TRIANGULATION METHOD | SCIENCE 10 - Week 2
Summary
TLDRThis educational video script discusses the triangulation method for determining earthquake epicenters. It explains the concept of seismic waves, including P-waves, S-waves, and surface waves, and how they are used to calculate the distance to an epicenter. The script also covers the distribution of earthquakes along tectonic plate boundaries and the challenges in predicting earthquakes. It concludes with a lesson on the global pattern of earthquake occurrences and the limitations of current forecasting methods.
Takeaways
- 🌏 **Global Distribution**: Earthquakes are not randomly distributed and tend to occur along the boundaries of tectonic plates.
- 🔍 **Triangulation Method**: The location of an earthquake's epicenter can be determined using the triangulation method by analyzing data from multiple seismic stations.
- 📊 **Seismic Waves**: There are three types of seismic waves - P-waves (primary), S-waves (secondary), and surface waves, each with different characteristics and speeds.
- 📈 **Seismograph Readings**: Seismographs record seismic waves, and the time difference between P and S waves can be used to calculate the distance to the epicenter.
- ⏱️ **Lag Time Calculation**: The lag time, or the time difference between the arrival of P-waves and S-waves, is crucial for determining the distance of an epicenter.
- 📐 **Distance Formula**: The distance to an epicenter can be calculated using the formula d = (lag time ÷ 8) × 100 kilometers.
- 🌋 **Focus and Epicenter**: The focus is the point of origin of an earthquake underground, while the epicenter is the point on the Earth's surface directly above the focus.
- 🌐 **Tectonic Theory**: The theory of plate tectonics explains the distribution of active volcanoes, earthquake epicenters, and mountain belts.
- 📉 **Surface Waves**: Surface waves are the most destructive but lose energy quickly and cannot travel as far as P-waves or S-waves.
- 🔬 **Predictive Challenges**: Despite ongoing research, there is currently no reliable method to predict the exact time or location of an earthquake.
Q & A
What is the focus of a lesson on earthquake triangulation method?
-The focus is to enable students to compute mathematically the distance of an epicenter and locate the epicenter of an earthquake using the triangulation method.
What are the three types of seismic waves mentioned in the script?
-The three types of seismic waves are P-waves (primary waves), S-waves (secondary waves or shear waves), and surface waves.
How do P-waves and S-waves differ in terms of their motion and speed?
-P-waves are compression waves that travel the fastest and cause a push-pull motion. S-waves cause a side-to-side motion and are slower than P-waves.
What is the significance of the lag time between the arrival of P-waves and S-waves?
-The lag time is used to calculate the distance of the epicenter from the seismic station by using the formula d = (lag time / 8 seconds) * 100 kilometers.
How does the triangulation method help in determining the epicenter of an earthquake?
-The triangulation method involves drawing circles on a map from the distances of the earthquake from three or more seismic stations. The epicenter is located at the intersection of these circles.
What tool is used to detect and record seismic waves?
-A seismometer is used to detect seismic waves, and the data is recorded in the form of a seismogram.
Why are earthquakes not randomly distributed across the world?
-Earthquakes tend to occur at the boundaries of tectonic plates, indicating that the Earth's crust is divided into segments that interact with each other.
What is an example of an intraplate earthquake mentioned in the script?
-The 1968 Meckering earthquake in Western Australia, which had a magnitude of 6.8, is an example of an intraplate earthquake.
What is the current state of earthquake prediction technology according to the script?
-As of the information in the script, there are no devices that can accurately measure when or where an earthquake may occur.
What is the role of stress release in intraplate earthquakes?
-In intraplate earthquakes, stress release in rocks can cause earthquakes to occur, even in areas not located at plate boundaries.
