Earthquake
Earthquake is the sudden shaking of the ground that we feel when rock layers of Earth suddenly
slip past one another
The fracture in the surface of the crust where the two blocks of rocks slip is called the Fault
Faults
Active faults are areas along which all shallow earthquakes occur
Inactive faults are areas which have not displayed any seismic activity for more than thousands
of years
Types of Faults
Normal Fault Reverse Fault Strike-Slip Fault
Earthquake
Among the layers of the Earth, an earthquake originates somewhere between the crust and the
mantle
The upper mantle or the asthenosphere consists of semi-fluid materials and partially molten
rocks
The entire crust extending to the uppermost portion of the mantle is called the lithosphere
Lithospheric plates are constantly moving and because of the friction and of the rigidity of the
rocks, they cannot flow past each other
Where Does An Earthquake
Occur?
Countries bordering the
Pacific Ocean including
the Philippines, Japan,
China, Canada, New
Zealand, North and
South America, Chile,
Russia, Indonesia, and
Mexico are mostly hit by
earthquakes
Plate Boundaries
Divergent Boundaries
A feature that exists when two tectonic plates move away from each other
Convergent Boundaries
A place where two tectonic plates move toward each other
(1) Oceanic – Oceanic Convergence, (2) Oceanic – Continental Convergence, (3) Continental –
Continental Convergence
Oceanic – Oceanic Convergence Oceanic – Continental Convergence
Continental – Continental Convergence
Transform Boundaries
Formed when two plates slide past each other, horizontally
Measuring Earthquakes
Magnitude measures the
amount of energy released at the
source of an earthquake
Intensity measures the amount
of damage by the shaking
produced by the earthquake
Mercalli Scale
Invented by Giuseppe Mercalli in
1902
Uses the observation of people who experience the earthquakes to estimate its intensity
Richter Scale
Developed in 1934 by Charles Richter
Richter scale uses the amplitude of the largest recorded seismic wave
Transverse Wave
Effects of Earthquake
Earthquakes pose great danger and destruction because they do not happen at once
Foreshock
Foreshocks are small earthquakes that commonly precede a major earthquake
It can be felt from few minutes to days or even years prior to the main shock
Aftershock
After the major earthquake, smaller earthquakes called aftershocks occur
They are formed as the crust adjust to the effects of the main shock
Tsunami
Tsunami is a Japanese word for “big wave in the port”
A series of extremely long waves cause by a large and sudden displacement of the ocean,
usually the result of an earthquake below or near the ocean floor
Tsunamis can also be produced by other natural phenomena aside from an undersea
earthquake:
a. underwater landslide
b. volcanic eruptions
c. very rarely by large meteorite impacts
Not all earthquakes can produce tsunamis. Below are the three things that will allow to generate
tsunamis:
1. A minimum of magnitude 7 on the Richter scale must be recorded
2. The seabed must be lifted or lowered by the quake
3. The focus of the earthquake must be near the Earth’s surface
Active Faults in the Philippines
1. Marikina Valley Fault (Montalban – San Mateo – Marikina – Pasig – Taguig – Muntinlupa – San
Pedro – Biñan – Carmona – Sta. Rosa – Calamba – Tagaytay – Oriental Mindoro)
2. Western Philippine Fault (Luzon Sea – Mindoro Strait – Panay Gulf – Sulu Sea)
3. Eastern Philippine Fault (Philippine Sea)
4. Southern Mindanao Fault (Moro Gulf – Celebes Sea)
5. Central Philippine Fault (Entire Ilocos Norte – Aurora – Quezon – Masbate – Eastern Leyte –
Southern Leyte – Agusan Del Norte – Agusan Del Sur – Davao Del Norte)
1990 Central Luzon Earthquake
Magnitude 7.7 earthquake struck and seriously damaged Central Luzon and Baguio
The event was a result of strike-slip movements along the Philippine Fault and the Digdig Fault
2013 Bohol Earthquake
Magnitude 7.2 earthquake affects the whole Central Visayas, particularly Bohol and Cebu
Generated by the North Bohol Fault
By December 6, 4,026 aftershocks were recorded, 114 of which were felt
1976 Moro Gulf Earthquake
The 1976 Moro Gulf Earthquake initially measures 8.9 magnitude
The epicenter of the tsunami, which reached a height of 9 to 14 meters, was located 40
kilometers from Sultan Kudarat
Earthquake Preparedness
Before An Earthquake
1. Examine every part of the house – know the safe and dangerous spots
2. Repair any deep cracks in ceilings or walls
3. Bolt or fix heavy furniture to the walls
4. Have a regular inspection of the stability of hanging objects
5. Easy-to-break objects must be placed securely
6. Keep the dangerous chemicals outside the house, in the garage or outside shed
7. Turn off the gas tanks when not in use
8. Prepare a bag filled with emergency supplies and basic needs
9. Learn and practice first aid
10. Always recharge the cellphones if it is needed
11. Participate in earthquake drills
12. Unplug the appliances if not in use
13. If possible, make fire extinguisher available and put it in a safe place
14. Be familiar with the doorways or emergency exits
During An Earthquake
If indoors:
1. Stay inside, be calm and do the “Drop, Cover, and Hold”
2. Stay away where there are glass windows, shelves, cabinets, and other heavy objects
3. Be alert and keep your eyes open
4. Do not stand in doorways
5. Do not use elevators
If outdoors:
1. Move to an open area
2. If driving, do not attempt to cross bridges, overpass, or flyovers
3. If you are near the shore, go immediately to higher places
4. If you are in a crowded place, stay calm and do not rush for the doors
After An Earthquake
1. Keep calm and expect aftershocks, so be alert
2. Check yourself and others for injuries
3. Do not operate electrical switches
4. Check the electrical and water lines for damage and the gas leaks
5. Turn on the radio and listen to news
6. Avoid driving to clear the streets for emergency vehicles
7. If you will leave your home, bring the emergency kit
8. If you are not seriously harmed, look around you to help others
