lecture 6

Question 1

magnitude scale

Answer 1

descirbes the size of an earthquake

Question 2

Richter original scale

Answer 2

magnitude determined using peak amplitude of waves

Question 3

seismic moment

Answer 3

truer measure of an earthquakes energy

- product of earthquake rupture area and the average slip that occurs and the shear modulus

Question 4

earthquake moment equation

Answer 4

moment (nm) = rupture area (m2) x slip (m) x shear modulus (n/m2)

Question 5

moment magnitude

Answer 5

Mw - modern earthquake magnitude scale

- more related to moment than Richters scale

Question 6

moment magnitude equation

Answer 6

(log10 moment - 9) / 1.5

Question 7

relationship of rupture area and average slip

Answer 7

rupture area is key to governing the moment and moment magnitude of an earthquake
ex. smalle arthquakes rupture small areas

Question 8

cascadia vs san andreas- same length

Answer 8

cascadia is subducting at a low angle and can host an earthquake at a larger area
has larger rupture availability

Question 9

megathrust earthquakes

Answer 9

rupture long, gently dipping interface faults
very large (Mw> 8.4)

Question 10

largest possible magnitude of earthquake

Answer 10

10.0
- 6000km length, 100m slip, 80km dip
(log10moment -9 ) / 1.5)

Question 11

mainshocks and aftershocks

Answer 11

mainshock - largest event
aftershock- series of smaller events
as you go forward in time they get less frequent (decays with time)

Question 12

MMI scale

Answer 12

modified mercalli intensity scale- describes the severity of shaking felt in an earthquake
- every earthquake has a range of intensities depending on how close you are

Question 13

isoseismals

Answer 13

lines of equal intensities

Question 14

2 ways to report earthquake intensity

Answer 14

1. accelerometers: seismometer records strong ground motion from earthquakes
2. felt reports: websites

Question 15

directivity effect

Answer 15

rupture amplifies surface waves in direction

Question 16

attenuation

Answer 16

The waves are largest where they are formed and gradually get smaller as they move away
- furthur from hypocenter the lower the intensity

Question 17

what do contours show

Answer 17

the depth of the top of subducting oceanic lithosphere

Question 18

basin amplification

Answer 18

increase in the size of seismic waves as they pass from hard bedrock (fast v) into loose sediment (slow v)
damage during earthquake is affected by intensity of shaking and engineering

Question 19

liquefaction

Answer 19

water saturated soils lose strength during shaking

Question 20

earthquake fatalities

Answer 20

continental earthquakes killed more people than subduction zone earthquakes despite being smaller