Outlines
🌋 Earthquake Triangulation Method
This paragraph introduces the concept of earthquake triangulation, a method used to locate the epicenter of an earthquake. It discusses the nature of earthquakes as vibrations caused by rock breaking under stress, leading to the release of energy in the form of seismic waves. The paragraph distinguishes between three types of seismic waves: P-waves (primary, fastest), S-waves (secondary, side-to-side motion), and surface waves (most destructive, roll along the surface). Seismologists use seismometers to detect these waves and create seismograms, which help determine the distance to the epicenter by measuring the time difference between P and S waves. The triangulation method involves plotting circles on a map from three or more seismic stations, with the intersection point indicating the epicenter. An example using Chicago as a seismic station is provided, demonstrating how to calculate the lag time and use it to determine the epicenter's distance.
🌏 Distribution of Earthquakes and Plate Boundaries
The second paragraph shifts focus to the global distribution of earthquakes, highlighting their tendency to occur along the boundaries of tectonic plates. It uses a visual aid of yellow dots representing earthquake epicenters to show that earthquakes are not randomly distributed but are associated with plate movements. The paragraph also mentions intraplate earthquakes, which occur due to stress release within a plate, exemplified by the 1968 Meckering earthquake in Western Australia. It concludes with a note on the ongoing research into earthquake prediction, acknowledging the current lack of devices that can accurately measure the timing or location of future earthquakes.
Mindmap
Keywords
💡Triangulation Method
💡Epicenter
💡Seismic Waves
💡Seismometer
💡P-waves
💡S-waves
💡Surface Waves
💡Focus
💡Seismologist
💡Lag Time
💡Plate Tectonics
Highlights
Introduction to the learning competency on describing and relating the distribution of active volcanoes, earthquake epicenters, and major mountain belts to plate tectonic theory.
Lesson one focuses on the triangulation method for locating earthquake epicenters.
Earthquakes are vibrations caused by rock breaking under stress, releasing energy through seismic waves.
The point of origin of an earthquake is called the focus, and the point directly above it on the surface is the epicenter.
There are three types of seismic waves: P-waves, S-waves, and surface waves, each with different characteristics.
Seismologists use seismometers to detect and record seismic waves, creating seismograms to analyze earthquake data.
The distance of an earthquake from a seismic station can be determined by the time difference between P and S wave arrivals.
The triangulation method involves drawing circles on a map from multiple seismic stations to locate the epicenter.
An example is provided to compute lag time by subtracting the arrival time of P-waves from S-waves.
A formula is introduced to calculate the distance to the epicenter using the lag time.
The triangulation method is demonstrated using a map and compass to draw circles representing the distance from seismic stations.
Lesson two discusses the global distribution of earthquakes, which tends to occur along plate boundaries.
Earthquakes are not randomly distributed and are associated with plate tectonics, though some occur due to stress release within plates.
The 1968 Meckering earthquake in Western Australia is cited as an example of an intraplate earthquake.
Current scientific efforts to predict earthquakes are mentioned, acknowledging the lack of devices that can measure exact timing or location.
Conclusion of lesson two and the end of the presentation, thanking the audience for their attention.
