Travel-time tomography of the northern Canadian cordillera

Work done in collaboration with Drs. Michael Bostock, John VanDecar, and John Cassidy

For details of this project, see this article. An interpretation of mantle xenoliths in light of these results is found here.

Map of station locations Map of earthquake locations

Using a small array of permanent (black) and portable (red) seismographs, we recorded teleseismic (distant) earthquakes from July, 1995 through July, 1996. P-wave arrival times were determined using multi-channel cross-correlation.

plots for individual stations

Azimuthal variations in station residuals indicate substantial variations in upper-mantle velocity structure. We inverted the travel-time residuals using a 3-D tomography code developed by John VanDecar.

Checkerboard resolution test, horizontal sections Checkerboard 
resolution test, east-west sections

A checkerboard resolution test revealed the limitations of the model's resolution.

Final P velocity model, plan sections Final 
P velocity model, cross-sections

In addition to the high-velocity edge of the Alaskan slab (blue), the model reveals a substantial low-velocity model beneath the northern Cordillera (red), which we interpret as a mantle upwelling driven by the opening of a slab window and the retreat of the slab edge.

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Andrew Frederiksen /