This document discusses earthquake intensity and magnitude. It defines an earthquake as the sudden release of energy in the Earth's crust that creates seismic waves. Earthquake intensity is a measure of the effects on the Earth's surface based on the Mercalli scale, while magnitude measures the energy released using seismograph recordings. The document provides details on what causes earthquakes, the relationship between intensity and magnitude, and examples of intensity scales like the Modified Mercalli scale. Tables show the correlation between typical intensities and magnitudes.

1. Earthquake Intensity
Mustafa Fahmi HasanMustafa Mohammed Rashid
201311 November

3.  DEFINITION OF AN EARTHQUAKE
• An earthquake (also known as a quake, tremor or
temblor) is the result of a sudden release of energy in the
Earth's crust that creates seismic wave’s. The seismicity,
seismic or seismic activity of an area refers to the
frequency, type and size of earthquakes experienced over
a period of time. Earthquakes are measured using
observations from seismometers .

4.  What causes an earthquake?
• The earth’s outer surface is broken into places called
(Tectoni Plates). These plates constantly move away
from to wards or past each other. As the continents are
part of these plates, they will also move. An earthquake
occurs when the stresses caused by plate movement are
released.
 Which area are prone to earthquakes ?
• Most earthquakes occur at the circum. Pacific seismic
belt known as the (Rim of Fire). 95% of all the world’s
earthquake occur at active plate boundaries. The
Philippines, Japan, California, Alaska and South America
are all on the plate boundaries.

5.  EARTHQUAKE INTENSITY
Earthquake intensity (Geology) a measure of the
size of an earthquake based on observation of the
effects of the shock at the earth's surface.
Specified on the Mercalli scale .

7.  INTENSITY
The intensity is a number (written as a roman numeral)
describing the severity of an earthquake in terms of its effects
on the earth's surface and on humans and their structures.
Several scales exist, but the ones most commonly used in the
united states are the modified mercalli scale and the rossi-forel
scale. There are many intensities for an earthquake, depending
on where you are, unlike the magnitude, which is one number
for each earthquake.

8. Map showing intensity for the New Madrid earthquake. (Image
courtesy of the Central U.S. Earthquake Consortium)

9.  MORE INFORMATION ABOUT INTENSITY
1- the state or quality of being intense
2- extreme force, degree, or amount
3- Physics:
a- a measure of field strength or of the energy
transmitted by radiation
See → radiant intensity → luminous intensity
b- (of sound in a specified direction) the average rate of
flow of sound energy, usually in watts, for one period
through unit area at right angles to the specified
direction .

10.  SHAKING INTENSITY
• The size of an earthquake is often described using
magnitude, which is the amount of energy released
during an earthquake. However, not all of the energy
released in an earthquake will necessarily be felt at
the surface, depending on the earthquake's depth.
• In New Zealand, where earthquakes occur from near
the surface right down to a depth of over 600 km, the
Modified Mercalli intensity scale is a better indicator
of an earthquake's effects on people and their
environment.

11.  SHAKING INTENSITY
.

12.  MODIFIED MERCALLI
INTENSITY SCALE:
The Mercalli intensity scale is a seismic scale used for
measuring the intensity of an earthquake. It measures
the effects of an earthquake, and is distinct from the
moment magnitude usually reported for an earthquake
(sometimes misreported as the Richter magnitude),
which is a measure of the energy released. The intensity
of an earthquake is not totally determined by its
magnitude.
The lower degrees of the Modified Mercalli Intensity
scale generally deal with the manner in which the
earthquake is felt by people. The higher numbers of the
scale are based on observed structural damage.

13.  The small table is a rough guide to the degrees of
the Modified Mercalli Intensity scale. The colors
and descriptive names shown here differ from those
used on certain shake maps in other articles.
The large table gives Modified Mercalli scale
intensities that are typically observed at locations
near the epicenter of the earthquake.

14.  ABBREVIATED MODIFIED MERCALLI
INTENSITY SCALE

19. A magnitude scale is simply a metric for quantifying the
energy released in an earthquake and the amplitude of the
waves the earthquake emits.
 MAGNITUDE

20. • In 1935 Charles Richter
developed a method to compare the
sizes of California earthquakes
based on waves recorded by
seismographs. In his method, a
single magnitude is assigned based
on maximum wave amplitudes.
• Modern seismologists have modified his method
and now analyze a large section of the waves
recorded on a seismograph to calculate a seismic
moment. The seismic moment is then converted to
moment magnitude, which is the standard size
reported by the U.S. Geological Survey.

22.  RICHTER MAGNITUDE SCALE
Distance S – P Magnitude Amplitude
km sec ML mm

23.  INTENSITY& MAGNITUDE OF AN
EARTHQUAKE.COMPARISON
Intensity
▪ Intensity measures the
strength of shaking
produced by the
earthquake at a certain
location.
▪ Intensity is determined
from effects on people,
human structures, and
the natural environment
Magnitude
▪ Magnitude measures the
energy released at the
source of the earthquake.
▪ Magnitude is determined
from measurements on
seismographs.

24.  RELATIONSHIP BETWEEN INTENSITYAND
MAGNITUDE OF AN EARTHQUAKE
• The relation between intensity and magnitude, which are
substantially different quantities by nature. In consideration
of the necessity “to translate” magnitude values into
intensity values, to find magnitude values for historical
earthquakes, we have searched for a correspondence that
may exist between intensity and magnitude, hypothesizing
that magnitude values were distributed as a known function.
• Therefore, we have analyzed two distribution functions,
first the Gaussian distribution, then a box function, of which
the goodness of fit has been estimated by the χ2 test. In
conclusion, the probability distribution of magnitude vs
intensity seems better described by a Gaussian curve.

25.  TABLE OF MAGNITUDE AND TYPICAL
MODIFIED MERCALLI INTENSITY SCALE:

26. • This map shows earthquake
intensities, by county, based on the
modified mercalli intensity scale. The
intensities shown on this map are the
highest likely under the most adverse
geologic conditions that would be
produced by a combination of the
august 31, 1886, Charleston, S.C.,
Earthquake and the January 1, 1913,
union county, S.C., Earthquake. The
rossi-forel scale initially used to
describe the January 1, 1913, union
county, S.C.,

27.  HISTORICALANALYSIS OF INTENSITY
AND MAGNITUDE OF EARTHQUAKE

28. • The recording of the acceleration of the ground
during an earthquake .
Acceleration, Velocity, Displacement (Image courtesy of Charles Ammon,
Penn State)
ACCELEROGRAM

29.  ACCELEROGRAPH
Kinemetrics FBA-23 accelerograph.
• An instrument that records the acceleration of the
ground during an earthquake, also commonly called an
accelerometer.