Sunday, October 2, 2011
Thursday, March 27, 2008
Basic Concepts of Earthquakes
Earthquakes
Earthquake may be defined as Vibrations induced in the earth’ crust due to external or internal causes, ranging from a faint tremor to a wild motion capable of shaking buildings apart and causing gaping fissures to open up in the ground. It is a form of energy of wave motion transmitted through the surface layer of the earth in widening circles from a point of sudden energy release--“the earthquake focus”. It is, however, evident that no earthquake possibly originates at a mere point alone.
Terminology associated with earthquakes.
1) Seismology:-The science dealing with the study of earthquakes in all their aspects is called seismology. It is an interdisciplinary science which is partly Geology & partly Physics .
2) Focus:-It is the exact spot underneath the earth’s surface at which an earthquake originates. It is also known as Hypocentre.
3) Epicentre:-The point or place on the surface vertically above the focus of a particular earthquake is termed as Epicentre. It is that (Geographical)place on the surface of the earth where vibrations from a particular earthquake reaches first of all. Generally it is the location of maximum damage due to earthquakes.
4) Isoseismal line or Isoseist:-Line joining all points at which the intensity of the earthquake is same is known as isoseismal or isoseist. It is infact, an isodiastrophic line of equal damage.
5) Homoseismal or Coseismal or Homoseists: - Lines joining places where shocks arrive at the same time.
Types of Earthquakes:-
Based on the depth of origin , there are 3 types of earthquakes :-
a) Shallow focus earthquake:- In this case, the seismic shocks originate at a depth upto 60 kms, below the earth surface. A great majority of the earthquakes in the past had been of this type.
b) Intermediate focus earthquake :-In this case the shock waves originate at a depth between 60-300 kms. They are rare in occurrence.
c) Deep focus earthquake :- Here the point of origin of the shock is at a depth between 300-700 km and is a very rare phenomena.
Based on the cause of origin: There are 3 types of earthquake based on origin.
a) Tectonic earthquake :- Caused due to faulting or relative displacement of blocks of the earth crust along rupture planes. Most commonly earthquakes are tectonic is origin.
b) Non Tectonic earthquake :- that owes their origin to causes distinctly different from faulting such as volcanic eruptions, atomic explosions or due to landslides and subsidence.
c) Submarine earthquake:-They of the generates vary large waves on the surface of the seas and destroy the coastal tracts. These submarine earthquakes are known as Tsunamis
Based on Magnitude:- Earthquakes are grouped into five classes on the basis of magnitude as follows:-
a) Class A→ 7.8 and above
b) Class B→ 7.0 – 7.7
c) Class C→ 6.0-7.0
d) Class D→ 5.3-6.0
e) Class E→ Less than 5.3
Types of seismic waves: - during each earthquake, elastic waves are generated at the focus. Theses waves are called seismic waves.They travel in all directions with their characteristic velocities.
There are 3 types of seismic waves-
1. The P-waves: - These are also called Primary waves, Push and pull waves, Longitudinal and compressional waves. These are fastest of the seismic waves (similar to sound waves). They travel in all solid, liquid and gaseous media. They have short wave length & high frequency.
2. The Secondary or S-waves: - These are transverse waves also known as sheer waves. They travel only in solid media. They are slow in comparison to P- waves. They are also having short wavelength and high frequency.
3. L-waves:-These are transverse vibrations and are confined to the outer skin of the crust. They are also known as surface waves because their journey is confined mainly to the surface layer of the earth crust
This is of two types based on their characteristics :-
a. The Rayleigh waves- In this case displacement of the particles is of a complex nature, partly being in the direction of propagation and partly at right angles to it.
b. The Love waves - In this case the displacement of the particles is practically horizontal, that is in the direction of propagation.
In terms of their effects on solid material of the earth crust, the Rayleigh waves tend to distort the horizontal surface into a wavy, Zigzag shape. The Love waves however tend to create shearing (breaking) ruptures.
Causes of earthquakes:-
There are two main causes of earthquakes occurrence:-Tectonic & Volcanic causes.
1. Tectonic earthquake:-Earthquake are produced by sudden movements along faults and are mostly, therefore of tectonic origin. The concept of possible mode of origin of tectonic earthquakes is known as Elastic Rebound theorySuch earthquake generally result from sudden yielding to strain produced on the rocks by accumulating stresses. This causes the breaking of rocks and produces relative displacements of rocks such faulting causes shaking because displacement of rocks can only be possible by overcoming frictional resistance against the walls of the fault plane. The association of earthquakes with fault lines is an established fact.
