I just found something interesting in Ptolemy's Tetrabiblos. Ptolemy does appear to suggest that both Saturn and Mars in transiting in opposition to the great luminaries (Sol/Luna) and stationed in an earth sign (which Capricorn is) can cause earthquakes.

[link to www.sacred-texts.com]
Ptolemy's (c. AD 100-170) (Tetrabiblos Book IV, Chap. VIII

Saturn and Mars, if controlling the luminaries, and, especially, if placed distant from each other, 1 will produce great dangers, and at the same time render the journey fruitless and unavailing. Should they be in watery signs, the dangers will arise by shipwreck, or among deserts and wilderness 2; if in fixed signs, by precipices, and adverse blasts of wind; in tropical and equinoctial signs, by want of food and other necessaries, and by some unwholesome state of the atmosphere; in signs of human form, by robbery, treachery, and various depredations; and, if in terrestrial signs, by the attack of wild beasts, or from earth-quakes.

+++the Latin of Perugio says, "si sint oppositi secundum longitudinem." [if they are in opposition to one another in longitude]

CHAPTER XIV
The tropical signs are two : viz. the first thirty degrees after the summer solstice, which compose the sign of Cancer ; and the first thirty-degrees after the winter solstice, composing the sign of Capricorn. These are called tropical^ because the Sun, after he has arrived at their first points, seems to turn, and to change his course towards a contrary latitude ; causing summer by the turn he makes in Cancer, and winter by that which he makes in Capricorn.