Volcano Watch: What's shaking? Earthquake alerts explained Big ...

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is by University of Hawaiʻi Research Corporation seismic analyst Maddie Hawk.

Earthquakes are a common occurrence in Hawaiʻi. If you subscribe to emergency, earthquake or volcano notifications, the shaking you feel might be followed by a message summarizing the earthquake.

Have you ever wondered why the magnitude of an earthquake you felt might differ slightly between a message you received, a post you saw on social media or what the local news reported?

When an earthquake strikes in Hawaiʻi, there are three agencies that analyze the temblor for its location and magnitude:

• The U.S. Geological Survey National Earthquake Information Center serves as the repository of earthquake catalogs and a backup to the regional networks.
• The National Oceanic and Atmospheric Administration Pacific Tsunami Warning Center monitors for tsunami and releases an earthquake’s automatically calculated information to Hawaiʻi County Civil Defense within 30 seconds.
• The U.S. Geological Survey Hawaiian Volcano Observatory releases the authoritative information after reviewing the event.

Earliest earthquake information will typically come from automated solutions generated by computer algorithms from Pacific Tsunami Warning Center and Hawaiian Volcano Observatory.

Human analysts from the volcano observatory and National Earthquake Information Center then review magnitude-2.5 or larger earthquakes to get a more accurate magnitude and location.

Large earthquakes can potentially be damaging and/or trigger tsunami; it is important to report that information to affected residents/visitors as soon as possible.

Depending on the magnitude and intensity of the event, Hawaiʻi County Civil Defense has the option to send out a message to emergency alert subscribers or all local cellphones, regardless of whether they are subscribed to local emergency alerts.

Another way to receive earthquake information is via the U.S. Geological Survey Earthquake Notification Service, a free, customizable notification system that allows users to sign up to receive earthquake email or SMS notifications for a region the user defines.

New Earthquake Notification Service accounts automatically receive alerts for all earthquakes of at least magnitude-6 by default, but users can adjust their preferences to receive alerts for lower magnitude events.

As helpful as automated seismic systems are, however, they aren’t perfect.

Seismic analysts at Hawaiian Volcano Observatory refine the automated system’s calculations to produce a more accurate location, depth and magnitude of the earthquake. For example, a magnitude-3.1 earthquake the morning of Feb. 13 was a magnitude-2.8 before analyst review.

The difference in an earthquake’s location and depth before and after analyst review can be noticeably different based on the event and network coverage nearby.

Hawaiian Volcano Observatory’s seismic analyst review process can take anywhere from 10 to 30 minutes, depending on the time of day, availability of analysts and complexity of the earthquake.

This is why initial automated alerts are so valuable, providing preliminary information immediately.

Calculating the location and magnitude of an earthquake requires analyzing aspects of data from several seismic stations around the island, such as the maximum amplitudes and arrival times of different seismic waves.

Distinct waves travel at different speeds within the ground and therefore arrive at different times at the seismic stations. That time difference between the distinct seismic wave arrivals is shorter for stations closer to the earthquake epicenter and longer for stations farther away.

Think of two people racing: one on a bicycle and one on foot. The farther away the finish line from the start point, the greater the distance increases between the two racers.

If you feel an earthquake, don’t forget to let us know by making a “Felt Report” online.

Earthquakes in Hawaiʻi widely felt — generally around magnitude-4 or higher — also prompt Hawaiian Volcano Observatory to publish an information statement via the U.S. Geological Survey Volano Notification Service (another subscription service).

Those information statements are typically published after an observatory analyst reviews the earthquake magnitude. They include the reviewed magnitude, an interpretation of what caused the earthquake, the number of felt reports and shaking intensity.

The next time you’re looking up a specific earthquake on the U.S. Geological Survey Latest Earthquakes website, look at the “Origin” box, which contains the event’s “Review Status.”

An event will either be labeled as “AUTOMATIC” or “REVIEWED,” and you can toggle through the event information, including the seismic stations used in the magnitude calculations and the number of felt reports.

Volcano Activity Updates

Kīlauea has been erupting intermittently within the summit caldera since Dec. 23, 2024. Its U.S. Geological Survey Volcano Alert Level remains at Watch.

The eruption’s latest Episode 9 of eruptive activity lasted 22 and a half hours, producing vigorous lava fountains more than 300 feet high at times and lava flows onto the floor of Halemaʻumaʻu Crater. Fountains and flows were active from the morning of Feb. 11 until the morning of Feb. 12.

Kīlauea summit has been inflating since Episode 9 ended. Resumption of eruptive activity is possible from Feb. 15-18 if summit inflation continues at its current rate.

Sulfur dioxide emission rates are elevated in the summit region during active eruption episodes. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

Mauna Loa is not erupting. Its Volcano Alert Level is at Normal.

No earthquakes were reported felt in the Hawaiian Islands during the past week.

Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.

Visit the volcano observatory’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.