2017 Komandorski Islands earthquake
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  | |
| UTC time | 2017-07-17 23:34:13 |
|---|---|
| ISC event | 610785483 |
| USGS-ANSS | ComCat |
| Local date | July 18, 2017 |
| Local time | 11:34:13 |
| Duration | > 80 seconds |
| Magnitude | 7.8 Mw[1] |
| Depth | 8.4 km[1] |
| Epicenter | 54°26′35″N 168°51′25″E / 54.443°N 168.857°E |
| Fault | Bering Fracture Zone |
| Type | Strike-slip (Dextral) |
| Areas affected | Russia |
| Total damage | None |
| Max. intensity | MMI VII (Very strong) |
| Tsunami | 0.3 ft |
| Foreshocks | Yes |
| Aftershocks | Yes |
On July 18, 2017, an earthquake struck near the Komandorski Islands, east of the Kamchatka Peninsula in the Bering Sea at 11:34 local time (23:34 UTC on July 17). Although there were no casualties from this earthquake, it was notable for a rare characteristic known as supershear, and is one of the few times a large supershear earthquake has been observed. It was preceded by a few foreshocks months earlier, and aftershocks that continued for nearly six months.[2]
The Mw 7.8 earthquake nucleated along the Bering fracture zone, parallel to the Aleutian Islands arc and Aleutian Subduction Zone. This is a transform fault between the Pacific and North American plates, and in between, the Komandorski Sliver. Formed from the highly oblique movement of the Pacific plate, the direction of convergence is nearly parallel to the trench at 7.8 mm/yr.[3] The Bearing Fracture Zone acts as a back-arc fault to accommodate the lateral motion at a rate of 5.1 mm/yr. The same fracture zone may have produced a similar sized earthquake in 1929 close to the Near Islands of Alaska.[4] Energy released from this earthquake was sufficient to accommodate strain built-up since the last earthquake on that section of fault in 1858.[3]
Earthquake
Initially registering a magnitude 7.4, the earthquake was quickly revised to a 7.7 by the US Geological Survey.[5] No loss of life or property damage was reported following the earthquake due to the remoteness of the event, although it could be felt by people. Shaking intensities V to VI was felt at Bering Island, and in Petropavlovsk-Kamchatsky, was felt as II.[6] Tsunami warning was issued but cancelled a few less than two hours later.[7] A non-destructive tsunami of 0.3 feet was observed.[8] The small tsunami was attributed to the lack of vertical displacement during the event.
The earthquake focal mechanism was almost pure strike-slip, and the entire rupture process took more than 80 seconds.[2] Displacements of 4 to 8.5 meters along the upper 15 km of the crust, with evidence of extension at 20 to 30 km depth.[3] Evidence of supershear was discovered when researchers realized that rupture velocity of this event increased from 2.1 km/s to 5.0 km/s after the rupture jumped onto another segment at a step-over.[9] The rupture speed far exceeded the shear wave velocity. Its rupture length of 400 km is also one of the longest in the world for a strike-slip fault, comparable to the 1906 San Francisco and 2001 Kokoxili earthquake.[2]