EARTHQUAKES UNDER PACIFIC

Evening Star, Issue 21711, 4 May 1934, Page 4

EARTHQUAKES UNDER PACIFIC

COASTAL DAMAGE FROM JAPAN TO HAWAII TIDAL WAVES GF GREAT HEIGHT DU March 9, 1.933, it Was known all over the World that a great earthquake had Occurred off the Past coast 6f Japan (Writes Charles Davison) Sc.D.) in the ‘ Manchester Guardian’). The earthquake itself, as it proved, caused little damage Oh land, the origin being about 100 miles out in the Pacific ocean, but it was followed in about half an hour by a series of sea waves—tunami, as they are called in Japan— that caused the destruction of nearly 7,090 house# and the loss of more than 3,000 lives. immediately after the earthquake a nulnber of the assistants Of t.he Earthquake Research Institute at Tokio were a sent to the devastated region with in- * struments to determine the area swept by the Waves, the height reached byf theln, the damage to and the forms of the coast in Which the de« structioh was greatest. Sofne of tire early reports have recently reached this country, and already they have thrown welcome light on the magnitude and rush of the waves.' The origin of the earthquake, it wa# found from the records of seism ofraphs, lay on the Steep slope of the uscaroora Deep, to the east Of Japan one of the deepest of our Ocean troughs, for its bed descends more than five miles below thp level of the sea.' This slope has been the scene of many a great earthquake in the past, one especially, in 189&, that swept away many towns and Villages on the northeast coast of Japan and caused th«j death of 27,000 persons and the destruction of more than i8,09d houses. CliriOlisly enough, though the loss of life last March was little more' than Otte-tenti) of that in 1.896, the waves were nearly as high; From the mark# that they left oh trees, posts, slopes, and so Oil good estimates could he made Of the heights attained in various placeS. The WavCs flooded the whole north-eastern coasts of the islands, to a distance in places of a mile Or two inland. In most parts their heights ranged from 15 to 30 feOt,' but at two places to _ the South of Kanidisl they 1 rose as high as 62 and 75 feet. Such heights wore usually reached at the heads ef the v-shaped inlets that abound on this coast and face the Tuscaroora Deep, ffoih which the waves always come. Besides their great height, however, they owe their destructive power in part ,tO the speed with which they travelled. Near Kamaisi a motor boat capable of doing 12 miles an hour could make no headway against the advancing stream.According to the Japanese seismologist# their maximum speed probably, amounted to at least 18 miles an hour,HARBOUR MASTERS WARNED. The waves were registered at nearly all the tidal stations on the east coast of Japan. They also sped to great distances across the Pacific, and were recorded by tide gauges at Honolulu in the Hawaiian Islands, . and even at San. Francisco and Santa Monica, on the cOaSt of America. At the first place some interesting observations , were made. The earthquake itself was recorded at three Hawaiian observatories. The diagrams obtained-at them showed that, the distance of the origin was about 3,950 miles in the direction of Japan. Guided by former experience,it was feared that the movement might be followed in about 81 hours by great earthquake sea waves. Notice Was accordingly sent to the different harbourmasters in the islands that WaVOs might be expected about 3.30 p.m. (Hawaiian time); Most of them took advantage of the Warning, and fishing boats Were mbvdd out to sea; many were thus saved from destruction. At the time given, large crowds gathered oil the hillsides to watch the incoming Waves, and at 3.36 p.m, those on the east side of Hawaii saW. the..first Waves entering-the harbour of Hilo. For tWO hours the waves continued to sweep in, the range of motion lying between two and three feet; On the West Side Of Hawaii, in the largest wave, the ,sea fell eight feet, end then rose nine ghd a-hal£ feet; walls Were broken down, and' many boats in harbours in Which the warnings were .neglected were carried away and capsized. STRANGE LIGHTS. , * With nearly every great earthquake there are reports Of curious lights being Seen With and after the shock. Seismologists HaVe hitherto doubted the reality of the lights, or, at any rate, their.’connection with the earthquake.Those seen With the destructive Japanese earthquake Of November 26, 1930, have set the matter, definitely at rest. There can be no doubt as to the existence of the lights, though we have as yet no idea as to their cause. They ‘were seen again with the earthquake of March 3. They varied much in form and brightness; the strangest perhaps being a dull light, like that of an aurora borealis, seen by several persons at Rartlaisi, as the Sea waves entered the hay. Tile light seeilled to come from the se&, and' the most plausible explanation ( of its origin is that tile turbulence of the water in front of tile incoming wave excited some planktons, such as noctiluca, to a continuous add simultaneous luminosity. It. is known that the noctiluca has a habit of forming large Swarms, and one of the Japanese seismologists has estimated that a' flash of light so excited might attain to a considerable intensity. . Earthquake sea waves have occurred many times along the north-east coast of japan, especially itt the years 869, 1611, and 1896. They are all dim to earthquakes originating in the : same region, and every time they come there is a heavy loss' of life. Their Advent cannot, of course, be prevented, but there are ways of lessening the qayoo wrought by them, and the Japanese seismologists have issued a volume Of notes on the prevention of dafiiage. When the villages must be left found . the harbours they suggest that , they sliodld he protected by sea walls or breakwaters, of even groves of trees. They also insist that avenues of escape to the surrounding hills must be left, Mdst valuable Of all; perhaps, Would he the issue of sea-Wave warnings. The experience of Hawaii has shown how this may be done, and even so brief an interval as half an limitI—the 1 —the usual time in Japan—should be enough.