Helium/radon precursory anomalies of Chamoli earthquake, Garhwal Himalaya, India

In the Garhwal Himalaya, the Bhagirthi and Alaknanda valleys were rocked respectively by two major earthquakes; the Uttarkashi earthquake of magnitude mb=6.5, Ms= 7.0 on 20 October, 1991 and the Chamoli earthquake of mb =6.8, Ms=6.5 on 29 March 1999, during this decade only. Both these seismic events are associated with ongoing deformation along the main central thrust (MCT) of the Himalayas. The helium and radon anomalies on 24 and 27 March 1999, respectively, were recorded at Palampur which is about 393 km from the Chamoli earthquake epicentre. A helium/radon ratio anomaly was recorded on 20 March, 9 days before the Chamoli earthquake. The precursory nature of radon and helium anomalies is a strong indicator of the physical basis of earthquake prediction and a preliminary test for the proposed conceptual helium/radon ratio model.