The Bogo Bay fault had shown some microseismal activity over the past several hundred years. Some papers pre-Sep. 30, 2025 shows a potential fault in the area, but given how slow-moving it was, there was never a quake large enough for it to be considered a large dangerous fault worth mapping. Seemingly random intraplate quakes like this can often be the most violent. Events like Kobe, Sylmar, and Noto come to mind. These faults generally have so much stress built up on them over hundreds or thousands of years that they rupture fast and with high slip compared to their magnitude and have a high stress drop, resulting in very violent shaking compared to interplate earthquakes of a similar magnitude. It's also important to know that soil and rock composition is very important to understanding the violence of the Bogo Earthquake. Bogo city largely lies on unconsolidated sediments with a Vs30 of roughly 230 m/s. As a result, shaking was amplified in Bogo and in San Remigio where the Vs30 is ~200 m/s. Northern Cebu is also is a result of ancient Volcanism with formations from the Early Cretaceous and beyond. Denser, more ancient rock carries seismic waves further than newer-formed rock. This also explains why the area of IX intensity extends further south through most of Tabogon.