Imaging a paleovalley with passive seismic methods: Evidence for glacial
carving of Unaweep Canyon (Colorado, US)
Abstract
High-resolution passive seismic imaging of shallow subsurface structures
is often challenged by the scarcity of coherent body-wave energy in
ambient noise recorded at surface stations. We show that
autocorreleation (AC) of teleseismic P-wave coda extracted from just
1-month of continuous recording at 5 Hz geophones can overcome this
limitation. We apply this method to investigate the longitudinal
subsurface structure of Unaweep Canyon, a paleovalley in western
Colorado (US) with complex evolution. Both fluvial and glacial processes
have been proposed to explain the canyon’s genesis and morphology. The
teleseismic P-wave coda AC retrieves zero-offset reflections from the
shallow (200 – 500 m depth) basement interface at 120 stations along a
5 km long profile. Additionally, we invert interferometrically retrieved
surface wave dispersion for the shear-wave structure of the sedimentary
fill. Combined interpretation of these results and other geophysical and
well data suggests an overdeepened basement geometry due to glacial
processes.