S-wave attenuation structure in the Taiwan area and its correlation to seismicity

S-wave amplitude data from the Taiwan Telemetered Seismographic Network (TTSN) and the Central Weather Bureau Seismographic Network (CWBSN) are used in a tomographical inversion for a three-dimensional S-wave attenuation structure beneath the Taiwan area. The data consist of three-dimensional, digital seismograms of 137 earthquakes with magnitudes between 3.0 and 5.0. The S-wave attenuation structure is obtained through the use of the damped least-squares method from attenuation time value (t*) and travel times. Attenuation time value is calculated by using the spectral decay method under the assumption that t* is independent of frequency. S-wave spectra are corrected for a ω² source spectrum model. The frequencies of instrument response above 25 Hz or below 4 Hz usually have large uncertainty. Therefore, the least-squares line fitting is performed in the frequency band of 4 to 25 Hz. The results here show that the distribution pattern of the Q_S values in the Taiwan area correlates well with seismicity. In the upper crust (depths of between 0 to 15 km), the region of lower Q_S area correlates with higher seismicity. However, in the lower crust and upper mantle (15 to 75 km), the area of higher seismicity correlates with the regions of higher Q_S values.