| dc.description.abstract | Seismic attenuation, especially in subduction zones, has been studied successfully by some previous studies using local or regional earthquake data. The capability of being sensitive to the high temperature and fluid saturation could help understand the subduction zone structure. In this study, we attempt to use this method to focus on the general characteristics of seismic attenuation in the Sumatra subduction zone and correlating to the physical properties such as slab tear in particular. Seismic attenuation refers to the energy loss of seismic waves while propagating on a medium, represented by the opposite of quality factor (Q). Seismic attenuation could occur because some of the energy may convert into heat during propagation or be reflected and refracted while passing through materials with different properties. This study utilizes broadband seismic data from 38 stations of the Meteorological, Climatological, and Geophysical Agency of Indonesia (BMKG) that are located throughout Sumatra, collected from January 2013 to July 2018. It has 271 events around 100 - 350 km depth with magnitude ranges between 3.9 and 6.5 Mw. Corner frequency and seismic attenuation are processed separately to avoid the trade-off between source and path parameters during the data processing section. To consider the site amplification factor, we solve the attenuation parameter for each station by using a matrix approach and try to fit between the observed and calculated displacement power spectra, assuming that the attenuation is frequency-independent. The results indicate that the Australian slab sunk beneath Sumatra signifies a relatively high-Q zone, around 677 and 776 for Qp and Qs, respectively. In contrast, the mantle wedge has a significant low-Q value. It is a common seismological characteristic in the subduction zone where the cooled dense lithospheric plate is subducted into the mantle, whereas the mantle wedge may reflect the slab dehydration. In the high-Q zone recorded in fore-arc stations, some lower-Q anomalies exist in northern Sumatra, especially coincide with the area beneath Lake Toba, which could be additional evidence to the existence of the slab tear. The consequence of this slab tear, which may increase the active melting, is revealed by the lower-Q zone recorded in the stations of the mountains around Lake Toba. | en_US |