Understanding ongoing processes of terrestrial mud diapirism through absolute gravimetry and geodetic approaches in SW Taiwan: implications for geological hazards

Abstract

Mud diapirs and mud volcanoes are widespread geological features driven by subsurface seepage or extrusion of liquid and over-pressured mudstone. These formations pose significant hazards due to the emission of flammable gases, formation of mudflows, and release of atmospheric methane. In southwestern Taiwan, mud diapirism is a complex process involving multiple factors, including regional tectonics and geological history. Despite its significance, the contribution of mud diapirism to present-day crustal deformation during ongoing orogeny and its involvement in hazard assessments are still unclear. This study presents a comprehensive investigation of subsurface mass redistribution using a combination of absolute gravimetry and geodetic approaches at a site near Wandan mud volcano in southwestern Taiwan. High-precision time-lapse gravity data collected over 5 years reveal a significant linear trend of +2.891 ± 0.618 μGal/year, with hydrology-induced effects around 0.807 ± 0.054 μGal/year. Geodetic measurements reveal a slight uplift, which results in a gravity decrease rate of –0.010 μGal/year. These suggest that subsurface mass addition is the most plausible explanation for the net gravity increase rate of +2.073 μGal/year. Forward modeling under assumptions identifies critical values for key parameters of a mud diapir (size, depth, and intruding rate) required to produce the observed gravity increase rate on the surface: a radius of 50 m or greater and an intruding rate of 0.409 m/year or larger. These critical values found are in line with other studies and significantly narrow down the possible parameter space. Our findings suggest that subsurface mass addition is a significant factor and should be considered in the models for studies of the development of the fold-and-thrust belt in southwestern Taiwan. The results provide new insights into the activity of mud diapirism and highlight the importance of combining absolute gravimetry and geodetic approaches in addressing such processes. Graphical Abstract