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New US Geological Survey Model Shows Earthquake Hazard Probability for Hawaiian Islands

File webcam images from the USGS Hawaiian Volcano Observatory

Hawai’i is a seismically active state, with thousands of earthquakes recorded each year by the USGS Hawaiian Volcano Observatory.

Damaging ground shaking in Hawaiʻi has occurred over the decades, with two 6.7 plus magnitude earthquakes in 2006 and 2018. This year, a 5.2 magnitude earthquake on July 5 was felt by more than 1,300 people and a 6.2 magnitude earthquake on October 10 was felt by more than 3,500 people.

Earthquakes are often associated with volcanic activity. Monitoring current volcanic activity — including the Kīlauea volcano eruption that began Sept. 29 — is important because it could lead to large earthquakes.

The US Geological Survey’s updated ground shaking model, published on-line in the journal Earthquake Spectra, shows a 90% chance the 345,000 people on the islands of Hawai’i and Maui could experience damaging levels of shaking during the next 100 years.

A lower but significant chance of damaging shaking is expected across O’ahu; within the southeastern portion of the island near Honolulu there is a greater than 50% chance of damaging shaking occurring during this period. Levels of shaking on the southernmost islands are comparable to shaking levels expected across portions of coastal California. 

“The previous hazard model was developed over 20 years ago and since that time we have experienced several large earthquakes and volcanic eruptions; and we have collected deformation, soil and strong motion data that can be used to improve this forecast,” said Mark Petersen, USGS research geophysicist and lead author of the publication.

“We collaborated with scientists and engineers across Hawai’i and the rest of the United States to build these models. The new seismic hazard maps can be used to update building codes and other planning documents, which should improve seismic safety across Hawai’i.”

The map and publication feature new earthquake catalogs, assessments of activity on active faults using geologic and geodetic (GPS) measurements, and evaluations of strong shaking data to define the ground shaking levels expected from earthquakes on the Hawaiian Islands.

Ground shaking is forecasted to be highest near the active volcanos of Kīlauea and Mauna Loa in the southernmost portion of the Island of Hawai‘i. Here magmatic activity pushes the crust outward toward the ocean along a nearly horizontal fault located about 6 miles beneath the surface.

Large earthquakes occurred on this zone in 1868, 1975, 2018 and 2021. The 2018 earthquake was followed by a volcanic sequence that included numerous seismogenic collapses of Kīlauea volcano’s summit crater floor. These provided data that helped define the shaking levels predicted by the model. 

“Repeated collapses of the volcanic caldera may have also caused damaging ground shaking during the 2018 volcanic eruption, so a new model was developed to evaluate this risk,” Petersen said.

While earthquake activity remains high today, it seems to have decreased compared to the preceding century, which could be related to less volcanic activity at Mauna Loa. Variations in earthquake activity are considered in the new models with the expectation that earthquake activity could revert back to previous levels or continue at the current level. 

Forecasted shaking levels on the islands to the northwest of Maui are lower, and damaging earthquakes are less common since this region is farther from the magma source that currently lies beneath the Island of Hawai‘i. Earthquakes in this region result from bending of the earth’s crust due to the weight of overlying volcanos and from nearby oceanic fracture zones. 

Despite less frequent earthquake activity and a lower chance of damaging shaking, earthquakes on the northern Island of Hawai’i and on Maui, Lānaʻi, Moloka’i, O’ahu, Kaui’i and Ni’ihau are still possible and can occur at depths that range from near the surface down to 25 miles.

A deep earthquake in 2006 occurred at a depth of about 18 miles and was strongly felt on the northern portion of the Island of Hawai‘i and on Maui, causing extensive damage and losses. Other deep earthquakes occurred in 1938 near Maui, 1929 near Hualālai, and 1973 near Homomū.

A large earthquake in 1871 near Lāna‘i is thought to have ruptured an oceanic fracture zone, and a 1948 earthquake near O‘ahu caused minor damage in Honolulu. These earthquakes signal the lower but significant risk to the northwestern portion of the Hawaiian island chain.

For More Information

  • Learn About Earthquake Hazards 
  • Seismic Hazard Maps and Site-Specific Data 
  • Hawaiian Volcano Observatory 

Original source: https://mauinow.com/2021/12/23/new-us-geological-survey-model-shows-earthquake-hazard-probability-for-hawaiian-islands/

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