Evaluation of the Seismic Potential of Herat Fault in the West of Afghanistan Based on Seismotectonic Parameters and Seismic Moment Rate

جغرافیا و مخاطرات محیطی

Article 5, Volume 14, Issue 1 - Serial Number 53, March 2025, Pages 79-98   

Document Type: Research Article

DOI: 10.22067/geoeh.2024.88810.1500

Authors

Amin Mohammadi¹; Saeed Zarei^{* 2}

¹MSc. in Department of Geophysics, Faculty of Nano and Bio Science and Technology, Persian Gulf University, Bushehr, Iran

²Assistant Professor in Department of Geophysics, Faculty of Nano and Bio Science and Technology, Persian Gulf University, Bushehr, Iran

Abstract

The western Herat Fault system is one of Afghanistan's most seismotectonically active regions, having experienced four Mw >6 earthquakes in 2023. Given the significance of this region and the occurrence of successive seismic events, this study investigated the seismotectonic dynamics of the area through seismicity parameters and fractal analysis. Here, changes in the seismicity rate were analyzed based on variations in the seismic parameter (b-value) and the fractal dimension of fracturing and seismicity (D-value) using available seismic data.
The study area was divided into nine primary zones, with each zone's parameters calculated. The largest fault fractal dimensions were identified in the southeastern, central, and northwestern zones, while the highest seismic fractal dimension was associated with the central and northwestern regions. The calculated b-values in the center of the study area, coinciding with the Herat Fault, indicate elevated stress accumulation, potentially signaling future large earthquakes.
The seismic moment rate, representing the rate of energy change released through seismic activity, was estimated at 1.18 × 10¹⁸ Nm/yr for the entire study area. Combined fractal analysis and seismic moment calculations suggest that the Zendeh-Jan, Injil, Ghurian, and Kushan districts are potential candidates for future earthquakes. These results reinforce the interpretation that western Afghanistan, as an evolving deformation zone, remains highly susceptible to seismic events.
Extended Abstract
Introduction
The Alpine-Himalayan seismic belt passes through Afghanistan, making the country prone to frequent earthquakes that cause significant human and financial losses. The northeastern regions experience the highest rate of seismic activity. Recently, several earthquakes have occurred along the Herat Fault system, highlighting this region's seismic potential.
Fractal analysis is a statistical approach extensively used to analyze spatial variability (Turcotte, 1997; Dimiri, 2000). This research builds upon recent developments in seismic studies, including fractal analysis of earthquake distributions conducted in Turkey, Japan, and India (Nanjo & Nagahama, 2004; Singh et al., 2012), applying these methods to the Herat Fault system. The study estimates the b-value as an indicator of seismicity and the D-value as an indicator of earthquake and fault fractal dimensions using square-counting and least squares methods. The seismic moment rate is further estimated to study energy dissipation and tectonic mechanisms (Bridges & Gao, 2006; Pal, 2008). This represents one of the first comprehensive studies of seismic activity along the Herat Fault in Afghanistan.
Material and Methods
Seismic data from 2011 to 2024 were extracted from regional and global earthquake catalogs, including ISC, USGS, and historical earthquake reports. The data were refined using the Reasenberg spatial-temporal window in Zmap software to remove foreshocks and aftershocks. Earthquakes were plotted on fault and topographic layers in ArcGIS. Main fractures and faults were identified from USGS 1:500,000 geological maps and enhanced with remote sensing techniques using ETM+ and ASTER imagery in ENVI 5.6 and ER Mapper.
The b-value was calculated using the least squares method, where lower values indicate higher shear stress. Fractal dimensions were computed using the box-counting method and mapped using kriging in ArcGIS (D-value). Seismic moment rates in 36 subregions (30×30 km each) were estimated using instrumental and historical data, revealing stress concentrations on the Siyah Bobak and Herat faults.
Results and Discussion
The fractal dimension of fault zones reveals their geometry and complexity. Higher values indicate denser, more complex fault networks (Charchi et al., 2001). In this study, section 9 faults showed the highest fractal dimension, suggesting greater fault density and potentially higher seismic risk, particularly in southern and southeastern areas due to stress concentration.
Fractal analysis of earthquake distribution showed high fractal dimensions in central, northwest, and western subregions, indicating greater seismic clustering. However, these findings depend on catalog completeness, and Afghanistan's limited monitoring infrastructure necessitates reliance on corrected global databases.
The b-value (relative frequency of large vs. small earthquakes) is inversely proportional to stress. Values <1, as found along the Herat and Siyah Bobak faults, indicate higher shear stress and greater likelihood of large earthquakes (Scholz, 1968; Wyss, 1973). The D-value/b-value ratio suggests areas with low b-values and high D-values are more prone to significant seismic activity. High seismic moment rates around the Herat Fault correlate with 2023 seismic events, indicating blind faults and ongoing seismic potential (Johnston, 1996; Hanks, 1979; Kanamori, 1977).
Conclusions
The study reveals active deformation in Herat resulting from Indian-Eurasian plate movement, releasing substantial seismic energy. Zendeh-Jan, Injil, Ghurian, and Kushan represent high-risk areas, with the northwestern region showing particularly high seismicity. These findings underscore the need for improved fault mapping and infrastructure development.
Acknowledgment
The authors thank Persian Gulf University for their support and research environment. Special gratitude to Dr. Shabir Ashkpoor Motlagh and Dr. Sayyed Reza Mansouri for their valuable suggestions and article review.
 

