New geological insights from legacy seismic sections: Decoding the Granada Basin (Spain)

Abstract

Seismic surveys are crucial for investigating subsurface geological formations and require significant logistical and economic resources. This study reuses legacy seismic surveys from the Granada Basin conducted by the Chevron Oil Company in the mid-1980s to gain new geological insights. In a previous paper, data from two deep boreholes and 30 legacy seismic sections were recovered and reprocessed using Machine Learning; this work interprets the results to generate three complete pseudo-three-dimensional models of the entire basin: a P-wave velocity model, a sedimentary sequences model, and a fault systems model. The sedimentary sequence model identified five distinct depocenters with varying sediment compositions throughout the basin. The study found a progressive decline in sediment accumulation rates over time, from 0.18 mm/yr in the Tortonian to 0.10 mm/yr in the Pliocene-Quaternary. This trend reflects changes in the sedimentary system, moving from transitional platforms to regression and transgression episodes and finally to a stable continental state. The differences in sediment accumulation rates suggest that greater disparities are linked to intense tectonic activity, while smaller differences indicate reduced tectonic activity and a consistent sedimentation rate since the Pliocene. Additionally, 17 new faults were detected. Using the fault model and seismic activity data from 1984 to 2023 provided by the Andalusian Institute of Geophysics (IAG), a hazard analysis was performed based on the maximum magnitude supported by each fault, demonstrating the value of reusing vintage seismic data to update geological models and improve our understanding of subsurface formations and seismic hazards.