eARTHQUAKE ENGINEERING

4.  The Earth is an oblate spheroid. It is composed
of a number of different layers as determined
by deep drilling and seismic evidence.
 These layers are:
◦ The core
◦ The mantle
◦ The crust

5. ◦ The CORE
 The Earth's core is the part of earth in the middle of
our planet.
◦ It has a solid inner core and a liquid outer core.
◦ Outer core
 The outer core of the Earth is a liquid layer about
2,266 kilometers thick.
 It is made of iron and nickel.
 Its outer boundary is 2,890 km (1,800 mi) beneath the
Earth's surface.
 The transition between the inner core and outer core
is approximately 5,150 km beneath the Earth's
surface.

6. ◦ Inner core
◦ The inner core of the earth, as detected
by seismology, is a solid sphere about 1,216 km
(760 mi) in radius, or about 70% that of the moon.
◦ It is believed to be an iron–nickel alloy, and may have
a temperature similar to the sun's surface,
approximately 5778 K (5505 °C).

7. ◦ The MANTLE
 The mantle is the second layer of the Earth.
 It is the biggest and takes up 84 percent of the
Earth.
◦ It is divided into two sections.
 The Asthenosphere, the bottom layer of the
mantle made of plastic like fluid.
 The Lithosphere the top part of the mantle made
of a cold dense rock.

8. ◦ The MANTLE
◦ The average temperature of the mantle is 3000° celsius.
◦ It is composed of silicates of iron and magnesium,
sulphides and oxides of silicon and magnesium.
◦ It is about 2900 km thick. It is the largest layer of the
Earth, taking up 84% of the Earth.
◦ Convection currents happen inside the mantle caused by
continuous circular motion of rocks in the lithosphere being
pushed down by hot molasses liquid from
the asthenosphere.

9. ◦ The CRUST
 The crust describes the outermost shell of
a terrestrial planet.
 Our planet’s thin, 40-kilometer (25-mile) deep
crust—just 1% of Earth’s mass—contains all known
life in the universe.
 It is the outer hard layer of the Earth, and is less
than 1% of Earth's volume.
 It is made up of different types of rocks; igneous,
metamorphic, and sedimentary rocks.

10.  Earth formed around 4.54 billion years ago
by accretion from the solar nebula. A volcanic out
gassing probably created the primordial atmosphere,
but it contained almost no oxygen and would have
been toxic to humans and most modern life. Much of
the Earth was molten because of frequent collisions
with other bodies which led to extreme volcanism.
One very large collision is thought to have been
responsible for tilting the Earth at an angle and
forming the Moon. Over time, the planet cooled and
formed a solid crust, allowing liquid water to exist on
the surface.

11.  Largely thought to be a hot, steaming, and forbidding
landscape, the primitive crust of the newly condensed
planet continued to cool. The crust consisted largely
of igneous intrusions and volcanic rocks, and
sediments that were eroded from this irregular
surface. Geologic remnants from this time are the
highly deformed and metamorphosed cratons of the
continents. The Precambrian is subdivided, from
oldest to youngest, into three eons,
the Hadean (4600−3900 million years
ago),Archean (3900−2500 million years ago),
and Proterozoic (2500−570 million years ago).

12.  Little is known about the Hadean because there are so
few rocks of that age, and those that do exist are
intensely deformed and metamorphosed. The Archean
was dominated by crustal building and the
development of extensive volcanic belts, arcs, and
sedimentary basins that were probably related to plate
tectonic activity. Marine rocks including chert contain
the fossil remains of microscopic algae and bacteria.
The Proterozoic is known for large‐scale rifting of
continental crust across the world and the filling of
these rifts with huge amounts of sedimentary and
volcanic rocks.

13.  Extensive iron deposits formed in shallow Proterozoic
seas, indicating there was enough free oxygen to
precipitate iron oxide minerals (for example,
hematite [Fe 2O 3]) from the iron in the water. The
increase in the amount of free oxygen is thought to
be a result of photosynthetic action by primitive life
forms in the sea. The fossil record has preserved
layered algal mounds called stromatolites, an
abundance of microscopic species, and trails and
burrows from wormlike organisms.

