A Coastal Aquifer Study Using Magnetotelluric and Gravity Methods in Abo Zenema, Egypt     

Mohamed Abdelzaher  Jun Nishijima  Hakim Saibi  Gad El-Qady  Usama Massoud  Mamdouh Soliman  Abdellatif Younis  Sachio Ehara 《Pure and Applied Geophysics》2012,169(9):1679-1692

Magnetotelluric (MT) soundings and gravity methods were employed to study the deep freshwater aquifer in the area north of Abo Zenema city on the eastern side of the Gulf of Suez, Egypt. Seven MT sites and 48 gravity stations were surveyed along northeast–southwest profiles as close as possible to a line perpendicular to the coast of the Gulf of Suez. The MT survey was conducted using high and low frequencies to investigate shallow and deep areas, respectively. One-dimensional inversion was conducted using a heuristic inversion scheme of the Bostick algorithm. The MT data were also inverted with a 2-D smooth model inversion routine using the nonlinear conjugate gradient method to infer variation in vertical and lateral resistivity inside the Earth. A 100-Ohm-m homogeneous half-space initial model was used to invert the TE mode data only. Then, the inverted model obtained from the TE mode data was used as an initial model for inversion of the TM mode data. The inverted model thus obtained from the TM mode data inversion was used as an initial model for the inversion of the joint TE and TM responses. Two-dimensional (2-D) forward modeling of the gravity data was conducted using the 2-D polygon method of Talwani’s algorithm for an arbitrarily shaped body and was based on the subsurface information from the MT survey and the available information about the geological structure of the study area. This method enabled us to obtain the basement structure of the coastal aquifer in the study area. The results from the analysis and the interpretation of MT and gravity data were used to detect and delineate the groundwater coastal aquifer in the study area.  相似文献   

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake     

Toshitaka Baba  Phil R. Cummins  Hong Kie Thio  Hiroaki Tsushima 《Pure and Applied Geophysics》2009,166(1-2):55-76

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.  相似文献   

Interpretation of Gravity and Gamma-Ray Spectrometry Data in Low Temperature Hydrothermal Systems,Southeastern Part of Fukuoka,Japan     

Jun Nishijima  Yasuhiro Fujimitsu 《Acta Geophysica》2016,64(6):2289-2304

The Hakata hot springs area is located in Fukuoka City, which is in the southwestern part of Japan. Gamma-ray and gravity surveys were conducted to understand the relationship between the low-temperature hydrothermal systems and geophysical data of the area. The depth of the reservoir basement, which was derived from gravity data, gradually deepens toward the east; it includes some steep depth gradients in the Hakata hot springs area. High intensities of gamma-rays were detected around these gradients. In addition, higher hot spring temperatures and flow rates can be observed in this area. These results indicate that some part of the level of the basement where the hot springs are concentrated is a part of the Kego Fault and is similar to the fracture zone created by past activities of the fault. Moreover, these steep depth gradients act as a path for hot spring water from the deeper side of the granitic body to the surface.  相似文献   

Enrichment of adsorbed methane in authigenic carbonate concretions of the Japan Trench     

Akira Ijiri  Urumu Tsunogai  Toshitaka Gamo  Fumiko Nakagawa  Tatsuhiko Sakamoto  Saneatsu Saito 《Geo-Marine Letters》2009,29(5):301-308

Substantial amounts of adsorbed methane were detected in authigenic carbonate concretions recovered from sedimentary layers from depths between 245 and 1,108 m below seafloor during Ocean Drilling Program Leg 186 to ODP sites 1150 and 1151 on the deep-sea terrace of the Japan Trench. Methane contents were almost two orders of magnitude higher in the concretions (291–4,528 nmol/g wet wt) than in the surrounding bulk sediments (5–93 nmol/g wet wt), whereas methane/ethane ratios and stable carbon isotopic compositions were very similar. Carbonate content of surrounding bulk sediments (0.02–3.2 wet wt%) and methane content of the surrounding bulk sediments correlated positively. Extrapolation of the carbonate contents of bulk sediments suggests that 100 wt% carbonate would correspond to 1,886±732 nmol methane per g bulk sediment, which is similar to the average value observed in the carbonate concretions (1,321±1,067 nmol/g wet wt, n = 13). These data support the hypothesis that, in sediments, adsorbed hydrocarbon gases are strongly associated with authigenic carbonates.  相似文献   

Distribution of heterotrophic nanoflagellates and their importance as the bacterial consumer in a eutrophic coastal seawater   总被引：4，自引：0，他引：4  

Kimio Fukami  Noriyuki Murata  Yuuki Morio  Toshitaka Nishijima 《Journal of Oceanography》1996,52(4):399-407

