Introduction to Geophysics Introduction to Elastic Rebound Theory Introduction to Earthquake

1. Why is Geophysics important for civil engineering ?
Geophysics is the most promising branch of geology in terms of
operational use of geological information.
Geophysics provide geophysical analyses, recommendations,
and design correlations with human development and diverse
structures such as sub-surface constructions, Sub-surface
Geology (off shore: oil), and (under ground mines).

2. The seismic data recorded should give us the Earth’s reflectivity sequence

3. VIBRATOR

7. MV SAGAR SANDHANI
(DEPARTMENTAL SEISMIC SURVEY VESSEL)

10. Marine Seismic Data Acquisition

11. Hydrophone
Layer-1
Layer-2
Layer-3
Shots
Receivers
SEISMIC DATA ACQUISITION - 2D
Seismic Source On Land : Vibrator
Offshore : Air Gun
Seismic Receiver On Land :
Offshore :
Geophone
Dynamite or

12. Seismic Imaging in Offshore

13. 0
surface
Layer-1
Layer-2
Layer-3
Arrival
time
Depth & Time
Shot
receivers

14. GATHERS OF DIFFERENT TYPES
Shot
receivers
Common shot gather

15. GATHERS OF DIFFERENT TYPES
Shots
receiver
Common Receiver gather

16. GATHERS OF DIFFERENT TYPES
Shots
receiver
Common Mid Point gather
Mid Point

17. First Arrivals
Groundroll
Reflections

18. Tail Buoy
Tail Buoy
To Vessel
Tail Buoy
Vessel
Energy
source
CMP
Seismic Data Acquisition
(Marine)

26. Based on the causes responsible for their occurrence, earthquake
and described as Tectonic and non-Tectonic.
Tectonic Earthquake: Due to internal causes, due to disturbances
or adjustments of geological formations taking place in the earth’s
interior, they are less frequent but more intensive and hence more
destructive in nature.
Non-Tectonic Earthquake: Due to external or surficial causes.
This type of Earthquake are frequent, but minor in intensity and
generally not destructive in nature.
Man-Made Earthquakes: The impounding of large quantities of
water behind dams disturbs the crustal balance. The shock waves
through rocks set up by the underground testing of Atoms bombs
or Hydrogen bombs may be severe to cause acoustic energy.

37. Primary Waves (P - waves)
Speed of P - Waves are 330 m/s in air,
1450 m/s in water and
5000 m/s in granite

50. Effects of Earthquake
•Earthquakes are a natural hazard. If a tremor of high
magnitude takes place, it can cause heavy damage to the life
and property of people. The following are the immediate
hazardous effects of earthquake:
• Ground Shaking
• Differential ground settlement
• Land and mudslides
• Fires
• Ground lurching
• Avalanches
• Ground displacement
• Floods from dam and levee failures
• Structural collapse
• Tsunami

55. Simple Horizontal motion seismograph

57. Aftershock: A tremor that follows a larger earthquake, or
main shock, that originates at or near the focus of the larger
earthquake. Generally major earthquakes are usually
followed by many aftershocks, which gradually decrease in
frequency and magnitude with time. Depending on the size
of the main event, aftershocks may last from days to several
months.
Focus/Hypocenter: The initial rupture point of an
earthquake at some depth within the earth.
Epicenter: Epicenter is a point on the surface of the Earth
that is directly above the underground point (called the
focus) where fault rupture commences

58. The Global distribution of earthquakes is as follows:
Over 80 per cent of large earthquakes occur around
the edges of the Pacific Ocean, an area known as the
'Ring of Fire'; this where the Pacific plate is being
subducted beneath the surrounding plates. The Ring
of Fire is the most seismically and volcanically active
zone in the world. around the Pacific Ocean such as
New Zealand, New Guinea, Japan, Alaska and the
western coasts of North and South America

59. Global Distribution of Earthquakes
Earthquakes can strike any location at any time, but history shows they
occur in the same general patterns year after year, principally in three
large zones of the earth:
•The Circum-Pacific seismic belt, the world's greatest earthquake
belt, about 81 percent of the world's largest earthquakes.
•The Alpine earthquake belt (mid Continental belt) extends from Java
to Sumatra through the Himalayas, the Mediterranean, and out into the
Atlantic about 17 percent of the world's largest earthquakes.
•The mid-Atlantic Ridge. The ridge marks where two tectonic plates are
spreading apart (a divergent plate boundary).

61. a total of ~59% of the land mass of India
(covering all states of India) is prone to
earthquakes of different intensities. As per the
seismic zoning map of the country, the total
area is classified into four seismic zones.
Zone V is seismically the most active region,
while zone II is the least.
Approximately,
~ 11% area falls in zone V,
~18% in zone IV,
~ 30% in zone III and remaining
~ 41% in zone II.