Earthquake

General Definition: The momentary shocks experienced by earth at different locations & different time.

Technical Definition : Vibration induced in earth's crust due to internal  and external causes that virtually shake up a part of crust , structures & living & non-living thins existing on it.

Terminology :

1.       Seismology : The science dealing with the study of earthquake in all their aspect is called seismology.

2.       Seismic : Used to qualify anything related to earthquake e.g.: seismic wave seismic intensity, seismic zone, seismic region.

3.       Focus : Place or point of origin of an earthquake below surface of earth is focus (hypocenter). It may lie from a few hundred meters to hundred of km below earth's surface.

4.       Epicenter : Point or place on the surface vertically above focus is epicenter. Its placed on surface of earth where vibration of particular earth quake  reach first of all .

5.       Seismic wave : During each earthquake elastic wave are generated at the focus. These wave are called seismic wave & they travel in all directions. with their characteristics and   velocity.

Types of seismic wave :

1.       P Waves :

a)       Primary waves

b)       Push & pull / long compression wave

c)       Fastest wave

d)       Velocity (Vp =

e)       P wave should travel fast in rigid bodies.

2.       S- waves :

a)       Secondary waves

b)       Shear waves, transverse wave, directional wave

c)       Vs=

d)       S – wave wouldn't be propagated through a liquid medium

P waves + S waves = Body waves.

3.       L-waves

a)       Long wave or surface wave

b)       Sluggish wave, only recorded after the arrival of P and S –wave

c)       Type of L wave

-          Rayleigh wave

-          Love wave.

Rayleigh wave	Love wave
1.       The complex nature partly in the direction of propagation & party in rt. angle. 2.       Tend to distort horz. surface into a wavy shape.	1.            Horizontal Propagation in direction of propagation. 2.            To create shearing , breaking & rupture

 Magnitude: Rating of an earthquake on the basis of amplitude of seismic wave recorded in seismograph. The scale used is Richter scale (8.9 highest ever)            

Intensity	Type	Magnitude	Effects
I	Instrumental		Recorded by  sismograph only
II	Very feeble	3.5-4.2	Felt by some person
III	Slight		Felt by every one at rest
IV	Moderate	4.3 - 4.8	Felt by people in motion
V	Rather strong		Felt outdoors and indoors
VI	Strong	4.9-5.4	General Panic
VII	Very strong	5.5-6.1	Breaking of furniture
VIII	Destructive	6.2 - 6.9	Fall of tanks projection C-D class building collapsing
IX	Ruinous		Cracks develop in the ground
X	Disastrous	7-7.3	General destruction of all classes of building, bridges dams.
XI	Very disastrous	7.4-8.1	Fissuring of ground
XII	Catastrophic	>8.1(8.9)	Total destruction in the region in terms of life.

Intensity :

Rating in a qualitative manner on the basis of its effect on living & non-living things. Scale used is Mercalli scale

Classification of Earthquake :

a)   Based on depth of focus.

1.   Shallow – up 60 km

2.   Intermediate 60-300

3.   Deep seated 300-700

b)   Based on magnitude

                 Class                                                        Magnitude

                    A                                                        7.8 and above

                    B                                                              7.0-7.7

                    C                                                              6.0-7.7

                    D                                                              5.3-6.0

                    E                                                          less than 5.3

c)   Based on cause of origin :

1)   Tectonic earthquake : due to faulting or relative displacement of plates along rupture surface

2)   Non tectonic earthquake : Volcanic eruption, landslide, atomic explosion., subsidence.

Engg. Consideration

a)      To know seismic history of any area

b)      Assessment of seismic risk

c)      A seismic designing

Geo Physics

i)        Is a tool to detect the physical properties of the subsurface materials

ii)      Main methods used are

a)      Resistively method

b)      Seismic method.

c)      Reflection method

d)     Magnetic

iii)                The sensing devices used are called geophones (microphone) converts seismic vibration or motions of the earth to electrical impulses.

Used to Detect

1.      Depth of bedrock

2.      Shape of bedrock surface

3.      Depth of water table

4.      Fault location

5.      Rip ability assessment

6.      Blasting assessment

7.      Sand and gravel assessment

8.      Cavity detection

9.      Determination of dynamic elastic constant.

General Rules

1.      Velocity is roughly proportional to the degree of consolidation of rock or soil.

2.      In consolidated materials, velocity increases with water content.

3.      Weathering of rock will greatly reduce it's velocity.

4.      A particular rock type will include a range of velocities and these ranges may overlap for different rock types.

5.      Correlation of velocity with the type of earth materials, to a great extent will depon upon the overall geological characteristics of the area under study.

Electric resistivity method – Give a physical property that characterizes a material almost as definitely as its density.

-          Resistivity depends upon the quality and the quantity of the water filling the open spaces in the rock.

-          The flow of current through soil and rock is by ion conduction which is dependent on a combination of the conductively of the fluid present, porosity and percentage of saturation.

