Natural Hazards and Disasters: Nepal/Gorkha Earthquake kills over 7000

On 25^th April 06:11 (UTC) a shallow (15 km) magnitude 7.8 earthquake struck 34 km (21 miles) ESE of Lamjung in Nepal causing devastation. The earthquake was felt as far away as southern India including Karnataka and Kerala, Bangladesh, Pakistan, Bhutan and south western China including Tibet.

Location of the earthquake (Source: USGS)

A total 7250 people have been confirmed dead on 3^rd May and the number of fatalities keeps rising everyday. The majority of deaths have occurred in Nepal and a further 100 people have been killed in India (78), China/Tibet (25) and Bangladesh (4). In Nepal the worse affected district is Sindhupalchok where 3,360 fatalities have been confirmed. 14,021 people have also been injured including 200 in Bangladesh, 383 in China and 288 in India.

The earthquake triggered an avalanche on Mount Everest which claimed 19 lives at the base camp. Several climbers had to be rescued by helicopters. It has not been confirmed whether the route will reopen or remain closed for climbers since extensive damage has been caused. Another avalanche triggered by the earthquake destroyed the entire village of Langtang leaving 250 people missing.

Deaths and injuries by districts on 1 May (Source: MapAction)

The earthquake has also triggered several landslides, of which the ones reported are shown on the map below. Landslides have not only damaged buildings and infrastructure but have also caused temporary dams in rivers which could cause floods downstream when they fail. Glacial lakes may also pose a risk due to the effects of the earthquakes and landslides which could have weakened them leading to sudden draining in the future. Further concerns are growing regarding potential fatal landslides which could be triggered during the monsoon next month.

Reported Landslide Locations (Source: Pacific Disaster Center)

Langtang Valley Landslides and damaged buildings (Source: Pacific Disaster Center)

The capital Kathmandu located 77 km (48 miles) from the earthquakes epicentre has been severely impacted. Apart from damage to buildings and infrastructure, Kathmandu Durbar Square, a UNESCO World Heritage Site has been destroyed along with numerous temples built decades and centuries ago. Dharahara tower built in 1832 has also been destroyed and caused the death of an estimated 180 people.

Numerous villages in the surrounding remote areas have suffered catastrophic devastation; some have been entirely lost by the event.

Severity of Districts (Source: United Nations)

According to officials 160,786 buildings have collapsed and 143,642 have been damaged. This figure may rise and be confirmed as further damage assessments are carried out over the next few weeks. The Government is projecting that the number of destroyed buildings could total 500,000.

Some reports suggest ¾ of buildings in the country have been left unsafe. In Gorkha and Sindupalchowk, the worse affected districts, estimates suggest 90% of houses have been destroyed and in Dhading, Dolakha, Rasuwa and Nuwakot districts more than 80% of houses have been destroyed. Buildings have also been damaged or destroyed in neighbouring countries such as Bihar and Odisha in India. According to the Government 1383 schools have also been destroyed or damaged in the 26 districts.

Several villages have not been accessed yet due to landslides, damaged and destroyed infrastructure and lack of communication. It is likely that the number of fatalities and damaged buildings will increase over the next few days as the true scale of the disaster becomes clear.

Collapsed and damaged public buildings by district (Source: MapAction)

Collapsed and damaged government buildings by district (Source: MapAction)

Preliminary damage assessments (Source: Pacific Disaster Center)

Search and rescue efforts are now beginning to slow down as the likelihood of finding survivors is very low. Many have been pulled out alive from the rubble days after the earthquake. On 3^rd May a 101 year old man was found alive 7 days after the earthquake. Current concerns have now shifted from search and rescue to relief including the provision of aid to the victims.

Thousands are still in need of essentials such as shelter, food and water. Many isolated villages in the mountains have yet to receive any aid. Relief efforts have been further hampered by rain, continuing aftershocks and landslides, damaged and destroyed infrastructure including roads, power outages and lack of communication and coordination. A ban on large planes flying to the airport has posed a challenge for agencies trying to fly aid into the country. Concerns are also growing over the approaching monsoon season which could worsen the conditions.

The United Nations and its Partner organisation have stated in their report released on 3^rd May that $415 million is needed for vital humanitarian relief, 3 million people are in need of food aid and 24,000 people are currently living in temporary shelters. An estimated 28 million people have been affected by the earthquake according to the UN.

Humanitarian Infrastructure (Source: MapAction)

Aerial images released have shown the shocking destruction caused by the earthquake in Nepal. According to reports the earthquake has caused over £3.3 billion worth of damage and over £6.5 billion will be required for reconstruction. Being one of the poorest countries in the world, Nepal will require assistance to deal with the aftermath and economic cost of the disaster.

Science behind the earthquake

The earthquake was generated by a convergent/diffuse plate boundary where two continental plates (Indian and Eurasian) are colliding to form the Himalayas mountain range. The Indian plate boundary is moving northward and being subducted by the Eurasian plate at a rate of 40-50mm/year. The earthquake was a result of a thrust fault between these two plates and the fault area is an estimated ~120x80 km.

This region is one of the most seismically active regions in the world and experiences numerous earthquakes including a magnitude 8 in 1934 which resulted in 10,600 fatalities.

The map below shows the tectonic summary of the region and the shake map from the earthquake.

Tectonic summary (Source: USGS)

Cross section of slip distribution (Source: USGS)

Surface projection of slip distribution (Source: USGS)

Seismic Hazard Map (Source: USGS)

Shakemap of the earthquake showing intensity felt across the region (Source: USGS)

Community Internet Intensity Map showing the intensity felt by the public (Source: USGS)

Peak Acceleration Map (Source: USGS)

Peak Velocity Map (Source: USGS)

Satellite images acquired by ESA before and after the earthquake have shown land displacement. These images are shown below. According to the data Mount Everest shrank by about an inch and land around Kathmandu was lifted 1 metre.

(Source: European Space Agency)

Summary of the displacement (Source: Incorporated Research Institutions for Seismology IRIS)

Seissound animation from IRIS:

Animation

The link below is for Incorporated Research Institutions for Seismology. They have some very interesting technical details of the earthquake including a single fault model and some useful links:

IRIS

Aftershocks

Hundreds of aftershocks have occurred varying in size after the main earthquake including a magnitude 6.6 located 49km (30 miles) east of Lamjung on 25^th April at 6:45 (UTC) and a magnitude 6.7 located 19km (12 miles) SSE of Kodari on 26^th April at 07:09 (UTC).

According to the USGS the probability of further aftershocks is now lower than their 27^th April forecast due to the decreasing number of occurring aftershocks at a faster rate than expected. However, even though there will be fewer, aftershocks will continue to occur over the next few weeks or even months. These may increase the risk of further damage and landslides.

The preliminary numerical forecast table below by the USGS shows that there is a 78% probability of a magnitude greater than 5 of occurring and a 14% probability of a magnitude greater than 6 occurring between 1^st and 7^th May. This information will be updated each week and can be found on their website.