Mapping Seismic Attenuation Structures of the Volcanic Area in Northern Taiwan

Three-dimensional body-wave attenuation structures beneath the volcanic area in northern Taiwan are obtained by using the seismic tomographical inversion method. In total, both Pand S-waves of 137 local earthquakes with magnitudes between 2.0 and 5.0 were analyzed. Those events with 3-component digital seismograms were recorded by the Central Weather Bureau Seismographic Network (CWBSN). The results show that a low Qp and Qs zone was found at depths between 0 and 15 km. Two lower Qp/Qs areas beneath the Tatun Volcano Group were found at depths between 25 and 40 km. These features are similar to those of a molten magma body in other volcanic areas, such as Mt. Vesuvius Volcano. Lateral variations in the shallow depths (0~6 km) of the three-dimensional Pand S-wave attenuation structures show that they are generally consistent with the topography of geomagnetic basement. Based on the gradients of Q structures, a weak attenuation discontinuity area within 25.1 and 25.3 N is found, which might be interpreted as the southern boundary of the magma chamber.