Wednesday, September 28, 2011

Will there be another big earthquake tonight? plus this and that...

      • Judging by the periodicity of occurrence of mega-quakes shown above, it is extremely  unlikely that a big quake will occur here in the near future.
        So those who are busy spreading rumors about another big one rattling us tonight, just shut up and let ordinary people get on with their lives and more importantly, let the relief and reconstruction work go thru without people jumping out of their skins at the slightest noise or vibration by a passing vehicle.
      • And there is no volcano in north Sikkim (despite the hot springs which exist there) so where is the question of one erupting ?
      • What is far more likely to happen is, there will be landslides if it rains the way it did two days ago (yes! the monsoons are still active in this region and the cyclone season in the Bay of Bengal lasts upto Nov - see here). The reason for this is obvious :-
        • The soil is absolutely saturated after almost 5 months of rain.
        • Many places are cracked and weakened by the recent 6.9 Richter earthquake and   are likely to crumble in intense, heavy downpours.  
      • So with all our buildings and homes cracked and damaged, I think we all learnt a lesson and should get our home insured as soon as possible, right?
        What I was told by an insurance company representative is that most probably insurance companies will stop insurance against earthquakes and maybe landslides too in this region (since it makes poor business sense to insure property in a high risk area).
        So before you dole out the premium to the insurance agent, just turn the page and check the fine print – you might just end up insuring your house against fire and theft only !

        Praful Rao

      Monday, September 26, 2011

      Image of the day (26Sep2011)

      48hr rainfall statistics
      of Darjeeling
      26Sep2011 - 44mm
      25Sep2011 - 37mm

      Impact on Education
      Since the landslide makes the school, St Joseph's School, North Point,  virtually unapproachable by taxis and conventional transport, the administration has declared an extended Puja festival vacation from today (26Sep2011) until 17Oct201.
      Mt Hermon School, in the same area, is another institution which will decide on whether they should close early.

      Praful Rao

      Photo credit : Mr Mohan Lama (Darjeeling)

      STH storm watch : Bad news - Low pressure west of Darjeeling / Sikkim

      I have been tracking this depression/low pressure since 22Sep2011 (see here). After moving  inland on 22Sep, it has somehow swerved towards us and now lies to the west of us (red dot). As per meteorologists the system is likely to move in a northeasterly direction and may come over the Darjeeling-Sikkim Himalaya which has already had heavy and incessant rain for 24hrs. This is certainly bad news for us, who are struggling to cope with the aftermath of the 6.9 Richter EQ of 18Sep2011 and also because the heavy rain is coming down on earth which is thoroughly saturated after 5 months of rain.
      I urge all readers of this blog from this region to remain updated about the movement of the system from this page.
      Rainfall in Kalimpong for the past two days has been :-
      • 26Sep2011 - 28mm till 11.30am
      • 25Sep2011 - 52mm
      • 24Sep2011 - 31mm

        Praful Rao

      Thursday, September 22, 2011

      STH storm watch : Depression in the Bay of Bengal, 22Sep2011

      Since most of the landslides in this region are rain-induced, it is our business to keep a close track of developments in Bay of Bengal in order to give early warning of adverse weather.
      Placed below is the Infra -Red image of a depression in the Bay along with the IMetD forecast.

      “The well marked low (WML)over Nothwest Bay off Orissa-West Bengal coast has further concentrated into a Depression over North Orissa -West Bengal Coast and lay centered this morning at 0830 hrs IST near latitude 21.5 deg North and longitude 87.5 deg East. 50 km SSE off Digha and 50 km ESE off Balasoere. The system likely move West Northwest direction and cross coast between Balasore and Digha by today evening dated 22.09.11.”
      - Source

      Praful Rao

      Detailed report from IMetD on Earthquake (M:6.8),18Sep2011 in Sikkim-Nepal border