14.  Most earthquakes originate from the sudden
movements of the earth's tectonic plates , close to
the earth's surface, along zones of pre-existing
weakness called faults. The animation on this page
shows the main concepts that define a seismic
event, as well as some of the consequent effects.
 The rock fracturing determines the sudden release
of elastic energy stored before the movement and
producing seismic waves that radiate outwards
around the fault. During travel, waves lose their
energy (attenuation) so much that, for long
distances, earthquake arrival can be detected and
recorded only by special instruments
called seismograph.

15.  The destructive effects of an earthquake on
the ground surface are not always related to
the distance from the seismic source
(hypocentre). Different earth materials
respond differently to seismic shaking; likewise
different geological and geomorphological
conditions may influence the level of shaking
inducing local amplification. An appropriate
choice of building design and construction
method can considerably mitigate the effects
of the seismic shaking.

16.  A seismic wave is a mechanical disturbance or
energy packet that can propagate from point to
point in the Earth. Seismic waves can be generated
by a sudden release of energy such as an
earthquake, volcanic eruption, or chemical
explosion. There are several types of seismic
waves, often classified as body waves, which
propagate through the volume of the Earth, and
surface waves, which travel along the surface of
the Earth. Compressional and Shear waves are the
two main types of body wave and Rayleigh and Love
waves are the most common forms of surface wave.

17.  Compressional Waves
◦ Mechanical longitudinal waves are also called
compressional waves or compression waves, because
they produce compressionand rarefaction when
traveling through a medium.
 Shear Waves
◦ A type of elastic wave, the S-wave, secondary wave,
or shear wave (sometimes called an elastic S-wave) is
one of the two main types of elastic body waves, so
named because they move through the body of an
object, unlike surface waves.

18.  Rayleigh Waves
◦ Rayleigh waves are a type of surface
acousticwave that travel on solids. They can be
produced in materials in many ways, such as by a
localized impact or by piezo-electric transduction, and
are frequently used in non-destructive testing for
detecting defects.
 Love Waves
◦ Love waves (also known as Q waves (Quer: German for
lateral)) are surface seismic waves that cause
horizontal shifting of the Earth during an earthquake.

19.  The phenomena of earthquakes differ greatly in
accordance with the number, duration, and intensity of
the shocks, and with the distance of the place of
observation from that of the origin of the disturbance.
One of the greatest of modern earthquakes is that of
northern India of 1897, which is well summed up in the
official report.
 Violent earthquakes, which affect extensive areas, are
almost always followed by a succession of after-shocks,
which may continue for weeks, months, or even years.
These may be very violent, though never equaling the
primary shock in this respect, but gradually die away, until
the region once more comes to rest.

20.  In the sea the elastic waves producing shock soon
die away in the water. Observations made on the
several ships affected by the same quake
frequently show a lineal arrangement of the
disturbances. A special manifestation of
earthquakes in the bed of the sea is the great sea-
wave (sometimes erroneously called the tidal wave),
which is a gravity wave produced by disturbances
of the sea-floor or by a submarine volcanic
eruption. The great sea-wave, though not strikingly
displayed in the open sea, piles up on the coast into
enormous breakers, which often are more terribly
destructive than the earth-waves themselves.

21.  The vibrations produced by earthquakes are
detected, recorded, and measured by instruments
call seismographs. The zig-zag line made by a
seismograph, called a "seismogram," reflects the
changing intensity of the vibrations by responding
to the motion of the ground surface beneath the
instrument. From the data expressed in
seismograms, scientists can determine the time,
the epicenter, the focal depth, and the type of
faulting of an earthquake and can estimate how
much energy was released.

22. Magnitude Earthquake Effects Estimated Number
Each Year
2.5 or less
Usually not felt, but can
be recorded by
seismograph.
900,000
2.5 to 5.4
Often felt, but only
causes minor damage.
30,000
5.5 to 6.0
Slight damage to buildings
and other structures.
500
6.1 to 6.9
May cause a lot of damage
in very populated areas.
100
7.0 to 7.9
Major earthquake. Serious
damage.
20
8.0 or greater
Great earthquake. Can
totally destroy
communities near the
epicenter.
One every 5 to 10 years

23. Class Magnitude
Great 8 or more
Major 7 - 7.9
Strong 6 - 6.9
Moderate 5 - 5.9
Light 4 - 4.9
Minor 3 -3.9
Earthquakes are also classified in categories ranging
from minor to great, depending on their magnitude

24.  SEISMICITTY
◦ the occurrence or frequency of earthquakes in a
region.
◦ the frequency, intensity, and distribution of earthqua
kes in a given area.
◦ seismic activity; the phenomenon of earthquake activi
ty or the occurrence of artificially produced earth tr
emors.

