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.
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.
Locations and Numbers of Hawaiian Earthquakes
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 Kama‘ehuakanaloa (formerly Lō‘ihi Seamount) 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||111||32|
|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)|
1. Earthquakes in HVO catalog between 1960 and 2013 (inconsistent magnitude reporting before 1960).
2. Includes earthquakes from 1823 to 2013. Magnitudes before 1960 from Klein and Wright (2000).
Average number of earthquakes per year and days between earthquakes are for magnitude ranges from 3.0 and above. Data from earthquake catalogs between 1823 and 2013.
Types of Hawaiian Earthquakes
Hawaiian earthquakes fall into three main classes.
Magma movement within, and eruptions from, the presently active volcanoes in Hawaii (Kīlauea, Mauna Loa, Hualālai, Haleakalā, and Kama‘ehuakanaloa [formerly Lō‘ihi]) are usually accompanied by hundreds to thousands of small earthquakes with magnitudes of less than 4. 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:
- tremor – due to resonating subsurface fluids or gases, or magma rapidly rising toward the surface
- long period (LP), and very long period (VLP) – due to discrete movements of subsurface fluids or gases
- hybrid or composite – usually due to rockfalls into lava lakes
- volcano-tectonic – due to brittle fracturing of rock from pressures exerted by migrating magma
Schematic cross-section of Kīlauea Volcano's south flank on the southeast part of the Island of Hawai‘i—yellow stars indicate two dominant sources of damaging earthquakes larger than magnitude 5.
Earthquakes involving slippage along tectonic faults comprise the second class of seismic sources in Hawaii. There are two main types:
- Minor to moderate earthquakes (up to M5) occur on upper crustal faults beneath and within the volcanoes. These are the most numerous type of earthquake in Hawaii.
- Large flank (up to M8) earthquakes occur along the décollement fault, which separates the ancient oceanic crust and the overlying volcanoes at roughly 8-10 km (5-6 mi) depth. These are the most dangerous type of earthquake in Hawaii since both large earthquakes and local tsunamis originate there. This fault plane was the source of the 1868 M7.9 Ka‘ū and the 1975 M7.7 Kalapana earthquakes. Slow slip earthquakes, during which motion occurs over days rather than seconds, also occur along the décollement on Kīlauea's south flank.
Schematic cross-section of how the weight of the Hawaiian Islands bends and increases stress in the lithosphere, which is released during mantle earthquakes.
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.