Estimation of Mechanism of Earthquakes in Active Seismic Areas around Tehran, Mashhad and Tabriz Cities

جغرافیا و مخاطرات محیطی

Article 6, Volume 13, Issue 2 - Serial Number 50, June 2024, Pages 115-139   

Document Type: Research Article

DOI: 10.22067/geoeh.2022.77045.1241

Authors

Fatemeh Naghdi Doudaran¹; Majid Nemati^{* 2}

¹MsC Student in Environment, Shahid Bahonar University of Kerman,Kerman,Iran

²Professor in Geophysics, Shahid Bahonar University of Kerman Kerman,Iran

Abstract

In this study the data required to solve the mechanism of earthquakes were collected from a combination of waveform data from the Institute of Geophysics, the University of Tehran and the International Institute of Seismology and Earthquake Engineering. The first P-wave polarization method for the broadband, seismic stations were used to solve the earthquake mechanism. The location error of these earthquakes was about 5 km and the maximum rotation of the nodal plains in the mechanisms was considered 5 degrees. These mechanisms have been processed with the least error in the number of wrong polarizations for seismic mechanisms around the most populous cities of Tehran, Mashhad, and Tabriz. Based on the solution of seismic mechanism in this study, Mosha, north Tehran, Ipack, Garmsar and Ivanki faults, are considered to have the dominant mechanism of strike-slip right lateral with the small normal component, reverse, strike-slip left lateral, strike-slip with small reverse component and inverted mechanism, respectively. This research showed that the faults around Mashhad city like Bahler and Ashkabad left lateral strike slip with a small reverse component and reverse, respectively. The dominant mechanism of the 2017 Fariman aftershocks, is also inverse with the strike-slip right lateral component. Also, the resolved mechanisms of earthquakes around the historical city of Tabriz show that earthquakes with a dominant mechanism of strike-slip right lateral with a small reverse component are related to the North Tabriz fault. Other earthquakes, which are the aftershocks of the 2012 Ahar-Varzeqan doublete earthquakes, also have a strike-slip right lateral with a small reverse component. The 2012 Ahar-Varzeqan earthquakes also have a pure right lateral mechanism. The mechanism of some of these faults, which were studied in previous works (geologically or seismologically), are consistent with the mechanism solved in this study.

Keywords

Earthquake Mechanisms; Faults of Iran; Initial Polarizations of P Waves; Metropolises of Iran; Ahar-Varzeqan Earthquake; Tehran Earthquake

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