Vertical movement during the quiescent phase of the Murono mud volcano, Niigata, Japan

In order to quantify vertical movements during the quiescent phase of the Murono mud volcano area located in Niigata, Japan, we set up 61 benchmarks and conducted leveling measurements five times in 2012. We also performed a dense gravity survey on the benchmarks to obtain information on subsurface structures. Uplifting of approximately 26 mm and subsidence of 14 mm were detected from observations. The uplift area corresponded to a previously uplifted area and had low gravity, which is suggestive of the presence of fluid mud. We propose that overpressure changes in the fluid mud led to surface deformation.