Abstract:
Natural Hazards are severe and extreme weather and climate events that occur naturally. These refer to all atmospheric, hydrologic, and geologic phenomena that have the potential to affect humans, their structures, or their activities adversely, because of their location, severity, and frequency. Natural Hazards can happen at any point of time, day or night, and thus, unexpected and unmanaged events. The various disasters include Earthquake, Landslide, Flood, Tsunami, Drought, Cyclone, Cloud Burst, Forest Fire, and many others.
Natural Hazards in Arunachal Pradesh include Earthquake, Landslide, Cloud Burst, Flash Flood and Forest Fire. Of these, Earthquakes, Landslides and Cloud Burst are the most destructive, in terms of loss of life and destruction of property and environmental degradation. Although these natural hazards cannot be stopped, however, the adverse affect of these calamities can be minimized. It is, thus, essential to understand the processes involved in occurrence of these phenomena, particularly in context of Arunachal Pradesh.
The geology of Arunachal Pradesh is very complex as it exhibits three different mountain systems of different origin in juxtaposition. These are : i) the Himalayan Ranges, ii) the Mishmi Hill Ranges, and iii) the Naga-Patkai-Arakan Ranges . The Himalayan Ranges in Arunachal forms a continuation of that in Darjeeling, Sikkim and Bhutan in its western part and continue up to the eastern part in Upper and East Siang districts and partly in Dibang Valley and Lohit districts. Geologically, the Himalayan Ranges in Arunachal Pradesh are divisible into three domain : Outer Himalaya, Lesser Himalaya and Higher Himalaya. As in other parts of the Eastern Himalaya, the Arunachal Himalaya also contains distinctive litho-tectonic units. The Mishmi Hill Ranges, which form a part of the Shan-Malaysia Plate, abut against the Himalayan Ranges along the Tuting-Tidding Suture Zone and are mostly present in the Dibang Valley and Lohit districts. These are represented by Mishmi Massif that abut against the Himalayan Ranges along a suture zone, named as the Tuting-Tidding Suture Zone. The Naga-Patkai-Arakan Ranges that abut against the Himalayan and Mishmi Hill ranges are present in Changlang and Tirap districts. These are represented by the Schuppean Belt of Upper Tertiary sequence.
The major litho-stratigraphic units of Arunachal Himalaya are thrust bound. Three major tectonic features of regional scale are present in Arunachal Himalaya, viz., Himalayan Frontal Fault (HFF), Main Boundary Thrust (MBT) and Main Central Thrust (MCT). Of these, MBT is a continuous tectonic datum between the Siwaliks and the pre-Tertiary sequences trending more or less in WSW-ENE direction; whereas MCT marks the datum between the Lesser and Higher Himalaya. Large-scale differential tectonic transport of the crystalline sheets have taken place along these thrust planes. The Mishmi Massif comprises predominantly of granodiorite and diorite bodies and granite plutons (Tuting Granite). The Tuting Granite is thrusted over the metavolcanic of the Tuting -Tidding Belt along the Yang Sang Chu Thrust, which is considered to be a continuation of the Lohit Thrust. The Tertiary sequence of the Naga-Patkai-Arakan Terrane forms a part of the well-known Schuppen Belt, and is bounded by two major thrusts, viz., Disang Thrust and Naga Thrust. In addition, there are several transverse faults, which have truncated litho-tectonic units of the Lesser and Higher Himalaya.
It is a well known fact that Arunachal Pradesh falls under the high seismic zone, i.e. Zone V. It is because of its geographic position and geodynamically active three mountain systems, viz., the Himalayan ranges, the Mishmi hill ranges, and the Naga-Patkai-Arakan ranges. Movements in these mountains cause large number of earthquakes periodically along the thrust/faults planes, and quite a large part of the region is being affected by frequent landslides.
Various records show that earthquakes of different magnitude have been occurring frequently in Arunachal Pradesh. For example, a team of Wadia Institute of Himalayan Geology operated 10 seismic stations in different parts of Arunachal Pradesh for a period of 4-5 months in 1994. The study showed micro-seismic activity with a cluster of earthquakes of magnitudes 2 to 5 in West Kameng and Tawang districts, and another cluster with magnitudes ranging from 1 to 5 in the upper reaches of the Lohit Valley. Further, a linear zone of seismicity between magnitudes 2 to 4 occurs approximately along the MBT zone in foothill area. There are other institutions, such as North East Institute of Science & Technology (NEIST) formerly known as Regional Research Laboratory (RRL), National Geophysical Research Institute (NGRI), Manipur University, etc., which have been recording occurrence of earthquakes in the entire North-Eastern Region.
This shows that the seismic activity in Arunachal Himalaya is not uncommon and rather is a regular natural phenomenon, which however, cannot be predicted in terms of time, magnitude and place. On the other hand, unplanned developmental activities in Arunachal Pradesh, particularly the concrete construction for their modern life style, are increasing day by day without considering the vulnerability to the earthquakes.
The natural hazards, particularly the Earthquake and Landslide hazards, thus, need attention for comprehensive plan for preparedness and mitigation for sustainable reduction in disaster risk in hazard-prone areas through an integrated approach with active participation of the scientific community and society. Preparedness for Earthquake especially is very important particularly in metro cities having high density of life and property, where Earthquake can result in a large-scale disaster due to inappropriate structures.
The need of the day is to educate the general public regarding the danger from earthquake hazards and their mitigation. It is also important to follow strict enforcement of proper building codes. People themselves should realize to adopt the suitable building codes for their own safety. Keeping in view the vulnerability to the earthquake hazards, DOs and DON'Ts in case of an earthquake event have been suggested, which every one must follow for their personal protection.
Following studies are proposed and suitable actions are suggested :
i. Set up of Seismic Observatories
ii. Preparation of Hazards Zonation Maps (1:50,000 scale)
a. Sub-Seismic Zonation Maps,
b. Landslide Hazards Zonation Maps, and
c. Lineament Maps with demarcation of active faults.
iii. Study of Historical Earthquakes (Palaeoseismicity)
iv. Landslides Studies
a. Preparing database of old, active and inactive landslides;
b. Preparation of Landslides Hazards Zonation Maps;
c. Monitoring of active landslides and high risk areas; and
d. To suggest remedial measures.
v. Set up Global Positioning System (GPS) Stations
vi. Creation of Public Awareness
vii. Education in Hazards Mitigation
viii. Training Programs and Workshops
ix. Law Enforcement