-          Dissolved salt – provide ion conductance of the electrical current

-          Rock forming mineral-high resistive to current flow.

-          The resistivity method is a valuable one for identifying layered subsurface materials that have different electrical properties.

Volcanic processes

-          1984-<500 volcanoes have been active

-          Around the margin of the pacific ocean

-          Location where molten rock or magma, issues from deep within the earth.

-          Explosiveness a viscosity and water content

-          volcanic Hazards Lava flows, Hot avalanches, mudflows and flood, volcanic ash (Tephra) and gases.

-          Mitigation

a)      Prevent land use regulation in high hazard area.

b)      Explosives and barriers to divert lave flow.

Glacier Lakes

Criteria for defining "potentially dangerous or critical lakes"

1.      Large lake size and rapid growth in area

2.      Increase in lake water level

3.      Activity of supra glacial lakes at different times

4.      Position of the lakes in relation to moraines and associated glacier

5.      Dam condition

i)                    Narrow crest area

ii)                  No drainage outflow

iii)                Steepness of slope of the moraine walls

iv)                Existence and stability of ice care

v)                  Height of moraine

vi)                Mass movement or potential mass movement

vii)              seepage through the moraine walls

6.      Glacier condition

i)                    Condition of associated glacier

ii)                  Hanging glacier in contact with lake.

iii)                Large glacier area

iv)                Rapid glacier Retreat

v)                  Debris cover on the lower glacier tongue

vi)                Gradient of glacier tongue

vii)              Toppling/Collapsing of ice

viii)            ICE blocks draining to lake

7.      Physical conditions of Surroundings

i)                    Potential rock fall/Slide (mass movement)

ii)                  Large snow avalanche sites immediate are the lake.

iii)                Neo-tectonic and earthquake activities around or near the lake.

iv)                Climatic conditions (large inter annual variations)

v)                  Very recent moraines of tributary glaciers

vi)                Have main glacier with well - developed frontal lake.

Earth Hazard Control

Hazard (Source of risk) are defined as phenomenon that pose a threat to people, structure, environmental resources and economy assets and which may cause a disaster.

            Also hazard is a source of risk that may cause damage to or loss of life and property.

Classification of Hazard

1 Relative Hazard is assessed by assigning rating to different factors contributing to Hazard.

2 Absolute Hazard is expressed deterministically. (e.g. Factor of safety).

3 Monitored Hazard is assessed by actual measurement of the effects.

 (Eg deformations).

Types of Hazard

            1. Natural Hazard      

1)      Water and Climatic re-laid:- flood, cyclones, tornadoes, huricans, hailstone, drough.

2)      Geologically: - earthquake, tsunami, landslide.

3)      Biologically: - epidemics, pest attack.  

4)      Chemically: - industries and nuclear.

5)      Accidentally related: - Forest Fire, serial bomb blast, air, rail, road accidents.                           

            2. Man made Hazard

1)      War

2)      Armed Conflict

3)      Technological failure

4)      Oil spillage

5)       Factory expansion

6)      Fire

7)      Gas leakage

8)      Transport collisions ,etc

Disaster: it is a serious disruption of the functioning of society causing human material and environmental losses which exceeds the ability of society to cope using its own resources.

* The impacts of disaster are multidimensional, social, economic and environmental

* A Disaster is a product of Hazards and vulnerability.

Vulnerability [V] as the extreme to which a community,structure,service or geographic area is likely to be damaged or disrupted by the impact of particular hazard, on occrent of their nature, construction and proximity to hazardneous terrain.

Vulnerability means the degree of loss to a given elements or set of elements at risk, resulting from the occurrence of a natural phenomenon of a given magnitude. It is expressed on a scale from 0(no damage) to 1 (total loss).

Risk= Hazard X Potential worth of loss

            Is a potential loss of life and property and may be defined as “the combined effect of the probability of occurrence of an undesirable events and the magnitude of the event”.

Specific Risk [R_s] means the expected degree of loss due to a particular natural phenomenon. It may be expressed by the product of H times V.

                                    R_s = H x V

Element at Risk [E] means the population, properties, economic activities, encluding public services etc at risk in a given area.

Total Risk [R_t] means the expected number of lives lost, person enjured, damage to property or disruption of economic activity due to a particular natural phenomenon and is therefore the product of specific risk [R_s] and elements at risk [E].

                                   

                                    R_t = E x R_s  = E x (V x H)

Stages of Risk Assessments

i)                    Identification   -   possible risk

ii)                  Estimation       -   possible damage

iii)                Evaluation        -  mitigation effect should be undertaken

Risk Elements in Different Disaster

Hazard                                                           Risk

            Flood                                       Every thing located in the flood plain.

            Earthquake                              Every thing located in earthquake prone zone.

            Tsunami/cyclone                     Anything close to costal area.

Landslide                                Anything located on or at base of steep slopes or cliff tops.

Drought                                   Live and health of those involved in drought prone area.