      An earthquake of magnitude 6.8 occurred on 18th September at 18:11 hrs IST in Sikkim-Nepal Border region. The preliminary hypo-central parameters of this earthquake, as estimated by the Seismic Monitoring Network of India Meteorological Department (IMD) are given below:
      Date of occurrence : 18/09/2011
      Time : 18:11 hrs (IST)
      Magnitude : 6.8
      Focal depth : 10 Km
      Latitude & Longitude : 27.7o N & 88.2 o E
      Region : Sikkim-Nepal Border region.
      The event, which comes under the category of “Moderate earthquake”, was also reported widely felt in Sikkim, Assam, Meghalaya, northern parts of West Bengal, Bihar, parts of other eastern and northern regions of India. The epicentre lies in a seismically known and active belt called, Alpide-Himalayan seismic belt. The location of the earthquake is shown on the seismicity map of Sikkim and neighbouring areas given at Annexure-1. The main shock was followed by a few aftershocks. A list of aftershocks of magnitude 3.0 and above recorded till 09.30 hours IST of 19th September, 2011, is given below. It may, however, be mentioned that the magnitude and frequency of aftershocks will reduce with the passage of time.

      Time of aftershocks
      Hr:Min (In IST)
      18 :42

      The earthquake source parameters have been disseminated to all concerned state and central government agencies related with initiating relief and rescue operations in the region. The information is also put on IMDs website for public use. The aftershock activity is being continuously monitored and information on significant aftershocks is being transmitted to all the concerned agencies.
      The source parameters of the event are estimated using data of a total of 77 seismic stations in India and across the globe spread more or less in all azimuths (Annexure-2). The details of various magnitude estimates are given in Annexure-3. The preliminary faulting mechanism of the subject earthquake, as estimated through Centroid Moment Tensor (CMT) and Moment Tensor (MT) solutions are given in (Annexure- 4 & -5). The faulting mechanism indicates reverse faulting associated with the tectonic processes related to the collision of Indian and Eurasian plates along the major thrusts in the region. The centroid moment depth indicated by the CMT solution (10 km.) for the present event matches well with the hypo-central estimates. The CMT and MT solutions are obtained from waveform modelling making use of Body and Surface waves respectively.The process essentially involves in simulating the synthetic seismograms by assuming a known source, path and instrumental characteristics. These synthetic seismograms are then matched with the observed ones at various stations in an attempt to arrive at the characteristics of the source, which produces the best synthetic seismograms matching with the observed ones.
      2. A slight magnitude earthquake (M:3.9) also occurred at 06 hours 22 minutes IST on 19th September, 2011 in the Latur district of Maharashtra. This event is located about 1500 kms away from the epicenter of the earthquake in Sikkim-Nepal border region of 18th September, 2011 and hence felt not directly related to it.
      3. Strong Motion Accelerographs (SMAs), meant for recording strong ground vibrations of the kind experienced during the subject event, are deployed by academic institutions, viz., IIT (Roorkee), IIT (Kharagpur), etc. in the Himalayan region including northeast India through sponsored projects supported by MoES. These data sets would provide valuable information for designing earthquake resistant structures in the region in future.
      4. Past seismicity of the region
      Historical and instrumentally recorded data on earthquakes show that the Sikkim and adjoining area lies in a region prone to be affected by moderate to great earthquakes in the past. Some noteworthy earthquakes that have affected the region are:
      (i) Cachar earthquake of 10.01.1869 (M: 7.5),
      (ii) Shillong plateau earthquake of 12.06.1897 (M: 8.7),
      (iii) Dhubri earthquake of 02.07.1930 (M: 7.1),
      (iv) Bihar-Nepal Border earthquake of 15.01.1934 (M: 8.3),
      (v) Arunachal Pradesh – China Border earthquake of 15.08.1950 (M: 8.5),
      (vi) Nepal-India Border earthquake of 21.08.1988 (M: 6.4)
      (vii) Sikkim earthquake of 14.02.2006 (M: 5.7)
      (viii) Bhutan earthquake of 21.09.2009 (M:6.2)
      The Sikkim and adjoining region is known to be part of the seismically active region of the "Alpide-Himalayan global seismic belt", with four great earthquakes of the world of magnitude 8.0 and above occurring in this region. The occurrence of earthquakes in the region is broadly associated with the tectonic activity along well known faults in the Himalayas, namely, Main Boundary Thrust (MBT), Main Central Thrust (MCT). Other prominent geological / tectonic features in and around Sikkim include: Tista lineament, Kunchenjunga lineament, Purnea-Everest lineament, Arun lineament and Dhubri fault in the southeast.
      In the seismic zoning map of India prepared under the auspices of Bureau of Indian Standards (BIS code IS: 1893: Part I 2002), by a committee of experts representing various scientific institutions including India Meteorological Department (IMD), the entire area of Sikkim lies in Zone IV. The seismic Zone IV is broadly associated with seismic intensity VIII on the Modified Mercalli Intensity (MMI) scale. It may be mentioned that the seismic intensity VIII on MMI scale corresponds to a horizontal ground acceleration range of 51-350 cm / sec2 or an average acceleration of 172 cm / sec2 in any direction. The ground acceleration and hence the intensity of an earthquake at a place depends on magnitude of earthquake, distance from the focus, duration of earthquake, type of underlying soil and its damping characteristics and liquefaction potential. The damage to the buildings founded on soft soil or filled up earth is higher than that in the similar type of buildings having their foundation on hard bedrock. Also, the damage will be higher for higher magnitude and long duration earthquakes, less epicentral distance soft soil conditions and areas with high liquefaction potential.
