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TitreModeling wide-angle seismic data for crustal structure: southeastern Grenville Province
AuteurZelt, C A; Forsyth, D A
SourceJournal of Geophysical Research, Solid Earth vol. 99, no. B6, 1994 p. 11,687-11,704,
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 41392
Séries alt.Lithoprobe Publication 473
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC30N; 31C
Lat/Long OENS -77.0000 -75.0000 45.0000 44.0000
Sujetsétudes de la croûte; données sismiques; établissement de modèles; méthodes sismiques; modèles; vitesse des ondes sismiques; levés de reflexion sismiques; Province de Grenville; géophysique; géomathématique
Illustrationsgeological sketch maps; seismic reflection profiles; tables; graphs
Diffusé2012 09 20
Résumé(disponible en anglais seulement)
A modeling methodology for obtaining two-dimensional (2-D) crustal structure from wide-angle seismic data is applied to data from the southeastern Grenville Province. Pre-modeling steps include (1) assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal-to-noise ratio, (2) using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity, and (3) identifying data unsuitable for 2-D modeling. The goal of the travel time inversion-amplitude modeling approach is to obtain a minimum-structure and minimum-parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide-angle data. Each step of a layer-stripping procedure involves a series of inversions in which a one-dimensional or simple starting model is improved with additional velocity and/or interface nodes until a satisfactory trade-off between travel time fit, parameter resolution and complete ray coverage of all source-receiver pairs is achieved. Using zero vertical-velocity gradient layers and head waves during preliminary first-arrival inversion can (1) decrease the number of intermediate models, (2) allow greater lateral heterogeneity to be imaged, and (3) simplify incorporation of amplitude modeling constraints into the final model. Using amplitude-distance curves allows quantitative modeling of the relative amplitude and offset variations of phases. Discrepancies between observed and calculated reflection amplitudes are used to infer fundamental, non step-like velocity changes at layer boundaries. Later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that "float" within the model without an associated velocity structure. These reflectors provide a spatial image like that obtained from vertical-incidence reflection data, as opposed to a velocity image. The model of Grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data. A crustal-scale zone of wide-angle reflectors with an average easterly apparent dip of 13° defines a major Grenvillian terrane boundary.