Thousands of earthquakes occur every year in the State of Hawaii. They are caused by eruptive processes within the active volcanoes or by deep structural adjustments due to the weight of the islands on Earth's underlying crust. Most are so small that they can only be detected by sensitive instruments, known as seismometers. Some are strong enough to be felt on one or more of the islands. A few earthquakes are large enough to cause significant damage and impact residents across the State.
The overwhelming majority of earthquakes in Hawai‘i occur on and around the Island of Hawai‘i, especially in the southern districts of the island where Kīlauea, Mauna Loa, and Lō‘ihi volcanoes are the most active in the State. Most of these earthquakes are directly related to magma moving within the volcanoes, accumulating in shallow reservoirs, or erupting at their summits or rift zones. Other earthquakes occur along tectonic faults in the crust and upper mantle.
The earthquake record since 1823 shows that each year the State of Hawaii averages about 100 magnitude-3 (M3) or greater earthquakes, ten M4 or greater earthquakes, and one M5 or greater earthquake. Additionally, the State experiences, on average, one M6 or greater earthquake every 10 years, and two M7 or greater earthquakes every 100 years. The table below shows how many days you can expect between events of each magnitude range.
|Magnitude||Average Earthquakes Per Year||Average Days Between Earthquakes|
|3.0 - 3.9||1021||3.5|
|4.0 - 4.9
|5.0 - 5.9||0.71||533 (1.5 years)|
|6.0 - 6.9||0.11||2,818 (7.7 years)|
|7+||0.022||20,378 (55.8 years)|
Magma movement within, and eruptions from, the presently active volcanoes in Hawaii (Kīlauea, Mauna Loa, Hualālai, Haleakalā, and Lō‘ihi) are usually accompanied by hundreds to thousands of small earthquakes with magnitudes of less than4. They originate in magma storage regions or along the paths that magma travels as it moves upward or laterally prior to an eruption. Such earthquakes, loosely termed volcanic earthquakes, are important for volcano activity monitoring. Some types of volcanic seismic sources common in Hawaii include:
The third type of Hawaiian earthquake reflects the flexing or bending of Earth's crust and upper mantle, known as the lithosphere, due to the weight of the islands above. This is the most common source of damaging earthquakes north of the Island of Hawai‘i. This type of earthquake generally occurs in excess of 20 km (12mi) below sea level. The 2006 M6.9 Kīholo Bay earthquake occurred due to lithospheric bending, as did the 1973 M6.2 Honomu earthquake.