Study of Macro Earthquake Attenuation Using Q-Factor Coda Waves Around Matano Fault

Abstract

All Several macro earthquakes have occurred at the Matano fault so it is interesting to study how the energy attenuation in the coda wave. Coda wave is a signal that follows a secondary wave on a seismogram recording. Some macro earthquakes can be monitored well by BMKG through LUWI Station at a distance of 200-300 km from the epicenter. The coda Q-factor is analysed using coda waves at range 2-4 Hz and 4-8 Hz frequencies of lapse times at 20 seconds in vertical component. Variation of coda Q-factor is influenced by the rock medium in the Matano Fault. This Matano Fault is very unique because it is a collision of continental and oceanic rocks that extend from western to eastern part. The study area is divided into three zones, namely the western, central, and eastern zones. The objective of this study is to identify vulnerabilities at low or high level in each zones by the Coda Q-factor that will classify hazardous earthquakes. The value of coda Q-factor is obtained 126.27 in the west, 162.80 in the middle, and 181.96 in the eastern part of the fault. The western part is the most vulnerable area because low coda Q-factor is associated with sediments layer. It is formed by metamorphic rocks close to the active Fault of Palu Koro. The highest coda Q-factor is located at the eastern part of the fault which hazardous zone and has the potential to cause a large earthquake. The eastern zone has a composition of ultrabasic rocks with high rock stress. In general, the average value of Q-factor in the Matano Fault is 157.01, where the value indicates that the characteristics of the Matano Fault are seismic active zones.