      Presently, there is no scientific technique available anywhere in the world to predict occurrence of earthquakes with reasonable degree of accuracy with regard to space, time and magnitude. It is, therefore suggested that appropriate steps may be taken to ensure that the dwellings and other structures in the region are designed and constructed as per guidelines laid down by Bureau of Indian Standards (BIS) to minimize the losses caused by earthquakes. The choice of seismic factor to be adopted for designing and engineering the structures depends on horizontal ground acceleration and various other factors including type of structures, the ground conditions and also importance of structures. For important and critical structures, site specific spectral studies have to be carried out before assessing the seismic design parameters. Suitable seismic design parameters may be adopted as per recommendations of National Committee on Seismic Design Parameters (NCSDP) for designing and engineering Hydroelectric Projects.
      5. Causes of earthquakes
      Earthquakes are the result of a process, wherein the underground rocks suddenly break, along a plane of weakness called „fault’, when the prevalent stresses exceed the elastic strength of the rock. The buildup of stresses and subsequent release of the strain energy in the form of earthquakes is a continuous process, which keeps repeating in geological time scale. A number of theoretical assumptions that explain the forces, which cause accumulation of stresses inside the earth include: drifting of continents and mountain building process, shortening of Earth‟s Crust due to cooling and contraction, disturbance of mass distribution on the Earth‟s surface as a result of erosion of high lands and deposition of sediments in the sea and generation of heat by radioactive material inside the Earth‟s Crust.
      6. Classification of earthquakes
      Based on magnitude (M), earthquakes may be classified as Micro- (M<3.0), Slight- (M:3.0 -4.9), Moderate- (M:5.0-6.9), Great- (M:7.0-8.0) and Very great- (M>8.0). Earthquakes may also be classified as shallow-focus, intermediate-focus and deep-focus depending upon their focal depths. Shallow-focus earthquakes, which constitute about 80% of total energy release on the globe, have their foci at a depth between 0 and 70 km. and occur along collision and subduction zones, oceanic ridges and transform faults. Intermediate-focus earthquakes (focal depth between 71 and 300 km.) and deep-focus earthquakes (focal depth greater than 300 km.) occur in subduction zones, such as Andaman-Nicobar island region and northeast India. Most earthquakes originate within the crust and beneath the Moho, the number falls abruptly and dies down to zero at a depth of about 700 km. On an average, it is expected that about two earthquakes of M~8.0, ~20 earthquakes of M~7.0, ~100 earthquakes of M~6.0 and ~3000 earthquakes of M~5.0 are likely to occur every year over the globe. A list of significant earthquakes in the recent past in and around India is given below:
      •  Uttarkashi earthquake of October 20, 1991 (M: 6.6).
      •  Latur earthquake of September 30, 1993 (M: 6.3).
      •  Jabalpur earthquake of May 22, 1997 (M: 6.0).
      •  Chamoli earthquake of March 29, 1999 (M: 6.8).
      •  Bhuj earthquake of January 26, 2001 (M: 7.7).
      • Sumatra earthquake of December 26, 2004 (Mw:9.3)
      •  Muzaffarabad earthquake of October 8, 2005 (Ms:7.6)
      7. Seismic Zoning of India
      Bureau of Indian Standards [IS-1893 (Part-1): 2002], based on various scientific inputs collected from a number of agencies, has grouped the country into four seismic zones, viz. Zone-II, -III, -IV and –V. Of these, Zone V is seismically the most prone region, while zone II is the least. The Modified Mercalli (MM) intensity, which measures the impact of the earthquakes on the surface of the earth, broadly associated with various zones is as follows:
                     Seismic Zone MM Intensity
                    II (Low intensity zone) VI (or less)
                    III (Moderate intensity zone) VII
                    IV (Severe intensity zone) VIII
                    V (Very severe intensity zone) IX (and above)
      Broadly, Zone-V (12% of land) comprises of entire northeastern India, parts of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Rann of Kutch in Gujarat, parts of North Bihar and Andaman & Nicobar islands. Zone-IV (18%) covers remaining parts of Jammu & Kashmir and Himachal Pradesh, Union Territory of Delhi, Sikkim, northern parts of Uttar Pradesh, Bihar and West Bengal, parts of Gujarat and some portion of Maharashtra near the west coast and Rajasthan. Zone-III (27%) comprises of Kerala, Goa, Lakshadweep islands, remaining parts of Uttar Pradesh, Gujarat and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhatisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamilnadu and Karnataka. Zone-II (43%) covers remaining parts of the country.
      8. Seismic Hazard and Risk Microzonation
