Large variations of crustal thickness across the Taiwan orogeny constrained by Moho-refraction recorded by the Formosa Array

Abstract The Taiwan orogenic belt is formed by the strong convergence between Philippine Sea Plate and Eurasian Plate. detailed mountain building process still under debated largely due to poor constraint of deep crustal structures, particularly geometry at Moho-depth. Here Moho-refracted P waves are identified from seismic data recorded a dense array (Formosa Array) in northern Taiwan. Although refracted energy often weak each individual station, waveform similarity nearby stations provides reliable for estimating apparent velocity array. forward modeling observed shows larger thickness (~ 52 km) beneath Backbone Ranges than adjacent Hsuehshan 36 km). Such result not only confirming Moho variations along few NW-SE profiles previous studies, but also showing variation well extended NE-SW direction. large change across orogeny strongly indicate that deformation might extend beyond shallow crust, possibly involving crust upper mantle. may be reaching isostatic equilibrium yet.