Interactive GIS mapping of local site effects in Dalmatia region in Croatia

In order to produce an input for more accurate Ground motion prediction equations (GMPE) that will include site effects, an array of geophysical measurements was done in Dalmatia region in Croatia, as part of CRONOS Project – Investigation of seismically vulnerable areas in Croatia and seismic ground motion assessment. Research methods used were Horizontal/vertical spectral ratio (HVSR) and Multichannel analysis surface waves (MASW), measured at 21 locations with different site effects across this seismically active region. That included over 230 microtremor HVSR measurements, enabling local soil conditions characterization, alongside seismic microzonation mapping of town of Sinj. Around 40 MASW profiles were studied, providing site Vs30 estimation. Also, continuous borehole and surface accelerographs were installed at 14 locations to assemble strong motion database for the region.

Based on this research, an interactive and open access Geographic information system (GIS) map was constructed, showing locations of measurements and all related geophysical and geological data. The regional extent of map displays locations of all measurements, combining those that are close. The local map extent shows more detail about every measurement site, in form of a label, symbol classification or a pop-up window. Additionally, in case of dense measurement data at one location (e.g. microzonation of Sinj), interpolation map of area was created, offering a fast and visually intuitive way of understanding results. Adding geological layers to the map allowed for correlation with geological site conditions, which facilitated analyses results interpretation and detection of sites that required additional measurements.