from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A line on a map joining points of equal seismic intensity produced by an earthquake. Also know as an isoseismal line.
from The Century Dictionary and Cyclopedia
- n. A curve or line connecting points at which an earthquake-shock is felt with equal intensity, or at which there is an “equal overthrow” (Mallet). See homoseismal.
- Belonging or related to an isoseismal; having the character of an isoseismal: as, an isoseismal curve.
Sorry, no etymologies found.
The isoseismal 6 is 105 miles long, 87 miles wide, and contains 7,300 square miles; and the isoseismal 5, 157 miles long, 143 miles wide, and about 17,000 square miles in area.
The resistance offered by the Sierra Nevada to the propagation of the earth-waves is shown in the former map by the approximation of the first and second isoseismals at the east end, and in the latter by the great bay in the third isoseismal line.
Again, in slight earthquakes, such as the Cornwall earthquake of April 1, 1898,  the curves of equal sound intensity, while their axes are parallel to those of the isoseismal lines, are displaced laterally with respect to these curves, owing to the arrival of the strongest sound-vibrations from the upper margin of an inclined seismic focus.
In traversing this range, the shock lost a great part of its strength, while it continued to be felt severely along its eastern foot, thus giving rise to the south-westerly extension of the third isoseismal in Fig. 20, and, though to a less extent, that of the second in Fig. 19.
_ -- Within the third isoseismal line Mallet made altogether 177 measurements of the direction of the wave-path at 78 places.
The isoseismal 7, which includes places where the shock was strong enough to overthrow ornaments, vases, etc., is also very nearly an ellipse, whose axes are 80 and 56 miles in length, and whose area is
If the meizoseismal area had been a thickly populated one, the evidence of ruined and damaged houses would have provided materials for the construction of isoseismal lines surrounding the two epicentres.
Mallet himself recognised that these facts required explanation, and he suggested that the situation and character of the towns were in part responsible for their ruin, and the physical structure of the country for the course of the isoseismal lines.
It will be seen that they differ considerably in form, but at the same time they present certain points of agreement, such as the east and west elongation of the meizoseismal area, and the great extension of the two outer isoseismals towards the west and south-west The greatest difference is to be found in the eastern portion of the third isoseismal, which, according to the
Mercalli is probably more trustworthy, it is interesting to compare his isoseismal lines with those obtained by his French colleagues, which are reproduced in Fig. 20.
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