On July 16, 1990, the major 1990 Luzon earthquake of magnitude 7.7 struck northern Central Luzon and the Cordilleras. This was the largest earthquake recorded in 1990, comparable in size to the 1906 San Francisco earthquake and the 2008 Sichuan earthquake. Its epicenter was in the municipality of Rizal, Nueva Ecija, about northeast of Pinatubo, and faulted northwest-southeast through three provinces. It also followed the Philippine Fault System west as far as Baguio, which was devastated, and is located about north-northeast of Pinatubo, leading volcanologists to speculate that it might ultimately have triggered the 1991 eruption, although this is impossible to prove conclusively.