A magnitude 7.8 earthquake struck off the Pacific coast of Russia in the same area where an even bigger quake hit earlier this year. A tsunami advisory has been issued.

Earthquakes of magnitude 8.5 and larger are rare beasts on our planet and only 17 have been recorded since the era of seismographs beginning in the late 19th century.

According to the Alaska Earthquake Center, the Aleutian megathrust is the primary cause of the strongest earthquakes in the region. The Aleutian megathrust is a major subduction zone fault, an area where two tectonic plates meet.

Test earthquake, tsunami and all-clear alerts would be issued at 9:21am, 9:30am and 10am respectively on Friday, aimed at improving emergency response capabilities and optimizing disaster warning systems, the Central Weather Administration (CWA) said today.

The Juan de Fuca Plate has been steadily pushing against the Pacific Coast as it slides beneath the North American Plate. But the roughly 47-million-square-mile North American Plate isn’t budging. Instead, it’s locked tightly against the Juan de Fuca’s surface.

The largest recorded earthquake in United States history was the 1964 Great Alaska earthquake, which struck on March 27, 1964, and registered magnitude 9.2 on the moment magnitude scale, according to the USGS.