An Innovative Vibroseis Experiment to Detect the Moho Below the Valles Caldera, New Mexico




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In this study, we present a new 1-D velocity-structure model that reveals several geological structures beneath the Valles Caldera. The result is obtained by applying a sequence of processing techniques that mainly include extended cross-correlation, NMO correction, and horizontal super- gather stacking on Vibroseis (P-wave reflection) data collected from Valles Grande. For validating and evaluating the robustness of the processed result, we implement and test the model by iteratively forwarding modeling to a suite of travel time observed in processed data. These lead to a quantitative constrained 1-D model that resolves three shallow caldera structures at depths of 1.2 km, 2.1 km, and 3 km, the possible upper and lower bound of the magma reservoir at the middle crust with a depth of ~ 5 km and ~ 10 km respectively, and the possible Moho at near a depth of 34 km. We also found a good match of multiples that relates to the detected geological features by incorporating and comparing the modeled data with the observed real data. In our result, the depth of the Moho beneath the Valles Caldera is shallower compared to those results obtained from the teleseismic data with surface waves, possibly related to the uprising materials from the mantle that uplifts the Moho to a shallower depth as part of the Rio Grande Rift zone. This is an implication that the Rio Grande rifting process is possibly driven by upwelling mantle flow beneath this region.