The 1932 Changma earthquake occurred at 10:04:27 local time (02:04:07 UTC) on 25 December. With an estimated magnitude of 7.6 on the surface wave magnitude scale, and a maximum felt intensity of X (''Extreme'') 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 ef ...

, the quake destroyed 1,167 houses and caused 275 to 70,000 deaths and 320 injuries.

Tectonic setting

The

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

was located close to the northern margin of the

Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Ti ...

. This area of thickened crust is a result of the ongoing collision of the

Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...

with the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent an ...

. The way in which this zone accommodates the collision remains unclear with two end-member models being proposed. The first regards the crust as being made up of a mosaic of strong blocks separated by weak fault zones, the microplate model. The second regards the deformation as being continuous within the mid to lower crust, the continuum model. The change in width of the deformed zone along the collisional belt, with the narrow zone of western Tibet compared to the main part of the Tibetan Plateau, is explained as either lateral escape to the east along the

Altyn Tagh Altyn-Tagh (also Altun Mountains, Altun Shan; , Pinyin: ''A'erjin Shan'', Wade–Giles: ''A-erh-chin Shan;'' Uyghur'':ئالتۇن تاغ'') is a mountain range in Northwestern China that separates the Eastern Tarim Basin from the Tibetan Plate ...

and

Karakorum Karakorum ( Khalkha Mongolian: Хархорум, ''Kharkhorum''; Mongolian Script:, ''Qaraqorum''; ) was the capital of the Mongol Empire between 1235 and 1260 and of the Northern Yuan dynasty in the 14–15th centuries. Its ruins lie in t ...

faults in the microplate model or as the effect of the rigid Tarim Basin block causing heterogeneous deformation within a generally weaker lithosphere in the continuum model. At its northern end, the Altyn Tagh fault progressively loses displacement by its interaction with a series of WNW–ESE trending structures, mostly with components of reverse displacement and sinistral (left lateral) strike-slip. The Changma fault is one of those structures.

Damage

The region stricken by this earthquake included the entire

Changma Basin The East Asian Monsoon is a monsoonal flow that carries moist air from the Indian Ocean and Pacific Ocean to East Asia. It affects approximately one-third of the global population, influencing the climate of Japan, the Korean Peninsula, Taiwan, C ...

and the western part of the

Hexi Corridor The Hexi Corridor (, Xiao'erjing: حْسِ ظِوْلاْ, IPA: ), also known as the Gansu Corridor, is an important historical region located in the modern western Gansu province of China. It refers to a narrow stretch of traversable and rela ...

Gansu province Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibet ...

. The greatest damage occurred in Changma. In Gaotai, Jinta, Anxi and Dingxin part of the city walls and some buildings collapsed and many houses were damaged. In the town of Changma all 800 families were affected, 270 people died and at least another 300 were injured; deaths were also recorded in Gaotai (3) and Jinta (2).

Characteristics

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where th ...

of about 116 km was identified after the earthquake, including five separate fault segments, the largest rupture observed for a reverse-slip event in Asia in the twentieth century. Four of the segments that ruptured were reverse faults, the fifth was a strike-slip fault. Vertical offsets of more than a metre were observed on most of the segments, with a maximum of 5 m.

Seismic hazard implications

The 1932 Changma earthquake shows that apparently separate mapped intracontinental reverse faults may rupture simultaneously in an earthquake. Estimates of the

seismic hazard A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and incl ...

in an area based on the rupture of single reverse faults may lead to a major underestimate of the magnitudes of the largest possible earthquake.

References

External links

* {{Earthquakes in China

Changma The East Asian Monsoon is a monsoonal flow that carries moist air from the Indian Ocean and Pacific Ocean to East Asia. It affects approximately one-third of the global population, influencing the climate of Japan, the Korean Peninsula, Taiwan, Ch ...