Focal mechanism determinations of earthquakes along the North Anatolian fault, beneath the Sea of Marmara and the Aegean Sea

Masaru Nakano,Seckin Citak,Doğan Kalafat

doi:10.1186/s40623-015-0330-z

Abstract

We determined the centroid moment tensor (CMT) solutions of earthquakes that occurred along the North Anatolian fault (NAF) beneath the Sea of Marmara and the Aegean Sea, using data obtained from Turkey’s broad-band seismograph network. The CMT solution of the 2014 Aegean Sea earthquake (Mw 6.9) represents a strike-slip fault, consistent with the geometry of the NAF, and the source-time function indicates that this event comprised several distinct subevents. Each subevent is considered to have ruptured a different fault segment. This observation indicates the existence of a mechanical barrier, namely a NAF segment boundary, at the hypocenter. CMT solutions of background seismicity beneath the Aegean Sea represent strike-slip or normal faulting along the NAF or its branch faults. The tensional axes of these events are oriented northeast–southwest, indicating a transtensional tectonic regime. Beneath the Sea of Marmara, the CMT solutions represent mostly strike-slip faulting, consistent with the motion of the NAF, but we identified a normal fault event with a tensional axis parallel to the strike of the NAF. This mechanism indicates that a pull-apart basin, marking a segment boundary of the NAF, is developing there. Because ruptures of a fault system and large earthquake magnitudes are strongly controlled by the fault system geometry and fault length, mapping fault segments along NAF can help to improve the accuracy of scenarios developed for future disastrous earthquakes in the Marmara region.

Highlights

The North Anatolian fault (NAF) is a strike-slip fault system running from east to west in northern Turkey that forms the boundary between the Anatolia and Eurasia plates (Fig. 1)
The existence of a mechanical barrier prevents the simultaneous rupture of the two segments. These observations and simulations imply that there exists a mechanical barrier, possibly a segment boundary of the NAF, at the hypocenter of the 2014 Aegean Sea earthquake, this geometry has not been mapped yet because the fault trace is beneath the sea
Nakano et al (2010) inferred that Coulomb stress increases both interseismically and coseismically at a segment boundary and that ruptures tend to initiate there. This model is consistent with the observation of the 2014 Aegean Sea earthquake if we assume that a segment boundary exists at the hypocenter

Summary

Introduction

The North Anatolian fault (NAF) is a strike-slip fault system running from east to west in northern Turkey that forms the boundary between the Anatolia and Eurasia plates (Fig. 1). The fault system extends westward into the Aegean Sea (AS) (e.g., Barka and Kadinsky-Cade 1988). Historical investigations of major earthquakes along the NAF have revealed that in the twentieth century, ruptures migrated westward after the 1939 Erzincan earthquake in eastern Turkey (Barka and Kadinsky-Cade 1988; Barka 1996). The 1999 İzmit (Mw 7.6) and Düzce (Mw 7.2) earthquakes occurred along the NAF just east of the SOM. Beneath the AS, moderate earthquakes have occurred repeatedly in recent years. The 2014 Aegean Sea earthquake (Mw 6.9, Global Centroid Moment Tensor Project, Dziewonski et al 1981; Ekström et al 2012) occurred west of the Ganos fault (Evangelidis 2015).

Methods

Results

Discussion

Conclusion