Local site effects and seismic microzonation around Suban Area, Curup Rejang Lebong, Bengkulu deduced by ambient noise measurements

The Suban area of Curup Rejang Lebong is a tourist region in Bengkulu Province, Indonesia, close to the active Ketaun and Musi faults, which are segments of the Sumatra Fault System (SFS). However, no studies have been conducted in this area to assess how geological structures affect seismic ground motions and contribute to seismic hazard and risk assessment. The first study of seismic microzonation in the Suban area of Curup City by ambient noise measurements was conducted at 100 sites, spaced ~ 1 km apart, with 60 min of data acquisition for each site. All microseismic data were processed using the Horizontal to Vertical Spectral Ratios (HVSR) method. The HVSR method revealed the amplification factors (A0) ranging from 1.23 to 8.26 times, corresponding to natural frequency (f0) variations between 1.24 and 9.67 Hz. About 13% and 55% of the sites show high (6 ≤ A0 ≤ 9) and medium (3 ≤ A0 ≤ 6) amplifications, respectively, predominantly in the western parts of the study area, consistent with a high seismic vulnerability index (Kg). Furthermore, we also estimated the ground shear strain (GSS) of the region using the Kanai method with two large historical earthquakes at the Ketahun segment in 1943 (Mw 7.4) and the Musi segment in 1979 (Mw 6.0). The Kg value is consistent with the GSS values and indicates areas of severe damage during the historic earthquakes. Thus, the western parts of the Suban region are vulnerable to severe damage from an earthquake. These findings could provide valuable insights for future planning and risk management efforts aimed at minimizing the impact of earthquakes in the Suban region.