P- and S-Wave Travel-Time Characteristics and Station-Dependent Residuals from Local Earthquakes in Ghana

Eric Hovor, Anuoluwa Olamide Olatunji, Mutalabi Alhassan, Yakubu Seidu Bubaki

Understanding P- and S-wave travel-time behaviour is important for characterizing seismic-wave propagation and identifying station-dependent variability within regional seismic networks. This study investigates P- and S-wave travel-time characteristics and station-dependent residuals using local earthquakes recorded by the Ghana Digital Seismic Network (GHDSN). The analysis reexamines the published GHDSN earthquake bulletin and waveform dataset for 2012–2014, comprising 73 detected earthquakes recorded by six broadband stations. Event selection was based on phase coverage, yielding nine earthquakes with paired P- and S-wave arrivals at at least five stations and 47 station-level P+S observations. Hypocentral distances were calculated from earthquake coordinates and focal depths, and first-order linear regressions were used to characterize P- and S-wave travel times. The resulting effective velocities were 6.51 km s⁻¹ for P waves (R² = 0.985) and 3.88 km s⁻¹ for S waves (R² = 0.985). Station median residuals ranged from −0.40 to +1.17 s for P waves and −1.39 to +1.27 s for S waves. Within-event permutation tests yielded p = 0.0080 for P waves and p = 0.0110 for S waves, indicating statistically significant station-associated variability in the selected observations. However, the small ΔR² values indicate that the magnitude of this station-associated contribution is limited. The results provide an empirical characterization of local seismic-wave propagation across the investigated GHDSN stations in southern Ghana and identify station-dependent variability that warrants further investigation using larger datasets, improved earthquake locations, and joint velocity–location–station analyses.