Where has the Flat-Fattened-Farallon Slab gone?

It has been hypothesized that much of the Laramide orogeny producing the Rock Mountain Front was caused by dynamic effects induced by flat-slabs during a period of subducting plateaus. It has further been hypothesized that a particularly flat block containing the Shatsky Rise conjugate left a foot print from Southern California to Colorado with dimensions of about 500 km in width and 1000km in length. Here we rediscovered this block beneath the Midwest at a depth of about 660km and dipping northeastward at about 35°. This resolution was accomplished by exploiting the USArray seismic observations where detailed waveform modeling allowed both the shape and sharpness of a candidate tomographic image as box-like. This structure when migrated back in time to California (using G-plate mapping) fits the above hypothesized block quite well lending strong support for the above hypothesis.