Topic 15 - Dynamic Earth Part 2: Earthquakes

Why do we study earthquakes?

To guide us where to build, to avoid tsunamis, to interpret Earth history

What is an earthquake?

Strong vibrations that travel through the ground, due to a release of energy

What happens when the ground breaks (ruptures)?

When the ground breaks (ruptures), the energy is released

What are the waves of energy called?

the waves of energy are called seismic waves

What is a fault?

this is the crack in the ground, along which the ground moves

What is the relationship between earthquakes and volcanoes?

they often occur near or in the same locations

What are other causes of earthquakes?

fracking (hydraulic fracturing), bomb testing, blasting in a quarry

what are seismic waves?

energy released during an earthquake. They show up as three distinct wave forms. The ground actually moves

what is a P-wave?

primary wave, arrives 1st

how does a p-wave move?

Push pull, like a spring, this is a sound wave

Through what kind of materials can a p-wave move through?

solid, gas and liquids

what is a S-wave?

secondary wave, arrives 2nd

how does a s-wave move?

Up and down, side to side

Through what kind of materials can a s-wave move through?

only solids

what is a L-wave?

long waves, arrive 3rd

how does a l-wave move?

side to side, roll like waves across the surface

Through what kind of materials can a l-wave move through?

only solids

How are earthquakes detected ?

use seismographs

what is a seismograph?

This is the machine that detects seismic waves

what does a seismograph do?

Use the arrival times of the different waves to calculate and determine the location of an earthquake

what is a seismogram?

the printout of the wave history, reminds you of an EKG

what is a focus?

the place where the ground ruptured, this is the start of the earthquake

what is the epicenter?

The location on the surface directly above the focus

Earthquake strength and severity is defined by?

defined by intensity and magnitude

Intensity is very ?

subjective

Intensity is measured with ?

modified mercalli scale

The modified mercalli scale is a function of?

strength of the quake, building materials, building design, type of ground material - how people perceive the quake

what is magnitude?

measures the amount of energy released

Magnitude is measured by?

Richter Scale

How do you measure the amount of energy released with the Richter scale?

Using a seismogram - the scale measures the amplitude (height) of the largest wave recorded

what is the relationship of the # on the scale to energy released?

10X increase in wave amplitude = increase of 1 on the scale