A new U.S. Geological Survey study indicates that the Hawaiian Islands, especially the Island of Hawaiʻi and neighboring islands with active volcanic activity, are likely to experience damaging ground shaking from an earthquake in the next century.
New USGS Model Shows Earthquake Hazard Probability for Hawaiian Islands
Hawaiʻi is a seismically active state, as indicated by the thousands of earthquakes recorded each year by the USGS Hawaiian Volcano Observatory. Damaging ground shaking has occurred over the decades, with two M6.7+ earthquakes in 2006 and 2018 and most recently a M5.2 earthquake on July 5, 2021 that was felt by more than 1300 people and a M6.2 earthquake on October 10, 2021 that was felt by more than 3500 people.
Earthquakes are often associated with volcanic activity and, therefore, monitoring current volcanic activity (e.g., Kilauea volcano has been erupting since September 29, 2021) is important as it could lead to large earthquakes.
This updated ground shaking model, published on-line in the journal Earthquake Spectra, shows a 90% chance that the 345,000 people on the islands of Hawaiʻi and Maui could experience damaging levels of shaking during the next 100 years. A lower but significant chance of damaging shaking is expected across Oahu; within the southeastern portion of the island near Honolulu there is a greater than 50% chance of damaging shaking occurring during this period (Figure 1). 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, volcanic eruptions, and 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 Hawaiʻi and the rest of the U.S. 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 Hawaiʻi.”
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 Hawaiʻi (Figure 2). Here magmatic activity pushes the crust outward toward the ocean along a nearly horizontal fault located about 6 miles (10 kilometers) 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,” said Petersen.
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 (Figure 3). 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 Hawaiʻi. 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.
“The Hawaiʻi Earthquake and Tsunami Advisory Committee thanks the USGS and University of Hawaii at Mānoa for their close collaboration in updating the seismological science since the previous hazard model was considered,” said Rhett Butler.
Despite less frequent earthquake activity and a lower chance of damaging shaking, earthquakes on the northern Island of Hawaiʻi and on Maui, Lānaʻi, Molokaʻi, Oʻahu, Kauiʻi and Niʻihau are still possible and can occur at depths that range from near the surface down to 25 miles (40 kilometers). A deep earthquake in 2006 occurred at a depth of about 18 miles (29 kilometers) and was strongly felt on the northern portion of the Island of Hawaiʻi 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 Lānaʻi is thought to have ruptured an oceanic fracture zone, and a 1948 earthquake near Oʻahu caused minor damage in Honolulu. These earthquakes signal the lower but significant risk to the northwestern portion of the Hawaiian island chain.
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