THE WORLD'S MOST CRUEL EARTHQUAKE 



393 



plane or system of planes and its sudden 

 arrest. The sudden dropping of a sec- 

 tion of the crust for only a few inches 

 could cause excessive jarring of the 

 ground. Earthwaves or undulations are 

 caused by these jarrings, which are trans- 

 mitted outward from the center or cen- 

 ters of disturbance. The rate of propa- 

 gation is relatively fast through rock 

 masses, but the waves are much im- 

 peded in rate and increased in amplitude 

 when they traverse beds of gravel, sand, 

 or clay. It is therefore found that the 

 most destructive effects are confined to 

 areas where the surface is occupied by 

 unconsolidated materials, while on ad- 

 joining tracts, where solid rock forms the 

 foundation, the buildings often escape in- 

 jury. 



The rock formations which constitute 

 the mountainous masses of the Calabrian 

 province and the northern part of Sicily 

 consist essentially of crystalline schists 

 and gneiss, intruding which are granitic 

 rocks exposed in the northern portion of 

 the area (see map above). The low 

 lands and bottoms of the valleys, on 

 the other hand, are occupied by slightly 

 indurated shales and sandstones of Ter- 

 tiary and Quaternary ages, and along 

 the shore lines are bench deposits of un- 

 consolidated gravels of recent age. In 

 the vicinity of Mount Etna the area is 

 covered by lava flows and tufaceous beds. 



POSSIBLE CAUSES OF THE EARTHQUAKE 



The Straits of Messina occupy a deep 

 channel between the two ancient moun- 

 tain ranges and are bordered by rock 

 formations of relatively recent age. That 

 isostatic readjustment between these two 

 land masses is taking place is believed by 

 many, though whether the crustal move- 

 ment is due mainly to the transfer of 

 molten rock magma from points below 

 the solid crust, the evidence of which is 

 expressed in the volcanic eruptions, 

 whether there is a sufficient transfer of 

 material on the surface due to erosion 

 to cause excessive local strains in the 

 •crust because of this transfer of weight, 

 -or whether it may be attributed to some 







I 



o 



sr/PA/rs or messina \ 













Scale. 

 0 ^ zooo ^ ^ | 4000 Ft 



SKETCH SHOWING GRAVEL BEACH DEPOSITS 

 AT REGGI0 AND DISPLACEMENTS 

 CAUSED BY LOCAL LAND- 

 SLIPPING 



other cause are hypothetical questions. 

 The occurrence of fault planes has been 

 conjectured to be along the bottom of the 

 straits, and, though they have never been 

 seen, there is sufficient geologic and seis- 

 mographic evidence to believe that they 

 exist, though whether the movement is 

 along one plane or whether it has been 

 taken up by a system of fracture planes 

 or parallel dislocations is not known. 



Locally along the shore line of the 

 straits changes occurred, and portions of 

 the quays both in Messina and Reggio 

 were faulted below water level, the local 

 displacements being from i to 6 feet. 

 Along the coast are benches of gravel and 

 sand sloping gradually toward the straits 

 and extending a short distance out under 

 tide water, where they end abruptly, and 

 just beyond these the channel has a depth 

 of 1,000 feet, and toward the center it is 

 2,500 feet below the surface. The earth- 

 quake caused a local landslipping of 

 these partially submarine benches, thus 

 producing the displacements observed 

 (see page 393). The greater local sink- 

 ing at Reggio than at Messina may be at- 

 tributed to the greater depth of the chan- 

 nel close to the shore, thus causing a 

 greater fall. 



If there has been any considerable dis- 

 placement between the opposite sides of 

 these straits, it must have been a hori- 

 zontal one, as there has been little or no 

 general vertical change in elevaton of 

 either shore line. This possibility of a 

 horizontal movement of the Sicilian side 

 of the straits to the northwest is suggested 



