1. EARTHQUAKES

2. WHAT IS AN EARTHQUAKE?
• intense ground shaking caused by sudden release
of energy
• can be generated by bomb blasts, volcanic
eruptions and sudden slippage along faults
• a geologic hazard for those living in earthquake-
prone areas
• also provided valuable information about the
Earth’s interior

3. Elastic Rebound Theory

6. Body and Surface
waves

8. EARTHQUAKE MAGNITUDE SCALE
Magnitude Earthquake Effects Estimated Number
Each Year
2.5 or less Usually not felt, but can be 900,000
recorded by seismograph.
2.5 to 5.4 Often felt, but only causes 30,000
minor damage
5.5 to 6.0 Slight damage to buildings 500
and other structures
6.1 to 6.9 May cause a lot of damage 100
in very populated areas.
7.0 to 7.9 Major earthquake. Serious 20
damage.
8.0 or greater Great earthquake. Can One every 5 to 10
totally destroy communities years
near the epicenter.

10. for each whole number you go up on the Richter scale, the
amplitude of the ground motion recorded by a seismograph
goes up ten times.
Using this scale, a magnitude 5 earthquake would result in ten
times the level of ground shaking as a magnitude 4 earthquake
(and 32 times as much energy would be released).
To give you an idea how these numbers can add up, think of it
in terms of the energy released by explosives: a magnitude 1
seismic wave releases as much energy as blowing up 6 ounces
of TNT. A magnitude 8 earthquake releases as much energy as
detonating 6 million tons of TNT.
TNT

12. DESCRIBING THE STRENGTH OF AN EARTHQUAKE
Intensity is the degree of ground shaking at a given locale
based on the amount of damage
Depends on distance to earthquake
& strength of earthquake
Modified Mercalli Intensity Scale
Philippine Earthquake Intensity Scale
Magnitude is calculated from seismic records and
estimates the amount of energy released at the source
Depends on size of fault that breaks
Richter Scale

13. MAGNITUDE OF AN EARTHQUAKE

14. INTENSITY OF AN EARTHQUAKE
Philippine Earthquake Intensity Scale – I to X (PHIVOLCS)

16. STRUCTURAL DAMAGE DUE TO EARTHQUAKE
VIBRATIONS DEPENDS ON:
Wave amplitudes
Duration of
vibrations
Nature of material
upon which the
structure rests
Design of structure

17. Earthquake Destruction
important factors:
Nature of material upon
which structure rests
A building on bedrock experiences
less movement compared to a
structure built on loosely
consolidated sediments (tend to
amplify shaking)

19. Earthquake Destruction
important factors:
Intensity & duration of shaking
Mexico City, 1985

20. Earthquake Destruction
important factors:
Building design
:

21. DESTRUCTIVE EFFECTS OF EARTHQUAKES

22. SECONDARY EFFECTS OF EARTHQUAKES
tsunamis
landslides
ground subsidence
Fire
Liquefaction

23. SECONDARY EFFECTS OF EARTHQUAKES: TSUNAMIS

24. SECONDARY EFFECTS OF EARTHQUAKES:
LANDSLIDES

25. SECONDARY EFFECTS OF EARTHQUAKES:
GROUND SUBSIDENCE

26. SECONDARY EFFECTS OF EARTHQUAKES:
FIRES

27. SECONDARY EFFECTS OF EARTHQUAKES:
LIQUEFACTION

28. PHILIPPINE EARTHQUAKE GENERATORS
Oblique convergence
of two subducting
oceanic plates
Collision zones
Active faults

29. RECENT
EARTHQUAKE
21.17 km
BNPP
occurred at 6:55 (Jan 12,
2009) with Magnitude 5
-USGS

30. RECENT DESTRUCTIVE EARTHQUAKES
July 16, 1990, Luzon
(7.7)
Nov. 15, 1994,
Mindoro (7.8)
Mar. 6, 2002, Sultan
Kudarat (6.8)
Feb. 15, 2003,
Masbate (6.2)

32. Recurrence interval of Marikina fault – 200 years
We have our own stress system so we have different
‘waiting time’ – Rimando , R.

33. EARTHQUAKE
MONITORING

34. EARTHQUAKE PREDICTION: SHORT TERM
• Monitor to look for patterns of recurrence
• Strange animal behavior
• Increase in seismic tremors (mini-quakes)
• Seismic gaps
• Gas emissions
• Electromagnetic signals

35. EARTHQUAKE PREDICTION: EARTHQUAKE CYCLES

36. EARTHQUAKE PREDICTION: SEISMIC GAPS
Seismicity map
(1608 – 2004)

37. drill a deep hole in
order to install
instruments directly
within the San Andreas
Fault Zone
electronic laser, ground movement
monitoring system in California to
study the San Andreas Fault
seismograph
seismic sensor