Influence of interaction between small asperities on various types of slow earthquakes in a 3-D simulation for a subduction plate boundary   总被引：3，自引：1，他引：2  

Keisuke Ariyoshi  Takane Hori  Jean-Paul Ampuero  Yoshiyuki Kaneda  Toru Matsuzawa  Ryota Hino  Akira Hasegawa 《Gondwana Research》2009,16(3-4):534-544

Recently, the occurrence of slow earthquakes such as low-frequency earthquakes and very low-frequency earthquakes have been recognized at depths of about 30 km in southwest Japan and Cascadia. These slow earthquakes occur sometimes in isolation and sometimes break into chain-reaction, producing tremor that migrates at a speed of about 5–15 km/day and suggesting a strong interaction among nearby small asperities. In this study, we formulate a 3-D subduction plate boundary model with two types of small asperities chained along the trench at the depth of 30 km. Our simulation succeeds in representing various types of slow earthquakes including low-frequency earthquakes and rapid slip velocity in the same asperity, and indicates that interaction between asperities may cause the very low-frequency earthquakes. Our simulation also shows chain reaction along trench with propagation speed that can be made consistent with observations by adjusting model parameters, which suggests that the interactions also explain the observed migration of slow earthquakes.  相似文献   

On the divergence of the ionospheric electric field around the westward travelling surge     

Naoko Hori  Takashi Yamamoto 《Planetary and Space Science》1987,35(12):1489-1500

The pattern of the ionospheric electric field around the westward travelling surge (WTS) is theoretically studied. This is obtained by solving the current continuity equation at the ionospheric altitude for temporal and spatial development of the field-aligned current density modelled as the WTS phenomenon. The results show that the divergence of the ionospheric electric field is significantly changed depending on the dawn-to-dusk convection electric field E₀ because of non-uniformity in the ionospheric conductivity: the ionospheric electric field diverges in the upward current region (around the head of the WTS) when a westward electric field E₀ of 10 mV m⁻¹ is uniformly applied. On the other hand, the ionospheric electric field converges without E₀. From the observational inference that the ionospheric electric field converges around the head of the WTS, it is suggested that the WTS phenomenon may not be accounted for by the discharging process in the presence of the enhanced dawn-to-dusk convection electric field and non-uniform conductivity as was studied by previous authors.  相似文献   

Monothalamous Soft-Shelled Foraminifera at an Abyssal Site in the North Pacific: A Preliminary Report     

Andrew J. Gooday  Hiroshi Kitazato  Saori Hori  Takashi Toyofuku 《Journal of Oceanography》2001,57(3):377-384

Soft-shelled monothalamous foraminifera, including species belonging to the suborders Allogromiida and Astrorhizida (families Saccamminidae and Psammosphaeridae), are an abundant and diverse component of the meiofauna in the deep NE Atlantic but have never been systematically documented in the Pacific Ocean. We examined the 32–63 µm and >63 µm fractions of a sample (0–1 cm layer, surface area 52.8 cm²) from an abyssal plain in the subarctic North Pacific, close to the Aleutian Trench (48°05.43 N, 176°55.06 E; 5289 m water depth). The residues yielded an estimated 2876 stained foraminifera (=545 per 10 cm²) of which >75% occurred in the upper 0.5 cm layer and almost half in the 32–63 µm fraction. Rather less than a third (30.5%) of individuals, and about half of the morphospecies (56 out of 121), were soft-shelled monothalamous forms. Many of these, particularly the saccamminids, were tiny, <120 µm in maximum dimension. Based on our analysis of this sample, and previous results in the North Atlantic and NW Indian Oceans, we suggest that these poorly known taxa are a consistently important component of the abyssal meiofauna in well-oxygenated areas.  相似文献   

Estimation of field irrigation water demand based on lumped kinematic wave model considering soil moisture balance     

Tomoharu Hori  Takeyuki Sugimoto  Yutaka Ichikawa 《Physics and Chemistry of the Earth》2008,33(5):376-381

An estimation model of farm field irrigation water demand is developed. The model is based on the lumped kinematic wave model considering soil water balance. The lumped model approach reduces the computational load in rainfall-runoff analysis and allows application to large river basins. Evapotranspiration is estimated on hourly basis by the improvement of FAO’s method. Not only water volume necessary for farm field irrigation but also the number of the water charge and its interval can be estimated by the combined use of the lumped runoff model and the hourly evapotranspiration model.  相似文献   

Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Minoru Tanda  Takehiko Manabe  Kuninao Tada 《Estuaries and Coasts》2010,33(2):417-427

Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year^?1, and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to ~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration.  相似文献   

First Report of Sapphirine-bearing Rocks from the Palghat-Cauvery Shear Zone System, Southern India     

M. Santosh  Toshiaki Tsunogae  Saori Koshimoto 《Gondwana Research》2004,7(2):620-626

Silica deficient Mg-Al granulites from Paramati within the Palghat-Cauvery Shear System contain sapphirine in association with corundum, spinel and sillimanite. Gedrite, which occurs commonly in this locality, coexists with cordierite, corundum and sillimanite. Mineral assemblages and reaction textures indicate peak metamorphism at ultrahigh- temperature conditions. This new locality provides evidence for extreme crustal metamorphism along the Archean-Proterozoic collision boundary in southern India.  相似文献   

Development of regional simulation of seismic ground‐motion and induced liquefaction enhanced by GPU computing     

Ryota Kusakabe  Kohei Fujita  Tsuyoshi Ichimura  Takuma Yamaguchi  Muneo Hori  Lalith Wijerathne 《地震工程与结构动力学》2021,50(1):197-213

