Evaluation of crustal stress from estimation of b-value based on tectonic regions in North part of the Zagros in Iran

Articles in Press

Document Type : Research Article

Authors

1 international institute of Earthquake Engineering and Seismology

2 seismology research center

Abstract

Abstract: In this study, high-resolution map of the Gutenberg–Richter b-value and differential stress field and stress drop contour map are provided for the north part of the Zagros region. This region is important because more than 10 earthquakes with magnitude greater than 6 occurred in this region in the last century. In order to understand tectonic stress pattern of the region, the catalogue of seismicity between 1900 and 2020 was used (most of the events that could be used in this region) in order to explore the spatial and temporal variations of the b-value, which corresponds to the slope of the frequency-magnitude distribution of the earthquakes. The differential crustal stress from the b-value was estimated and focused on estimating b-value first in the whole north of Zagros belt and then in 3 sub regions. For entire north of Zagros and it's sub regions, the average content of Mc is 4.0 for the region that have catalogs with different Mc in time domain and content of b-value in this regions is around 1.03 to 1.12 and the b-value is gradually have lower value, from west to the East of Zagros. In all earlier studies, b-value was estimated for the entire of the Zagros but in this study, we estimated the b-value based on the tectonic units of the region. In temporal variation of b-value, one minimum in the diagram of b-value in MFF region can be seen exactly before 12 Nov. 2017 Ezgeleh earthquake (Mw=7.3) and another minimum in the diagram would be related to the 18 August 2014 Mormori earthquake (Mw=6.2).

The stress drop was estimated from M0 for north part of the Zagros and then this value was compared in time period before and after Ezgele earthquake. The stress drop value before and after Ezgeleh earthquake, around the epicenter was changed between 0.024-0.03 before earthquake to 0.13-0.261 MPa after the earthquake respectively. Finally the differential stress value is calculated in time period before and after Ezgele Earthquake, around the epicenter, and it is changed between 300-322 MPa before earthquake to 238-295 MPa after the earthquake respectively. Therefore, we infer that stress transmitted from north part of the area to the central part of it.The differential stress in the northern part of the studied area has higher values, so this area will be a stress center for magor earthquakes in the future moving towards the center and south of the region, the tension difference decreases.

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Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 03 April 2024

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