EARTHQUAKES AND THE FOREST* 



BY 



MYRON L. FULLER 



United States Geological Survey. 



TTIE question of the relation of 

 * earthquakes to the forest is par- 

 ticularly pertinent at this time when 

 the public interest, aroused by the re- 

 cent terrifying shock and appalling 

 conflagration at San Francisco, is still 

 at a high pitch. In the accounts of the 

 destruction wrought by these great 

 convulsions of nature, little is usually 

 said of the effect of the disturbances 

 on the forest growth. Nevertheless, 

 there is hardly a shock, at least of the 

 severe ones, which does not affect it 

 to a greater or less extent. In some 

 instances the havoc wrought is both 

 widespread and complete. 



Earthquake waves may be popularly 

 divided into (i) vibrations and (2) 

 actual visible waves like the broad low 

 swells of the ocean. The former are 

 felt as relatively sharp and sudden 

 jars, or shakings of the ground, while 

 during the passage of the latter the 

 earth is felt to rise, sway, and fall with 

 the sickening motion so vividly im- 

 pressed upon everyone who has ex- 

 perienced it. The sharp vibrations are 

 often destructive to artificial struc- 

 tures, chimneys being snapped off, ma- 

 sonry walls parted and shattered, and 

 buildings jarred from their founda- 

 tions. To the larger earth waves are 

 to be ascribed most of the twistings 

 of the surface, the warping and fold- 

 ing of the ground, the Assuring of the 

 soil, and the slipping of the hillside 

 materials, as well as the destruction of 

 buildings and other works of man. 



Usually, however, the vibrations are 

 not sharp enough to seriously affect 

 the forests, although in the case of cer- 

 tain of the heavier shocks trees are 

 said to have been snapped off short 

 near their butts, but the landslides 

 arising from the larger waves, aided 



perhaps by the vibrations, are often 

 very destructive to the trees of the 

 steeper hillisdes. Not only are the 

 trees directly overthrown by the shock, 

 but bv the warping of the surface and 

 the formation of swamps and lakes- 

 through the obstruction of drainage, 

 large numbers are often killed by sub- 

 mergence. Of our three greatest earth- 

 quakes the famous New Madrid 

 earthquake which shook the Missis- 

 sippi valley in 181 1 and 1812, the 

 Charleston earthquake of 1886, and 

 the San Francisco of April 18th of this 

 year only the former had a marked 

 effect on the forests. At Charleston, 

 notwithstanding the severity of the 

 shock, there was almost no effect on 

 the trees, which remained upright and 

 unbroken. In the San Francisco re- 

 gion, the action was somewhat great- 

 er, the trees of the slopes and hillsides 

 often being tilted and overthrown by 

 slippings started by the shock, but on 

 the whole the forests were but little 

 affected. Not so, however, was it in 

 the case of the New Madrid area in 

 which, as described in the following 

 paragraphs, the destruction was great. 



New Madrid, from which the earth- 

 quake of 1811-1812 was named, is a 

 small town on the banks of the Missis- 

 sippi in southeastern Missouri not far 

 from the Arkansas line. It was near 

 here that the earthquake reached its 

 maximum intensity, but its area of de- 

 struction reached westward to the St. 

 Francis River, eastward into Tennes- 

 see, and southward nearly to the pres- 

 ent site of Memphis. The first shock 

 was felt at 2 A. M. on December 16, 

 181 1, being sufficient to awaken the 

 settlers and to cause them to rush to 

 the open to escape the falling chim- 

 neys and other objects. Here they re- 



*Published by permission of the Director of the United States Geological Survey. 



