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THE EARTHQUAKE OF 25 JANUARY 2001 IN GUJARAT, INDIA

George Pararas-Carayannis

Introduction

On 25 January 2001, a major earthquake occurred in Gujarat, a prosperous industrial and agricultural state on India's west coast, close to the border with Pakistan.

The quake was the most powerful to strike this region of India in the last fifty years. It was also the most destructive in terms of lives lost and property damage.

 

 

 

 

 

 

Earthquake Epicenter, Origin Time, Magnitude and Aftershocks

The preliminary magnitude of the earthquake was initially reported as 7.9. It was later revised to 7.7 Ms. According to the USGS, it occurred at 8:16 PM MST, Jan 25, 2001 (Jan 26 at 8:46 AM local time in India). The epicenter was at 23.40 N 70.32 E, approximately 12.5 miles northeast of the town of Bhachau and about 65 miles (110 km) NNE of Jamnagar. The quake's depth was 23.6 km. Ground motions lasted about 90 seconds. Its tensor solution is given below (source USGS)

The quake was felt in New Delhi, 600 miles (966 kilometers) away, where high rises swayed. It was also felt in Calcutta, 800 miles away, in Nepal and in coastal Bangladesh 1,200 miles (1,931 kilometers) away. Strong aftershocks (more than 300) continued to strike the Kutch district of Gujarat, in the days and weeks following the main shock. One aftershock with 5.3-magnitude had its epicenter was 12.5 miles northeast of Bhachau, a town that was badly damaged by the main quake. The aftershocks are expected to continue for many weeks and even months.

 

Death Toll and Damages

Because of its size and location, this quake was very destructive in terms of lives lost and damage to property. All the deaths occurred in India'a western state of Gujarat, near the Pakistan border. Bhuj , a coastal resort only 20 kilometers (14 miles) from the epicenter, was the worse affected town.

As many as 15,000 -20,000 people were initially reported dead but within a few days after the earthquake, the death toll kept on rising. As of 3 February 2001, the official toll had climbed to more than 30,000. However, the final death toll may never be known with certainty. At least 30,000 more people were reported as injured. This too may be an underestimate.

The quake destroyed 90 percent of the homes in Bhuj, several schools, and flattened the hospital. Considerable damage occurred also at Bhachau. In Ahmedabad, Gujarat's commercial capital and a city of 4.5 million, as many as 50 multistory buildings collapsed and several hundred people were killed. Total property damage was estimated at more than $5.5 billion.

Recent Earthquakes in India.

T
he Gujarat earthquake was the most powerful to strike India since 15 August 1950, when an 8.5 magnitude quake killed 1,538 people in the northeastern Assam state. The recent quake was also very similar to the powerful, 8.3 magnitude earthquake which struck the Gujarat region in 1919 and killed about 2,500 people. The 1919 event had ruptured the earth's surface for about 80 km long, creating a fault known as Allah Bundh (a dam created by God). This fault is slightly to the North West of the new rupture caused by the 25 January 2001 quake.

 

 

 

 

 

 

Tectonic Setting - Geological Instability of the Region.

The quake of 25 January 2001 occurred along a tectonic boundary which, as the adjacent USGS map illustrates, is characterized by high seismic activity.

This seismic boundary has been formed by the movement of the Indian tectonic plate in a north and northeast direction as it collides with the Eurasian and Arabian tectonic plates. This process has continued for millions of years as the India plate drifted northward.

Compression along this boundary resulted in a thrust or reverse type of faulting with the net result being an upward displacement of the Indian plate and the formation of the Himalayan Mountain Range and the Tibetan Plateau.

 

(USGS graphics)

 

 

 

 

The more intense seismic activity occurs by the thrust which is developing at the Himalayan foothills of India's Uttar Pradesh state, to the east. In the last hundred years eight earthquakes with magnitude of more than 6 have been recorded in the Uttar Pradesh region. These quakes resulted by the gradual shifting of the India tectonic plate beneath the Tibetan plate in the geologically young Himalayan Mountain range and along the Himalayan arc.

Most recently, on 29 March 1999, a destructive earthquake with magnitude of 6.8 struck the Kumaon hills of Uttar Pradesh,185 miles (295 kilometers) northeast of New Delhi near India's border with China. Another destructive earthquake in 1991, measuring 6.1, killed more than 1,000 people near the town of Uttarkashi in the same region.

Although not as frequent as in Uttar Pradesh, earthquakes in India's western region of Gujarat - as that of 25 January 2001 - have been more powerful and extremely destructive.

 

 

 

Tsunami Generation is not Possible in this Region.

Although the earthquake of 25 January 2001 was large and occurred near India's western coastal zone, no significant tsunami activity was expected and none was reported.

Earthquakes in this region of India result from compression due to continental-continental type of convergence, rather than from subduction of tectonic plates. Large, destructive tsunamis are usually generated from large earthquakes in zones of tectonic subduction. No subduction takes place along this tectonic boundary in India because both of the interacting blocks are continental have the same material density. For subduction to occur there must be convergence between oceanic and continental tectonic plates.

Subduction occurs because the denser oceanic plate sinks below the less dense continental plate. Most of the vertical crustal uplift from earthquakes in India occurs primarily over land areas thus seismo-tectonic coupling in this particular region is not conducive to tsunamigenesis.

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