The 1974 Zhaotong earthquake occurred at 19:25
UTC on 10 May. It had a magnitude that was measured at 7.0 on the
moment magnitude scale[ and 7.1 on the ]surface wave magnitude
The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This ma ...
scale. It had a maximum perceived intensity of IX (''Violent'') on the Mercalli intensity scale
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
. The epicenter was located in Zhaotong prefecture in Yunnan province and it caused between 1,641 and 20,000 deaths.
Earthquake
The earthquake has been ascribed to slip on a thrust fault trending north-south with a dip of 60° to the east, from geodetic data analysis.[
The earthquake consisted of more than ten separate sub-events. The sequence began with a few shocks in the first two to three seconds with magnitudes less than 5. These were followed by several shocks approaching magnitude 7 over a period of about a minute. The areal distribution of the individual shocks showed no progression along the fault plane as would be expected with a propagating fracture.]landslide
Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...
s in the epicentral area. The bedrock
In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface mater ...
geology in the area contains rocks of almost all ages from Neoproterozoic through to Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
. Landslides were mainly confined to areas that experienced intensities of VII or greater and had slopes of moderate dip (26°–45°). In all but one case, the landslides involved Quaternary material, the exception being a slide that was controlled by bedding planes in a Permian limestone. Rock avalanches occurred on steeper slopes, particularly affecting jointed and weathered Permian limestone and Triassic sandstone/shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
sequences.
Damage
An area of about 400,000 square kilometres was affected by the earthquake. 28,000 houses collapsed and a further 38,000 were damaged. Houses with wooden frames in the epicentral area remained undamaged.[ with a further 1,600 injured.
The largest landslide formed a dam up to 30 m high across the Yangtze River, turning the valley above it into a lake.][
]
See also
* List of earthquakes in 1974
*List of earthquakes in Yunnan
This is a list of earthquakes that have occurred in or have affected Yunnan Province in China.
Major earthquakes (≥Magnitude 7.0)
Major earthquakes (Magnitude 6.0–6.9)
Moderately large earthquakes (≤Magnitude 5.9)
See also
* ...
* List of earthquakes in Sichuan
* List of earthquakes in China
References
External links
*
{{Earthquakes in China
1974 earthquakes
Earthquakes in Yunnan
1974 in China
Geography of Zhaotong
Earthquakes in Sichuan
1974 disasters in China