                                               

Assessment of Hazard and Risk

i)                    State of nature mapping

ii)                  Danger mapping

iii)                Hazard  mapping

iv)                Risk Determination

v)                  Action

Geological Sub-division of the Himalaya of Nepal

 The process of collision of the Indian subcontinent with the Tibetan plate and the subsequent folding ,faulting and upheavals of rock masses  led to the formation of the world’s highest and one of its most active mountain ranges the Himalaya. The Himalaya range can be subdivided into the following zones for South to North.

1)      The Gangetic plain formed on the Indian shield as a result of the accumulation of sediments transported by rivers and streams from the Himalayas.

2)      Sub-Himalaya (Siwalik)-MFT delineated the Gangetic plain and Siwalik.

3)      Lesser Himalaya

a)      Mahabharata Range

b)      Ludands

4)      Higher Himalaya the boundary between LH and HH  is the MCT

5)      The Higher Himalaya Which is gradually passed into the sedimentary belt of the Tibetan –Tethys Zone.

a) Sub-Himalaya or Siwalik (Unstable Zone)

i)              The youngest rock in the Himalaya

ii)                  The main rock types are mudstone, sandstone and conglomerate.

iii)                It is further classified in to-

a.        Lower Siwalik

b.      Middle Siwalik

c.       Upper Siwalik

The lower Siwalik are represented by interbreed soft mud rock and sst.

The Middle Siwalik comprised of thick bedded sst and mudstone and   Constituted steep river gorges’ Tinau Khola.

The upper Siwalik comprised of conglomerate of gravel. It has also

Experienced tectonic movement and therefore the beds are tilted.

iv)                The Siwaliks Rocks are gently folded and often dislocated by steep  faults

Which become gentler below the surface and join with each other. They are called Imbricate Faults  

v)                  It is seismically the most active region of the Himalaya.

vi)                The Siwaliks are delimited from the North by the MBT, one of the active fault of the Himalaya Rocks are generally crushed near the fault.

vii)              They are generally covered with thick forest,

 b) The Lesser Himalaya   (4000 m)  

1)      Mahabharata Range is an outer lesser Himalaya exhibits a young topography with active gullies deep slope and many imbricate faults.

2)      The Mud lands is an inner lesser Himalaya are characterized by the mature topography and wide development of red soil in slate, Phyllite and Schist.

3)      Consists of thick sequence of low grade metamorphic rock in the bed while the upper beds are of high grade metamorphic rock lesser Himalaya crystal lines.

4)      It is also intricately folded and faulted.

5)      The lesser Himalaya is divided in to Sedimentary belts and Metamorphic Belt

     Sedimentary Belts

i)                    Covered North of MBT in central west Nepal.

ii)                  Imbricate fault, tight fold and various system of joint are occasionally encountered.

iii)                Rock range from weak slate to massive and thick bedded Dolomite.

iv)                Common type of mass movements, rock side, rock fall, rock topple,  avalanches debris , deep gully erosion etc.

Rock type

1)      Very fracture and crumbly slate easily breakable land.

Immediately north of the MBT

2)      Inter bedded high joint quartzite and shale near the MBT and inner part of      lesser Himalaya.

3)      Medium to thick bedded Dolomite with thin beds of clay stone or slate.

4)      Massive and cliff fairly Dolomite and Quartzite- stable and normal.

5)      Deeply weathered soil, colluvium and loose mass.

6)      Weatherly product, rotated slide as common ,slope less than 25⁰

Water may crust, Hazard.

  Metamorphic Belt

1)      Low graded metamorphic rocks with high grade metamorphic rock such as gneiss.

2)      Phyllite, Marble, Quarzite, Schist, Gneissis.

A)    Phyllite and Quartzite alternate

1.      Thick succession

2.      No of small scale fold

3.      less rugged the Mahabharata range

4.      River flows from N to S, various river terraces level are encountered.

5.      Major mass waste process is debris slides, debris flow and slurry.

B)    Thick bedded Quartzite, marble or Limestone.

                                                                          i.      Narrow band of about 500 m in thickness.

                                                                        ii.      Formed steep slope.

                                                                      iii.      Rock is quite stable, good site for bridge construction.  

                                                                      iv.      Rock fracturing – wedge failure.

 c) Higher Himalaya

1. Rock type: - Gneiss, Magnetite, Schist, Marble and Granite.

2. Competent and Massive.

3. Produced very rugged and high mountain terrain (8000 m)

4. Rock are divided in to

                                    -The Tibetan Tethys Zone-fossils, ferrous, sedimentary rock

                                    - The Central Crystalline.

5. Debris falls, Gully Avalanches.

6. Glacier lake- creates a high hazard for the area below the region.

The Tibetan zone

            Incompetent rock such as Shale, Sandstone, Siltstome and Conglomerate.

            - Are many river terraces.

            - Rocks are folded and faulted

            - Rapid mass wasting

            - Rock and ice avalanches are common.