Analysis of Attenuation Characteristics of Seismic Waves in the Anambra Basin Using Coda Wave Decay

Seismic wave attenuation, parameterized by the quality factor Q, provides valuable information about the mechanical properties and fluid content of crustal materials and is essential for accurate seismic hazard and ground motion modeling. This study analyzes the attenuation characteristics of seismic waves in the Anambra Basin using the coda wave decay method applied to local earthquake recordings from the Nnamdi Azikiwe University seismic network. Coda wave data from 92 well-recorded local earthquakes (Ml 0.8 to 3.1) at epicentral distances of 15 to 95 km were analyzed using the single-scattering model. Coda Q values were computed in seven frequency bands between 1 and 20 Hz by fitting exponential decay functions to the coda wave amplitude envelopes measured at consistent lapse times from the earthquake origin time. The frequency dependence of coda Q follows a power-law relationship, indicating strong frequency dependence characteristic of heterogeneous sedimentary basin environments. Qc values at 1 Hz range from 52 to 89, while values at 10 Hz range from 280 to 420, reflecting frequency-dependent energy dissipation behavior. The relatively low Qc values at low frequencies are attributed to the presence of fluids, fractures, and sedimentary layering within the Cretaceous basin fill. Backscattering coefficient maps derived from the inversion reveal spatial variations in crustal heterogeneity that correlate with known structural features of the Anambra Basin. These attenuation parameters are directly applicable to stochastic ground motion simulation and seismic hazard assessment for the region.

Keywords: coda Q, seismic attenuation, Anambra Basin, ground motion, quality factor