Keywords

Herat Fault; Fractal analysis of seismicity; Seismotectonics; Seismic Moment Rate; b-Value; D-value; Western Afghanistan; Stress Accumulation

References

Abdullah, S. (1993). Seismic hazard assessment in the Islamic state of Afghanistan. The practice of earthquake hazard assessment, IASPEI/ESC Publication, McGuire RK, ed, 284. https://www.researchgate.net/publication/316643937

Abdullah, S. H., Chmyriov, V. M., & Dronov, V. I. (2008). Geology and mineral resources of Afghanistan. https://nora.nerc.ac.uk/id/eprint/3723

Ambraseys, N. N., Melville, C. (1982). A seismic history of Persian earthquakes. Cambridge: Cambridge University Press. https://doi.org/10.1002/eqe.4290110412

Bayrak, Y., & Bayrak, E. (2012). Regional variations and correlations of Gutenberg–Richter parameters and fractal dimension for the different seismogenic zones in Western Anatolia. Journal of Asian Earth Sciences, 58, 98-107. http://dx.doi.org/10.1016/j.jseaes.2012.06.018

Bayrak, Y., & Öztürk, S. (2004). Spatial and temporal variations of the aftershock sequence of the 1999 Izmit and Duzce earthquake. Earth Planets Space, 56, 933-944. https://doi.org/10.1186/BF03351791

Bridges, D. L., & Gao, S. S. (2006). Spatial variation of seismic b-values beneath Makushin Volcano, Unalaska Island, Alaska. Earth and Planetary Science Letters, 245(1-2), 408-415. https://doi.org/10.1016/j.epsl.2006.03.010

Charchi, A., Khatib, M. M., Mozafarkhah, M., & Barjasteh, A. (2011). Fractal analysis for determination of Tectonic activity in the north of Lali, NE Khuzestan. Advanced Applied Geology, 1(1), 37-47. [In Persian] https://aag.scu.ac.ir/article_11542.html?

Cheng, Q., Agterberg, F. P., & Ballantyne, S. B. (1994). The separation of geochemical anomalies from background by fractal methods. Journal of Geochemical exploration, 51(2), 109-130. https://doi.org/10.1016/0375-6742(94)90013-2

Dimiri, V. P. (2000). Application of fractals in the earth sciences. CRC Press, A Balkema Publishers.

Fadami, M., Zarei, S., & Ashkpoor Motlagh, S. (2021). The Seismicity Dissimilarity Investigation of Khuzestan in the Southwest of Zagros using by Fractal Analysis. Bulletin of Earthquake Science and Engineering, 8(3), 1-15. [In Persian] https://doi.org/10.48303/bese.2021.245995

Hubbard, J., & Bradley, K. (2023). Two magnitude 6.3 earthquakes strike northwestern Afghanistan. Earthquake Insights. https://doi.org/10.62481/5776c220

Kanamori, H. (1977). Seismic and aseismic slip along subduction zones and their tectonic implications. Island Arcs, Deep Sea Trenches and Back‐Arc Basins, 1, 163-174. https://doi.org/10.1029/ME001p0163  

Nanjo, K., & Nagahama, H. (2004). Fractal properties of spatial distributions of aftershocks and active faults. Chaos, Solitons & Fractals, 19(2), 387-397. https://doi.org/10.1016/S0960-0779(03)00051-1