27.  SINGLE DEGREE OF FREEDOM SYSTEM
◦ The simplest vibratory system can be described by a
single mass connected to a spring (and possibly a
dashpot). The mass is allowed to travel only along the
spring elongation direction.

28.  Processing of vibration records is necessary
because the visual inspection of a time history only
reveals maximum amplitude and duration but not
influences of potential noise caused by the
recoding system/process and/or background
(environment). Besides that, vibration records may
contain various errors. Corrections of two basic
errors are described in Sections 4.2 and 4.3.
Douglas (2003), for example, listed types of
possible non-basic errors in strong-motion records,
Table 4.1: insufficient digitizer resolution , S-wave
trigger , insufficient sampling rate , multiple
baselines , spikes , early termination , and
amplitude clipping .

29.  EARTHQUAKE SPECTRUM
◦ The response spectrum for a given ground motion
component (e.g., a(t)) is developed using the following
steps: Obtain the ground motion for an earthquake.
Typically the acceleration values should be defined at
time steps of 0.02 second, or less.
 DESIGN SPECTRUM

30.  Ground motion is the movement of the earth's surface
from earthquakes or explosions. Ground motion is
produced by waves that are generated by sudden slip on
a fault or sudden pressure at the explosive source and
travel through the earth and along its surface.
 strong ground motion as the strong earthquake shaking
that occurs close to (less than about 50 km from) a
causative fault.The strength of the shaking involved in
strong ground motion usually overwhelms
a seismometer.forcing the use of accelerographs (or
strong ground motion accelerometerfor recording. The
science of strong ground motion also deals with the
variations of fault rupture, both in total displacement,
energy released, and rupture velocity.

32.  The effects of an earthquake are strongest in a broad
zone surrounding the epicenter. Surface ground
cracking associated with faults that reach the surface
often occurs, with horizontal and vertical displacements
of several yards common. Such movement does not have
to occur during a major earthquake; slight periodic
movements called fault creep can be accompanied by
micro earthquakes too small to be felt. The extent of
earthquake vibration and subsequent damage to a region
is partly dependent on characteristics of the ground.
For example, earthquake vibrations last longer and are
of greater wave amplitudes in unconsolidated surface
material, such as poorly compacted fill or river
deposits; bedrock areas receive fewer effects.

33.  The worst damage occurs in densely populated urban
areas where structures are not built to withstand
intense shaking. There, L waves can produce destructive
vibrations in buildings and break water and gas lines,
starting uncontrollable fires.
 Damage and loss of life sustained during an earthquake
result from falling structures and flying glass and
objects. Flexible structures built on bedrock are
generally more resistant to earthquake damage than
rigid structures built on loose soil. In certain areas, an
earthquake can trigger mudslides, which slip down
mountain slopes and can bury habitations below. A
submarine earthquake can cause a tsunami, a series of
damaging waves that ripple outward from the
earthquake epicenter and inundate coastal cities.

35.  Currently no single publication exists that provides up-to-date
information necessary to architects, presented in a form that is
attractive, readable, and intelligible to a non-specialist audience.
This revised publication will fill that gap. The present
publication consists of a series of chapters that provide the
foundation for an understanding of seismic design, each
authored by an expert in the field. The authors were given
freedom to decide the scope of their chapters; and thus this
publication represents expert opinion rather than consensus.
Designing for Earthquakes: a Manual for Architects is intended
to explain the principles of seismic design for those without a
technical background in engineering and seismology. The primary
intended audience is that of architects and includes practicing
architects, architectural students, and faculty in architectural
schools who teach structures and seismic design.

36.  A design code is a document that sets rules for
the design of a new development in the United
Kingdom. It is a tool that can be used in the
design and planning process, but goes further and
is more regulatory than other forms of guidance
commonly used in the English planning system over
recent decades.
 Examples of developments where design codes are
being used include:
◦ Poundbury, Dorchester
◦ Fairford Leys, Aylesbury
◦ Fairfield Park, Letchworth
◦ Ashford Barracks, Ashford
◦ Upton, Northampton