"Sevgi" can be used for all forms of love. For instance, insan sevgisi (human love) , doğa sevgisi (love of nature) , eşya sevgisi (love of things) etc. "Aşk" is more dense form of love. For example, hayatımın aşkı (love of my life), tanrı aşkı (love of god). In colloqual, aşk is used mostly for romantic relations.