Lecture 7: Seismic Waves and EQs

Question 1

Strike

Answer 1

Azimuth or bearing of a horizontal line in the plane

Question 2

Dip

Answer 2

The slope of the plane in the direction perpendicular to strike

Question 3

Fractures

Answer 3

Break in rocks or sediments

Question 4

Faults

Answer 4

Fractures that have motion (slip, displacement) along them in some direction

Question 5

Fault plane

Answer 5

The plane of the fracture; not usually an flat surface, but curved or irregular

Question 6

Hypocenter

Answer 6

Where on the fault plane the rupture began (in seconds it can travel over a larger area)

Question 7

Epicenter

Answer 7

The location on the Earth’s surface projected directly above the hypocentre

Question 8

Seismic

Answer 8

Related to EQ

Question 9

Seismograph

Answer 9

Instrument that records vibrations Need one in every direction

Question 10

Seismogram

Answer 10

Record of vibrations recorded by seismograph

Question 11

Seismic wave

Answer 11

Any of the waves that are generated by an earthquake

Question 12

Seismic moment

Answer 12

Direct measure of the energy radiated during an EQ A measure of the size of an earthquake based on the area of fault rupture, the average amount of slip, and the force that was required to overcome the friction sticking the rocks together that were offset by faulting Moment = shear modulus x area of rupture x average displacement during rupture

Question 13

S waves

Answer 13

Secondary waves, slower

Increases velocity and decreases amplitude

Question 14

P waves

Answer 14

Primary waves

Can be felt by animals

Increases velocity and decreases amplitude

Use difference between arrival of P and S wave to determine how far away EQ is

Compression waves

Question 15

Surface waves

Answer 15

Constant velocity

Question 16

How to locate epicenter

Answer 16

Need 3 seismometers Triangulate position of epicenter and focus

Question 17

Richter scale

Answer 17

Used for local EQ only

Question 18

Using seismogram to determine dip slip fault

Answer 18

Will see either initial pull down, or push up depending on what size of fault seismograph is on

Question 19

Body waves

Answer 19

P and S waves Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves

Question 20

Surface waves

Answer 20

Travelling only through the crust, surface waves are of a lower frequency than body waves, and are easily distinguished on a seismogram as a result. Though they arrive after body waves, it is surface waves that are almost enitrely responsible for the damage and destruction associated with earthquakes. This damage and the strength of the surface waves are reduced in deeper earthquakes

Question 21

Answer 21

Normal fault

Question 22

Answer 22

Reverse fault

Question 23

Answer 23

Strike-slip fault