Abstract
The magnitude-6.9 Noto Hanto Earthquake struck at 9 : 41 a.m. 25th March 2007, off the north coast of Ishikawa Prefecture, Japan. The quake started under the ocean about 30km southwest of Wajima, shaking up Ishikawa, Toyama and Niigata prefectures and killing one person and damaging hundreds of houses. The quake crippled public transportation, traffic network, including highway at Noto Peninsula, because of landslide, subsidence, chasm and cracks. Radon has measured in air and ground fissures using portable natural gamma ray system while the Noto Hanto Earthquake struck the Noto Peninsula, in April 4, 8, 10, 12, and 19th 2007. The car-borne and hand-borne measurement system was assembled for easily and rapidly detecting full features of the fissures buried in the ground, and the applicability of the system was detected in the field, such as geological feature, fault fissure zone, distribution/accumulation of new/old chasm and cracks in the surface layer, and direct earthquake itself. The amount of radon reflects the scale of fissures and an abnormal increase in earthquake and new chasm or cracks. The quite high gammaray of 2300cpm was detected in April 4th 8 : 20 at Ozawa, Monzen, Wazima City, near the fault fissure zone, and 1500cpm was detected in April 4th 13 : 20 at Kowashudo, Monzen, Wajima City. Both high radon counts were due to the earthquake of M 3.8, depth 10km, hypocenter was Noto region 37.2N, 136.7E, and the other earthquake of M 3.3 was relatively shallow depth, hypocenter at Noto offshore 37.2N, 136.5E, respectively. The abnormal increase (100-200cpm) detected at large deep subsidence and new crack on the paved road. For comparison, normal air radon without earthquake counted as low as 40-80cpm. Observation of radon at earthquake region such as Monzen-cho related to radon anomaly to compare with other normal region in Kanazawa City has been studied.
