Crustal deformation on land can now be measured and monitored routinely and precisely using space geodetic techniques. The same is not true of the seafloor, which covers about 70 percent of the earth surface, and is critical in terms of plate tectonics, submarine volcanism, and earthquake mechanisms of plate boundary types. We develop new data processing strategies for quantifying crustal deformation at the ocean floor: single- and double-difference methods. Theoretically, the single difference method can eliminate systematic errors of long period, while the double difference method is able to almost completely eliminate all depth-dependent and spatialdependent systematic errors. The simulations have shown that the transponders on the seafloor and thus the deformation of the seafloor can be determined with the accuracy of one centimeter in the single point positioning mode. Since almost all systematic errors (of temporal or spatial nature) have been removed by the double difference operator, the double difference method has been simulated to be capable of determining the threedimensional, relative position between two transponders on the seafloor even at the accuracy of sub-centimeters by employing and accumulating small changes in geometry over time. While the surveying strategy employed by the Scripps Institution of Oceanography (SIO) requires the ship maintain station, our technique requires the ship to move freely. The SIO approach requires a seafloor array of at least three transponders and that the relative positions of the transponders be pre-determined. Our approach directly positions a single transponder or relative positions of transponders, and thus measures deformation unambiguously.

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Four subsets of earthquakes recorded by an island-wide seismic network from 1991 to 2002 in the Taiwan area are relocated using the joint hypocenter determination (JHD) technique. Relatively large horizontal and vertical shifts are observed during the relocation, which indicates there may be systematic earthquake miss-locations in the Taiwan earthquake catalog due to the over-simplification of complicated earth structures to a simple 1-D velocity model. Generally, earthquakes are more clustered after the JHD relocation. Subsurface structures defined by the relocated seismicity become clearer, while they are not as clear in the initial hypocenters. Significant subsurface structures defined by the relocated seismicity are fault systems beneath the Central Mountain Range, beneath the northern Longitudinal Valley and Coastal Range, beneath the southern Longitudinal Valley and Coastal Range, and beneath the Chao-Chou fault in southern Taiwan. Another set of results from the JHD analysis, P- and S-wave station corrections, provide valuable information on the lateral velocity variations. The JHD station corrections indicate that upper crustal materials in the Central Mountain Range are characterized by higher velocity than those in the Western Foothills and Coastal Plain. The patterns of the observed JHD station corrections are also thoroughly consistent with surface geology observations. Analysis of the four clusters of earthquakes resulted in a remarkable similarity in JHD station corrections, indicating that the overlapping subsurfaces where two or more clusters of rays had traveled through were relatively shallow. These subsurfaces are responsible for the observed patterns of positive and negative JHD station corrections.

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We carried out high density aftershock observations a week after the 2000 Western Tottori Earthquake for 40 days. We deployed 72 seismic stations in and around the aftershock area. The average spacing of the stations in the aftershock area was 4-5 km. We determined accurate hypocenters and focal mechanisms for -1, 000 aftershocks and obtained a high resolution 3-D velocity structure in the source region. High P and S wave velocity anomalies (> 4%) near the southeasternmost aftershock area at 2 km depth correlated with Jurassic to Late Cretaceous plutonic and high pressure metamorphic rocks. The depth distribution of the P and S wave velocities along the mainshock fault showed that high velocity anomalies were located at the shallow southeastern edge and the deeper central part of the aftershock area. The ratio between P and S wave velocities in the high velocity anomalies was a little higher (-1.75) than the average value (-1.70) in the upper crust. These results indicate that the high velocity anomalies could correspond to the plutonic or metamorphic rocks. The distributions of the high velocity anomalies and large slips of the mainshock were complementary. These suggest that the high velocity anomalies could be stronger than the surrounding materials and might behave as barriers to the mainshock rupture.

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A detailed paleomagnetic study of a young Late Holocene olivine-basalt flow from the Xitle volcano in the southern Basin of Mexico was completed to evaluate the consistency and reliability of the record derived from fresh well-preserved and exposed lava flows. One-hundred oriented standard paleomagnetic cores corresponding to 10 different lava effusion episodes were collected from unit-flow V. Thermomagnetic analyses show that bulk magnetic properties and remanence is carried in most cases by Ti-poor titanomagnetite, presumably resulting from oxy-exsolution processes during the initial flow cooling. Unblocking temperature and coercivity suggests pseudo-single domain magnetic grains for these (titano) magnetites. Thermal and alternating field demagnetizations show well-defined univectorial magnetizations. Most sites present a mean direction with small angular dispersion around the dipolar direction for central Mexico. The overall mean direction (N = 10, Dec = 1.1°, Inc = 34.1°, k = 531 and α₉₅ = 2.1°) is characterized by small angular dispersion and inclination close to the dipolar value for the locality. Anisotropy ofmagnetic susceptibility lineation agrees with the geologically-inferred flow direction. Various samples from the 10 lava flows were selected for Thellier paleointensity experiments because of their stable remanent magnetization and relatively low within-site dispersion. According to reliability parameters, the obtained paleointensities are of reasonably good quality. Nine mean paleointensities range between 48.6 and 73.9 μT. The overall mean paleointensity of 59.9-7.7 μT is higher than the present-day field of 43 μT, consistent with the global data for this time-period. Most samples presented alteration during the cooling rate test, and no correction was made to these samples. Those samples on which cooling-rate correction was applied give a flow mean lower than the raw paleointensity data, as was expected.

