We assess the first mission of the GEOSTAR (GEophysical and Oceanographic STation for Abyssal Research) deep-sea multidisciplinary observatory for its technical capacity, performance and quality of recorded data. The functioning of the system was verified by analyzing oceanographic, seismological and geomagnetic measurements. Despite the mission's short duration (21 days), its data demonstrated the observatory's technological reliability and scientific value. After analyzing the oceanographic data, we found two different regimes of seawater circulation and a sharp and deepening pycnocline, linked to a down-welling phenomenon. The reliability of the magnetic and seismological measurements was evaluated by comparison with those made using on-land sensors. Such comparison of magnetic signals recorded by permanent land geomagnetic stations and GEOSTAR during a “quiet”day and one with a magnetic storm confirmed the correct functioning of the sensor and allowed us to estimate the seafloor observatory's orientation. The magnitudes of regional seismic events recorded by our GEOSTAR seismometer agreed with those computed from land stations. GEOSTAR has thus proven itself reliable for integrating other deep-sea observation systems, such as modular observatories, arrays, and instrumented submarine cables.

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Eruptive and caldera-forming activity at Miyakejima volcano island, Japan, commenced on 26 June 2000 was accompanied by more than 40 day of seismic swarms and significant crustal deformation in the nearby islands and sea region besides those at Miyakejima itself. The migration of the hypocenters in the early stage suggests that they were triggered by magma intrusion from Miyakejima. However, it remains uncertain whether the long-lasting seismic swarms and ground displacements in the northern Izu-islands were totally maintained by the magma flow from Miyakejima, because another magma source nearby Kozushima was suggested previously, which is 40 km north-west of Miyakejima, based upon anomalous ground displacements. Here we report the detection of associated changes with the 2000 activity in both absolute gravity and elevation at Kozushima as well as those at Miyakejima. Combining these data with horizontal GPS displacements, we extend the analysis of Nishimura et al. (2001) and construct an optimum source model, so that we can account for the observed changes in geodetic data and determine the mass budget of the magma flow. The total mass of the newly intruded dike offshore of Miyakejima and nearby Kozushima turned out to be 130% or greater than the lost mass at Miyakejima. As long as there are no other source elements, another magma reservoir near Kozushima is required and is suggested to have been activated, causing the seismic swarms and crustal deformation. We may speculate as a phenomenology that the rapid lateral magma flow from Miyakejima in the very beginning of the unrest awakened a dormant reservoir offshore of Miyakejima and Kozushima.

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In the recently developed Spatial Reference System that is designed to check and control the accuracy of the three-dimensional coordinate measuring machines and tooling equipment (Metronom US., Inc., Ann Arbor: http: //www. metronomus. com), the coordinates of the edges of the instrument are computed from distances of the bars. The use of distances in industrial application is fast gaining momentum just as in Geodesy and in Geophysical applications and thus necessitating efficient algorithms to solve the nonlinear distance equations. Whereas the ranging problem with minimum known stations was considered in our previous contribution in the same Journal, the present contribution extends to the case where one is faced with many distance observations than unknowns (overdetermined case) as is usually the case in practise. Using the Gauss-Jacobi Combinatorial approach, we demonstrate how one can proceed to position without reverting to iterative and linearizing procedures such as Newton's or Least Squares approach.

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An arbitrary point distribution consisting of a finite number of points on a unit sphere may be completely and uniquely represented by an analytic function in the form of a spherical harmonic expansion. The applications of this representation function are illustrated in an analysis of the symmetries in the virtual geomagnetic pole (VGP) distribution of the polarity reversal records of the past 10 million years. We find that the longitudinal confinements in the VGP distribution are (a) persistent only in the equatorially symmetric part (of the non-zonal symmetries) of the VGP distribution and (b) strong along the east coast of the North American continent and weak along the longitudes of East Asia-Australia. We also find that the equatorially symmetric patterns in the VGP distribution appear to extend preferentially into the Pacific Ocean and are relatively depleted in the longitude band associated with Africa.

