Lesson 5

Question 1

“_________defined as a trembling or shaking of the ground caused by the
sudden release of energy stored in the rocks beneath the earth’s surface.”

Answer 1

Earthquake

Question 2

“change in their shape (distortion) or volume
(dilation), a process known as ________”

Answer 2

Strain

Question 3

“rocks are also considered to be ______, meaning that if the force (stress) is removed
they will return to their original shape.”

Answer 3

Elastic

Question 4

_________is the maximum amount of strain they can accumulate before either fracturing or undergoing plastic deformation;

Answer 4

Elastic Limit

Question 5

What are the two types of earthquake?

Answer 5

Tectonic and Volcanic

Question 6

“______ are vibrational waves that travel through solid earth materials which
may be magmatic, tectonic, or artificial in origin.”

Answer 6

Seismic Waves

Question 7

“T or F: structures are usually the strongest in
the vertical direction, and Ph construction only focuses on it making building more vulnerable to lateral forces”

Answer 7

TRUE

Question 8

Two types of seismic wave

Answer 8

Body waves, and Surface waves

Question 9

P wave velocity is approximately ______

Answer 9

4-7 km/s

Question 10

_____ is an instrument used to detect seismic waves.

Answer 10

Seismometer

Question 11

“a seismometer with a recording device that produces a
permanent record of earth motion, usually in the form of wiggly line drawn
on a moving strip of paper.”

Answer 11

Seismomgraph

Question 12

how deep is a deep earthquake?

Answer 12

350-670km

Question 13

“is a seismic scale used and developed by the Philippine Institute of
Volcanology and Seismology (PHIVOLCS) to measure the intensity of an
earthquake.”

Answer 13

Philippine Earthquake Intensity Scale (PEIS)

Question 14

“areas where tensional forces dominate the friction
along faults is naturally low, allowing them to slip in an almost continuous
process known as _______”

Answer 14

fault creep

Question 15

Enumerate the types of plate boundaries

Answer 15

Convergent, Divergent, Transoform

Question 16

How earthquakes occur

Answer 16

Earthquakes happen when giant, rigid slabs of Earth’s crust, called tectonic plates, grind past each other. The immense pressure causes these plates to suddenly slip, releasing energy in the form of waves that travel through the Earth’s interior and cause the shaking we feel on the surface.

Question 17

Difference between intensity and magnitude scales

Answer 17

Magnitude, like on the Richter scale, reflects the total energy released at the source, and is the same everywhere for a specific earthquake. Intensity, like the Modified Mercalli scale, describes how strong the shaking feels at a particular location, so it weakens with distance from the epicenter.

Question 18

Difference between body and surface waves.

Answer 18

Body waves travel through the interior of the Earth, while surface waves travel along the surface. Surface waves cause stronger shaking at the Earth’s surface, and are often more destructive.

Question 18

What are some earthquake precursors?

Answer 18

Increase in Foreshocks,
Slight swelling or tilting of the ground surface,
Decreased electrical resistance, Fluctuating water levels in wells, Increased concentration of radon gas in ground water,
Generation of radio signals.

Question 19

why earthquakes do not occur deeper than 435 miles (700 km) below the surface

Answer 19

“because the higher temperatures cause the rocks to become so ductile that
they deform only by plastic flow, hence do not rupture”

Question 20

Relate earthquakes to plate tectonics

Answer 20

“at convergent boundaries where compressive
forces dominate, rocks are able to accumulate much more strain before
rupturing than at divergent boundaries where tensional forces are dominant.”

Question 21

Explain a Fault Zone

Answer 21

“network of interlocking faults located on either side. This
means that as tectonic forces cause strain to accumulate
along the boundary, some of the strain is distributed among
the different faults within the fault zone.”

Question 22

Explain an Intraplate Earthquake

Answer 22

“earthquakes that occur far from a plate boundary or active
mountain belt and are generally believed to be related to tectonic forces
that are being transmitted through the rigid plates. forces cause
crustal rocks to slowly accumulate strain, which is then released along
buried fault systems, producing earthquakes”

Question 23

Why surface waves are destructive in construction?

Answer 23

“they cause the ground to vibrate in a lateral direction, and at the same
time, roll up and down like an ocean wave.”

Question 24

What is an epicentral distance?

Answer 24

“The distance of a seismic station from the epicenter of an
earthquake. The travel-times of P- and S-waves from an earthquake through
the body of the Earth to an observer are dependent on it.”

Question 24

What is the relationship between Natural vibration frequency and building height

Answer 24

building height increases, the natural vibration
frequency decreases— a city with multistory buildings of different heights, some
buildings will have a relatively low vibration frequency and others will have a relatively high frequency.”

Question 25

Explain attenuation

Answer 25

decrease of amplitude with increasing distsnce from the source

Question 26

Explain the concept of pancaking on building

Answer 26

After a strong earthquake, a floor of a building collapses causing it to fall down the floors due to lack of support, in a cascading manner

Question 27

How do Brittle failure of steel-reinforced concrete columns occur?

Answer 27

“when swaying motion causes the columns to reach their
elastic limit. Note that the steel rods themselves are not
strong enough to support the weight of the structure.”

Question 28

Enumerate secondary earthquake hazards.