      Microzonation is the process of dividing a geographic domain into small units of likely uniform hazard level and nature. This classification is done based on Geoscientific, Geotechnical, Seismological and Engineering seismological parameters. The Hazard micro zone map is transformed into seismic risk microzonation map with inputs on Vulnerability of Built environment and Anthropological / Sociological inputs. As earthquake prediction is not possible precisely in time and space, seismic Hazard microzonation provides an important tool for generating parameters for site specific structural designing, land use planning and disaster mitigation. Seismic microzonation studies have been completed for Delhi (1:50,000 scale), Guwahati (1:25,000 scale), Sikkim (1:25,000 scale) and Bangalore city (1:25,000 scale). Microzonation map for NCT of Delhi is further being refined at 1:10,000 scale. It is planned to take up microzonation studies for all State Capitals and cities with a population density of half a million lying in Zones III, IV and V. The work will be taken up in phased manner and 30 cities have been indentified to start with. In this connection, detailed guidelines have been prepared for standardization of procedures / methods for adoption taking up these studies.
      9. Disaster mitigation
      Loss of lives during an earthquake is mostly due to damage or collapse of houses/ structures. However, any structure can bear the vibration from an earthquake if it has enough strength and sturdiness. Bureau of Indian Standards (BIS) has published criterion for construction of
      earthquake resistant structures. The design of structure should be such that the whole structure behaves as one unit at the time of vibration rather than assemblage of parts. Important structures like hospitals, fire stations etc. should be made earthquake resistant. However, it is not economical to demolish and reconstruct most of the poorly built structures; for such poorly built structures BIS has prepared guidelines for their retrofitting. In addition to this, HUDCO & BMTPC have also published guidelines and brochures for construction and retrofitting of buildings. Further, losses due to earthquakes can be considerably reduced through proper planning and implementation of pre- and post-disaster preparedness and management strategies by respective state government agencies by working out the possible earthquake effects for various seismic zones.
      10. National Program on Earthquake Precursors (NPEP)
      It is now recognized that earthquake generation processes are so complex and site specific that often, no two different tectonic environments behave in similar manner in terms of providing clues about the ongoing physical processes in the earthquake source region. It is, thus, necessary to adopt an integrated approach of generation, assimilation and analyses of a variety of earthquake precursory phenomena in critical seismotectonic environments in the country in a comprehensive manner. Towards meeting this objective, a National Program on Earthquake Precursors (NPEP) has been initiated recently by MoES through a multi-institutional and multi-disciplinary mechanism. As part of this, a suite of Multi-Parametric Geophysical Observatories (MPGOs) have been set up at Ghuttu, Shillong and Koyna to monitor various earthquake precursory phenomenon such as, seismicity patterns, crustal deformations, gravity anomalies, electrical resistivity changes, electromagnetic perturbations, water level changes, geo-hydrochemical changes, Radon and Helium anomalies and thermal anomalies, etc. Preliminary analyses of these data sets have provided useful leads on the ongoing tectonic processes in the Koyna-Warna region. It is proposed to intensity these investigations during the XII FYP.
      11. Deep drilling program in Koyna region
      The Koyna Dam located in Maharashtra, western India is the most outstanding example of Reservoir Triggered Seismicity (RTS), where triggered earthquakes have been occurring in a restricted area of 20x30 sq km since the impoundment of Shivajisagar Lake in 1962. These include the largest triggered earthquake of M~6.3 on Dec 10 1967, 22 earthquakes of M>5, about 200 earthquakes of M~4, and several thousand smaller earthquakes since 1962. Considering the importance of deep borehole investigations, it is proposed to undertake a suite of observations in deep borehole(s) in the Koyna area. The work will be carried out in collaboration with ICDP and the observations will include stress regime, pore fluid pressure and its variations, heat flow and its variation, orientation of faults, study of chemical properties of fluids, before, during and after earthquake. The proposed investigations through the borehole will facilitate i) observation and analysis of data, generated through the operation of borehole for 4-5 year of time, when it is anticipated that a few earthquakes of magnitude ~3 would occur in the immediate vicinity of borehole, ii) continuous observation to study the data in the far and near field of the earthquake and temporal variation w.r.t. occurrence of earthquake and iii) development of a model of RTS mechanism.
      12. The critical structures viz., nuclear power plants and dams in the country are designed taking into consideration the past seismicity and the expected ground motions in the region, estimated through a detailed site specific analysis using probabilistic and deterministic approaches carried out by earthquake engineering community.
      13. Efforts are being made to improve the understanding of earthquake processes and their impacts towards better management and mitigation of the effects of earthquakes in future. A document detailing the proposals planned to be taken up during the XII FYP is attached for kind information.

