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The Japanese Islands are located in an active position of seismic activity and therefore often have been afflicted by the damage of an earthquake. There is a report that disorder of an electro-magnetic (EM) wave occurs in nature as a precursor of crustal activity. In order to detect the sign, we have been measuring EM waves of 223 Hz at about 40 sites in Japan. Our final goal is to determine the EM source more correctly. To locate the radiation source by multi point observations of EM power, EM wave propagation characteristic needs to be clear. In the presumed method of a generation source, we assume the attenuation model that EM wave intensity declines by the α power of the distance from the EM source. α is an unknown value, however, this paper analyzes α by locating the thundercloud position which generates the EM wave.