The 1995 Neftegorsk earthquake occurred on 28 May at 1:04 local time[4] on northern Sakhalin Island in the Russian Far East.[5] It was the most destructive earthquake known within the current territory of Russia,[6] with a magnitude of Ms7.1 and maximum Mercalli intensity of IX (Violent)[7] that devastated the oil town of Neftegorsk, where 1,989 of its 3,977 citizens were killed, and another 750 injured.[8]
Geology
This quake was not only catastrophic, but was completely unexpected: earthquakes with magnitudes greater than 6 were not known to occur in the area of northern Sakhalin Island.[9] The earthquake generated 35 km (22 mi) of observable surface rupture (46 km (29 mi) including a branching fault), with an estimated average lateral displacement of about 4 m (13 ft), but up to 8 m (9 yd) in some places.[10] This compares to 14 km (8.7 mi) of slip estimated to have accumulated on the Sakhalin–Hokkaido fault in the last 4 million years.[11] The unusual strength of this quake and length of rupturing, and the low level of seismic activity beforehand, has been attributed to the accumulation of strain over a long period of time on a locked fault segment.[12]
The event was of great scientific interest (25 papers have been published[13]) because it occurred near a poorly-known tectonic plate boundary where the Okhotsk Plate (connected with the North American Plate) is colliding into the Amurian Plate (part of the Eurasian Plate),[14] and suggests the plate boundary is associated with a north–south striking seismic belt that runs the length of Sakhalin. More precisely, this earthquake occurred on the Upper Piltoun fault (also known as the Gyrgylan'i–Ossoy fault[15]), which branches off the main Sakhalin–Hokkaido fault that runs along the east side of the island.[16]
Impact
Ninety percent of fatalities were attributed to the collapse of 17 five-story residential buildings.[17] While Western media generally attributed the collapses to allegedly poor construction and shoddy materials of the Soviet era,[18] a geotechnical study faulted a failure to accommodate the possibility of soil liquefaction in an area that was considered "practically aseismic".[19]
While apartments collapsed, other town infrastructures including schools and offices did not, but were heavily damaged. Communication, water and electrical services were disrupted. Officials said environmental consequences were expected after an oil pipeline between Okha and Neftegorsk was damaged in multiple places. Railway tracks and bridges were also destroyed or badly damaged.[20] At Okha, balconies toppled from two buildings. Many homes were cracked and furniture damaged. Villages away from the town areas were also affected.[21]
^Earth Chronicles (2017) attributes the fatality numbers to the Russian Ministry of Emergencies. The ISC, without citing a source, says "[a]s many as 1,989 people killed" (ISC-EHB Event 106336 [IRIS].) Other sources attribute the "more than 2000" number to Japanese language sources.
