A Tomographic Model of the Canadian Lithosphere via Two-Station Surface-Wave Analysis

Abstract:

The relationship between lithospheric and crustal tectonics in continental regions is not entirely understood; in order to understand past and present lithospheric tectonic participation in tectonic processes, we need to image the lithosphere at terrane scale. We are developing an improved continental-scale image of the Canadian lithosphere using surface waves from distant earthquakes. Existing continental-scale models are primarily based on single-station analyses, which provide constraints on individual event-station paths and so are limited by the available seismicity in the study area; as much of Canada is essentially aseismic, such models have had limited resolution. Instead, we employ two-station measurement, in which seismograms from global earthquakes are compared between pairs of instruments; phase delays between two seismograms record structure along the path between the two stations and cancel out the contribution of the earthquake itself. We have developed a software suite that allows for efficient two-station phase velocity analysis, and will present results showing differing surface-wave dispersion responses between tectonic environments and dispersion maps of central and western Canada. One hundred and six station pairs were used to create dispersion curves of western Canada. Early tomographic inversion results show slower lithospheric velocity to the west of the Cordilleran deformation front and faster lithospheric velocity to its east. These maps also show that the position of the velocity transition varies with period, implying that the contact surface between cordillera and craton is not vertical. These measurements will ultimately be incorporated into a three-dimensional model of mantle structure for Canada as a whole.