Autocorrelation Seismic Imaging of Northern Taiwan Using Ambient Noise Data

Abstract Over the past few million years, northern Taiwan records a tectonic history of subduction to arc–continent collision followed by post‐collisional collapse. This evolution motivates constraints on crustal structure, including crustal layering and thickness. We analyze 7 months of continuous vertical‐component recordings from the dense Formosa Array and retrieve zero‐offset P‐wave reflectivity using ambient noise autocorrelation. Stacked autocorrelation functions image three laterally persistent positive polarity arrivals beneath northern Taiwan. The deepest arrival is interpreted as the Moho (PmP) at 11–15 s two‐way travel time (TWT), corresponding to depths of ∼30–47 km. The Moho deepens beneath the mountain belt and shallows toward the Ilan Plain. A second reflector occurs, on average, ∼5 km above the Moho and forms a laterally continuous, Moho‐parallel band in the lowermost crust. A shallow intracrustal reflector lies at 5–8 s TWT (∼12–22 km depth) and dips gently to the east–southeast; crustal seismicity is predominantly located above this interface. Synthetic modeling and depth‐conversion sensitivity tests indicate that the principal arrivals are robust and that depth uncertainties are modest. These observations provide new constraints on crustal layering and interface geometry beneath northern Taiwan derived from dense‐array ambient‐noise reflectivity imaging.