Bayesian Source Characterization of Oceanic Transform Fault Earthquakes Using Relative Teleseismic Rayleigh Wave Spectra

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Abstract Oceanic transform faults frequently generate moderate‐sized earthquakes in quasi‐periodic cycles, offering attractive cases for studying earthquake physics. However, characterizing these remote events remains challenging due to the scarcity of local seismic data. Teleseismic body waves can provide some constraints, but they are most effective for larger events with strong signals and suffer from significant uncertainties caused by 3‐D Earth structures along the traveling path. To improve source characterization, we develop a Bayesian inversion method based on relative spectra of teleseismic Rayleigh waves—defined as the amplitude ratios and phase shifts between target and reference events. This approach effectively mitigates the 3‐D structure effects and significantly improves the accuracy of source parameters such as horizontal locations and centroid depths. In contrast to conventional methods that assume fixed data errors, our approach infers them directly from observations—crucial for evaluating uncertainty of model parameters by the Bayesian inversion. Applying the method to five Mw ≥ 5.8 earthquakes on the Blanco transform fault yields results consistent with prior 3‐D teleseismic body wave inversions, validating the method's accuracy. Extending the analysis to 23 Mw ≥ 4.8 earthquakes indicates that coseismic slips are predominantly confined above the 600°C isotherm. Furthermore, we resolve more complex rupture processes in two Mw ≥ 6.2 events, demonstrating the method's capability to capture complex rupture behavior beyond the single point source approximation. This new method offers a promising tool for analyzing moderate‐sized earthquakes on oceanic transform faults globally using teleseismic surface waves.

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