Magnetic Anomalies Related to Active Folds in the North Anatolian Fault Zone.

Tunçer, Mustafa; Honkura, Yoshimori; Oshiman, Naoto; Ikeda, Yasutaka; Işıkara, A. M.

doi:10.5636/jgg.43.813

Cited by 4 publications

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References 12 publications

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“…Some linear fault traces are clear in the southern Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. branch, whereas the northern branch is complicated as characterized by some geomorphological evidence showing compressional features (Ikeda, 1988;Tunçer et al, 1991), in contrast to transtensional features implied by focal mechanisms of earthquakes (Evans et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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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.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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“…The AMT-B and AMT-C pro les crossed the IMF in a manner similar to AMT-A crossing the IAF, but here the exact location of the fault was inferred from geological and geomorphological investigations (Sipahioglu and Matsuda, 1986) and also from magnetic anomaly observations (Tunçer et al, 1991). The AMT-B pro le consisted of 10 AMT sites with 5 of them on both sides of the fault trace (Figs.…”

Section: 2i̇znik-mekece Fault (Imf)mentioning

confidence: 91%

Fault zone conductors in Northwest Turkey inferred from audio frequency magnetotellurics

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2012

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A comparison of the electrical properties of the two main branches of the North Anatolian Fault is made based on audio-frequency magnetotelluric (AMT) surveys carried out along three typical pro les across the North Anatolian Fault Zone (NAFZ). These two branches are (i) the active northern branch (Izmit-Adapazar Fault (IAF)) where the 17 August, 1999, Izmit earthquake took place, and (ii) the less active southern branch (IznikMekece Fault (IMF)). In this paper, we focus on the shallow depths (surface-1.5 km) in search for conductors near the fault zone for the purpose of comparing these two branches with each other, as well as other strike-slip faults. Phase tensor analyses and Groom-Bailey decompositions were applied to check the dimensionality of the AMT data. Following the tensor analyses and decompositions, two-dimensional inversions were carried out to yield models based on the transverse electric (TE), and transverse magnetic (TM), modes. These models suggest that the North Anatolian Fault exhibits signs of fault zone conductors (FZC) regardless of being active or less active.

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Three-dimensional structure of Vp, Vs and Vp/Vs in the upper crust of the Marmara region, NW Turkey

et al. 2005

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We applied a 3-D seismic tomography inversion algorithm to arrival-time data obtained, during 18 years from 1985 to 2002, from local seismic networks and aftershock studies in the Marmara region, in order to better understand the upper crustal structure of the complex tectonic region. We integrated all the available data set into a common data set and relocated the events, using a 1-D velocity model. We then selected 3,949 earthquakes and obtained 92355 arrival times, in total, consisting of 59,313 P-wave and 33,042 S-wave arrival times. In this paper we present detailed crustal structures for V p, V s and V p/V s ratios from the surface down to 15 km depth with good resolution in terms of the hit count analysis of seismic rays, the checkerboard and restoring resolution tests for the studied region. The results obtained from the inversion suggest that the western part of the North Anatolian Fault Zone shows strong lateral heterogeneity. We concluded that no clear pattern exists between the distribution of microearthquakes and aftershocks and the velocity perturbations presented in this paper. This is probably due to complex tectonic and geological structures. Large coseismic slip associated with the two recent strong earthquakes was found to correspond to higher velocity anomalies, as was often found recently. On the other hand, low velocity values correspond to the sedimentary units or the alluvium regions, as supported by the low resistivity and gravity values. Thus the results presented in this paper are quite consistent with the other data such as gravity, resistivity and magnetic anomalies, indicating that our model is reliable and efficient and it should be useful for further interpretation of tectonic and geological problems in this region. It should be pointed out, however, that the results of S-wave perturbations and V p/V s ratio could not be discussed in detail because of insufficient quality of the S-wave data and the reliability of the results is not very high. Nonetheless, the fact that recent large Izmit earthquake and moderate aftershocks that occurred in or around the high velocity zones near the low velocity region suggests that high velocity regions found in the area close to Istanbul in the Marmara Sea and also at the Iznik-Mekece fault are potential sites for strain energy accumulation and release.

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Magnetic Anomalies Related to Active Folds in the North Anatolian Fault Zone.

Cited by 4 publications

References 12 publications

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

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

Fault zone conductors in Northwest Turkey inferred from audio frequency magnetotellurics

Three-dimensional structure of Vp, Vs and Vp/Vs in the upper crust of the Marmara region, NW Turkey

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