Do earthquakes occur frequently in the DR?
Tremors occur frequently in the DR with the one felt today being about as strong as a tremor gets.
Earthquakes occur less frequently than tremors.
Keep in mind that the reason the Caribbean islands exists is due to two factors:
1. Active volcanoes which is how every island (including Hispaniola) got its start. The only islands with active volcanoes today are small islands in the Lesser Antilles (ie. St. Lucia, etc). Montserrat has the most infamous volcano when half of the island (including its capital) was destroyed when their volcano erupted spewing toxic ash for days (so much ash was released into the air that it actually affected the air quality of places as far away as San Juan, Puerto Rico and to a lesser extent the south eastern portion of the DR) and a giant clyroplasmic avanlanche which pretty much wiped everything in its path.
2. Each and every single island sits on major fault lines which is where the Caribbean tectonic plate meets the Atlantic plate. Hispaniola has the largest number of faults of any island and is among the most active parts of the Caribbean as far as earthquakes are concerned.
The two most worrisome fault lines is the one which crosses the Cibao from east to west and is gradually causing the Cibao Valley to rift apart and the second one (and presumably more power) is just off the north coast.
There are other fault lines south of the island and in other areas which, once they become active, you will feel them on Hispaniola.
The last major earthquake to hit the DR occured 3 or 4 years ago, with the most affected areas being Puerto Plata and the Cibao. If you do a search you might find the threads of expats writing about their ordeal with the earthquake and the aftershocks.
-NALs