研究期間：10108~10207;The four dimensional (space and time) magnetotelluric (MT) study in the area from Chih-Shin-Shan (七星山) to Da-You-Kan (大油坑) during the past 2 years needs to continue. The preliminary results indicate that a dome structure extending more than 10 km beneath the Da-You-Kan was recognized. Low resistivity at top layer with 500m thick might indicate circulation of heated water. A high resistivity layer at depth between 2 and 6 km was detected, and this layer could be associated with high micro-earthquakes zone. The characteristic of this layer is produced by either the magma chamber or geothermal activity. A dome structure of medium resistivity at depth of 6 km was significance; this structure could be interpreted as a magma chamber in which the magma is possibly cooling down, as judged by its higher resistivity. In addition, MT monitoring from January 2011 to May 2011 at Da-You-Kan also indicates that the resistivity increase gradually at a depth around 5 km. One of the possible implications of the finding is that the degassed volatiles migrated not only vertically through the conduit but also laterally through a fracture network, mixing with groundwater and thereby causing the observed resistivity change. It is thus proposed to further investigate whether the above mentioned magmatic system beneath the Da-You-Kan shows promise and is the representative structure of Tatun volcano group. The four dimensional MT study shall move to different site as for the checking from the other site will be revealing if the structure truth. For finding the suitable sites for MT survey efficiently, care born scanning of time domain electromagnetic survey will be employed before the MT soundings in Tatun volcano group. By correlating with the other geophysical and geology data, the possible location of the magma chamber and its movement will be inferred from this 4D MT study .
