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Seismotectonic investigation in northwest Zagros, Iran: analysis of Ezgeleh Mw 7.3 aftershocks

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Abstract

Zagros, on the Alpine-Himalayan belt, has undergone significant tectonic tension due to the convergence of the Arabian and Eurasian plates, resulting in numerous faults, folds, and thrusts. Despite extensive research, uncertainties persist regarding its seismotectonic features and active faults. This study aims to identify causative faults for earthquakes within this region by calculating focal mechanisms of 47 earthquakes that occurred in northwest Zagros and examining seismicity at depth. In this pursuit, 12 cross-sections have been delineated within the region. The spatial distribution of earthquakes within these sections, coupled with the computed focal mechanisms, serves as indicators of the causative fault. The study attributes a significant proportion of the recorded earthquakes to different segments of the Mountain Front Fault and estimates the length of some segments to exceed what is depicted in geological maps. Clear trends in the depth distribution of earthquakes and alignment of some features with previous studies suggest the activity of hidden faults and the influence of an arc in the study area. The collective results provide a comprehensive understanding of the proposed arc, further reinforced by the identification of a strike-slip fault intersecting the High Zagros Fault, serving as tangible evidence of the arc’s existence.

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Data availability

The data that supports the findings of this study are available from the reputable website http://irsc.ut.ac.ir/bulletin.php.

Code availability

The code used in this study was developed by the authors and is available upon reasonable request from the corresponding author.

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Authors and Affiliations

  1. Graduate University of Advanced Technology, Kerman, Iran

    Zahra Nazarinezhad, Mohammadreza Sepahvand & Afsaneh Nasrabadi

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  1. Zahra Nazarinezhad
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  2. Mohammadreza Sepahvand
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  3. Afsaneh Nasrabadi
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Contributions

ZN performed data analysis, and drafted the manuscript. MS conceived the study design and methodology and contributed to data collection and interpretation. AN revised and improved the manuscript draft.

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Correspondence to Mohammadreza Sepahvand.

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Highlights

• This research, through the calculation of the focal mechanisms of earthquakes that occurred up to 1 year after the 2017 Ezgeleh earthquake and the examination of the seismic activity pattern in the region, has contributed to the study of certain characteristics of seismogenic faults in the northwestern Zagros region.

• Focal mechanisms have been calculated using the ISOLA software, which is an extension of the Kikuchi and Kanamori method. Subsequently, to examine the pattern of earthquake distribution in depth, 12 cross-sections in the region have been delineated and subjected to analysis and interpretation.

• The findings of this study provide evidence suggesting a greater length of the segments of the Mountain Front Fault. Additionally, the results indicate the activity of faults with a trend separate from the known active faults in the region. This research, through the examination of the arc-shaped trend of earthquake distribution and the presentation of surface evidence, offers an interpretation based on the influence of an arc on the movement resulting from reverse faults in the region.

Appendix

Appendix

Table 1

Table 2

Table 3

Table 4

Table 1 The characteristics of seismic events studied in the research, including information such as the assigned number to each seismic event, origin time, longitude, latitude, depth (reported by IRSC and calculated in this study), magnitude (reported by IRSC), distance relative to recording stations, and the number of components used in the inversion process
Full size table
Table 2 The velocity model utilized in this study
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Table 3 Quality assessment parameters and focal mechanisms for seismic events. Columns show assigned number, fault plane characteristics, focal mechanism, double couple percentage (DC%), variance reduction value (VR), Kagan angle, correlation between observed and synthetic waveforms, space–time variability index (STVAR), and moment magnitude (Mw)
Full size table
Table 4 Seismic Source Parameters of Select Earthquakes Computed in This Study and Reported by Other Agencies. The discrepancies between our findings and those of other agencies could potentially stem from differences in input data, computational methodologies, or even measurement inaccuracies. Table 3 provides the values associated with the quality parameters of the focal mechanisms computed in this research
Full size table

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Nazarinezhad, Z., Sepahvand, M. & Nasrabadi, A. Seismotectonic investigation in northwest Zagros, Iran: analysis of Ezgeleh Mw 7.3 aftershocks. J Seismol 28, 81–101 (2024). https://doi.org/10.1007/s10950-023-10184-2

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