The purpose of this study is to understand the effect of the fluctuation of the water level in Lake Nasser on the seismicity in the Aswan area, Egypt. Two statistical methods have been applied using the sequence of seismic events between 1982-1998 with local magnitude m ≥ 2.0, recorded by the Aswan Regional Seismological Center in Egypt. Firstly, a cross-correlation method is adopted to find the relationship between the water level and the seismicity. A maximum correlation coefficient of +0.55 was obtained for the period (1982-1985) at a 60 days time lag. However, coefficients are very small for other periods. Secondly, a point-process procedure is applied to the seismicity for the period (1992-1998), where a hazard function includes a term presenting reservoir-induced seismicity. This analysis confirms a weak relation between the fluctuation of the water level and the seismicity in the area. The result suggests that the seismicity in the area becomes active during a period when the water level is decreasing from the maximum to the minimum.

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Polarization anomalies of Love waves, sometimes called quasi-Love waves, are likely to be caused by lateral variations of azimuthal anisotropy in the upper mantle. Polarization anomalies of Love waves from the 9 October 1995 earthquake near the coast of Jalisco, Mexico, have been recorded by the Pacific21, IRIS, and Japan Meteorological Agency networks of broadband seismometers in and around Japan. The Love-to-Rayleigh conversion areas for the clearly detected quasi-Love waves are located by using the group velocities of the observed surface waves. In the cases of the stations in the northern part of Japan and Philippine, the locations of the Love-to-Rayleigh conversions mostly concentrate near the trenches, and suggest that the properties of the azimuthal anisotropies in the upper mantle have lateral variations across the trenches. We infer that the lateral variations of the azimuthal anisotropies may reflect the changes of the mantle flow due to the subducting slabs. The Love-to-Rayleigh conversion areas for the other stations mainly concentrate near the Emperor seamounts and the Mid-Pacific mountains. Several results of surface wave tomographic studies show that the azimuthal anisotropies in these regions are much weaker than those in the central part of the Pacific along the paths. The lateral variation in azimuthal anisotropy may cause the Love-to-Rayleigh conversions.

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We perform three-dimensional numerical simulation of rock fracturing under uniaxial compression by extending the discrete element method (DEM). Rock sample is modeled as an assemblage of about four thousand spheres having the same radius. Each element satisfies equations of motion for both translation and rotation. In extension of the DEM, we assume cohesion between elements and constrained rotation of the elements; these assumptions are required to treat the continuum by the DEM. We study two cases of uniaxial compression tests: A homogeneous sample having an equal cohesion force between elements and heterogeneous sample having weak parts of cohesion in one percent of the total number of the bonds of elements. We present the detail of fracturing process of model rock samples and obtain stress-strain curve for each case. The homogeneous sample shows a cone-shaped fault system, whereas the heterogeneous sample shows complex fault system consisting of major and sub faults. We find that the inner stress and rotation of elements show the negative correlation during fracturing process. The results are in good agreement with both experimental and theoretical results.

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The day-to-day variation of the geomagnetic daily variation has been examined using hourly data of the Z component at Chichijima (geographic 27.15°N, 142.30°E; geomagnetic 18.11°N) in the northwestern Pacific Ocean. Principal component analysis is applied to the data from 1970 to 1992, and 2-day, 3-day, and 5-6-day oscillations were extracted from the day-to-day variation of the daily profile. The temporal variations of both the waveform and amplitude of each oscillation were clarified. The fluctuation associated with any of these oscillations is confined to the sunlit hours, which infers the oscillations are originated from ionospheric currents. Although the amplitudes of the oscillations are variable, they seem to be present almost continuously. Each oscillation is expressed primarily by the periodic increase and decrease of the amplitude of the quiet time daily variation, and the deviation from the normal level statistically amounts to 12% (3-day oscillation), 15% (5-6-day oscillation), and 17% (2-day oscillation) of the mean amplitude of the daily variation. There are cases, however, for which the magnitude is considerably amplified during a short duration. There also exist the oscillations that show the three periods in the pattern of the daily variation as well as in intensity. The result of analysis of day-to-day variations at other four stations indicates that the oscillations are phenomena having some latitudinal extent across the geomagnetic equator.

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Data of electrical voltage measured between the ends of the CAM-1 cable, during fifteen months, have been analysed in order to determine the electrical stability of the cable and to obtain some preliminary information related to water transport. The monthly average of the potential measured during days with low geomagnetic activity suggests a periodicity of 120 days that was tentatively interpreted as having origin in water flow. These results show a small trend that is compatible with no drift in the cable. The mean electric field estimated from quiet days is 0.206 ± 0.022 mV/km. If the variations of this potential are attributable to ocean water transport a total water flow of ±0.09 cm/s is estimated. This value represents a maximum value for temporal variations of the spatially averaged water-flow velocity.

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Cenozoic northward drift of the Australian plate was determined from paleomagnetism of Middle Eocene through Pleistocene sediment cores from ODP Leg 182 (Sites 1126, 1128, and 1134) in the Great Australian Bight. Paleolatitude estimates are based on stepwise AF and thermal demagnetization of -400 discrete samples, of which -250 provided reliable data. The characteristic magnetization of the sediments resides in magnetite and magnetic sulfides. Middle Eocene through Lower Oligocene (-36 Ma) paleolatitudes of -52° (±2°) change gradually to Late Miocene (-9 Ma) paleolatitudes of -48° (±2°). These data, combined with Australian paleomagnetic pole data, indicate a slow rate of northward motion through much of the Cenozoic (-28 mm/yr). These data also indicate an abrupt acceleration in the Late Miocene (drift rate -115 mm/yr), coinciding with tectonic events in Southeast Asia. Paleolatitude estimates support Miocene versions of the Australian apparent polar wander path that place the Oligocene-Miocene pole (-25 Ma) at -70°S-125°E and the Late Miocene pole at -70°S-105°E (e.g., Idnurm, 1985, 1994). Inclination data for discrete samples also provide a refined magnetostratigraphy for portions of the Miocene, Oligocene, and Eocene carbonate and siliciclastic section of the Great Australian Bight.

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Using the model of a spherical symmetric atmosphere the large-scale electric fields generated by the global thunderstorms are investigated. Theoretical formulations have been developed to calculate high-altitude electric fields due to global thunderstorms, taking into account the presence of the ionosphere. We make use of the assumption that in the ionosphere the geomagnetic field lines are equipotentials. The calculations indicate that the solution is highly sensitive to the variation of this upper boundary condition.

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Atmospheric mountain lee waves excited by a strong westerly wind ahead of approaching cold front are shown to have significant effect on GPS positioning. Before the approach of the cold front significant atmospheric gradients caused by the inhomogeneous water vapor are detected at the sites along the east coast of the Izu Peninsula because of a wet atmosphere to the west of these sites. In contrast, the island site 6 km east of the coast detects a strong gradient with the opposite sense. The Geostationary Meteorological Satellite cloud shows rows of the clouds due to mountain lee waves consistent with the GPS measurements. A numerical simulation explains the mountain lee waves. The atmospheric perturbations induce large systematic errors in the estimates of horizontal positions of the sites in the region.

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