These slides explain the different seismic maps of India and the difference between intensity and magnitude of an Earthquake

1. Sanjivani College of Engineering, Kopargaon-423603
An Autonomous Institute Affiliated to Savitribai Phule Pune University, Approved by
AICTE, Accredited by NBA, Accredited ‘A’ Grade by NAAC
First Year M.Tech. (II Semester)
Subject: Structural Dynamics and Earthquake Engineering
(Subject Code: ST 608)
Professional Core Subject
By
Dr. Nitin Shankarrao Naik
Department of Structural Engineering
Sanjivani College of Engineering, Kopargaon

2. SEISMICZONESOF INDIA…….
The varying geology at different locations in the
country implies that the likelihood of damaging
earthquakes taking place at different locations is
different. Thus, a seismic zone map is required to
identify these regions. Based on the levels of
intensities sustained during damaging past
earthquakes, the 1970 version of the zone map
subdivided India into five zones – I, II, III, IV and
V.
Parts of Himalayan boundary in the north and
northeast, and the Kachchh area in the west were
classified as zone V.
The seismic zone maps are revised from time to
time as more understanding is gained on the
geology, the seismotectonics and the seismic
activity in the country. The Indian Standards
provided the first seismic zone map in 1962, which
was later revised in 1967 and again in 1970

3. The map has been revised again in 2002, and
it now has only four seismic zones – II, III, IV
and V. The areas falling in seismic zone I in
the 1970 version of the map are merged with
those of seismic zone II. Also, the seismic
zone map in the peninsular region has been
modified.
Madras now comes in seismic zone III as
against in zone II in the 1970 version of the
map.

5. 1970

6. EARTHQUAKE SIZE…
• Intensity of an Earthquake: Seismic intensity scale is a way of measuring or rating the effects
of an earthquake at different sites. The assignment of intensity of an earthquake does not
require any instrumental records. It depends vary much on the acuity (sharpness) of the
observer.
Intensity to different places of an affected area can be assigned based on visual observations
and interviews of people from that area.
Earthquake intensity data is used in the preparation of seismic risk maps of a region or
country. Such maps are useful in planning safe sites for important structures like nuclear
plant or large dams.
There are different types of intensity scales viz.
1) Rossi- Forel Intensity Scale
2) Mercalli Intensity Scale
3) Medvedev- Spoonheuer- Karnik (MSK) intensity scale

7. Modified Mercalli Intensity Scale

8. • What is the difference between Intensity and Magnitude?
• Magnitude is a measure of earthquake size and remains unchanged with distance from the
earthquake epicenter.
• Intensity, however, describes the degree of shaking caused by an earthquake at a given place
and decreases with distance from the earthquake epicenter.
• For an earthquake, there may be different intensities but only one magnitude.
To elaborate this distinction, consider the
analogy of an electric bulb. The illumination at a
location near a 100-Watt bulb is higher than that
farther away from it. While the bulb releases 100
Watts of energy, the intensity of light (or
illumination, measured in lumens) at a location
depends on the wattage of the bulb and its
distance from the bulb. Here, the size of the bulb
(100-Watt) is like the magnitude of an
earthquake, and the illumination at a location
like the intensity of shaking at that location
Lumen= quantity of light

9. • Magnitude of an Earthquake……
• Earthquake magnitude is a measure of the amount of energy released during an earthquake.
Magnitude of an earthquake is the representative of the earthquake it self, thus there is only one
magnitude.
• Richter Magnitude:(ML) (Local Magnitude)
• Dr. Charles Richter identified that; the seismic waves radiated by earthquakes could provide
good estimates of their magnitudes. Richter plotted a diagram of peak ground motion versus
distance. He used logarithm of recorded amplitude due to great variation in amplitudes.
Richter concluded that the larger the released energy of the earthquake, the larger the amplitude
of ground motion at a given distance.
From the plot ,magnitude of the earthquake can be obtained.
According to Richter a zero-magnitude earthquake is the
one which produces a record amplitude of 1.0 micro meter
at a distance of 100 km from the epicenter.
A0= Amplitude of zero magnitude earthquake at different
epicentral distances
A= Recorded amplitude in micro meter.
10 10 0
log A log A
L
M  

10. • https://www.sms-tsunami-warning.com

11. A seismogram is the recording of the ground shaking at the
specific location of the instrument. On a seismogram, the
HORIZONTAL axis = time (measured in seconds) and the
VERTICAL axis= ground displacement (usually measured in
millimeters). When there is NO EARTHQUAKE reading, there is
just a straight line except for small wiggles caused by local
disturbance or "noise" and the time markers. Seismograms are
digital now - there are no more paper recordings.
Calculation of Richter Magnitude