TRIANGULATION METHOD | SCIENCE 10 - Week 2

Summary

This 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

00:00

🌋 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.

05:01

🌏 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.

Keywords

💡Triangulation Method

The triangulation method is a technique used to determine the location of an earthquake's epicenter. It involves drawing circles around seismic stations based on the distance calculated from the time lag between the arrival of P-waves and S-waves. The point where these circles intersect is the epicenter. In the video, this method is used to demonstrate how seismologists can locate the source of an earthquake using data from multiple seismic stations.

💡Epicenter

The epicenter is the point on the Earth's surface directly above the focus, where the earthquake originates. It is a critical concept in the video as it helps understand where the earthquake's energy is most directly released. The video script describes how to calculate the distance to the epicenter using the time difference between P-waves and S-waves and then locate it using the triangulation method.

💡Seismic Waves

Seismic waves are the vibrations that travel through the Earth's crust when an earthquake occurs. The video mentions three types: P-waves (primary waves), S-waves (secondary waves), and surface waves. These waves are essential for understanding how earthquakes are detected and measured, as their arrival times at seismic stations provide data for calculating the earthquake's distance and location.

💡Seismometer

A seismometer is an instrument used to detect and measure seismic waves. It records the vibrations caused by earthquakes, creating a seismogram that shows the arrival times of different types of waves. In the video, seismometers are used to obtain data about earthquake vibrations, which is then analyzed to determine the epicenter using the triangulation method.

💡P-waves

P-waves, or primary waves, are the fastest and first seismic waves to be detected by a seismometer during an earthquake. They are compressional waves that move through the Earth's interior. The video script uses the arrival time of P-waves to calculate the lag time, which is crucial for determining the distance to the epicenter.

💡S-waves

S-waves, or secondary waves, are slower than P-waves and cause a side-to-side motion in the Earth's crust. They are the second type of waves to be detected by a seismometer. The video explains how the time difference between the arrival of P-waves and S-waves, known as lag time, is used to calculate the distance to the epicenter.

💡Surface Waves

Surface waves are the slowest and most destructive seismic waves, as they cause the ground to move up and down. They are not used for calculating the epicenter's distance but are significant for understanding the impact of earthquakes. The video mentions that surface waves lose energy quickly and do not travel as far as P- or S-waves.

💡Focus

The focus is the point within the Earth where an earthquake originates. It is located underground and is distinct from the epicenter, which is the point on the surface directly above the focus. The video script does not delve deeply into the focus, but it is an essential concept in understanding the origin of earthquakes.

💡Seismologist

A seismologist is a scientist who studies earthquakes and seismic waves. In the context of the video, seismologists use data from seismometers and their knowledge of seismic waves to determine the location and magnitude of earthquakes. The video script describes how seismologists use the triangulation method to locate epicenters.

💡Lag Time

Lag time refers to the time difference between the arrival of P-waves and S-waves at a seismometer. This measurement is crucial for calculating the distance to an earthquake's epicenter. The video script provides an example of how to compute lag time by subtracting the arrival time of P-waves from that of S-waves.

💡Plate Tectonics

Plate tectonics is the theory that the Earth's lithosphere is divided into several large plates that move over the asthenosphere. The video script mentions that the distribution of earthquakes is related to the boundaries of these plates, indicating that most earthquakes occur along plate boundaries. This concept is fundamental to understanding the geological processes that lead to earthquakes.

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]