Implications for Seismic Hazard Analysis

John G. Anderson, Haluk Sucuoglu, Murat A. Erberik, Tolga Yilmaz, Engin Inan, Eser Durukal, Mustafa Erdik, Abdolrasool Anooshehpoor, James N. Brune, & Shean-Der Ni

Published December 2000, SCEC Contribution #537

In 1999, Turkey experienced two major earthquakes on the North Anatolian fault system. The first, with moment magnitude 7.6 on August 17, 1999, ruptured the fault for 140 km from Golcuk to Melen Lake (Golu). The second, with moment magnitude 7.2 on November 12, 1999, ruptured an additional 30 km of the fault from Melen Lake (Golu) to Kaynasli. These earthquakes produced significant strong motion records. This paper reports a summary of the data including the characteristics of the nearest stations to the fault based on site visits to all of the significant stations. Peak accelerations were smaller than expected based on published regressions. Anderson and Brune (1999) have previously discussed the contradiction between precarious rock observations near the San Andreas fault and probabilistic seismic hazard analyses. They proposed that one way to remove the contradiction is to treat uncertainties of ground motion prediction equations differently. The data from these earthquakes suggest an alternative way to resolve the contradiction. If the mean value of the ground motions for earthquakes this size on the San Andreas fault is comparable to the values observed from these two major Turkish earthquakes, then seismic hazard analyses which predict ground motions significantly greater than the mean may still be below the bounds on accelerations established by the precarious rocks. Two other particularly interesting features of these strong motion records are their evidence for directivity effects, and the evidence from the Sakarya station that the major slip event there was initiated by arrival of the P-wave from the hypocenter.

Anderson, J. G., Sucuoglu, H., Erberik, M. A., Yilmaz, T., Inan, E., Durukal, E., Erdik, M., Anooshehpoor, A., Brune, J. N., & Ni, S. (2000). Implications for Seismic Hazard Analysis. Earthquake Spectra, 16(S1), 113-137. doi: 10.1193/1.1586150.