An integrated model simulating the initiation and motion of earthquake and rain induced rapid landslides and its application to the 2006 Leyte landslide   总被引：10，自引：7，他引：3  

Kyoji?SassaEmail author  Osamu?Nagai  Renato?Solidum  Yoichi?Yamazaki  Hidemasa?Ohta 《Landslides》2010,7(3):219-236

A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide.  相似文献   

Gravity measurements with a portable absolute gravimeter A10 in Syowa Station and Langhovde,East Antarctica     

Takahito Kazama  Hideaki Hayakawa  Toshihiro Higashi  Shingo Ohsono  Shunsuke Iwanami  Tomoko Hanyu  Harumi Ohta  Koichiro Doi  Yuichi Aoyama  Yoichi Fukuda  Jun Nishijima  Kazuo Shibuya 《Polar Science》2013,7(3-4):260-277

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10^?8 [m/s²]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection.  相似文献   

Optimum design of the ocean acoustic tomography system for the Sea of Japan     

Arata Kaneko  Gang Yuan  Noriaki Gohda  Iwao Nakano 《Journal of Oceanography》1994,50(3):281-293

An ocean acoustic tomography system covering the region of 800×1000 km with the spatial resolution of eddy-resolving scales has been designed on the basis of computer experiments using the hydrographic data collected in the Sea of Japan. The optimum number of acoustic sources required for 20 acoustic receivers was estimated as 13 by changing the source number. The spatial resolution for the optimum system was 41 km smaller than the dominant size of meso-scale eddies in the Sea of Japan. The effect of travel-time errors on tomographic maps is also quantified.  相似文献   

Intermediate Circulation in the Northwestern North Pacific Derived from Subsurface Floats     

Takanori Iwao  Masahiro Endoh  Nobuyuki Shikama  Toshiya Nakano 《Journal of Oceanography》2003,59(6):893-904

In order to examine the formation, distribution and synoptic scale circulation structure of North Pacific Intermediate Water (NPIW), 21 subsurface floats were deployed in the sea east of Japan. A Eulerian image of the intermediate layer (density range: 26.6–27.0σ_θ) circulation in the northwestern North Pacific was obtained by the combined analysis of the movements of the subsurface floats in the period from May 1998 to November 2002 and historical hydrographic observations. The intermediate flow field derived from the floats showed stronger flow speeds in general than that of geostrophic flow field calculated from historical hydrographic observations. In the intermediate layer, 8 Sv (1 Sv ≡ 10⁶ m³s⁻¹) Oyashio and Kuroshio waters are found flowing into the sea east of Japan. Three strong eastward flows are seen in the region from 150°E to 170°E, the first two flows are considered as the Subarctic Current and the Kuroshio Extension or the North Pacific Current. Both volume transports are estimated as 5.5 Sv. The third one flows along the Subarctic Boundary with a volume transport of 5 Sv. Water mass analysis indicates that the intermediate flow of the Subarctic Current consists of 4 Sv Oyashio water and 1.5 Sv Kuroshio water. The intermediate North Pacific Current consists of 2 Sv Oyashio water and 3.5 Sv Kuroshio water. The intermediate flow along the Subarctic Boundary contains 2 Sv Oyashio water and 3 Sv Kuroshio water. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

On the Influence of Sea Surface Height Variability on Satellite Altimeter Derived Gravity     

Leni Sophia Heliani  Yoichi Fukuda 《Marine Geodesy》2001,24(2):73-84

The effect of sea surface height (SSH) variability is one of the primary factors that limit the accuracy and resolution of altimeter-derived gravity values. We propose a method to estimate the influence of variation of the sea surface height on the accuracy of satellite-derived gravity by simulation technique, with a case study around Indonesian waters. Wederived an Indonesian marine gravity map using the Geosat-geodetic mission (GM). Since most of the area studied is located around coastal and shallow areas, the measurement of SSH of this area is less accurate. To obtain a distribution of SSH variability over the study area, Topex/Poseidon (T/P) data were first processed and assessed. Processing 52 cycles of the Topex/Poseidon data, the root mean square (RMS) of SSH variability for each cycle was found to vary from 1 to 179 cm. Further, for the purpose of estimating the accuracy of altimeter-derived gravity, we derived several levels of Gaussian noise, computed simulation data by adding the Gaussian noise to Geosat data, and determined simulated gravity maps. Based on the distribution of RMS values from T/P data and standard deviation (STD) differences between the simulated and the original gravity maps, we estimated the accuracy of the gravity map. Around Indonesian waters, the accuracy of the gravity map influenced by SSH variation was estimated to be within the range 0.8~93 mgal.  相似文献   

