Earthquakes

Summary

In this educational video, Teacher Joanna explains the dynamic nature of Earth’s tectonic plates and how they cause earthquakes. The lesson covers the different types of seismic waves, including body waves (P-waves and S-waves) and surface waves (Love waves and Rayleigh waves). The anatomy of an earthquake is explored, highlighting the focus, epicenter, and fault lines. The video also details the different types of faults—normal, thrust (reverse), and strike-slip—and their impact, with a special focus on the potential for a major earthquake in Metro Manila. It’s an engaging overview of seismology and tectonic plate movements.

Takeaways

• 😀 The Earth is made up of around 20 tectonic plates, which are in constant motion, causing earthquakes when they interact.
• 😀 Earthquakes generate seismic waves, which are vibrations caused by the sudden breaking of rocks within the Earth.
• 😀 Seismology is the study of earthquakes and seismic waves, focusing on how these waves travel through the Earth's interior.
• 😀 There are two main types of seismic waves: body waves (which travel through the Earth's inner layers) and surface waves (which move along the surface).
• 😀 Body waves include P-waves (primary/compressional waves) which are the fastest and can travel through all states of matter, and S-waves (secondary/shear waves) which are slower and only travel through solid materials.
• 😀 Surface waves include Love waves (which cause horizontal ground movement) and Raleigh waves (which cause elliptical, ocean-like movement). Love waves are the most destructive.
• 😀 The 'focus' or hypocenter is the point inside the Earth where an earthquake originates, and seismic waves radiate from there.
• 😀 The 'epicenter' is the location on the Earth's surface directly above the focus where the most intense shaking occurs.
• 😀 Faults are fractures in the Earth's surface where tectonic plates move. They can be categorized into normal faults, reverse (thrust) faults, and strike-slip faults.
• 😀 The San Andreas Fault in California is an example of a strike-slip fault, where plates move sideways, and the Marikina West Valley Fault in the Philippines is another example of a strike-slip fault.
• 😀 The 'Big One' refers to a predicted 7.2 magnitude earthquake in Metro Manila, Philippines, caused by the Marikina West Valley Fault, which has a history of movement every 400 years.

Q & A

What are tectonic plates and how do they relate to earthquakes?

Tectonic plates are large pieces of Earth's lithosphere that move and interact with one another. Earthquakes are caused when these plates collide, slide past, or pull away from each other, creating stress that results in seismic waves.

What is the origin of the term 'seismic waves'?

The term 'seismic' comes from the Greek word meaning 'shaking'. Seismic waves are energy waves generated by the sudden breaking or shifting of rocks within the Earth.

What is seismology and what does it involve?

Seismology is the study of earthquakes and seismic waves. It involves analyzing how seismic waves travel through the Earth to understand the internal structure of the planet and predict earthquake behavior.

What are the two main types of seismic waves?

The two main types of seismic waves are body waves and surface waves. Body waves travel through the Earth's interior, while surface waves move along the Earth's surface.

How do P-waves differ from S-waves?

P-waves (Primary waves) are faster and can travel through solids, liquids, and gases, moving the ground in a compressional motion. S-waves (Secondary waves) are slower, can only travel through solids, and move the ground in a shear, up-and-down or side-to-side motion.

What is the difference between Love waves and Rayleigh waves?

Love waves cause the ground to move horizontally from side to side and are more destructive, while Rayleigh waves create an elliptical, rolling motion similar to ocean waves, shaking the ground in an up-and-down pattern.

What are the focus and epicenter of an earthquake?

The focus (or hypocenter) is the point within the Earth where the earthquake originates. The epicenter is the location on the Earth's surface directly above the focus, where the effects of the earthquake are most strongly felt.

What are faults and why are they important in earthquake studies?

Faults are fractures or zones of weakness in the Earth's crust where tectonic plates interact. Understanding faults is crucial because they are often the sites where earthquakes originate, as seismic waves are generated when the plates move along these fractures.

What are the three main types of faults and how do they differ?

The three main types of faults are normal faults, reverse (thrust) faults, and strike-slip faults. Normal faults occur when the hanging wall moves downward due to tension. Reverse faults happen when the hanging wall moves upward due to compression. Strike-slip faults involve horizontal lateral movement of blocks, with no vertical displacement.

Why is the Marikina West Valley Fault significant in the Philippines?

The Marikina West Valley Fault is significant because it is predicted to produce a large earthquake, potentially a magnitude 7.2, with serious consequences for Metro Manila and its neighboring provinces. The fault has moved in the past and is expected to move again in the near future, making it a major concern for earthquake preparedness.