Öncel, A. O., & Wilson, T. (2004). Correlation of seismotectonic variables and GPS strain measurements in western Turkey. Journal of Geophysical Research: Solid Earth, 109(B11). https://doi.org/10.1029/2004JB003101

Oncel, A. O., & Wilson, T. H. (2002). Space-time correlations of seismotectonic parameters: Examples from Japan and from Turkey preceding the Izmit earthquake. Bulletin of the Seismological Society of America, 92(1), 339-349. https://doi.org/10.1785/0120000844

Pal, P. K. (2008). Geomorphological, Fractal Dimension and b-Value Mapping in Northeast India. The Journal of Indian Geophysical Union, 12, 41-54. https://api.semanticscholar.org/CorpusID:73582101

Pan, Z., Yun, Z., & Shao, Z. (2020). Contemporary crustal deformation of Northeast Tibet from geodetic investigations and a comparison between the seismic and geodetic moment release rates. Physics of the Earth and Planetary Interiors, 304, 106489. https://doi.org/10.1016/j.pepi.2020.106489

Rashidi, A., Khatib, M. M., Mosavi, S. M., & Jamor, Y. (2017). Estimation of the active faults, based on Seismic, geologic and geodetic moment rates in the South and West of Lut block. Scientific Quarterly Journal of Geosciences, 26(104), 211-222. [In Persian] https://doi.org/10.22071/gsj.2017.50265

Roumina, A., Zarei, S., Mansouri, S. R., & Azadijou, O. (2023). Seismic distribution in the south of Zagros using the statistical correlation between b-Value and fractal dimension. Iranian Journal of Geophysics, 17(1), 89-107. [In Persian] https://doi.org/10.30499/ijg.2022.335123.1413

Scholz, C. H. (1968). The frequency-magnitude relation of micro fracturing in rock and its relation to earthquakes. Bulletin of the Seismological Society of America, 58(1), 399-415. https://doi.org/10.1785/BSSA0580010399

Shnizai, Z. (2020). Mapping of active and presumed active faults in Afghanistan by interpretation of 1-arcsecond SRTM anaglyph images. Journal of Seismology, 24(6), 1131-1157. https://doi.org/10.1007/s10950-020-09933-4

Siehl, A. (2017). Structural setting and evolution of the Afghan orogenic segment–a review. Geological Society, London, Special Publications, 427(1), 57-88.  https://doi.org/10.1144/SP427.8

Singh, A. P., Mishra, O. P., Kumar, D., Kumar, S., & Yadav, R. B. S. (2012). Spatial variation of the aftershock activity across the Kachchh Rift Basin and its seismotectonic implications. Journal of Earth System Science, 121, 439-451. https://doi.org/10.1007/s12040-012-0175-9 

Tavakoli Zadeh, N., Rahimi, B., Ghaemi, F. (2016). The study of seismotectonics and asperities in Zagros through the b-value parameter. 34th National and the 2nd International Geosciences Congress.[In Persian]

Tosi, P., De Rubeis, V., Loreto, V., & Pietronero, L. (2008). Space–time correlation of earthquakes. Geophysical Journal International, 173(3), 932-941. https://doi.org/10.1111/j.1365-246X.2008.03770.x

Treloar, P. J., & Izatt, C. N. (1993). Tectonics of the Himalayan collision between the Indian plate and the Afghan block: A synthesis. Geological Society, London, Special Publications, 74(1), 69-87. https://doi.org/10.1144/GSL.SP.1993.074.01.06  

Turcotte, D. L. (1997). Fractals and Chaos in Geology and Geophysics. New York: Cambridge University Press. https://doi.org/10.1017/CBO9781139174695

Wyss, M. (1973). Towards a physical understanding of the earthquake frequency distribution.  Geophysical Journal International, 31(4), 341-359. https://doi.org/10.1111/j.1365-246X.1973.tb06506.x

Yadav, R. B. S., Gahalaut, V. K., Chopra, S., & Shan, B. (2012). Tectonic implications and seismicity triggering during the 2008 Baluchistan, Pakistan earthquake sequence. Journal of Asian Earth Sciences, 45, 167-178. https://doi.org/10.1016/j.jseaes.2011.10.003

Zarei, S., Khatib, M. M., Zare, M., & Moussavi, S. M. (2020). Estimation of the Seismicity Potential, Based on Geodetic, Seismic, and Geological Moment Rate in the Lut Block. Bulletin of Earthquake Science and Engineering, 7(1), 15-36. [In Persian] https://www.bese.ir/article_240420.html