The HVSR analysis for determining the seismic vulnerability and soil characteristics of the Randugunting Dam

Abstract The Randugunting Dam is a multipurpose infrastructure project in Indonesia. It benefits 630 hectares of irrigation, produces approximately 200 liters per second of raw water, and reduces flood discharge by 75%. As a vital infrastructure, the dam’s safety is a priority. To monitor the dam’s behavior, a nondestructive method such as HVSR (Horizontal to Vertical Spectral Ratio) analysis of microtremor data is required. HVSR analysis is a widely recognized technique for determining the predominant frequency of a structure, which can be used for various purposes, including the assessment of amplification in the area under study. Numerous studies have demonstrated that HVSR analysis correlates with soil characteristics and can be employed for seismic vulnerability classification. In this research, a Raspberry 4D Shake microtremor device was utilized to measure microseismic activity at the Randugunting Dam. Microtremor measurements were conducted at 11 points along the dam’s crest, from RS 5 on the left abutment to RS 15 on the right abutment. The predominant frequency (f0) and amplification (A0) values obtained from the microtremor data were calculated using Geopsy software. These values were subsequently used to determine the seismic vulnerability index (Kg) and soil classification. The measurement results revealed significant variations in predominant frequency. The left abutment of the Randugunting Dam is characterized by hard rock, with frequencies ranging from 4 Hz to over 20 Hz. In contrast, the right side of the main dam has frequencies in the range of 0.5 Hz to 0.9 Hz, typically associated with thick and soft sediment. The seismic vulnerability index for the Randugunting Dam is generally classified as low, with Kg values below 3.