Download Geographic Distribution of Earthquakes

Geographic Distribution of
Earthquakes
Earthquakes are distributed unevenly on the
globe.
In certain places they are more frequent and
intense whereas in other places they are
extremely rare and feeble or their effect is hardly
perceptible
Studies on the occurrence of earthquakes on the
globe have indicated that there are certain zones
within the continents along which seismic
shocks are felt rather frequently
 MSK is the seismic intensity scale used to
evaluate the severity of ground shaking.
 It has 12 intensity degrees
 MEDVEDAV-USSR
 SPONHEUER-EAST GERMANY
 KARNIK - CZECHOSLOVAKIA
The Indian subcontinent has a history of
devastating earthquakes.
The major reason for the high frequency and
intensity of the earthquakes is that the Indian
plate is driving into Asia at a rate of
approximately 47 mm/year.
Geographical statistics of India show that
almost 54% of the land is vulnerable to
earthquakes
The earthquake zoning map of India divides
India into 4 seismic zones (Zone 2, 3, 4 and 5)
 According to the present zoning map, Zone 5
expects the highest level of seismicity whereas
Zone 2 is associated with the lowest level of
seismicity
The MSK (Medvedev-Sponheuer-Karnik) scale
intensity broadly associated with the various
seismic zones is VI (or less), VII, VIII and IX
(and above) for Zones 2, 3, 4 and 5,
respectively, corresponding to Maximum
Considered Earthquake(MCE)
Zone 5:
Zone 5 covers the areas with the highest risks
zone that suffers earthquakes of intensity MSK
IX or greater
 It is referred to as the Very High Damage Risk
Zone.
The state of Kashmir, the western and
central Himalayas, the North-East Indian region
and the Rann of Kutch fall in this zone
Zone 4:
 This zone is called the High Damage Risk Zone and
covers areas liable to MSK VIII.
 The Indo-Gangetic basin and the capital of the
country (Delhi), Jammu and Kashmir fall in Zone 4.
In Maharashtra the Patan area (Koyananager) is also
in zone 4
Zone 3:
 The Andaman and Nicobar Islands, parts
of Kashmir, Western Himalayas fall under this zone.
 This zone is classified as Moderate Damage Risk
Zone which is liable to MSK VII and also 7.8
Zone 2:
This region is liable to MSK VI or less and is
classified as the Low Damage Risk Zone
Earthquake Prediction:
Earth quake prediction is done by the following
methods
(i) Time Interval Analysis
(ii) Seismic Gap
Time Interval Analysis
 include laboratory and field studies of rocks before, during, and
after earthquakes
 monitor activity along major faults
 produce risk assessments
Seismic Gap
• Look at the location of earthquakes
• Areas (Gaps) where no earthquake has
happened is an area of accumulating strain
• Gaps represent locations of future
earthquakes
Focuses on patterns in seismicity.
Predicts based on irregular activities.
Also if there is a large gap in activity on an
active fault.
If a change in the pattern occurs, there is a
chance for an earthquake
Statistical Methods
 Collecting adequate amounts of data allows for
predictions to be made as to the location and
magnitude of earthquakes.
– Works out for smaller earthquakes but not for larger
earthquakes
Recurrence Frequency:
– Relationship between the magnitude and repetition
of earthquakes.
– Assumes that the same set of conditions leading to
an earthquake occur each time.
– Dependent on large amounts of historical data
Physical and Geophysical measurements
and observations
• Studies of precursors and events that occur before an
earthquake.
– Increase in the rate of a seismic creep and the slow
movement along the fault
– Gradual tilting of the land near the fault zone
– Drop or rise in the water level of a well
– Decrease in the number of micro quakes and
foreshocks
– Flashes and other lights in the sky
– Animal behavior
Physical and Geophysical measurements
and observations
• Fault Creep Measurements
– Measures the slow rate of movement on the
fault.
– Where lots of fault creep occur there is a
small chance of a big earthquake.
– Where little amounts of fault creep occur
there is a high chance of a big earthquake.
Physical and Geophysical measurements
and observations
• Drop or rise in the water level of a well
– Large amplitude surface seismic waves force the
particles of the rock near the surface to move
adjusting the level in the well.
– Before an earthquake water wells are also affected
by any fault creeps, crust tilts, or other seismic
activity.
– Drilling wells in certain locations and measuring
the water level and quality can aid in earthquake
predictions.
Physical and Geophysical measurements
and observations
• Animal behavior
– Recognizing unusual animal behavior in a
systematic way can be used to predict
earthquakes
– The Chinese started recording unusual
animal behavior and successfully predicted
an earthquake in 1975 3 months before it
struck.
Physical and Geophysical measurements
and observations
• Unusual animal behavior:
– Hibernating animals leaving their underground
nests
– Animals refusing to go into pens
– Animals seeking higher ground
– Birds vacating the area
– Deep water fish come closer to the surface
Conclusion
• No 100% accurate way to predict an
earthquake.
• As more data is collected, predictions will get
better.
• From data mining, more patterns will be found
increasing the accuracy of predictions.