Interesting! The adjective historical appeared about 1495, 100 years before the adjective historic. Historic had appeared as a noun (a book about history) around 1560. They started to be confused, as adjectives, almost immediately.
The distinctions, if there were/are any, have been chiefly lost and may depend on whether either adjective is used attributively or predicatively and even then, the use is not regular.
One possible distinction might be in:
The two presidents came to an historic (one that creates history) agreement.
The historical (relating to the past) agreement had been that both countries could fish in the river which formed the border, the new agreement divided the river north and south with the northern country having the northern part of the river.
It is less clear (if it exists) in
The historic landscape (that exists in the present as it did in history) before you is exactly as it would have appeared to a man in the 10th century
The historical landscape (that existed only in history), which was rural, has long since gone and is now replaced by houses and factories.
The above landscape example is how I would probably use the two words, but I'm not sure that I would raise an eyebrow if they were exchanged.
(If you want another word, there is historial (belonging to history, or of history) - fortunately, it is very rare.)