Molucca Sea
The southern part of the Philippines lies above the complex collisional zone between the Philippine Sea Plate and the Sunda Plate. The convergence between these two plates of between 6–11 cm per year is accommodated by a series of smaller plates. One of these, the Molucca Sea Plate, is currently being subducted beneath both the Philippine Sea Plate and the Sangihe Microplate, causing it to have an inverted U-shape seismic zone. The earthquakes were caused by the continuing distortion of the Molucca Sea Plate. These three quakes of similar magnitude occurring in such close proximity of each other location-wise and time-wise can be regarded as an example of a triplet earthquake.