Nature of the crust beneath northwest Basin and Range province from teleseismic receiver function data

We utilized teleseismic receiver function techniques complemented by active source refraction seismology to study the crustal structure and continental rift processes responsible for the development of the northwest corner of the Basin and Range province in northwest Nevada. Our passive seismic array of 28 short-period stations, spanning 70 km west to east, and 5 broadband USArray transportable array stations that extended our aperture to 230 km provided data on crustal properties independent of the results of our active source refraction experiment. Combining data from the two experiments provides better constraints on Moho depth, V-p/V-s ratio, and the structure and composition of the crust beneath the northwestern Basin and Range province than possible from either experiment alone. Our new data indicate Moho depths that vary from 29.5 on the east to 36.5 km in the west along the passive source array and V-p/V-s ratios that systematically span a wide range from 1.68 to 1.83. Velocity modeling of data collected from the 300 km, wide-angle refraction/reflection survey provides comparable Moho depths of 32-37 km under the same region. Decreasing V-p/V-s is correlated with decreasing crustal thickness, with V-p/V-s ratio > 1.80 in northeast California and V-p/V-s < 1.74 in the thinner crust of the Basin and Range province. We associate the high V-p/V-s of northeast California with mafic additions to the crust during formation of the Modoc Plateau in a region of accreted Paleozoic island arc terrans similar to those exposed in the eastern Klamaths and northwestern Sierra Nevada. Unusually low V-p/V-s in conjunction with low absolute V-p and V-s is observed beneath the central part of our array and may be due to the roots of the Sierra Nevada batholith, now dismembered by Basin and Range faults. Back azimuthal stacking of our receiver function data suggests a northwest oriented crustal anisotropy fast direction beneath this region, parallel to the northwest to southeast oriented Cenozoic extension experienced by the Basin and Range province and suggestive of a similar flow direction in the middle to lower crust.