TOWARDS A NEW DATASET OF STRONG MOTION RECORDS FROM NEAR-SOURCE REGIONS: PRELIMINARY ANALYSIS

Abstract

The availability of waveforms from moderate-to-strong earthquakes recorded in epicentral areas is a key factor for investigating ground-motion characteristics close to the seismic source and constraining ground motion prediction equations at short source-to-site distances. To investigate near-source effects on ground-motion, worldwide records were selected from different repositories with the aim of compiling a Near-Source Strong Motion (NSSM05) dataset and the related flat-file of intensity measures and event/station metadata. This dataset consists of more than 1000 manually processed waveforms belonging to 88 events with moment magnitude greater than 5 and recorded in the 1933 – 2016 period. For each NSSM05 event, the corresponding source model and fault geometry were retrieved from literature and catalogues. In order to establish a criterion suitable for representing the near-source condition, and recognize the most relevant features of the ground motion in this region, we considered various distance metrics and performed preliminary statistical analysis of ground motion intensity measures. In agreement with previous studies, it was found that, at short distance from the fault plane (< 5 km) and at long periods (T > 1 s), the fault normal ground motion component is, on average, larger than the fault parallel one, when the intensity is the spectral acceleration. Evidence of directionality effects was also observed at short distances, where the ratio between the maximum value (over all horizontal orientations) of spectral acceleration ordinates and the corresponding median is largest and tends to increase at longer period. Finally, the ratio between the vertical and median values of spectral acceleration is close to unity at high-frequency, while is lower than 2/3 at long periods.