Answer 28

liquifaction, ground displacement, ground fissures, earthquake mass wasting, fires, tsunamis

Question 29

Enumerate 6 Earthquake Precursors

Answer 29

Increaase in foreshocks, Slight swelling or tilting of the ground surface, decreased electrical resistance, fluctuating water levels in wells, Increased concentration of radon gas in geoundwater, generation of radio signals

Question 30

What is liquifaction

Answer 30

“– compacted sand-rich layers of sediment that are normally in
contact with one another behave as fluid”

Question 31

key differences os P-wAave and S-wave

Answer 31

P-waves can squeeze through any material, like a pulsating slinky. S-waves are slower and require solid rock to wiggle sideways, like shaking a jump rope.

Question 31

Enumerate ways on how to reduce earthquake risks

Answer 31

Seismic Engineering, Early Warning Systems, Planning and Education

Question 31

Hazard vs Risk

Answer 31

The “what if” - it’s anything that could potentially cause harm, like a wet floor or a lightning storm. The “how likely” - it considers how probable the hazard is to cause harm and how severe the consequences could be

Question 31

How do we measure seismic waves

Answer 31

measured using seismometers, which detect ground motion caused by earthquakes or other seismic events. These instruments record the movement of the ground in terms of amplitude and frequency, providing data used to analyze the characteristics of the waves and the source of the seismic activity.

Question 32

Explain how can we locate earthquakes

Answer 32

Earthquakes are located using seismometers positioned around the world, which detect the arrival times of seismic waves. By analyzing the time differences between when the waves arrive at various seismometer stations, scientists can triangulate the epicenter of the earthquake.

Question 33

“Explain why subduction zone earthquakes are capable of releasing unusually large
amounts of energy”

Answer 33

“the way the overriding plate buckles and
becomes locked. the surface area over which the slippage or rupture occurs
can be quite large compared to that in other plate settings.descending oceanic plate is relatively cool,
which makes the rocks more brittle and capable of accumulating more strain before
rupturing.”

Question 34

“Explain why the most dangerous types of homes are those constructed of unreinforced
masonry”

Answer 34

Unreinforced masonry houses crumble during earthquakes. The bricks are strong when compressed but crack easily from shaking. Unlike flexible structures, these buildings can’t sway with the ground, causing walls to crack and potentially collapse entirely.

Question 35

Are earthquakes important to the evolution of life? Why?

Answer 35

Earthquakes indirectly influence the evolution of life by shaping landscapes and altering habitats, which can drive evolutionary changes in species. Additionally, seismic events can trigger geological processes like volcanic eruptions or tsunamis, which can have profound effects on ecosystems and species distributions over time.

Question 36

“What are the dynamics between earthquakes and the exponentially
growing human population?”

Answer 36

”
The exponential growth of the human population leads to increased urbanization and infrastructure development in seismically active regions, resulting in higher exposure to earthquake hazards. This can escalate the risk of casualties and damage to property during seismic events. “

Question 37

What are the possible factors that increase earthquake hazard risks?

Answer 37

geological conditions like proximity to fault lines or tectonic plate boundaries, population density in earthquake-prone areas, poor infrastructure resilience, inadequate urban planning, and climate change-induced effects such as changes in groundwater levels or the stability of geological formations.

Question 38

Draw the three main types of fault and their focal mechanisms.

Question 39

How can seismic gaps be used to determine possible area of an earthquake?

Answer 39

Seismic gaps are segments along fault lines that have not experienced significant earthquake activity in a long time, suggesting accumulating stress. By monitoring these gaps and studying historical earthquake patterns, scientists can predict areas more likely to experience future earthquakes.

Question 40

“How does a tsunami originate? Why are tsunami
barely noticeable over the open ocean but very dangerous
near shore?”

Answer 40

”
Tsunamis form from large water displacements, like earthquakes or underwater landslides, and appear inconspicuous in the open ocean due to their long wavelengths. Near the coast, their energy compresses, leading to increased wave height and destructive potential upon reaching shore.”

Question 41

” What is the Mohoroviçiç discontinuity? What is the
seismic evidence for this feature? “

Answer 41

”
The Mohorovičić discontinuity, or Moho, is the boundary between the Earth’s crust and the underlying mantle. Seismic evidence for this feature comes from observations of seismic waves abruptly changing velocity and direction as they pass through this boundary, indicating a significant difference in the composition and density of the Earth’s layers.”

Question 42

“How does the elastic rebound model explain the
origin of a tectonic earthquake?”

Answer 42

The elastic rebound model proposes that stress builds up along a locked fault due to tectonic plate movement. When the stress exceeds the frictional resistance, the fault slips suddenly, releasing stored energy as seismic waves, causing an earthquake. This sudden release allows the surrounding rock to rebound to a less strained state.

Question 43

“If the magnitude of an earthquake is 0.5 greater than
that of another, how much greater is the amount of
energy it releases?”

Answer 43

”
Roughly, each unit increase in magnitude corresponds to about 31.6

Question 44

“Describe the geographical distribution of the Earth’s
seismically active zones.”

Answer 44

Seismically active zones primarily occur along tectonic plate boundaries, including the Ring of Fire around the Pacific Ocean and the Mid-Atlantic Ridge. Intra-plate seismic activity within continents is also observed but less frequent compared to plate boundary zones.

Question 45

How do seismic waves help scientists understand the internal structure of the Earth and its tectonic plate movements?

Answer 45

By analyzing the speed, direction, and amplitude of seismic waves recorded by seismometers, scientists can infer properties such as density, composition, and temperature of the Earth’s layers.