Evidence of a highly attenuative aseismic zone in the active collision orogen of Taiwan

Seismic attenuation across an aseismic zone in the southeastern Central Range of Taiwan is investigated in terms of t* data with inverted Q models. The t* data are obtained by fitting the observed spectra of P and S waves with an ω2 source model using broadband records of a 25-station linear array deployed across southern Taiwan. Both tp* and ts* data at the eastern stations show remarkable decreasing trends with depth down to 40 km in contrast to the western stations. The inverted Qp and Qs profiles across southern Taiwan reveal a high attenuation zone (Qp = 288, Qs = 219) at depth about 20 km beneath the eastern stations traversing the southeastern Central Range. High temperature and possible presence of fluids in the high attenuation zone are derived from the Q models. This high attenuation zone happens to coincide with the aseismic zone, suggesting that the aseismic zone may be due to high geothermal and partial melting effects of a very active collision orogeny. The area is also marked by other geological and geophysical indicators in support of this interpretation.