2. Volcanic earthquake:-Usually earthquakes with volcanoes are more localized both in extent of damage and in intensity of the waves produced in comparison to those which are associated with faulting motions A shock may be produced by any of the following mechanisms.
a. Explosion of the volcano upon the release and expansion of gases and lava ash.
b. Faulting within the volcano resulting from premises in the chamber of molten rock &
c. Collapse of the centre of volcano into the sace formed by the extrusion of gases and molten matters
Scale of intensity :-
Various scales have been proposed to the estimate the intensity of earthquake from the amount of damage caused. Theses scales are
1. Rosiforrel Scale:- For measuring Intensity
2. Mercalli Scale :- For measuring Intensity
3. Richter Scale :- For measuring Magnitude
1. In the Rosi Forrel Scale the intensity has been clarified into- SEVERE CATASTROPHIC & DISASTROUS.
2. In the Mercali scale this is divided into 12 numbers with increase of intensity. In this case number 1 is detected only by seismographs. Gradually the number increase when the earthquake intensity becomes disastrous at number 10 and at number 12 the effect is totally catastrophic where there is total destruction and objects thrown into air.
3. In the Richter scale the scale number ranges from 0 to 9. Here it is particularly important to notice that a magnitude & earthquake is 10 times larger than a magnitude 7 earthquake, 100 times larger than a magnitude 6 earthquake an 1000 times larger than a magnitude 5 earthquakes
Effects:-
Richter classified the effects of earthquakes into 2 main categories:-
1. Primary effects & 2. Secondary effects.
1. Primary effects:- Theses includes all such effects which are related to the cause of origin of an earthquake. The tectonic earthquake are often responsible for producing many important changes in the geological structure of an areas, creation of slaps or scales, figures, warping of strata, emergence or substance of coastlines changes in the causes of stream, origin of new springs and creation of sand dykes in which saturated layers of sand may be forced up into existing cracks & crevices.
2. Secondary effects:- All those effects which are related to passage of seismic waves and associated shaking motion of the ground during an earthquake are broadly grouped as secondary effects.
The instrument use for recording of seismic shocks is known as Seismograph and the records of seismic shocks prepared and presented seismographs are known as Seismograms.
Distribution of earthquakes
A study of occurrence of earthquakes in the past reveals at once a striking fact that earthquake are very common features in some regions of the world whereas certain other parts have remained virtually stable since times immemorial proudly speaking shocks of the past had been largely confined to only two large geographical; belts. The circumparific belts and the Mediterranean belt.
a) The circumparific belt forms a ring closing North America most of Asia and Europe and accounts for more than 75.6 % of world’s seism city.
b) The Mediterranean belt also called the Alp rive-Asiatic belt accounts for 22.1% of the world seism city and includes areas of India, Arafic Africa, S-America and Australia.
c) Another belt extends over Himalayas, KUNLUN, Tien Shan and Altai Range upto Rake Baikal.
d) Another belt extends from the gult of Aden Between Seychelles and Maldives Islands turns to the west soutgh of Africa and goes upto the fallan Island.
DISASTER MANAGEMENT ACT-2005
DISASTER MANAGEMENT ACT-2005
•The ACT Received Assent of President of India on 23/12/2005.
•Notified in the Official Gazette of the Govt. of India ON 26/12/2005
•The act is formally known as DISASTER MANAGEMENT ACT, 2005.
( ACT NO. 53 OF 2005)
•The act is applicable to the whole country.
•NO. OF SECTIONS – 79
•NO. OF CHAPTERS – 11
Chapter 1 & 2
1-2 Preliminary & Terminology associated with DM.
3. Establishment of NDMA.
4. Meeting of NDMA.
5. Appointment of officers & other employees of NDMA
6. Power and Functions of NDMA.
7. Constitution of Advisory Committee by NDMA.
8. Constitution of National Executive Committee (NEC).
9. Constitution of sub committee.
10. Powers and functions of NEC.
11. National Plan for Disaster Management.
12. Guidelines for minimum standards of Relief.
13. Relief in loan Repayment etc.
Chap-(3)
14. State Disaster Management Authority (SDMA)
Establishment of SDMA.
15. Meeting of the State Authority.
16. Appointment of officers & other Employees of State Authority.
17. Constitution of Advisory Comm. by the State Authority.
18. Power and Functions of state Authority.
19. Guidelines for minimum standard of relief by state Authority.
20. Constitution of State Executive Committee (SEC)
21. Constitution of State Sub committee by SEC.
22. Functions of SEC.
23. State Disaster Management Plan
24. Powers and Functions of SEC in the Event of threatening Disaster situation.
Chap-IV (4)
25. Constitution of District Disaster Management Authority (DDMA).
26. Powers of Chairperson of DDMA.
27. Meeting of DDMA.
28. Constitution of Advisory committees and other committees.
29. Appointment of officers and other employees of District Authority (DDMA)
30. Powers and Functions of DDMA.
31. District Disaster Management Plan.
32. Plans by different authorities at district level and their implementation.
33. Requisition by the District Authority (DDMA).
34. Powers and Functions of DDMA in the event of any threatening disaster situation or disaster.
Chap-V (5)
