Constraining Regional Phase Amplitude Models for Eurasia, Part 2: Frequency‐Dependent Attenuation and Site Results

Abstract Fisk and Phillips (2013) motivated the need to constrain trade‐offs among correction parameters for regional phase amplitudes to improve seismic discrimination and magnitude (yield) estimation. Using an empirical Green’s function approach to cancel path and site effects, relative spectra of direct regional phases and coda were fit for many thousands of nearby, similar earthquake pairs of different moments, to estimate reliable source corner frequencies and relative moments. Detailed comparisons demonstrated the benefit of using independent measurements of coda and direct phases to provide a large set of corroborated source terms for earthquakes throughout Eurasia. The spectra were subsequently corrected for source terms to estimate more reliable Q , geometric spreading rates, and site effects. Regression analysis was used to estimate geometric spreading rates and to establish a very consistent set of absolute moments. Here, frequency‐dependent Q and site terms are examined for , Sn , , and Pn spectra. Comparisons to independent Q estimates from amplitude tomography exhibit good agreement for many paths. Large discrepancies are shown for higher frequencies, in low Q regions, and/or at the edges of the tomography grid, which significantly impact P / S discrimination. Our frequency‐dependent site terms are compared with independent estimates from coda tomography, showing good agreement (even for and Pn , at many stations) but also some substantial differences.