Earthquake Hazards: Effect and
its Mitigation
Dr. J. N. JhaProfessor and Head (Civil Engineering)
Guru Nanak Dev Engineering College, Ludhiana
About 500,000 quakes occur every year: About 100 are
potentially dangerous
(Magnitude> 6 on Richter Scale )
On an average 2 major quakes occur annually
(Magnitude> 8 on Richter Scale )
Very large quakes occur perhaps once in a decade:
Releases nearly all the Earth’s seismic energy
90% of the seismic energy released between 1900 &
1975 was by 10 great quakes only.
Energy released during the 2001 Bhuj (India) earthquake
is about 400 times (or more) that released by the 1945
Atom Bomb dropped on Hiroshima!!
Tectonic hazards: earthquakes
Over 40 countries are under threat from major
destructive quakes
The biggest losses occur where major quakes
coincide with concentrations of people and
structures
Kobe earthquake in the year 1999 resulted in
economic losses of US$ 200 bn
Gujarat earthquake in the year 2001 may have
affected over 100,000 people
Tectonic hazards: earthquakes
List of Major Historic Earthquakes
Year Location Deaths Magnitude
1556 China 5,30,000 8.0
1906 San Francisco 700 7.9
1960 S. Chile 2,230 9.5
1964 Alaska 131 9.2
1976 China 7,00,000 7.8
1985 Mexico City 9,500 8.1
1989 California 62 7.1
1995 Kobe 5,472 6.9
2001 Gujarat, India 16480 6.9
2004 Sumatra, Indonesia 2,30,210 9.3
2005 Pakistan 75000 7.6
2010 Haiti 46,000- 316,000 7.0
2011 Japan 15760 9.0
Some Past Earthquakes in India
7.8
8
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
1900 1920 1940 1960 1980 2000 2020
Magnitude
Year
Great (M > 8) Earthquakes Since 1900
Chile1906
List of major historic earthquakes
Where do earthquakes occur?
Source: wikipedia
Tectonic hazards: Critical issues
Seismic risk maps are not available for most of the
regions
All earthquakes do not occur along plate
boundaries
Precise prediction of earthquake (date and location
of earthquake ) not possible even today.
Vulnerability to earthquakes has increased
dramatically
More damages due to earthquake is occurring
because of increasing urbanization
Size of quake
Distance from epicenter
Depth of quake
Duration of shaking
The local geology
Meteorological
conditions
Construction
practice
Building code
enforcement
Factors determining the destructiveness of a
quake?
Earthquake damage in downtown Port-au-Prince (Source: wikimedia)
15
Major Earthquake Hazards
Ground Motion: Shaking of structures results in damage or
total collapse
Liquefaction: Happens in loose saturated cohesionless soils in
which the firm soil is converted into a fluid state which has
no shear strength and thus structures found on these soils fail
due to loss of bearing capacity of the ground
Landslides: Vibrations during earthquake trigger large slope
failures
Fire, Dust and Pollution : Indirect effect of earthquakes (large
scale damage triggered by EQ to gas pipe line and power
lines)
Tsunamis: large waves created by the instantaneous
displacement of the sea floor during submarine earthquakes
Frequency of shaking differs for different seismic waves.
High frequency body waves shake low buildings more.
Low frequency surface waves shake high buildings more.
Intensity of shaking also depends on type of subsurface material.
Unconsolidated materials amplify shaking more than rocks do.
Buildings respond differently to shaking depending on the
construction styles and materials
-Wood is more more flexible, holds up well
-Earthen materials, unreinforced concrete are very vulnerable to shaking.
Earthquake Destruction: Ground Shaking
Different Types of Waves
Arrival of Seismic waves at site
19
Earthquake Destruction: Ground Shaking
Collapse of Buildings
Image of Bachau in Kutch region of Gujarat after earthquake
20
Earthquake Destruction: Ground Shaking
Building design: Buildings that are not designed for earthquake loads suffer more
Image of a collapsed building in Ahmedabad during Bhuj earthquake
21
Earthquake Destruction: Ground Shaking
Causes failure of lifelines
Source: google images
22
Earthquake Destruction: Landslides
La Conchita, California- landslide and debris flow in1995Source: wikipedia
Alaska Earthquake 1964: Major landslide
25
Annual Landslide Costs
0 1 2 3 4
Japan
Italy
USA
India
China
Ex USSR
Spain
Canada
Sweden
New Zealand
Norway
Country
Annual Landslide Cost (1990 US$ Billion)
Global: US$ 10-20 Billion
Source: wikipedia
26
Earthquake Destruction: Liquefaction
Buildings founded on saturated cohesionless soils are
vulnerable – Nigata, JAPAN 1964
Source: http://www.ce.washington.edu
29
Earthquake Destruction: Liquefaction
Flow failures of structures are caused by loss of strength of underlying soil
Nishinomia Bridge 1995 Kobe earthquake, Japan
Earthquake Destruction: Liquefaction
Sand Boil: Ground water rushing to the surface due to liquefaction
Sand boils in Gujarat earthquake
Earthquake Destruction: Liquefaction
Sand boils that erupted during the 2011 Canterbury earthquake, New Zealand.
