EARTHQUAKE

CHARACTERISTICS

EARTHQUAKE ENGINEERING
ELECTIVE 2
Engr. CHRISTOPHER S. PALADIO
 EARTHQUAKE CHARACTERISTICS
• INTRODUCTION
• CLASSIFICATION OF EARTHQUAKE
• CAUSES OF EARTHQUAKE
• EARTHQUAKE PHENOMENA
• INTENSITY
• MAGNITUDE
• SEISMIC ENERGY
• PROBABILITY OF OCCURRENCE
• FREQUENCY OF OCCURRENCE

.
CHRISTOPHER S. PALADIO, CE ASCOT
 INTRODUCTION

Earthquake is an oscillatory, sometimes violent

movement of the ground‟s surface that follows a
release energy in the Earth‟s crust.

Phenomenon of strong vibration occurring on the

ground due to the release of large amount of energy
within a short period of time through a sudden
disturbance in the earth‟s crust or in the upper part of
the mantle.

CHRISTOPHER S. PALADIO, CE ASCOT

 INTRODUCTION

CHRISTOPHER S. PALADIO, CE ASCOT

 CLASSIFICATION OF EARTHQUAKE

• Shallow Earthquake
o Focal depth is less than approximately 60 km
o Caused by the fracturing of brittle rock in the crust or by internal
strain energy that overcomes the friction locking opposite sides
of a fault
• Intermediate Earthquake
o Focal depths approximately in the range 60 – 300 km
underground
• Deep Earthquake
o Focal depths approximately in the range 300 – 700 km
underground

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
TECTONIC EARTHQUAKE
Disturbances resulting from rupture or a sudden
movement along an existing fault in the crust.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE

TECTONIC EARTHQUAKE
• The theory of plate tectonics derives from the
theory of continental drift and sea floor spreading.
• Earthquakes are now recognized to be the
symptoms of active tectonic movements.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
TECTONIC EARTHQUAKE
• The tectonic plates are in continuous movement
against each other. Friction forces between these
plates prevent differential displacements at the
boundaries of the plates.
• Elastic rebound releases the stored energy in the
form of seismic strain waves in all directions.
• According to the theory of continental drift, the
lithosphere is divided into 15 rigid plates, including
continental and oceanic crusts.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
PRINCIPAL TYPES OF PLATE BOUNDARIES
• Divergent or rift zones:
o Plates separate themselves from one another
and either an effusion of magma occurs or the
lithosphere diverges from the interior of the
Earth.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
PRINCIPAL TYPES OF PLATE BOUNDARIES
• Convergent or subduction zones:
o Adjacent plates converge and collide. A
subduction process carries the slab - like plate,
known as the „under - thrusting plate‟, into a
dipping zone, also referred to as the „Wadati –
Benioff zone‟ , as far downward as 650 – 700
km into the Earth‟s interior.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
PRINCIPAL TYPES OF PLATE BOUNDARIES
• Two types of convergent zones exist:
o oceanic - when two plates consisting of
oceanic lithosphere collide.
o continental lithosphere convergent boundaries -
occurs when both grinding plates consist of
continental lithosphere.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
PRINCIPAL TYPES OF PLATE BOUNDARIES
• Transform zones or transcurrent horizontal slip:
o Two plates glide past one another but without
creating new lithosphere or subducting old
lithosphere.

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE

CHRISTOPHER S. PALADIO, CE ASCOT

 CAUSES OF EARTHQUAKE
VOLCANIC EARTHQUAKE
Those associated
with volcanic
eruption or
subterranean
movements of
magma.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA

SEISMIC TREMORS
In the vibration of the earth‟s surface, it is normal for
faint tremors to continue for a brief period followed by
severe vibrations which gradually disappear.

CRUSTAL MOVEMENT
These are ground displacements in both horizontal
and vertical directions after the occurrence of an
earthquake.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA

FAULTS
These are discontinued plane in the form of a band
that moves on the two sides of a boundary line
consisting of a narrow belt of land.

