Proxy-based V_s30 modelling of the Muzaffarabad, northern Pakistan

The time-averaged shear wave velocity in the upper 30 m of soil, also known as V_s30 is the basic criteria employed in the seismic site condition and site response analysis. V_s30 is globally utilized in preparing Seismic Site Characterization Maps (SSCMs) regardless of its considerable limitations. This paper presents the acquisition, and interpretation of 280 real-field V_s30 measurements using a geophysical instrument named Tromino. Models have been derived based on the three proxies i.e., geological age, lithology and topographic slope. Data analysis and statistical approaches show a good correlation between measured V_s30 values with the adopted proxies. The models presented in this work consider topographic slope based on a 30 m resolution digital elevation model (DEM) in addition to the three geological age and four lithological groups. Cross-correlation of the proxies is performed to correlate the proxies for constructing proxy-based models. Proxy performance evaluation is carried out on the basis of residual analysis and the correlation between real-field V_s30 measurements and V_s30 values estimated from proxies is offered to assess the V_s30 predictive capacity of these proxies. The study establishes a strong correlation between measured V_s30 values in densely populated areas and V_s30 values estimated through proxies, suggesting the viability of geological age, lithology, and slope as effective proxies for local-scale V_s30 estimation. The models introduced in the study are assessed for proxy performance, and scatter plots for slope-dependent geological units are provided for further evaluation. The final SSCM (V_s30 map) categorizes the area into National Earthquake Hazard Reduction Programme (NEHRP) site classes which shows that most of the area is prone to amplified seismic response.