Earthquakes and Earth Layers

• An earthquake involves shaking and trembling of the ground, due to the sudden release of energy from inside the Earth.
• Earthquakes occur in the crust and lithosphere layers of earth.

Earth Layers

• Crust is the outermost solid portion of Earth, where all living things are found.
• Lithosphere is the region containing the crust that extends down to the upper portion of the asthenosphere.
• Mantle, also known as the asthenosphere, lies beneath the lithosphere and is approximately 100-650km deep.

Earthquake Generation

• Tectonic forces cause extremely slow movement, resulting in lithospheric plates colliding, separating, or sliding past each other.
• As the lithosphere and crust move over time, rocks interlock and deform.

Pacific Ring of Fire

• The Pacific Ring of Fire is a region around the Pacific Ocean known for frequent earthquakes and volcanic eruptions.
• 75% of the world's dormant and active volcanoes are located here.
• It accounts for 90% of the world's earthquakes and more than 80% of the strongest ones.

Philippines

• The Philippines is in the Pacific Belt of Fire or Pacific Ring of Fire.
• The country is prone to massive earthquakes and volcanic eruptions.
• The Philippines has 24 active volcanoes and five active fault lines.

Faults

• A fault is a thin zone of crushed rock separating blocks of the Earth's crust.
• The hanging wall is the block above an inclined fault.
• A foot wall is the block below the fault.
• Earthquakes originate in a fault.
• Faults or fault lines are associated with earthquakes.
• Faulting occurs during rock mass movement along a fault. It results from tectonic forces applied to rock masses in the crust.

Types of Tectonic Forces

• Compressional force pushes rocks together. This force can create mountains.
• Tensional force pulls rocks away from each other and can create valleys.
• Shearing force enables rocks in the crust to slide past each other.

Types of Faults

• Reverse fault forms when a rock mass in the crust is pushed up relative to another due to compressional force.
• Normal fault occurs when tensional force causes one rock mass to move downward relative to another.
• Transform fault is produced when a rock mass slides past another, often causing violent earthquakes.

Active and Inactive Faults

• Active faults are areas where shallow earthquakes occur.
• Active faults exhibit evidence of strong and frequent earthquakes.
• Active faults are common in boundaries where plates bump into or move away from each other.
• Inactive faults consist of areas without seismic activity for thousands of years.
• Inactive faults may trigger bigger quakes.

Fault Examples

• The San Andreas Fault in California is an active fault.
• The Sierra Nevada Fault in the USA is an inactive fault.

Active Fault Lines in the Philippines, and Affected Areas

• Marikina Valley Fault: Montalban, San Mateo, Marikina, Pasig, Taguig, Muntinlupa, San Pedro, Binan, Carmona, Santa Rosa, Calamba, Tagaytay, Oriental Mindoro
• Western Philippine Fault: Luzon Sea, Mindoro Strait, Panay Gulf, Sulu Sea
• Eastern Philippine Fault: Philippine Sea
• Southern Mindanao Fault: Moro Gulf, Celebes Sea
• Central Philippine Fault: Ilocos Norte, Aurora, Quezon, Masbate, Eastern Leyte, Southern Leyte, Agusan Del Norte, Agusan Del Sur, Davao del Norte

Earthquake Parts

• Focus is the point where the earthquake begins. It is the source from which energy is released, radiating in all directions.
• Epicenter is the point on the ground directly above the focus, experiencing the first sudden movement and the most severe earthquake damage.

Philippines Vulnerability

• The Philippines is near the Pacific Ring of Fire, making it vulnerable to seismic activities and earthquakes.
• It also is visited by approximately twenty typhoons per year due to its geographical location.