The geophysical crust-to-mantle transition from receiver function analysis: a case study on the appalachian front in Quebec, Canada

Receiver function analysis is useful for studying relative variations of seismic discontinuities at the lithospheric scale. This study uses receiver functions computed from a densely spaced 2D grid of six receivers that collected passive seismic data over a decade in the lower St. Lawrence River, Quebec, Canada. The lower crustal structure and lithospheric mantle are not well constrained in this study area, which is centered on the tectonic boundary between the Grenville and Appalachian provinces. Thus, the goals of this study are: 1) to establish the consistency and resolution limits of receiver functions from a large data set and dense permanent array of receivers; and 2) to use this grid to identify the geophysical Moho and describe the lithospheric mantle-to-crust transition across the Appalachian front (AF), the western boundary of Appalachian deformation. The relative seismic velocity changes under the AF resolved by Receiver Function Analysis provide evidence of local variability in the Moho’s depth and sharpness. Frequency-based analysis of the receiver functions in the northwest region of the study area produces variable Moho depth estimates from 50 to 35 km, and exhibits a gradational transition from the crust to the mantle. In the southeast region, the Moho has more consistent depth and is sharper. The likely cause of this variability is either deep-reaching shear zones that offset the Moho, or a high-velocity layer in the lower crust that is only apparent in areas where it produces significant impedance contrasts between layers.M.S.Includes bibliographical referencesby Benjamin Dunha