1932 Changma earthquake
Encyclopedia
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 (Intense) on the Mercalli intensity scale
, the quake destroyed 1,167 houses, and 275 people were killed with a further 320 injured.
was located close to the northern margin of the Tibetan Plateau
. This area of thickened crust is a result of the ongoing collision of the Indo-Australian Plate
with the Eurasian Plate
. 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- and Karakorum 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.
in Gansu province.
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).
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.
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
) on 25 December. With an estimated magnitude of 7.6 on the surface wave magnitude
Surface wave magnitude
The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost layers of the earth...
scale, and a maximum felt intensity of X (Intense) on the Mercalli intensity scale
Mercalli intensity scale
The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake , which is a measure of the energy released...
, the quake destroyed 1,167 houses, and 275 people were killed with a further 320 injured.
Tectonic setting
The earthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
was located close to the northern margin of the Tibetan Plateau
Tibetan Plateau
The Tibetan Plateau , also known as the Qinghai–Tibetan Plateau is a vast, elevated plateau in Central Asia covering most of the Tibet Autonomous Region and Qinghai, in addition to smaller portions of western Sichuan, southwestern Gansu, and northern Yunnan in Western China and Ladakh in...
. This area of thickened crust is a result of the ongoing collision of the Indo-Australian Plate
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
with the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
. 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- and Karakorum 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 and the western part of the Hexi CorridorHexi Corridor
Hexi Corridor or Gansu Corridor refers to the historical route in Gansu province of China. As part of the Northern Silk Road running northwest from the bank of the Yellow River, it was the most important route from North China to the Tarim Basin and Central Asia for traders and the military. The...
in Gansu province.
The greatest damage occurred in Changma. In Gaotai
Gaotai County
Gaotai County is an administrative district in Gansu, the People's Republic of China. It is one of 58 counties of Gansu. It is part of the Zhangye prefecture, with the city of the same name being the prefecture seat...
, Jinta
Jinta County
Jinta County is an administrative district in Gansu, the People's Republic of China. It is one of 58 counties of Gansu. It is part of the Jiuquan prefecture, with the city of the same name being the prefecture seat. Its postal code is 735300, and in 1999 its population was 137,816...
, Anxi
Guazhou County
Guazhou County , formerly Anxi County , is an administrative district in Gansu, the People's Republic of China. It is one of 58 counties of Gansu...
and Dingxin
Dingxing County
Dingxing County is a county under the jurisdiction of the prefecture-level city of Baoding in Hebei province, People's Republic of China. It has an area of 714 km² and 600,000 inhabitants.*area code: 0312*postal code: 072650-Administrative Divisions:...
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
A surface rupture 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 hazardSeismic hazard
Seismic hazard refers to the study of expected earthquake ground motions at the earth's surface, and its likely effects on existing natural conditions and man-made structures for public safety considerations; the results of such studies are published as seismic hazard maps, which identify the...
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.