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

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 Indo-Australian and Eurasian plates. Seismic activities around the island include devastating megathrust earthquakes, such as the 2004 MW 9.2 Sumatra-Andaman and 2005 MW 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.

Keywords

• ambient noise
• amplification factor
• fundamental frequency
• H/V spectral ratio
• site response
• Simeulue Island