Source: wikipedia
Earthquake Destruction: Liquefaction
Lateral Spreading: Liquefaction related phenomenon
Fissures caused by lateral spreading during Haiti earthquake
Source: wikipedia
Earthquake Destruction: Liquefaction
Lateral spreading in the soil beneath embankment causes the embankment to be pulled apart, producing the large crack down the center of the road.
Cracked Highway, Alaska earthquake,
1964
Source: google images
Earthquake Destruction: Liquefaction
Liquefied soil exerts higher pressure on retaining walls,which can cause them to tilt or slide.
Source: google images
Earthquake Destruction: Liquefaction
Increased water pressure causes collapse of dams
Source: wikipedia
36
Earthquake Destruction: Liquefaction
τ = c + σn tanø
τ = c’+ (σn –u)tanø’
During an earthquake,
static pore pressure `u’ may
increase by an amount udyn
τ = c’+ [(σn – (u + udyn)]tanø’
Let us consider a situation
when u + udyn= σn, then τ = c’
In cohesionless soil, c’= 0,
hence τ = 0
Earthquake Destruction: Fire
Earthquakes sometimes cause
fire due to broken gas lines,
contributing to the loss of life
and economy.
The destruction of lifelines and
utilities make impossible for
firefighters to reach fires started and
make the situation worse
eg. 1989 Loma Prieta
1906 San Francisco
2011 Japan
Source: International Business Times
38
Earthquake Destruction: Fire
Northridge, 1994
Source: wikimedia
What is a tsunami?
Definition: a ‘gravity wave’
in the sea (or other body of
water) produced by sudden
displacement of the seafloor
and the water column above
it
Damaging tsunami waves
propagate much further than
damaging earthquake waves
Tsunami can cause
simultaneous catastrophic
losses on opposite sides of
ocean basins
soo-NAH-mee or Harbor Wave is a Japanese word: tsu means harbor & nami means wave
Tsunami Movement: ~600 mph in deep water
~250 mph in medium depth water
~35 mph in shallow water
Earthquake Destruction: Tsunami
Source: USGS public domain
53
At least 1500 (possibly ~3000) active volcanoes
Around 50 erupt annually
Over 82,000 people killed in 20th century
Two eruptions killed over 20,000
500 million people threatened
Perhaps 150 volcanoes monitored
Earthquake Destruction: Volcanoes
Etna (Sicily)Source: wikipedia
Earthquake Destruction: Volcanoes
•Geo-morphological changes are often caused by an earthquake:
e.g., movements--either vertical or horizontal--along geological
fault traces; the raising, lowering, and tilting of the ground
surface with related effects on the flow of groundwater;
•An earthquake produces a permanent displacement across the
fault.
•Once a fault has been produced, it is a weakness within the rock,
and is the likely location for future earthquakes.
•After many earthquakes, the total displacement on a large fault
may build up to many kilometers, and the length of the fault may
propagate for hundreds of kilometers.
Geo-morphological Changes
Mitigation Options
•Avoiding the hazard
•Building Earthquake resistant structures
•Ground Improvement
56
Mitigation Options: Avoiding hazard
Where the potential for failure is beyond the acceptable level and notpreventable by practical means, the locations of seismic threat can beavoided and the structures should be relocated sufficiently far awayfrom the threat.
57
Mitigation Options: Earthquake Resistant Structures
Methods to increase capacity/ Decrease demand:
•Special Construction materials•Special Foundation Techniques•Special Construction Techniques
Seismic demand should be less than the Computed capacity
‘Seismic demand’ is the effect of the earthquake on the structure.‘Computed capacity’ is the structure’s ability to resist that effectwithout failure.
58
Building Earthquake resistant structures
Affect of Architectural Features on Building during EQ
Behaviour of Brick Masonary Houses during EQ
Effect of Earth Quake on RC Building
Affect of Architectural Features on Bld during EQ
• Horizontal Movement is very large in tall building(Ht /Base)• Damaging effects are many in long buildings• Horizontal seismic force becomes excessive in case of building with large plan area (force
to be carried by column/wall)
Size of the Building
• Bld. With simple geometry in plan performs well during EQ• Bld. With U,V,H & +shape sustains significant damage• L-Shaped Building- Can be converted in simple plan into 2 rectangular block using
separation joint at the junction• column/wall carries equally distributed load in case of simple plan
Horizontal layout of the building
Vertical layout of buildings
• EQ force travels through the shortest path alongthe height of the building(Developed at different floor level of the bld.)
