Earthquakes are common in Hawaii, which is one of the most seismically active regions in the United States. The high level of seismic activity is unique because it is driven by the archipelago’s persistent volcanism, not the collision of tectonic plates found along the Pacific Rim. While the state records an extraordinary number of earthquakes annually, the vast majority are small and unfelt by residents and visitors. These tremors represent the perpetual state of dynamic geologic movement beneath the surface.
Frequency and Distribution Across the Archipelago
Hawaii experiences thousands of low-magnitude earthquakes annually, most of which are only detected by sensitive instruments. On average, the region records approximately 12,000 seismic events each year, with the majority registering below magnitude 2.0.
Seismic activity is heavily concentrated on the Island of Hawaiʻi (the Big Island) due to its active volcanoes, Kīlauea and Mauna Loa. The southern districts of the island are consistently the most active areas in the state. The rest of the island chain experiences significantly fewer earthquakes, which are often deeper and more widely felt across multiple islands.
The state sees about 100 earthquakes of magnitude 3.0 or greater each year, which are often felt locally near the epicenter. Earthquakes of magnitude 5.0 or greater, which can cause minor to moderate damage, occur roughly once every year.
The Unique Geological Drivers
The mechanisms generating Hawaiian earthquakes differ significantly from the plate-boundary fault systems found elsewhere. Hawaiian seismicity is primarily categorized into two processes: volcanic activity and lithospheric flexure. The most frequent earthquakes are shallow and directly related to the movement of magma within active volcanic systems.
As magma moves upward from the deep mantle plume and accumulates in reservoirs beneath volcanoes, it exerts immense pressure on the surrounding rock. This pressure, combined with magma moving into fissures or dikes, causes the brittle crust to fracture, resulting in frequent, short-lived earthquake swarms. These events are generally less than magnitude 4.0 and provide scientists with a valuable tool for tracking subsurface magma flow and predicting potential eruptions.
A second mechanism involves the sheer weight of the islands pressing down on the Pacific Plate’s lithosphere, known as lithospheric flexure. The enormous mass of the volcanic islands causes the Earth’s crust to bend downward. This bending creates stress that is released in deeper earthquakes, often occurring at depths between 10 and 40 kilometers.
The most damaging earthquakes often occur along a décollement fault, a shallow, nearly horizontal zone 8 to 10 kilometers beneath the volcanoes’ flanks. This fault acts as a boundary between the volcanic rock and the underlying oceanic crust. Magma pressure and gravity continually push the volcanoes’ flanks seaward, and sudden slippage along this surface generates large, destructive flank earthquakes, such as the magnitude 7.2 Kalapana event in 1975.
Understanding Magnitude and Associated Risks
Although the majority of Hawaiian earthquakes are minor, the region has a history of significant, damaging events. Historically, the state averages one earthquake of magnitude 6.0 or greater every 10 years, and two events of magnitude 7.0 or greater every 100 years. The strongest recorded earthquake occurred in 1868 beneath the Kaʻū district, estimated between magnitude 7.5 and 8.1.
The primary hazards associated with larger Hawaiian earthquakes include intense ground shaking and ground failure, such as fissuring and landslides. The shallow nature of the flank earthquakes means that even a moderate magnitude event can generate strong shaking that impacts structures. The 2018 magnitude 6.9 earthquake accompanying the Kīlauea eruption caused widespread damage, including structural collapse and extensive ground cracking in the Puna district.
A particularly serious risk is the potential for a locally generated tsunami. Unlike tsunamis caused by distant subduction zone earthquakes, a local tsunami can arrive minutes after a large earthquake. The 1975 Kalapana earthquake caused the coastline to subside by several meters and generated a fast-moving tsunami that claimed lives and destroyed coastal property.
The Hawaiian Volcano Observatory (HVO) continuously monitors seismic activity across the islands, providing real-time data to assess volcanic unrest and earthquake hazards. This monitoring, combined with the Pacific Tsunami Warning Center’s alert capabilities, supports public safety. Residents and visitors should be aware of the natural warning signs of a local tsunami, such as severe ground shaking, and immediately move to higher ground without waiting for an official alert.