GEOLOGICAL PRINCIPLES Flashcards
What forms the bedrock of safe and sustainable civil engineering?
Geological knowledge
Understanding seismic hazards and groundwater dynamics is crucial for civil engineering.
What are the critical intersections between geology and civil engineering discussed in the report?
Earthquake genesis and hydrological prospecting
These aspects have implications for infrastructure resilience.
What modern technique integrates real-time groundwater monitoring to address liquefaction risks?
Seismic retrofitting techniques
This approach enhances disaster mitigation strategies.
What advances allow precise mapping of fault zones beneath urban centers?
Geophysical imaging
This represents a paradigm shift from reactive to proactive disaster mitigation.
How many seismic events does the Philippines experience daily?
20+ seismic events
This is due to its dynamic tectonic setting.
What tectonic plates converge in the Philippine Archipelago?
Eurasian, Philippine Sea, and Indo-Australian plates
This convergence creates a seismogenic powerhouse.
What is the width of the Philippine Mobile Belt?
300 km-wide
It is a zone of intense crustal deformation.
What is the northwestward motion of the Philippine Sea Plate relative to Sundaland?
8-10 cm/yr
This motion drives megathrust earthquakes and strike-slip faulting.
What is the role of the Philippine Mobile Belt?
Acts as a buffer between tectonic plates
It facilitates interactions between subduction systems.
True or False: The Philippine Archipelago is located in a tectonically stable region.
False
It is one of Earth’s most dynamic tectonic intersections.
Fill in the blank: The Philippine Mobile Belt is a zone of intense crustal deformation bounded by opposing _______.
subduction systems
This defines the geological dynamics of the region.
What does the Philippine Mobile Belt act as a buffer between?
• Manila Trench (West)
• Philippine Trench (East)
• Cotaboato Trench (South)
These trenches involve different types of subduction interactions.
What is the rate of subduction of the Eurasian Plate beneath Lu20n?
2-5 cm/y
This subduction forms the Lu20n Volcanic Arc.
What is the depth of the Philippine Trench?
10,540 m
This makes it the Earth’s third deepest trench.
What type of boundary is the Cotaboato Trench?
Collisional boundary
It accommodates convergence through thrust faults.
What is the convergence rate accommodated by the Cotaboato Trench?
4 cm/yr
This rate is significant for seismic activity in the region.
What geological features manifest from the E-W compression at S-? kPa/yr?
• Uplifted coral terraces in Bondoc Peninsula
• Folding of Miocene limestone into anticlines beneath Metro Manila
• Oblique-slip mechanisms along the Philippine Fault Zone
These features illustrate the effects of tectonic compression.
What is the length and width of the Philippine Fault Zone?
1,200 km length, 5-40 km width
This structure plays a critical role in accommodating tectonic stress.
What percentage of oblique Philippine Sea Plate convergence transfers to trench-normal subduction?
70%
This highlights the dynamics of the subduction process.
What percentage of the convergence manifests as strike-slip along the Philippine Fault?
30%
This reflects the movement dynamics along the fault.
What are the GPS vectors indicating about slip rates near Leyte and Mindanao?
22 mm/yr slip near Leyte vs 35 mm/yr in Mindanao
This indicates increasing strain accumulation towards the south.
What is the recurrence interval for M?+ earthquakes along the Philippine Fault?
200-400 years
This is influenced by the fault’s segmented structure.
What is the thickness of the accretionary wedge in the Manila Trench?
8 km thick
The accretionary wedge is characterized by a 3° dip angle and is prone to shallow thrust events.
What magnitude events can the locked megathrust in the Manila Trench potentially generate?
M8.3 events
It extends 150 km downdip and has a co-seismic slip of 6-8 m based on coral microatoll data.
What type of eruptions are correlated with the slab depth of 120-180 km in the Manila Trench?
Andesitic eruptions
Mayon Volcano’s eruptions exhibit SiO₂ content of 58-63%.
At what rate is the Philippine Trench propagating southward?
50 mm/yr
The trench is classified as young, being less than 9 million years old.
What is the dip angle of the Benioff zone in the Philippine Trench?
45°W
This geometry limits deep seismicity to less than 150 km depth.
What does the duplex structure at 50-70 km depth in the Philippine Trench suggest?
Slab dehydration embrittlement
This is related to the double seismic zone observed in the trench.
What tsunami risk was associated with the 2017 M6.5 Surigao earthquake?
Generated 2 m waves
This was caused by splay fault activation.
What is the length of the West Valley Fault (wVF) in Metro Manila?
100 km long
It has a magnitude capability of M7.2 with a recurrence interval of 400 years.
What vertical offsets were revealed in paleoseismic trenches in relation to the West Valley Fault?
2-4 m vertical offsets
These offsets are found in Holocene alluvium.
What is the potential impact of an M8.2 scenario from the Manila Trench Megathrust?
Induce 0.89 PGA
This is particularly concerning for reclaimed areas like Parañaque.
