Path-averaged seismic attenuation in the Northern Canadian Cordillera, Yukon, from USArray P- and S-wave attenuation of local earthquakes

The Northern Canadian Cordillera in the Northern Yukon Province comprises the North American Craton and several sedimentary basins. The craton transitions abruptly to a complex network of accreted terranes across the Tintina Fault. Whether this distinct change is marked by a change in crustal and upper mantle attenuation is unknown. We determine path-averaged Qp and Qs from earthquakes along-strike of the Northern Mackenzie Mountains, Yukon, by measuring t* (integrated path attenuation) at 25 USArray seismic stations. Preliminary results from 12 shallow (<20 km) earthquakes, resulting in 300 total P- and S-wave measurements, show consistent high attenuation (Qs<500) near the Eagle Plain Basin. Moderate attenuation (500<Q<1000) appears throughout much of the Northern Yukon Territory (both in Qp and Qs). South of the Ogilvie mountains, stations extending ~400 km north to south across the Tintina Fault show low attenuation (Q>1000). This may indicate that there is no significant change in average crustal and upper mantle attenuation across the craton/accreted terrane boundary. We plan to expand the catalog of earthquakes to the three-year operating period of the USArray stations to increase the number of observations and explore variations in Q from deeper earthquakes with varying event-station azimuths to resolve possible variations across the craton/accreted terrane boundary. Values of Qp and Qs are comparable to the upper 25 km of interior Alaska as determined by the BEAAR seismic experiment. This study can help to determine whether or not complex tectonic history in Alaska and the Canadian Cordillera is recorded in seismic properties of the crust and upper mantle.