The San Fermín earthquake,[2][3] also known as the Puerto Rico earthquake of 1918, was a major earthquake that struck the island of Puerto Rico at 10:14am on October 11, 1918. The magnitude for the earthquake was a 7.5 (or Level IX in the Rossi-Forel scale); however, that might not be an exact number. The main-shock epicenter occurred offshore about 5 km (3.1 mi) from the northwestern coast of the island, somewhere along the Puerto Rico Trench.