Guatemala's highlands lie along the Motagua Fault, part of the boundary between the Caribbean and North American tectonic plates. This fault has been responsible for several major earthquakes in historic times, including a 7.5 magnitude tremor on 4 February 1976 which killed more than 25,000 people. In addition, the Middle America Trench, a major subduction zone lies off the Pacific coast. Here, the Cocos Plate is sinking beneath the Caribbean Plate, producing volcanic activity inland of the coast. Guatemala has 37 volcanoes, four of them active: Pacaya, Santiaguito, Fuego, and Tacaná.