Tara Nidhi Bhattarai, a PhD in Engineering Geology from Kyushu University, Japan is Associate Professor at the Department of Geology at Tri-Chandra Campus. He is one of very few Nepali experts on earthquakes and disaster management. Mahabir Paudyal and Kosh Raj Koirala met him Tuesday evening.

How would do you describe the April 25 earthquake and the subsequent aftershocks?
Geologists have been predicting an eight-Richter-scale earthquake in Nepal for a long time. Since the April 25 quake measured 7.9, there is less chance of another big earthquake hitting the region between Pokhara and Kathmandu anytime soon. However, the region between Pokhara in the east and Dehradun (India) in the west could see a big one anytime. This belt is extremely vulnerable.

Will it be right to say that a major earthquake in Kathmandu has been averted for another 80-90 years?
That's a dangerous prediction. Even if earthquake strikes the region beyond Mahakali we will still feel tremors. So it is not true that the April 25 quake completely negates the possibility. We need to understand that the whole of Himalaya (which in geology refers to the region from Burma to Tibet) is earthquake prone. In a way, the Himalaya, including our country, was born from one big earthquake. So there will be earthquakes as long as there is earth. Studies show that it takes around 100 years for a mega-earthquake (above 8 Richter scale) to hit the region. So, with this logic, we can say that there won't be big quake for the next 90 to 100 years. Yet we cannot be sure. We better be prepared for anything.

How can we better prepare?
Make earthquake resistant houses. Our bridges, dams, roads and hydro power plants should be made in such a way they do not suffer great damage from earthquake.

How do we understand the series of aftershocks we have felt over the past one week?
Generally, an earthquake hits in one of two ways. There could be minor tremors before a great quake. We call it pre-shocks. Or a big quake is followed by a series of tremors, or aftershocks. We had 7.9 Richter scale quake on April 25, followed by 6.9 the next day. Now it is coming to 5 and 4. We need not worry. But we must be alert if the aftershock increases in magnitude.

In a way, the recent quake is similar to that of 2005 Pakistan earthquake. A 7.6 Richter scale earthquake had hit the country then. But aftershocks continued for a month. The same might happen here. We had aftershocks even after the 1934 great earthquake. Historical evidence suggests aftershocks lasted for at least six days.

Why do we have aftershocks?
The quake has lifted up nearly 300 kilometer of earth surface; in the process there have been many cracks and ruptures. Imagine a falling tree. If the big earthquake is the event of the big tree falling down, the small twigs and branches that are broken in the process represent aftershocks. These cracks and ruptures will take time to get stable. That is nothing to worry about. However, one also needs to understand that sometimes the scale of aftershocks fluctuates. It is a sign of concern if their magnitude goes increasing.

The general impression is Kathmandu is more vulnerable than other parts of the country. Is that the case?
Earthquake ruptures land in one area but sends tremors everywhere. Areas with rocks do not shake as much. The hills surrounding Kathmandu valley are rocky so they are relatively safer. Kathmandu is a different land. Its soil is like curd in a bowl. When the earthquake hits, it churns in the curd. Now imagine what happens. The curd undergoes rapid liquefaction. This is why Kathmandu is more at risk. There is another reason as well. Kathmandu stands over water. When there is an earthquake, the level of underground water rises. There are cases of water levels rising in wells and roar-pump taps in Kathmandu. Kathmandu's ground may have been badly disturbed by the recent quake. This is why some houses have collapsed.

Are you suggesting that quality of soil determines longevity of houses?
Exactly. Therefore it is important to lay foundation stones only after testing the soil. If your soil is rough and sandy (as in riverbanks), that's good. If it's just sandy, still good enough. But if it is fine sand or alluvial soil, that could be dangerous. Again there is nothing to worry about. If we test foundation soil and build houses only by consulting engineers, our houses will be safe. Some houses in Kathmandu that collapsed must have been built either on the wrong kind of soil or they must have flouted the building code.

How do you know if your piece of land has the right kind of soil?
It's not difficult. Japan International Cooperation Agency (JICA) has carried out a study in coordination with Ministry of Home Affairs and identified and mapped the areas prone to liquefaction in Kathmandu. The map clearly shows liquefaction areas on riverbanks. This map will be helpful.

But a number of houses on riverbank are intact while those away from rivers have suffered damages.
There is another side to it. This is probably because we in Kathmandu have been extracting underground water for several years. Perhaps we have pushed the water level down by 70 to 80 feet. This otherwise suicidal move perhaps saved Kathmandu. The earthquake could not raise water level, which would otherwise have weakened foundation and caused the buildings to collapse. The timing also saved us. If it were rainy season the water level would have risen more and there would have been greater liquefaction and greater damages.

The quake has shaken up all physical structures. Like I said, it has churned the soft soil of Kathmandu Valley and left it prone to liquefaction. As for hilly districts, it has created several ruptures and cracks. When it rains, rainwater seeps into those cracks, triggering landslides. There is high chance of major landslides in earthquake affected areas this monsoon.

What can we do then?
The government must identify those soft areas and alert the people at the earliest. Who knows, even makeshift tents stand over precarious land? Experts need to identify safe areas and resettle people there. Kathmandu is relatively safe from landslides but houses on slopes may be vulnerable, if cracks have appeared and if rainwater seeps in. Those who have their houses on the slopes and riverbanks in Kathmandu must be alert this monsoon.

What kinds of houses are safe?
That's a difficult question for geologists. We study patterns, causes and nature of earthquakes. But we alone cannot assess post-earthquake scenario. Structural engineers are the right authorities to explain how earthquake affects houses and whether existing houses are safe. But based on my studies and experiences I can say your house is safe if it is supported by pillars and beams, and if there are no cracks on them. Don't worry if there are cracks on the wall; it is pillars and beams that support your house not the walls. Again, like I said, we geologists can tell you about magnitude, aftershock, pre-shock, prediction and safety measures regarding earthquake. Regarding building safety, only structural engineers can tell you what to do.

Houses are built on soil. So even structural engineers may not be able to tell you everything. In that case, you need to consult engineering geologists and geo-technical engineers as well. Five specialists—geologists, structural engineers, geo-technical engineers, earthquake engineers and seismologists—are needed to make proper assessment of building safety. Thus I ask media houses to bring these five actors together for roundtable discussion so that they can address the concerns and anxieties of common people.

Those staying in high-rise apartment buildings are really scared. Do they face greater danger?
It's not true that Kathmandu cannot have high-rise buildings. If they have been built after soil testing and by strictly observing building codes, they should be safe. Our problem is we have no credible body to see that these norms are complied.

What can the government do to help us better prepare for earthquakes?
Everyone knew a big earthquake was due. Even Prime Minister and the President would speak about it and demonstrate duck-cover-hold in mock sessions. Sadly, when the earthquake hit, Home Minister and President were among the first people to rush out. This also helped spread panic.

The rich of Kathmandu rushed to open grounds of government schools which are otherwise mostly neglected. This should serve as a wake-up call. It's time to raise taxes for developing open spaces in the valley. We are always vulnerable. Post-quake discussions alone won't help. We have no university and research agencies to study earthquakes. We need to have a separate research body like, say Earthquake Research Institute, for conducting studies and raising awareness. Pakistan has done this. We should as well.

source/photo: republica,6 may 2015