      My thanks to Mr GN Raha of IMetD (Gangtok) for this report, the pdf version is here

      Praful Rao

      Tuesday, September 20, 2011

      6.9 Richter Earthquake in Darjeeling - Sikkim Himalayas : The Kalimpong Chapter

      Rainfall data of Kalimpong from 14Sep -19Sep2011.
      • 14Sep - 16mm
      • 15Sep - 57mm
      • 16Sep - 25mm
      • 17Sep - 11mm
      • 18Sep -114mm ( mostly from 9am to 2.30pm) . The quake hit us at 6.10pm
      • 19Sep - 14mm
      • Total rainfall from 14-19Sep2011 - 237mm
      • Average rainfall for Sep (Darjeeling district) - 388mm ( Source

        Thus we received approx 61% of the monthly rainfall in just 6 days and  the quake struck us barely 4 hrs after a spell of very heavy rainfall.

        Fact Sheet :-
      • As on date there were 4 fatalities in Kalimpong caused directly or indirectly by the quake.
      • There has been huge damage to infrastructure all over Kalimpong sub-division with most of the damage being to older type homes/ buildings.

        Why we escaped :-
      • The quake lasted barely 20secs.
      • The first 10days of Sep2011 was more or less dry hence despite the heavy rain (see above), there were no major earthquake-induced landslides.
      • The timing (6.10pm IST) of the quake ensured that all were wide awake and that we could help each other.
      • There was absolutely no rain during or after the quake so we could wait for some hours in the open for the after shocks to get past.
      • On 18Sep2011 night (after the quake), it was cool outside and not the depth of winters when we would have frozen while remaining out doors.

