UH researchers return to South Kona after 6.0 quake damage

A dense web of temporary seismic sensors is back on the west flank of Mauna Loa, giving South Kona a closer look at the fault that snapped during the magnitude-6.0 earthquake. The work is meant to explain why neighborhoods around Hōnaunau-Nāpōopoo, Captain Cook and the surrounding South Kona corridor saw such heavy damage, after county officials logged about 207 damage reports and later said five homes were destroyed and 85 properties sustained major damage.

The University of Hawaii team is led by seismologist Sin-Mei Wu and includes graduate students Pablo Urra Tapia and Ian Wynn, along with assistant professors Helen Janiszewski and Thomas Lee. In a rapid three-day field campaign funded by the SOEST Dean’s Office and using sensors from the NSF EarthScope Consortium, the researchers deployed a dense temporary array across the west flank of Mauna Loa. The goal is practical: capture close-range aftershocks and fill in gaps left by the island’s permanent network, which is built mostly around areas of high volcanic activity and has relatively few instruments near this epicentral zone.

The quake struck at 9:46 p.m. HST on May 22, about 7 miles south of Hōnaunau-Nāpōopoo, at a depth of about 22 kilometers. The U.S. Geological Survey said it was caused by oblique reverse faulting linked to lithospheric flexure, not volcanic processes, and treated it as the potential mainshock of an earthquake sequence that already included at least 33 events. Its one-week forecast put the chance of another magnitude-6 or larger quake at less than 1 percent, and the chance of a magnitude-3 or larger aftershock at 6 percent.

For South Kona, the value of the temporary array is in the details it can deliver after the shaking stops. Better local data could show which parts of the fault moved, why some neighborhoods absorbed more damage than others, and how future aftershocks might behave across homes, farms and roadways in the hardest-hit areas. More than 7,000 people in Hawaii submitted Did You Feel It? reports, the highest response ever recorded for a Hawaii earthquake, while the county said more than 2,662 felt reports came in during the first hour and shaking reached Modified Mercalli Intensity VII.

Thomas Lee is also comparing the new data with the 2006 Kīholo Bay-Māhukona earthquakes, which caused about $200 million in losses and damaged at least 1,000 buildings, and with the 1975 Kalapana quake. UH Hilo says Hawaii Island typically sees about 100 magnitude-3-or-greater earthquakes a year, about 10 magnitude-4-or-greater quakes a year and about one magnitude-5-or-greater event every one to two years, but large tectonic earthquakes still arrive with little warning. In Captain Cook, county officials met with residents on May 29 to focus recovery efforts as the science campaign moved quickly to capture what the ground is still telling them.