• Any discontinuity in this load transfer path resultsin poor performance of the bld
• Bld. With vertical set backs causes a sudden jumpin earthquake force at the level of discontinuity
• Bld. With fewer column/wall in a particular storeyor with unusually tall storey tend to damage orcollapse
Contd………
Vertical layout of buildings
• Building with open ground story tends to damage during EQ(2001 –Bhuj EQ-Ahmedabad)
• Unequal height of the column along the slope caused illeffects like twisting and damage is more in shorter column
• Building with hanging and floating column havediscontinuities in load transfer path
• Building with RCC Walls that stops at an upper level getsseverely damaged
Affect of Architectural Features on Bld during EQ
Suggestions• Architectural features detrimental to EQ response of building should be avoided.
If not, they must be minimised• In case irregular features included in building, higher level of engineering efforts is
required in structural design• Decision made at the planning stage on building configuration are very important• Building with simple architectural feature will always behave better during EQ
Behaviour of Wall• All walls if joined properly to the adjacent wall ensures
good seismic performance• Walls loaded in weak direction take advantage of the
good lateral resistance offered in their strong direction• Walls need to be tied to the roof and foundation to
reserve their overall integrity
Behaviour of Brick Masonary Houses during EQ
Box Action in Masonary Bld.• Separate block can oscillate independently and even
hammer each other (If too close during EQ)• Adequate gap required betn such blocks• Gap not necessary if horizontal projections in Bld are small• An integrally connected inclined stair case slab acts like a
cross brace betn floors• It transfers large horizontal forces at the roof and the lower
level (Area of Potential Damage)
Simple Structural Configuration required for Masonary
Building
Horizontal and Vertical Band necessary in Masonary
Building
Contd………
Strength Hierarchy
Effect of Earth Quake on RC Building
• Building to remain safe during EQ :----Column should be stronger than Beam--Foundation should be stronger than Column--Connection between beams & Column and Columns & Foundation should not fail
Reinforcement and Seismic Design
Reinforcement and Seismic Design
Reinforcement and Seismic Design
Reinforcement and
Seismic Design
Reinforcement and Seismic Design
How do Beam Column Joins in RC bld Resist EQ
EQ behaviour of Joints Three stage procedure for providing
horizontal ties in the joints
Beam and column in the open ground storey are required to be designed for 2.5 times the forces obtained from bare frame analysis
Soft Storey
Special Construction Materials
Some of the special materials:
Rubber, lead, copper, brass, aluminum, stainless steel, fibre-reinforced plastics and shape-memory alloys
These materials absorb a part of seismic energy and thereby reduces theeffect of earthquake on structure.
These materials are strategically used to modify the force–deformationresponse of structural components and/or enhance their energydissipation potential.
76
Mitigation Options: Special Construction Techniques
•Base Isolation Systems
•Energy Dissipation Systems
•Active Control Systems
Special construction techniques are adapted to reduce the seismicdemand on the superstructure by sharing the earthquake loadsthrough non-conventional structural elements.
Some of these Techniques Include:
77
Base Isolation Systems
In base-isolated systems, the superstructure is isolated
from the foundation by certain devices, which reduce the
ground motion transmitted to the structure. These devices
help decouple the superstructure from damaging
earthquake components and absorb seismic energy by
adding significant damping .
78
Passive Energy Dissipation Systems
Various Energy Dissipating Devices (EDD) are used to dissipate
the seismic energy. These devices are like ‘add-ons’ to
conventional fixed-base system, to share the seismic demand
along with primary structural members.
79
Active Control Systems
They control the seismic response through appropriate adjustments within
the structure, as the seismic excitation changes. In other words, active
control systems introduce elements of dynamism and adaptability into the
structure, thereby augmenting the capability to resist exceptional
earthquake loads.
A majority of these techniques
involve adjusting lateral strength,
stiffness and dynamic properties of
the structure during the earthquake
to reduce the structural response
80
Mitigation Options: Ground Improvement
Earthquake damage is greater in poorer soil areas, and significant life and
property losses are often associated with soil-related failures.
Buildings and lifelines located in earthquake-prone regions, especially
structures founded upon loose saturated sands, reclaimed or otherwise
created lands, and deep deposits of soft clays, are vulnerable to a variety of
earthquake-induced ground damage such as liquefaction, landslides,
settlement, and ground cracking.