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The traditional Chapman-Miller analysis for the solar, S, and lunar, L, geomagnetic variations is generalized by incorporating a time description of the seasonal changes of the harmonic coefficients. The modulation model consists of the sum of harmonic oscillators with basic carriers having the fundamental frequencies of the solar and lunar daily components, which are being amplitude and phase modulated by the annual variation and its harmonics. The solar cycle effect is a priori taken into account by using the daily sunspot numbers as an auxiliary input and including the Wolf ratios in the amplitude and phase terms. For the station Dourbes (Belgium), solar and lunar harmonics show a marked increase in amplitude from winter to summer, but the seasonal changes of L significantly exceed that of S. The phase shift from winter to summer in L is about three times that of S. The Wolf ratios of the Fourier amplitudes are of the same order of magnitude for both the S and L variations. Removal of the relatively important ocean dynamo contribution does not have an appreciable consequence for the determination of the seasonal changes and the sunspot cycle influence.

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A comparison is performed between monthly-mean nonmigrating diurnal tide wind components at 95 km derived from Upper Atmosphere Research Satellite (UARS) wind observations, the Middle Atmosphere Circulation Model at Kyushu University (MACMKU), and the Global Scale Wave Model (GSWM) driven by latent heating due to deep tropical convection. A degree of overall agreement is obtained in the sense that annual-mean spectra at 95 km indicate that the UARS data, MACMKU and GSWM all share the same nonmigrating tide components (eastward-propagating with zonal wavenumber s = -3; westward-propagating with s = 2; standing or zonallysymmetric with s = 0; DE3, DW2, D0) at about the same power level. In combination with the migrating tide these wave components give rise to significant longitude variability in the total diurnal tidal fields. Beyond the above model/measurement agreements, significant discrepancies remain between the latitudinal-seasonal structures delineated by models and observation. For MACMKU, some of these discrepancies may be related to the specifics of the convective parameterization that is employed. Significant work remains to better delineate tropospheric forcing mechanisms and nonlinear wave-wave interactions as sources for nonmigrating tides.

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In the context of the space weather predictions, forecasting ring current strength (and of the Dst index) based on the solar wind upstream conditions is of specific interest for predicting the occurrence of geomagnetic storms. In the present paper, we have studied separately its two components: the Dst injection and decay. In particular, we have verified the validity of the Burton's equation for estimating the ring current energy balance using the equatorial electric merging field instead of the original parameter V B_s (V is the solar wind speed and B_s is the southward component of the Interplanetary Magnetic Field, IMF). Then, based on this equation, we have used the phasespace method to determine the best-fit approximations for the ring current injection and decay as functions of the equatorial merging electric field (E_m). Results indicate that the interplanetary injection is statistically higher than in previous estimations using V B_s . Specifically, weak but not-null ring current injection can be observed even during northward IMF, when previous studies considered it to be always zero. Moreover, results about the ring current decay indicate that the rate of Dst decay is faster than its predictions derived by using V B_s . In addition, smaller quiet time ring current and solar wind pressure corrections are contributing to Dst estimates obtained by Em instead of V B_s . These effects are compensated, so that the statistical Dst predictions using the equatorial electric merging field or using V B_s are about equivalent.

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Magnetotelluric (MT) surveys were carried out along some profiles crossing the fault rupture zone associated with the Izmit earthquake which took place on 17 August 1999 in the western part of the North Anatolian Fault Zone (NAFZ). In this paper, we focus on the western part of the fault rupture zone where two different groups of seismicity followed the Izmit earthquake. One group was seen along a narrow belt and corresponds to aftershocks occurring along the fault rupture zone. The other was seen in a circular region and represents a swarm activity, presumably triggered by the occurrence of the Izmit earthquake. Two-dimensional inversion was performed for the MT data acquired along two profiles; one crosses the western end of the fault rupture zone and the other is located in the west of the swarm activity area. In the former case, aftershocks tended to occur in a resistive zone underlain by a moderately conductive zone, as was the case for the hypocenter area. In the latter case, the swarm activity tends to be confined in a conductive zone below a highly resistive zone. This activity is likely to be triggered through pore-pressure changes associated with the Izmit earthquake.

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