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Helicopter-borne aeromagnetic surveys at two different times separated by three years were conducted to better understand the shallow subsurface structure of the Vulcano and Lipari volcanic complex, Aeolian Islands, southern Italy, and also to monitor the volcanic activity of the area. As there was no meaningful difference between the two magnetic datasets to imply an apparent change of the volcanic activity, the datasets were merged to produce an aeromagnetic map with wider coverage than was given by a single dataset. Apparent magnetisation intensity mapping was applied to terrain-corrected magnetic anomalies, and showed local magnetisation highs in and around Fossa Cone, suggesting heterogeneity of the cone. Magnetic modelling was conducted for three of those magnetisation highs. Each model implied the presence of concealed volcanic products overlain by pyroclastic rocks from the Fossa crater. The model for the Fossa crater area suggests a buried trachytic lava flow on the southern edge of the present crater. The magnetic model at Forgia Vecchia suggests that phreatic cones can be interpreted as resulting from a concealed eruptive centre, with thick latitic lavas that fill up Fossa Caldera. However, the distribution of lavas seems to be limited to a smaller area than was expected from drilling results. This can be explained partly by alteration of the lavas by intense hydrothermal activity, as seen at geothermal areas close to Porto Levante. The magnetic model at the north-eastern Fossa Cone implies that thick lavas accumulated as another eruption centre in the early stage of the activity of Fossa. Recent geoelectric surveys showed high-resistivity zones in the areas of the last two magnetic models.

A gravity survey was carried out January in 2013 in order to understand a shallow and whole underground structure. The measurement points were arranged at every 300m interval along the road and the number of measurement points became 141 points. The characteristic Bouguer anomalies are that the gravity high anomalies corresponding to anticline structure extend from

SUMMARY The phenomenon of shear-wave splitting has been observed at two seismic stations with three-component seismographs above shallow microcarthquakes which occurred at depths of 1-2 km in the Takinoue geothermal area of northern Honshu. An almost uniform alignment of the polarizations of the faster-split shear wave in the direction of ENE-WSW may result from the presence of non-randomly distributed liquid-filled microcracks. Two models of crack distribution reproduce the observed polarization pattern. In the first model vertical microcracks are aligned in the ENE-WSW direction, while the second supposes a distribution of microcracks striking in the ENE-WSW direction but dipping randomly. The ENE-WSW strike of the cracks in both models is consistent with the direction of the ENE-WSW maximum horizontal compressive stress inferred from the analysis of earthquake mechanisms in the study area. It differs slightly from the strike of vertical fractures (WNW-ESE) obtained by hydraulic fracturing experiments at sites about 10 km west of the study area. The tectonic stress regime obtained from an analysis of focal mechanisms of microearthquakes occurring in this area seems to be consistent with the latter model of the crack distribution from the shear-wave analysis, at least at depths less than about 700 m. An analysis of the delay times between the faster- and the slower-split shear waves has revealed a region with anomalously large delay times normalized to ray path lengths. A 3-D P-wave velocity inversion indicates that this region is a low P-wave velocity zone. The low P-wave velocities and high shear-wave birefringence is consistent with a relatively dense distribution of liquid-filled microcracks.