CAUSE OF EARTHQUAKES—HOBBS 263 
of earlier earthquakes within this much-racked province clearly 
showed, have been repeatedly the seats of movement. In the same 
year the writer pointed out in a discussion of seismic sea waves that 
these indicate a deepening of trenches on the sea floor at the time of 
such waves, when the neighboring coasts are usually elevated. To 
cite: 
Such depressions of the deeps and uplifts of the neighboring shores prob- 
ably stand in some sort of balance, and both alike call for an initial recession 
of the water from all near-lying shores toward the area of depression at that 
instant when the movement occurs. Such a mass of water as would pile up 
over the depressed area of the sea floor as a result of the inrush of water 
from all sides, should be later spread in all directions and roll in to inundate 
the shores.’ 
At the time it was written this explanation seemed to call for 
mass movements upon the floor of the sea too large for ready 
acceptance by geologists, and the view appeared to find little support. 
Sixteen years later, nothing daunted, the writer had the temerity 
to state his belief that “the floor of the ocean has undergone sudden 
changes of elevation measured not in tens of feet, as have the zones 
of unrest upon the continents, but rather in hundreds and even 
thousands of feet.” 1° Within a few months came the great Japanese 
earthquake in connection with which there occurred a seismic sea 
wave, an elevated coast, and a sudden adjustment of the floor of 
Sagami Bay off the coast. The volume of the area dropped meas- 
ured some 50 cubic kilometers and the amount of the drop measured 
over large areas 50 fathoms or more (300 feet). 
Willard D. Johnson, 1907-1910.—In the early spring of 1907 at 
the writer’s suggestion Mr. Willard D. Johnson undertook a field 
study of the scene of the Owens Valley earthquake of 1872. This 
occurred within a desert region of California in which the disloca- 
tions had suffered little change in aspect within the subsequent 38 
years. For the first time in history an accurate map was prepared 
of a fault network which had suffered a mosaic-like adjustment at the 
time of an earthquake.” 
°W. H. Hobbs, “ Earthquakes, an introduction to seismic geology,” Appleton, 1907, Ch. 
XV, especially pp. 253-254. 
170 The rate of movement in vertical earth adjustments connected with the growth of 
mountains,” Proc. Am. Phil. Soc., vol. 62, 1923, p. 70. 
uA. Imamura, “ Preliminary note on the great earthquake of southeastern Japan on 
September 1, 1923,” Seismological Notes, No. 6, Imp. Earthq. Invest. Comm., Tokyo, July, 
1924, p. 16, pl. 4. T. Kato, ‘‘ Preliminary notes on the Kwantd earthquake in Japan, 
September 1, 1923,” Journ. Geol. Soc. Tokyo, vol. 30, No. 361, p. 8. K. Suda, “On the 
great Japanese earthquake of September 1, 1923,’’ Mem, Imp. Marine Observatory, vol. 2, 
1922-1924. A. Imamura, ‘ The great Kwant6d (southeast Japan) earthquake on Septem- 
ber 1, 1923,” Repts. Imp. Earthquake Invest. Comm., Tokyo, 1925. Takuji Ogawa, “On 
the great earthquake in Central Japan,’ Journ. Geol., vol. 3, pp. 1-11, map; reprinted 
in Kotd Commemoration Volume, Tokyo, 1925. 
2 W. H. Hobbs, ‘“ The earthquake of 1872 in the Owens Valley, California,’ Gerlands 
Beitriige zur Geophysik, vol. 10, Leipzig, 1910, pp, 351-384, Pls. X—XXIII. (Read before 
the Association of American Geographers at Chicago, December, 1907.) 
