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Small Earthquake Cluster on Mauna Loa, Latest USGS Weekly Update

10:06 PM · Mar 18, 2021

Starting early this morning, March 18, a cluster of shallow earthquakes on the slopes of Mauna Loa in the upper Kaʻōiki area has been recorded by seismometers. The majority of today’s earthquakes in upper Kaʻōiki have occurred above sea-level, the largest earthquake being a M3.5 at 8:23am HST with a depth of -2.4km. Within the last 24 hours, there have been 23 earthquakes in the cluster: 14 between M1.0 and M1.9, 7 between M2.0 and M2.9, and only 2 above M3.0. The Kaʻōiki seismic zone is an area of adjustment between the active volcanoes of Mauna Loa and Kīlauea, with events possibly triggered by either volcanic activity or flank instability (Walter & Amelung, 2006). Adjustments in this region are common and last occurred in early March 2020, when a cluster of earthquakes registered slightly upslope from today’s grouping at a depth roughly around sea-level. Today’s small cluster of shallow earthquakes in upper Kaʻōiki on its own does NOT indicate an increase of activity on Mauna Loa. As of the time of writing, earthquake activity has diminished with no earthquakes on Mauna Loa in the last hour. Daily earthquake rates are significantly below the thresholds seen in the build-up to the 1975 and 1984 eruptions, when they maintained levels of several hundred events per day over several weeks, even spiking to ~1000 quakes per day in the weeks preceding both eruptions. During the last month of activity, earthquake rates on Mauna Loa have not even reached 50 events per day. USGS-HVO has also released their weekly update on Mauna Loa. No specific mention of today’s earthquake activity is noted: ---- USGS-HVO Mauna Loa - Volcano Update - Thursday, March 18, 2021, 9:14 AM HST Current Volcano Alert Level: ADVISORY Current Aviation Color Code: YELLOW Activity Summary: Mauna Loa Volcano is not erupting. Rates of deformation and seismicity at the summit remain slightly elevated and above long-term background levels. Other Mauna Loa monitoring data streams show no significant change in deformation rates or patterns that would indicate increased volcanic hazard at this time. Observations: During the past week, HVO seismometers recorded approximately 250 small-magnitude earthquakes below Mauna Loa, 163 of which were below the summit and upper-elevation flanks of the volcano. The majority of the earthquakes were less than M2.5 and occurred at shallow depths of less than 6 km (about 4 mi) below ground level. These patterns of seismicity are typical of the past several weeks for Mauna Loa. Global Positioning System (GPS) measurements continue to show slow, long-term summit inflation, consistent with magma supply to the volcano's shallow storage system. A slight increase in the rate of inflation at the summit that began in January is continuing. Gas concentrations (0 ppm SO2) and fumarole temperatures (below 100 degrees Celsius or 212 degrees Fahrenheit) at both the summit and at Sulphur Cone on the Southwest Rift Zone remain stable. Webcam views have shown no changes to the volcanic landscape on Mauna Loa over the past week.


USGS put out a statement on the EQ cluster: "ACTIVITY SUMMARY Mauna Loa Volcano is not erupting. A small swarm of shallow seismicity, that began at 1:00 a.m. HST this morning, is occurring beneath the upper Ka‘ōiki seismic zone, under Mauna Loa’s southeast flank and northwest of Kīlauea's summit. Other Mauna Loa monitoring data streams remain stable and show no signs of increased activity."

Mar 19, 2021

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