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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS013 Oral Presentation 2218
Beam Formed Receiver Functions from the
Mr. Will Levandowski
Department of Geosciences Princeton University IASPEI
Single station receiver functions in the southern Sierra Nevada, California show considerable variation in
Moho P-S conversion intensity. Specifically, in the ranges western foothills, a region termed the Moho
Hole (e.g. Zandt et al, 2004), the Moho appears to be completely absent on single station receiver
functions. I explore the possibility that signal-generated reverberations have sufficiently obscured the
seismograms to disguise a Moho P-S conversion. Using data from the 1997 Sierra Paradox Experiment,
seismograms from 3 station sub-arrays (~20 km aperture) are slant-stacked to make the radial,
transverse, and vertical components used in deconvolution. By stacking before deconvolution, signals
from the Moho and intra-crustal discontinuities become more pronounced while reflections off of
structures near individual receivers destructively interfere with one another. Receiver functions for these
3 station beams compare favorably with post-deconvolution stacking of the receiver functions calculated
for their constituent stations. Of paramount interest is the use of this technique in the region interpreted
as the Moho Hole. Here, beam formed receiver functions better constrain the extent and geometry of
the small amplitude Moho conversion. In fact, it seems that this region is part of a larger trend:
weakening of P-S conversion signals west from the range crest. This weakening trend mirrors a
westward thickening of the crust observed in increasing P to P-S lag times. I propose that the two
trends are cogenetic, caused by large scale (~100 km horizontally) downwarping of the Moho due to
viscous coupling to downwelling delaminated lower lithosphere. This observed Moho geometry has
implications for the mechanical response of upper crustal material to delamination events and the
kinematics of uplift of the Sierra.
Keywords: delamination, receiver functions, beam forming