Kaʻū News Briefs, Friday, Oct. 14, 2022

A few items fell off shelves and broke at Aun Tee's at Pāhala Center during 4.6 and 5.0 earthquakes Friday. Staff relocated other items onto the floor  during the aftershocks. The coffee and gift shop  reopened when electricity came back on. Photo by Julia Neal

    Ken Hon, Hawaiian Volcano Observatory Scientist in Charge, said the cause could be the shear weight of the island releasing pressure on the southwest flank of Mauna Loa.
    The quakes prompted Kaʻū High & Pāhala Elementary School Principal Sharon Beck to send out the alarm, evacuating all students into the schoolyard. At the adjacent Robert E. Herkes Kaʻū District Gym, which is also the regional disaster shelter, some ceiling panels fell. Light fixtures fell inside Pāhala Post Office, which shut its front door and announced it would hand out packages out the back door, and continue to service the postal boxes, with no counter service until further notice.

     Items fell off shelves at Mizuno Superette and Aun Tee's coffee shop at Pāhala Center. Electricity went off for hours in Pāhala and both Bank of Hawai'i and Long's shut their doors. Mizuno's and Aun Tee's opened with the return of electricity. Kaʻū Hospital remained opened and was largely unscathed with inspectors making a check on structural stability.

    "The two larger earthquakes were reported by hundreds of people from the Island of Hawaiʻi and felt to a lesser extent across the entire State of Hawai’i. Shaking from the larger earthquakes may have been strong enough to do minor local damage, especially to older buildings. The two earthquakes occurred within 24 seconds of each other creating shaking of longer duration and possibly greater intensity than either of the earthquakes would have created on their own.
    "This sequence of earthquakes appears to be related to readjustments along the southeast flank of Mauna Loa volcano. There has been no immediate effect on the continuing unrest beneath Mauna Loa summit, which remains elevated at levels similar to the past week. On several occasions large earthquakes have

Longs Drugs shutdown after the  earthquake due to power outage. Photo by Julia Neal

preceded past eruptions of Mauna Loa, though these have typically been larger than today’s earthquakes. It is not known at this time if this sequence of earthquakes is directly related to the ongoing unrest on Mauna Loa.
    The Hawaiian Volcano Observatory will continue to closely monitor Mauna Loa for any changes. "

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THE DAY BEFORE THE 5.0 QUAKE, the weekly VolcanoWatch column by USGS Hawaiian Volcano Observatory and scientists focused on preparedness for quakes and lava flows, particularly from Mauna Loa. It was written by geophysicist Jefferson Chang: 
   Feeling occasional earthquakes is part of the experience of living in the State of Hawai'i. Most of the

earthquakes are small, but the less common large earthquakes can be damaging, so it is important to be prepared.
   The U.S. Geological Survey Hawaiian Volcano Observatory records tens of thousands of earthquakes beneath our islands every year. Luckily, most of these are less than magnitude-2, and are not felt. Over the past 30 years, Hawai'i has had four earthquakes of magnitude-6 or larger. Three of them were deep (greater than 12 miles or 20 kilometers) and likely the result of the stresses brought forth by the Hawaiian Islands sitting on top of the Pacific plate. A recent example was the magnitude-6.2 earthquake that struck 17 miles (27 kilometers) south of Nā‘ālehu, a few minutes before midnight on Oct. 10, 2021.
   Another was a magnitude-6.9 on May 4, 2018, which is the largest earthquake recorded in Hawai'i in the past 30 years. This event was much shallower (less than 9 miles or 15 kilometers) and was likely related to magma moving through the Kīlauea plumbing system at the start of the 2018 lower East Rift Zone eruption.
    It is a bit of a chicken or egg problem, whether these large, shallow earthquakes under volcanoes lead to eruptions, or if it is the magma shifting stresses along faults that trigger earthquakes. These are two end-member hypotheses, and in reality, it is most likely a combination of both. Earthquakes and volcanic eruptions go hand-in-hand.
    We see this kind of interplay between magma movement and seismicity with the ongoing swarm of earthquakes under Mauna Loa summit caldera (Moku'āweoweo) and the upper northwest flank. This elevated seismic activity is accompanied by slight ground inflation (or swelling), which suggests that the Mauna Loa magma reservoir is filling.
    Does this mean that Mauna Loa will erupt soon? Not necessarily.
    Mauna Loa has been in a period of prolonged unrest. The sleeping giant may just be snoring a little louder than it did a few years ago, but it does not necessarily mean that it will wake up soon.
    Scientists at HVO look at many different monitoring streams to document changes in Mauna Loa’s behavior. Some of these changes may alert scientists when an eruption is more likely. Large shallow earthquakes are one of the indicators that move the probability of an eruption of Mauna Loa from “not necessarily” to “highly likely”. For example, a magnitude-6.7 earthquake happened a few months before the last eruption of Mauna Loa in 1984. The 1950 eruption was also preceded by a large earthquake, but only 2 days prior to the onset of the eruption.

See shakeout.org for the Great Hawai'i Shakeout event Oct. 20.

    However, not all Mauna Loa eruptions are preceded by large earthquakes. And some large earthquakes, such as the 1975 magnitude-7.7 Kalapana earthquake was not accompanied by a major eruption of Kīlauea volcano.
    Large shallow earthquakes are not just a potential precursor to volcanic eruptions, but can be a disaster on their own. Damage done by large earthquakes can be mitigated to reduce the hazards and risks associated with violent shaking. Modern building codes make houses much more resistant to damage. Efforts like securing tall heavy objects to the wall so they are less likely to tip over and fall will reduce the likelihood of damage and injury when a large earthquake hits. Earthquake safety drills for “Drop. Cover. Hold On.” should be practiced regularly so that instinct kicks in when the initial shaking is felt.
    Join us, and the rest of the world, on Thursday, Oct. 20 at 10:20 a.m. local time for the Great Hawai'i ShakeOut.
    Visit shakeout.org to sign-up and learn more about ways to prepare for large damaging earthquakes.