Podcast
Questions and Answers
What characterizes a fault?
What characterizes a fault?
- A break in Earth's crust with observable movement (correct)
- A uniform area of rock without any fractures
- A permanent fracture that never changes
- A fault line that is always active
Which type of stress refers to rocks being pushed toward each other?
Which type of stress refers to rocks being pushed toward each other?
- Shear stress
- Tensional stress
- Compressional stress (correct)
- Rotational stress
Which of the following statements about fault zones is correct?
Which of the following statements about fault zones is correct?
- Fault zones can contain a series of associated faults over an area (correct)
- Fault zones only occur at the Earth's surface
- Fault zones indicate a complete lack of tectonic activity
- Fault zones are exclusively made up of shear faults
How do rocks typically respond to stress compared to clay?
How do rocks typically respond to stress compared to clay?
What does tensional stress do to rocks?
What does tensional stress do to rocks?
What is the primary characteristic of the Central Mindoro Fault?
What is the primary characteristic of the Central Mindoro Fault?
How long is the Philippine Fault Zone (PFZ)?
How long is the Philippine Fault Zone (PFZ)?
What type of fault movement is most commonly associated with the Valley Fault System?
What type of fault movement is most commonly associated with the Valley Fault System?
Which area does the Lubang Fault primarily run through?
Which area does the Lubang Fault primarily run through?
What is the average movement rate of faults in the Philippine Fault Zone?
What is the average movement rate of faults in the Philippine Fault Zone?
What characterizes active faults?
What characterizes active faults?
Which situation makes it difficult to interpret fault activity?
Which situation makes it difficult to interpret fault activity?
What does the term 'creep' refer to in relation to faults?
What does the term 'creep' refer to in relation to faults?
What is a defining feature of inactive faults?
What is a defining feature of inactive faults?
What might indicate noticeable creep in a fault?
What might indicate noticeable creep in a fault?
What type of fault is characterized by the hanging wall moving down relative to the footwall?
What type of fault is characterized by the hanging wall moving down relative to the footwall?
Which of the following dip angles is associated with a thrust fault?
Which of the following dip angles is associated with a thrust fault?
What is the primary effect of a normal fault on the length of the rock body?
What is the primary effect of a normal fault on the length of the rock body?
In a reverse fault, how does the movement of the hanging wall compare to that of the footwall?
In a reverse fault, how does the movement of the hanging wall compare to that of the footwall?
What type of fault is a special case of a reverse fault with a dip angle less than 45°?
What type of fault is a special case of a reverse fault with a dip angle less than 45°?
How does the movement in a normal fault differ from that in a reverse fault?
How does the movement in a normal fault differ from that in a reverse fault?
What is the typical dip angle for a normal fault?
What is the typical dip angle for a normal fault?
Which tool developed by DOST-PHIVOLCS helps engineers assess potential hazards for building structures?
Which tool developed by DOST-PHIVOLCS helps engineers assess potential hazards for building structures?
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Study Notes
Earth's Crust and Faults
- Earth's crust is fragmented and constantly interacts
- Faults are fractures in the crust where earthquakes are most likely to occur
- Faults form due to compression or stretching of rocks caused by plate movement
- A fault zone is a series of associated faults spread over a large area
Types of Stress
- Tensional stress: Rocks are pulled apart
- Compressional stress: Rocks are pushed together
- Shear stress: Rocks slide past each other
Dip-Slip Faults
- Normal faults:
- Rocks are stretched
- Hanging wall moves down relative to the footwall
- Dip angle is greater than 45°
- Rock length increases
- Reverse faults:
- Rocks are compressed
- Hanging wall moves up relative to the footwall
- Dip angle can be less than 45° in thrust faults
- Rock length decreases
- Thrust faults:
- A special type of reverse fault
- Dip angle is less than 45°
- Rock length decreases
Active and Inactive Faults
- Active faults: Generated earthquakes within the last 10,000 years and could generate future earthquakes
- Inactive faults: No known earthquakes in the past 10,000 years, but may generate future earthquakes
- Creep: A slow type of fault movement that can cause ground subsidence and deformed structures
Faults in the Philippines
- The National Building Code of the Philippines guides engineers and architects
- The DOST-PHIVOLCS developed the Spectral Acceleration Maps of the Philippines (SAM PH) Atlas
- SAM PH Atlas provides engineers with information about potential hazards and risks in specific locations
Philippine Fault Zone (PFZ)
- The PFZ is 1200 km long and extends throughout Luzon, Visayas, and Mindanao
- It's composed of multiple interconnected faults
- Faults move at varying rates, approximately 2-3 centimeters per year
Central Mindoro Fault
- This fault is marked by a break in slope along the coast of Mindoro
- Primarily a right-lateral strike-slip fault, with some sections showing normal dip-slip movement
- A 7.1 magnitude earthquake in 1994 was associated with this fault
Valley Fault System
- Extends from Angat Dam in Bulacan through Metro Manila, and possibly south to the Tagaytay Ridge
- Some segments show normal dip-slip or oblique movements
- Scientists have identified significant earthquakes along this system in the last 1500 years
Lubang Fault
- Runs offshore in the Verde Island Passage, between Batangas and Mindoro
- Starts as a left-lateral strike-slip fault, shifting towards a mixed oblique-slip fault near the Manila Trench
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