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|mapsize = |caption = |date = |origintime = 23:16 UTC |duration = 5–13 seconds |magnitude = 6.4 Mw 〔 |depth = 〔 |location = |type = Strike-slip |countries affected = Baja California (Mexico) Southern California (United States) |damage = $30 million USD 〔 |intensity = IX (''Violent'') 〔 |PGA = 1.74''g'' 〔 |landslide = |foreshocks = |aftershocks = |casualties = 91 injured, no deaths 〔 }} The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time (23:16 UTC) on October 15 just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at $30 million USD. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier. The earthquake was 6.4 on the moment magnitude scale, with a maximum perceived intensity of IX (''Violent'') on the Mercalli intensity scale. However, most of the intensity measurements were consistent with an overall maximum intensity of VII (''Very strong''), and only the damage to a single structure, the Imperial County Services building in El Centro, was judged to be of intensity IX. Several comprehensive studies on the total structural failure of this building were conducted with a focus on how the building responded to the earthquake's vibration. It was one of the first heavily instrumented office buildings to be severely damaged by seismic forces. The Imperial Valley is surrounded by a number of interconnected fault systems and is vulnerable to both moderate and strong earthquakes as well as earthquake swarms. The area was equipped with an array of strong motion seismographs for analyzing the fault mechanisms of nearby earthquakes and seismic characteristics of the sediments in the valley. The earthquake was significant in the scientific community for studies of both fault mechanics and repeat events. Four of the region's known strike-slip faults and one additional newly discovered normal fault all broke the surface during the earthquake. ==Tectonic setting== The Salton Trough is part of the complex plate boundary between the Pacific Plate and the North American Plate where it undergoes a transition from the continental transform of the San Andreas Fault system to the series of short spreading centers of the East Pacific Rise linked by oceanic transforms in the Gulf of California. The two main right–lateral strike-slip fault strands that extend across the southern part of the trough are the Elsinore Fault Zone/Laguna Salada Fault to the western side of the trough and the Imperial Fault to the east. The Imperial Fault is linked to the San Andreas Fault through the Brawley Seismic Zone, which is a spreading center beneath the southern end of the Salton Sea. With the San Jacinto Fault Zone to the northwest, the Elsinore fault to the south-southwest, and the Imperial fault centered directly under the Imperial Valley, the area frequently encounters seismic activity, including moderate and damaging earthquakes. Other events in 1852, 1892, 1915, 1940, 1942, and 1987 have impacted the region. More small to moderate events of less than 6.0 (local magnitude) have occurred in this area than any other section of the San Andreas fault system. 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「1979 Imperial Valley earthquake」の詳細全文を読む スポンサード リンク
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