The Earth has been quite active, seismically speaking, over this past week. Earthquakes originated from an array of locations – convergent boundaries between continents, oceanic subduction zones, and divergent boundaries as well as typically stable continental interior.
Overall, according to the United States Geological Survey’s website, a total of 221 earthquakes with a magnitude of 2.5 or greater were recorded during the last seven days, with 72 of these being M4.5 or greater. The largest was an M6.9 that struck in Micronesia on August 3.
Largest Earthquake of the Week: M6.9 Micronesia
A significant subduction-related quake occurred in Micronesia on August 3, a product of the complex interaction between the Pacific and Australian plates. Located along the Pacific plate’s infamous Ring of Fire, this area is no stranger to large earthquakes.
Although subduction is an ongoing process, this particular region near Micronesia has been very seismically active recently; since March 2014, 13 earthquakes were previously recorded within a 150 km (93.2 mile) radius from the location of this week’s quake, ranging in size from M4.9 up to M7.2.
Tsunamis, or large waves created from the sudden movement of the sea floor, can also accompany earthquakes in the region, though this week’s event posed no immediate tsunami threat.
China Earthquake: M5.2 & M6.1 on August 3
China experienced two earthquakes on August 3, an M5.2 near Saga and an M6.1 near Wenping. Both of these events can be attributed to the ongoing collision between the Indian plate and the Eurasian plate.
The M5.2 Saga quake occurred directly north of this continental convergent boundary, in a very seismically active region. As the Indian plate collides with the Eurasian plate, the Himalaya Mountains continue to be uplifted, creating widespread tectonic instability.
Though the epicenter of the M6.1 quake near Wenping was located much further east than the M5.2 Saga quake and further away from the convergent boundary, the continental collision occurring between the Indian and Eurasian plate is nevertheless responsible.
As the Indian plate moves in a generally northwest direction relative to the Eurasian plate, areas to the east of this region develop strike-slip faulting to accommodate its movement.
This resulting fault structure then allows lateral movement on either side, allowing the Indian plate to continue its progression northwest, past the regions to the east – in much the same way the San Andreas fault allows lateral movement between the Pacific and North American plate on the US west coast.
Human-induced Quakes in Oklahoma and South Africa
The earthquake swarm centered in Oklahoma showed no signs of ceasing this week. Although not large or damaging (magnitudes ranged from 2.5 to 3.4), 20 tremors were detected within the state during the past seven days.
While this region is not immune to naturally-occurring seismic activity, hydraulic fracturing (also known as “fracking”) operations in the area continue to be the prime suspect as the cause of this ongoing regional phenomenon.
On August 5, an M5.3 quake struck in Orkney, South Africa, an area known for its intensive gold mining practices. These subterranean operations have been linked to regional earthquake activity in the past, and though yet unconfirmed, is believed to be the cause of this most recent tremor.
Seismically Active Spreading Centers
The Mid-Atlantic Ridge, a divergent plate boundary where plates on either side are moving away from one another (the North American and Eurasian plates in the north and the South American and African plates in the south) saw three quakes this week, ranging from M4.7 to M5.5.
The Mid-Indian Ridge, which separates the Indo-Australian plate from the African plate, experienced an M5.0 on August 2 as the plates continue their divergence from one another.
Seismic Activity This Week
This week’s seismic activity provides excellent examples of how earthquakes are generated from the variety of configurations of plate boundaries. As plates converge, diverge or slip past one another, these movements from within the Earth also serve as a reminder of the dynamic nature of the planet’s tectonic processes.