により and によって are conjunctive, they go before another clause. により is often used in written language.
による needs to go before a noun. Usually reserved for formal, written Japanese, if the noun expresses a condition it can be used in everyday speech.
火事によって多くの森林が焼けてしまった。 Here, によって is showing the agent; although this sentence is not passive, the verb itself works like one as it is intransitive. "Much of the forests were burned by the fire."
今回の地震による津波の心配はない。The による is showing cause. Worries do not spring up on their own, after all. "There is no fear of tsunami caused by this (recent) earthquake.