Wednesday, May 20, 2015

Four maps which speak a thousand words...

The USGS is undeniably one of the most authoritative bodies in the world, when it comes to seismic studies. In its tectonic summary of the Himalaya and its vicinity, it states "The northward under thrusting of India beneath Eurasia generates numerous earthquakes and consequently makes this area one of the most seismically hazardous regions on Earth."
Unfortunately, the subduction zone running from Kashmir to Arunachal Pradesh (see map above or pdf file here) passes almost directly below where we live (Darjeeling-Sikkim position in above map is approximate and not from USGS).
In India, the IMD is responsible for seismicity of the region and the seismic map of India with a focus on the Darjeeling-Sikkim region is placed above.
The GSI is the nodal body in the country looking after landslide hazards and as per them, the Darjeeling-Sikkim Himalaya is amongst the most hazardous areas (see above) in the country with regard to landslides.
Dr David Petley is a world authority on landslides and we consider an honour that STH has been featured a number of times on his famous landslide blog
Placed above is his map on fatal landslides in Asia and without a doubt, he states the most fatalities  in the world due to landslides takes place along the ' southern edge of the Himalayan arc' - which is, sadly where we live.

What never ceases to amaze me is how in the face of such stark, cold scientific evidence and the huge spurt in disaster along the Himalayas, we still continue to bury our heads in the sand and think disasters can happen to everyone - except us.

Praful Rao,
Dist Darjeeling

Sunday, May 17, 2015

Nepal Earthquake: Some questions and answers from an expert regarding the 16May2015 aftershocks felt in the Darjeeling-Sikkim Himalaya

On  16May2015, we in the Darjeeling-Sikkim Himalaya felt two aftershocks and after checking their positions in the USGS map, I could not help feeling the 'epicentre' of the aftershocks had shifted eastwards towards us. I posed this question to Dr Malay Mukul of IIT Mumbai; placed below are my questions/statements (in Italics) and Dr Mukul's answers :-

1. Can't even imagine how it must be in Nepal; we in the Darjeeling-Sikkim region felt 2 aftershocks on 16May2015 (centred East of Banepa at 0920h IST and North of Ramechhap at 1704h IST).

Nepal obviously is feeling the brunt of it. Again, for a 7.3 triggered shock one would expect aftershocks typically up to 6.3. For the two events we have had the following:-

Fig 1(above): The epicentral plot of the main events and the major aftershocks associated with the Nepal 2015 Earthquake.
For 7.8 event we had 6.1, 6.6, and 6.7 aftershocks. For the 7.3 we have had 6.3 and 5.7. So far no real anomalies except that 7.8 shock triggered a 7.3 event farther east. The aftershocks associated with the 7.3 event were located near the epicenter of the 7.3 event so nothing abnormal about that. The orange event (Fig 1) was yesterday's aftershock. Pretty much within the cluster. Not suggesting that the rupture is going farther east. At least not yet!

2. What I find disturbing is the fact that the aftershock 'epicentres' SEEM to be moving from west of Kathmandu initially, eastwards towards our area.Which I think you also pointed out in yr last letter (published here). Can this be correct?

Yes! The aftershocks did tend to follow the Main Himalayan fault (MHT) from west to east. However, the map below (Fig 2) shows that apart from the Mirik event (27Apr2015), the earthquakes have been clustered within the area more or less defined by the two 7+ events. So I would say, no evidence of the aftershocks propagating farther east as of now. If aftershocks transcend the East and Central Nepal boundary, we really need to start worrying.

Fig 2: Epicentral plots of the main events and the aftershocks associated with the Nepal earthquake 2015.

3. Without being an alarmist, I do hope our administration and political leaders are aware of the possibilities and consequences should an event take place here- having served in the IAF and worked in disaster management, I believe it is better to overreact in crisis situations rather than not react at all.

I agree that we need to have a realistic disaster management plan in place in our region both in the short and the long term. That is the least we can do in the light of the fact that we have been made acutely aware of our vulnerability to big Himalayan earthquakes by the Nepal 2015 event and future projections of a 8.2 to 8.7 earthquake in our part of the Himalaya (Fig 3).

Fig 3: Darjiling-Sikkim is projected to be vulnerable to a 8.2 decollement earthquake in the future.

