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

Abstract

Background 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. Methods 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. Results 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. Conclusions 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.

Vulnerability Index Assessment for Mapping Ground Movements Using the Microtremor Method as Geological Hazard Mitigation

“…The seismic vulnerability index values and the level of building damage have a positive correlation of up to 80% in the case of the 2011 Van earthquake in Turkey [27]. A positive correlation between the seismic vulnerability index and earthquake damage levels is also demonstrated in the findings of Siburian et al (2024). In their stud y, high seismic vulnerability index values were consistent with high ground shear strain (GSS) values in historical earthquake events in the Suban area, Curup, Rejanglebong, and Bengkulu [14].…”

“…The seismic vulnerability index can provide information about local effects that influence seismic vulnerability in a region. Siburian et al (2024) linked the distribution of seismic vulnerability index values to the ground shear strain (GSS) values of historical earthquakes in the Suban area, Curup Rejang Lebong, Bengkulu, Indonesia. These studies show that besides building construction, soil's physical and mechanical properties also play a crucial role in influencing the level of building damage due to geological disasters, especially earthquakes [14].…”