Are the disasters becoming frequent?
Are you convinced that the frequency of disaster incidences is increasing?
Whatever the database, or assertion to support your views, and despite you possibly being right; I have one point to make that the available data shows that the frequency of earthquakes has not changed. On an average every year we on this earth experience one of magnitude 8.0 or more, 15 of magnitude 7.0-7.9, 234 of magnitude 6.0-6.9, 130000 of magnitude 3.0-3.9, and like that 1300000 of magnitude 2.0-2.9.
At this consistency, I really wonder if there are really more disasters taking place presently, or this is a perception created by media? I am however not an expert on it, and would therefore drop this issue right here.
Earthquake prone Himalayas
As we know from various sources including the media that movement of tectonic plates of continental dimensions fuels the earthquakes, and subduction of the India Plate beneath the Eurasian Plate makes Himalayas seismically vulnerable. Seismic records suggest that the Himalayan mountain range has experienced 6 “great earthquake” (of magnitude around 8.0 on Richter Scale) in the previous 120 years; Shillong 1897, Kangara 1905, Bihar–Nepal 1934, Assam now Arunachal 1950, Kashmir 2005, and Gorkha 2015.
You would have noticed that these “great earthquakes” are not evenly distributed along the length of the Himalayan arc, and some stretches have not experienced a “great earthquake” for a quite long time. This simply implies that the stresses getting accumulated continuously due to the plate movement in these stretches are yet to be released. Scientists call these stretches “seismic gap”, and based on the assessed unreleased stresses mark these areas with high potential of housing major earthquakes in future or as being areas of high seismic risk.
Uttarakhand: High seismic hazard
Uttarakhand is located in the seismic gap of 1905 Kangara, and 1934 Bihar–Nepal earthquakes, and Magnitude 7.5 Garhwal Earthquake of September 1, 1803 is considered the last major earthquake to hit this region. So for the previous 218 years this region has not witnessed any major seismic event.
Records of earthquakes in the region prior to Garhwal Earthquake are not available but the region would certainly have experienced seismicity before that as well, and some scientists believe that the region witnessed a major earthquake in 1720; Kumaun Earthquake.
It is important out here to understand that all earthquake induced losses are caused by damage to the structures during seismic shaking. If we could somehow rule out possibility of structures getting damaged, there would be no earthquake induced losses, and hence no cause of concern for us.
You would have also experienced with the house of cards that we used to make when young; these became increasingly unstable as we increased their height, and collapsed with the slightest vibration of the table.
The laws of physics govern the stability of all structures, small or big including the house of cards we used to build. With the increase in height both centre of gravity, and centre of mass of the structure move upward, and away from ground. For the structure to remain stable the laws of physics require that the centre of gravity, and centre of mass of the structure remain close to each other, and in close proximity to the ground. So without adequate engineering measures a tall structure is to collapse by the slightest ground vibration, and not wait for an earthquake to strike.
You would agree that all human beings learn from their experiences, and people living in the areas often witnessing seismic shaking would have witnessed tall structures getting razed to ground by earthquakes. Based on this experience the people of these regions are expected to construct only low rise houses that remain safe in an earthquake.
Tradition of multistories houses
Being aware of the seismic vulnerability of the region, I was utterly confused when I went around Uttarakhand for the first time. These people must be daredevils building four to five storeyed houses in this region, was the first impression casted on my mind.
May be, not having witnessed a major earthquake for almost 200 odd years these people have somehow lost track of their seismic vulnerability. Closer interaction, and intimacy with the masses however revealed something that was not in keeping with what I had contemplated. These people had a distinct word, chalak, in local parlance (Kumaoni) for earthquake. Moreover, there also existed several references to earthquakes in the folklores, and folksongs.
It was a reality I was experiencing; despite high seismic vulnerability the region had a tradition of multistoried houses, and except for chani (cattle sheds as they call it in local parlance) I could locate not even one single storied traditional houses in the region, and I did came across upto five storied traditional houses at several places.
I tried reconciling me that the multistoried houses so far observed by me could well be exceptions. I could not however continue with this perception for long.
What I came across next shattered all this, and I was left with no other option but to start working on it over again from scratch.
