Structural controls and earthquake response of Taiwan mud volcanoes

Earthquakes can influence the activity of mud volcanoes and other fluid expulsion systems, which may erupt or change their activity shortly after the seismic event. This study investigates the influence of static and dynamic stresses, produced by some important earthquakes in Taiwan, on fluid expulsion systems that have coseismically responded to such events. Peak dynamic stresses have been estimated at the considered seepage features using available peak ground velocities, while computation of static stress changes has been performed considering the orientation of the feeder systems that are structurally controlling mud volcano development. Feeder dike orientations have been determined on the basis of the geometric characteristics of mud volcanoes (e.g., volcano elongation, vent alignments), and their spatial distribution shows some correlation with regional structures and the active tectonic stress field. The responses of Taiwanese fluid expulsion systems to earthquakes are correlated with the amplitude of dynamic stresses generated by seismic waves, while static stresses have or have not contributed to the triggering depending on the case. This observation suggests that static stresses are unlikely to be a necessary causative mechanism, as seepage systems do respond to earthquakes even when changes in static stress are unfavourable.