Imaging the Deep Crustal Structure of Central Oklahoma using Stacking
and Inversion of Local Earthquake Waveforms
Abstract
The southern Granite-Rhyolite province contains a comprehensive record
of lithospheric evolution in North America. During the last decade,
increased seismicity along with improved seismic monitoring
installations in Oklahoma provided a rich catalog of local earthquakes.
The source-receiver geometry of this dataset is well posed to illuminate
the middle and lower crust through long offset recordings of the Pg
phase. We present a 3-D P-wave velocity model for central and north
Oklahoma developed through a non-standard processing scheme applied to
local earthquake waveforms recorded from 2010-2017, focusing on the
deeper crust. We employed common-mid-point sorting, stacking, and
inversion of Pg-phases which resulted in a set of localized
velocity-depth functions up to depths of 40 km. Using this methodology,
we significantly increased the S/N ratio for far offset
(~250 km) local earthquake waveforms which led to the
increase in depth of investigation for our final 3-D velocity model. We
find high velocity (> 7 km/s) lower crust throughout the
investigated area which suggests a mafic lower crust. The high
velocities support previously established models which state that the
lower crust of the Granite-Rhyolite province was derived from melting of
older crust. We further relate shallow and middle crustal velocity
anomalies to other data sets such as gravimetric and magnetic anomalies,
and the spatial distribution of earthquakes. We interpret the Nemaha
Fault system as a deep-rooted discontinuity which separates two crustal
domains. On the contrary, we do not find clear evidence for the
existence of the Midcontinent rift (MCR) in northern Oklahoma.