A strong, damaging earthquake struck the Big Island of Hawaii last night, giving a protracted jolt not just to Hawaii Island, but much of the state too. According to USGS, at 9:46 pm local time, a magnitude 6.0 earthquake struck from a depth of 22.6 km on the western flank of the Mauna Loa volcano near Honaunau-Napoopoo, south of Kona. Hawaii Volcano Observatory said the earthquake was felt widely across the islands of Hawaiian, Maui, and Oahu.
The earthquake caused considerable damage on the Big Island, especially around the area of the epicenter, with items thrown from store shelves, artwork and mirrors tossed from walls and furniture, and kitchens thrown into disarray with moved/knocked over refrigerators and kitchen cabinets rattled of their contents onto the floor.
USGS says that earthquakes with a magnitude of 2.0 or less are rarely felt or heard by people, but once they exceed 2.0 , more and more people can feel them. While damage is possible with magnitude 3.0 events or greater, significant damage and casualties usually don’t occur until the magnitude of a seismic event rises to a 5.5 or greater rated event.
Big Island Mayor Kimo Alameda said roadway crews have been out clearing debris from roadways since the earthquake struck; rock and land slides were reported south of Kona, with trees and utility wires also knocked over by the force of the earthquake. The Mayor also said that minor damage was reported at Kona Hospital.
“If you need to drive, drive with caution,” the Mayor said in remarks posted on Facebook after the earthquake struck.
The magnitude 6.0 earthquake occurred due to oblique reverse faulting at a depth of 22 km or 14 miles. Large magnitude earthquakes in Hawaii that occur at this depth are typically caused by lithospheric flexure due to the weight of the Hawaiian Islands pressing down on the underlying oceanic plate. Given the depth, location and the observed typical mainshock-aftershock behavior, the May 23 event is not directly related to magmatic processes.
The Island of Hawaii is the youngest island in a chain of volcanoes that stretches about 3,400 miles across the northern Pacific Ocean. The island chain results from magma generated by a source deep within the mantle, the Hawaiian hotspot. The ocean crust and lithosphere above the hotspot, within the Pacific tectonic plate, move to the northwest with respect to the deep magma source. Over millions of years, new island volcanoes form, and older volcanoes are carried away from the hotspot (towards the northwest), erode, and eventually subside beneath sea level.
According to USGS, non-volcanic or non-magmatic Hawaiian earthquakes reflect the long-term accumulation and release of lithospheric stresses rather than short-term processes associated with the motion of magma before or during an eruption. The long-term stresses are partly generated in the crust and mantle by the weight of the volcanic rock that composes the islands. In that sense, most Hawaiian earthquakes not directly associated with eruptions are nonetheless broadly related to volcanic activity.
While this strong earthquake doesn’t appear to be magmatic in nature, Kilauea is due to erupt as soon as this weekend. According to the Hawaiian Volcano Observatory (HVO), glow has been visible in Kilauea’s eruptive vents overnight last night while summit inflation is underway. HVO says forecast models suggest the next eruption will occur sometime between Sunday, May 24, and Wednesday, May 27.
Moderate-magnitude earthquakes are common in Hawaii. In the last 50 years, there have been 36 other earthquakes of magnitude 5 or greater within 60 miles of this big earthquake. Hawaii has also experienced larger earthquakes, including the M 7.7 Kalapana earthquake in 1975 and the M 6.7 Kīholo Bay earthquake that caused minor injuries, damaged roads and at least 1,000 buildings, and triggered landslides that blocked roads on Hawaii.
