Interseismic strain build-up on the submarine North Anatolian Fault offshore Istanbul

Dietrich Lange,Semih Ergintav,Valerie Ballu,Pierre Sakic,Pierre Henry,Florian Petersen,Heidrun Kopp,Jean-Yves Royer,Mehmet Sinan Özeren,Ziyadin Çakir,Jörg Bialas,Louis Géli

doi:10.1038/s41467-019-11016-z

Abstract

Using offshore geodetic observations, we show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and therefore accumulating strain. The strain accumulation along this fault segment was previously extrapolated from onshore observations or inferred from the absence of seismicity, but both methods could not distinguish between fully locked or fully creeping fault behavior. A network of acoustic transponders measured crustal deformation with mm-precision on the seafloor for 2.5 years and did not detect any significant fault displacement. Absence of deformation together with sparse seismicity monitored by ocean bottom seismometers indicates complete fault locking to at least 3 km depth and presumably into the crystalline basement. The slip-deficit of at least 4 m since the last known rupture in 1766 is equivalent to an earthquake of magnitude 7.1 to 7.4 in the Sea of Marmara offshore metropolitan Istanbul.

Highlights

Using offshore geodetic observations, we show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and accumulating strain
It is well known that Istanbul city and populations along the coasts of the Sea of Marmara were previously severely affected by earthquakes related to the submerged North Anatolian Fault (NAF) in the Sea of Marmara[1]
The seismic gap beneath the Kumburgaz Basin, together with the high level of seismicity on either side rather suggests that this section of the NAF is either completely locked or fully creeping

Summary

Introduction

We show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and accumulating strain. The strain accumulation along this fault segment was previously extrapolated from onshore observations or inferred from the absence of seismicity, but both methods could not distinguish between fully locked or fully creeping fault behavior. The slip-deficit of at least 4 m since the last known rupture in 1766 is equivalent to an earthquake of magnitude 7.1 to 7.4 in the Sea of Marmara offshore metropolitan Istanbul. 1234567890():,; It is well known that Istanbul city and populations along the coasts of the Sea of Marmara were previously severely affected by earthquakes related to the submerged North Anatolian Fault (NAF) in the Sea of Marmara[1]. Inferring the slip rate of faults from seismicity[11,12,13] includes assumptions about the frictional behaviour of the fault because deformation is known to be partitioned into seismic moment

Methods

Results

Conclusion