Praful Rao,
Dist Darjeeling

Monsoons 2015 progress and seasonal rainfall

Praful |Rao,
Dist Darjeeling

Friday, May 15, 2015

Quote of the Day and two images

"The haphazard construction of buildings scares me. People here love to encroach and have no regard of rules. They don't listen to anything."                                                                                                                                            Shri Nitish Kumar,
Chief Minister of Bihar,
talking at the 1st Bihar Conference on DRR

      Both Gangtok (Sikkim) and Darjeeling (W Bengal) are booming towns in the Himalayas, located in seismic zone IV and also in one of the most landslide prone areas of the country. I wonder whether Shri Nitish Kumar, Chief Minister of Bihar was also alluding to the many townships, all along the Himalayas which are becoming recipes for disasters?                               

Praful Rao,
Dist Darjeeling                                               

Wednesday, May 13, 2015

The 12May2015 Nepal Quake : An expert's view

Dr Malay Mukul of IIT Mumbai (Dept of Earth Sciences) hails from Kalimpong and has contributed numerous articles to this blog. After yesterday's quakes which rattled much of India, I posed him this question :
'What the hell is happening in our region?'
His reply is placed below :-
The 12May2015, 7.3 earthquake in eastern Nepal was not completely unexpected. When we had the December 2004, 9.1 Indian Ocean Earthquake, there was similar 8.6 shock in March 2005. There were also two 8+ events in 2007. So once the beast wakes up, it will take its own time to settle down. We can do precious little to change this except either to get out of the way and live in safer places in peninsular India or, if that is not an option, to live in houses that will not kill us during a great earthquake (magnitude 8 and above).
Today's 7.3 earthquake appears to be identical to the 7.8 event. Same fault plane at almost identical depths. The fault that got active is the basal decollement fault of the Himalaya called the Main Himalayan Thrust. This is a fault that is present at the base of the Himalaya and extends from Kashmir to Arunachal Pradesh. Obviously, it is present below us in the Darjeeling-Sikkim Himalaya too.
All the GPS work people have been doing in the Himalaya tells us how much this fault is slipping per year in different parts of the Himalaya. It was about 18 mm/year in the Nepal Himalaya and looks like it is about 16 mm/yr in Darjeeling-Sikkim.
Imagine a beaker filling up with water at this rate. So the question is when will the beaker completely fill up? Once it does, nature empties it out in an event like the Nepal 7.9 earthquake.After that it starts filling up again.
Two scenarios can arise because of this:
1.The 7.9 event also causes a southward lurch of the Himalaya. In the 7.9 event, the Himalaya lurched south by about 4m at 15km depth which was effectively about 1m at the surface. This lurch would also add strain (or water in our example to the beaker that is filling up nearby)to the whole
system. If this sudden addition causes the beaker to fill up in an adjacent region,another event would occur. Strictly speaking it is not an aftershock and a separate event by itself with its own aftershocks.
However, it is an event that is triggered by the main event.
2. The beaker did not empty completely during the 7.9 event. In that case the beaker simply empties itself in two events rather that one. This is definitely better than having a single bigger event. Two 7+ earthquakes are better than one 9 event!
The aftershocks of the 7.9 event showed that the earthquake rupture was propagating east. In fact today's event was very close to the region where we saw a 6.7 aftershock earlier. Would it trigger an event in Darjeeling-Sikkim? It could, if we think the first scenario was operational.
Yes! I totally agree with you, having an earthquake on the decollement or the Main Himalayan Thrust in the Darjeeling-Sikkim Himalaya would be our worst nightmare. We have been very lucky. Nature has given us three warnings!  September 2011 and the 2015 Nepal events.
All projections seem to point to us and say that we could be next. We need to get our act straight! The NIMBY (not in my backyard) syndrome may no longer be applicable to us!
Comment by Praful Rao

The writing on the wall is writ large and clear.
Increasingly and every year, disasters in and around the Himalayas (hydrological and geo) are taking a huge toll both in terms of human lives and economic losses. Yet, despite 'the three warnings' Prof Mukul talks about or the recent Kashmir and Uttarakhand disasters I am sure nothing much will change and we will continue our 'normal activities' as if nothing ever happened.

Praful Rao,
Dist Darjeeling

Sunday, May 10, 2015

Nepal 7.9R Earthquake (25Apr2015) : 96 Aftershocks (in two weeks) and still counting...

