Earthquakes

Question 1

Why Earthquakes Happen?

Answer 1

Tectonic Forces lead to elastic deformation
-Slip on fault/formation of new faults released elastic strain (energy released as a seismic wave)

Question 2

Elastic Deformation

Answer 2

Temporary deformation of a materials shape that is self-reversing after removing force/load
(within materials elastic limit)

Question 3

Body Waves
-relative arrival times?

Answer 3

Through interior
1.) p-waves (8.0km/s)
-(compression)=faster; up/down
moves parallel
2.) s-waves (4.5km/s)
-(shear); Side-to-side
moves perpendicular
doesn’t travel through liquid

Question 4

Surface Waves
-relative arrival times?

Answer 4

Over Surface
Die with depth and have the highest amplitude, resulting in the most structural damage

1.) Love Waves: (4.2 km/s)
-vertical s-wave
-vibration= side to side
2.) Rayleigh Wave : (4.0 km/s)
- vertical p-wave
-vibration=up and down

Question 5

Earthquake Locations

Answer 5

Triangulation

Question 6

Magnitude Moment (Mw)

Answer 6

area of slip and displacement of a fault
-measures energy released
-Robust for larger earthquakes ; Bigger earthquake=bigger energy release=more and longer shaking/greater seismic wave amplitude

*Magnitude scales are logarithmic

Question 7

Logarithmic Nature of Magnitude Scales

Answer 7

Every 1 increases in log scale=10x magnitude

Question 8

Seismic Hazards

Answer 8

1.) Ground-Shaking -structural damages
2.) Tsunamis- wave submerges/flood low-land
3.) Liquefication: Transformation of wet sediment into a slurry as a result of seismic activity.
-compacted mud and unconsolidated sand
4.) Amplification
-Sedimentary Basins: seismic waves slow down and bounce leading to greater ground motion

Question 9

Earthquake area determined by __a__. Rupture area dependent on __b__.

Answer 9

a.) Slip Area
b.) depth to Brittle-ductile transition

Question 10

What causes the most fatalities and destruction in earthquakes worldwide?

Answer 10

-Fires
-Structure collapse/ Falling Masonry

Question 11

Richter Scale measures earthquake “size” by its energy release (magnitude).
What are two limitations?

Answer 11

1.) Designed for CA crust which has a thinner lithosphere
2.) Saturates at high values.

Question 12

Richter Scale is __a__, meaning a 1 unit inc corresponds to a __b__ increase in seismic wave amplitude.
__c__ describes how strong the earthquake shaking is at some location.

Answer 12

a.) logarithmic
b.) 10-fold
c.) Intensity

Question 13

Formation and Occurance of Tsunamis?

Answer 13

-occur when large volumes of water are displaced
-If an earthquake occurs and there’s a tsunami alert, head to high ground immediately
-Tsunami waves can reach more than 15 m (50 ft) in height.