Effects of seismic activity on the fluorescence signal of groundwater

Abstract

Background Peroxy defects in minerals from stressed igneous and high grade metamorphic rocks release charge carriers which are highly mobile. This process is proposed as the main cause of observed pre-seismic phenomena such as infrared emission on the surface, positive air ionization or a change of ground water chemistry. The primary changes in groundwater chemistry is caused through an increase in oxidation on the rock-water-boundary. This can be detected by observing a rise in fluorescence due to an O. addition on an aromatic ring which can change a substance. For example a terephthalate can change from a non-fluorescent to a partially fluorescent compound due to O. additions. Results In this paper we present results of groundwater fluorescence monitoring over a period of approximately three months. We observe distinct wavelengths with an on-line flow-through fluorometer in two different thermal springs in the northern part of Switzerland. We will also show that fluorescent intensities fluctuate widely and display clear increases and sharp rapid drops. During the measuring period many smaller earthquakes with a magnitude between 1.0 and 2.6 occurred close to the measuring stations but a strong earthquake was absent. Nevertheless, an increase in fluorescent intensity was measured in both springs prior to a magnitude 2.2 earthquake. After this seismic event the fluorescent intensities suddenly decreased. Conclusions The presented results comply with the anticipated theoretical considerations.