(SEM1Q1, SCI) 1.2 - Location of an Earthquake

What is the focus or hypocenter?

point where the fault break begins

Where can you find the focus?

beneath the ground within the fault plane

What is an epicenter?

location directly above the focus on the surface of the Earth

What are large earthquakes often named after?

local geography (close places)

What are seismic waves?

waves that travel through the Earth in all directions from the epicenter

What are seismographs?

instrument that detects, measures, and records seismic waves

Based on what law of motion do seismographs operate on?

Law of Inertia (if an object is at rest, it will remain at rest)

What is a seismograph made up of?

heavy suspended weight which makes it motionless while Earth moves

What are the three directions seismographs can measure?

(1) up-down
(2) north-south
(3) east-west

How does a seismograph work?

A needle touches the strip of paper around a revolving clock which is firmly on the ground. When the ground vibrates, the drum also vibrates which records seismograms.

What is a seismogram?

record of an earthquake

What are the two types of seismic waves?

body waves and surface waves

What are body waves?

waves that pass through Earth's interior

What is the first waves recorded by the seismograph due to it being the fastest body wave?

primary waves

What type of wave is a primary wave?

longitudinal or compressional wave

What is the motion in a primary wave?

back and forth

What materials can a primary wave travel through?

solid, liquid, and gas

Dogs commonly start barking just before the surface waves because it can hear what body wave?

primary wave

What type of wave is secondary waves?

transverse

What mediums can secondary waves travel through?

solid rocks

What is the motion in a secondary wave?

right angle; up-down, side-to-side

What type of body wave is formed when shearing forces are transmitted?

secondary wave

What is a surface wave?

pass through the Earth's outer layer with complex motions

What type of seismic wave causes the ground to move?

surface wave

What is the motion of surface waves? (2)

up-down, side-to-side

What type of seismic wave causes damage to foundation of buildings?

surface waves

What is the fastest surface wave that moves the ground from side to side?

love waves

What is the motion of a love wave?

perpendicular to the direction of wave

What type of surface wave produces a rolling motion?

rayleigh waves

What is the motion of a rayleigh wave? (2)

up and down, back-and-forth

What kind of action is produced in a rayleigh wave?

rolling, elliptical action

What are the two ways to locate the epicenter?

graphical and triangulation method

How many times do you need to do the graphical method in order to move on to the triangulation method?

Three times (because you need the epicenter of 3 seismic stations)

Who developed the first pendulum seismoscope?

Father Andrea Bina

What is shearing force?

force in the Earth's crust that pushes the crust in opposite directions

What does a seismograph measure?

ground motion during an earthquake

What does the difference in the arrival times of the P and S waves at a seismograph determine?

the distance of that seismic station to the epicenter

What is a tiltmeter used for?

to monitor the upward movement along a fault or tilting of the ground

As P-waves move through the ground, what happens to it?

It compresses and expands.

How can you collect data when monitoring a fault?

through instruments that measure stress and deformation

What does a creep meter measure?

horizontal movement of the ground

What does a leaser-ranging device measure?

tiny fault movements