In-Depth Analysis of The Harnai Earthquake on October 7, 2021: A Comprehensive Study in Balochistan, Pakistan


Nasrullah*, Ali Ahmed, Sajjad Khan, Muhammad Hussain, Mustahsan Shuaib, Jahanzeb Khan


On October 7, 2021, a significant seismic event measuring 5.9 Mb on the Richter scale struck the Harnai District of Balochistan at 03:01:08 PST, with epicentral coordinates recorded at 30.2203 N and 68.0142 E, and a depth of 9 km. Preceding this, a foreshock of magnitude 4.6 Mb occurred at 00:00:57 GMT, with epicentral coordinates noted at 30.1172 N and 68.0341 E, and a depth of 10 km. The earthquake’s tremors were felt across most regions of Balochistan, including certain adjacent areas of Afghanistan. The geological fieldwork for this study took place shortly after the earthquake for gathering field and geological data. The study combines field investigations and satellite interpretations to analyze structures surrounding the seismic zones. The analysis of earthquake distribution in the area allows for a geological explanation to be made. By plotting seismic epicenters on a geological map, it was observed that a majority of these epicenters align with major faults. Further structural interpretations, field observations, and a review of data on the Sulaiman fold and thrust belt indicate that earthquakes in the Harnai area are predominantly shallow. The Harnai region is confined between significant faults, namely the Harnai thrust fault and Karahi dextral strike-slip fault. Analysis of seismic data from 1973 to 2021 reveals a concentration of high-magnitude earthquakes. Three distinct fracture zones were near the epicenter of the earthquake and at Harnai city, numerous cracks were seen also on the ground. Both field observations and seismicity patterns indicate that earthquakes in the studied area are shallow, primarily resulting from a combination of strike-slip, oblique/normal, and reverse faulting along the western portion of the Indian plate.

KEYWORDS: Harnai district, Earthquakes, Tectonics, Faults, Seismicity Pattern, Sulaiman Fold and Thrust Belt.