Characteristics and generation mechanisms of tremors across a mountain belt

We analyze ∼7000 tectonic tremors recorded between 2012 and 2022 across five clusters along Taiwan's mountain belt at depths of 30–50 km, providing new insights into slow fault slip within an active continental collision zone. All clusters occur above the Moho, exhibit thrust-dominant focal mechanisms, and are distinct from crustal seismicity. Tidal sensitivity varies spatially, with Clusters 2–5, located in zones of active collision and subduction termination, showing strong modulation (α = 0.53–0.75), while Cluster 1, situated in a post-collisional extensional environment near the Okinawa Trough, exhibits weaker sensitivity (α ≈ 0.3). These variations correlate with differences in tidal stress amplitude and tectonic regime. Moment tensor inversions reveal consistent thrusting styles, but principal stress orientations vary with depth, with σ₁ rotating from vertical in the upper crust to horizontal at tremor depths. This supports a two-layer deformation model shaped by orogenic collapse and lower crustal convergence-parallel shear. Our findings demonstrate that tremor generation in Taiwan reflects evolving stress regimes, fluid-assisted weakening, and structural heterogeneity associated with the interplay of collision, subduction, and back-arc extension. Tremors thus serve as sensitive indicators of deep-seated tectonic processes in dynamically evolving mountain belts. • Tremors in Taiwan lower crust show thrust mechanisms and high tidal sensitivity. • Stress field rotates from vertical to horizontal with depth in collision zone. • Five tremor clusters reflect collision, subduction, and back-arc processes.