Ground motion model using simulated scenario earthquake records in Azores Plateau (Portugal) at bedrock

Abstract

The Azores archipelago in Portugal, located within a seismically active region, experienced several moderate to strong earthquakes throughout its history, including significant events in 1980 (moment magnitude, Mw 6.9) and 1998 (Mw 6.2). Despite its moderate to high seismicity, the region lacks a comprehensive database of recorded ground motions due to limited instrumental seismic data. To address this gap, ground motion simulation techniques provide alternative region-specific time series for areas with sparse seismic networks or a lack of catastrophic earthquake events. This study develops a region-specific ground motion model (GMM) for the Azores Plateau in Portugal, utilizing a homogeneous dataset of region-specific simulated records that have been generated in the bedrock through a stochastic finite-fault approach. The GMM is constructed using a mixed-effects algorithm to predict peak ground acceleration, peak ground velocity, and spectral acceleration ordinates at periods between 0.02 and 2.0 s. The model utilizes input parameters for prediction, including Mw, Joyner-Boore distance (RJB), and focal depth (FD). The model is formulated for shallow seismic events ranging from magnitude Mw 5.0 to 6.8, FD 5–17 km, and RJB up to 150 km on bedrock sites. Uncertainty quantification is performed through residual analysis, offering insights into inter-event and intra-event variabilities. The results demonstrate that the proposed model effectively predicts ground motion parameters across the considered range of magnitudes, distances, and periods, providing a valuable tool for assessing the earthquake hazard in the Azores region.