Seismicity parameters and probability of earthquakes in the east of Iran (Lut block)

Most of the areas of the Iranian Plateau are high seismicity regions and there is a considerable difference between them. These differences in the eastern Iranian Plateau including the Lut block compared to the surrounding areas are so substantial that can be studied independently. A brief look at the seismic maps of this region shows that around the Lut block, the activity of strike-slip and reverse faults has caused many and devastating earthquakes but in the inner parts, it can be considered as a small rigid plate regarding the relative stability. In this research, using the most updated catalog as the main source, a catalog of 1760 historical and instrumental declustered earthquakes was provided for the area bounded in 56.5°-61°E and 28°-35.5°N in eastern Iran. The data was divided into a historical part and four instrumental parts of 1900 to 1963, 1964 to 1999, 2000 to 2005 and 2006 to 2022. Using the maximum curvature method for each of the four time intervals, the data completeness thresholds were determined to be 5.7, 4.7, 4 and 3.1, respectively. The seismicity parameters were estimated taking into account the uncertainty of the magnitudes. Substantially, the estimated b-value is equal to 1.06 and the mean annual occurrence rate for magnitude equal or greater than 3.1 is 58. The maximum magnitude of the earthquakes is estimated to be 7.9, which indicates the high seismicity of the region. The probability of annual exceedance for different magnitudes is estimated for the return periods of 50, 475, and 2475 years. Comparing the results of this study with the results of the other studies performed based on the same data and the same method for the Central-East Iran seismotectonic province confirms that the seismicity of the Lut block and its margin can be determined independently from the other parts of the Central-East Iran seismotectonic province.