Radon Gas as Precursor of Earthquakes Along the Philippine Fault Zone in the Leyte Geothermal Field, Philippines

Abstract

A joint project of PNOC EDC and SARAD GmbH of Germany was conducted from 2002 to 2005 to study the behavior of Radon gas and other geochemical parameters as potential earthquake precursor. An online monitoring system called the Modular Environmental Data Acquisition System (MEDAS) was installed in the Mahanagdong Sector of the Leyte Geothermal Production Field. The active geological setting of the Leyte Island combined with the availability of deep geothermal wells and other facilities was the ideal set up for the study.

Four geothermal production wells (MG18D, MG19D, MG23D and MG32D) with depths of 220-2600 meters were continuously monitored for radon gas concentrations. The two-phase discharge from the wells passed through mini-separators, and then the water and steam phases go into a cooling system before entering the sensors that monitor the concentration of Radon and other parameters. Results of the study indicate that localized micro earthquakes have no effect on the background radon concentration in the wells, while anomalies in radon levels were correlated to a 4.2Ms tectonic earthquake that was generated from the Philippine Fault Zone with an epicenter within the geothermal field and a focus at 4km depth. Initial results indicate that Radon in the geothermal wells can be used as earthquake precursor in the vicinity of the study area.