Seasonal and vertical changes in abundances of bacteria and heterotrophic nanoflagellates (HNF), and HNF grazing on bacteria were investigated in a small eutrophic inlet of Uranouchi-Wan throughout the years. Bacterial densities in the surface water ranged from 1.2 to 11 (average 4.3)×10⁶ cells ml^–1 with a couple of maxima following the algal blooming. Densities of HNF ranged from 0.54 to 73 (average 16.4)×10³ cells ml^–1 in the surface, and showed almost similar fluctuation pattern to that of bacteria with a time lag of about 1 to 2 weeks. Grazing rates of HNF on bacteria obtained by FLB method were 4.78 to 16.9 (average 10.3±SD 4.8) cells HNF^–1h^–1 in the surface layer in summer, and consequent total bacterial consumption rates by HNF fluctuated from 4 to 99×10⁴ cells ml^–1h^–1. In deeper layers, however, as HNF densities and grazing rates on bacteria were low, the grazing pressure of HNF on bacteria was small. Turnover times of bacteria by HNF grazing in the surface layer were calculated as relatively constant values of 40 to 60 h, however, it decreased to as low as 6 to 7 h when the HNF activity was highest. These results indicate that bacteria grew so actively by consuming organic matter in seawater as to compensate high HNF grazing pressure, and that bacteria and HNF in the microbial loop play important roles on the turnover of substrates in coastal ecosystems.  相似文献   

Helium isotopes of seawater in the Japan Sea     

Naoto Takahata  Yuji Sano  Keika Horiguchi  Kotaro Shirai  Toshitaka Gamo 《Journal of Oceanography》2008,64(2):293-301

We have collected fifty-five seawater samples at seven stations at various depths in the Yamato and Japan Basins of the Japan Sea and measured their helium isotopic ratios. The ³He/⁴He ratios vary from 0.997 R_atm to 1.085 R_atm where R_atm is the atmospheric ratio. The maximum ³He excesses about 8%, are observed at mid-depth (1000 m), and these values are significantly lower than those observed in deep Pacific waters. This implies that mantle-derived helium in deep Pacific water cannot enter the Japan Sea since it is an almost landlocked marginal sea. The observed 8% excess ³He may be attributable to the decay product of tritium. Slightly higher ³He/⁴He ratios in the Bottom Water were observed in the Yamato Basin than in the Japan Basin. The ventilation ages of seawater shallower than 1000 m are calculated as about 5 to 20 years, which is consistent with the CFC ages reported in the literature. There is a positive correlation between the apparent oxygen utilization and ³H-³He ages. The estimated oxygen utilization rate from the correlation in a layer between 500 m and 1000 m is about 3 μmol/kg/yr, which is similar to that in the eastern subtropical North Atlantic.  相似文献   

Spatial variability of chemical tracers in surface snow along the traverse route from the coast to 1000 km inland at east Dronning Maud Land, Antarctica   总被引：1，自引：0，他引：1  

Toshitaka Suzuki  Yoshinori Iizuka  Teruo Furukawa  Kenichi Matsuoka  Kokichi Kamiyama  Okitsugu Watanabe 《极地研究(英文版)》2003,14(1)

1　IntroductionAntarcticicesheetisaburialgroundforatmosphericdeposition .Sincethereiscon tinuousinteractionbetweentheicesheetandtheatmosphere,variousatmosphericsub stancesareinjectedtotheicesheetsequentiallyintimeandspace.Therefore,verticalanalysesoftheicesheetprovideuswithinformationaboutpastclimaticchange (Delmas1 992 ;LegrandandMayewski 1 997)andhorizontalanalysesoftheicesheetprovideuswithknowledgeregardinglong rangetransportofairbornematerials (Kamiyamaetal.1 989;KreutzandMayewski 1 999)…  相似文献   

Fe–Mg partitioning between post-perovskite and ferropericlase in the lowermost mantle     

Takeshi Sakai  Eiji Ohtani  Hidenori Terasaki  Masaaki Miyahara  Masahiko Nishijima  Naohisa Hirao  Yasuo Ohishi  Nagayoshi Sata 《Physics and Chemistry of Minerals》2010,37(7):487-496

Fe–Mg partitioning between post-perovskite and ferropericlase has been studied using a laser-heated diamond anvil cell at pressures up to 154 GPa and 2,010 K which corresponds to the conditions in the lowermost mantle. The composition of the phases in the recovered samples was determined using analytical transmission electron microscopy. Our results reveal that the Fe–Mg partition coefficient between post-perovskite and ferropericlase (K _D^PPv/Fp) increases with decreasing bulk iron content. The compositional dependence of K _D^PPv/Fp on the bulk iron content explains the inconsistency in previous studies, and the effect of the bulk iron content is the most dominant factor compared to other factors, such as temperature and aluminum content. Iron prefers ferropericlase compared to post-perovskite over a wide compositional range, whereas the iron content of post-perovskite (X _Fe^PPv, the mole fraction) does not exceed a value of 0.10. The iron-rich ferropericlase phase may have significant influence on the physical properties, such as the seismic velocity and electrical conductivity at the core–mantle boundary region.  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   

Tomographic inversion of P‐wave velocity and Q structures beneath the Kirishima volcanic complex, southern Japan, based on finite difference calculations of complex traveltimes     

Toshitaka Tomatsu  Hiroyuki Kumagai  Phillip B. Dawson 《Geophysical Journal International》2001,146(3):781-794

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