Recent experiences show that engineering techniques for ground
improvement can mitigate earthquake related damage and reduce losses.
81
Mitigation Options: Ground Improvement
Fundamental approaches of Ground Improvement to mitigate earthquake
damages are either to increase capacity of soil or to decrease the
earthquake demand on the soil using several techniques.
Increasing Capacity Decreasing Demand
Soil Densification
Providing drains for rapid
dissipation of pore pressures
Grouting
Soil Reinforcement
82
Ground Improvement: Soil Densification
Soil densification techniques:
•Compaction
•Vibro-replacement (Vibroflotation & Stone Columns)
•Blasting
•Grouting
•Compaction Piles
83
Field Compaction
• Pneumatic rubber tired roller
Different types of rollers (clockwise from right):
Vibratory roller
Smooth-wheel roller
Sheepsfoot roller
84
Dynamic Compaction
- pounding the ground by a heavy weight
Suitable for granular soils and landfilles
Crater created by the impact
Pounder (Tamper)
(to be backfilled)
85
Source: http://www.geoforum.com
Dynamic Compaction
Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m
86
Source: http://www.geoforum.com
Dynamic Compaction
87
Source: http://www.geoforum.com
Ground Densification: Vibro-Compaction
Vibro-Compaction also knows as VibroFlotation is used to densify clean, cohesionless soils. The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular forces between the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 to 85 percent. Compaction is achieved above and below the water table.
88
Source: http://www.geoforum.com
vibrator makes a hole
in the weak groundhole backfilled ..and compacted Densely compacted stone
column
Vibroflotation
89
Source: http://www.geoforum.com
Vibroflotation
90
Source: http://www.geoforum.com
Ground Densification: Vibro-Compaction
91
• Generally used to improve density of silty sands-sandy gravels (non-cohesive soils)
• Makes use of dynamic/undrained loading conditions to cause liquefaction-induced settlement
• Sudden dynamic loading breaks cohesion and any cementation
• Shockwave temporarily liquefies soil layer
• Settlement occurs as excess pore water pressure approaches zero.
• Typical vertical strain between 2% and 10%
Ground Densification: Blasting
92
Aftermath of blasting
For densifying granular soils
Ground Densification: Blasting
93
Grouting is is a technique whereby a slow-flowing water/sand/cement mix is
injected under pressure into a granular soil.
The grout forms a bulb that displaces and hence densifies, the surrounding
soil.
Compaction grouting is a good option if the foundation of an existing
building requires improvement, since it is possible to inject the grout from the
side or at an inclined angle to reach beneath the building.
Jet grouting involves the injection of low viscosity liquid grout into the pore
spaces of granular soils. This creates hardened soils to replace loose
liquefiable soils.
Soil Densification: Grouting
94
Soil Densification: Compaction Grouting
Compaction Grouting uses displacement to improve ground conditions.
A highly viscous aggregate grout is pumped in stages, forming grout bulbs, which displace and densify the surrounding soils.
Used for loose soils, liquefiable Soils and collapsible Soils
95
Soil Densification: Cement Grouting
Cement Grouting, also known as Slurry Grouting, is the intrusion of microfine cement slurry (fine portland cement mixed with a dispersant and larger quantities of water) into fine sand and finely cracked rock under pressure
96
Jet Grouting
Grout is pumped through the rod and exits the horizontal nozzle(s) at high velocity [approximately 200m/sec]. This energy breaks down the soil matrix and replaces it with a mixture of grout slurry and in-situ soil (soilcrete). Jet grouting is most effective in cohesionless soils.
97
Jet Grouting
98
Ground Densification: Deep soil mixing
Deep Mixing Method is the mechanical blending of the in situ soil with cementitious materials using a hollow stem auger and paddle arrangement. These materials could be Cement or Fly ash or Ground Blast Furnace Slag or Lime or Additives or Combination of these. Soil mixing has the ability to strengthen soft and wet cohesive soils in a very short time period to permit many types of construction projects.
99
Source: http://www.geoforum.com
Ground Improvement: Vertical Drains
The installation of prefabricated vertical drains provides shortened drainage paths for the water to exit the soil. Drainage remediation methods mitigate liquefaction hazards by enhancing the rate of excess pore pressure dissipation. The most common methods of drainage remediation are through the use of gravel, sand or wick drains. Drains are suitable for silts or clays.