Transcripts
hello great then welcome to the second
week of our discussion
our discussion will focus on the
learning competency describe and relate
the distribution of active volcanoes
earthquake epicenter and major mounting
belts of the blade tectonic theory
now let's start with lesson one
earthquakes triangulation method
at the end of the lesson you should be
able to
one compute mathematically the distance
of an epicenter and two locate the
epicenter of an earthquake using the
triangulation method
earthquakes are vibrations caused by
rock breaking under stress
this vibration travels and reach the
surface of the earth
this movement is sudden and releases a
lot of energy which is transmitted
through rocks as seismic waves
the point where an earthquake originate
from underground is called focus
the location directly above the surface
of the earth is called the epicenter
there are three types of seismic waves
the p wave the s wave and the surface
wave
p-wave or primary waves are compression
waves also known as push-pull weights
they travel the fastest and the first
wave to be detected in a seismic station
s-wave or secondary waves or shear waves
move to a side to side motion they are
the second wave to be detected in a
seismic station
surface wave
roll along the surface of the earth
they are the most destructive waves as
they move the ground up and down but
lose their energy the fastest and cannot
travel as far
seismic waves are detected and recorded
using seismometer to create seismogram
seismologists can determine how far away
the earthquakes strike by plotting the
difference in arrival between p and s
waves on the graph
seismologists determine the earthquake's
epicenter by drawing circles on the
mouth showing the ridges from the
distance of the earthquake of three or
more seismic stations the point where
these circles intersect determines the
epicenter of the earthquake this method
is known as the triangulation method
now how do we determine the epicenter of
an earthquake using triangulation method
now for example we have a reading from a
seismometer
like this one
the reading in a seismometer looks
something like this
we have the p waves the s waves and the
surface waves
the p waves
this one
is the first wave to arrive in a
seismometer
followed by the secondary waves or the s
waves
and the surface waves
the report printed out by seismometer is
called the seismogram now this diagram
can tell us
the distance of the epicenter from the
seismic station
now first thing that we need to look at
is the first time the seismogram jumps
and that is the arrival of the p wave
followed by the second jump and that is
the arrival of the
s wave
now we can determine the distance of the
epicenter of the earthquake by simply
calculating the time difference
in the arrival of the s and b wave and
we call that lag time
now let's use the activity in your
module as an example
we have activity 1 lag time using the
earthquake chart below
compute for the lag time by subtracting
s wave and p p wave
so as you can see we have four records
of
earthquake in four seismic stations we
have chicago kansas city santa barbara
and seattle below are the time of
arrival 0 15 30 45 60 75 92 150
now let's use chicago as an example so
the first time
the seismogram jumps
is we have 18 seconds and that is the
arrival of the p wave p wave is 18
seconds
and then if you are going to look at the
record
we have minor quakes and the second jump
is
153
so the arrival of the s wave is
153
seconds
[Music]
now to
to compute for the log time
what we need to do is to simply subtract
p wave with s wave so if we have 153
seconds minus 18 seconds we have
a lag time of 135 seconds
so example chicago p wave 18 seconds s
weigh 153 seconds lag time is 135
seconds
now do the same for other three seismic
stations
next is determining the distance of the
epicenter to the station
now to compute let's use the formula d
is equal to td over 8 seconds times 100
kilometer
and let's use the lug time which is 135
seconds now how do we solve for the
distance of the epicenter
to compute follow the formula
this one d is equal to let's use 135
seconds the lag time over eight seconds
times 100 kilometer
just multiply cancel the units we have d
is equal to thirteen thousand
five hundred kilometer divided by eight
seconds and the distance is
one thousand six hundred eighty seven
point five kilometer
now after determining the distance
let's now do the triangulation method
first we have the record of chicago
we will be needing a compass
and below the map we have
a
what's the scaling
now
now after getting the scale simply draw
a circle with chicago as the
center
do this for the other seismic stations
and the point where this three
intersects
that is the location of the epicenter
of the earthquake
[Music]
now let's have another example you can
find it in your module where is the
epicenter we have three seismic stations
one two and three the first seismic
station records the distance
of the earthquake 700 kilometers
the second seismic station
records a distance of three thousand
and the third seismic station records
3500
the epicenter of the earthquake is
located at the intersection of the three
circles now that is how we determine the
epicenter of an earthquake
and that's the end of lesson one
now let's start with lesson two
distribution of earthquake in the world
one of the evidences that the cross is
divided into segments of landmasses is
the distribution of earthquake in the
world the yellow dots represents the
earthquakes
as you can see
earthquakes are not randomly distributed
in the world they tend to occur in the
boundaries of plates
however not all earthquakes occur at
late boundaries
there are interplayed earthquakes that
occur because of the stress of rocks
being released
this is what caused the 1968 meccaring
earthquake that happens in western
australia that has a magnitude of 6.8
which caused major damage in structures
and infrastructures
scientists are researching on ways to
predict the occurrence of earthquake but
until now there are no devices that can
measure when or where an earthquake may
occur
and that's the end of lesson two
thank you for watching
thank you
[Music]
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