Reference only

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
1) Foreshocks
2) Main shock
3) Aftershocks
4) Earthquake Swarm
5) Normal Seismic activity

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

5. EARTHQUAKE MAGNITUDE
Richter Magnitude ML (Local Magnitude)
ML = log A - log Ao ( )
Body-wave Magnitude (mb)
mb = log (A/T) - f (,h)
Surface-wave Magnitude (Ms)
Ms= log AHmax - log Ao (o)
MS = log (A/T)max + 1.66 log + 3.3
Moment Magnitude (Mw)
Mw = 2/3 log Mo - 10.7
Mo = A u
Duration Magnitude (MD)
MD = - 0.87 + 2.00 log  + 0.0035 
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
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
Magnitude Ground Motion Energy
Magnitude versus ground motion and energy

9. POWER LAW RELATIONS
Frequency- magnitude Relation
Log10N = a – bM
Aftershock Attenuation (p-value)
N(t)  t -p
Fractal Dimension
2
~
)
( D
r
r
C

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 = 0.77
Magnitude
Log
N
An example showing frequency-magnitude relation in NE India
b-value:

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

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

14. Foot wall
h
d
55°
35°
Fault
Hanging wall
N
o
r
t
h
F
a
u
l
t
l
i
n
e
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