It is a fracture in the Earth‟s crust along which two

blocks slip relative to each other

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
• TYPES OF FAULTS

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
PARAMETERS USED TO DESCRIBE FAULT MOTION
1. Azimuth (∅): the angle between the trace of the
fault, i.e. the intersection of the fault plane with the
horizontal, and the northerly direction
0𝑂 ≤ ∅ ≤ 360𝑂 . The angle is measured so that the
fault plane dips to the right - hand side;
2. Dip (𝛿) : the angle between the fault and the
horizontal plane 0𝑂 ≤ 𝛿 ≤ 90𝑂 ;
3. Slip or rake (λ) : the angle between the direction of
relative displacement and the horizontal direction n
−180𝑂 ≤ λ ≤ 180𝑂 . It is measured on the fault plane;

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
PARAMETERS USED TO DESCRIBE FAULT MOTION
4. Relative displacement (∆𝑢) : the distance travelled
by a point on either side of the fault plane. If ∆𝑢
varies along the fault plane, its mean value is
generally used;
5. Area (𝑆) : surface area of the highly stressed region
within the fault plane.

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES
• COMPRESSION WAVES
o Also known as Longitudinal Waves
o Also termed as “Primary Tremors”
o Travel at great speed (19,000 ft/sec or 5800 m/s,
in granite) and ordinarily reach the surface first
o Also known as P – Waves or Primary Waves
o Only wave that can pass through Earth‟s molten
core

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES
• SHEAR WAVES
o Also known as Transverse Waves or S – Waves or
Secondary Waves
o Travels at 10000 ft/sec or 3000 m/s, in granite
o Displace material at right angles to their path

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES

• Propagation velocity of Pand S wave are

𝐸 1−𝑣 𝐸
• 𝑣𝑃 = 𝜌 1+𝑣 1−2𝑣
and 𝑣𝑆 = 2𝜌 1+𝑣

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES
Procedure to locate an earthquake epicenter and
origin time:
a) Obtain seismogram records for a given observation site.
b) Select the arrival time of the body waves on the record
traces.
c) Compute the time delay ∆𝑡 in the arrival of P- and S-
waves.
d) Subtract the travel time ∆𝑡 from the arrival time at the
observation site to obtain the origin time.
e) Use the following equations to evaluate the distance ∆𝑥
between the seismic station and the epicenter. The use
of either equations depends on the data available for
the soil profile and approximation accepted.

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES
𝑣𝑃 𝑣𝑆
∆𝑥 = ∆𝑡
𝑣𝑃 − 𝑣𝑆

∆𝑥 = 7.42∆𝑡
f) Draw a circle on a map around the station location (or
centre) with a radius equal to ∆𝑥. The curve plotted
shows a series of possible locations for the earthquake
epicentre.
g) Repeat steps (a) to (f) for a second seismic station. A
new circle is drawn; the latter intersects the circle of the
first station at two points.
h) Repeat steps (a) to (f) for a third seismic station. It
identifies which of the two previous possible points is
acceptable and corresponds to the earthquake
source.
CHRISTOPHER S. PALADIO, CE ASCOT
 SEISMIC WAVES
• SURFACE WAVES
o Also known as R – Waves for Rayleigh Waves or L
– Waves for Love Waves
o In granite, R – Waves move at approximately
9000 ft/sec or 2700 m/s
o This wave may or may not form
o May arrive after the primary and secondary
waves

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC WAVES

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA

TSUNAMIS
These are long waves which are swept up to coastal
region when disturbances occur at the bottom of the
sea.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
• MAINSHOCK
o largest earthquake in a sequence, sometimes
preceded by one or more foreshocks, and
almost always followed by many aftershocks.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
• AFTERSHOCKS
o These are earthquakes that usually occur near the
mainshock (within 1-2 rupture lengths distance from
the mainshock).
o Earthquake will be called an aftershock as long as
the rate of earthquakes is higher than it was before
the mainshock.
o It is an earthquake that follow the largest shock of an
earthquake sequence.
o The day after the mainshock has about half the
aftershocks of the first day. Ten days after the
mainshock there are only a tenth the number of
aftershocks.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
• FORESHOCKS
o Relatively smaller earthquakes that precede the
largest earthquake in a series, which is termed
the mainshock.
o Not all mainshock have foreshocks.
o The chance of this happening dies off quickly
with time just like aftershocks.
o After three days the risk is almost gone.