        What did not work :-
      •  Cell phones :- They just went dead and for hours we could not get any news from any one.
        The reasons could be technical malfunction or congestion on the lines with too much traffic from anxious people.
        Possible solution 1 :- Making people aware about making short, precise calls and avoid jamming the networks with long avoidable chats.
        Possible solution 2 :- Use land line phones where possible.
      • Power supply :- Whether intentional or accidental, the power blinked off so we were left with what ever backup systems (battery powered inverters) we had and sooner than later they also packed up leaving us in the dark.
        Possible solution 1 :- Solar powered backup lights.
        Possilbe solution 2 :- See  "What worked" below.
      • Internet -Never the most dependable or stable means of communication - the net also packed up.

        What worked :-
      • The warmth of people who helped, cared and phoned or called.
      • The much forgotten and neglected Kerosene hurricane lamps.
      • Candles and matchsticks.
      • Warm clothes.
      • Transistor radio.
      • A hot meal!

        What we could do better and lessons learnt
      • Never assume it cannot happen to us.
      • Learn to be self reliant and try to survive the disaster and 3 days after without external help.
      • Get a family survival kit ready.
      • Get the community involved - they are the weakest link which could transpose into the strongest one.
      • Make a disaster management plan at the family and community level and REHEARSE the plan with all members ie go thru mock drills!
      • Don't spread rumors - no one knows when the next quake will occur, but being prepared will help.

        Praful Rao

        Sunday, September 18, 2011

        The 2nd Indian Landslide Congress (2ILC), Guwahati, 15-16Sep2011

         We attended the 1st Indian Landslide Congress in Lucknow last year and it was again a unique privilege to attend the second one in Guwahati, in the state of Assam, on the 15-16Sep2011.
        The Congress was the initiative of Indian Landslides (NIIM, Shillong) with Dr RK Avasthy (former Director, Geological Survey of India) as the convenor - and it was backed to the hilt by NEC member, Shri PP Shrivastav (IAS).
        There were 24 presentations made in 4 technical sessions and what emerged from the Congress was :-
        • Recognition that landslides are perhaps the most devastating of disaster forms (because of its frequency of occurrence and destruction of life and property) and also the most neglected - as such the necessity to give it much more importance.
        • The North East India had along with landslides, multiple hazards such as earthquakes which could trigger landslides and hence the necessity of developing a holistic strategy to combat these hazards.
        • All the north eastern states (ie the 7 sisters and the lone brother ie Sikkim) were supposed to submit the geographical location and details of two major landslides which were impacting human lives and property to the Member, NEC (Shri PP Shrivastava, IAS) by 31Oct2011. Further analysis of these landslides with respect to early warning and landslide prediction would be undertaken by IIT Mumbai under the stewardship of Prof TN Singh.
        • I am glad to say that they have agreed to include 2 landslides from Darjeeling district also even though the district is in West Bengal and as such not a part of NEC. I shall be forwarding the required details to Member NEC soon.

          My grateful thanks to Dr RK Avasthy, Convener of the 2ILC and Shri PP Shrivastava (IAS), Member, North Eastern Council (NEC) for organizing this congress and bringing to focus what is a long neglected issue.

          Praful Rao

        Tuesday, September 6, 2011

        Rainfall data and landslide report - Aug2011

        Rainfall was more or less normal for all three towns in the district with Kurseong again receiving the heaviest rain. The only  landslide which took place in Darjeeling was in the town on 24/25Aug2011 with no casualties. It was a different in west Sikkim where a landslide killed 3 during the heavy downpour of the same period. In both cases it was not only the heavy rainfall which caused the landslides - anthropogenic factors such as road construction and lack of drainage were also the main causative factors.
        Regrettably, I could not get either the rainfall data nor photos from the landslide in West Sikkim

        Praful Rao

        Friday, September 2, 2011

        Garbage dump landslides

        You can read more about the garbage dump landslide in the Philippines in Dr David Petley's blog here and I have covered the Alaichikhop landslides in this blog here