Placed above is a record of aftershocks (source) following the 7.9R earthquake which devastated large parts of Nepal on 25Apr2015. There have been 96 aftershocks till date (including the induced 5.1R quake which was epicentred around Mirik.
In order to generate awareness about quakes especially amongst the people of the Himalayas, I posed several questions to experts.
The questions and answers (in this case given by Dr Malay Mukul, of IIT Mumbai, Dept of Earth Sciences) are placed below :-
Q. Regarding the Nepal quake, why are there so many aftershocks WITHIN a short time frame - 96 within a time span of 2 weeks? The 6.8R (18Sep2011) Sikkim earthquake which we experienced never generated so many aftershocks.
A. This is normal. If you just see the aftershock records for the Bhuj earthquake,you will find that they continued for months after the main shock. You would see is a gradual decrease in the aftershock magnitude as well as number of events. Now we are mostly getting 3s and 4s.
The aftershock activity is also a function of the magnitude and depth of the main earthquake. Shallower and large magnitude main shocks create more intense aftershock activity.
The Sikkim earthquake was much lower in magnitude as well as deeper.
Q. Are the continuous rattling (aftershocks) dangerous for installations and structures already weakened by previous tremors? I know that 2 hydel projects in Darjeeling district suffered some damage during the recent quake.
A. Yes! Aftershocks tend to add to the damage created by the main shock and in many cases topple structures that were still standing at the end of the main shock. So if your building has suffered structural damage you need to make sure you either fix it or stay away from it.


Comment by Praful Rao
My thanks to Dr Malay Mukul for his prompt answers. 

Two major earthquakes have shaken in this region within the last 4 years, (6.8RSikkim and the recent Nepal one), yet we continue to flout all regulations regarding building codes and continue to construct thousands of 8-9storey buildings on these fragile mountains. I also wonder whether the numerous dams that we have constructed or are constructing  are safe?

Praful Rao,

Dist Darjeeling

Thursday, May 7, 2015

Earthquake induced landslides and the onset of the SW monsoons 2015

Placed above is a preliminary map of Earthquake Induced Landslides in Nepal (read Dr Dave Petley's report here). I am aware of a similar study being carried out by a team from the GSI in the Darjeeling-Sikkim region.
With the SW monsoons knocking at our doorsteps and almost 3000mm of rain ahead (for Darjeeling district) in the next 5months, my biggest fear is how our injured mountains will bear up with this onslaught... and don't forget that 'developmental activities' such as road building and construction work including those of dams have gone ahead over the years, at breakneck speed in this entire region, with little regard to the environment.
In this regard, placed below is an article by Ranit Chatterjee, a graduate of TISS and now a student at Kyoto University(Japan):-


In the back drop of the recent earthquake in Nepal followed by temblor in the hills with epicentre located in Mirik and keeping in mind the approaching monsoon season ,the area may get hit badly by landslide in the coming months. The occurrence of earthquakes in steep landslide-prone areas greatly increases the likelihood that landslides will occur, either because of ground shaking or shaking-caused dilation of soil materials, which allows rapid infiltration of water. The second condition is more serious for Darjeeling considering the soil and rock conditions. The Darjeeling area may see an increase in landslides as an after effect of the series of recent earthquakes and onset of rainy season. Interestingly, it has been noticed that the rainfall pattern has changed in the region. The annual rainfall though has not changed much but the rainfall pattern is no longer uniformly spread over five months but happen in concentrated pockets over a short span of time mainly in July and August. This increases the runoff and chances of landslides increases.
In order to increase the level of awareness and preparedness at both institutional and personal level following measures can reduce the risk to a certain extent.  
1. Early warning system especially for heavy rainfall, landslide is an effective measure for saving lives. In the hills due to very spread out settlements it is important to set up a mechanism to transmit message across to villages. The banging of electric poles  can be used effectively to alert people when power supply is down and SMS is not available.
2. Identify safe locations for each area and the knowledge of safe location should be communicated to the community. A general system needs to be practiced where community leaders can guide them to the safe house. Like practiced in Japan once a year a real time mock drill for evacuation may be useful to put down a protocol and understand the evacuation process.
3. In case of houses, which have been damaged in the recent earthquake or aftershocks. It is recommended to get a structural safety check done by a qualified structural engineer or Civil engineer. Architects are trained in design and basics of structures and can handle up to 4 storied buildings unless he or she has a specialization in structures. Draftsman and masons are equivalent to quacks please avoid their advise on design and structural safety.
5.  Check for possible signs of landslides like tilting of trees, fences, and electric poles. Cracks in the lintel and sill of doors and windows.
6. Observe the weather closely everyday on your smart phone or Internet. A good practice is to keep a check on the weather forecast and warnings for the day.
7. Know the emergency contact numbers of the local fire service, police, disaster management department, ambulance etc.
8. Keep important documents inside plastic packet to protect from damage by water. Laminating important document is another of protecting the documents.
9. Preparation of an emergency kit at household level.

