EARTHQUAKE MAGNITUDE, INTENSITY, EARTHQUAKE MAGNITUDE, INTENSITY,

ENERGY, POWER LAW RELATIONS AND ENERGY, POWER LAW RELATIONS AND

SOURCE MECHANISMSOURCE MECHANISM

Walter D. MooneyU.S. Geological Survey

California, USAe-mail: mooney @ usgs.gov

EARTHQUAKE CLASSIFICATIONEARTHQUAKE 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

NATURE OF EARTHQUAKESNATURE OF EARTHQUAKES

1) Foreshocks

2) Main shock

3) Aftershocks

4) Earthquake Swarm

5) Normal Seismic activity

CLASSIFICATION DISTANCE

1) Teleseismic Earthquake > 1000 km

2) Regional Earthquake > 500 km

3) Local Earthquake < 500 km

TYPES OF EARTHQUAKESTYPES OF EARTHQUAKES

1) Tectonic Earthquake

2) Volcanic Earthquake

3) Collapse Earthquake

4) Explosion Earthquake

EARTHQUAKE MAGNITUDEEARTHQUAKE 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

Richter Magnitude Scale

Distance S – P Magnitude Amplitude km sec ML mm

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.

EARTHQUAKE ENERGYEARTHQUAKE 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 times0.5 3.2 times about 5.5 times0.3 2.0 times about 3 times0.1 1.3 times about 1.4 times

Magnitude Ground Motion Magnitude Ground Motion Energy Energy

Magnitude versus ground motion and energy

POWER LAW RELATIONSPOWER LAW RELATIONS

Frequency- magnitude Relation

Log10N = a – bM

Aftershock Attenuation (p-value)

N(t) t -p

Fractal Dimension2~)( DrrC

b - VALUE ESTIMATIONb - 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

b = 0.77

Magnitude

Log

N

An example showing frequency-magnitude relation in NE India

b-value:

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

Normal fault Regime Thrust fault Regime

Strike-slip fault Regime

4 CHAPTER FIG. 1

Foot wall

hd

55°

35° Hanging wall

Fault Dimension

Different Types of Faulting

Graben & Horst in Fault System

Dynamics of FaultingDynamics of Faulting

Elastic Rebound TheoryElastic Rebound Theory

Reid, 1910

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

Equal Area Plot of a Plane and its Pole

P-wave first-motion plot and fault plane solution

Kayal, 1984

Source mechanisms of earthquakes at spreading centre

Source mechanisms of earthquakes at the subduction zone, Indo-Burma ranges

Rao & Kalpana, 2005