DYNAMIC RESPONSE OF LOCAL SOIL USING MICROTREMOR ANALYSIS AFTER THE MAY 23, 2025 BENGKULU EARTHQUAKE

Abstract

The Mw 6.0 earthquake that occurred on May 23, 2025, caused significant damage to the Rafflesia Asri Housing Complex in Bengkulu City. This study aims to examine the dynamic response of the soil and the seismic vulnerability level of the area using the microtremor method and the Horizontal-to-Vertical Spectral Ratio (HVSR) approach. The parameters analyzed include soil dominant frequency (𝑓0), amplification factor (𝐴0), seismic vulnerability index (𝐾𝑔), Peak Ground Acceleration (PGA) estimates, and shear wave velocity (𝑉𝑠). Measurements were taken at 40 observation points. The analysis results show that 𝑓0 values range from 1.56 to 6.73 Hz, 𝐴0 ranges from 1.97 to 6.46, 𝐾𝑔 ranges from 1.15 to 10.38, PGA ranges from 0.15 to 0.32 g, and 𝑉𝑠 ranges from 143 to 400 m/s. Zones with low 𝑓0, high 𝐴0 and 𝐾𝑔, and PGA followed by low 𝑉𝑠 correlated with more significant building damage. These findings confirm that local soil dynamics play a dominant role in controlling seismic amplification and building damage patterns, underscoring the importance of microtremor-based seismic microzonation analysis for earthquake risk mitigation in Bengkulu City