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Earthquake source physics - NGEO074

Title:	Fyzika zemětřesného zdroje
Guaranteed by:	Department of Geophysics (32-KG)
Faculty:	Faculty of Mathematics and Physics
Actual:	from 2019
Semester:	summer
E-Credits:	5
Hours per week, examination:	summer s.:2/1, C+Ex [HT]
Capacity:	unlimited
Min. number of students:	unlimited
4EU+:	no
Virtual mobility / capacity:	no
State of the course:	taught
Language:	Czech, English
Teaching methods:	full-time
Teaching methods:	full-time

Guarantor:	prof. RNDr. František Gallovič, Ph.D. prof. RNDr. Jiří Zahradník, DrSc.
Classification:	Physics > Geophysics

Opinion survey results Examination dates SS schedule Noticeboard

Annotation -

Last update: T_KG (29.04.2013)

Green's tensor (far- and near-field terms, statics). Seismic moment tensor. Wave field. Absorption. Source time function (directivity). Calculating moment tensors from waveforms. Estimating size of fault plane and stress drop. Energy of seismic waves. Moment magnitude. Principles of slip inversion from seismic and geodetic data. Inversion of stress filed from focal mechanisms. Coulomb stress. Basic dynamic models of seismic sources. Forward modeling of seismic strong-ground motions (deterministic and stochastic component).

Aim of the course -

Last update: T_KG (29.04.2013)

The aim is to provide students with basic mathematical formulation of relations between earthquake source processes and seismic wavefield. To understand theoretical basis of inverse seismic-source problems and forward modeling of strong ground motions.

Course completion requirements - Czech

Last update: prof. RNDr. František Gallovič, Ph.D. (06.10.2017)

Podmínkou udělení zápočtu je aktivní účast na cvičeních.

Povaha kontroly studia předmětu vylučuje opravné termíny zápočtu.

Získání zápočtu je podmínkou pro konání zkoušky.

Literature - Czech

Last update: T_KG (29.04.2013)

T. Lay, T.C. Wallace: Modern global seismology. Academic Press 1995.

P.M. Shearer: Introduction to seismology. Cambridge University Press 1999.

K. Aki, P.G. Richards, Quantitative seismology. University Science Books 2002.

F.A. Dahlen, J. Tromp: Theoretical global seismology. Princeton University Press 1998.

Teaching methods -

Last update: T_KG (29.04.2013)

Lecture + exercises

Requirements to the exam - Czech

Last update: prof. RNDr. František Gallovič, Ph.D. (06.10.2017)

Zkouška je ústní, požadavky odpovídají sylabu v rozsahu prezentovaném na přednášce.

Syllabus -

Last update: T_KG (29.04.2013)

Green's tensor

Definition of Green's tensor for elastodynamic problem, units. Green's tensor for a homogeneous space, the near and far field. Space derivative of Green's tensor in the far-field approximation, relation to time derivative. Complete space derivative of Green's tensor; the near, intermediate and far-field terms.

Seismic moment tensor

Surface moment density, complete moment tensor. Displacement discontinuity; general and pure-shear case. Eigenvalues and eigenvectors, relation with the P-T-N axes. The moment-tensor norm; scalar seismic moment. Volume and deviatoric part of the moment tensor. The double-couple (DC) and non-DC parts. Source model with tensile component. Equivalent body forces. Relation between individual focal mechanisms and the regional stress field.

Wave field

Representation theorem and its use for the kinematically prescribed ruptures. Relations between the radiated wave field, Green's tensor and seismic moment tensor. Radiation pattern. The source time function of finite-extent sources and directivity. Haskell's source. Circular source. Principles of the moment tensor retrieval from waveforms. Estimation of the rupture propagation direction from apparent source time functions (empirical Green's function approach). Static displacement field.

Absorption

Viscoelasticity, general Boltzman model. Complex viscoelastic modulus, complex wave speed, attenuation coefficient and phase velocity. Quality factor (Q) and logarithmic decrement; Qp and Qs. Attenuation-dispersion relations. Maxwell's, Futterman's and Kjartansson's model. Dissipation operators. Intrinsic and scattering attenuation effects. Near-surface attenuation (kappa effect).

Seismic energy and stress drop

Ray approximation and single-station estimate of radiated energy. Relations between seismic energy and moment. Stress drop. Moment magnitude. Empirical relations between moment and fault size.

Calculation of moment tensors from complete waveforms

Discrete wavenumber method and program AXITRA. Elementary seismograms. Various parametrizations of the inverse problem (e.g. with fixed or free source position, fixed or free time function). Uncertainty estimate. Multiple point sources. Computer code ISOLA.

Calculation of slip from complete waveforms

Determination of fault surface. Parametrization of finite-extent sources. Linear and non-linear formulation of the inverse problem. Regularization. Uncertainty estimation. Combining seismic and geodetic data. Coulomb stress. Slip inversion from apparent source time functions.

Basics of dynamic source models

Strength of rocks, fracture, friction. Modes of fractures. Stresses acting on faults, Mohr’s diagrame. Anderson's theory of faulting. Dynamic models of ruptures with imposed rupture velocity, stress drop of a crack model. Evolution of stress on faults during rupturing, dynamic and station stress drop. Friction laws (Slip weakening, Rate-and-state). Dynamic modeling of spontaneous rupture and seismic cycles. Co-seismic and post-seismic slip, creep, slow earthquakes. Models of subduction earthquakes.

Forward modeling of strong ground motions

Principles of kinematic and composite models, their directivity. Combined deterministic and stochastic models. Use of empirical Green's functions. Rupture-process scenarios for seismic hazard assessment. Modeling local site effects.