Seismic interferometry using non-volcanic tremor in Cascadia

Abstract

Seismic interferometry to date has focussed on surface waves, due to paucity of deep, high-frequency noise sources. Here, we investigate use of non-volcanic tremor on the Cascadia subduction zone as a noise source to recover scattered body-wave contributions to the Green's function. Tremor data for 2004-2005 recorded at Polaris-BC stations TWKB, MGCB and LZB were filtered and cross-correlated. TWKB and MGCB correlations generate a highly reproducible arrival at 4.5 s for combinations of vertical with radial or transverse components. TWKB and LZB correlations are less reproducible, but yield a strong arrival at 3.5 s for 2005. Upon consideration of source/receiver geometry, polarity and timing, we interpret these arrivals to represent reflection-conversions. Arrival times imply that these signals originate at depths between 9 and 12 km, coincident with an interval of strong reflectivity imaged in the 1987 Lithoprobe Southern Cordillera transect. Copyright 2007 by the American Geophysical Union.