CHRISTOPHER S. PALADIO, CE ASCOT

 EARTHQUAKE PHENOMENA
• EARTHQUAKE SWARMS
o Events where a local area experiences
sequences of many earthquakes striking in a
relatively short period of time.
o They are differentiated from earthquakes
succeeded by a series of aftershocks by the
observation that no single earthquake in the
sequence is obviously the main shock.

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY

 Is a non-instrumental perceptibility measure of

damage and other observed effects on people,
buildings and other features.

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY
• MOST COMMON INTENSITY SCALES
 Mercalli – Cancani – Seiberg (MCS): 12 -level
scale used in southern Europe;

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY
• MOST COMMON INTENSITY
SCALES
 Modified Mercalli (MM): 12
- level scale proposed in
1931 by Wood and
Neumann, who adapted
the MCS scale to the
California data set. It is used
in North America and
several other countries;

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY
• MOST COMMON INTENSITY SCALES
 Medvedev – Sponheuer – Karnik (MSK): 12 - level
scale developed in Central and Eastern Europe
and used in several other countries;

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY
• MOST COMMON INTENSITY SCALES
 European Macroseismic Scale (EMS): 12 -level
scale adopted since 1998 in Europe. It is a
development of the MM scale;

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY
• MOST COMMON INTENSITY SCALES
 Japanese Meteorological Agency (JMA): 7 - level
scale used in Japan. It has been revised over the
years and has recently been correlated to maximum
horizontal acceleration of the ground.

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY

CHRISTOPHER S. PALADIO, CE ASCOT

 INTENSITY

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

 It is a quantitative measure of earthquake size

and fault dimensions.
 It is based on the maximum amplitudes of the
body or surface seismic waves.
 It is therefore an instrumental, quantitative and
objective scale.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
• MOST COMMON MAGNITUDE SCALES
Local (or Richter ) magnitude 𝑀𝐿 :
• measures the maximum seismic wave amplitude A
(in microns) recorded on standard Wood – Anderson
seismographs located at a distance of 100 km from
the earthquake epicenter.

𝑀𝐿 = 𝑙𝑜𝑔 𝐴 − 𝑙𝑜𝑔 𝐴0

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

• MOST COMMON MAGNITUDE SCALES

 Body Wave Magnitude 𝑚𝑏 :
• measures the amplitude of P - waves with a
period of about 1.0 second, i.e. less than 10 - km
wavelengths. This scale is suitable for deep
earthquakes that have few surface waves.
Moreover, 𝑚𝑏 can measure distant events, e.g.
epicentral distances not less than 600 km.

𝐴
𝑚𝑏 = 𝑙𝑜𝑔 +𝜎 ∆
𝑇

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

• MOST COMMON MAGNITUDE SCALES

 Surface Wave Magnitude 𝑀𝑠 :
• measure of the amplitudes of LR - waves with a
period of 20 seconds, i.e. wavelength of about
60 km, which are common for very distant
earthquakes. 𝑀𝑠 is used for large earthquakes,
however, it cannot be used to characterize
deep or relatively small, regional earthquakes.

𝐴
𝑀𝑠 = 𝑙𝑜𝑔 + 1.66𝑙𝑜𝑔 ∆ + 3.30
𝑇

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

• MOST COMMON MAGNITUDE SCALES

 Moment Magnitude 𝑀𝑤 :
• accounts for the mechanism of shear that takes
place at earthquake sources. It is not related to
any wavelength. As a result, it can be used to
measure the whole spectrum of ground motions.

