Electrical characterization of the North Anatolian Fault Zone underneath the Marmara Sea, Turkey by ocean bottom magnetotellurics

Abstract

The first magnetotelluric study in the Marmara Sea, Turkey, was undertaken to resolve the structure of the crust and upper mantle in the region, and to determine the location of the westward extension of the North Anatolian Fault (NAF) in the C ¸ınarcık area. Long-period ocean bottom magnetotelluric data were acquired at six sites along two profiles crossing the C ¸ınarcık Basin, where a significant increase in microseismic activity was observed following the devastating 1999 İzmit and Düzce earthquakes. 2-D resistivity models indicate the existence of a conductor at a depth of ∼10 km in the middle of both profiles along with a deeper extension into the upper mantle, implying the presence of fluid in the crust and partial melting in the upper mantle. The northern and southern boundaries of this conductor are interpreted to represent the northern and southern branches of the NAF in the Marmara Sea, respectively. These conductors have been previously identified farther to the east along the NAF, suggesting that the electrical characteristics of this fault are continuous from onland areas into the Marmara Sea. Microseismic activity in the C ¸ınarcık area is located above the conductor documented here, and indicates a possible seismogenic role of crustal fluids present in the conductive zone. In comparison, resistive zones along the NAF may act as asperities that could eventually result in a large earthquake.

Electrical resistivity structure at the North-Central Turkey inferred from three-dimensional magnetotellurics

“…Spatial position of this conductor was interpreted to be related to the observed post-seismic creep and aftershock distribution along the segment after the 1999, İzmit Earthquake. Similar type of mechanism was observed beneath the Marmara Sea where the resistivity variations were found to be related to microseismic activity in the region (Kaya et al 2013). Kaya et al (2009) were able to image the resistive asperity zone and claimed that this zone was responsible for super-shear earthquake occurred along the Düzce Fault in 1999.…”

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

“…Such complex tectonic settings suggest complex subsurface structures that may be related to the characteristic seismicity. Because electrical resistivity is sensitive to the presence of fluids, and subsequently the elasticity of the media, it is important to investigate how resistivity structures relate to earthquake generation Fujinawa et al 2002;Goto et al 2005;Guerer and Bayrak 2007;Wannamaker et al 2009;Yoshimura et al 2009;Ichihara et al 2011Ichihara et al , 2014Ichihara et al , 2016Ogawa et al 2014;Kaya et al 2013). To investigate the relationship between earthquakes and electrical resistivity structure, we gathered and analyzed the broadband (typically 0.003-10,000 s) magnetotelluric (MT) and telluric data, which resolve the resistivity structure from the surface to the depth of the upper mantle.…”

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

“…3), which is seen especially well in the S-wave velocity model at shallow depths. We suggest that it might correspond to the thick sedimentary deposits of the Plio-Pleistocene or to the alluvium regions as supported by the low resistivity and gravity values (Kaya et al 2013;Bayrakci et al 2013).…”