling ordination) based on binary (presence/absence) data of the 10 taxa delineate four sample groups, each of which corresponds to different depositional environments: nearshore zone/bay inlet; back‐reef to fore‐reef; outer shelf to shelf slope; and shelf slope distant from coral reefs. Next, these modern data were applied to reconstruct the depositional environment of a rock section distributed in the Shiratorizaki area (Irabu Island, Ryukyu Islands), which consists of larger foraminiferal limestone of the Pleistocene Ryukyu Group. Multivariate analyses were performed on the fossil plus the modern foraminiferal data to explore the possible relationship of the fossil associations with variations in modern associations, demonstrating that the fossil foraminiferal associations resemble the modern outer shelf associations. The modern analog technique was also applied to estimate paleobathymetry using fossil foraminiferal data. The results indicate that the section studied was deposited in outer shelf environments at depths between 53.5 and 98.6 m. These paleoenvironmental interpretations are consistent with previous studies based on sedimentary facies and the computer‐based expert system. The modern dataset and methods used in our work would be particularly useful for paleoenvironmental reconstructions of Quaternary reef and shelf carbonates along active margins of the northwest Pacific.  相似文献   

Statistical discrimination of foreshocks from other earthquake clusters   总被引：1，自引：0，他引：1  

Yosihiko Ogata  Tokuji Utsu  Koichi Katsura 《Geophysical Journal International》1996,127(1):17-30

When earthquake activity begins, it may be a foreshock sequence to a larger earthquake, a swarm, or a simple main-shock-aftershock sequence. This paper is concerned with the conditional probability that it will be foreshock activity of a later larger earthquake, depending on the occurrence pattern of some early events in the sequence. The earthquake catalogue of the Japan Meteorological Agency (1926-1993, M_J≥4) is decomposed into a large number of clusters in time and space in order to compare statistical features of foreshocks with those of swarms and aftershocks. Using such a data set, Ogata, Utsu & Katsura (1995) revealed some discriminating features of foreshocks relative to the other types of clusters, for example the events' closer proximity in time and space, and a tendency towards chronologically increasing magnitudes, which encouraged us to construct models which forecast the probability of the earthquakes being foreshocks. Specifically, the probability is a function of the history of magnitude differences, spans between origin times and distances between epicentres within a cluster. For purposes of illustration, the models were fitted to the early part of the data (1926-1975) and the validity of the forecasting procedure was checked on data from the later period (1976-1993). Two procedures for evaluating the performance of the probability forecast are suggested. Furthermore, for the case where only a single event is available (i.e. either it is the first event in a cluster or an isolated event), we also forecast the probability of the event being a foreshock as a function of its geographic location. Then, the validity of the forecast is demonstrated in a similar manner. Finally, making use of the multi-element prediction formula, we show that the forecasting performance is enhanced by the joint use of the information in the location of the first event, and that in the subsequent interevent history in the cluster.  相似文献