EARTHQUAKE MAGNITUDE INTENSITY ENERGY POWER LAW RELATIONS AND

EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM J R Kayal Geological Survey of India Kolkata e-mail: jr_kayal@hotmail. com

EARTHQUAKE CLASSIFICATION MAGNITUDE M ≥ 8. 0 CLASSIFICATION 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 EARTHQUAKES 1) Foreshocks 2) Main shock 3) Aftershocks 4) Earthquake Swarm 5) Normal Seismic activity

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

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. 5 Io + log h + 0. 35

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

EARTHQUAKE INTENSITY Ø Rossi-Forel Intensity Scale (I – X) Ø Modified Mercalli (MM) Intensity Scale (1956 version), (I – XII) Ø Medvedev-Sponheuer-Karnik (MSK) Intensity Scale (1992 Version), (I – XII) Isoseismals 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 ACCELERATION log a = 2 or a=100 cm/sec 2 = 0. 1 g, when I = 7 and a = 1 g , when I = 10 Richter, 1958

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 1. 0 0. 5 0. 3 0. 1 10. 0 times 3. 2 times 2. 0 times 1. 3 times Energy about 32 times about 5. 5 times about 3 times about 1. 4 times

POWER LAW RELATIONS Frequency- magnitude Relation Log 10 N = a – b. M Aftershock Attenuation (p-value) N(t) t -p Fractal 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 =log 10 e/M-M 0

b-value: Log N b = 0. 77 Magnitude An example showing frequency-magnitude relation in NE India

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

p-value: p = 0. 91 Log-Log Plot of no. of aftershocks with time

Examples of Euclidean Shapes Examples of Fractal Shapes

Fractal Dimension D 2 = 1. 56 Example of Correlation integral versus distance plot

Fractal Map Contour Map showing variation of Fractal Dimension in NE India

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

Normal fault Regime Thrust fault Regime Strike-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 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

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