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2001 Gujarat earthquake
The 2001 Gujarat earthquake, also known as the Bhuj earthquake, occurred on 26 January at 08:46 am IST. The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch district in Gujarat, India. The earthquake had a maximum Mercalli intensity of XII (Extreme).
The intraplate earthquake measured 7.6 on the moment magnitude scale and occurred at a depth of 17.4 km (10.8 mi). The earthquake killed at least 20,023 people, injured another 166,000 and destroyed about 400,000 buildings in Gujarat, India and Sindh, Pakistan. The vast majority of deaths and damage were observed in Kutch district, while nearly 1,600 additional deaths occurred in the cities of Ahmedabad, Rajkot, Jamnagar, Surendranagar, Surat, Gandhinagar and Vadodara.
Gujarat lies 300–400 km from the plate boundary between the Indian plate and the Eurasian plate, but the current tectonics are still governed by the effects of the continuing continental collision along this boundary. During the break-up of Gondwana in the Jurassic, this area was affected by rifting with a roughly west–east trend. During the collision with Eurasia the area has undergone shortening, involving both reactivation of the original rift faults and development of new low-angle thrust faults. The related folding has formed a series of ranges, particularly in central Kutch.
The focal mechanism of most earthquakes is consistent with reverse faulting on reactivated rift faults. The pattern of uplift and subsidence associated with the 1819 Rann of Kutch earthquake is consistent with reactivation of such a fault.
The earthquake was caused by movement on a previously unknown south-dipping fault, trending parallel to the inferred rift structures. No major surface ruptures were associated with the shock, classifying it as a blind thrust earthquake. Lateral spreading was widely reported and strike-slip faulting was observed at Bharodia and Manfara. On the moment magnitude scale, the International Seismological Centre said it measured a magnitude of 7.6, while the United States Geological Survey put it at 7.7.
A finite fault model from the USGS estimated that the earthquake rupture had an area of 141 km (88 mi) x 18 km (11 mi), lasting approximately 25 seconds. Slip was mostly concentrated around the northern patches of the rupture, with a maximum slip of 9.695 m (31.81 ft) recorded in the village of Chobari. The full rupture also extended through the cities of Bhuj and Rapar, although slip in these areas was extremely minor. Despite the large magnitude and rupture area, no visible surface ruptures could be identified in the epicentral area.
The earthquake had a maximum Modified Mercalli intensity of IX-XII (Violent-Extreme). It also registered X (Devastating) on the Medvedev–Sponheuer–Karnik scale, with the maximum intensity observed over an east-northeast elongated zone of approximately 2,100 km2 (810 sq mi); much of Gujarat recorded tremors of VII (Very Strong) or higher. Ahmedabad recorded a maximum peak ground acceleration of 0.11 g. Shaking from the earthquake lasted several minutes, with stronger ground motion lasting at least 85 seconds. Numerous rockfalls and landslides occurred in the Bhuj and Bhachau areas. There was extensive evidence of soil liquefaction at the Rann of Kutch, Banni Grasslands Reserve, coastal areas of the Gulf of Kutch and numerous sand boils in dry lakebeds northeast of Bhuj. After the earthquake, these sand boils had fountains of saline groundwater rising 2–3 m (6.6–9.8 ft). Widespread subsidence and lateral spreading also occurred at Kandla and Navlakhi ports.
By 31 December 2001, there were 107 aftershocks exceeding Mw 4.0 which were recorded by the USGS, including 9 events measuring Mw 5.0 or higher; most aftershocks occurred south of the epicenter near Bhachau. The largest aftershock occurred on 28 January, had a magnitude of Mwc 5.8 and was located 15 km (9.3 mi) west-southwest of Rapar.
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2001 Gujarat earthquake
The 2001 Gujarat earthquake, also known as the Bhuj earthquake, occurred on 26 January at 08:46 am IST. The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch district in Gujarat, India. The earthquake had a maximum Mercalli intensity of XII (Extreme).
The intraplate earthquake measured 7.6 on the moment magnitude scale and occurred at a depth of 17.4 km (10.8 mi). The earthquake killed at least 20,023 people, injured another 166,000 and destroyed about 400,000 buildings in Gujarat, India and Sindh, Pakistan. The vast majority of deaths and damage were observed in Kutch district, while nearly 1,600 additional deaths occurred in the cities of Ahmedabad, Rajkot, Jamnagar, Surendranagar, Surat, Gandhinagar and Vadodara.
Gujarat lies 300–400 km from the plate boundary between the Indian plate and the Eurasian plate, but the current tectonics are still governed by the effects of the continuing continental collision along this boundary. During the break-up of Gondwana in the Jurassic, this area was affected by rifting with a roughly west–east trend. During the collision with Eurasia the area has undergone shortening, involving both reactivation of the original rift faults and development of new low-angle thrust faults. The related folding has formed a series of ranges, particularly in central Kutch.
The focal mechanism of most earthquakes is consistent with reverse faulting on reactivated rift faults. The pattern of uplift and subsidence associated with the 1819 Rann of Kutch earthquake is consistent with reactivation of such a fault.
The earthquake was caused by movement on a previously unknown south-dipping fault, trending parallel to the inferred rift structures. No major surface ruptures were associated with the shock, classifying it as a blind thrust earthquake. Lateral spreading was widely reported and strike-slip faulting was observed at Bharodia and Manfara. On the moment magnitude scale, the International Seismological Centre said it measured a magnitude of 7.6, while the United States Geological Survey put it at 7.7.
A finite fault model from the USGS estimated that the earthquake rupture had an area of 141 km (88 mi) x 18 km (11 mi), lasting approximately 25 seconds. Slip was mostly concentrated around the northern patches of the rupture, with a maximum slip of 9.695 m (31.81 ft) recorded in the village of Chobari. The full rupture also extended through the cities of Bhuj and Rapar, although slip in these areas was extremely minor. Despite the large magnitude and rupture area, no visible surface ruptures could be identified in the epicentral area.
The earthquake had a maximum Modified Mercalli intensity of IX-XII (Violent-Extreme). It also registered X (Devastating) on the Medvedev–Sponheuer–Karnik scale, with the maximum intensity observed over an east-northeast elongated zone of approximately 2,100 km2 (810 sq mi); much of Gujarat recorded tremors of VII (Very Strong) or higher. Ahmedabad recorded a maximum peak ground acceleration of 0.11 g. Shaking from the earthquake lasted several minutes, with stronger ground motion lasting at least 85 seconds. Numerous rockfalls and landslides occurred in the Bhuj and Bhachau areas. There was extensive evidence of soil liquefaction at the Rann of Kutch, Banni Grasslands Reserve, coastal areas of the Gulf of Kutch and numerous sand boils in dry lakebeds northeast of Bhuj. After the earthquake, these sand boils had fountains of saline groundwater rising 2–3 m (6.6–9.8 ft). Widespread subsidence and lateral spreading also occurred at Kandla and Navlakhi ports.
By 31 December 2001, there were 107 aftershocks exceeding Mw 4.0 which were recorded by the USGS, including 9 events measuring Mw 5.0 or higher; most aftershocks occurred south of the epicenter near Bhachau. The largest aftershock occurred on 28 January, had a magnitude of Mwc 5.8 and was located 15 km (9.3 mi) west-southwest of Rapar.