Comparisons and characteristics of site amplifications using noise and earthquake data: Examples from the Malta Seismic Network

In the past decade, numerous studies on the amplification effects due to the local geology have been conducted in the Maltese islands (Central Mediterranean). Due to the lack of permanent seismic stations on geological areas of concern, ambient noise techniques were utilised. The areas of interest are characterised by clay, that can reach a thickness of 75 m, buried beneath limestone which introduces a velocity inversion in the stratigraphy. With the expansion of the Malta Seismic Network (MSN) to three stations in such zones, the possibility of confirming and further investigating the results using empirical data arises. Here we present results, using 3 years of data including time domain and frequency-domain analysis in terms of Standard Spectral Ratio (SSR) and earthquake H/V. In particular, we note that the amplifications obtained using the SSR technique are significantly higher than those obtained using both noise and earthquake H/V techniques. Additional peaks below 1 Hz of significant amplitude are also obtained on the SSR curves. By separating the earthquake data set on the basis of distance from the islands, we show that this amplification is source-dependent, and that the high amplification values originate from larger, more distant earthquakes in the Hellenic arc.