JAPANESE EARTHQUAKES — HECK 211 



ing pier suffered severely. Off Yokosuka, part of the breakwater sank 

 18 feet. Eleven lighthouses were destroyed. 



Damage to the water systems included effects of landslides and shift- 

 ing of underground conduits. This was the more serious since the 

 use of water carts increased the danger of epidemics of water-borne 

 diseases; but fortunately that danger was fairly well avoided. lie- 

 placing of house services was a major task since pipes were broken and 

 pulled apart. The tanks of the gas works were generally uninjured, 

 but the distribution systems were badly wrecked. A number of ex- 

 plosions occurred in large pipes where gas was trapped. It required 

 7 months to make replacement complete. Sewers were chiefly affected 

 by breaks at watercourses or where sewers met. Many manholes were 

 damaged. 



It will be seen that damage was caused by earthquake waves, by slip- 

 ping or cracking or sliding of the ground, by fire, and by tsunami. 

 Evidently, a major earthquake is an effective agent of destruction. 



A phenomenon of unusual interest occurred in a town in the Boso 

 Peninsula. In an old rice field filled with water, the teachers in a 

 nearby school saw two fissures 130 feet long spurting muddy water to 

 a height of 10 feet, repeating like a geyser six times before ceasing. 

 The only comparable actual observation of the same phenomenon was 

 in the Bihar, India, earthquake of 1934. Only rarely has the effect of 

 earthquake on ground water been actually observed. 



There were great landslides on several peninsulas (pi. 1, fig. 2) . A 

 village of 700 people was buried under an immense avalanche of soil 

 and rock. During the last week in September there were 1,256 after- 

 shocks of all degrees of intensity. 



In the northern Idu earthquake of 1930 near Ito and Awami, on the 

 west shore of Sagami Bay, 7,000 buildings were damaged and several 

 hundred lives were lost; but this is relatively minor for the region. 

 There were 2 notable features, swarm earthquakes and luminous 

 phenomena. The main earthquake occurred on November 26. A seis- 

 mograph at Misaki, 31 miles away across the bay, recorded 3,684 after- 

 shocks of a wide variety of intensity from February 13 to April 11. 

 The greatest number, 209, and the strongest shock, which was some- 

 what destructive, occurred on March 9. After a pause, the shocks 

 started again on May 7, and attained their greatest frequency about 

 the middle of the month. Few occurred after May, and all stopped 

 in August. The number recorded in the two series reached 6,000, of 

 which about 4,900 were felt at Ito. During March, additional seismo- 

 graphs were installed and positions and depths of epicenter were 

 studied. Early in November, the shocks started again. Great num- 

 bers occurred, the greatest in a single day being 690 on November 25. 



