Two shallow M5.9 earthquakes hit off the coast of southern Oregon, U.S. at 07:52 and 08:17 UTC on June 4, 2021, at a depth of 16.6 km (10.3 miles) and 14.5 km (9 miles), respectively. They were located around 12 km (7.4 miles) from each other and followed by 5 moderately strong aftershocks over the next 15 hours. 13 M6+ earthquakes have occurred within 200 km (124 miles) in the last 50 years. The largest of which was a M7.2 earthquake on June 15, 2005.
These earthquakes occurred as the result of shallow strike-slip faulting within a deformed section of the southernmost oceanic crust of the Juan de Fuca plate, commonly called the Gorda plate, west of the Cascadia subduction zone, the USGS said.
Focal mechanism solutions indicate that rupture occurred on either a left-lateral northeast-southwest-striking fault or on a right-lateral southeast-northwest-striking fault. Near the location of the earthquakes, the Juan de Fuca plate moves to the northeast relative to the North America plate at a velocity of about 30 mm (1.18 inches) per year.
"Earthquakes are common in the Gorda plate, which is subjected to internal deformation originating from interactions with both the Pacific plate to the south and the North American plate to the east," USGS said.
The eastern edge of the Gorda plate subducts northeastward beneath the North American plate, while the southern edge forms a transform boundary with the Pacific plate west of the Mendocino Triple Junction. The western edge of the Gorda plate is a divergent boundary with the Pacific plate.
Image credit: TW/SAM, Google
Thirteen earthquakes magnitude 6 and larger have occurred within 200 km (124 miles) of these recent earthquakes in the last 50 years.
The largest of which was a M7.2 earthquake on June 15, 2005, that struck about 100 km (62 miles) to the south of the June 4, 2021 earthquakes.
Image credit: USGS
Featured image credit: TW/SAM, Google