Geological magazine . C. Davison—Vorticose Earthquake Shocks. 263 elliptical in the figure, for simplicity) consisting of a fissure approxi-mately plane, and inclined to the horizon;and let us consider the effect at a pointP nearly above its upper end. The shockwill consist of vibrations vi^hich will atfirst be nearly vertical (or sussultatore ),but will gradually become more horizontal,their direction changing in the order indicatedby the numbered arrowheads, so that theshock will end by being slightly rotatoryin the direction of the curved arrow. IfP be taken on the other side of the line ab
Geological magazine . C. Davison—Vorticose Earthquake Shocks. 263 elliptical in the figure, for simplicity) consisting of a fissure approxi-mately plane, and inclined to the horizon;and let us consider the effect at a pointP nearly above its upper end. The shockwill consist of vibrations vi^hich will atfirst be nearly vertical (or sussultatore ),but will gradually become more horizontal,their direction changing in the order indicatedby the numbered arrowheads, so that theshock will end by being slightly rotatoryin the direction of the curved arrow. IfP be taken on the other side of the line ab,the rotary movement will be in the oppositedirection. Lastly, if P be taken on or nearah, the shock will be at first vertical andafterwards undulatory in the direction b to a. Sometimes vertical shocks of long durationare observed, as, for instance, the earthquakeat Coquimbo on Feb. 25, 1853, which wasdescribed as being vertical and lasting 75seconds. The seismic focus was probablya vertical plane fissure several m
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Keywords: ., bookcentury1800, bookdecade1880, bookidgeologicalma, bookyear1882
