Surface Wave Diffraction Pattern Recorded on AlpArray: Cameroon Volcanic Line Case Study.

Area of Science:

• Geophysics
• Seismology
• Earth Sciences

Background:

• Stripe-like surface wave arrival angle deviations are globally observed but lack explanation.
• Previous studies noted these patterns without identifying the cause.

Purpose of the Study:

• To test the hypothesis that seismic wave diffraction at small-scale velocity anomalies causes observed arrival angle deviations.
• To locate and characterize a specific upper mantle anomaly using seismic data.

Main Methods:

• Analyzing Rayleigh wave patterns from Southern Atlantic Ocean earthquakes recorded by the AlpArray seismic network.
• Employing a modeling approach to simulate seismic wavefield interaction with velocity anomalies.
• Utilizing a grid search inversion scheme to pinpoint and define anomaly characteristics.

Main Results:

• The study identified a significant upper mantle anomaly located in Central Africa, primarily under Cameroon.
• The anomaly is estimated to be 320-420 km wide, aligning with the Cameroon volcanic line's known low-velocity region.
• The observed arrival angle deviations are explained as interference patterns from surface wave diffraction.

Conclusions:

• Diffraction of surface waves at small-scale velocity anomalies can generate systematic arrival angle deviations.
• A specific upper mantle anomaly beneath Cameroon has been successfully located and characterized.
• The developed methodology offers a general approach for studying upper mantle anomalies globally.