𝑀𝑤 = 0.67𝑙𝑜𝑔 𝑀𝑜 − 10.70

𝑀𝑜 = 𝐺𝐴∆𝑢

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

• MOST COMMON MAGNITUDE SCALES

 Other Magnitude Scale:
𝑀 = 𝑙𝑜𝑔 𝐴 + 𝑓 𝑑, 𝑕 + 𝐶𝑆 + 𝐶𝑅
• 𝑓 𝑑, 𝑕 accounts for epicentral distance, d and
focal depth, h
• 𝐶𝑆 is the station correction
• 𝐶𝑅 is the regional
 Japanese Meteorological Agency (JMA)
• is a long -period measurement related to Richter
magnitude 𝑀𝐿 .
𝑀𝐽𝑀𝐴 = 2.0𝑀𝐿 − 9.7

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

SEISMIC INSTRUMENTS :
 SEISMOMETER

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE

SEISMIC INSTRUMENTS :
 ACCELEROGRAPH

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 TILTMETER
Installed in the ground works on the same principle
as a carpenter‟s level. The slightest movement of
a bubble floating in a spherical dome is
electronically detected to reveal tilting of the
ground

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 MAGNETOMETER
Used to measure strain
(deformation) of rock
under pressure. Such
strain changes the
permeability of the
rock, resulting in a local
change in the
magnetic field of the
Earth.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 STRAIN GAUGES
Measures how much the Earth deforms.

 SCINTILLATION COUNTERS
Installed in wells to measure the amount of
radioactive radon gas in the water.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 DILATOMETER
Measures the Earth‟s dilations.
It is a closed, fluid-filled tube approximately 10
ft long that is buried in the ground. Changes in
the earth‟s “squeeze” are detected and
measured by a pressure sensor or gauge at
the top of the tube.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 RESISTIVITY GAUGES
Measures the changes in the resistance of
rock which is an indication of density and
water content changes.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 CREEPMETER
Measures minute gradual movement along a
fault.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 GRAVIMETER
Responds to vibrations in
the local force of gravity.
Such vibrations are the
result of changes in
underground rock density.

CHRISTOPHER S. PALADIO, CE ASCOT

 MAGNITUDE
SEISMIC INSTRUMENTS:
 LASER
Measures the round-trip travel time of a light
beam between two points. When the relative
positioning of the two points changes as a
direct result of an earthquake, the travel time
also changes.

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC ENERGY, E

 Earthquake magnitude can be used to quantify the

amount of energy released during fault ruptures.
 Energy propagating by seismic waves is proportional
to the square root of amplitude – period ratios.
log 𝐸 = 1.5𝑀𝑆 + 11.8

 As the magnitude increases by one unit, the energy

increases by a factor of 31.6 and the difference
between two units of magnitude is a factor of 1,000
on energy release.
 Similarly
log 𝐸 = 2.4𝑚𝑏 − 1.3
log 𝐸 = 1.5𝑀𝑆 + 4.2

CHRISTOPHER S. PALADIO, CE ASCOT

 SEISMIC ENERGY, E

∆𝜏
𝐸= 𝑀𝑜
2𝐺
∆𝜏 = 𝜏1 − 𝜏2
For moderate - to - large earthquakes,
CHRISTOPHER S. PALADIO, CE
∆𝜏 = 6.0 𝑀𝑃𝑎 ASCOT
 PROBABILITY OF OCCURRENCE
𝑀
−
𝑝 𝑀 = 𝑒 𝐵
where:
B - earthquake parameter
M - earthquake magnitude

Recurrence Formula:
𝑀
−
𝑁= 𝐶𝑌𝑒 𝐵
 where:
Y - number of years

CHRISTOPHER S. PALADIO, CE ASCOT

 FREQUENCY OF OCCURRENCE

𝑙𝑜𝑔10 𝑁 = 𝑎 − 𝑏𝑀

For other nations, approx;

𝑙𝑜𝑔10 𝑁 = 7.7 − 0.9𝑀
𝑀 = 8.2

CHRISTOPHER S. PALADIO, CE ASCOT