Public domain. Earthquakes involving slippage along tectonic faults comprise the second class of seismic sources in Hawaii. There are two main types:. This bending creates compressional stresses in the upper portion of the flexed plate and extensional stresses in the lower portion of the plate. Schematic cross-section of how the weight of the Hawaiian Islands bends and increases stress in the lithosphere, which is released during mantle earthquakes.
The third type of Hawaiian earthquakereflects the flexing or bending of Earth's crust and upper mantle, known as the lithosphere, due to the weight of the islands above. This type of earthquake generally occurs in excess of 20 km 12mi below sea level. The M6. Skip to main content. Search Search.
Hawaiian Volcano Observatory. Damage to a home from the November 29, earthquake 7 km 4. Public domain. Modified from Klein et al, and Klein et al, Many of these earthquakes are directly related to volcanic activity; these earthquakes are seldom large enough to cause widespread damage, but they may produce locally extensive ground fractures and subsidence.
Earthquakes that generate the strongest and most damaging ground shaking originate in zones of structural weakness at the base of the volcanoes and in the underlying lithosphere includes the oceanic crust and upper mantle. For example, the magnitude 7. These deeper earthquakes also occur beneath and near the other Hawaiian Islands.
Seismic hazard for the State of Hawaii based on past earthquakes and corresponding ground shaking. For source data description, see Klein et al plus associated published online data. The historical earthquake record in Hawaii, which extends from the early 's to the present, can be used to estimate likely locations of future damaging earthquakes and the hazard they might pose in terms of ground shaking.
These scenarios are used by land managers, government officials, and disaster response personnel to understand and plan for potential damage from and needed response to future earthquakes. This amount of acceleration would make it difficult to stand and could topple structures.
Engineers use this type of information to develop building codes and design earthquake resistant structures. Like a bowling ball resting on a soft mattress, this bows the lithosphere downward in a moat-like depression centered on the main loading center under the Island of Hawaii.
This results in stresses that can lead to earthquakes. The massive Island of Hawaii produces the largest force on the lithosphere because of its relatively young age, which results in forces on the underlying lithosphere that have not yet evened out. The zone of maximum bending stress from this load extends about km 62 mi offshore from the island. As the plate readjusts back to a neutral position, it results in a raised bulge in the lithosphere that extends around Oahu about km mi away.
This is why earthquakes occasionally happen so far from the main area of seismic and volcanic activity on Hawaii Island. There have been two examples of offshore flexural earthquakes in the past month. They include a magnitude The January event was too small and distant for anyone to feel. It was the largest earthquake felt in Hawaii since Aug. Most earthquakes felt beyond Hawaii Island are presumed flexural earthquakes based on their estimated locations.
Friday, Nov. About 1, earthquakes with magnitudes greater than 1 and at depths over 20 km 12 mi on and around the Island of Hawaii since August are depicted on this map. Most of the earthquakes were clustered beneath the southern edge of the island near the town of Pahala.
Blue and purple dots indicate earthquakes at km mi and more than 40 km 25 mi depths, respectively. This area produces numerous deep earthquakes, mostly at depths of km mi , beneath the town of Pahala and extending about 10 km 6 mi offshore. The largest of these was a magnitude In fact, 34 deep events have been reported felt in the region since , including a magnitude The uptick in seismicity in recent months is the latest chapter in a decades-long history of observed earthquakes in the area.
This persistent source of seismicity was first identified on seismic records by HVO staff at least as far back as the s. They characterized episodes of harmonic tremor, ascribing it to upwelling of magma within fluid-filled cracks deep beneath the island. For example, a USGS study published in characterized earthquakes in the region in addition to tremor. Using this data, researchers in discovered a broad zone of low seismic velocity down to at least 1, km mi beneath the southern portion of the island where the deep seismicity takes place.
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