5.5 Magnitude Earthquake in Russia Rattled the Countryside

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Sunday in Russia, a magnitude 5.5 earthquake occurred, which rattled the remote countryside. It happened at 10:56 UTC, at 46.919°N 145.291°E and a depth of 379.4 km (235.7 mi).

The three closest cities to the quake’s epicenter were Yuzhno-Sakhalinsk, Korsakov, and Dolininsk. Each was 194 km (121 mi) away from the epicenter, so were largely unaffected by the earthquake.

The moderate earthquake’s epicenter places it in the seismotectonically active area of the Kuri-Kamchatka arc. It extends approximately 2,100 km from Hokkaido, Japan, along the Kuril Islands  and the Pacific coast of the Kamchatka Peninsula to its intersection with the Aleutian arc near the Commander Islands, Russia.

This is the area where the Pacific plate subducts into the mantle beneath the Okhotsk microplate, part of the larger North America plate. This subduction is responsible for the generation of the Kuril Islands chain, which are actually active volcanoes located along the entire arc, and the deep offshore Kuril-Kamchatka trench.

The central section of the arc is comprised of an oceanic island arc system. This differs from the continental arc systems of the northern and southern sections.

Oblique convergence in the southern Kuril arc results in the partitioning of stresses into both trench-normal thrust earthquakes and trench-parallel strike-slip earthquakes, as well as the westward movement of the Kuril forearc.

This westward migration of the Kuril forearc currently results in collision between the Kuril arc in the north and the Japan arc in the south, resulting in the deformation and uplift of the Hidaka Mountains in central Hokkaido.

The Kuril-Kamchatka arc is considered one of the most seismically active regions in the world. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the subduction zone interface between the Pacific and North America plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km.

At greater depths, Kuril-Kamchatka arc earthquakes occur within the subducting Pacific plate and can reach depths of approximately 650 km.

Large (M>7) earthquakes have frequently occurred in this region over the past century. Seven great earthquakes (M8.3 or larger) since 1900 have also occurred along the arc, with mechanisms that include interplate thrust faulting, and intraplate faulting.

Damaging tsunamis followed several of the large interplate megathrust earthquakes. These events include the February 3, 1923 M8.4 Kamchatka, the November 6,1958 M8.4 Etorofu, and the September 25, 2003 M8.3 Hokkaido earthquakes.

A large M8.5 megathrust earthquake occurred on October 13, 1963 off the coast of Urup, an island along the southern Kuril arc, which generated a large tsunami in the Pacific Ocean and the Sea of Okhotsk, and caused run-up wave heights of up to 4-5 m along the Kuril arc.

The largest megathrust earthquake to occur along the entire Kurile-Kamchatka arc in the 20th century was the November 4, 1952 M9.0 event. This earthquake was followed by a devastating tsunami with run-up wave heights as high as 12 m along the coast of Paramushir, a small island immediately south of Kamchatka, causing significant damage to the city of Severo-Kurilsk.

A large (M8.3) intraplate event on October 4,1994,occurred within the subducted oceanic lithosphere off the coast of Shikotan Island causing intense ground shaking, landslides, and a tsunami with run-up heights of up to 10 m on the island.

The most recent megathrust earthquake in the region was the November 15, 2006 M8.3 Kuril Island event. It was located in the central section of the arc.

Prior to this rupture, this part of the subduction zone had been recognized as a seismic gap spanning from the northeastern end of the 1963 rupture zone to the southwestern end of the 1952 rupture.

A great (M8.1) normal faulting earthquake two months after the 2006 event occurred on January 13, 2007 in the adjacent outer rise region of the Pacific plate. Some scientists have theorized that the 2007 event may have been caused by the stresses generated from the 2006 earthquake.

Sunday’s 5.5 magnitude earthquake pales in comparison to some of these examples of earthquakes of larger magnitude, but it rattled windows of houses located in the remote countryside, and serves as the latest example that a large earthquake can occur at any time in this highly seismic region of Russia.

Written by: Douglas Cobb

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