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EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM

Explore the classification, magnitude scales, intensity levels, energy, power law relations, and source mechanisms of earthquakes. Learn about different types, distances, and nature of seismic activities in this informative guide.

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EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM

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  1. EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM Walter D. Mooney U.S. Geological Survey California, USA e-mail: mooney @ usgs.gov

  2. EARTHQUAKE CLASSIFICATION MAGNITUDE CLASSIFICATION M ≥ 8.0 Great Earthquake 7.0 ≥ M < 8.0 Major / Large Earthquake 5.0 ≥ M < 7.0 Moderate Earthquake 3.0 ≥ M < 5.0 Small Earthquake 1.0 ≥ M < 3.0 Microearthquake M < 1.0 Ultra Microearthquake Hagiwara, 1964

  3. NATURE OF EARTHQUAKES • Foreshocks • Main shock • Aftershocks • Earthquake Swarm • Normal Seismic activity

  4. TYPES OF EARTHQUAKES • Tectonic Earthquake • Volcanic Earthquake • Collapse Earthquake • Explosion Earthquake CLASSIFICATION DISTANCE 1) Teleseismic Earthquake > 1000 km 2) Regional Earthquake > 500 km 3) Local Earthquake < 500 km

  5. EARTHQUAKE MAGNITUDE Richter Magnitude ML (Local Magnitude) ML = log A - log Ao ( ) Body-wave Magnitude (mb) Surface-wave Magnitude (Ms) Ms= log AHmax - log Ao (o) mb = log (A/T) - f (,h) MS = log (A/T)max + 1.66 log + 3.3 Moment Magnitude (Mw) Duration Magnitude (MD) Mw = 2/3 log Mo - 10.7 MD = - 0.87 + 2.00 log  + 0.0035  Mo = A u Macroseismic Magnitude (Mms) Mms = 0.5Io + log h + 0.35

  6. Richter Magnitude Scale Distance S – P Magnitude Amplitude km sec ML mm

  7. EARTHQUAKE INTENSITY • Rossi-Forel Intensity Scale (I – X) • Modified Mercalli (MM) Intensity Scale (1956 version), (I – XII) • Medvedev-Sponheuer-Karnik (MSK) Intensity Scale • (1992 Version), (I – XII) Isoseismals Isoseismals are the curved lines joining the localities of same intensity.

  8. EARTHQUAKE ENERGY log E = 12 + 1.8 ML log E = 5.8 + 2.4 mb log E = 11.4 + 1.5 Ms Magnitude versus ground motion and energy Magnitude Ground Motion Energy 1.0 10.0 times about 32 times 0.5 3.2 times about 5.5 times 0.3 2.0 times about 3 times 0.1 1.3 times about 1.4 times

  9. POWER LAW RELATIONS Frequency- magnitude Relation Log10N = a – bM Aftershock Attenuation (p-value) N(t)  t -p Fractal Dimension

  10. b - VALUE ESTIMATION The Least-Square Fit Method: The log values of the cumulative number of earthquakes (N) are plotted against magnitude (M). The Maximum Likelihood Method : The maximum likelihood estimate of b-value is given by Aki ( 1965) : b =log10e/M-M0

  11. b-value: b = 0.77 Log N Magnitude An example showing frequency-magnitude relationin NE India

  12. SOURCE MECHANISM (fault-plane solution) Classification of Faults • Thrust Fault • Normal Fault • Strike-slip Fault Dynamics of Faulting • Single Couple • Double Couple Elastic Rebound Theory

  13. Normal fault Regime Thrust fault Regime Strike-slip fault Regime

  14. Fault Dimension

  15. Different Types of Faulting

  16. Graben & Horst in Fault System

  17. Dynamics of Faulting

  18. Elastic Rebound Theory Reid, 1910

  19. Plotting of P-wave First-motion (Equal Area Projection)

  20. Equal Area Plot of a Plane and its Pole

  21. P-wave first-motion plot and fault plane solution Kayal, 1984

  22. Source mechanisms of earthquakes at spreading centre

  23. Source mechanisms of earthquakes at the subduction zone, Indo-Burma ranges Rao & Kalpana, 2005

  24. Thank you

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