Component 2

Development of attenuation relations for predicting seismic ground motion (GMPE)

The second component would enable the development of hybrid-empirical attenuation relations by combining empirical data of recorded earthquakes and stochastic modelling using characteristic regional seismic parameters of the investigated areas. In order to successfully complete this task, a new accelerometric network must be installed in the chosen area (area of Split-Dalmatia County).

The purchase of at least eleven accelerographs and three borehole accelerographs is planned. If possible, spatial gaps between highly sensitive but high price seismic instruments can be filled with 5-10 with less sensitive but lower-cost alternative instruments (such as Raspberry Shake Additionally, the detailed prospecting of the potential instrument locations is needed. Those locations must be prepared for instrument installation, which also implies 3×30 m borehole drilling for borehole accelerographs. Location preparation and area research imply as well detailed soil conditions analysis which is why the purchase of one full MASW system (determination of the shear wave velocity profiles on the selected locations) and seven HVSR instruments (determination of the site fundamental frequencies and bedrock depths) with additional IT equipment (data storage, PCs, laptops, required software, …) is necessary.

Having a reliable method for evaluating the level of the earthquake ground shaking as a function of magnitude and distance is an important prerequisite for evaluating the seismic hazard in a region. For seismic hazard applications, ground-motion amplitudes are often estimated using ground-motion prediction equations (GMPEs). Deriving a GMPE requires a high-quality dataset of earthquake ground motions covering a wide magnitude- and distance range. GMPEs relate ground-motion intensity measures (GMIMs), such as peak ground acceleration (PGA), peak ground velocity, and 5% damped pseudoacceleration linear-elastic response spectral acceleration (PSA), to seismological parameters in a specified region, such as earthquake magnitude, source-to-site distance, local site conditions, and style of faulting. Attenuation relations (ground motion prediction equation – GMPE) do not exist for Croatian territory due to the practically non-existent accelerometric network. There are only a few recorded earthquake accelerations on the territory of the Republic of Croatia. Therefore, the main goal is to place accelerometers on different seismic areas and different types of soil and we expect to collect a sufficient number of acceleration records. Then the assessment of local soil conditions using geophysical measurements and microseismic noise measurements can be initiated.

Moreover, it is important to have a good accelerometric network that complements the seismographic/velocimetric network mostly in a case of a strong and near earthquake (due to technical problems with saturation of seismographs). As already mentioned, current accelerograph coverage is not sufficient. Accelerometric network after the end of the project, can also be integrated into the network of the Seismological Survey and/or the purchased instruments can be temporarily set up for seismic monitoring of tall buildings (built and under construction), seismic monitoring of dams before and after earthquakes or possibly leased to neighbouring countries seeking to join the EU but do not have the necessary instruments for seismic monitoring.

Within project component 2, a detailed analysis of the regional seismicity of the chosen part of Croatia will be implemented. Additionally, the organized database of seismological, geophysical, seismotectonic and geological data that are necessary for the overall project objectives will be created.

Principal investigator for the Component 2 is Assoc. prof. Snježana Markušić

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