Chapter 2 : Earthquake Seismology Flashcards
What are the classic divisions of the earth?
Crust, Mantle, Core
What are the modern divisions of the earth?
Lithosphere, Asthenosphere, Mesosphere, Outer core, inner core
What are the changes in pressure and temperature with depth?
Linear increase in pressure, non-linear increase in temperature
Where is lithosphere created and destroyed?
Created at divergent boundaries (mid-ocean ridges), consumed at convergent plate boundaries (subduction zones)
Where do earthquakes generally occur?
Concentrated along tectonic boundaries
What is the Elastic rebound theory for earthquakes?
Elastic stress stored as deformation is created from faults locked by friction, but when stress > friction, fault ruptures = earthquake
What are characteristics of cascadia seismicity?
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)
What prevents earthquakes from occurring at too deep depths?
Once the plates become too warm, they start to melt and stress cannot build up
Evidence of past megathrust EQ?
Sediment layer sequences (peat, sand from tsunami, landslides, peat)
What occurs between megathrust events?
Plate convergence with locked fault leads to deformation (uplift and shortening) or over-riding plate
What happens during megathrust event?
Strain > friction, fault ruptures, deformation reversed (subsidence and extension)
What is the min and max separation of megathrust EQ?
Min = 300 yrs, Max = 900yrs, Avg = 600yrs
Ray parameter
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
Forward problem
Use a Model for the earth radial velocity structure to compute the expected data
Inverse problem
Given measured data, estimate a model of earth velocity structure
How do p-wave and s-wave velocity change with depth through the lithosphere?
Increase
What happens to p-wave and s-wave velocity at lithosphere/asthenosphere boundary?
Decrease
What happens to p-wave and s-wave velocity through the asthenosphere
Increase
What happens to p-wave and s-wave velocity at asthenosphere/mesosphere boundary
Increase
What happens to p-wave and s-wave velocity through the mesosphere?
Increase
What happens to p-wave and s-wave velocity at the outer core boundary?
Decrease
What happens to p-wave and s-wave velocity through the outer core?
P-wave increases, s-waves disappear
What happens to p-wave and s-wave velocity at outer core boundary?
Increase
Bulk modulus
Relative volume change due to pressure change (incompressibility) of a material
Adams-Williamson eq
Gives change in density from compression
Seismic tomography
Technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions
Fermat’s principles
raypath is stationary with respect to medium velocity (slowness) distribution
