M ≥ 7 earthquake rupture forecast and time‐dependent probability for the sea of Marmara region, Turkey

Abstract

We forecast time‐independent and time‐dependent earthquake ruptures in the Marmara region of Turkey for the next 30 years using a new fault segmentation model. We also augment time‐dependent Brownian passage time (BPT) probability with static Coulomb stress changes (ΔCFF) from interacting faults. We calculate Mw > 6.5 probability from 26 individual fault sources in the Marmara region. We also consider a multisegment rupture model that allows higher‐magnitude ruptures over some segments of the northern branch of the North Anatolian Fault Zone beneath the Marmara Sea. A total of 10 different Mw = 7.0 to Mw = 8.0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation. We use Gaussian random distributions to treat parameter uncertainties (e.g., aperiodicity, maximum expected magnitude, slip rate, and consequently mean recurrence time) of the statistical distributions associated with each fault source. We then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models (Poisson, BPT, and BPT + ΔCFF) using a Monte Carlo procedure. The Gerede fault segment located at the eastern end of the Marmara region shows the highest 30 year probability, with a Poisson value of 29% and a time‐dependent interaction probability of 48%. We find an aggregated 30 year Poisson probability of M > 7.3 earthquakes at Istanbul of 35%, which increases to 47% if time dependence and stress transfer are considered. We calculate a twofold probability gain (ratio time dependent to time independent) on the southern strands of the North Anatolian Fault Zone.

No significant steady state surface creep along the North Anatolian Fault offshore Istanbul: Results of 6 months of seafloor acoustic ranging

“…In the central Marmara Sea, the 70 km long Istanbul-Silivri segment (ISS) of the NAF has had no significant seismic events since at least 1766 and perhaps as far back as 989 [Ambraseys, 2002]. The probability of rupture of NAF segments in the central part of the Marmara Sea is considered to be significant [Murru et al, 2016;Aochi and Ulrich, 2015;Parsons, 2004], and Schmittbuhl et al [2015] recently interpreted the low level of present-day seismicity along the ISS as the signature of a locked behavior. Although Bohnhoff et al [2016] suggest that the maximum expected earthquake in the Istanbul area would probably not exceed a magnitude 7.5, geomechanical models generally predict high strain accumulation along the ISS, sufficient to produce a magnitude 7+ event [Hergert and Heidbach, 2010;Pondard et al, 2007;Armijo et al, 2005;.…”

Planar seismic source characterization models developed for probabilistic seismic hazard assessment of Istanbul

“…Unfortunately, the seismic source model proposed by Gülerce and Ocak (2013) cannot be directly implemented in the PSHA for Istanbul since the model does not include the fault segments on the west of the 1999 Kocaeli earthquake rupture zone. The geometry of the fault segments defined in Murru et al (2016) is generally similar to the Erdik et al (2004) model. Furthermore, Murru et al (2016 provided the complete set of parameters required for a faultbased PSHA analysis (e.g., slip rates, fault widths, rupture models and rates, parameter uncertainties).…”

“…Recently proposed SSC models for the western segments of the NAFZ (Gülerce and Ocak, 2013;Murru et al, 2016) are more detailed in terms of the segmentation models, magnitude recurrence relations, and estimation of the activity rates. In the Gülerce and Ocak (2013) SSC model, the length of segments and the segmentation points were determined and incorporated with the help of then-available fault maps and traced source lines on the satellite images.…”

“…The seismological database is taken from the Integrated and Homogeneous Turkish Earthquake Catalog published by the Kandilli Observatory and Earthquake Research Institute (Kalafat et al, 2011). Seismotectonic information related to the active faults and the fault systems that are available in these databases and in the current scientific literature are used in combination with the segmentation models proposed by Gülerce and Ocak (2013) and Murru et al (2016) to define the rupture systems. Fault segments, rupture sources, rupture scenarios, and fault rupture models are determined using the terminology given in the Working Group of California Earthquake Probabilities (WGCEP-2003) report and multi-segment rupture scenarios are considered in a systematic manner.…”

“…Supporting the estimations based on waveforms using aerial photographs, satellite imagery, digital elevation models, bathymetry, and field measurements, Aksoy et al (2010) proposed 120 ± 30 km long fault rupture for the 9 August 1912 event. Murru et al (2016) defined two segments covering the 120 ± 30 km long fault rupture of the 1912 Ganos earthquake: a 74 km long segment that includes the onshore section and a 46 km long offshore segment (segments 6 and 7 in Fig. 1a).…”