Vancouver Island is mostly made up of volcanic and sedimentary rock which was formed offshore on the now disappeared Kula oceanic plate. Around 55 million years ago, a microplate of the Kula Plate subducted below the North American continental margin with great strain. A volcanic arc on the surface of the Kula Plate was thus accreted and fused onto the western edge of North America. These terranes were subjected to extreme warping from continued subduction of the Kula plate, leading to the formation of the distorted Insular Mountains. Much of the central mountainous region around Strathcona Park is part of the Karmutsen Formation, which is a sequence of tholeiitic pillow basalts and breccias. Since Vancouver Island has become an accretionary wedge on the North American continent, the Kula Plate has fully subducted beneath it and the remnants of the Farallon Plate, the Juan de Fuca Plate, are now subducting below the island. This process has led to Vancouver Island being one of the most seismically active regions in Canada. The subduction zone off the coast of the island forms a section of the Ring of Fire. The area has been known to host megathrust earthquakes in the past, the last being the Cascadia earthquake of 1700. The Forbidden Plateau, in the east of the Vancouver Island Ranges, was the epicentre of the 1946 Vancouver Island earthquake that registered 7.3 on the moment magnitude scale, the strongest ever recorded on land in Canada.