Earthquakes and Faults - Grade 7 Earth and Space

• Introduction to Earthquakes and Faults - Grade 7 Earth and Space - Week 1

Pacific Ring of Fire

• A tectonic belt surrounds most of the Pacific Ocean
• Pacific Ring of Fire includes a region of frequent earthquakes and volcanic eruptions
• Plate tectonics are the result of tectonic plates that meet, move apart, or slide past each other
• Ground movement is responsible for the geological activity
• About 75% of the world's active volcanoes are located in the Pacific Ring of Fire
• Two ASEAN countries lie directly on the path of the ring of fire: Indonesia and the Philippines

Faults

• Faults include normal, reverse, and strike-slip faults
• Fault is a fracture in the Earth's crust through which movement occurs
• Earthquake is a sudden and violent shaking of the ground caused by the movement of tectonic plates beneath the earth
• Can occur on land or under the ocean
• Seismicity refers to the occurrence and distribution of earthquakes in a region

Normal Faults

• Characterized by a fault plane angle inclined less than 45 degrees from horizontal
• Vertical motion is present, where the hanging wall moves downward relative to the footwall
• This type of faulting occurs in extensional tectonic settings, such as divergent plate boundaries
• Normal faults form in areas undergoing extensional tectonic stress, where the Earth's crust is pulled apart (divergent movement)
• Formation of valleys
• Tensional stress builds along the fault plane as the hanging wall moves downward relative to the footwall
• The accumulated stress exceeds the strength of the rocks, which causes them to rupture and release energy as seismic waves

Reverse Faults (Thrust Faults)

• The fault plane angle is inclined at an angle greater than 45 degrees from the horizontal
• Vertical motion where the hanging wall moves upward relative to the footwall
• Typically form in compressional tectonic settings, such as convergent plate boundaries
• Reverse faults form in areas undergoing compressional tectonic stress, where the Earth's crust is pushed together
• Compressional stress builds up along the fault plane as the hanging wall moves upward relative to the footwall
• Accumulated stress exceeds the strength of the rocks, the rocks break the fault, and it releases stored energy as seismic waves

Strike-Slip Faults

• Display a nearly vertical fault plane angle, with minimal inclination from the horizontal
• Horizontal motion where the movement is predominantly lateral along the fault plane
• Commonly found in transform plate boundaries, where two tectonic plates slide past horizontally
• Strike-slip faults form in areas undergoing lateral tectonic stress, where the Earth's crust moves horizontally past each other
• Stress builds due to friction between the moving plates
• When frictional resistance is overcome, the side of the fault slips past each other suddenly, releasing energy as seismic waves

Faults in the Philippines

• Most common types of faults are strike-slip and thrust (reverse) faults
• Located along the boundary of the Philippine Sea Plate and the Eurasian Plate
• Movement is predominantly lateral (strike-slip) and compressional (thrust)
• Account for the significant seismic activity and earthquakes experienced in the region
• The Philippine Fault or Philippine Fault Zone (PFZ) is a 1200-km fault zone cutting almost the whole archipelago
• The Philippine fault zone is a transform boundary formed by the movement of the Philippine Sea Plate and the Eurasian Plate
• Active faults are structures where displacement is expected to occur
• Shallow earthquakes are mechanisms that cause displacement across a fault, they must all occur on active faults
• Marikina Valley Fault System (MVFS) is the most active fault line
• Other active faults: Valley Fault System or Marikina Valley Fault, Legazpi Lineament, Macolod Corridor, Tablas Lineament, Lubang-Verde Passage Fault System, Mindanao Fault, Mindoro or Aglubang Fault, Offshore Cebu-Bohol Faults, and Sibuyan Sea Fault
• Inactive Faults are features that can be recognized but do not produce earthquakes

An introductory lesson for Grade 7 Earth and Space about earthquakes and faults. The Pacific Ring of Fire has frequent earthquakes and volcanic eruptions due to plate tectonics. Faults are fractures in the Earth's crust where movement occurs, leading to earthquakes.