Mechanisms for anhydrite and gypsum formation in the Kuroko massive sulfide–sulfate deposits,north Japan     

Yasumasa Ogawa  Naotatsu Shikazono  Daizo Ishiyama  Hinako Sato  Toshio Mizuta  Takanori Nakano 《Mineralium Deposita》2007,42(3):219-233

The Sr, Ba, and rare earth elements (REEs) concentrations and Sr isotopic composition of anhydrite and gypsum have been determined for samples from the Matsumine, Shakanai, and Hanaoka Kuroko-type massive sulfide–sulfate deposits of northern Japan to evaluate the mechanisms of sekko (anhydrite and gypsum) ore formation. The Sr isotopic compositions of the samples fall in the range of 0.7077–0.7087, intermediate between that for middle Miocene (13–15 Ma) seawater (0.7088) (Peterman et al., Geochim Cosmochim Acta, 34:105–120, 1970) and that for country rocks (e.g., 0.7030–0.7050) (Shuto, Assn Geol Collab Japan Monograph 18:91–105, 1974). The Kuroko anhydrite samples exhibit two types of chondrite-normalized REE patterns: one with a decrease from light REEs (LREEs) to heavy REEs (HREEs) (type I), and another with a LREE-depleted pattern (type II). Based on the Sr content and isotopic ratio (assuming an Sr/Ca (mM/M) of 8.7 for seawater), anhydrite is considered to have formed by mixing of preheated seawater with a hydrothermal solution of Sr/Ca (mM/M) = ca. 0.59–1.36 under the condition in which the partition coefficient (Kd) ranges between ca. 0.5 and 0.7. This results in the formation of anhydrite with higher Sr content with an Sr isotopic value close to that of seawater under seawater-dominant conditions. Larger crystals of type II anhydrite are partly replaced by smaller ones, indicating that anhydrite dissolution and recrystallization occurred after or during the formation of sekko ore. Gypsum, which partially replaces anhydrite in the Kuroko deposits, also exhibits two distinct chondrite-normalized REE patterns. Because LREEs are likely to be more readily mobilized during dissolution and recrystallization, it is hypothesized that LREEs are leached from type I anhydrite, resulting in the formation of type II anhydrite with LREE-depleted profiles.  相似文献   

Crustal anatexis and formation of two types of granitic magmas in the Kontum massif, central Vietnam: Implications for magma processes in collision zones   总被引：1，自引：0，他引：1  

M. Owada  Y. Osanai  N. Nakano  T. Matsushita  Tran Ngoc Nam  T. Tsunogae  T. Toyoshima  Pham Binh  H. Kagami 《Gondwana Research》2007,12(4):428-437

Asia grew in the Late Permian by the collision of a number of micro-continents. Syn- to post-collisional magmatism occurred along the continental collision zones . In this study, we report two types of granitic rocks, garnet granite (Grt granite) and orthopyroxene granite (Opx granite), from the Kontum massif, central Vietnam, which is situated on the continental collision zone between the South China and Indochina cratons. These granitic rocks were formed at ca. 250 Ma when high-temperature (HT) and ultrahigh-temperature (UHT) metamorphism took place in the same zone. Based on the petrological and geochemical features compared with previously reported experimental results, garnet-bearing granite is derived from pelitic gneisses by partial melting, whereas orthopyroxene-bearing granite is produced by the partial melting of garnet-bearing mafic granulites. We inferred that a significantly high-geothermal gradient is required to produce Vietnamese granitic magmatism and related HT to UHT metamorphism. This geotherm may be attributed to upwelling mantle plume beneath the Kontum massif during the Late Permian.  相似文献   

Geologic and metamorphic evolution of the basement complexes in the Kontum Massif, central Vietnam   总被引：3，自引：0，他引：3  

N. Nakano  Y. Osanai  M. Owada  Tran Ngoc Nam  T. Toyoshima  P. Binh  T. Tsunogae  H. Kagami 《Gondwana Research》2007,12(4):438-453

