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Earthquake Seismology Review

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Presentation on theme: "Earthquake Seismology Review"— Presentation transcript:

1 Earthquake Seismology Review
epicenter S P |Tp-Ts| Tp-Ts = d/(Vp-Vs) hypocenter

2 Outline Epicenter Locations Magnitude Calculations
Focal+Radiation Patterns Epicenter Locations Magnitude Calculations

3 Outline Epicenter Locations Magnitude Calculations
Focal+Radiation Patterns Epicenter Locations Magnitude Calculations

4 Vertical Displacement Point Source
Intensity: u^2 + v^2 P Intensity *Polarity u( u^2 + v^2) S Particle velocity P arrival S arrival Particle velocity

5 Horizontal Displacement Point Source
Intensity: u^2 + v^2 Intensity *Polarity u( u^2 + v^2) P S Particle velocity S arrival P arrival Particle velocity

6 Horizontal Displacement Point Source
Intensity: u^2 + v^2 Intensity *Polarity v( u^2 + v^2) P S Particle velocity S arrival P arrival Particle velocity

7 Single Couple Point Source
Intensity: u^2 + v^2 Intensity *Polarity u( u^2 + v^2) P S Particle velocity S arrival Particle velocity P arrival

8 Single Couple Point Source
Intensity: u^2 + v^2 Intensity *Polarity u( u^2 + v^2) P S Particle velocity S arrival Particle velocity P arrival

9 Single Couple Point Source
Intensity: u^2 + v^2 Intensity *Polarity v( u^2 + v^2) P S Particle velocity S arrival Particle velocity P arrival

10 S-Wave Radiation Pattern of Earthquakes
+ - S P Conjugate plane needed to prevent rotation (double couple) ? ? Plan view of S-radiation pattern

11 Double Couple Point Source
Intensity: u^2 + v^2 Intensity *Polarity v( u^2 + v^2) P S Particle velocity S arrival Particle velocity P arrival

12 Elastic Green’s Function
Monopole direction Receiver

13 Outline Radiation Patterns Eathquakes Epicenter Locations
Magnitude Calculations Radiation Patterns Epicenter Locations Magnitude Calculations

14 Strike Slip Fault Strike Slip No rotation + + - - + - - + + - +
P-wave 1st breaks up or down + + - - + - - + + - + Fault Scarp - - - No rotation - - - - - - - - - - - - - - - - - - - - - - + - - - + + - - - + + + - + + Strike Slip - + Auxillary Plane Radiation pattern can’t Distinguish conjugate plane from fault plane

15 Strike Slip Fault - + - + - - - No rotation Fault Scarp
Auxillary Plane - + P-wave 1st breaks up or down - + + - - + Fault Scarp Auxillary Plane No rotation - - + + - - - - - - - + - - - - - - - - - - - - - - - - - - - + - - - + + - - epicenter - + + - + + - + + up motion for P - - + - - hypocenter down motion for P Radiation pattern can’t Distinguish conjugate plane from fault plane

16 Plotting polarity on projection plane
Strike Slip Fault Fault Scarp Auxillary Plane - + Plotting polarity on projection plane gives focal mechanism + -

17 Stereographic ProjectionStrike Slip Fault
Stations around the globe will reveal same focal mechanism pattern as stations just above focus This is an overview of some salient results from our 2003 UTAM research. 1st motion down 1st motion up

18 Stereographic Projection Shallow
Strike Slip Fault Stations around the globe will reveal same focal mechanism pattern as stations just above focus This is an overview of some salient results from our 2003 UTAM research. 1st motion down 1st motion up

19 Rotated Great Circle Projects as Ellipse
This is an overview of some salient results from our 2003 UTAM research.

20 Rotated Great Circle Projects as Ellipse
This is an overview of some salient results from our 2003 UTAM research.

21 Stereographic Projection Reverse Fault
This is an overview of some salient results from our 2003 UTAM research. 1st motion down 1st motion up

22 Stereographic Projection Normal Fault
This is an overview of some salient results from our 2003 UTAM research. 1st motion up 1st motion down

23 Focal Plane Strike Slip + + - - - - + + + - + - - - - - - - - - - - -
P-wave 1st breaks up or down + + - - - - + + + - + - - - - - - - - - - - - - - - - - - - - - - - - - + - - - + + - - - + + + - + + Strike Slip - +

