Another seismically active week is in the books, with a number of earthquakes occurring within the US, and plenty of worldwide activity as well.
Movement amongst plates around Asia and the Caribbean created a flurry of earthquakes, while the US experienced tremors in several regions – California and the desert Southwest, the island of Hawaii, Alaska and Oklahoma.
The largest quake of the week was an M6.0, emanating off the coast of Japan.
As reported by the United States Geological Survey’s website, 203 earthquakes of M2.5 or greater were recorded worldwide over the past week, with 70 of those measuring M4.5 or greater.
This Week’s Largest Quake: M6.0 Mutsu, Japan
Situated at the confluence of four tectonic plates (North American, Pacific, Eurasian and Philippine), Japan is one of the most seismically active countries in the world. In total this week, Japan experienced nine earthquakes, ranging from magnitudes 4.4 to 6.0, the week’s largest.
The M6.0 quake was produced as a result of the subduction of the Pacific plate beneath the North American plate. Emanating from 41 kilometers (25.5 miles) below the Earth’s surface, the depth of this quake reveals that its focus was located on the downgoing slab of the Pacific plate as it descends into the mantle.
Continental US Quakes: California, Nevada and Arizona
California experienced 16 earthquakes over the past week, ranging from M2.5 to M3.4. The majority of these were the result of movement along the San Andreas Fault, the transform boundary between the North American plate and the Pacific plate.
The desert interior also saw earthquake activity this past week. Nevada recorded four tremors, with three of them occurring in Alamo and the largest being an M3.9 on August 10. Arizona also experienced two earthquakes, an M2.8 on August 13 and an M3.0 on August 9.
These desert quakes were likely caused by the stretching of the interior of the continent, created by a hot spot underneath North America. As buoyant magma wells up underneath the continent, this heat and stress exerted on the plate results in weakening and spreading of the overlying crust.
Oklahoma (unsurprisingly) saw 18 earthquakes this week in the north-central region of the state, ranging from M2.5 to M3.4. Ongoing fracking operations in the region continue to be the suspected source of these tremors.
Pacific US: Hawaii and Alaska
Five earthquakes were recorded on the island of Hawaii, ranging from M2.5 to M4.5. This type of seismic activity is not uncommon here; as the only island in the Hawaiian chain remaining volcanically active, the movement of magma underneath such a land mass can often trigger small quakes like these.
Alaska led the US states in earthquake totals this week with 33, and for the largest earthquake in the US; an M5.0 emanating from the Aleutian Islands chain. This region experiences frequent seismic activity as the Pacific plate subducts underneath the North American plate, producing earthquakes and volcanism.
Several islands in the Caribbean Sea have experienced earthquake activity over the last week, with Puerto Rico seeing the largest tremor of M4.6 on August 13. The Dominican Republic and both the British and US Virgin Islands also recorded quakes.
All of these islands are located along the transform boundary between the North American plate and the Caribbean plate; the Caribbean plate (to the south) is moving eastward, while the North American plate (to the north) moves westward. This lateral plate movement is similar to what is seen on the San Andreas Fault along the US west coast.
This week’s seismic activity provides classic examples of earthquakes originating from expected locations – subduction zones, transform boundaries and volcanic hotspots beneath plates. Although no significant quakes occurred, the Earth is by no means inactive.