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.

Keywords: EN-Detector; Earthquake; Radon; Thermal neutron.