page_title: 1970 Tonghai earthquake
section_title: Background and tectonics
hierarchical_section_title: 1970 Tonghai earthquake / Background and tectonics
caption_attribution_description: English: The semi-urban, semi-agricultural area on the north side of Tonghai County seat. A mile-wide strip of fertile land between Tonghai's urban core and Qilu Lake's embankment is intensively farmed for vegetables. 中文（简体）‎: 云南省通海县:位于秀山西路和杞麓湖之间的蔬菜田
context_page_description: The 1970 Tonghai earthquake occurred at 01:00:41 local time on January 5 with a moment magnitude of 7.1 and a maximum Mercalli intensity of X. The strike-slip rupture originated on the Red River Fault, which had not experienced an earthquake above magnitude 7 since 1700, and affected Tonghai County, Yunnan province, China. At least 10,000 people were killed, making it one of the deadliest in its decade. The tremor caused between US$5 to $25 million in damage, felt over an area of 8,781 km². In Hanoi, North Vietnam, almost 483 km from the epicenter, victims left their homes as the rupture rumbled through the city.
  Occurring during the height of the Cultural Revolution, it was not widely publicized by the Chinese government for well over a decade. The amount of aid and finances distributed was described by the Beijing Morning Post as "pathetically small". Much of the aid provided to survivors was in "spiritual" form, including Mao Zedong badges and condolence letters. Nevertheless, the earthquake was among the first to be studied over a long term by the Chinese government.
context_section_description: Yunnan, the epicentral region, is one of the more seismically active Chinese provinces. The earliest earthquake recorded there was in the 9th century; however, moderate to strong ones have been observed since the 15th century. Since the 9th century, 32 earthquakes with a magnitude of 7 or greater have occurred in the province. Shallow strike-slip faulting is a characteristic of Yunnan quakes.
  Earthquakes in southwestern Yunnan, such as the 1970 Tonghai event, are less frequent than in other parts of the province. The Red River Fault, the fault line on which this quake is alleged to have occurred, has lacked seismological activity as a whole. Red River temblors generally rise at high angles, as shown in a 1962 Ministry of Geology report. Marking in sedimentary rocks indicate that several large earthquakes formed on the fault during the Pleistocene and Holocene epochs. Until this quake, no earthquake above magnitude 7.0 on the Richter scale had occurred on this fault since about 1700, and the fault was believed to be "dead". Since the 1970 Tonghai rupture, it is believed that the Red River fault is instead experiencing a long seismic gap similar to that of the Japan Median Tectonic Line, on which no major temblor has formed since 700 but produced massive ones during the Holocene epoch.
caption: Fertile plains around Qilu Lake in Tonghai County
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