The Hawaiian Islands exist because of the Hawaiian hotspot, a plume of superheated material rising from deep within the Earth’s mantle. As the Pacific Plate slowly drifts northwestward over this hotspot, a continuous chain of islands is created. This process means that earthquakes are an expected, constant feature of the Hawaiian environment, not an occasional hazard. The geological forces constantly stress the crust, resulting in a high level of seismicity tied directly to the archipelago’s formation.
The Volcanic Engine Driving Hawaiian Earthquakes
The vast majority of seismic activity in Hawaii is directly powered by active volcanism. These events can be categorized into two primary types: those driven by magma movement and those caused by structural stress on the volcanic edifices. Volcanic earthquakes occur as magma pushes through the crust, accumulating in shallow reservoirs or moving laterally through rift zones. The fracturing of rock caused by this internal pressure creates hundreds of small tremors, which are monitored to track the volcano’s unrest.
The most powerful earthquakes, however, are typically tectonic, resulting from the immense weight of the volcanoes themselves. The colossal mass of the volcanic shield volcanoes, like Kīlauea and Mauna Loa, places tremendous gravitational stress on the underlying oceanic crust. This stress causes the flanks of the volcanoes to slip seaward along a deep, nearly horizontal fault zone, known as a décollement. This flank failure mechanism is responsible for the largest recorded events in Hawaii’s history, some reaching magnitudes near 8.0.
Measuring the Frequency and Strength of Shaking
Hawaii experiences earthquakes constantly, although most are too small for residents to feel. Sensitive seismic instruments record thousands of events every year across the state. The total annual count can be around 12,000, with the overwhelming majority registering below magnitude 2.0.
When considering quakes that people can perceive, the frequency decreases but remains significant. On an annual average, the state experiences approximately 100 earthquakes of magnitude 3.0 or greater. Events of magnitude 4.0 or larger, which are often felt widely, occur about ten times per year. Larger earthquakes, magnitude 5.0 or greater, occur on average about once a year, potentially causing minor to moderate damage near the epicenter. Statistically, a magnitude 6.0 or greater earthquake occurs roughly once every ten years, and a magnitude 7.0 or greater event occurs about twice every century.
Where Earthquakes Concentrate Across the Islands
The geographical distribution of earthquake activity across the Hawaiian chain is highly uneven, directly correlating with the age and activity of the islands’ volcanoes. The overwhelming majority of seismic events, including both small tremors and large tectonic quakes, are concentrated on the Island of Hawaii, or the Big Island. This is because it is the youngest island and currently hosts the most active volcanoes, Kīlauea and Mauna Loa. The southern districts of the Big Island, especially around the active rift zones, are the most seismically active areas.
The older, dormant islands situated further northwest, such as Maui, Oʻahu, and Kauaʻi, experience significantly fewer earthquakes. The quakes that occur in these older regions are often related to the bending, or flexure, of the Pacific Plate beneath the weight of the island chain. This flexural stress can cause occasional deep earthquakes, sometimes felt hundreds of miles away from the main volcanic centers. The seismic hazard on these older islands is considerably lower than the continuous, high-frequency activity observed on the Big Island.
Understanding Tsunami Risk and Preparation
The frequent seismic activity presents a dual hazard: ground shaking and the potential for tsunamis. Tsunami risk is categorized into two types: far-field and near-field events, each requiring a different response time. Far-field tsunamis are generated by powerful earthquakes, typically magnitude 7.9 or greater, occurring thousands of miles away along the Pacific Ring of Fire. These distant events allow for several hours of warning time, facilitated by the Pacific Tsunami Warning Center (PTWC) and the statewide siren system.
Near-field tsunamis are the most dangerous, as they can be generated locally by a large earthquake, like a flank failure event, or a submarine landslide, with waves arriving in minutes. In these situations, the only reliable warning is the strong ground shaking itself. If you are near the shoreline and feel intense shaking that makes standing difficult, immediately evacuate to higher ground or move inland without waiting for an official siren or alert.
For any earthquake, the immediate safety measure is to “Drop, Cover, and Hold On” to protect yourself from falling debris. Tsunami preparation involves knowing your local evacuation zone and having a plan to reach a safe area quickly. This safe area is either high ground or a reinforced building’s third floor or higher. Recognizing the natural signs—strong shaking, a sudden drop or rise in sea level, or a loud roar from the ocean—can save lives when official warning time is minimal.