Seismic Microzonation of Dusun Langkob, Majalaya, Cianjur, Using HVSR and Vs30 Inversion

Abstract

Seismic microzonation at the local scale is essential for reducing earthquake risk in tectonically active regions such as Cianjur Regency, West Java. This study presents a hamlet-scale microzonation of Dusun Langkob based on Horizontal-to-Vertical Spectral Ratio (HVSR) analysis and Vs30 inversion. A total of 25 microtremor measurements were conducted using a 5 × 5 grid with 1/4250 m spacing. Site-response parameters, including resonance frequency (f0), amplification factor (A0), and vulnerability index (Kg), were extracted from HVSR curves, while average shear-wave velocity in the upper 30 m (Vs30) was derived through inversion using the Dinver module in Geopsy. Ordinary kriging interpolation was applied to generate spatial distributions of these parameters. The results show significant spatial variability of site effects within the hamlet. High hazard zones (C2, D1) are characterized by high amplification (A0 > 4), large vulnerability indices (Kg > 2), and soft soils (Vs30 < 500 m/s). Moderate hazard zones (A2, A4, B1, B2, C1, C3, D2, D3, D4, E2) occur mostly along sediment- volcanic boundaries and residential areas. Low hazard zones dominate ridge and volcanic rock sites, where amplification is minimal and soils are stiff. These findings demonstrate that even within a small hamlet, seismic hazard varies sharply due to topography, geology, and land use. The resulting microzonation map provides critical input for earthquake risk reduction strategies, including structural retrofitting and land-use planning. By supporting safer and more resilient rural communities, this study contributes directly to Sustainable Development Goal (SDG) 11: Sustainable Cities and Communities.