35. Central Government to take measures for DM.
36. Responsibilities of Ministries or Deptts. of Government of India (ref. to Disasters).
37. DM Plan of ministries or Deptts. of Government of India.
38. State Government to take measures of the State Government.
39. Responsibilities of Deptts. of the State Government.
40. DM Plan of the Deptts. of the State Government.
Local Authorities
Chapt.6
41. Functions of the Local Authority.
NIDM
Chap-VII (7)
42. Constitution and Role of NIDM.
43. Officers and other employers of the NIDM.
National Disasters Response Force (NDRF)
Chap-VIII (8)
44. Constitution of national Disasters Response Force (NDRF).
45. Control, Direction etc of (NDRF).
Finance, Accounts & Audit
Chap-IX (9)
46. National Disasters Response Fund (NDRF).
47. National Disasters Response Mitigation Fund (NDMF).
48. State, Disaster Response Fund (SDRF).
District Disaster Response Fund, (DDRF).
State Disasters Mitigation Fund (SDMF).
District Disasters Mitigation Fund (DDMF).
49. Allocation of Fund by Ministries and Departments of Government of India.
50. Emergency procurement & Accounting.
Offence & Penalties
Chap-X (10)
51. Punishment for obstruction etc.
52. Punishment for false claim.
53. Punishment for misappropriation of Money or materials etc.
54. Punishment for false warning.
55. Offences by the Deptts of the Government.
56. Failure of Officer in duty or his connivance at the contravention of the provisions of this Act.
57. Penalty for contravention of any order regarding requisitioning.
58. Offences by companies.
59. Previous sanction for prosecution.
60. Cognizance of offences.
Miscellaneous
Chap-XI (11)
61. Prohibition against discrimination.
62. Power to issue direction by Central Government.
63. Powers to be made available for rescue operations.
64. Making or amending rules in certain circumstance.
65. Power of requisition of resources provisions, Vehicles etc. for rescue operations etc.
66. Payment of compensation.
67. Direction to media for communication of warnings etc.
68. Authentication of orders or decisions.
69. Delegation of powers.
70. NDMA shall prepare Annual Report once every year.
71. Bar of Jurisdiction of Court.
72. Act to have overriding effect.
73. No suit or prosecution etc. on action taken in good faith.
74. Immunity from legal process.
75. Power of Central Government.
76. Power to make regulations.
77. Rules and regulations to be laid before Parliament.
78. Power of the State Government to make rules.
79. Power to remove difficulties.
Basics of Remote Sensing
The human body perceives the surrounding world through five senses that is Touch, Taste, Smell, Hear, and See. The first two senses (Touch, Taste) require contact of our sense organs with the objects. However, we acquire much information about our surrounding through senses of sight and hear which do not require close contact of sense organs with the external objects. In other words, the human body perform remote sensing to acquire information about the surrounding world.
The term Remote Sensing refers to the activities of recording, observing, perceiving information of objects or events at far away ( Remote) places. In Remote Sensing application, the sensors are not in direct contact with the objects or events being observed. The electromagnetic radiation is normally used as an information carrier in remote sensing.
What is REMOTE SENSING ?
The internationally accepted definition of remote sensing is “the science and art of obtaining information about an object, area or phenomena through analysis of data acquired by a device that is not in contact with the object, area or phenomena under investigation.”
The following seven elements are essential for remote sensing interpretation ----
1. ENERGY SOURCE or ILLUMINATION
The first and the essential requirement for remote sensing is to have an energy source, which illuminates or provides electromagnetic energy to the target. The sun is considered as the prime source of energy.
2. RADIATION & THE ATMOSPHERE
The solar energy while traveling from source to target and further from target to the sensor comes in contact with the atmosphere. This interaction between energy and atmosphere is useful in the interpretation of objects on the earth.
3. TARGET
Once the energy make its way to the target though the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.
4. SENSOR
The Electromagnetic Radiation when scattered by or emitted from the target is collected and recorded by the sensor, which is not in contact with the target. A sensor highly sensitive to all wavelengths, yielding spatially detailed data on the absolute brightness( Radiance) from a scene as a function of wavelength throughout the spectrum.
5. TRANSMISSION ,RECEPTION AND PROCESSING
The Electromagnetic Radiation recorded by the sensor is transmitted (in electronic form) to a receiving and processing station, where the satellite data are processed into an image (Hardcopy and/or Softcopy). As soon as the radiance Vs wavelength responses over a terrain element is generated ,it would be processed into an interpretable format and then recognized as unique to the particular terrain elements from which it is received .
6. INTERPRETATION & ANALYSIS
The processed image is interpreted and analyzed by skilled scientists visually and digitally in order to extract information about the target, which was illuminated. The multiple data users are people ,who have knowledge in greater depth ,both in their respective disciplines and in remote sensing data acquisition, analysis techniques.
7. APPLICATION
The interpreted and analyzed data is combined with ground check in solving a particular problem.
These seven elements comprise the remote sensing process from beginning to end.
