Thousands of people across southern California and the Big Island of Hawaii used the “Did you feel it?” web reporting tool to say they felt moderate earthquakes to strike each state this evening. The largest of the pair was a magnitude 5.1 event which struck just 1.9 km deep inside Hawaii Volcanoes National Park east of the summit of the Kilauea Volcano; the Hawaii earthquake struck at 5:53 pm local time. Just 16 minutes later a magnitude 3.5 earthquake struck a heavily populated portion of southern California near Fullerton. That earthquake, which had a depth of 10.7 km, was preceded by 2 weaker nearby earthquakes near Banning and Ocotillo, also outside of the Los Angeles metro area.
The Hawaiian earthquake was strong enough for the National Weather Service Pacific Tsunami Warning Center (PTWC) to issue a bulletin about the quake, but the quake itself didn’t create any tsunami. “No tsunami is expected. However, some areas may have experienced shaking,” said the PTWC in their single bulletin on the event. Other aftershocks have hit Hawaii since the magnitude 5.1, but all have been weaker and none have prompted the PTWC to issue any more bulletins.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. According to the National Ocean Service, the speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves. The location, depth, movement, and intensity associated with today’s earthquake wasn’t enough to trigger a tsunami from today’s earthquake.
The southern California earthquakes did not have characteristics that would make a tsunami possible.
According to USGS, 2,583 people reported to them they felt the California earthquake while 1,013 in Hawaii reported they felt the earthquake there. Reports came from across the entire Big Island of Hawaii.
Tonight’s earthquakes in Hawaii and California strike just 2 days after a powerful 7.0 earthquake hit the Philippines, leading to at least one death there. While a minor regional tsunami occurred with that seismic event, there was no Pacific-wide tsunami threat from that earthquake.