EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISMJ R KayalGeological Survey of IndiaKolkatae-mail: jr_kayal@hotmail.com

EARTHQUAKE CLASSIFICATION

MAGNITUDECLASSIFICATION 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 MicroearthquakeHagiwara, 1964

NATURE OF EARTHQUAKES

Foreshocks

Main shock

Aftershocks

Earthquake Swarm

Normal Seismic activity

CLASSIFICATIONDISTANCE1) Teleseismic Earthquake> 1000 km2) Regional Earthquake> 500 km3) Local Earthquake< 500 kmTYPES OF EARTHQUAKES

Tectonic EarthquakeVolcanic EarthquakeCollapse EarthquakeExplosion Earthquake

EARTHQUAKE MAGNITUDERichter 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 ScaleDistance 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)IsoseismalsIsoseismals are the curved lines joining the localities of same intensity.

Isoseismal of the 2001 Bhuj

Earthquake, Mw 7.7

Isoseismals of large earthquakes in India

INTENSITY AND ACCELERATIONlog a = 2 or a=100 cm/sec2 = 0.1g, when I = 7

a = 1g , when I = 10andRichter, 1958

EARTHQUAKE ENERGYlog E = 12 + 1.8 MLlog E = 5.8 + 2.4 mb log E = 11.4 + 1.5 Ms 1.010.0 timesabout 32 times0.5 3.2 timesabout 5.5 times0.3 2.0 timesabout 3 times0.1 1.3 timesabout 1.4 timesMagnitude Ground Motion Energy Magnitude versus ground motion and energy

POWER LAW RELATIONSFrequency- magnitude RelationLog10N = a bM Aftershock Attenuation (p-value)N(t) t -pFractal Dimension

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

b = 0.77MagnitudeLog NAn example showing frequency-magnitude relation in NE Indiab-value:

Contour Map showing the variation of b-value in NE Indiab-value Map

p = 0.91

Log-Log Plot of no. of aftershocks with timep-value:

Examples of Fractal ShapesExamples of Euclidean Shapes

Example of Correlation integral versus distance plot Fractal DimensionD2 = 1.56

Contour Map showing variation of Fractal Dimension in NE IndiaFractal Map

SOURCE MECHANISM(fault-plane solution) Classification of Faults Thrust Fault Normal Fault Strike-slip Fault Dynamics of FaultingElastic Rebound Theory Single Couple Double Couple

Normal fault RegimeThrust fault RegimeStrike-slip fault Regime

Fault Dimension

Different Types of Faulting

Graben & Horst in Fault System

Stress System Fracture Criteria: Mohr Circle

Dynamics of Faulting

Elastic Rebound TheoryReid, 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

Source mechanisms of earthquakes at the Himalayan collision zone Ni & Barazangi, 1984

Source mechanisms of intraplate earthquakes, peninsular India Kayal, 2000

( Kayal 2000, JGS )

( Kayal, 2000 JGS )

(a) Fault-plane solutions of the Bhuj earthquakes (b) N-S depth section of the earthquakes (Kayal et al. 2002, JGS )

Seismotectonic Model of 26th January, 2001 Bhuj Earthquake(Kayal et al. 2002, JGS )