Most mountains in Sendai are dormant volcanoes, much older than the more famous Mount Zaō and Naruko volcanoes in nearby municipalities. However, many hot springs can be found in the city, indicating hydrothermal activity. The Miyagi Oki earthquake occurs offshore Sendai once every 25 to 40 years. The 7.2 magnitude 2005 Miyagi earthquake, which occurred on August 16, 2005, had an epicenter close to the "Miyagi Oki" earthquake area. However, the Headquarters for Earthquake Research Promotion concluded that it was not the "Miyagi Oki" earthquake, saying "...the recent event is not thought to be this earthquake. This is because the magnitude of the earthquake was small, and the source area, which was estimated from the aftershock distribution and seismic waves, didn't cover the whole expected source region. Although, the recent event ruptured a part of the focal region of the expected earthquake." In 2011, the 9.0 magnitude 2011 Tōhoku earthquake occurred offshore Sendai, resulting in a devastating tsunami.