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

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 broadband 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.

Discriminating non-seismic long-period pulses and noise to improve earthquake source inversion

“…The seismic moment is estimated from the moment function deconvolved from its bandpassed form (Nakano et al 2008). SWIFT has been used to study source mechanisms of earthquakes in various regions: Indonesia (Nakano et al 2008(Nakano et al , 2010a, the Philippines (Punongbayan et al 2015;Bonita et al 2015), Turkey (Görgün 2013;Görgün and Görgün 2015;Nakano et al 2015), and Japan (Ando et al 2012;Kumagai et al 2012).…”

Analysis of the focal characteristics of two strong earthquakes in Turkey: differences in earthquake characteristics rupture process and spatiotemporal evolution of the rupture

“…The formation and distribution characteristics of seismic disasters are closely related to the source characteristics, such as the earthquake mechanism and rupture process (Bouchon et al, 2001;Lay et al, 2010;Taymaz et al, 2021a). The occurrence of an earthquake can be simply consider as the relative displacement and dislocation on both sides of the fault plane, and the focal mechanism characterizing the earthquake characteristics can directly re ect the geometrical shape and motion mode of the seism genic fault (Nakano et al, 2015). At the same time, the occurrence of a large earthquake generally not only has a longer duration and larger rupture scale (Ambraseys, 1988;Avouac et al, 2014;Ma et al, 2014;McClusky et al, 2000;Okamoto, 1973;Reilinger et al, 2006;Sunkar, 2018), the earthquake rupture process (Lay et al, 2010) and the temporal and spatial evolution characteristics (Ma et al, 2014) re ect and reproduce the dynamic and continuous changes of earthquake rupture in time and space (Yagi & Kikuchi, 2000).…”

Special issue “The next Marmara earthquake: disaster mitigation, recovery, and early warning”

“…Further information on the fault segmentation of NAF in the Marmara Sea and north Aegean Sea regions is determined by modeling the waveforms at broadband land stations to retrieve the source properties of moderate to large events, estimating the CMT parameters and source time functions (Nakano et al 2016). The source time function of the 2014 North Aegean earthquake (Mw = 6.9) provides evidence on ruptures of different fault segments associated with the mainshock.…”