Kathmandu It is said that there is no place on earth where earthquake up to magnitude 6 cannot occur. Thus, it can occur almost anywhere. But it is well known that earthquakes are most common around the edges of the great tectonic plates of the earth’s crust and earthquakes in these areas are deadly. Two-third of the continental crust is seismically active, that means about one billion people in this beautiful earth are living on seismic disaster prone area. As a record, in 1556 one earthquake in China had claimed lives of about 830,000 people. If we look at the statistics of past three centuries, more than three million people have been killed due to the earthquake and its related disasters. Earthquakes are not the manifestations of a god’s displeasure or mysterious dark forces, instead they are the shaking caused by the sudden release of strain energy in the earth’s crust that has been accumulating for decades, centuries or millennia. More than 90 per cent of earthquakes occur between tectonic plates — the giant, constantly moving puzzle pieces of rock that support all continents and ocean basins. Each year nearly 1.5 million earthquakes greater than magnitude 2 are recorded around the world. Most are so small that only sensitive seismometers can detect them. However, a few dozen earthquakes strike each year that are large enough to inflict loss of life, property and economic activity. Despite continuous and great effort made by scientists and non-scientists around the world, there is no reliable method of predicting exactly where and when destructive earthquakes will occur. Best known for levelling buildings, bridges and other types of structures, large earthquakes often induce other secondary effects like landslides, tsunamis, soil liquefaction, and structure fires that add to the fatalities and destruction. The significant damage by an earthquake also depends on factors such as distance from the earthquake source, building construction standards, local geological structure, level of public awareness, and preparedness. Due to its geographical and geological setting, Nepal is susceptible to multiple natural hazards — floods and landslides during the monsoon, wildfires in the dry season, glacial lake outbursts, and of course, earthquakes, which can happen at any time and season. The 2,500 km long arc of the Himalayan range results from the collision of the Indian and Eurasian tectonic plates, which started around 45 million years ago. Precision Global Positioning System (GPS) surveys of the Nepal Himalaya conducted by the National Seismological Centre and California Institute of Technology show the Indian plate being thrust under the southern portion of the Eurasian plate at about 20 mm per year and loading strain on a wide zone of the Eurasian plate that lies under the highest peaks of the Himalayas. All these evidences show that earthquakes are the fact of life in Nepal. Our country has notorious earthquake history. Numerous people have been killed by earthquake and earthquake-related disasters like tsunami, landslides et cetera. Fortunately Nepal doesn’t have risk of tsunami and volcano. The great 1255 earthquake in the eastern Nepal is the oldest well documented earthquake in Nepal. As mentioned in the history, this earthquake claimed life of then king Abhaye Malla and one-third of the Nepal was perished by that earthquake. The largest earthquake that occurred in Nepal is 1505 earthquake which occurred in the western part of Nepal. We don’t have detail information about this earthquake. The magnitude is estimated about 8.5. The Bihar-Nepal earthquake of magnitude 8.3 that occurred on January 16, 1934 is well known earthquake of Nepal. It killed more than 8,615 people only in Nepal. More than 16,000 people were killed by this earthquake in Nepal and India. Recently, on April 25, 2015, at about 11:56 hrs local time (NST) Nepal was hit by a 7.6 Richter scale (7.8 Moment Magnitude) Gorkha Earthquake leading to the death of 8,856 people and 22,309 injured. More than 800,000 houses were collapsed or damaged leaving about 350,000 population homeless. The casualties and destruction was severe in the district north of Kathmandu Valley. A total of 28 districts have been affected by this earthquake, out of which emergency has been declared in the 14 severely affected districts where the damage of more than70 per cent households has been reported. At the same time the damage in Kathmandu Valley was localised and was very less than expected by this Gorkha Earthquake. Most of the damage in Kathmandu Valley was in Sankhu (northern part of the Valley), Bungmati, Gongabu Buspark area, Basantapur area, Dhapasi area and in Bhaktapur. The iconic Dharahara tower (Bhimsen Stambha) of Kathmandu was destroyed by this earthquake — it had also been destroyed in the 1990 Bihar-Nepal earthquake. Tall buildings and old buildings in Kathmandu Valley suffered more damage than small buildings. According to the data from National Seismological Centre, Department of Mines and Geology, the epicentre of the Gorkha Earthquake was Barpak of Gorkha district, which is about 70 km far from Kathmandu. The strong shaking in Kathmandu Valley was about 200 gal — which is four times less than the shaking due to the 1995 Kobe earthquake (the great Hansin-Awaji Earthquake) of magnitude 6.9 (Mw) which killed 6,434 people in Japan. In Kathmandu Valley shaking lasted for about one minute while in the Kobe earthquake, it shook for 20 seconds. The low value of acceleration and concentration of seismic energy in the low frequency wave is the main cause of low destruction in Kathmandu Valley. Kathmandu was really lucky during this Gorkha Earthquake. Similarly it was Saturday and the season was dry, unfavourable for liquefaction. Most energy from the Gorkha earthquake was concentrated in the north of Kathmandu Valley, from Gorkha district in the west to the Dolakha district in the east. The maximum earthquake energy in the Kathmandu Valley was also concentrated in the low frequency wave, which means less damage to the short structures. It is safe to say that the accumulating strain under Nepal will one day be released in the form of a devastating earthquake but, as stated earlier, the exact timing cannot be predicted. This leaves us with no alternative other than to be prepared. The awareness and risk reduction programme called ‘National Earthquake Safety Day’ started on January 16, 1998 to avoid repeating the destruction and loss of life caused by the 1934 earthquake. At present, though, the growing population, haphazard urbanisation, and unregulated construction of thousands of poorly made buildings have greatly increased the risk. How will we meet this challenge? The answer is that it will take all of us — scientists, non-scientists, government, NGOs, INGOs, private sector, media, and civil society — working together for earthquake risk reduction. It will take improvements in how we use electronic, newspaper, TV and social media to make common citizens aware of the hazard and how to prepare. It will take improving and enforcing the building code. It will take training and strengthening communities, hospitals, emergency services, Nepal Police, Armed Police Force and the Nepal Army to prepare before, and to provide rescue after the earthquake. It will require teaching students and strengthening our schools. It will also require preparing trained quick response team and quick rescue team. There is much work to do. This is the message from the April 25, 2015, Gorkha Earthquake also. Let’s intensify the integrated effort to spread awareness and prepare before it is too late, and also concentrate on the work of reconstruction as per the theme of this year’s 18th earthquake safety day — ‘Baishakh 12 Ma Gaihalyo Bhuinchalo, Surakhsit Pun Nirmanma Jutne Aba Hamro Palo’. (The author is the Chief at National Seismological Centre, Department of Mines and Geology)