1819 Rann of Kutch earthquake

Details

The earthquake lasted for two to three minutes. It was felt over an enormous area, from Chennai to Kolkata in the east, as far north as Kathmandu and as far west as Balochistan. The main shock was followed by prolonged aftershock activity, with major earthquakes continuing for at least 50 years, including one with estimated magnitude of more than 6.5 in 1846.^[4]

Maximum displacement during the earthquake is estimated at 12 m (39 ft), based on the height of the bund and the amount of subsidence to the south. Combined with a lateral extent of at least 80 km (50 mi), this gives an estimated moment magnitude of 7.7±0.2. This matches well with magnitudes estimated using both the total felt area and the area of VIII intensity.^[4] Other estimates based on intensity measurements give magnitudes as high as 8.2.^[5]

Modelling of the surface deformation indicates that the fault that slipped during the earthquake dipped to the north at between about 50°–67°. As faults that dip in excess of 50° are normally unfavourable for slip, it has been suggested that there was relatively high pore-fluid pressure developed at depth to allow this displacement to occur.^[4] There is evidence that the Indus river shifted westwards after this earthquake.^[6]

1819 damage

The towns of Kothara, Mothala, Naliya and Vinzan suffered particularly heavy damage. Anjar, Bhuj, Lakhpat, Mandvi and Tera were also severely affected.^[2] At least 1,543 people were killed in the larger towns; the number of casualties in smaller towns and villages is unknown. There was some degree of damage to buildings over most of Gujarat, including the destruction of the "shaking minarets" of the Jama Masjid in Ahmedabad. At Jaisalmer in Rajasthan, "at least 500 guests were smothered at a wedding feast".^[2]

Damming of Nara river with formation of Allah Bund and Kori Creek

Before 1819, the Nara was a massive, active freshwater branch of the Indus. It was the "main road" for trade. It flowed directly south, past Sindri Fort, and emptied into the sea through the Kori Mouth. It was deep enough for large ships and supported lush rice agriculture. The 1819 earthquake transformed a complex, organized river delta into the chaotic, marshy "wasteland" of creeks and salt lakes we see today. The Sir Creek, Vianwari Creek and the channels that became Harami Nala existed as secondary tidal spillways or smaller distributaries to the west of the Nara. They were part of the "western" delta drainage. While they might have interconnected with the Nara during heavy floods, they were distinct maritime inlets.

The most obvious topographic effect of this earthquake was the formation of a ridge about 6 m (20 ft) high, extending for 80 km (possibly as much as 150 km (93 mi)) that formed a natural dam across the Puram or Kori River.^[7][8] To distinguish it from the man-made dams that were common in the region, the uplifted area became known as the Allah Bund, or Dam of God.^[4] The mound produced had a markedly asymmetric geometry, with a shorter and steeper south-dipping margin, about 600 m wide and a dip of 0.65°, and a broader north-dipping margin over 5 km wide with a dip of only about 0.05°.^[4]

Present-day Allah Bund, just east of disputed Sir Creek in Great Rann of Kutch, has numerous mega solar projects near India–Pakistan border.

Formation of upstream Shakoor Lake

Shakoor Lake was formed north of Allah Bund with the emergence of Allah Bund and damming of Nara/Kori River system.

Formation of downstream Sindri Lake

Sindri Lake, south of the Allah Bund, with a surface area of more than 1,000 km² (390 sq mi), was formed due to subsidence of up to 3 m (9.8 ft). Initially, the lake was cut off from the river (damming further upstream had stopped the flow) and was filled with seawater. On the western margin of the Sindri Lake, a small delta (Shakoor Lake) formed from the eastern part of the larger Indus Delta. After 1826 the Nara River broke through the artificial dam and eventually broke through the Allah Bund itself, causing the Sindri Lake to become freshwater again with the waters from Shakoor Lake.^[4]

Sindhri Fort submerged in Sindri Lake

There was a local tsunami that flooded the area known as the Great Rann of Kutch immediately after the earthquake. The fort at Sindri was destroyed by the earthquake and then partly submerged by the tsunami, "forcing survivors to climb to the top of the ruins."^[4]