24 P-Wave Radiation Pattern of Earthquakes
Double Couple Event to Prevent Rotation Red indicates positive polarity of 1st P arrival Green indicates negative polarity of 1st P arrival - + S P - - + + + + + - + - + - - Plan view of P-radiation pattern

25 S-Wave Radiation Pattern of Earthquakes
+ - S P Conjugate plane needed to prevent rotation (double couple) ? ? Plan view of S-radiation pattern

26 Double Couple Earthquakes

27 Double Couple Earthquakes

28 Double Couple Earthquakes
Thrust Strike slip normal normal

29 Seismology of Submarine Slumps
No confining verical stress, so free to rotate. Single couple earthquake

30 Seismology of Submarine Slumps

31 Geology of Faulted Earthquakes
Rich in shear Keystone block Rich in shear Earthquakes that result from brittle failure are most commonly referred to simply as ordinary "earthquakes."

32 Seismology of Explosions
Explosions are rich in compressional energy. Earthquakes that result from brittle failure are most commonly referred to simply as ordinary "earthquakes."

33 Seismology of Volcanoes
Harmonic tremor describes continuous rhythmic earthquakes that can be detected by seismographs. Harmonic tremors often precede or accompany volcanic eruptions. Fluid dynamic processes driven by pressure and (or) temperature gradients associated with crustal magma may excite seismic waves by a variety of processes including resonances within fluid-filled cracks (Chouet, 1992) and unsteady, nonlinear flow along conduits with irregular geometry (Julian, 1994). The seismic waves generated by such processes typically produce earthquakes deficient in frequencies above 5 to 10 Hz and with extended coda that "ring" for many cycles at a nearly constant frequency (fig. C2). Spectra from seismograms of these earthquakes are typically comb-like with individual peaks showing a harmonic relation to a fundamental mode or a period-doubling relation characteristic of nonlinear systems (Julian, 1994). Such earthquakes are variously referred to as long-period (LP) earthquakes, low-frequency earthquakes, or B-type, volcanic earthquakes (Chouet, 1996; McNutt, 2000). The dominant frequencies for these volcanic earthquakes are typically in the range 1 to 5 Hz. At shallow depths (less than 5 km or 3 miles), LP earthquakes appear to involve the resonance of bubbly fluids in fluid-filled cracks associated with degassing or boiling (Chouet, 1992). At greater depths, non-steady fluid flow may be a more common process (Julian, 1994), although basaltic magmas may behave as a bubbly fluid at pressures typical of mid-crustal depths (10 to 20 km or 6 to 12 miles) with carbon dioxide as the gaseous phase. The deep LP earthquakes beneath Mammoth Mountain that began in late 1989, for example, may be associated with resonances within a basalt-carbon dioxide froth (Pitt and Hill, 1994).

34 Outline Radiation Patterns Passive Epicenter Locations
Magnitude Calculations Radiation Patterns Epicenter Locations Magnitude Calculations

35 Seismology of Hydrofracs
Monitoring well locates events and polarity analysis Identifies type Injection fluid in rock cracks rock Injection fluid in rock explodes rock

36 Outline Radiation Patterns Epicenter Locations Magnitude Calculations

37 Epicenter Location of Earthquakes
|Tp-Ts | d epicenter S P |Tp-Ts| Tp-Ts = d (Vp-Vs) -1 -1 hypocenter S P S P d=300 km

38 Outline Radiation Patterns Epicenter Locations Magnitude Calculations

39 Magnitude of Earthquakes
After determining d=300km, you then use magnitude chart to determine strength epicenter Amplitude Amplitude S P 400 300 100 d hypocenter

40 P-Wave Radiation Pattern of Earthquakes
Double Couple Event to Prevent Rotation Red indicates positive polarity of 1st P arrival Green indicates negative polarity of 1st P arrival - + S P - - + + + + + - + - + - - Plan view of P-radiation pattern

41 S-Wave Radiation Pattern of Earthquakes
+ - S P Conjugate plane needed to prevent rotation (double couple) ? ? Plan view of S-radiation pattern

42 Double Couple Earthquakes

43 Double Couple Earthquakes

44 Double Couple Earthquakes
Thrust Strike slip normal normal

45 Seismology of Submarine Slumps
No confining verical stress, so free to rotate. Single couple earthquake

46 Seismology of Submarine Slumps

47 1. Radiation Pattern-> Source Mechanism:
Summary 1. Radiation Pattern-> Source Mechanism: ? 2. Epicentral Location: 3 or more stations S P S P 3. Magnitude Estimation: Rayleigh Amp.-> Mag. d=300 km

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