Improving and Testing Regional Attenuation and Spreading Models Using Well-Constrained Source Terms, Multiple Methods and Datasets

Abstract : We have developed and tested methods to constrain trade-offs among source, attenuation, geometric spreading, and site effects to improve the accuracy of regional phase amplitude corrections. Our use of both coda and direct phases has corroborated a large set of source terms for Eurasia. Using distinct data and methods, we confirmed Q estimates for many paths (e.g., Fisk and Phillips, 2012, 2013a, 2013b), and delivered our results to LANL. From discrepancies, we have identified three critical ways that calibration must be improved and evaluated: (1) constrain Q near grid edges (emphasizing the Middle East), where data sampling issues are problematic for tomography, but not our method; (2) develop physically-based criteria to better control data quality for secondary phases; and (3) improve and validate Pn Q and spreading models. These issues cause large errors in P/S discrimination, illustrated for the Iranian Plateau. We are testing advanced methods to significantly improve attenuation and spreading models, site terms, and their uncertainties for Pn, Pg, Sn and Lg in Eurasia, extending to the Middle East, to corroborate and improve tomography results. We will use independent sets of coda and direct-phase measurements, and orthogonal methods to not only validate correction parameters, but also assess impacts on P/S discrimination. We will document and deliver the algorithms, parameter estimates, uncertainties, and evaluations. We will compare and merge our results with calibration efforts at LANL and LLNL, for incorporation in the Knowledge Base.