Re-Examination of Probabilistic Seismic Hazard in the

Marmara Sea Region

Bulletin of Seismological Society of America, Vol. 99, No. 4, pp. 2127–2146, August 2009

Erol Kalkan, U.S. Geological Survey, Menlo Park, ekalkan@usgs.gov

Polat Gulkan, Middle East Technical University, Ankara, pgulkan@ce.metu.edu.tr

Nazan Yilmaz, General Directorate of Disaster Affair, Ankara, nazany@deprem.gov.tr

**Plain English Summary** [Turkish Summary]

Based on a probabilistic approach, seismic risk in the Marmara (Turkey) region are quantified on a set of hazard maps that provide peak horizontal ground acceleration (PGA) and spectral acceleration at 0.2 sec, and 1.0 sec on rock site condition. These acceleration levels were computed for maximum credible earthquake for 2% and 10% probabilities of being exceeded in 50 years corresponding to return periods of about 2475 and 475 years, respectively. The maximum PGA computed (at rock site) is 1.5 g along the fault segments of the NAF zone extending into the Sea of Marmara. The new maps generally show 10% to 15% increase for PGA, 0.2 sec, and 1.0 sec spectral acceleration across much of Marmara compared to previous regional hazard maps. Hazard curves and smooth design spectra for three site conditions—rock, soil, and soft-soil—are provided for the Istanbul Metropolitan area as possible tools in future risk estimates.

DOWNLOAD Media Friendly (High Resolution) Marmara Hazard, Seismicity and Fault Maps (8.5 Mb)

**Related Journal Papers and Presentations**

1 Kalkan E., Gulkan, P., Yilmaz, N. and Celebi, M.(2009). “Re-Examination of Probabilistic Seismic Hazard in the Marmara Sea Region”,Bulletin of Seismological Society of America, 99(4): 2127–2146. [DOWNLOAD COLOR VERSION]2. Kalkan, E., Gulkan, P., Ozturk, N.Y., and Celebi, M.(2008). “Seismic Hazard in the Istanbul Metropolitan Area: A Preliminary Re-examination”,Journal of Earthquake Engineering, 12(S2): 151-164, Jan.

Google Earth: Interactive Marmara Seismic Hazard Map

Marmara Earthquake Potential Map, Low Res. (2.5 Mb) | High Res. (43.5 Mb)

**General Methodology**

Based on our current state of knowledge about the seismicity and tectonic environment of the Marmara basin, regional probabilistic seismic hazard analyses are performed using two different classes of earthquake source models: (1) smoothed-gridded seismicity model, and (2) fault model. The first model is based on the earthquake catalog and characterizes the hazard from earthquakes between M4.0 - 6.5. The faults contribute to the hazard for earthquakes larger than M6.5. As a recurrence forecasting process, the Poisson equation (time independent) is used to estimate the probability of being exceeded over finite time interval. All the analyses were conducted using the 2008 USGS seismic hazard code. Seismic hazard curves for the Istanbul Metropolitan area were also computed for PGA, SA at 0.2 sec, and SA at 1.0 sec for uniform firm rock (VS30 = 760 m/sec), soil (VS30 = 360 m/sec), and soft-soil (VS30 = 180 m/sec) sites.

**Copyright**

You are welcome to download and use
any of these materials as long as you acknowledge the paper or this web-site as the source.

**Downloadable Hazard Maps for Marmara Region; VS30 =
760 m/sec (Zip Format):**

2% PE in 50 years………………………… PGA | SA
(0.2 sec) | SA (1.0 sec)

10% PE in 50 years……………………….. PGA | SA
(0.2 sec) | SA
(1.0 sec)

**Downloadable Site Amplification Maps and
Amplification Coefficients (ASCII Format):**

2% PE in 50
years………………..……….. Site
Amplification Maps & Data

10% PE in 50 years…......………..………. Site
Amplification Maps & Data

**Downloadable Hazard Curves
Data Files; Vs30 = 760 m/sec (ASCII Format):** PGA | SA (0.2
sec) | SA (1.0
sec)

The files contain hazard curves for the gridded geographic points as described above. All the hazard curves in the file share the same set of x-values (intensity measure levels). The third line specifies the spectral period (in seconds) used when computing the hazard curves for the file. The following lines (with 1 value per line) contain the x-values (intensity measure levels) for all the curves in the file. Subsequent lines contain hazard curves with a single geographic point per line. The first two values specify the longitude and latitude (respectively) for the curve while subsequent values (on that same line) contain mean annual frequencies of exceedance ordered corresponding to the x-values at the top of the file.