H/V spectral ratio: A tool for seismic microzonation of the urban area of the city of Manta – Ecuador

Abstract

This study addresses the importance of providing reliable estimates of ground motion for future earthquakes, highlighting the impact of local site conditions. Using the H/V spectral ratio, the site effect in Manta, Ecuador, was evaluated based on microtremors measured at 186 points. Of these, 164 valid points were used to calculate predominant periods, generating a seismic microzonation map. Five microzones were identified, correlated with local geology, revealing that areas with rock outcrops have shorter periods, while alluvial deposits in Tarqui parish showed longer periods. This explains the greater damage suffered in these areas during the Mw 7.8 earthquake. Additionally, periods vary significantly with sediment thickness and deposit age, with recent alluvial soils presenting higher periods than older rock outcrops.