Praful Rao,
Dist Darjeeling

Thursday, April 30, 2015

From the Telegraph (India) today : Non-functioning Indian Seismic Sensors during the Nepal Quake

Indian sensors slept through quake- Assessment hampered

 New Delhi, April 29: A network of 293 ground motion sensors located across northern, eastern and northeastern India lay crippled during Nepal's 7.9 magnitude earthquake and its aftershocks, handicapping researchers trying to assess how the quakes affected cities and towns in these regions.
No one knows how many of the 293 sensors designed to measure ground acceleration during earthquakes were actually recording data during the weekend earthquakes because funding for maintenance of the instruments was stopped in September 2014.
The Indian Institute of Technology, Roorkee, had established the network between 2005 and 2008, installing the sensors in district headquarters across northern and eastern states, including Bengal and Bihar, under a project funded by the Union science and technology ministry.

But the earth sciences ministry stopped funding the project in September last year, and informed IIT Roorkee in February this year to prepare to hand over the sensors to the National Centre for Seismology (NCS), an institution under the ministry.
Read full story here

Comment by Praful Rao

Automatic sensors and instruments perform an all important task of recording scientific data without human intervention even under the most adverse circumstances and are especially valuable for measuring data in remote mountainous regions.
Some years ago IMD did the laudable task of installing numerous AWS (Automatic Weather Stations) and ARGs (Automatic Weather Stations) covering almost the entire country and even neighboring countries like Bhutan, the data from which is available, free of cost here.
Unfortunately, like the seismic sensors which were dead, resulting in loss of valuable data when  the Nepal quake occurred, many of the AWS/ARG stations have not been working or give erroneous meteorological data - some for many years now.
I have personally brought this information to the notice of concerned government officials at the highest levels by email and otherwise - only to receive a stoney silence as the reply.
Some of the AWS/ARG stations which are dead (and this list is far from complete)  as on date are given below:-

Automatic Weather Stations (State and locations)
Uttharkhand: Purola, Pant Nagar Agro, Rudraprayag, Nainital, Joshimath, Mussoorie
Sikkim: Mangan
WBengal: Darjeeling, Hashimara
Nagaland: Dimapur, Zunheboto
Himachal Pradesh: Una, Palampur
Arunachal Pradesh: Upper Subansiri, Papumpare

Automatic Rain Gauges  (State and Locations)
WBengal: Kharibari, Chengmari
Sikkim: Namtham, Yukson
Uttarkhand: Ranikhet, Someshwar, Bageshwar, Kalsi, Kasya, Ukhimath, Jakholi
Nagaland: Satakha, Phek
Himachal Pradesh: Dharampur, Baijnath
Arunachal Pradesh: Dirang
Mizoram: Vairengte

Praful Rao,
Dist Darjeeling

Wednesday, April 29, 2015

Hope amidst Hopelessness and an Expert's view

In a bid to throw light on the probable cause, duration and impact of the 25th April 2015 Nepal earthquake, STH has been contacting several renowned experts in seismology and disaster management. Thus the grim foreboding for the Darjeeling-Sikkim region from Prof. Malay Mukul of IIT, Mumbai (Dept. of earth sciences) is placed here.

A clarification/assessment of the frequent aftershocks following the 7.9 R earthquake by Prof. Dave Petley (Pro-VCO), University of East Anglia, UK, is placed here.

Prof. Rajendra Bhandari is acknowledged as one of the leading experts in the world on landslides. An excerpt of his letter to STH regarding the Nepal earthquake is published below:-

"The Nepal earthquake should not have surprised us because a number of studies expected a repeat of 1934 Bihar-Nepal earthquake. Similarly, India should not be surprised if the 1897 Shillong earthquake repeats anytime. Unfortunate we begin to speak of earthquakes and landslides only after the events and do nothing between the events. Then we fool ourselves by throwing up the argument that earthquakes are to be accepted because we cannot predict them. Why can we not fix all the major landslides in Shillong, Darjeeling and other parts of NE by spending 1000 crores before the Shillong earthquake arrives? 

Perhaps this 1000 crore is reserved for the families of those who would die in the quake. Why do we not retrofit all our hospitals so that victims will not have to wait for the Pakistani plane to arrive! Why do we not train communities, make earthquake-proof shelters and improve communication systems. We need a strong will to do something before our own day of departure comes. 

The aftershocks post Gujarat earthquake were also as alarming. My gut feeling is that the major event for the time being is over even though some aftershocks may keep repeating. The magnitude of aftershocks would also diminish within a few days. Had this earthquake been of magnitude 5.5-6 to begin with, perhaps those would have been fore shocks, appearing as the advance team of the main event to follow."

Praful Rao
Dist Darjeeling

Photo credits: CNN