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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2034
Statistical study of the relationship between seismic electric signals and
earthquakes at Kozu-Shima Island, Japan
Dr. Masashi Kamogawa
Department of Physics Tokyo Gakugei University
Yoshiaki Orihara, Toshiyasu Nagao, Seiya Uyeda
Geoelectric potential difference monitoring has been conducted in Kozu-shima Island about 170 km
south of Tokyo. During the monitoring period (May 14, 1997 - June 25, 2000), there were 20
anomalous geoelectric changes that practically satisfy the criteria for Seismic Electric Signals (SES) in
the VAN method. In the same period, 25 earthquakes of which magnitude was greater than 3 within 20
km focal distance occurred. Some selectivity relation, including SES polarities, was noticed. In this
paper, statistical correlation between the anomalous geoelectric changes and the earthquakes is
examined. When 30-day leadtime was chosen, anomaly appearance rate (AAR) and earthquake
occurrence rate (EOR) were 44 % and 55 %, even no selectivity was considered. Note that AAR was
defined by the ratio of the number of SES appearances and the number of EQs and EOR was defined by
the ratio of the number of EQ occurrences and the number of SES appearances. The AAR exceeded 2
sigma of AARs and EORs in simple random testing. In order to ascertain the correlation, the leadtime,
area, and magnitude dependences are also examined. If the selectivity map is taken into account, both
AAR and EOR are much higher.
Keywords: earthquakes, ses, kozu island