Abstract
Prior to major earthquakes many changes in the environment have been documented. Though often subtle and fleeting, these changes are noticeable at the land surface, in water, in the air, and in the ionosphere. Key to understanding these diverse pre-earthquake phenomena has been the discovery that, when tectonic stresses build up in the Earth’s crust, highly mobile electronic charge carriers are activated. These charge carriers are defect electrons on the oxygen anion sublattice of silicate minerals, known as positive holes, chemically equivalent to O− in a matrix of O2−. They are remarkable inasmuch as they can flow out of the stressed rock volume and spread into the surrounding unstressed rocks. Travelling fast and far the positive holes cause a range of follow-on reactions when they arrive at the Earth’s surface, where they cause air ionization, injecting massive amounts of primarily positive air ions into the lower atmosphere. When they arrive at the rock-water interface, they act as •O radicals, oxidizing water to hydrogen peroxide. Other reactions at the rock-water interface include the oxidation or partial oxidation of dissolved organic compounds, leading to changes of their fluorescence spectra. Some compounds thus formed may be irritants or toxins to certain species of animals. Common toads, Bufo bufo, were observed to exhibit a highly unusual behavior prior to a M6.3 earthquake that hit L’Aquila, Italy, on April 06, 2009: a few days before the seismic event the toads suddenly disappeared from their breeding site in a small lake about 75 km from the epicenter and did not return until after the aftershock series. In this paper we discuss potential changes in groundwater chemistry prior to seismic events and their possible effects on animals.
Highlights
Earthquakes are the most feared among all natural disasters because they seem to strike suddenly, without any forewarning
Unusual animal behavior before major earthquakes has been reported through the ages [1,38]
A recent example of unusual animal behavior has been given by Grant and Halliday, who reported that the activity of common toads at a breeding site in a small lake about 75 km north of L’Aquila, Italy, declined dramatically five days before the M6.3 L’Aquila earthquake on April 6, 2009 [43]
Summary
Earthquakes are the most feared among all natural disasters because they seem to strike suddenly, without any forewarning. There have been innumerable reports of non-seismic preearthquake signals hours, days, and sometimes even weeks before major seismic events These signals are often fleeting and subtle, seemingly ―unreliable‖, but occasionally distinct and strong. Nobody seemed to be able to identify a physical process, or a sequence of processes, capable of explaining the diversity of the reported pre-earthquake signals or how they may be linked to each other and/or traced back to a physical cause. This lack of understanding has been largely overcome by the discovery of a previously unknown form of electrification when rocks are subjected to mechanical stress [2,3,4]
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