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Anisotropy of magnetic susceptibility (AMS) and rock magnetic studies have been carried out for the metasedimentary rocks in the central Okcheon Metamorphic Belt. The study area is divided into three metamorphic zones: the biotite zone, the garnet zone, and the sillimanite + andalusite zone from southeast to northwest. Magnetic foliation dipping to the northwest is the dominant magnetic fabric in the biotite zone. Magnetic lineation plunging down-dip of the vertical cleavage plane is appeared in the southeastern part of the garnet zone, while magnetic lineation plunging to southeast prevails in the middle and northwestern parts of the garnet zone. It is interpreted that this apparent synform structure, defined by AMS fabric data, was formed by successive top-to-the-southeast vergent thrusting followed by back-steepening process during the regional metamorphism in the Late Paleozoic. In the sillimanite + andalusite zone, AMS fabric is clearly defined and may reflect a tectonic fabric, recorded during the thermal metamorphism in the middle Jurassic, despite the scarcity of rock fabric in the field. The spatial distribution of magnetic mineralogy, defined by the rock magnetic results, implies the 500°C isotherm at the boundary between the biotite and garnet zones, which is associated with the transformation of pyrrhotite into magnetite above 500°C under the oxidizing condition.

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This paper presents for the first time a study of HINOTORI satellite measurements of electron density and electron temperature in the topside ionosphere exclusively for magnetic storm departures. Special focus was given to the major storm of 1 March, 1982. While large enhancements in T_e characterize the day time storm response, marked increases in N_e dominate the night time deviations. The night time N_e enhancements which are rather remarkable during 0000-0400 LT are also found to be accompanied by significant T_e increases, by as much as 300 K. The statistical picture that emerges from the study of a large number of storms suggests significant nocturnal T_e enhancements which correlate with the magnitudes of storm intensities. Ring current particles through charge exchange processes seem to be a major source of heat input to thermal electrons, though other sources may also be important.

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The SRP-4 rocket was launched at 12:07 LT on 18 March 2002. The objective of this rocket experiment is the investigation of the electron density profile in the high-latitude D-region of the ionosphere at noon. The Low frequency and Medium frequency band radio Receiver (LMR) and the DC Probe System (DPS) were installed on-board the rocket to estimate the D-region electron density. The LMR measured the intensities of radio waves received from ground-based stations operating at 257 kHz, 660 kHz and 820 kHz, respectively. The DPS measured the electron current and the positive ion current using the biased electrodes. The electron density profile at altitudes below 90 km was estimated from the measured absorption of these radio waves. It was found that the electron density began to increase at the altitude of 52 km and was larger than that estimated by the International Reference Ionosphere model at altitudes from 74 km to 89 km.

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Velocity distribution of the solar wind electrons that penetrate through the lunar wake boundary is investigated by calculating orbits of the electrons injected into model structures of layers of electric fields. Only the electrons with sufficient energy to overcome the potential difference penetrate through the wake boundary. The electrons injected along the magnetic field lines which intersect the model structure undergo pitch angle scattering due to electric field component perpendicular to the magnetic field. After the passage through the electric field, the electrons have significant perpendicular component of velocity as well as the parallel component larger than a lower limit, which is dependent on the electric potential of the wake boundary. The velocity distribution can account for the cyclotron resonance with sunward-propagating whistler mode waves that were detected by GEOTAIL at 27 lunar radii upstream of the moon on October 25, 1994.

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We have studied the possibility of short time-scale energy transfer from the ice sheet loading and unloading processes to the Earth's interior via viscous dissipation associated with the transient viscoelastic flow in the mantle. We have focussed on the magnitude of glacially induced deformations and the corresponding shear heating for an ice sheet of the spatial extent of Laurentide region in Maxwellian viscoelastic compressible models with a Newtonian viscosity. We have used a discretization method based on the method of lines for integrating the time-dependent evolutionary equations of self-gravitational, viscoelastic flow. We have found that shear heating from the transient viscoelastic flow can represent a non-negligible mantle energy source with cryogenic origins. Volumetric heating by viscous deformation associated with these flows can be locally greater than chondritic heating by radioactivity. In the presence of an abrupt change in the ice loading history, the time average of the integral of the dissipation over depth corresponds to a mantle heat flow of the order of magnitude of mW/m² below the periphery of ancient ice sheets or below their central areas. However, the peak values of this integral in time are almost two orders higher. Our results would suggest that some degree of volcanism may be associated with dramatic episodes in ice loading.

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This investigation was undertaken for searching the source of linear trends in JASC submarine cable data over the time interval of 6 years and estimating the electrode noise level. One of the reasons for a trend is probably the potential instability in the cable ground, which happened because the titanium electrodes of the ground were placed in sea water that is electrochemically active. To study this phenomenon, we have registered the voltage variations of three titanium JASC cable electrodes, which were closely spaced (-15 cm) and placed at a depth of -15 m near the coast for 70 days, synchronously with JASC cable voltage observations. The electrode noise level and coherence between channels were estimated and linear trends in electrode pair voltage variation were revealed. The estimated linear trend magnitude is about 0.28 mV/day, which is comparable with 0.21 mV/day earlier observed in JASC submarine cable data. We concluded that the linear trend in JASC cable data is, at least partly, probably caused by the titanium electrodes potential variations. This linear trend should be registered simultaneously with JASC cable voltage observation, keeping in mind the possibility of finding a procedure for removing it, in order to enhance the signal/noise ratio in data.

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Mn-Cr chronology of four quenched angrites showed that they formed nearly at the same time (4562 Ma) on the surface of the parent-body. Based on the chemical compositions, the cosmic ray exposure ages, and considerations on the thermal history of an achondrite parent-body, we suggest that the four angrites formed on top of a shallow magma ocean on the angrite parent body.

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