In El Hierro, the smallest and farthest south and west of the Canary Islands, hundreds of small earthquakes were recorded from July 2011 until October 2011 during the 2011–12 El Hierro eruption. The accumulated energy released by the swarm increased dramatically on 28 September. The swarm was due to the movement of magma beneath the island, and on 9 October a submarine volcanic eruption was detected. Indian Ocean An earthquake swarm began east of Mayotte on 10 May 2018. The strongest quake (M5.9), the largest-magnitude event ever recorded in the Comoro zone, struck on 15 May 2018. The swarm includes thousands of quakes, many of them felt by Maorais residents. Temporarily-installed ocean-bottom seismometers showed that the swarm active zone was sited 10 km east of Mayotte, deep into the oceanic lithosphere (in the 20–50-km depth range), a rather surprising result because the swarm was believed to be caused by the deflation of a magma reservoir located 45 km east of Mayotte, at a depth of 28 km. (Accordingly, an oceanographic campaign discovered in May 2019 a new submarine volcano, 800-m high and located 50 km east of Mayotte.) The swarm had been tapering off between August and November 2018 when the 11-November-2018 event occurred. This event had no detectable P nor S waves, but generated surface waves which could be observed worldwide by seismological observatories. Its origin is thought to be east of Mayotte. The swarm has continued to be active all through 2019. Pacific Ocean In January and February 2013, the Santa Cruz Islands experienced a large earthquake swarm with many magnitude 5 and 6 earthquakes: more than 40 quakes with magnitude 4.5 or larger took place during the previous 7 days, including 7 events with magnitude larger than 6. The swarm degenerated into the M8.0 2013 Solomon Islands earthquake (6 February 2013). See also 1951 East Rift Valley earthquakes 2009– Oklahoma earthquake swarms Blanco Fracture Zone Gutenberg–Richter law Guy-Greenbrier earthquake swarm Remotely triggered earthquakes References Earthquakes Types of earthquake