A Hole in Earth's Surface
|Research shows that a broken lithosphere underneath the island of Hawai'i could explain the island's patterns of seismic activity.|
Research shows that a broken lithosphere underneath the island of Hawai'i could explain the island's patterns of seismic activity.
Hawaii is one of the most seismically hazardous locations in the United States; the island has been rocked by strong earthquakes with magnitudes up to 7.9. These earthquakes occur when strain is released in the lithosphere—the Earth’s crust and uppermost mantle—beneath and next to the island.
This strain is caused by the bending of the lithosphere under the enormous load of the volcanoes. As the volcanoes grow and add more weight on the lithosphere, the crust flexes downward, away from the volcanoes. The downward flexion, in turn, causes the lithosphere close to the volcanoes to flex upward. Ultimately, when the lithosphere stops flexing, the accumulated strain is released in the form of earthquakes.
The resulting plate flexure forms a donut hole shape right underneath the island. The focal hole in the center lies approximately between Mauna Loa, Earth’s largest active volcano, and Mauna Kea, a dormant volcano whose peak is at the highest point of Hawaii.
The author used data taken from seismic stations around the island to understand the stress fields and focal mechanisms, which describe the slip that causes earthquakes and the orientation of the fault on which those quakes occur.
The seismic data give valuable information about the orientation of the stress field and the pressure and tension axis. By analyzing the seismic data, the author saw that the pressure axis—the point where two planes compress—radiated from the center of the hole in the lithosphere. These radial patterns, according to the author, suggest that the downward-flexing lithosphere surrounds a weak region at its center.
The study was published in the Journal of Geophysical Research