Seismic Hazard Assessment for a Dam Project at the Eurasian Indian Plate Boundary

This seismic hazard assessment aims to determine design parameters and develop design response spectrum for the dam body by evaluating nearby active faults, historical earthquake activity, and local site conditions in Pakistan. This project holds significant importance for optimizing water resource utilization and enhancing the country's infrastructure development.

The dam is situated at the Tethysides-Indian Craton boundary, a major paleotectonic division of Eurasia. This area lies within the Alpine-Himalayan orogenic belt, an extensive seismic and mountainous region spanning over 15000 km. Notably, the Kirthar Fold and Thrust Belt (KFTB) extends over 200 km along the western boundary of the Indian plate. The tectonic setting of the KFTB is primarily influenced by the Indian-Eurasian plate collision within the Central Kirthar Fold Belt. Detailed descriptions of the KFTB and adjacent active faults are available in the Active Faults of Eurasia Database which prepared by Geological Institute of the Russian Academy of Sciences.

The closest active fault is approximately 2 km from the dam site. Within a 200 km radius of the dam, 19 earthquakes with magnitudes of 6.00 or larger have occurred over the past 115 years. Significant seismic events include the M_w7.16 earthquake on October 20, 1909 (28 km away from dam body), the M_w6.75 event on October 15, 1928 (14 km away from dam), and the M_w6.05 event on May 15, 1935 (13 km away from dam).

A total of 2363 earthquake records with magnitudes of 4.00 or larger were collected from 17 different catalogs. After removing foreshocks and aftershocks using the Gardner and Knopoff (1974) method, 403 records remained. Recurrence parameters were then calculated using the Weichert (1980) approach. The site classification, based on a measured shear wave velocity of 600 m/s from the MASW report, corresponds to Classes "C" and "B" per ASCE 7-16 and Eurocode 8 standards for V_s30.

Ground motion predictions were generated using OpenQuake with GMPEs from Abrahamson et al. (2014), Boore et al. (2014), Campbell & Bozorgnia (2014), and Chiou & Youngs (2014), as recommended by the International Commission on Large Dams (ICOLD). These models contributed 50% to the final results. The remaining 50% was derived from GMPEs advised by the 2014 Earthquake Model of the Middle East (EMME14) Project under the European Earthquake Hazard and Risk Facilities (EFEHR), including models by Akkar et al. (2014), Chiou & Youngs (2008), Akkar & Çağnan (2010), and Zhao et al. (2006).

Both Deterministic Seismic Hazard Analysis (DSHA) and Probabilistic Seismic Hazard Analysis (PSHA) results will be presented using these GMPEs. Median and +1 standard deviation values are calculated for DSHA, while PSHA results include calculations for seven return periods (72, 144, 475, 975, 2475, 5000, and 10000 years). The final risk classification will follow the guidelines outlined in ICOLD documentation.