If you have been listening to the news in the last hours, you probably know already that a M6.3 earthquake has struck offshore Taiwan. As usual, the best information comes from the USGS.
The event happend at 18.05 UTC, and we don't yet have a focal mechanism solution for it. Anyway, in the attached figure you can have an idea of what is going on in there.
Taiwan is located in the boundary between the Phillipine Sea and the Eurasian plates. There is an approximated convergence rate of 80 mm/yr to the SE. What is really especial about this island is the presence of two subduction zones: One, where the South China Sea subducts beneath Eurasia, and another one, where Eurasia subducts beneath the South China Sea, forming both zones approximately a right angle.
You can see a great introduction (including the previous explanation) to the geology of Taiwan in the dedicated website of the California Institute of Technology: