THE JAMAICA EARTHQUAKE 



395 



Fig. 8, b. East and West Walls crushed. 



decreasing rapidly eastward, less rapidly westward and still less so to 

 the north. Haiti did not feel the shock, neither was it felt at Colon 

 or at Grand Cayman, 175 miles west, but Santiago, 120 miles north, 

 experienced a slight shock. 



Cracks in buildings, which at Kingston dip some 50 degrees east, 

 are always perpendicular to the path of the emergence of earthquake 

 waves. Hitherto, the intensity area and ejDicenter have been regarded 

 as synonymous. But the dip of the angling cracks at Kingston points 

 to a locus of disturbance much to the west of that city, while the lines 

 of isoseismals indicate the intensity area in the eastern half of Kings- 

 ton. It may readily be imagined, then, that the area of greatest de- 

 struction may not be directly above the focus. Suppose a highly elastic 

 rock is there situated, and some distance away is found a plain of 

 loosely-formed material. The destruction in the latter area will far 

 exceed that in the former in spite of its favorable location. Until we 

 register the actual amplitude, wave-length and period and, with the 

 elasticity of the rock underneath, calculate from the more readily-dis- 

 cerned data on adjacent but less elastic media the changes that have 

 occurred in the wave-motion, it will be difficult to determine with 

 accuracy in a region of rocks of widely varying elasticity the location 

 of epicenters. For outliers of rock in plains must deflect, refract and 

 reflect wave-motion and even shadow areas in these plains. The only 

 conclusion then is that the eastern end of the Liguanea plain was the 

 nearest area to the real epicenter that by nature of material w T ould give 

 the greatest amplitude to the destructive epifocal waves. Further, the 

 angle of emergence at Kingston coordinated with the proximity of a 

 probable epicenter, together with the limited area of disturbance, indi- 

 cates a shallow origin of about three miles. 



