Attenuation characteristics of coda wave in Northern Aceh, Sumatra, Indonesia

Abstract

Sumatra Island is located in the subduction zone between Indo-Australian and Eurasian Plates. The tectonic activity has resulted in an active region. Hence, it may cause more heterogeneous crust in the region. To understand the relationship between the attenuation factor and the tectonic setting, we apply coda wave attenuation study Sumatra Island. This preliminary result focuses at the northern Aceh from observation at LHMI station. A total of about 123 earthquake waveforms of local distance (less than 3°) with depth less than 40 km is analyzed in this study. We employ a back-scattering model assumption to determine the attenuation of coda waves. Our coda wave quality factor (Q_c) estimation covers frequencies from 1 to 8 Hz. Onset of the coda window is determined by considering twice the arrival time of shear wave, with varying window lengths between 20 and 120 s. The Q₀ (Q_c at frequency 1 Hz) varies from 65.84 ± 5.50 to 183.09 ± 7.17. We observe a decrease in the factor of frequency dependence (η) between 1.14 ± 0.06 and 1.04 ± 0.03. Depth dependent of coda wave attenuation can be seen from the increase of Q₀ (which is Q_c at 1 Hz) with window length. We suggest that the Low Q₀ (< 200) and high η (> 1) may be associated with high tectonic activity in this region.