100
Source: http://www.geoforum.com
Ground Improvement: Vertical Drains
Primary consolidation settlement will already be achieved during the construction period by using vertical drains
101
Earthquake drains
102
Earthquake DrainsSM
Earthquake Drains are prefabricated in the field to project specifications. The drain is fitted with a sacrificial
endplate. The completed drains are fed into the installation mandrel and driven to treatment depth. When the
mandrel is withdrawn, the endplate anchors in the soil leaving the drain in-place. 103
Earthquake Drains
• Dissipates excess pore pressures as they generate during a
seismic event
• Can be used to retrofit existing structures
• approximately one third the cost of traditional stone
columns
• installation times approximately one third to one half of
that for stone columns.
104
Earthquake drains
FINS: Transmit vibratory
motion to the soil for
densification
STEEL CASING: Protects
drain from driving stresses
PREFABRICATED
DRAIN
Figure 2.1: Cross section of casing and prefabricated drain
105
Earthquake drains
106
Earthquake drains
107Source: google images
Geosynthetic Reinforced Soil Retaining walls
Seismic wave action in GRS
Wall
Geosynthetics allow for the movement of the
earth to pass through the reinforced soil mass
similar to a wave passing through a body of
water.
Once the wave passes, the water returns to its
original state. As the wave of ground
movement passes through the soil mass, the
geosyntetic reinforcement flexes with the
movement of the earth but returns to its
prequake position
108
Performance of GRS walls during earthquakes
The wall was completed in 1992 for a total length was about 300 m. It was deformed and moved only slightly during the devastating earthquake that occurred in Japan, while more than half of the wooden houses in front
of the wall collapsed totally. This type of geogrid-reinforced soil retaining wall was broadly employed to reconstruct the damaged conventi onal type retaining walls after the earthquake since it performed so well.
Kobe , Japan - MW6.9
109
Turkey Earthquake of August 17, 1999
Mechanically stabilized earth wall within a few meters of the primary fault rupture. Although subjected to differential settlement, it suffered only minor
damage.
110
Rehabilitation of Koyna Bridge abutment in
Maharashtra, India, located on SH 78 in
seismic Zone-IV was done using geosynthetic
reinforced wall technique encapsulating the
cracked return wall.
The project was completed in the year1996 and
its performance in seismic Zone-IV, which is
vulnerable to frequent earthquake, is very
satisfactory in spite of repeated after shocks,
including recent ones
Koyna Bridge Abutment: GRS technique Employed
111
Forecasting Earthquakes: Earlier Methods
Strange Animal BehaviorStress in the rocks causes tiny hairline fractures. Cracking of the rocks emits high pitched sounds and minute vibrations imperceptible to humans but noticeable by many animals.
Unusual Weather Conditions and Clouds
A few scientists claim to have observed clouds associated with a seismic event, sometimes more than 50 days in advance of the earthquake.
Foreshocks
Foreshocks are minor tremors of the earth that precede a larger earthquake originating at approximately the same location. Unusual increase in the frequency of these foreshocks are sign for an earthquake.
Changes in water level
porosity increases or decreases with changes in strain, causing fluctuations in ground water level
112
Forecasting Earthquakes: Recent Developments
Changes in Seismic Velocities
Earthquakes are often accompanied by temporal changes in seismic wave velocities in the region
Radon Emission
Emission of radon gas as a quake precursor is recently being explored by the geophysicists for developing a worldwide seismic early warning system
The Van Method
The method is based on the detection of "seismic electric signals" (SES) via a telemetric network of conductive metal rods inserted in the ground. Researchers have claimed to be able to predict earthquakes of magnitude larger than 5 using this method.
Geodetic Measurements
Laser geodimeter measures changes in distance across the fault between points. Changes in distances may indicate a precursor to an upcoming earthquake. 113
Prediction of Earthquakes
Seismic hazard map of the San Francisco Bay Area, showing the probability of a major earthquake occurring by 2032
114Source: USGS public domain
Earthquake prediction has taken a scientific turn in late 1970s.
The first successful prediction was made in China in winter 1975 for the city of Haicheng(population about 1 million).
Scientists observed changes in land elevation and ground water levels in that region over a period of time. A regional increase in foreshocks had triggered a low-level alert.
Based on the reports from scientists, Chinese officials had ordered the evacuation of the city. On February 4, 1975, earthquake of magnitude 7.3 struck the region. Only very small fraction (2,041 people) died in this event. The number of fatalities and injuries would have exceeded 150,000 if no earthquake prediction and evacuation had been made.
First Successful Prediction
115
Acknowledgements
• The author wishes to acknowledge all the various sources used
during the preparation of this presentation which aided and
enhanced the quality either in the form of information, graph
data, figure, photo, or table.
Any Question ………..?
Thanks for your attention
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