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INTRODUCTION TO DEFORMATION IN ROCKS Malay Mukul CSIR Centre for Mathematical Modelling and Computer Simulation BANGALORE 560 037 PROCESS-RESPONSE MODEL RESPONSE MODEL Empirical Model (Predictive) Geometric Model (Observational) Statistical Model (Regression Analysis) Conceptual Model (Inferential) PROCESS MODEL Computer Simulations Mathematical Model Statistical Comparison (Observations vs Predictions) DEFORMATIONAL SETTING DEFORMING SYSTEM SPECIFICATIONS Initial Position Position Final Position ONE STATE CHANGE OF STATE (TWO STATE) Initial Position T1 T3 T0 Initial Position Final Position T2 Final Position (T4) SEQUENCE OF STATES DATED PATH (FULL HISTORY) DEFORMATION HISTORY • GPS Maximum: 9 years (1993-2002) GTS & Seismology (1800s – 2002) Geophysical data • Paleoseismology (100s to 1000s years) Sediments Neotectonics: 1, 000-150, 000 years Sediments in uplifted terraces • • Geology: 150, 000 years to Billions of years Rocks QUATERNARY DEFORMATION T3 T2 T1 QUATERNARY DEFORMATION T4 T3 SCALES OF DEFORMATION • PLATE SCALE: Typically 1000s of km Plate Motions and Stresses • WEDGE SCALE: Typically 100s of km Critical Wedge Models • THRUST SHEET SCALE: Typically 10s of km Slip and Propagation Rates of Thrust Faults • FAULT ZONE DEFORMATION: < 1 km Frictional and Plastic Microscopic grain-size reduction mechanisms PLATE SCALE DEFORMATION WEDGE SCALE DEFORMATION • PLATE SCALE: Typically 1000s of km Plate Motions and Stresses • WEDGE SCALE: Typically 100s of km Critical Wedge Models • THRUST SHEET SCALE: Typically 10s of km Slip and Propagation Rates of Thrust Faults • FAULT ZONE DEFORMATION: < 1 km Frictional and Plastic Microscopic grain-size reduction mechanisms WEDGE SCALE DEFORMATION Mukul, 2000 SCALES OF DEFORMATION • PLATE SCALE: Typically 1000s of km Plate Motions and Stresses • WEDGE SCALE: Typically 100s of km Critical Wedge Models • THRUST SHEET SCALE: Typically 10s of km Slip and Propagation Rates of Thrust Faults • FAULT ZONE DEFORMATION: < 1 km Frictional and Plastic Microscopic grain-size reduction mechanisms SHEET SCALE DEFORMATION FAULT ZONE SCALE DEFORMATION • PLATE SCALE: Typically 1000s of km Plate Motions and Stresses • WEDGE SCALE: Typically 100s of km Critical Wedge Models • THRUST SHEET SCALE: Typically 10s of km Slip and Propagation Rates of Thrust Faults • FAULT ZONE DEFORMATION: < 1 km Frictional and Plastic Microscopic grain-size reduction mechanisms IMPORTANCE OF SCALE • PLATE SCALE: Typically 1000s of km Can regards the deformed body as a continuum and look at its response to stress Can regard the plate to be elastic • WEDGE SCALE: Typically 100s of km Continuum but not completely elastic • THRUST SHEET SCALE: Typically 10s of km Continuum but not completely elastic • FAULT ZONE DEFORMATION: < 1 km Not Continuum, Metallurgical Approach STUDY OF ROCK DEFORMATION • Continuum Mechanics Approach Deformed Body is regarded to be continuous Look at response to stress • Metallurgical Approach Deformation studied at atomic scales using Atomic Scale Flow Laws and Deformation Mechanisms • Effects seen under Petrological Microscope DEFORMATION IN ROCKS [STRESS] = {MATERIAL PROPERTIES}* [STRAIN] STRESS - Cause of Deformation STRAIN - Effect MATERIAL PROPERTIES – Controlling Factor: Continuum Grain Scale Atomic Scale Scale