RAYLEIGH WAVE TOMOGRAPHY OF TEXAS FROM AMBIENT SEISMIC NOISE
Yao, Yao 1989-
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Texas has been one of the leading states in petroleum production since the discovery of the Spindletop oil field in 1901. Despite its huge economic value of petroleum and numerous geophysical explorations in several oil fields, the crustal structure of the Texas is not well studied. This thesis aims to investigate crustal structure in central and eastern Texas using seismic ambient noise data recorded at 87 broad-band stations from the Transportable Array of the USArray network between March 2010 and February 2011. Seismic observations based on cross-correlations of long ambient noise sequences between pairs of stations are used to obtain phase velocities at periods from 6 s to 40 s. Phase velocity maps show that positive anomaly area coincides with Laurentia craton crust and the negative anomaly area coincides with continental margin crust. The boundary between positive and negative anomaly is perfectly consistent with the Ouachita belt. From the inversion of phase velocity results, we construct 1-D and 3-D shear-wave model with four crust layers and one mantle layer. In the 3-D shear-wave velocity model, the high velocity province is imaged in central and northwestern Texas with the highest velocity beneath the Llano Uplift. This pattern extends across the whole crustal depth, reflecting cold cratonic crust in general and igneous influence at the Llano Uplift. The lowest velocity appears in northeastern and southeastern Texas at shallow crust, correlating with thick sediment layers. In deep crust and upper mantle, the lowest velocity is confined in southeastern Texas at the continental margin. Ouachita orogen could have brought old oceanic crust that contained large amount of water to the lower crust and upper mantle.