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| date = | time = 04:48:02 UTC | duration = | magnitude = 6.2 Ms〔 | depth = | location = | type = Strike-slip | affected = Montana, United States | damages = | intensity = VIII (''Severe'') | pga = | tsunami = | landslide = | foreshocks = | aftershocks = 6.0 Ms Oct 31 at 18:37 | casualties = 4 (2 from the mainshock and 2 from the aftershock of October 31) }} The 1935 Helena earthquake occurred at in Montana, with an epicenter near Helena.〔 It had a magnitude of 6.2 on the surface wave magnitude scale and a maximum perceived intensity of VIII (''Severe'') on the Mercalli intensity scale. The temblor on that date was the largest of a series of earthquakes that also included a large aftershock on October 31 of magnitude 6.0 and a maximum intensity of VIII.〔 Two people died in the mainshock and two others died as a result of the October 31 aftershock. Property damage was over $4 million.〔 == Tectonic setting == Helena lies within the northern part of the ''Intermountain Seismic Belt'' (ISB). This area of relatively intense seismicity runs roughly north-south from northwestern Arizona, through Utah, Idaho and Wyoming, before dying out in northwestern Montana.〔 It shows a marked deflection to the northwest near Helena, where it intersects with the Lewis and Clark fault zone, a zone of older WNW-trending faults.〔 The ISB is characterised by normal faulting of late Quaternary age, indicating active extensional tectonics, as recognised throughout the Basin and Range province to the south. The focal mechanism of the two largest earthquakes of the 1935 sequence are consistent with right lateral strike-slip faulting on faults similar in trend to two major mapped NW-SE faults, the Bald Butte and Helena Valley Faults.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「1935 Helena earthquake」の詳細全文を読む スポンサード リンク
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