CLASSIFICATION OF EARTHQUAKES 88i 



as seismic disturbances, of which earthquakes and sea-quakes are 

 the recognized effects, while the products of the disturbances are 

 tectonic structures.'^ 



Not all tectonic structures are accompanied in their formation 

 by seismic disturbances, for some deformations may go on so 

 gradually, and at such a uniform rate, that no surface manifesta- 

 tions are felt. In this class fall especially the large or epeirogenic 

 earth movements, and the bradyseisms noted below. 



Classification of Seismic Disturbances. 



Not all seismic disturbances are due to earth movements, as 

 the term is here used, for volcanic activities, especially of the ex- 

 plosive type, may generate such disturbances, these being sometimes 

 of considerable magnitude, as in the case of the explosive eruption 

 of Krakatoa in 1883. As there illustrated, the three inorganic 

 spheres — the litho, hydro, and atmosphere, not to mention the bio- 

 sphere — were disturbed by this explosion, and earthquakes, sea- 

 quakes, and air-quakes f resulted. The air-waves which charac- 

 terized the last passed around the earth several times; while the 

 sea disturbances or tsunamis % generated were noticeable more 

 than five hundred miles away. 



Recognizing the different modes of production of earthquakes, 

 seismologists have divided them according to origin into: (Suess- 

 38-) 



1. Dislocation or fault earthquakes. 



2. Volcanic, or explosive earthquakes. 



* The term tectonic, originally applied to all structures, has come of late to be 

 more especially applied to structures due to earth movements, or deformation 

 structures. These include faults, folds, torsion joints, etc., but not stratification, 

 unconformity, overlap, flow-structure, or any other original structures, nor such 

 secondary structures as concretions, enterolithic deformation, or any other 

 structures due to diagenetic or contactic metamorphism. 



t If we consider that the term seisma refers to the trembling or shaking of the 

 geos, or earth as a whole (geoseism), and not merely to the tremblings of the land, 

 we may extend the meaning of the term seismology so as to cover the shaking or 

 trembling of any portion of the earth as the result of such disturbances. We 

 could thus distinguish : lithoseisma, or earthquakes proper (land-quakes) ; hydro- 

 or thalassoseisma or sea-quakes and atmoseisma, or air-quakes. The bioseisma arc, 

 of course, a universal accompaniment of all these"disturbances. 



t The Japanese term for the "tidal wave," or "sea- wave" of sea-quakes. 

 Suggested for general adoption by Hobbs (17). 



