Seismicity distribution and locking depth along the Main Marmara Fault, Turkey

Abstract

The seismicity along the Main Marmara Fault (MMF) below the Marmara Sea is analyzed during the 2007-2012 period to provide insights on the recent evolution of this important regional seismic gap. High precision locations show that seismicity is strongly varying along strike and depth providing fine details of the fault behavior that are inaccessible from geodetic observations. The activity strongly clusters at the regions of transition between basins. The Central basin shows significant seismicity located below the shallow locking depth inferred from GPS measurements. Its b-value is low and the average seismic slip is high. All observations are consistent with a deep creep of this segment. On the contrary, the Kumburgaz basin at the center of the fault shows sparse seismicity with the hallmarks of a locked segment. In the eastern Marmara Sea, the seismicity distribution along the Princes Island segment in the Cinarcik basin, is consistent with the geodetic locking depth of 10 km and a low contribution to the regional seismic energy release. The assessment of the locked segment areas provide an estimate of the magnitude of the main forthcoming event to be about 7.3 assuming that the rupture will not enter significantly within creeping domains.

Long‐lasting seismic repeaters in the Central Basin of the Main Marmara Fault

“…The recent seismicity (between 2007 and 2012) around the Marmara Sea has been described in detail in Schmittbuhl et al [2016]. The study was based on an extended regional network of 132 stations.…”

“…Recently, Schmittbuhl et al [2016] concluded from the high-resolution analysis of the recent seismicity that the western part of the fault, i.e., the Central Basin, was hosting a significant creeping zone. Recently, Schmittbuhl et al [2016] concluded from the high-resolution analysis of the recent seismicity that the western part of the fault, i.e., the Central Basin, was hosting a significant creeping zone.…”

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

“…If this slip deficit corresponds to a steady state behavior of the fault, it implies that the NAF is currently accumulating stress at the surface. Over the width of the network, this information could help constraining the locking depth (see supporting information Figure S9); however, the current resolution is still insufficient to discriminate between shallow or deep estimates based on GPS or seismicity data [e.g., Ergintav et al, 2014;Schmittbuhl et al, 2015].…”

“…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;.…”

Investigating P- and S-wave velocity structure beneath the Marmara region (Turkey) and the surrounding area from local earthquake tomography

“…The NAF poses an important hazard for the large cities surrounding the Marmara Sea region, particularly the megalopolis of Istanbul. Indeed, the NAF is presently hosting a long unruptured segment below the Sea of Marmara (Schmittbuhl et al 2015). The Marmara Sea is located in a transition zone where the rightlateral strike-slip character of the NAF meets with the extensional character of Aegean (e.g., Smith et al 1995).…”