Much research has been conducted for physics‐based ground‐motion simulation to reproduce seismic response of soil and structures precisely and to mitigate damages caused by earthquakes. We aimed at enabling physics‐based ground‐motion simulations of complex three‐dimensional (3D) models with multiple materials, such as a digital twin (high‐fidelity 3D model of the physical world that is constructed in cyberspace). To perform one case of such simulation requires high computational cost and it is necessary to perform a number of simulations for the estimation of parameters or consideration of the uncertainty of underground soil structure data. To overcome this problem, we proposed a fast simulation method using graphics processing unit computing that enables a simulation with small computational resources. We developed a finite‐element‐based method for large‐scale 3D seismic response analysis with small programming effort and high maintainability by using OpenACC, a directive‐based parallel programming model. A lower precision variable format was introduced to achieve further speeding up of the simulation. For an example usage of the developed method, we applied the developed method to soil liquefaction analysis and conducted two sets of simulations that compared the effect of countermeasures against soil liquefaction: grid‐form ground improvement to strengthen the earthquake resistance of existing houses and replacement of liquefiable backfill soil of river wharves for seismic reinforcement of the wharf structure. The developed method accelerates the simulation and enables us to quantitatively estimate the effect of countermeasures using the high‐fidelity 3D soil‐structure models on a small cluster of computers.  相似文献   

Song Hong (Red River) delta evolution related to millennium-scale Holocene sea-level changes   总被引：2，自引：0，他引：2  

Susumu Tanabe  Kazuaki Hori  Yoshiki Saito  Shigeko Haruyama  Van Phai Vu  Akihisa Kitamura 《Quaternary Science Reviews》2003,22(21-22):2345-2361

The Song Hong (Red River) delta occurs on the northwest coast of the South China Sea. Its evolution in response to Holocene sea-level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long Duy Tien core from the delta plain, and using previously reported geological, geomorphological, and archaeological data. The delta prograded into the drowned valley as a result of early Holocene inundation from 9 to 6 cal. kyr BP, as sea-level rise decelerated. The sea-level highstand at +2–3 m from 6 to 4 cal. kyr BP allowed widespread mangrove development on the delta plain and the formation of marine notches in the Ha Long Bay and Ninh Binh areas. During sea-level lowering after 4 cal. kyr BP, the former delta plain emerged as a marine terrace, and the delta changed into the present tide- and wave-influenced delta with accompanying beach ridges. Delta morphology, depositional pattern, and sedimentary facies are closely related to Holocene sea-level changes. In particular, falling sea level at 4 cal. kyr BP had a major impact on the evolution of the Song Hong delta, and is considered to be linked to climate changes.  相似文献   

Reproducibility of spatial and temporal distribution of aseismic slips in Hyuga-nada of southwest Japan     

Ryoko Nakata  Shin’ichi Miyazaki  Mamoru Hyodo  Takane Hori 《Marine Geophysical Researches》2014,35(3):311-317

The Hyuga-nada region of southwest Japan, which is located off the east coast of Kyushu Island, may have the potential to generate great interplate earthquakes along the Nankai trough in the future. In this area, thrust earthquakes of M = 6.7–7.2 have occurred with recurrence intervals of approximately 30 years. In association with these earthquakes, possible local heterogeneities of plate coupling may be expected within 100 km from the coast in the Hyuga-nada region. We investigate numerical experiments to determine the spatial and temporal resolution of slip on the plate interface beneath the Hyuga-nada offshore region. For this purpose, we calculated synthetic displacement data from the result of numerical simulation conducted for the afterslip following an M_w 6.8 earthquake, for existing global positioning system stations on land and planned ocean floor seismic network stations. The spatial and temporal distribution of fault slip is then estimated using a Kalman filter-based inversion. The slip distribution estimated by using ocean floor stations demonstrates that the heterogeneity of plate coupling is resolved approximately within 50 km from the coastal area. This heterogeneity corresponds to the coseismic area of an M_w 6.8 earthquake with a radius of 10 km. Our study quantitatively evaluates the spatial resolution of aseismic slip in the Hyuga-nada region. Analysis based on continuous ocean floor data is useful for resolving the spatial variations of heterogeneities in plate couplings.  相似文献   

Intra-annual perturbations of stable isotopes in tufas: Effects of hydrological processes   总被引：1，自引：0，他引：1  

M. Hori  T. Kawai  A. Kano 《Geochimica et cosmochimica acta》2009,73(6):1684-1695

Tufas, which are freshwater carbonates, are potential archives of terrestrial paleoclimate. Time series of stable isotopic compositions commonly show regular seasonal patterns controlled by temperature-dependent processes, and some perturbation intrinsic to the locality. We examined three tufa-depositing sites in southwestern Japan with similar temperate climates, to understand the origin of local characteristics in the isotopic records. Seasonal change in the oxygen isotope is principally reflected by temperature-dependent fractionation between water and calcite but was perturbed after heavy rainfalls overwhelming the stability of the δ¹⁸O value of the groundwater at one site. Isotopic mass balance indicates an undersaturated and relatively small aquifer at this locality. Water δ¹⁸O values at the other two sites were stable, reflecting a regular seasonal change in the δ¹⁸O value of tufa. Perturbation of the δ¹³C values in tufa is largely due to CO₂ degassing from the stream, which significantly increases the δ¹³C values of dissolved inorganic carbon (DIC). At a site with remarkably high pCO₂ in springwater and a sensitive response of flow rate to rainfall, the amount of CO₂ degassing changed distinctly with flow rate. In contrast, the other two sites having low pCO₂ springwater reflect a regular seasonal pattern of δ¹³C in DIC and tufa specimens.  相似文献