Message #168445

[Bathos]

The severest earthquakes take place where the sea is full of currents
or the earth spongy and cavernous: so they occur near the Hellespont
and in Achaea and Sicily, and those parts of Euboea which correspond
to our description-where the sea is supposed to flow in channels below
the earth. The hot springs, too, near Aedepsus are due to a cause
of this kind. It is the confined character of these places that makes
them so liable to earthquakes. A great and therefore violent wind
is developed, which would naturally blow away from the earth: but
the onrush of the sea in a great mass thrusts it back into the earth.
The countries that are spongy below the surface are exposed to earthquakes
because they have room for so much wind.

For the same reason earthquakes usually take place in spring and autumn
and in times of wet and of drought-because these are the windiest
seasons. Summer with its heat and winter with its frost cause calm:
winter is too cold, summer too dry for winds to form. In time of drought
the air is full of wind; drought is just the predominance of the dry
over the moist evaporation. Again, excessive rain causes more of the
evaporation to form in the earth. Then this secretion is shut up in
a narrow compass and forced into a smaller space by the water that
fills the cavities. Thus a great wind is compressed into a smaller
space and so gets the upper hand, and then breaks out and beats against
the earth and shakes it violently.

We must suppose the action of the wind in the earth to be analogous
to the tremors and throbbings caused in us by the force of the wind
contained in our bodies. Thus some earthquakes are a sort of tremor,
others a sort of throbbing. Again, we must think of an earthquake
as something like the tremor that often runs through the body after
passing water as the wind returns inwards from without in one volume.

The force wind can have may be gathered not only from what happens
in the air (where one might suppose that it owed its power to produce
such effects to its volume), but also from what is observed in animal
bodies. Tetanus and spasms are motions of wind, and their force is
such that the united efforts of many men do not succeed in overcoming
the movements of the patients. We must suppose, then (to compare great
things with small), that what happens in the earth is just like that.
Our theory has been verified by actual observation in many places.
It has been known to happen that an earthquake has continued until
the wind that caused it burst through the earth into the air and appeared
visibly like a hurricane. This happened lately near Heracleia in Pontus
and some time past at the island Hiera, one of the group called the
Aeolian islands. Here a portion of the earth swelled up and a lump
like a mound rose with a noise: finally it burst, and a great wind
came out of it and threw up live cinders and ashes which buried the
neighbouring town of Lipara and reached some of the towns in Italy.
The spot where this eruption occurred is still to be seen.