206 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



though essentially correct, is an oversimplification. The classification 

 of Gutenberg will be followed : shallow earthquakes have a depth of 

 less than 36 miles; intermediate, between 36 and 180 miles; and deep, 

 more than 180 — the greatest known, 420 miles. The more destructive 

 Japanese earthquakes are shallow or in the upper portion of inter- 

 mediate depth. 



A belt of shallow earthquakes paralleled by a narrow belt of inter- 

 mediate earthquakes extends from Kamchatka to central Japan, 

 whence it follows the island groups toward the Marianas. Another 

 belt of shallow and intermediate earthquakes extends from Kyushu 

 Island toward Formosa and the Philippine Islands. A broad belt of 

 deep-focus earthquake epicenters crosses the Sea of Okhotsk to the 

 southern part of Sakhalin, paralleling the Kurile Islands. Opposite 

 Hokkaido and northern Honshu, the deep-focus belt is in the Japan 

 Sea or inside the adjacent Asiatic coast. This almost joins a belt 

 nearly at right angles to it which, beginning with a large group of 

 shocks on the continent, follows southward across the Japan Sea and 

 Honshu and then parallels to the westward the shallow and inter- 

 mediate belt extending toward the Marianas. The southwestern belt 

 has no deep-focus earthquakes until the Philippines are reached. 

 There is no need of further detail. It should be stated that deep- 

 focus earthquake waves must have great intensity to cause serious 

 destruction, because the waves have already traversed a considerable 

 distance before reaching the earth's surface. 



Geographical distribution of destructive earthquakes. — On account 

 of the high seismicity, discussion will be confined to Japan proper 

 (the four islands of Hokkaido, Honshu, Shikoku, and Kyushu) and 

 adjacent submarine areas, and to Formosa. The Japanese earthquakes 

 which have made the greatest impression are those originating on 

 the western side of the Tuscarora Deep from off Hokkaido to opposite 

 Tokyo, the great Mino-Owari earthquake of 1891, and those of the 

 Kwanto region (named for an extensive plain which includes Tokyo 

 and Yokohama). However, other parts of Japan have suffered earth- 

 quake catastrophes. For the sake of convenience, a number of princi- 

 pal areas will be listed and then characteristic earthquakes of each 

 will be discussed, particularly those which have some striking feature. 



DESTRUCTIVE EARTHQUAKES BY REGIONS 



Region I. Submarine area west of Tuscarora Deep. Shocks causing little direct 

 damage produce great tsunamis. 



Region II. Submarine region off southwestern Japan, Idu to Kyushu and ad- 

 jacent islands. Great damage both from earthquakes and tsunamis. 



Region III. Kwanto region, named for great plain. Shocks highly destructive 

 in region of great cities. Tsunamis secondary. 



Region IV. Central Japan. Mino-Owari, Kyoto, and Tazima-Tango areas. 

 Visible fault slips in severe earthquakes. No tsunamis. 



