T104 Combining Geology and Geophysics (Posters)

Monday, 10 October 2011
9:00 AM - 6:00 PM
Hall C

CRUSTAL STRUCTURE ACROSS THE RIO GRANDE RIFT AND COLORADO PLATEAU FROM AUTOCORRELATION OF AMBIENT NOISE RECORDED BY USArray

Paper number: T104-9
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Seismic interferometry has proven extremely successful in extracting surface waves from ambient noise for mapping subsurface velocity variations. Extraction of body waves using similar techniques has been demonstrated in a few studies, but has not yet found widespread application in crustal studies. Here we apply one of the earliest expressions of interferometry, i.e. that the reflection response at a seismic station can be obtained from the autocorrelation of the transmission response, to a subset of EarthScope’s Transportable Array to map lithospheric structure across the Rio Grande rift and adjacent Colorado Plateau. Extraction of the reflection response from autocorrelation has a number of computational advantages over cross-correlation between stations; complications due to timing errors, interstation variability in amplitude scaling and instrument response, and the need for contemporaneous recording are absent. However, single station autocorrelation estimates of reflectivity lack the normal moveout estimates that can be critical to distinguishing multiples from primaries and P from S mode returns.

As a test of this technique, we generated an east-west reflection profile by autocorrelating data from 10 stations of US Array’s transportable array. 5 of these stations were deployed on the Colorado Plateau, one within the Rio Grande Rift and 5 east of the rift on the Precambrian craton. These autocorrelations exhibit prominent variations that clearly correlate with previous measures of crustal thickness, intracrustal structure and Moho reflectivity. In spite of the relatively low frequency of the signals obtained and the large station spacing of the Transportable Array, these results demonstrate how USArray can provide a novel 3D reflection image of the lithosphere, and perhaps even critical discontinuities in the underlying mantle. Furthermore, it demonstrates that any seismic station can be transformed into a seismic reflection “borehole”, whose penetration is limited only by the length of record available for cross-correlation.