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

Abstract

The submarine Istanbul‐Silivri fault segment, within 15 km of Istanbul, is the only portion of the North Anatolian Fault that has not ruptured in the last 250 years. We report first results of a seafloor acoustic ranging experiment to quantify current horizontal deformation along this segment and assess whether the segment is creeping aseismically or accumulating stress to be released in a future event. Ten transponders were installed to monitor length variations along 15 baselines. A joint least squares inversion for across‐fault baseline changes, accounting for sound speed drift at each transponder, precludes fault displacement rates larger than a few millimeters per year during the 6 month observation period. Forward modeling shows that the data better fit a locked state or a very moderate surface creep—less than 6 mm/yr compared to a far‐field slip rate of over 20 mm/yr—suggesting that the fault segment is currently accumulating stress.

Repeating Marmara Sea earthquakes: indication for fault creep

“…This is in good agreement with earlier findings from the PIRES catalogue and GPS data that were interpreted as evidence of a locked status of the Princess Islands segment (Bohnhoff et al 2013;Ergintav et al 2014) and the westward adjacent Istanbul-Silivri fault (Sakic et al 2016).…”

“…Along its eastern portion, the Princess Island segment offshore Istanbul, a locked patch over a creeping base was identified based on both abundant local seismicity above 10 km depth (Bohnhoff et al 2013) and GPS data (Ergintav et al 2014). First results from seafloor deformation measurements along the adjacent segment to the west (Istanbul-Silivri fault) also tend to favour a locked over a creeping status there (Sakic et al 2016). For the western Marmara section at the central Basin, Schmittbuhl et al (2016) and Yamamoto et al (2016) The offshore Marmara section (pink) is bounded by the two last major ruptures of the region, the 1912 Ganos event (blue) to the west and the 1999 Izmit event (yellow) to the east.…”

Seafloor Geodesy Revealed Partial Creep of the North Anatolian Fault Submerged in the Sea of Marmara

“…Cetin et al (2014) used InSAR observations to report that the İsmetpaşa segment is creeping at a rate of 8 mm/year, while the other segment is fully locked to about 50 km away from İsmetpaşa (Gerede). Recently, Sakic et al (2016) carried out direct measurements of the fault locking state along NAF in the eastern part of the Sea of Marmara (Central High, CH in Figure 1) using the seafloor acoustic ranging technique. Ergintav et al (2014) investigated the slip deficit rate around the Sea of Marmara using onshore GNSS data of the surrounding region and suggested a heterogeneous slip deficit along the NAF.…”

Gas and seismicity within the Istanbul seismic gap

“…In the Western Sea of Marmara, events of magnitude greater than ~ 4.2 regularly occur, generating large sequences of aftershocks, that appear to be vertically distributed below sites where a high density of gas seeps have been identified along the MMF 21,22 . “Vertical swarms dramatically appear in the recently published map of relocated earthquakes 8 from 2007 to 2012, particularly for the aftershocks that followed the M L 4.2, 4.7 and 5.1 events of 24/01/2009, 25/07/2011 and 07/06/2012, which all occurred where the density of gas emissions is maximum 16,17 (in Fig. 1, note that along the Central High and Kumburgas fault segments, gas emissions are not found within the fault valley, but on adjacent structures, for instance on top of the Central High).…”

“…The presence of the water cover above the fault trace and the absence of islands to the south of the fault limits the use of GPS data in estimating the strain accumulation and slip deficit along each of the segments 15 . Efforts are presently on the way to collect acoustic-based geodetic data and encouraging results have recently been obtained 16 . Still, the detailed analysis of micro-seismicity maps remains critical.

Figure 1Seismicity (after ref.

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