1: Earthquake Location And Size Flashcards
Questions based on the Lecture 1: Earthquake Location and Size, as well as surrounding reading.
What percentage of earthquakes occur at plate boundaries?
95%
What are the three fault types?
Normal, reverse and strike-slip
Give an example and case study of mixed faulting
Oblique-slip, san-andreas 1906: 6m horizontal, a few vertical.
What are intraplate earthquakes?
Earthquakes which occur in the centre of a plate
Why do intraplate earthquakes occur (two potential reasons)?
Either former/failed plate boundaries, or unloading of crust – we don’t fully understand
What is the difference between the focus and the epicenter?
Focus – at depth, epicenter – at surface.
What is the deepest depth an earthquake can generally occur at?
690km
Besides at subduction zones, most earthquakes occur above what depth?
35km
What is a Watadi-Benioff zone?
The 3D zone upon which earthquakes occur in a subduction zone, the dipping plane.
Name the two types of body waves and explain how each works
P-waves: propel through rock in direct form (compressional-dilation), S-waves: traditional wave moving side to side as it propels forward (shearing motion).
Name the two types of surface waves and explain how each works
Love waves: side to side shearing, rayleigh waves: rolling motion
What is the typical velocity through a rock such as granite for each of these 4 waves?
P-waves (Vp): ~5 km s-1, S-waves (Vs): ~3 km s-1, Love waves: 0.9 of Vs, Rayleigh waves: slightly slower than Love waves.
Which type of waves are the most hazardous?
Love and Rayleigh waves as they cause the most destruction at the surface.
Which component of a three-component seismograph is best to measure P-wave velocity?
Vertical
What is needed to triangulate the position of an earthquake?
The difference between P-wave travel time and S-wave travel time for multiple locations
How many stations would be needed to triangulate the focus of an earthquake?
4
How many stations would be needed to triangulate the epicenter of an earthquake?
3
Give three examples of earthquake intensity scales
Modified Mercalli (MM), European Macro-scale (1998) (EMS-98) and the Japanese Meterological Agency (JMA).
Where is the MM primarily used, and how does it work?
USA official, has 12 levels of intensity
Where is the JMA primarily used, and how does it work?
Japan and Taiwan. There are 10 devisions, the scale is ranked 0-7, with ranks 5 and 6 divided into upper and lower
Where is the EMA-98 primarily used, and how does it work?
European countries with a number outside. 12 divisions similar to MM.
What is the biggest difference between EMA-98 and MM?
Slight differences on how the event is described: eg Destructive is at VIII on MM, while at IX on EMS.
How many values are given for each earthquake on a magnitude scale?
1
What does the symbol “μ” stand for in seismology?
Shear Modulus
