In Taiwan’s collision zone, the Earth’s crust sometimes slips quietly without producing traditional earthquakes. These silent movements, known as aseismic slip, include tremors, earthquake swarms, and repeating earthquakes. By analyzing 10 years of seismic data, we identified five tremor clusters along Taiwan’s mountain belt and studied how they respond to changes in groundwater levels and tides.

These three types of events occur at different depths but often align along the Central Range Fault. Tremors occur deep below the surface, swarms are shallow, and repeating earthquakes fall in between. We found that tremors and swarms are more likely to occur when groundwater levels drop, suggesting that fluid pressure helps trigger these events. Repeating earthquakes are less affected, possibly acting as a barrier between the fluid-sensitive deep and shallow zones. Tremors are also sensitive to tidal forces: about 80% occur during tidal unloading, compared to less than half of swarms and repeating earthquakes.

This depth-dependent behavior shows how fluids and stress interact differently across the crust. These insights help us better understand fault systems in mountain-building regions like Taiwan and may improve future assessments of earthquake and slow-slip hazards.