Two 4+ Magnitude Earthquake at Kīlauea This Week Are Likely Aftershocks from May 2018 Quake

USGS/HVO.

Two 4+ magnitude earthquakes at Kīlauea this week are confident with a slip along the south flank fault and were likely aftershocks of a large 6.9 earthquake in May of 2018.

The US Geological Survey’s Hawaiian Volcano Observatory recorded a magnitude-4.3 earthquake located beneath Kīlauea Volcano’s south flank on Friday, July 3, at 2:19 p.m., HST. This came following a 4.6 earthquake located beneath Kīlauea Volcano’s south flank on Thursday, July 2, at 11:20 p.m., HST.

Neither event resulted in a tsunami threat.

According to HVO seismologist Ashton Flinders, the first earthquake

Neither earthquake had an apparent effect on Kīlauea or Mauna Loa volcanoes. “It is not uncommon for aftershocks like these to happen in relatively short succession. Further aftershocks remain possible and may be felt,” said HVO seismologist Ashton Flinders.

HVO continues to monitor Kīlauea and other Hawaiian volcanoes for any changes.

Kīlauea’s south flank has been the site of 20 earthquakes of magnitude-4.0 or greater during the past 20 years. Most are caused by abrupt motion of the volcano’s south flank, which moves to the southeast over the oceanic crust, according to HVO seismologists.

The location, depth, and waveforms recorded as part of both earthquakes were consistent with slip along this south flank fault. Flinders said the earthquakes were likely aftershocks of the May 4, 2018 magnitude-6.9 earthquake as the volcano continues to settle.

While most earthquakes under Kīlauea’s south flank are caused by abrupt motion of the volcano to the southeast over the oceanic crust, some patches of the fault that did not slip during the larger earthquakes are primed to slip as subsequent aftershocks.

Friday’s earthquake was centered about 5.6 km (3.5 miles) south of Puʻu ʻŌʻō, about 1.7 km (1 mile) north of last night’s M4.6 earthquake, at approximately 7.1 km depth (4.4 miles). Thursday’s earthquake was centered about 7 km (4.3 miles) south of Pu’u ‘O’o, at approximately 6.8 km depth (4.2 miles).

Weak shaking, with maximum Intensity of III on the Modified Mercalli Intensity Scale, was reported across the Island of Hawai‘i during the recent earthquakes. At that intensity, significant damage to buildings or structures is not expected. The USGS “Did you feel it?” service received more than 220 felt reports within the first hour of Friday’s earthquake.

The HVO recorded very light shaking, with maximum Intensity of V, across the Islands of Hawai‘i, Maui, and Lāna‘i during Thursday’s quake. The USGS “Did you feel it?” service received more than 725 felt reports within the first hour of that earthquake.