Fig. 1. Earth as a capacitor.

Cap-type electrode

Al plate

Teflon rod

SUS cylinder

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LPF: Low pass filterDL: Data logger PC: Computer

The electrode is set on the roof of about 20 m high building

Fig. 2. Measurement system.

I. INTRODUCTION

Earth is consisted of conductive crust, insulating atmospheric air in the order of 30 km, and conductive ionosphere as depicted in Fig. 1. This system is a large capacitor. It is known to be Global circuit [1]. In average of about 10-12 A/m2 atmospheric ionic current, AIC, flows to the surface and return current is carried with lightnings. The crust has certain resistivity. With underground water, natural battery could be formed. If pressure inside the crust changes, underground water may move that results in change of voltage of the natural battery. With the change of internal pressure, Piezo-electric effect could also cause the change of surface voltage. Change of the surface voltage should induce counter charge of the capacitance of earth, or the change of the voltage of earth surface will produce movement of charge in the ionosphere. This movement of charge should affect the atmospheric electric field and AIC. There have been reports on generation of low frequency electromagnetic waves, abnormal transmission of electromagnetic wave, or change of ion density in atmosphere in conjunction with earthquake [2]. In our study, we measured AIC continuously to seek if there is any correlation between earthquakes.

II. MEASUREMENT SYSTEM

Only Fig. 2 shows the measurement system of AIC. The electrode is a 55 mm diameter cylinder covering the insulating support fixed on a roof of 6 stories building.

The electrode is connected to an Electrometer (Keythley) using coaxial cable of about 10 m length. At the output of the electrometer, a low pass filter (10 ms time constant) was inserted to cut the noise from commercial power

Possible Relation between Atmospheric Ionic Current and Earthquake

A. Mizuno, K. Takashima, and Y. Kinoshita Department of Environmental and Life Sciences, Toyohashi University of Technology, Japan

Abstract—Known as the global circuit, atmospheric ionic current (AIC) is flowing into the ground. In this study, the result of continuous measurement of AIC has been presented, with possible relation with major earthquakes. Daily time evolution of AIC is normally orderly, after sunset until sunrise AIC is small, then it increases gradually with time, reaching a peak around noon followed by a gradual decrease in the evening. However, clearly and significantly different signals were observed in some cases. The earth is a capacitor made of the crust and the ionosphere. If the pressure of the plate changes suddenly, it might cause the change of ground potential due to the Piezo-electric effect and/or to movement of underground water that constitutes a battery. Sudden change of the surface potential of the ground should induce counter charge in the ionosphere. Gradually this counter charge penetrates to the stratosphere. Mobility of charged ions is smaller and this charge generates transverse electric field, affecting rather long distances. This sudden change of the charge distribution in ionosphere could cause the change of AIC. The abnormal behavior of the measured AIC prior to major earthquakes might be an indication. Further study and international joint measurement of AIC is necessary to study the relation between AIC and earthquake.

Keywords—Global circuit, atmospheric electric field, atmospheric ionic current, earthquake, prediction of earthquake

Corresponding author: Akira Mizuno e-mail address: mizuno@ens.tut.ac.jp Received; March 27, 2011

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Fig. 3. Measured voltage Vm due to AIC (Jan. 2010).

lines. The measured voltage, Vm, is the multiple of AIC and the input impedance. At the meantime, this system has a long time constant in the order of 5 hours, the measured voltage also includes the current associated by induced charge corresponding to sudden change of the

atmospheric electric field. Other perturbation such as charged rain droplets can also be measured sensitively.

III. RESULTS Fig. 3 shows data of for 28 days in January 2010.

The meshed part is between 6:00 and 18:00. Daily time evolution of Vm normally shows a very small value after sunset until sunrise, then gradually increases with time, reaching a peak around noon followed by a gradual decrease to small values in the evening. These daily change may be due to the ray of sun that ionizes the ionosphere. The radiation from the sun also provides charged particles. Change of Vm follows the above time course in most cases. Occasionally, however, clear and

100 International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011

significant difference in Vm can be observed. An example is in between January 12 and 15. During this period, at first during Jan. 12th, Vm was very low even in daytime. Then, in the last part of this period, very large Vm was observed during night. Maximum voltage measurable in this system was 18 V, and occasionally the signal over-ranged. During this period, typical periodical daily change was not observed. This result suggests that the abnormal behavior of the potential is due not to the sunshine but some other causes. During this period, there was a major earthquake in Haiti at January 13, 6:54 am.

Fig. 4 shows the other example measured between January and March 2011. In this figure, square shows time 0:00 am. In January, Vm showed rather regular pattern of the daily change compare to Feb. and March. During February 10th and 22nd, Vm showed abnormal change. Again from Feb. 26th, Vm was abnormal. During Feb. 27th and March 1st, Vm stayed almost zero during daytime. Then Vm increased and overscaled during March 2nd and 6th. On March 7th, Vm became zero at 0:00, then again Vm increased abnormally during March 8th and 11th. On Feb. 22nd, there was a strong earthquake in New Zealand. On Feb. 27th at 2:18 and 5:38 there were M5.0 and 5.5 earthquakes about 150 km north of Toyohashi. On March 9th at 11:45 there was a large earthquake (M7.3, 38o19.7'N 143o16.7'E, 8 km depth), on March 10th (M6.8, 06:23 59.7, 38o10.3'N 143o2.6'E, 9 km depth) in north part of Japan, and on March 11th at 14:46 there was a most intense earthquake in the same area (M9.0 14:46 18.1, 38o6.2'N 142o51.6'E, 24 km depth), and several more in the order of M7 (M7.7, 15:15 34.4, 36o6.5'N 141o15.9'E, 43 km depth, etc.) [3].

IV. CONCLUDING REMARKS

As seen in the data of continuous measurement of Vm due to AIC, there seems certain correlation between intense earthquakes and Vm. Prior to major earthquakes, Vm shows irregular behaviors, such as increasing to higher value, sometimes over scaled, and the decrease to lower values during night time is not seen. Then, just very close to the occurrence of major earthquakes, there is a day in which no increase in Vm during daytime.

If counter charge is induced in the ionosphere due to sudden change of crust pressure, AIC should be affected. Debye length of the ionosphere is not long compare to the scale of earth, however, the induced charge is injected to insulating atmosphere, and the transverse electric field could be generated, affecting the AIC, even at long distance. This could be a reason for the day of no Vm increase prior to major earthquakes.

More theoretical considerations are required, and at the meantime, measurements of AIC in different locations are important to evaluate the relation between AIC and major earthquakes. Therefore, the authors propose an international cooperation for measurement of AIC with which earthquake prediction could possibly be made.

ACKNOWLEDGMENT The authors are grateful to Prof. Mineo Kumazawa and Prof. Naoyuki Fujii of Nagoya/Shizuoka University, Japan, Prof. Gerard Touchard of Poitiers University, France, Prof. Alain Toureille of University of Montpellier 2, France, and Prof. Jen-Shih Chang of McMaster University, Canada, for the discussions and suggestions given to this work.

REFERENCES [1] Taiki-Denki-Gaku Gairon (Introduction to Atmospheric

Electricity, in Japanese), Society of Atmospheric Electricity of Japan, Ed., Corona publishing Co., 2003.

[2] M. Hayakawa, K. Hattori, K. Ohta, "Correlation of fluctuation of ULF electromagnetic wave and earthquake," IEEJ Transaction FM, vol. 126, pp. 1238–1244, 2006.

[3] Japan Meteorological Agency, earthquake information. Available: http://www.seisvol.kishou.go.jp/eq/daily_map/japan/20110311.shtml

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