Chapter 2 : Earthquake Seismology

Question 1

What are the classic divisions of the earth?

Answer 1

Crust, Mantle, Core

Question 2

What are the modern divisions of the earth?

Answer 2

Lithosphere, Asthenosphere, Mesosphere, Outer core, inner core

Question 3

What are the changes in pressure and temperature with depth?

Answer 3

Linear increase in pressure, non-linear increase in temperature

Question 4

Where is lithosphere created and destroyed?

Answer 4

Created at divergent boundaries (mid-ocean ridges), consumed at convergent plate boundaries (subduction zones)

Question 5

Where do earthquakes generally occur?

Answer 5

Concentrated along tectonic boundaries

Question 6

What is the Elastic rebound theory for earthquakes?

Answer 6

Elastic stress stored as deformation is created from faults locked by friction, but when stress > friction, fault ruptures = earthquake

Question 7

What are characteristics of cascadia seismicity?

Answer 7

EQ in both oceanic/continental crust from compression of converging plates up to 35km depth (up to 7.5 magnitude)
EQ in cold subducting plate to 80km (up to 7. magnitude)

Question 8

What prevents earthquakes from occurring at too deep depths?

Answer 8

Once the plates become too warm, they start to melt and stress cannot build up

Question 9

Evidence of past megathrust EQ?

Answer 9

Sediment layer sequences (peat, sand from tsunami, landslides, peat)

Question 10

What occurs between megathrust events?

Answer 10

Plate convergence with locked fault leads to deformation (uplift and shortening) or over-riding plate

Question 11

What happens during megathrust event?

Answer 11

Strain > friction, fault ruptures, deformation reversed (subsidence and extension)

Question 12

What is the min and max separation of megathrust EQ?

Answer 12

Min = 300 yrs, Max = 900yrs, Avg = 600yrs

Question 13

Ray parameter

Answer 13

Geometric property that is constant along a ray, no matter if it is transmitted, reflected, refracted or transformed. Equal to the slope of the travel time curve

Question 14

Forward problem

Answer 14

Use a Model for the earth radial velocity structure to compute the expected data

Question 15

Inverse problem

Answer 15

Given measured data, estimate a model of earth velocity structure

Question 16

How do p-wave and s-wave velocity change with depth through the lithosphere?

Answer 16

Increase

Question 17

What happens to p-wave and s-wave velocity at lithosphere/asthenosphere boundary?

Answer 17

Decrease

Question 18

What happens to p-wave and s-wave velocity through the asthenosphere

Answer 18

Increase

Question 19

What happens to p-wave and s-wave velocity at asthenosphere/mesosphere boundary

Answer 19

Increase

Question 20

What happens to p-wave and s-wave velocity through the mesosphere?

Answer 20

Increase

Question 21

What happens to p-wave and s-wave velocity at the outer core boundary?

Answer 21

Decrease

Question 22

What happens to p-wave and s-wave velocity through the outer core?

Answer 22

P-wave increases, s-waves disappear

Question 23

What happens to p-wave and s-wave velocity at outer core boundary?

Answer 23

Increase

Question 24

Bulk modulus

Answer 24

Relative volume change due to pressure change (incompressibility) of a material

Question 25

Adams-Williamson eq

Answer 25

Gives change in density from compression

Question 26

Seismic tomography

Answer 26

Technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions

Question 27

Fermat’s principles

Answer 27

raypath is stationary with respect to medium velocity (slowness) distribution