Dinsar Approach To Seismotectonics and Seismic Gap: Erzincan Basin Section of the North Anatolian Fault Zone (Eastern Turkey)

Abstract

With the help of space geodesy techniques such as InSAR (Interferometric synthetic aperture radar) and GNSS (Global navigation satellite system), a number of models have been developed for the physical properties and rheology of upper crust and other layers of the lithosphere. These models are also used in InSAR studies for interseismic period in order to approach earthquake predictions. However, large earthquakes that release total strains in any fault segment occur over a period of several hundred to several thousand years, while deformation observations, which usually span a maximum period about ten years, represent a very small time interval in a complete earthquake cycle. To use these short-term deformation observations in seismic hazards, better models of how the fault zones deform in space and time are needed. Consequently, InSAR studies focusing on the deformations around the main segments and other structural elements in the tectonic basins and fault zones, also addressing the relationship between the observed deformations and the behavior of these structural elements, may be very important in terms of earthquake predictions. In this respect, we aimed in our paper to associate the tectonic characteristics of the Erzincan basin, a part of the North Anatolian Fault (NAF) zone, with the deformation clusters determined by the InSAR technique. To do this, instead of modern usage of InSAR technique in which hundreds of interferograms are calculated, we preferred its old-school usage which allows us to evaluate deformation areas in terms of structural geology by a few interferograms focused into the basin. In the last century, two destructive earthquakes happened in the Erzincan tectonic subsidence basin (1939, M: 7.8-8.2 and 1992, M:6.8). Previous studies suggest that the basin forms as a result of pull-apart type opening along the NAF zone. The Ovacık Fault (OF) activity widens the basin. In the east of the basin, there is a seismic gap zone extending for at least 75 km along the NAF. This seismic gap is thought to be made up of two main segments which are the nearly 22 km long Sansa in the west and the 53 km long Yedisu in the east. In our study we compared the deformation areas, observed on the interferogram generated by Differential SAR interferometry (DInSAR) technique from the ERS-1 satellite SAR data, acquired in the postseismic period of 2.5 years between 1993-1995 following the March 13 1992 earthquake in Erzincan (M: 6.8), with the structural aspects of the basin. Interferometric deformation findings were observed on tectonic zones near the boundaries of Erzincan plain. The amounts of displacements corresponding subsidence in vertical components of direction are higher around the northern boundary of the basin than those on the southern boundary. Along the northern boundary of the basin and the NAF zone, the deformations that occur in the northwest and north of Erzincan city have lower slip rates relative to deformations in the east and northeast. This sheds light on the development of transpressive zones and push-up structures in the relatively slower northwestern part while both areas collapse together. On the interferogram, deformation clusters are not observed in the eastern part of the Erzincan basin. Therefore, as it approaches the seismic gap zone towards the east of the basin, the NAF segment is thought to exhibit a behavior with lower slip rates. We have also shortly mentioned a quaint and venerable, a so said science-antique, field report (Stchepinsky et al., 1940) established under very harsh conditions that comprises 185 km long surface rupture mapping of the 1939 Erzincan earthquake (M: 8.0) between Ekşisu (Erzincan) and Bahçe village (Koyulhisar, Sivas). © 2019, Hacettepe Universitesi Yerbilmleri. All rights reserved.