1995 Northern Niigata Earthquake of M6.0 and its buried earthquake fault imaged by the distributions of seismic intensity and thermal anomaly of groundwater, Japan
Huilong Xu
Abstract：The 1995 Northern Niigata earthquake of M6.0 occurred at the eastern margin of the Niigata seismic gap and might have been a precursor of a large destructive earthquake. The epicenter was so shallow at 10 kilometers depth that 55 houses were complete collapsed and 165 houses were half collapsed. The distribution of seismic intensity was analyzed by the moment calculated for overturned gravestones. The seismic intensity 6 on the scale of the Japan Meteorological Agency (JMA) was a belt covering an area of 6.1 × 1 km2 trending NNE - SSW, which may indicate the existence of a buried earthquake fault beneath the plain of the epicentral area, was found. The anomaly areas in temperature, electrical conductivity and C1- concentration of groundwater were approximately coincident with the area of the seismic intensity 6 with linear distribution and convincingly demonstrated the presence of a buried fault beneath the epicentral area. This earthquake might have been triggered by the expulsion of geopressured hydrothermal system along the buried active fault. The accumulation of geopressured hydrothermal water in combination with high rock temperature might reduce fracture strength of the rock, and trigger earthquake occurrence.
Keywords：Buried active faultGroundwater anomaliesExpulsion of geopressured hydrothermal waterNorthern Niigata Earthquake
Publication Date：2003-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：13( 24-36 )