Deterministic and Probabilistic Assessment of Earthquake Hazard for Istanbul Metropolitan Area

Abstract eng:
Earthquakes that might plausibly nucleate in the westernmost part of the North Anatolian Fault Zone are the events that would serve as arbiters of the ground motions to be experienced in the extended area of Istanbul, the largest city in Turkey. The consequences of a destructive earthquake in the Sea of Marmara region would be enormous for the country. The continued focus on the estimate of the regional seismic hazard is based on this fact. In engineering applications, probabilistic or deterministic approaches for seismic hazard assessment may have precedence over one another depending upon how well quantified their parameters are. Using both approaches, estimates for peak values of ground-motions are made for the Istanbul metropolitan area. In the deterministic approach, six plausible earthquake scenarios are developed. These scenarios consist of individual and multiple rupturing of the submarine fault segments along the western part of the North Anatolian Fault Zone (NAFZ) extending into the Sea of Marmara. The probabilistic approach uses two different earthquake source models: (1) the smoothed-gridded seismicity model and (2) fault model. Alternate magnitude-frequency relations are used. The regional exposure is mapped on a set of hazard maps where a suite of appropriately selected ground motion prediction equations (GMPEs) have been used in a combinatorial approach to address epistemic uncertainty. In lieu of subjectively weighting the expressions, the GMPEs are weighted proportionally, with regard to their relative performance in predicting the measured peak ground motions of the 1999 M7.4 Kocaeli earthquake when it ruptured the Izmit segment of the NAFZ up to the eastern reaches of Istanbul. This computational approach has resulted in consistent but different weights for each GMPE at different spectral periods. High-resolution (0.002 deg by 0.002 deg, or approx. 250 m by 250 m) seismic hazard maps that incorporate site amplification due to softer sediments, provide peak horizontal ground acceleration (PGA) and spectral acceleration values at 0.2, 0.3, 0.5, 1, 1.5, 2, 3 and 4 s.

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