Slip along the décollement can be produced as a combination of gravity and changes in pressure occurring in the volcano that sits above. In the past 50 years, there have been three décollement earthquakes above M6 on Kīlauea's south flank.
The most recent was the
M6.9 earthquake that occurred on May 4, 2018. This earthquake was caused by the magmatic intrusion in Kīlauea's East Rift Zone, which led to the 2018 eruption in the lower East Rift Zone.
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Road destruction from M6.9 Kīlauea earthquake in 2018. USGS photo |
The décollement also produced a
M6.2 earthquake in 1989. This event caused injuries, destroyed or damaged houses in Puna District, caused landslides that blocked roads, and generated a small local
tsunami.
The most destructive of the three events was in 1975, and it was the largest earthquake in Hawai;i since 1868. A
M7.7 on the décollement fault beneath Kīlauea caused several meters (yards) of horizontal and vertical movement along faults in the summit and south flank regions. The earthquakes caused building and road damage, along with a tsunami that resulted in two local fatalities.
Within this greater context, Saturday's M4.1 was only a minor slip along Kīlauea's décollement, but its widely felt shaking serves as a reminder of the potential for this region to produce damaging and widely felt earthquakes. More than 700 people reported feeling the recent M4.1, spanning the Island of Hawaiʻi and even as far as Maui and Lanaʻi.
As residents of a very shaky island chain, the USGS "
Did you feel it?" website is a phenomenal resource that citizens and scientists alike can use to report how we individually feel earthquakes.
While the magnitude of an earthquake is the size derived from data collected by the network of seismic instruments, the intensity of an earthquake is a measure of shaking derived from the network of people reporting how they felt it. Based on the felt reports, "Community Internet Intensity Maps" or CIIMS are generated in near real-time and help us understand how different types of earthquakes can impact different regions in Hawaii.
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A coconut grove subsides into the ocean at Halape in 1975 M 7.7 Kīlauea earthquake. USGS photo |
The
USGS Fact Sheet "Did You Feel It? Citizens contribute to Earthquake Science" describes the importance of CIIMs: "...as a result of work by the U.S. Geological Survey and with the cooperation of various regional seismic networks, people who experience an earthquake can go online and share information about its effects to help create a map of shaking intensities and damage...CIIMs contribute greatly toward the quick assessment of the scope of an earthquake emergency and provide valuable data for earthquake research."
The next time you feel an earthquake, first ensure that you and your surroundings are safe. Then, if you would like to support the science happening in Hawai'i, please fill out your
felt report. Mahalo to everyone who reports feeling earthquakes in Hawai;i; your reports help us understand impacts of earthquakes in our dynamic environment.
Volcano Activity Updates Kīlauea is not erupting. Its USGS Volcano Alert level is ADVISORY.
Elevated earthquake activity and inflationary ground
deformation rates continue in Kīlauea's summit region, indicating that
magma is repressurizing the storage system. Over the past week, about 550 events
(most were smaller than M2) occurred beneath Kīlauea's summit region and extending southeast into the upper East Rift Zone. Unrest may continue to wax and wane with changes to the input of magma; changes can occur quickly, as can the potential for eruption. The most recent summit sulfur dioxide
emission rate measured was approximately 60 tonnes per day on July 9, 2024.
Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.
Four earthquakes were reported felt in the Hawaiian Islands during the week ending Thursday: a M3.4 earthquake 0 km (0 mi) W of Pāhala at 32 km (20 mi) depth on July 8 at 12:39 p.m. HST, a M1.9 earthquake 7 km (4 mi) SW of Volcano at 1 km (1 mi) depth on July 7 at 6:56 a.m. HST, a M3.3 earthquake 14 km (8 mi) S of Fern Forest at 6 km (4 mi) depth on July 6 at 8:51 p.m. HST, a M4.1 earthquake 15 km (9 mi) S of Fern Forest at 6 km (4 mi) depth on July 6 at 8:47 p.m. HST.
HVO continues to closely monitor Kīlauea and Mauna Loa.
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5,500 in the mail, 2,000 on the streets Volcano to Miloli'i See www.kaunews.com |