In this study, the P arrivals of 1726 ray paths with the epicentral distances longer than 200 km from 539 earthquakes that occurred in Taiwan are used to investigate the variation of P_n velocity. The results show that the lateral variation of P_n velocity in Taiwan is quite similar to the pattern of gravity anomaly and strongly related to several features of Taiwan's geological structure. The crust is a little thicker (about 39 km) in the Central Range and somewhat thinner toward the east and west. A relatively thin crust (about 35 km) is obtained in the area of Peikang High; however, an unexpected thick crust of greater than 40 km is also found at the corner of southwestern Taiwan. The degree of anisotropy of P_n velocity is found less than 10% and the fast direction is generally in the EWdirection. This direction is parallel to the axis of compressional stress or the direction of plate motion, indicating that the anisotropy results from the deformation of the upper mantle.

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In GPS atmospheric sounding, geodetic positioning, robotics and photogrammetric (perspective center and intersection) problems, distances (ranges) as observables play a key role in determining the unknown parameters. The measured distances (ranges) are however normally related to the desired parameters via nonlinear equations or nonlinear system of equations that require explicit or exact solutions. Procedures for solving such equations are either normally iterative, and thus require linearization or the existing analytical procedures require laborious forward and backward substitutions. We present in the present contribution direct procedures for solving distance nonlinear system of equations without linearization, iteration, forward and backward substitution. In particular, we exploit the advantage of faster computers with large storage capacities and the computer algebraic softwares of Mathematica, Maple and Matlab to test polynomial based approaches. These polynomial (algebraic based) approaches turn out to be the key to solving distance nonlinear system of equations. The algebraic techniques discussed here does not however solve all general types of nonlinear equations but only those nonlinear system of equations that can be converted into algebraic (polynomial) form.

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Diverse magnetotelluric data (apparent resistivity, phase or geomagnetic transfer function) used during the inversion process provide different information on the model as a consequence of data error. The relative influence of these data constitutes a subject of interest on the inversion process. This influence can be evaluated from the error ratio between two types of data; thus, when phase and the logarithm of apparent resistivity are involved, the wellknown ratio of one half is obtained. A new error ratio between the geomagnetic transfer function and the logarithm of apparent resistivity is presented. We deduced this ratio, which is bounded by one half of the amplitude of the geomagnetic transfer function. In order to verify this new ratio, we employed a technique based on the study of the RMS misfit, obtained after an intensive inversion computation whilst taking different error values for the different data. This technique was applied to synthetic and experimental data, and the results agree with the proposed value. This value should be taken into account for setting error floors when performing joint data inversion in order to obtain the same influence from the different data.

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A fast and stable inversion scheme has been developed using the localized nonlinear (LN) approximation to analyze electromagnetic fields obtained in a borehole. The medium is assumed to be cylindrically symmetric about the borehole, and to maintain the symmetry a vertical magnetic dipole is used as a source. The efficiency and robustness of an inversion scheme is very much dependent on the proper use of Lagrange multiplier, which is often provided manually to achieve a desired convergence. We utilize an automatic Lagrange multiplier selection scheme, which enhances the utility of the inversion scheme in handling field data. In this selection scheme, the integral equation (IE) method is quite attractive in speed because Green's functions, the most time consuming part in IE methods, are repeatedly re-usable throughout the selection procedure. The inversion scheme using the LN approximation has been tested to show its stability and efficiency using synthetic and field data. The inverted result from the field data is successfully compared with induction logging data measured in the same borehole.

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The auroral electrojet is enhanced in the polar ionosphere associated with charged particle precipitation and fieldaligned currents during substorms. In this paper the geometry of the elctrojet is determined by using the ionospheric equivalent current systems for every 5 minutes during March 18 and 19, 1978. The latitudinal and local time shifts of the oval are examined. Possible relationship of the electrojet oval with expansion of the auroral oval and the fieldaligned current belts during substorms are discussed. The electrojet oval in the polar region consists of westward and eastward electrojets, varying with AE index. As the magnetic activity increases, the westward electrojet has distinct latitudinal shifts in different local time sectors: it shifts poleward around the midnight (23: 00-03: 00 MLT), while moves equatorward in the morning sector (03: 00-10: 00 MLT) and afternoon sector (20: 00-23: 00 MLT. The eastward electrojet includes two insulated parts: a higher-latitude part around 80. latitude in the nighttime sector (21: 00-03: 00 MLT) and a lower-latitude part between 60°- 70°latitudes in other local time sectors. As AE index increases, the higher-latitude part of the eastward electrojet expands eastward from 03: 00 to 08: 00 MLT, while the lower-latitude part shows a equatorward shift in the afternoon sector, which is more or less similar to the westward electrojet.

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The growth of meter-sized bodies in the solar nebula by dust accretion is examined. The meter-sized bodies have velocity about 50 m/s relative to the gas and small dust aggregates. When a small dust aggregate hits a meter-sized body, the aggregate breaks into dust monomers. These monomers accrete onto the body after several bouncing as proposed by Wurm et al., Icarus (2001), if the mean free path of the gas molecules is larger than the radius of the body. On the other hand, the monomers never hit the surface of the body again, if the body is much larger than the mean free path of the molecules. The sizes of bodies would be limited to the order of 10 times the mean free path. Kilometer-sized planetesimals were hardly formed by dust accretion in the region within 5 AU from the sun where the mean free path is less than 1 m. The planetesimals were probably formed by the gravitational instabilities in this region.

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We describe performance of a new two-channel Fabry-Perot interferometer (FPI) with two thermoelectric-cooled CCD detectors to measure neutral winds for both the 558-nm (mesopause region) and 630-nm (thermosphere) airglow emissions simultaneously at Shigaraki (34.8°N, 136.1°E), Japan. The employment of the thermoelectric cooling system enables us continuous automatic operation of the FPI since October 2000. The random errors of wind measurement are estimated to be -5-8 m/s and -10-50 m/s for 558 nm and 630 nm, respectively. The wind velocities obtained by the FPI (558 and 630 nm) fit well with those obtained by the collocated Middle and Upper (MU) atmosphere radar.

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We attempt to detect the lineament structure inside the crust using a shear-wave splitting analysis. A seismicity map suggests several lineaments in southwest Japan. No clear active fault was found to support the lineaments. We researched shear-wave splitting in southwest Japan using two later phases: PpPms and PpSms. The PpPms is a later S-phase, which is reflected at the surface as a P wave, dives again, and reflected and converted from P to S at the Moho boundary. The PpSms is a later arriving S-phase, which is converted from P at the Earth's surface, and is reflected at the Moho discontinuity before arriving at a seismic station. The PpPms and PpSms phases are used to detect lineament structures inside the crust. The observed polarization directions obtained are ENE-WSW, NE-SW, and N-S with a lateral variation. The directions are not consistent with that of maximum principal stress in the area. The results of shear-wave splitting in southwest Japan could not be explained by crack-induced anisotropy caused by maximum principal stress. The direction NE-SW is consistent with that of the geological lineament structure in this area. The shear-wave splitting is probably caused by the lineament structure inside the crust.

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A high velocity passage of a meteoroid through the atmosphere generates a shock wave with a conical front. When the shock front arrives at the surface, it causes high frequency ground motions that are registered on the seismograms. We can use seismological data to determine the trajectory of the meteoroid in the atmosphere. A strong shock wave from the 1998 Miyako fireball is recorded by more than 20 stations in a dense array of seismographs installed in the northeastern region of Honshu Island, Japan. We determine the velocity and the trajectory of the fireball in the upper atmosphere using the arrival times of the shock wave at the stations.

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