Preliminary results of multidisciplinary observations before, during and after the Kocaeli (Izmit) earthquake in the western part of the North Anatolian Fault Zone

Abstract

On August 17, 1999, a destructive earthquake occurred in the western part of the North Anatolian Fault Zone, Turkey. The earthquake source region has been designated as a seismic gap and an M7-class earthquake has been supposed to occur someday in the future so as to fill this seismic gap. So far we have undertaken various kinds of observations in this area and we could obtain some valuable data before, during and after the mainshock. Here we report some of the preliminary results of our recent studies, which include field work started in late July this year and continued during and after the earthquake occurrence just in the earthquake source region and its vicinity, in addition to seismic observations carried out for several years before the mainshock. Much emphasis is put on magnetotelluric field data acquired during the mainshock; in fact, large variations caused by seismic waves were recorded. Such variations could be interpreted in terms of electromagnetic induction in the conducting crust caused by the velocity field interacting with the static magnetic field of the Earth. In particular, the first motion of seismic wave could be identified in the records and used for precise determination of the hypocenter of the mainshock.

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

“…These features are consistent with the observations using magnetotelluric equipment at locations close to other major earthquakes (Chen and Chen, 2000;Honkura et al, 2000). Rock susceptibilities change with accumulating stress (Stacey, 1962;Nagata, 1970) during the pre-earthquake period.…”

Fault zone conductors in Northwest Turkey inferred from audio frequency magnetotellurics

“…Honkura et al (2000) and Oshiman et al (2002) made similar MT surveys and showed the preliminary results as twodimensional Earth models. Tank et al (2003) then imaged the western part of the epicentral region of theİzmit earthquake, in order to study the electrical resistivity structure with respect to the characteristic seismic behavior.…”

Spectral peaks in electric field at resonance frequencies for seismically excited motion of ions in the Earth’s magnetic field

“…Pride and Morgan, 1991;Gershenzon, 1992;Pride, 1994;Pride and Haartsen, 1996;Haartsen and Pride, 1997;Garambois and Dietrich, 2002;Huang, 2002;Ren et al, 2010a, b). Appearance of unambiguous electric field changes was mostly synchronized with the arrival of seismic wave (Yamada and Murakami, 1982;Honkura et al, 2000Mogi et al, 2000;Nagao et al, 2000;Matsushima et al, 2002;Ujihara et al, 2004). Recently we proposed a new mechanism for electric field generation by seismic wave or more specifically by ground motion, based on some observational examples (Honkura et al, 2009).…”