Site Response Characteristics of Simeulue Island, Indonesia as Inferred from H/V Spectral Ratio of Ambient Noise Records

Abstract

Abstract. Simeulue Island is an outer island arc west of Sumatra Island. The island is located close to the interface of the subduction zone between the IndoAustralian and Eurasian plates. Seismic activities around the island include devastating megathrust earthquakes, such as the 2004 M W 9.2 Sumatra-Andaman and 2005 M W 8.7 Nias earthquakes. We have investigated site response characteristics using the Horizontal-to-Vertical (H/V) Spectral Ratio method based on continuous ambient noise records from eight broadband seismometers. From the calculation results, generally, strong peaks were observed in the H/V spectral ratio curves caused by strong impedance contrast in this area. However, the BATU, LABU and DEHI sites showed relatively flat H/V spectral ratio curves caused by a lack of sharp impedance contrast beneath the site. Multiple peaks were observed at several sites, which may indicate the presence of a more highly weathered soil/clay layer on top of a more compact medium. H/V peak frequencies, which reveal the fundamental resonant frequencies of the soil sites, were generally observed in the range of 2.0 Hz-16.4 Hz.

Quaternary Deposit Response to Earthquakes in Pemalang City Based on Peak Ground Acceleration, Earthquake Intensity, and Microtremor Method

“…The PGA.k adds a predominant period (inverse of predominant frequency) in the calculation, which describes the local site effect or geological characteristic of the area (Nakamura, 2000;Prabowo et al, 2019). The predominant frequency determined from the spectral ratio of the microtremor provided soil structure information to assess the soil amplification (Anggono et al, 2016). PGA.k was also used to calculate the earthquake intensity based on the Modified Mercalli Intensity (MMI) scale.…”