ALBERT

Description: Summary Global variations in the propagation of fundamental-mode and overtone surface waves provide unique constraints on the low-frequency source properties and structure of the Earth’s upper mantle, transition zone and mid mantle. We construct a reference dataset of multi-mode dispersion measurements by reconciling large and diverse catalogs of Love-wave (49.65 million) and Rayleigh-wave dispersion (177.66 million) from 8 groups worldwide. The reference dataset summarizes measurements of dispersion of fundamental-mode surface waves and up to six overtone branches from 44871 earthquakes recorded on 12222 globally distributed seismographic stations. Dispersion curves are specified at a set of reference periods between 25 and 250 s to determine propagation-phase anomalies with respect to a reference Earth model. Our procedures for reconciling datasets include: (1) controlling quality and salvaging missing metadata; (2) identifying discrepant measurements and reasons for discrepancies; (3) equalizing geographic coverage by constructing summary rays for travel-time observations; and (4) constructing phase velocity maps at various wavelengths with combination of data types to evaluate inter-dataset consistency. We retrieved missing station and earthquake metadata in several legacy compilations and codified scalable formats to facilitate reproducibility, easy storage and fast input/output on high-performance-computing systems. Outliers can be attributed to cycle skipping, station polarity issues or overtone interference at specific epicentral distances. By assessing inter-dataset consistency across similar paths, we empirically quantified uncertainties in travel-time measurements. More than 95 per cent measurements of fundamental-mode dispersion are internally consistent, but agreement deteriorates for overtones especially branches 5 and 6. Systematic discrepancies between raw phase anomalies from various techniques can be attributed to discrepant theoretical approximations, reference Earth models and processing schemes. Phase-velocity variations yielded by the inversion of the summary dataset are highly correlated (R ≥ 0.8) with those from the quality-controlled contributing datasets. Long-wavelength variations in fundamental-mode dispersion (50–100 s) are largely independent of the measurement technique with high correlations extending up to degree ∼ 25. Agreement degrades with increasing branch number and period; highly correlated structure is found only up to degree ∼ 10 at longer periods (T 〉 150 s) and up to degree ∼ 8 for overtones. Only 2ζ azimuthal variations in phase velocity of fundamental-mode Rayleigh waves were required by the reference dataset; maps of 2ζ azimuthal variations are highly consistent between catalogs (R = 0.6–0.8). Reference data with uncertainties are useful for improving existing measurement techniques, validating models of interior structure, calculating teleseismic data corrections in local or multi-scale investigations, and developing a 3D reference Earth model.