Uplift revealed by LASER scanner surveys in Murono mud volcano, Niigata Prefecture, Japan, and estimation of its source

Abstract:

Since mud volcanoes spew out pressurized material, such as natural gas, oil, mud including water from a deeper ground, the activities of the mud volcanoes are good indicators of the stress conditions/orientations as well as the tectonic controls. The Murono mud volcano area located in Tokamachi City, Niigata prefecture, Japan, is one of the active ground deforming areas associated with mud, natural gas, oil and water eruptions. This area is famous because rapid ground deformation events were recorded corresponding to neighboring large earthquakes. For instance, associated with Naganoken-Hokubu Earthquake (Mw. 6.7) which occurred in 2011, the area recorded a sudden large uplift of about 50 cm.

In order to reveal the source mechanism of the mud volcano, Toyama University has been conducting successive leveling surveys at 61 benchmarks. They revealed that the same area of the rapid uplift of 2011 has been still uplifting, even the amount of the uplift is much smaller (20 mm/yr). However, the source of the uplift could not be well identified due to the low spatial resolutions. Therefore, in order to obtain a high resolution land deformation pattern, we have conducted laser scanning surveys two times in June and October 2013, using TOPCON Imaging Station IS-301, which can obtain 3D point cloud data by the automatic laser scanning mode without reflector.

The surface deformations obtained by comparing the June and October datasets indicate clear uplifts where the sudden uplift occurred. Since the uplift area show a clear concentric pattern, we estimated the source of the uplift assuming a Mogi source model. The obtained source parameters are, depth=14[m], Volume=14[m³], assuming the Poisson's ratio of 0.25. Then the calculated uplift at the nearest benchmark also shows good agreement with the uplift obtained by the leveling survey.

The current uplift is much smaller than the 2011 uplift. Nevertheless both sources could be the same, because the areas of the uplifts are substantially coincident.