Spectral Response Characteristics and Building Response Periods: Insights from the 2023 M4.8 Sumedang Earthquake Ground Motion Analysis

An earthquake with a magnitude of M4.8 struck Sumedang, West Java, on December 31, 2023, at a shallow depth of 5 km. This study analyzes strong ground motion data from five nearby accelerograph stations (CSJM, TSJM, TOJI, ACBM, BALE) to evaluate the patterns of Fourier amplitude spectra, spectral response acceleration (PSA), and their implications for building response periods. The results reveal a significant relationship between the station's distance from the epicenter, local geological characteristics, and the earthquake's energy distribution. The CSJM station, located 14.4 km from the epicenter, recorded a dominant frequency of 4.8 Hz with a maximum PSA of 0.17 g in the 0.2–0.3 second spectral period range, reflecting the high-frequency dominance due to its location on dense volcanic deposits and lava formations. The TSJM station, situated 19.5 km away near the Cileunyi-Tanjungsari fault, exhibited the highest PSA amplitude (0.4 g) at a spectral period of 0.3 seconds. This is attributed to the influence of soft soil deposits and active fault proximity, which amplify high-frequency vibrations, presenting challenges for buildings with natural periods within this range. In contrast, the TOJI station (23.6 km) recorded a PSA of 0.1 g at a spectral period of 0.2 seconds with a dominant frequency of 3 Hz, while the ACBM station (34.7 km) showed a PSA of 0.1 g at 0.3 seconds and a dominant frequency of 1.84 Hz, reflecting attenuation of high-frequency seismic energy. The BALE station (35.7 km) exhibited the lowest PSA of 0.05 g at a spectral period of 0.2 seconds, with a dominant frequency of 4 Hz, influenced by its more stable and compact geological formations. These findings indicate that local surface geological effects contribute to the differences in the spectral response amplitude level as the representative of the level of earthquake ground motion itself. These also underscore the importance of understanding building response periods and their interaction with local seismic conditions. Regions near the epicenter, such as CSJM and TSJM, require structural designs that account for high vibrational intensity and shorter periods, while areas farther away, like ACBM and BALE, should consider energy distribution over longer periods for high-rise buildings. This study provides essential insights into seismic risk mitigation and informs earthquake-resistant design practices in compliance with the Indonesian National Standard (SNI 1726:2019).