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1.
We recorded clear transients in the electric and magnetic fields upon sudden slip in stick–slip experiments on dry, cylindrically shaped, quartz-free rock specimens of basalt and peridotite with a 30° saw-cut (representing a fault) at confining pressures of up to 120 MPa. The amplitudes of the measured electric field signals were always higher at the electrode pair oriented parallel to the strike of the fault than at the pair oriented perpendicular. This anisotropy suggests a preferred electric polarization normal to the slip surface. The transients in the electric and magnetic fields were observed only when the fault slip occurred by stick–slip mode, not by a stable mode of the sliding, and the amplitudes of the electric field signals increased with increasing stress drop. It is suggested that the generation process of the electromagnetic signals is closely related to the characteristic behavior of the fault at the time of the initiation of slip during stick–slip events, probably with respect to the intensity of the signals. We propose that one or both of the following two processes characteristic of the fault at the time of the initiation of slip during stick–slip events are essential for the generation of detectable electromagnetic signals: rapid slip along the simulated fault and separation of the rock masses across the fault. 相似文献
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Candidate precursors: pulse-like geoelectric signals possibly related to recent seismic activity in Japan 总被引:1,自引:0,他引:1
Yuji Enomoto Akito Tsutsumi Yukio Fujinawa Minoru Kasahara Hiroshi Hashimoto 《Geophysical Journal International》1997,131(3):485-494
Telemetric network observations of pulse-like geoelectric charge signals using a vertical dipole buried under the ground were undertaken at various observation sites over a wide area in Japan from April 1996. From continuous records of the signals during the six months following that, we attempted to select anomalous signals, possibly related to seismic electric activity. Special attention was paid to the elimination of noise resulting from industrial and meteorological electric activity, comparison with other electromagnetic signals in the VLF band and the relation between the precursor period and the distance from the eventual main shock that occurred in Japan. Four candidate precursor electric signals, which were not contaminated by industrial and meteorological electric activity, were then selected, of which the second appeared before the Akita-ken Nairiku-nanbu earthquake swarm, for which the maximum M = 5.9 occurred on 1996 August 11, and the third and fourth before the Chiba-ken Toho-oki earthquake, M = 6.6, on 1996 September 11. A tentative qualitative model explaining why the candidate precursory signal is related to stress building up before an earthquake is presented in terms of the electrification of gases released from fracturing rocks immediately prior to the main shock. 相似文献
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Ayaka Sakabe Ken Hamotani Yoshiko Kosugi Masahito Ueyama Kenshi Takahashi Akito Kanazawa Masayuki Itoh 《Theoretical and Applied Climatology》2012,109(1-2):39-49
Very few studies have conducted long-term observations of methane (CH4) flux over forest canopies. In this study, we continuously measured CH4 fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1?year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH4 probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH4 fluxes were sensitive to rainfall, probably because CH4 emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH4 fluxes changed from sink to source and vice versa. 相似文献
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Sensitive Ocean Bottom Implanted Tiltmeters (OBITs) with a sophisticated data retrieval system have been developed in order to observe directly the subduction of oceanic lithosphere. The OBIT is the first long-term geophysical instrument which was designed to be deployed by a manned deep-sea submersible. When the OBIT is put on oceanic lithosphere which is bending and is about to subduct under a deep sea trench, the OBIT records the subduction by observing the tilt of the surface of the lithosphere. The OBIT system has a sensitivity of 10-8 radian, which is enough to detect the ongoing subduction in months or years. The OBIT may give an answer to the question whether there are fluctuations in the subduction rate.Two OBITs were successfully deployed on a seaward slope of the Kuril Trench by the newly built French deep submersible, Nautile. The OBITs were installed on the northwest shoulder of Erimo seamount, at a depth of 3930 m, in the Kuril Trench. In order to attain stable long-term observations of crustal deformations, the sensing unit was cemented onto bare rock by mortar. We have not yet had an opportunity to recover the data.The life of the instruments is expected to be more than five years. An acoustic data transmission system has been developed for the OBIT data recovery. The stored data can be retrieved at any moment during the observation period, with no need to retrieve the instruments nor to interrupt the observation, by use of the acoustic system. The acoustic system has a high data transmission rate as well as extremely low power consumption. This will be the first long-term crustal deformation measurement on the sea floor. 相似文献
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The present study deals with the elucidation of sterol composition of the marine sediments in Kagoshima Bay. The identification of each sterol was performed by gas-liquid chromatography, Ag+ impregnated column chromatography, mass spectrometry, and nuclear magnetic resonance spectrometry. The sediment obtained near the estuary of River Koutsuki contained large portions of 5-stanols such as coprostanol and 24-ethylcoprostanol basides 5-stanols such as cholestanol, 24-methylcholestanol, and 24-ethylcholestanol in the sterol fraction. These 5-stanols in the marine sediment may be derived from the fecal contamination by domestic sewages. 相似文献