Response of the environmental thermal neutron flux to earthquakes

Abstract Some new results were obtained by the array of EN-detectors (Electron and Neutron detectors) developed in the frame of the PRISMA (PRImary Spectrum Measurement Array) project for Extensive Air Showers detection. Our EN-detectors running both on the Earth surface and underground are continuously measuring the environmental thermal neutron flux. Neutrons are partially produced by radioactive gas radon and its daughter decays through ( α ,n)-reactions in soil close to the detectors. Then neutrons thermalize in media and, being in equilibrium with it, they are sensitive to many geo-dynamic phenomena including earthquakes. In this work the EN-detectors were measuring the variations of an environmental neutron flux in Tibet (30.11 N, 90.53 E, 4300 m a.s.l) at a distance of ∼600 km from the collision zone of the Asian-Indian plates subduction zone (Nepal region). We have observed some anomalies in the dynamics of the neutron flux around the time of the catastrophic earthquakes of magnitude M = 7.8 happened in Gorkha (Nepal) on 25.04.2015 followed by a series of aftershocks of M > 6. The use of nuclear physics methods can provide novel results in geophysics and this work demonstrates the sensitivity of the environmental thermal neutron flux to changes in tense-deformed crust conditions caused by earthquakes with epicentral distances greater than 500 km.