This paper presents a regional scale observation of metamorphic geology and mineral assemblage variations of Kontum Massif, central Vietnam, supplemented by pressure–temperature estimates and reconnaissance geochronological results. The mineral assemblage variations and thermobarometric results classify the massif into a low- to medium-temperature and relatively high-pressure northern part characterised by kyanite-bearing rocks (570–700 °C at 0.79–0.86 GPa) and a more complex southern part. The southern part can be subdivided into western and eastern regions. The western region shows very high-temperature (> 900 °C) and -pressure conditions characterised by the presence of garnet and orthopyroxene in both mafic and pelitic granulites (900–980 °C at 1.0–1.5 GPa). The eastern region contains widespread medium- to high-temperature and low-pressure rocks, with metamorphic grade increasing from north to south; epidote- or muscovite-bearing gneisses in the north (< 700–740 °C at < 0.50 GPa) to garnet-free mafic and orthopyroxene-free pelitic granulites in the south (790–920 °C at 0.63–0.84 GPa). The Permo-Triassic Sm–Nd ages (247–240 Ma) from high-temperature and -pressure granulites and recent geochronological studies suggest that the south-eastern part of Kontum Massif is composed of a Siluro-Ordovician continental fragment probably showing a low-pressure/temperature continental geothermal gradient derived from the Gondwana era with subsequent Permo-Triassic collision-related high-pressure reactivation zones.  相似文献   

Variance Component Estimation in Linear Inverse Ill-posed Models   总被引：2，自引：4，他引：2  

Peiliang Xu  Yunzhong Shen  Yoichi Fukuda  Yumei Liu 《Journal of Geodesy》2006,80(2):69-81

Regularization has been applied by implicitly assuming that the weight matrix of measurements is known. If measurements are assumed to be heteroscedastic with different unknown variance components, all regularization techniques may not be proper to apply, unless techniques of variance component estimation are directly implemented. Although variance component estimation techniques have been proposed to simultaneously estimate the variance components and provide a means of regularization, the regularization parameter is treated as if it were also an extra variance component. In this paper, we assume no prior information on the model parameters and do not treat the regularization parameter as an extra variance component. Instead, we first analyze the biases of estimated variance components due to the regularization parameter and then propose bias-corrected variance component estimators. The results have shown that they work very well. Finally, we propose and investigate through simulations an iterative scheme to simultaneously estimate the variance components and the regularization parameter, in order to eliminate the effect of regularization parameter on variance components and the effect of incorrect prior weights or initial variance components on the regularization parameter.  相似文献   

Sequence-stratigraphic signatures of hemipelagic siltstones in deep-water successions: the Lower Pleistocene Kiwada and Otadai Formations, Boso Peninsula, Japan     

Sotaro Takano  Makoto Ito  Takanori Nakano  Keiji Horikawa  Yuzuru Nakamura  Takahiro Saito 《Sedimentary Geology》2004,170(3-4):189-206

Sequence-stratigraphic signatures of hemipelagic siltstones were investigated using profiles of the magnetic susceptibility and selected chemical composition of the Early Pleistocene deep-water successions of the Kiwada and Otadai Formations on the Boso Peninsula, Japan. In the context of an independently developed sequence-stratigraphic framework for the submarine-fan deposits of the Otadai Formation, the magnetic susceptibility and chemical composition, such as the concentrations of TiO₂, MgO and Fe₂O₃, show that the lowstand systems tract deposits have higher values of these parameters than the transgressive and highstand systems tract deposits. In contrast, the CaO contents have inverse relationships with the magnetic susceptibility and are higher in the transgressive and highstand systems tract deposits. The positions of sequence boundaries largely coincide with the horizons from which the magnetic susceptibility and the contents of mafic component increase abruptly. The sequence-stratigraphic variations in the magnetic susceptibility and chemical composition of the submarine-fan hemipelagic siltstones are due to increases in the input of fine-grained, terrigenous clastic sediments from midwater flow suspension, in addition to the direct fluvial supply of relatively unmodified terrigenous clastic sediments during relative sea-level lowstands, although grain size of hemipelagic siltstones does not exhibit any distinct variation through depositional sequences. The Kiwada Formation is characterized by siltstone-dominated basin-plain deposits and its sequence-stratigraphic classification has been difficult when using just lithofacies features. Nevertheless, the profiles of the magnetic susceptibility and chemical composition of the basin-plain deposits are similar to those of the submarine-fan deposits with duration largely equivalent to the 41,000-years obliquity cycle of the Early Pleistocene oxygen isotope sea-level index. This finding indicates that the profiles of the magnetic susceptibility and chemical composition of hemipelagic siltstones reflect sequence-stratigraphic variation in the input of fine-grained terrigenous clastic sediments to the deep-water environments and are crucial for the recognition of cryptic sequence boundaries in hemipelagic successions.  相似文献