TSUNAMI INFORMATION STATEMENT NUMBER 1 NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI 228 PM HST TUE JUN 19 2018 TO - EMERGENCY MANAGEMENT IN THE STATE OF HAWAII SUBJECT - LOCAL TSUNAMI INFORMATION STATEMENT THIS STATEMENT IS FOR INFORMATION ONLY. NO ACTION REQUIRED. AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS ORIGIN TIME - 0224 PM HST 19 JUN 2018 COORDINATES - 19.3 NORTH 155.1 WEST LOCATION - ON THE SOUTH FLANK OF KILAUEA VOLCANO MAGNITUDE - 4.4 EVALUATION NO TSUNAMI IS EXPECTED. REPEAT. NO TSUNAMI IS EXPECTED. HOWEVER...SOME AREAS MAY HAVE EXPERIENCED SHAKING. THIS WILL BE THE ONLY STATEMENT ISSUED FOR THIS EVENT UNLESS ADDITIONAL DATA ARE RECEIVED.
On May 4, 2018, the largest earthquake in 43 years struck Hawaiʻi with a moment magnitude of 6.9 in the Kalapana region of the Island of Hawaiʻi (the “Big Island”). This animation puts that earthquake in historic context by comparing its magnitude with those of other earthquakes that have struck these islands in the last 150 years.
The moment magnitude number is proportional to an earthquake’s total energy release such that each whole number increase in magnitude represents about a 32-fold increase in energy release. For example, a magnitude 7 earthquake releases about 32 times as much energy as a magnitude 6 earthquake. Therefore in this animation, the circle for a magnitude 7 earthquake has about 32 times the area of a magnitude 6 earthquake. Each circle is also labeled to show its magnitude, its location, and the year it happened. The animation reveals that three earthquakes are known to have been larger—that is, have released even more energy—than 2018 Kalapana earthquake. The animation concludes with a map showing where each of these earthquakes happened in Hawaiʻi.
USGS: How large does an earthquake have to be to cause a tsunami?
Magnitudes below 6.5
Earthquakes of this magnitude are very unlikely to trigger a tsunami.
Magnitudes between 6.5 and 7.5
Earthquakes of this size do not usually produce destructive tsunamis. However, small sea level changes may be observed in the vicinity of the epicenter. Tsunamis capable of producing damage or casualties are rare in this magnitude range but have occurred due to secondary effects such as landslides or submarine slumps.
Magnitudes between 7.6 and 7.8
Earthquakes of this size may produce destructive tsunamis especially near the epicenter; at greater distances small sea level changes may be observed. Tsunamis capable of producing damage at great distances are rare in the magnitude range.
Magnitude 7.9 and greater
Destructive local tsunamis are possible near the epicenter, and significant sea level changes and damage may occur in a broader region.
Note that with a magnitude 9.0 earthquake, the probability of an aftershock with a magnitude exceeding 7.5 is not negligible. To date, the largest aftershock recorded has been magnitude 7.1 that did not produce a damaging tsunami.