Introduction

The examination and evaluation of landforms and irregularities resulting from tectonic activities are considered fundamental topics in geomorphology. Morphotectonic studies are primarily focused on geodynamic analysis and the geomorphological interpretation of landscapes, and they serve as a key framework for understanding landscape evolution processes. These studies play an important role in assessing tectonic activities and, consequently, the seismic potential of different regions. For this reason, identifying areas with a high احتمال of earthquake occurrence is of great importance for planning aimed at reducing earthquake-related damages. The geographical and structural setting of Kerman Province, along with the distribution of various faults across its territory, has made it one of the most seismically active provinces in Iran. The occurrence of devastating earthquakes such as the Bam, Golbaf, and Hejdak earthquakes supports this claim. As mentioned, given that predicting the occurrence of earthquakes is generally not feasible, prioritizing regions based on the evaluation of their seismic potential plays a crucial role in earthquake crisis management and in minimizing associated damages. Accordingly, this study aims to evaluate and calculate morphotectonic indices in the Tanguieh basin of Sirjan and to analyze the relationship between these indices and seismic foci using statistical models.



Methodology

The present study is applied in terms of its objective and is classified as descriptive–analytical in terms of its nature and methodology. To carry out this research, the indices SMF, AF, SL, T, μ, HI, S, and BS were first calculated for different sub-basins. In the next stage, by calculating the IatIat index for each sub-basin, the relative tectonic activity of each sub-basin was determined, and the sub-basins were subsequently classified based on their level of tectonic activity. Finally, to evaluate the relationship between these indices and earthquake epicenters, Pearson correlation tests as well as linear and exponential regression models were employed.



Results and discussion

Considering the structural and tectonic setting of the Tanguieh basin, the area is characterized by a dense fault network, with fault density in sub-basins 1 and 2 being higher than in sub-basin 3. In addition to minor faults, the Balvard, Tanguieh–Baft, Shahrbabak, and Lalehzar faults are the most important major faults, all of which are located in the southern part of the basin and exert a stronger influence on the tectonic activity of the region.

The results of morphotectonic index analysis in the study area indicate that the IatIat index ranges between 1.5 and 2 for all sub-basins, reflecting high tectonic activity across all three sub-basins. However, it should be noted that the value of this index for sub-basin 3 is 2, indicating relatively lower tectonic activity compared to the other two sub-basins. Furthermore, the assessment of earthquake distribution in the study area from 1970 to 2025 shows that, out of a total of 42 recorded earthquakes in the Tanguieh basin, 21 events occurred in sub-basin 1, 16 in sub-basin 2, and 5 in sub-basin 3. The minimum recorded magnitude is 2.4 Richter, while the maximum is 5.2 Richter. Among these events, 17 earthquakes have magnitudes between 2.0 and 2.9, 7 events between 3.0 and 3.9, 15 events between 4.0 and 4.9, and 3 earthquakes exceed magnitude 5. The results of regression analysis between the number of earthquake epicenters and morphotectonic indices indicate that the strongest statistically significant relationship, at an error level of less than 0.05, is between seismic epicenters and the stream length–gradient index (SL), with a coefficient of determination of 0.999. Following this, the drainage density index (μ) shows the next strongest significant relationship with seismic epicenters, with a coefficient of determination of 0.940.

Additionally, regression analysis examining the relationship between fault density and morphotectonic indices reveals statistically significant relationships at the 95% confidence level. These include the relationship between fault density and the drainage basin asymmetry index (AF), with coefficients of determination of 0.87 (linear) and 0.70 (exponential); between fault density and the basin shape index (BS), with coefficients of 0.86 (linear) and 0.70 (exponential); and between fault density and the sinuosity index (S), with coefficients of 0.87 (linear) and 0.77 (exponential).



Conclusion

Although not all morphotectonic indices show a strong correspondence with earthquake epicenters, the most significant and robust indicators of tectonic activity, such as the stream length–gradient index and drainage density demonstrate a very high degree of correlation with seismic epicenters in the Tanguieh basin. In particular, the stream length gradient index (SL), with a coefficient of determination of 0.999, exhibits the strongest correspondence with earthquake epicenters. This finding indicates that areas characterized by more active and tectonically influenced river gradients are predominantly locations where earthquakes occur. Similarly, the drainage density index (μ), with a coefficient of determination of 0.940, also shows a very strong correlation with seismic epicenters, further confirming the role of tectonic activity in shaping drainage patterns and influencing earthquake occurrence. Overall, the results of this study highlight the importance of the SLSL and μμ indices as key criteria for identifying seismically prone areas within the Tanguieh basin and demonstrate that morphotectonic processes play a significant role in controlling the spatial distribution of earthquakes.



Keywords: Earthquake epicenter, Morphotectonics, Iat index, Tangueiyeh Basin