Tectonic geomorphology-based modeling reveals dominance of transpression in Taxila and the contiguous region in Pakistan: implications for seismic hazards

Mapping active tectonic features remains a critical step in understanding earthquake hazards and producing reliable and scientifically robust maps. The mapping is often combined with seismological, geological, geodetic, and structural datasets to improve the overall quality of the maps. However, site response analysis is usually not connected with a typical active tectonic mapping exercise, which is a significant problem in improving earthquake hazard mapping. The motivation of the present study is to demonstrate the robustness of methodology where mapping of active tectonic features is combined with the site response analysis, thus mapping the earthquake sources and the seismic amplification potential of the region. Initially, tectonic geomorphological mapping was done by manually tracing the evidence of faulting, including the topographic breaks, earthquake ruptures, ridge crests, deflected streams, triangular facets, and so on. The cross-cutting relationships between the faults and the Holocene sedimentary deposits differentiate active from inactive fault zones. However, older faults that do not reach the surface can also be active; therefore, to address the limitations, we have combined tectonic geomorphological mapping with the seismological, geological, geodetic, and earthquake centroid moment tensor (CMT) solutions data. The first segment of the study utilizes satellite imagery to produce the best quality tectonic geomorphological maps. The second part of the study evaluates the site response parameters such as fundamental frequency (f(0)), H/V amplitude (A(0)), and soft sediment thickness (H) by acquiring, processing, and interpreting ambient noise data within the urban settlements of Taxila city. The results reveal that the study area is part of the compressional bend formed by the fault interactions between the Tarbela and the Jhelum fault zones. The mapped faults are mainly similar to NE-SW-trending oblique reverse faults that show a component of a sinistral strike-slip sense of movement. Our conceptual modeling illustrated by 3D cartoons shows that fault restraining bend structural configuration explains the unusual topographic highs such as Margala Hills, suggesting significant sinistral strike-slip motion along the mapped faults. The ambient noise data show a variable f(0), A(0) and soft sediment thickness, thus attesting to the site's potential susceptibility to amplification in a significant earthquake, which poses a severe threat to the growing urbanization and population in the region. The findings from the study provide a platform for a detailed analysis of early earthquake hazards and disaster forecasting.

Automated summary

The present study demonstrates the reliability of combining mapping of active tectonic features with site response analysis to map earthquake sources and seismic amplification potential. The study utilizes various datasets and techniques to improve the overall quality of earthquake hazard mapping.