• Like

Earthquake Fault Mechanism

Uploaded on


More in: Technology , Education
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
No Downloads


Total Views
On Slideshare
From Embeds
Number of Embeds



Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

    No notes for slide


  • 1. Department of Earth Sciences KFUPM Introduction to Seismology Fault Mechanism Introduction to Seismology-KFUPM Ali Oncel [email_address]
  • 2. Previous Lecture
    • Faults and Their Types
    • Initial Ground Motions for P-waves
    • Initial P-wave Radiation Pattern
    • Case Work: Fault interpretation
    Introduction to Seismology-KFUPM
  • 3. Review: Earthquake Fault Mechanism
    • The radiation patterns of P-waves are used to construct a graphical representation of earthquake faulting geometry.
    • The symbols are called “ Focal Mechanisms ” or “ Beach Balls ”, and they contain information on the fault orientation and the direction of slip.
    Introduction to Seismology-KFUPM
  • 4. Review: Earthquake Fault Mechanism The type of faulting may be identified (reverse, normal, strike-slip) but the particular fault plane cannot be determined. So they both are shown as the possible solutions. The three stresses: two horizontal plus the vertical. Why is the significance to understand the style of faulting? Because, they are also telling us about the stresses acting within Earth. Introduction to Seismology-KFUPM
  • 5. Faulting Stresses
        • Intermediate Vertical Stress- Strike-Slip Faulting.
        • Compressional stresses
        • Largest vertical stress - Normal Faulting
        • Extension from Tensional stresses.
    Smallest vertical stress - Reverse Faulting/ Compressional stresses σ max σ min Introduction to Seismology-KFUPM
  • 6. Radiation Patterns
    • In seismology we call the direction a receiver is from a source the azimuth :
    source receiver North The azimuth is always measured clockwise from North and varies between 0 and 360 degrees. Introduction to Seismology-KFUPM Azimuth
  • 7. First Motions Introduction to Seismology-KFUPM
  • 8. Example: 2004 Sumatra EQ Source: http://iisee.kenken.go.jp/staff/yagi/eq/Sumatra2004/Sumatra2004.html Introduction to Seismology-KFUPM
  • 9. What types of Earthquake Software?
    • Based on Waveform Modeling : Teleseismic Body-Wave Inversion Program from:
    • http://www.eri.u- tokyo.ac.jp/ETAL/KIKUCHI/index.html
    • Based on First Motion Polarities (FOCMEC):
    • http://www.geol.vt.edu/outreach/vtso/focmec/
    Introduction to Seismology-KFUPM
  • 10. What are the sources of Seismic Data?
    • Over 16,000 seismometers are permanently deployed around the world
    • Seismometers are “ on ” 24 hrs, 7 days a week
    • Most seismic data is free and available over the internet in near real time
    Global Seismic Network Introduction to Seismology-KFUPM
  • 11. 1. visit to IRIS PAGE from http://www.iris.edu/seismon/ Introduction to Seismology-KFUPM
  • 12. 2. Then, click http://www.iris.edu/seismon/ Introduction to Seismology-KFUPM
  • 13.
    • Later, click http://www.iris.edu/seismon/last30days.phtml/
    • And click the event you want to get data
    Introduction to Seismology-KFUPM
  • 14. 4. Now, the station list is given where data is available. Introduction to Seismology-KFUPM
  • 15.
    • Select names of those station you want to have data
    Introduction to Seismology-KFUPM
  • 16.
    • Then, just click the proceed under the same page.
    Introduction to Seismology-KFUPM
  • 17.
    • Now, prefer the data for any component to plot
    Introduction to Seismology-KFUPM
  • 18. Let’s come back to discuss earthquake fault mechanism b d Introduction to Seismology-KFUPM
  • 19. Cross section of reverse fault, earthquake focus and quadrants of compression and dilatation. First motions observed at the surface reveal patterns of compression and dilatation. Introduction to Seismology-KFUPM
  • 20. Focal mechanism solution for a fault is commonly a lower focal sphere projection . For a dip-slip fault, this projection is equivalent to the compression/dilatation pattern viewed by a bird flying over the earthquake focus. Black = Compression White = Dilatation Introduction to Seismology-KFUPM
  • 21. Cross sections of Dip-Slip Faults C= Compression D= Dilatation The focal mechanism solution for a reverse fault (a) has a compression (black) in the inside portion of the circle, surrounded by regions of dilatation (white) The opposite pattern is observed for a normal fault (b) Introduction to Seismology-KFUPM
  • 22. Introduction to Seismology-KFUPM A=? B1=? B2=? C=?
  • 23. Introduction to Seismology-KFUPM