Nationwide Assessment of Seismic Hazard for Georgia

Abstract:

The work presents a framework for assessment of seismic hazards on national level for the Georgia. Based on a historical review of the compilation of seismic hazard zoning maps for the Georgia became evident that there were gaps in seismic hazard assessment and the present normative seismic hazard map needed a careful recalculation.

The methodology for the probabilistic assessment of seismic hazard used here includes the following steps: produce comprehensive catalogue of historical earthquakes (up to 1900) and the period of instrumental observations with uniform scale of magnitudes; produce models of seismic source zones (SSZ) and their parameterization; develop appropriate ground motion prediction equation (GMPE) models; develop seismic hazard curves for spectral amplitudes at each period and maps in digital format.

Firstly, the new seismic catalog of Georgia was created, with 1700 eqs from ancient times on 2012, Mw³4.0.

Secondly, were allocated seismic source zones (SSZ). The identification of area SSZ was obtained on the bases of structural geology, parameters of seismicity and seismotectonics. In constructing the SSZ, the slope of the appropriate active fault plane, the width of the dynamic influence of the fault, power of seismoactive layer are taken into account. Finally each SSZ was defined with the parameters: the geometry, the percentage of focal mechanism, predominant azimuth and dip angle values, activity rates, maximum magnitude, hypocenter depth distribution, lower and upper seismogenic depth values.

Thirdly, seismic hazard maps were calculated based on modern approach of selecting and ranking global and regional ground motion prediction equation for region.

Finally, probabilistic seismic hazard assessment in terms of ground acceleration were calculated for the territory of Georgia. On the basis of obtained area seismic sources probabilistic seismic hazard maps were calculated showing peak ground acceleration (PGA) and spectral accelerations (SA) at 0.2, 1sec periods for 10% probability and 2% probability in 50 years using selected GMPEs correspondingly for Rock (Vs=760m/s) and soil (Vs=300m/s).

Seismic hazard calculation have been performed with two software OpenQuake and EZFRISK. Bothe of them gave us equal value of seismic hazard for Georgia.