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

Abstract

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 ω 2 source model using broadband records of a 25-station linear array deployed across southern Taiwan. Both t p * and t s * data at the eastern stations show remarkable decreasing trends with depth down to 40 km in contrast to the western stations. The inverted Q p and Q s profiles across southern Taiwan reveal a high attenuation zone ( Q p = 288, Q s = 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.