The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei. A seismic array consisting of 5 stations equipped with both broadband and short-period sensors was installed in 2003 in order to monitor the seismic activity of the area. It recorded a variety of events including common volcano-tectonic earthquakes and volcanoseismic signals like tornillos, short duration monochromatic events (10–15 s) and long duration spasmodic bursts (∼15 min). An analysis of the complex frequencies of the tornillo/monochromatic signals shows that Q-values are of the order of several hundreds. Based on the model of a fluid-filled crack, such Q-values can result from the oscillations of a crack containing a misty or dusty gas. These observations put into doubt the long-standing suggestion that the Tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area.