MCE(R) “Risk Targeted Maximum Considered Earthquake”Analysis & Mapping for Pakistan under 2024 updated Probabilistic Seismic Hazard Assessment

Abstract

This study undertakes a comprehensive exploration of seismic risk assessment in Pakistan, focusing around the application of “MCE(R) Risk Targeted Maximum Considered Earthquake”, using the methodology devised by (USGS) United States Geological Survey. Preliminary stage involves an updated Probabilistic Seismic Hazard Analysis (PSHA) to establish a foundation for the primary objective, using procedures of Earthquake Model of the Middle East (EMME14) with US National Seismic Hazard Maps, in order to get more reliable and effective study of MCE(R). Unlike prior investigations, which did not comprehensively incorporate faultbased analysis, this study employs an advanced methodology, integrating conventional area sources, spatially smoothed gridded seismicity, crustal faults, and subduction source models. To ensure accuracy, an updated earthquake and fault catalogue for the region is also compiled, drawing from a range of international and national databases. This study includes the modeling of 51 crustal fault sources using the records established by the Global Earthquake Model (GEM). Furthermore, the Makran Subduction Zone (MSZ) is used as defined by [Asad et al., (2021)]. To estimate hazard at the bedrock level, this study employ Ground Motion Prediction Equations (GMPEs) established by PEER Next Generation Attenuation (NGA). Then, using a 1% target probability of collapse (Pc|gm) in 50 years, an iterative procedure is adopted to modify the hazard values corresponding to maximum considered earthquake (MCE, 2% probability of exceedance in 50 years). The analysis pinpoints the optimal combination of (β) “beta” and (Pc|gm) “target probability of collapse at a certain ground motion intensity” value by integrating sensitivity analysis, pivotal in finalizing the MCE(R). Essential to the understanding of MCE(R) is its role in the structural design process. This method seeks to design structures exposed to an acceptable and controlled risk level, expressed as the mean Annual Frequency of Collapse (AFoC). The Peak Ground Acceleration (PGA) or Spectral Accelerations (SA) is a key factor, form the hazard curves obtained from PSHA, to an iterative approach in solving the risk-targeting problem. This process, iteratively defines (RTGM) Risk Targeted Ground Motion to find the AFoC at a particular MCE level seismic intensity measure, to achieve target Pc|gm in 50 years. The maps for the PGA and SA at natural periods of 0.2, 1 and 2 sec are developed for the 10% and 2% probability of exceedance in 50 years (DBE and MCE levels, respectively), alongside the map of Risk Coefficients (RC) and “Risk Targeted” modified hazard maps for MCE levels are developed. In this procedure, for each site, the fragility curve and hazard curve are integrated by iteratively modifying the hazard parameters until the target risk is achieved. It guides to determine the risk-targeted design ground motions, aligning with the desired risk level Pc|gm. This research contributes significantly to seismic risk assessment and management, emphasizing the indispensable role of MCE(R) in steering effective structural design processes. The insights gleaned are invaluable for researchers, policymakers, and engineers in the region, aiding in the development of resilient infrastructures and enhancing overall disaster preparedness.