Lecture 2- Earthquake Lcoation And Magnitude Flashcards
How is the hypocentre of an earthquake found (three coordinates)
- Latitude
- Longitude
- Focal depth
What are the primary effects of earthquakes?
The permanent displacement of blocks either side of the fault (fertile or horizontal)
What are secondary effects of earthquakes?
-ground shaking, liquefaction, building damage, etc
What percentage of earthquakes occur at plate margins?
> 95%
What is the typical depth of earthquakes at constructive and conservative plate margins?
0-15 km (shallow)
What is the range of focal depth at convergent plate margins?
0-700 km (benioff zone)
Why is frequency forecasting difficult for intra -plate earthquakes?
They have long reoccurrence intervals and are randomly distributed
What does a seismograph measure?
Ground displacement, velocity or acceleration vs time
What is a seismograph?
The output of a seismograph
To what degree of accuracy can modern seismographs detect shaking?
10^-10 m
How many different seismographs exist at one station?
6
What are the six different seismographs located at a singular station?
- sensitive verticals
- strong motion vertical
- N/s sentisitve
- n/s strong motion
- e/w sensitive
- e/strong vertical
The time interval between what aids in epicentre location?
P and S waves
What causes an increase in the time interval between p and S waves?
Distance from the epicentre (of the seismograph station)
What allows for absolute identification of epicentre location?
The overlap between three different seismograph stations
How if the focal depth located? (One the epicentre has been)
The intersection of the 3D spheres of three different seismographs- this requires computer shit
How is the focal depth found (in relation to P and PP waves)?
Time time interval between the first P wave and first PP wave (reflected from the surface of the earth) can be used to calculate focal depth
What is seismic moment (Mo)
The size of the earthquake
How is seismic Moment calculated?
Mo= modulus of rigidity X Area of fault plane fracture X average displacement along fault
What does Mo range between?
10^10 and 10^23
What is A, and how is it estimated?
Area of fracture on the fault plane, measured via looking at the aftershock distribution
What is d, and how is it measure?
D is the average displacement along the fault, and is measured in the field or by GPS/SAR
How do modern seismographs calculate the seismic Moment?
By looking at the amplitude and frequencies of seismic waves in the field
How much does energy release increase with a 1.0Mw increase?
By a factor if 32
