Document Type : Research Article
Authors
1
M.Sc. Student, Department of Geology and Earthquake Research Department, Shahid Bahonar University of Kerman, Kerman, Iran
2
Professor, Department of Geology and Earthquake Research Group, Shahid Bahonar University of Kerman, Kerman, Iran
3
Associate Professor, Department of Geology, Shahid Bahonar University, Kerman, Kerman, Iran
Abstract
In the present study, the tectonics and seismicity of a part of central Iran were investigated. The study area includes the Lakarkuh, Ravar, Kuhbanan, Nayband, Tabas, Posht Badam, Cheshme Rostam, Bardsir, and Rafsanjan faults. In this research, the tectonic setting and active faults of the study area were first examined. The history of seismicity in this region, based on data from the Institute of Geophysics, University of Tehran, was reviewed, along with records of contemporary earthquakes from national seismic databases. These data show clear evidence of activity along the Lakarkuh, Kuhbanan, Ravar, Tabas, and Nayband faults. The presence of fault-displaced layers in the northern part of the study area, as observed in Google Earth imagery, confirms ongoing tectonic activity. Small earthquakes mostly occurred around the Tabas, Nayband, Lakarkuh, Bardsir, Davaran, Kuhbanan, and Rafsanjan faults, while larger earthquakes were concentrated at the Shahdad–Golbaf–Lakarkuh–Kuhbanan–Nayband multiple-fault junction. Analysis of earthquake mechanisms, using the first P-motion method and waveform modeling in Seisan software, revealed that some segments of the Kuhbanan fault exhibit reverse and right-lateral strike-slip movements. Based on potential future earthquakes, cities such as Tabas, Kuhbanan, Zarand, and Kerman, as well as many villages, are highly vulnerable to human and financial losses due to severe earthquakes. After compiling all seismic data, it was concluded that the surveyed area is at risk of devastating, high-intensity earthquakes. Therefore, seismological investigations in the eastern part of central Iran and surface geomorphological studies in the northern part of central Iran are crucial for understanding both the seismic and aseismic movements of faults in the region.
Introduction
The Iranian plateau, characterized by active faults, folding, volcanism, mountainous terrains, and variable crustal thickness, has historically been the site of numerous destructive earthquakes, caused by the convergence between the Eurasian and Arabian plates. In recent centuries, large-magnitude seismic events have occurred regularly, with seismicity concentrated in Central and Eastern Iran (removed "the"), particularly along orogenic belts such as the Dasht-e-Bayaz and Golbaf seismic zones. Notable events, including the 1978 Tabas, 2005 Zarand, and 2017 Hojedk earthquakes, underscore the importance of earthquake focal mechanism analysis in understanding crustal deformation patterns. Previous investigations, both global and regional, have examined active structures such as the Nayband, Kuhbanan, and Lakarkuh faults (corrected from Lekarkuh), integrating seismotectonic, geomorphic, and geological approaches. This study focuses on the Kuhbanan Fault and adjacent structures, assessing focal mechanisms of previously underexplored earthquakes and identifying young tectonic movements within the eastern and western sectors of Central Iran. While the eastern sector is seismically active, the western sector exhibits low seismicity, where geomorphological indicators become particularly valuable for detecting neotectonic activity.
Study Area
The investigated region forms part of Central Iran, encompassing the provinces of Kerman, Yazd, and portions of South Khorasan. This area contains numerous active faults, among which the Kuhbanan, Lakarkuh, Nayband, Golbaf, and Tabas faults are the most prominent. Geographically, the study area is located between longitudes 53°33′E and 57°53′E, and latitudes 29°59′N and 33°86′N (replaced "to" with "and" for precision).
Materials and Methods
Seismic hazard assessment was initiated by compiling a comprehensive earthquake catalog, incorporating historical events (pre-1900) from Ambraseys and Melville (2005) and instrumental records (post-1900) from the Institute of Geophysics, University of Tehran. Focal mechanisms were determined for nine earthquakes (2006–present) using P-wave first-motion polarity analysis, applying the double-couple model with P- and T-axes, following the approach of Stein and Wysession (2009). While seismotectonic analysis was prioritized in the active eastern sector of Central Iran, geomorphic and structural mapping using Google Earth imagery was employed to investigate neotectonic features in the low-seismicity western sector.
Discussion and Results
Approximately four-fifths of Iran is occupied by the folded mountain belts of the Zagros and Alborz ranges, while Central Iran comprises low-lying areas with complex tectonic structures. In the low-seismicity western sector of Central Iran, geomorphic evidence such as offsets of young strata along faults was used to infer neotectonic activity. Examples include a 3.19 km right-lateral displacement southwest of Tabas, likely associated with the northern branches of the Kuhbanan Fault, and a 1.09 km right-lateral offset near the Posht-Badam Fault.
Since 2006, a total of 6,496 earthquakes have been recorded in the study area, the majority with magnitudes below 4.0 and concentrated mainly in the eastern sector near the Kuhbanan and Lakarkuh faults. Major events include the 1923 Bardsir (M 5.5), 1981 Golbaf (M 7.1), and 2017 Hojedk (M 6.1) earthquakes. Focal mechanism analysis of nine well-constrained earthquakes (2006–2011) revealed a clustering of seismicity in the eastern part of the study area, highlighting the role of the Kuhbanan and Lakarkuh faults in accommodating active tectonic deformation.
Conclusions
Analysis of young stratal displacements in the northern and western parts of Central Iran indicates an active tectonic regime, with major structures such as the Kuhbanan and Lekarkuh faults playing a dominant role. Although the region’s overall seismicity is lower than that of other tectonic provinces in Iran, most earthquakes are concentrated in its eastern sector near these principal faults. Among recorded events, nine moderate-magnitude earthquakes had sufficient data for focal mechanism analysis, predominantly showing reverse and right-lateral strike-slip motion consistent with the orientation of the Kuhbanan and Lekarkuh faults. The findings suggest a significant potential for future large and destructive earthquakes, particularly if larger fault segments become reactivated.
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