What is the N₁ value in coastal districts like Pasay and Navotas?
Less than 10
This indicates the need for stone column densification due to liquefaction risks in saturated Holocene sands.
What is Base Isolation in the context of seismic design?
Base Isolation involves using lead-rubber bearings to withstand seismic shaking.
Example: San Beda College retrofit used 120 lead-rubber bearings (K=1.2 kN/mm) to withstand 0.69 shaking.
What is the purpose of Fault Setbacks according to PHIVOLCS?
Fault Setbacks mandate a 10 m exclusion zone from active fault traces.
This is challenging for developments in fault-crossing areas like Baguio.
What type of tsunami barriers are employed at Matina Coast in Davao?
8 m-high seawalls with energy-dissipating tetrapods are used.
Tetrapods are 35-ton units designed to absorb wave energy.
What was the magnitude and impact of the 1990 Luzon Earthquake?
Magnitude 7.8; caused $364M damage, 78% of collapsed buildings had soft-story weaknesses.
The earthquake was caused by the Philippine Fault rupture.
What geological event characterized the 2013 Bohol Earthquake?
A blind thrust reactivation tilted the Chocolate Hills 5 degrees, exposing limestone bedrock.
The earthquake had a magnitude of 7.2.
What was notable about the 2023 Masbate Earthquake?
It had a magnitude of 6.6 and involved strike-slip motion along an offshore segment.
This generated 5 cm of co-seismic uplift.
What does the volcanic activity of Mayon in 2018 reveal about volcano-tectonic interplay?
Mayon’s 2018 eruption (VEI 3) coincided with 142 M3+ earthquakes from magma-induced stress transfer.
Engineers must integrate real-time SO2 monitoring into evacuation protocols.
What is the rate of sea level rise and its impact on tsunami inundation in Manila?
Sea level rise is 3 mm/year, exacerbating tsunami inundation depths by 12-18% per RCP8.5.
RCP8.5 refers to a high greenhouse gas concentration scenario.
Fill in the blank: The 1990 Luzon Earthquake had a magnitude of _______.
7.8
True or False: The 2013 Bohol Earthquake resulted in the tilting of the Chocolate Hills.
True
What role does real-time SO2 monitoring play in civil engineering during volcanic eruptions?
It is integrated into evacuation protocols to ensure public safety.
Monitoring thresholds are set at 10-20 kt/day.
What is the rate of sea level rise that exacerbates tsunami inundation depths in Manila?
3 mm/yr
This subsidence increases inundation depths by 12-18% per RCP8.5.
What extreme weather event triggered 1,200 landslides in Leyte’s fault-weathered schists?
Typhoon Jolina (2021)
This event highlights the impact of extreme weather on geological stability.
What type of sensing network detects microtremors along EDSA?
Fiber Optic Sensing
The 150 km DAS network has a strain sensitivity of 10-6.
What system issues alerts 10-40 seconds before seismic shaking in the Philippines?
PHIVOLCS’ Terra system
It uses Bayesian source inversion for early warning.
What are continental plates?
Massive, rigid slabs of rock that form the Earth’s continents
They are thicker and less dense than oceanic plates.
What are oceanic plates?
Large, rigid slabs of rock that form the ocean floor
They are thinner and denser than continental plates.
What is the asthenosphere?
A hot, soft layer of the mantle beneath tectonic plates
It acts like a giant, slow-moving conveyor belt.
How do tectonic plates move?
They are dragged by currents in the asthenosphere
These currents are caused by heat from Earth’s core.
Fill in the blank: Continental plates are _______ and less dense.
thicker
Fill in the blank: Oceanic plates are _______ and denser.
thinner
What are the three types of plate boundaries?
Convergent, Divergent, Transform
These boundaries describe the movement and interaction of tectonic plates.
What happens at convergent boundaries?
Plates collide or come together
This can lead to geological phenomena such as mountain formation, volcanic activity, and earthquakes.
What geological phenomena can result from convergent boundaries?
- Mountain formation
- Volcanic activity
- Earthquakes
These phenomena occur due to the interactions of colliding tectonic plates.
What is the movement of plates at divergent boundaries?
Plates move away from each other
This movement leads to the creation of new crust.
What is created at divergent boundaries?
New crust as magma rises from the mantle
The magma solidifies and forms new oceanic crust.
What role do divergent boundaries play in Earth’s geology?
Responsible for continuous reshaping and formation of Earth’s crust
This process is essential for the dynamic nature of the planet’s surface.
What is the movement of plates at transform boundaries?
Plates slide past each other
This sliding motion can lead to earthquakes.
________ occur when two
plates slide past each other horizontally. The movement along these boundaries can cause earthquakes, as the plates grind
against each other.
Transform Boundaries
When continental
plates collide (e.g., the Himalayas).
Convergent
When the plates rub
each other (e.g. San Andreas Fault).
Transform
Where new oceanic
crust forms. (e.g. Mid-Atlantic Ridge).
Divergent
