Why was Poseidon associated with the sea, earthquakes, and horses?

In Greek religion, Poseidon is recognized as the god of the sea, earthquakes, and horses, reflecting his complex role in the ancient pantheon.12

• The Sea: Following the overthrow of their father, Cronus, the kingdom of the sea fell to Poseidon by lot. He is often depicted with a trident, a symbol of his power over the waters, and is frequently portrayed in a chariot drawn by sea creatures.1
• Earthquakes: Known as the "earth-shaker" (enosichthōn and ennosigaios), Poseidon’s association with earthquakes linked him to the land. Despite his maritime domain, many of his oldest places of worship were located inland, often near water sources. He was also worshipped as asphalios, or "stabilizer," in this capacity.1
• Horses: Poseidon is credited in some myths with creating the horse, and he was worshipped as hippios ("of horses"). His connection to horses is further illustrated by his ability to take the form of a stallion and his role as the father of famous horses like Pegasus. This association may stem from the introduction of horses to Greece by the early Hellenes, who are also thought to have introduced the worship of Poseidon.1