There are many sub-genres of thriller movies. There are medical thrillers, sci-fi thrillers, political thrillers and even techno thrillers... but what exactly is a sub-genre?
Well it simply means a category of a genre for example a disaster-thriller movie which is a thriller film where the scenes involve natural or artificial disasters such as earthquakes or nuclear disasters. '2012' is an example of disaster thriller movie including suspense, mystery and sense of uncertainty about the actions and what will happen next which appear commonly in thrillers but also there are earthquakes, volcano eruptions and floods. This helps to attract a wider target audience, people who enjoy watching thrillers as well as people who enjoy disaster movies or both.