FROM THE CORE OF THE CRATON TO THE EDGE OF THE RIFT: A SEISMIC TRANSECT FROM QUEBEC TO NOVA SCOTIA

In this presentation, we will provide an overview of the goals and structure of an ongoing seismological study of the North American lithosphere and the asthenosphere beneath it. Deployed in the summer of 2012 and expanded a year later, our project extends the reach of the Earthscope seismic array into the central part of the North American craton and the Canadian Maritime Provinces. This transect extends along a line from the shore of James Bay in Quebec to the southern tip of Nova Scotia. Nearly 2.5 billion years of geological history are represented by rocks along the transect. Using methods of passive seismology, we aim to address three broad themes: the architecture and properties of the lithosphere, and how it changes with geological age; the nature of boundaries between tectonic domains of different ages; and the nature of interactions between the lithosphere and the asthenosphere below.

We will present results of preliminary work based on data already available along the transect. A study of surface wave dispersion was carried out on a set of records from seismic stations in Maine, showing significant differences in seismic properties of both the crust and the upper mantle in areas north and south of the Norumbega fault zone. A study of shear wave birefringence (splitting) observed at a group of sites on opposite sides of the Appalachian Front showed clear uniformity of the upper mantle texture beneath them. This suggests that the Appalachian Front does not separate upper mantle volumes with distinct properties, and that the front itself is most likely dipping at a shallow angle.