Crustal structure of the northern Basin and Range province, Nevada: A new look

A major objective of the EarthScope Transportable Array (TA) is to investigate the crustal structure of the United States with uniformly spaced seismic coverage across the entire continent. Receiver functions (RFs) provide one means of estimating bulk crustal values of Vp/Vs and crustal thickness from the TA teleseismic data. Although the ~70 km average station spacing is too sparse to stack the data, the uniform coverage provides an opportunity to correlate crustal Ps phases and their multiples across a tectonic province such as the Basin and Range. We have calculated receiver functions from ~1 year of data for the TA stations in Nevada between latitude 37--42° N. The best results obtained were from the O and N lines located in northern Nevada. This particular corridor has been investigated in detail by the 1986 COCORP seismic reflection transect and the 1988-- 1989 PASSCAL experiments. This provides us with an opportunity to compare the correlated RF results to prior work in the area as well as crustal thickness estimates calculated by the EarthScope Automated Receiver Survey (EARS) system. Preliminary results show that most of the stations in the O and N lines have a high amplitude positive arrival, interpreted as the Moho Ps phase, that correlates across the entire state. The 2P1S Moho multiple is strong enough to correlate across the lines and the two phases can be used to estimate Vp/Vs and Moho depth across the transect. The Vp/Vs estimates range between 1.66 and 1.88, with most lying between 1.73 and 1.84. Crustal thickness estimates range from 28 km to 41 km, with most stations exhibiting a depth of 31--34 km. Other crustal features observed in the RFs include an upper crustal low-velocity layer at ~10 km depth and a mid-crustal high velocity layer located between 15-25 km depth. A new result is the observation of a lower crustal low-velocity layer at many stations. The top of this layer may correlate with the zone of lower crustal reflectivity observed in the COCORP lines. Our results roughly agree with previous active source experiments in that Moho depth increases from west to east and from south to north. With a few exceptions the EARS results for crustal thickness are generally within ~2 km of our estimates.