**5. Acknowledgements**

138 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

corresponds temporally to the later Manchester earthquakes but the late July period does

Noting the relative magnitudes and proximities of the Manchester earthquakes compared to the English Channel earthquake, it is perhaps surprising the there is no similarly welldefined time-domain anomaly in the radon time-series at the time of Manchester earthquakes. The reasons for this are not currently understood but there are essentially two possibilities. First, any such temporal correspondence between earthquake and timedomain anomalies in the radon time-series is coincidental, as discussed below. Second, the temporal correspondence is not coincidental but the natures of the geologies at and between Northampton and Manchester are such that any earthquake-related radonstimuli are blurred and attenuated. For information on geology see, for example, Boulton, 1992; Hains & Horton, 1969; Poole *et al.*, 1968; Smith *et al.*, 2000 and Toghill, 2003. However, having also identified time-domain radon anomalies which temporally correspond to the Market Rasen earthquake of 27 February 2008 (Crockett & Gillmore, 2010), the second reason is arguably more probable but more data are required, both

In these data, another potential geophysical explanation is possible: i.e. lunar-tidal influences, which have been reported for TS1b in terms of cyclic variations in radon concentration (Crockett *et al.*, 2006b). Tidal influences might account for the periods of 24 h coherence which temporally correspond to tidal maxima associated with the full moons of 24 July, 22 August, 21 September and 20 November, but not the absence of any coherence around the 21 October full moon. This potential explanation is further weakened by the absence of (a) consistent coherence around the new-moon maxima and (b) consistent correlation or phase coherence around both sets of maxima. Also, a tidal-maximum explanation does not account for the anomalies in the February 2008 time-series, which temporally correspond to the Market Rasen earthquake but not a tidal maximum. Lastly, despite the apparent similarities in timing, it is unknown whether there is any lunar-tidal influence on the English Channel, Dudley, Manchester and North Sea earthquakes and no

Both correlation and coherence show when two, or more, time-series behave similarly in the time domain, according to shape (correlation) or frequency composition (coherence). Thus, these techniques allow the identification of time-domain anomalies, i.e. periods in time when the common behaviour of two, or more, time-series changes from the typical to the anomalous. In the radon data used to illustrate the techniques, the paired time-series typically neither correlate nor cohere but do so anomalously for short periods. In other data, the emphasis might be different, e.g. the time series might typically both correlate and cohere but contain anomalous periods where they do not or, the time-series might typically cohere at some frequencies but contain anomalous periods where the cohering

Correlation does not imply causality, is not proof of causality: at most, correlation might be evidence to support causality. In the dataset analysed above, despite the clear temporal correspondence of the late September and late August time-domain anomalies to earthquakes, and the temporal correspondence of the mid-late November less well-defined time-domain anomaly to another earthquake, this is all that is shown, i.e. temporal

not correspond temporally to any recorded earthquake in the region.

earthquake and radon, to investigate this more fully.

such influence has been reported for UK earthquakes in general.

**4. Conclusions** 

frequencies change.

The author gratefully acknowledges members of the University of Northampton Radon Research Group for the collection of the data and also DEFRA (UK) for funding the research under which the 2002 data were collected (EPG 1/4/72, RW 8/1/64). The author also acknowledges UNESCO / IUGS / IGCP Project 571 for facilitating preparation and dissemination of earlier stages of this and related research.

The data-analysis was performed using the open-source R (http://www.r-project.org)) and Scilab (http://www.scilab.org) software packages, with the EMD and Seewave R libraries.

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**7** 

*Italy* 

**Radon as Earthquake Precursor** 

*Dipartimento di Fisica e Astronomia Università di Catania - INFN Sezione di Catania* 

Earthquake predictions are based mainly on the observation of precursory phenomena. However, the physical mechanism of earthquakes and precursors is at present poorly understood, because the factors and conditions governing them are so complicated. Methods of prediction based merely on precursory phenomena are therefore purely

A seismic precursor is a phenomenon which takes place sufficiently prior to the occurrence of an earthquake. These precursors are of various kind, such as ground deformation, changes in sea-level, in tilt and strain and in earth tidal strain, foreshocks, anomalous seismicity, change in b-value, in microsismicity, in earthquake source mechanism, hypocentral migration, crustal movements, changes in seismic wave velocities, in the geomagnetic field, in telluric currents, in resistivity, in radon content, in groundwater level, in oil flow, and so on. These phenomena provide the basis for prediction of the three main parameters of an earthquake: place and time

The most important problem with all these precursors is to distinguish signals from noise. A single precursor may not be helpful, the prediction program strategy must involve an

Moreover, in order to evaluate precursory phenomena properly and to be able to use them confidently for predictive purposes, one has to understand the physical processes that give rise to them. Physical models of precursory phenomena are classified in two broad categories: those based on fault constitutive relations, which predict fault slip behavior but no change in properties in material surrounding the fault, and those based on bulk rock constitutive relations, which predict physical property changes in a volume surrounding the fault. Nucleation and lithospheric loading models are the most prominent of the first type

During the past two decades efforts have been made to measure anomalous emanations of geo-gases in earthquake-prone regions of the world, in particular helium, radon, hydrogen, carbon dioxide. Among them radon has been the most preferred as earthquake precursor,

Radon is found in nature in three different isotopes: 222Rn, member of 238U series, with an half life of 3.8 days, 220Rn (also called thoron), member of 232Th series, with an half life of 54.5

Owing to his longer half-life, the most important of them is 222Rn, produced by 226Ra decaying. After his production in soil or rocks, 222Rn can leave the ground crust either by

**1. Introduction** 

empirical and involve many practical difficulties.

of occurrence and magnitude of the seismic event.

integral approach including several precursors.

and the dilatancy model is of the second type.

s and 219Rn, member of 235U series, with an half life of 3.92 s.

because it is easily detectable.

Giuseppina Immè and Daniela Morelli

