On October 10, 2021, a magnitude 6.2 earthquake near the south coast of the Big Island rocked residents and visitors to the state of Hawaii.
Through Liliane ML Burkhard, Lauren A. Ward, Helen A. Janiszewski, Ph.D., and Bridget R. Smith-Konter, Ph.D., University of Hawaii at Mānoa, and Jonathan R. Weiss, Ph.D., NOAA / NWS Pacific Tsunami Warning Center
Quote: Burkhard, LML, Ward, LA, Janiszewski, HA, Smith-Konter, BR, Weiss, JR, 2021, earthquake off Hawaii linked to tectonic plate bending, Temblor, http://doi.org/ 10.32858 / temblor.215
When a magnitude 6.2 earthquake struck off the southern tip of the Big Island of Hawaii last week, tremors were felt across the Hawaiian Range, including Honolulu on the Island of O ‘ahu, some 160 miles (260 kilometers).
The earthquake occurred at a depth of 22 miles (35 kilometers). According to the US Geological Survey (USGS), it results from simultaneous horizontal and vertical movement along an inverse fault below the Earth’s surface. This kind of “oblique reverse faultOccurs when rocks are both sheared and compressed.
Big Island earthquakes are often triggered by a flow of magma beneath Kīlauea or Mauna Loa, the island’s two active volcanoes. These shallow earthquakes are generally small and most are imperceptible to all except sensitive seismic instruments. Swarms of these earthquakes sometimes precede an eruption.
However, two other types of earthquakes also occur in Hawai’i. These are caused either by faults in the flanks of active volcanoes, or by the bending (“bending”) of the earth’s crust and upper mantle due to the weight of the islands (Watts and Ten-Brink, 1989; Wessel, 1993; Klein, 2016). Earthquakes related to the side of the volcano and bending can be quite severe.
Large Hawaiian Flank Quakes
The largest Hawaiian temblor in the past 150 years was the 1975 7.7 magnitude earthquake in Kalapana, which was a flanking event that struck along the southeastern shore of the Big Island. The event shifted the southern flank of the Kīlauea volcano southward (e.g. Swanson et al., 1976; Lipman et al., 1985; Nettles et al., 2004; Owen and Burgmann, 2006; Chen et al., 2019) and triggered a local tsunami, which left two people dead. It caused approximately $ 4.1 million in property damage.
In 2018, a similar type of flanking event occurred nearby at a depth of 3.6 miles (5.8 kilometers). This earthquake was linked to the formation of new lava vents in the region during the 2018 eruption (Neal et al., 2019) and was probably the result of a landslide on a large fault that separates the volcano from the crust. underlying oceanic (Lay et al., 2018; Chen et al., 2019).
Plate bending earthquakes are not uncommon
Bending-related earthquakes occur at depths ranging from 10 to 35 miles (15 to 60 kilometers) and are not unusual in Hawai’i. The event last week was most likely caused by the flexing of the plate. Similar to how a diving board flexes when a person is standing, the crust flexes under the weight of the islands. Among the Hawaiian Islands, the Big Island is currently pushing the plate down with the greatest force and sagging about 2.5 millimeters per year. In contrast, O’ahu is slowly lifted upward as he rests on a bulge that forms in response to bending. Bending earthquakes occur when the bending stresses are suddenly released during a fault slip.
What makes last week’s earthquake particularly interesting is its great magnitude. Most of these deep earthquakes have a magnitude less than about 5.0 (Klein, 2016). Only four bending-related earthquakes of magnitude 6.0 and above have been recorded since magnitude 6.2 earthquake in Honomu in 1973, which struck north of Hilo and caused over $ 5.6 million in damage. The largest bending earthquake on record was the 2006 Offshore Earthquake magnitude-6.7 event in Kīholo Bay, which produced a 6.0 magnitude aftershock (McGovern 2007).
Fortunately, despite widespread tremors that occurred, last week’s earthquake did not generate a tsunami. To date, the quake has been followed by at least 30 aftershocks, the largest of which was a magnitude of 4.2 that struck five minutes after the main quake. Neither the main shock nor any aftershock appears to have had any effect on the ongoing eruption in Kīlauea.
This event is also probably unrelated to an ongoing deep seismic swarm in the Pāhala region on the south-central coast of the Big Island, located about 50 kilometers to the northeast. Pāhala’s activity is likely related to an increase in mantle-derived magma leading to volcanic and seismic unrest at Kīlauea, Mauna Loa and the offshore volcano Kama’ehuakanaloa (formerly known as Lō’ihi) (Burgess and Roman, 2021).
Although major damage to the islands is unlikely due to the low level of tremors that have occurred, the Hawai’i County Civil Defense recommends residents inspect Their houses. This earthquake is a reminder that visitors and residents of Hawai’i should be prepare for a variety of geohazards, including earthquakes, tsunamis and volcanic eruptions.
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