With closer interaction with the masses I realised that in both the dialects of the region, Kumaoni, and Garhwali, these people have distinct words for four different floors of the house. It was not like first, second, third and fourth floor that we are used to in English. In Kumauni these are ghot, chak, paan, and chaj while in Garhwali these are koti, manjua, baund, and baurar.
Having a separate word simply means that these words were often required; no language can afford a separate word if it is to be sparingly used.
I was thus convinced that despite being located in a seismic hazard prone region these people have tradition of multistories houses.
Antiquity of the structures
Having been convinced of the reality of multistoried houses I wanted to reassure that these houses have actually survived some major earthquake. These houses no doubt looked quite old, and the people also told that they have been living in these continuously for generations. That was however not a scientific proof of the antiquity of these houses.
I was however told that these structures have been visited on many occasions by scientists of various institutions. When some people told convincingly that these scientists have taken wooden chips of the logs used in these houses, I was assured of solving this riddle.
I could soon Google to find out that these houses were built some 1000 years before present; this is what the radiocarbon dating done by these scientists had suggested.
This revelation was a turning point for me; I now started to look at these structures with awe, and admiration. There was suddenly great respect for the artisans, masons, and craftsmen who actually planned, and constructed these. I wanted to know more about them, as also intricacies of these constructions.
Though the village elders often advised me to maintain distance for reasons more obvious to them, this passion took me closer to the local masons, and didn’t spare even a single opportunity of intermingling with them. I knew if I had to learn the intricacies of this art, I have to have their faith, and confidence. I would thus often sit with then, eat, share, and interact with them, and more importantly listen to them patiently, and attentively for long. All through, I never forgot to take detailed notes that I used to review, analyse, and finalise during the night, and mark out missing links.
Roaming around in the remote areas of the region, I observed these hill people to be very hard working. They would routinely cover tens of miles every day in this arduous terrain, just for fetching water, fodder and fuelwood as also mending their agricultural fields.
There certainly seemed some striking commonality in most habitations of the region, apart from construction style, and building material. I was certainly missing something despite having the feel of it.
It suddenly popped up one day while I was discussing about foundation with one of the seasoned masons who was till that time working in traditional material only. I clearly remember him having told me that foundation was dug till a dal (hard rock in local parlance) was encountered.
I felt like calling Eureka! But for a few exceptions, these habitations were all located over hard rock, and at a relatively higher elevation.
In depth scrutiny now brought forth that both sources of water, and agricultural fields were invariably at a considerable distance from the habitations.
The fields over which these people traditionally practiced agriculture were either alluvial terraces, or fields developed over colluvial deposits. The former are invariably located on the lower slopes in the proximity of streams, and rivers while the latter were developed on the middle slopes where the debris generated by landslides tends to deposit, and stabilize.
Likewise the water of streams, and rivers was available at the lower slopes of the valley while the seepages that these people developed into dhara and naula were located around the middle slopes of the valley, around the slope break.
Interaction with structural engineers made me aware that the impact of seismic shaking was relatively gentler over the hard rocks as compared to that over soft soil, and landfill areas due to restricted secondary amplification of seismic waves.
Knowledge or coincidence
This convinced me that the decision of these people to settle down over firm rock at higher elevations that involved routine hard labour for fetching water, and mending fields was not a mere coincidence. It was a well thought of, and planned decision aimed at ensuring safety of the community, and according priority to safety over convenience, and comfort just reflected their farsightedness.
Aristotle (384-322 BC) had told that the impact of earthquakes was more over soft soil as compared to that over firm ground.
There however exists no evidence to prove that these people also knew this fact, and their decision to settle down over firm rocks was backed by this knowledge.
But then, there also exists nothing to negate that these people were aware of differential impact of earthquake waves, and this peculiar settlement pattern is just a coincidence.
May be this is right, but then it is hard to conceive so many coincidences.
In such a situation, despite being fully aware that there could be many other factors influencing the decision to settle over higher elevations, it would be uncouteous if I do not give credit to the ingenuity of these people.
I therefore suggest that like Aristotle these people were also aware that earthquake impact is relatively less over hard rocks, and it is based on this knowledge that they deliberately chose to settle at higher elevations. The burden of proving this lies entirely on us, and I am sure our scientists would do so very soon, and affirmatively.