(Seminar for Fall, 2012)
Date 
Speaker 
Subject 
Notes 

09/19/12 
Bharath Shekar 
Presentation about summer work. 

09/26/12 
Francesco Perrone 
Adjoint State Method 
In order to solve inverse problem in the framework of optimization theory we need the gradient of the objective function that defines our problem. In exploration seismology we want to estimate the physical parameters of an elastic medium using boundary value data (seismic waves recorded at the surface) and in order to do so we construct an inverse problem that links the wavefield in the medium with the model parameters. The adjointstate method is a standard numerical technique that allows us to compute the derivative of an objective function that depends on a set of variables (state variables) that describe the state of the dynamical system under investigation (e.g. the elastic Earth's subsurface), and it does that by solving a limited number of forward problems. In this presentation I describe the adjointstate method through a few examples, I use different flavors of Full Waveform Inversion to show the effects on inversion resolution, and I show how to compute the key element of the method, i.e. the sources of the adjoint problem. 

10/03/12 
Oscar Jarillo. 
Full Waveform Inversion of microseismic data in VTI media 
Monitoring of microseismic events triggered during the hydraulic stimulation of reservoirs is of great interest to obtain information about the fracturing process. In this talk I will present the outline of my project that involves fullwaveform estimation of source location, source mechanism and VTI parameters from synthetic microseismic data implementing the adjointstate method. I will also present the results from forward modeling using a momenttensor source and some basic aspects of momenttensor inversion from borehole data. 

10/10/12 
No seminar 

10/17/12 
Roundtable discussion 

10/24/12 
Bharath Shekar 
Pointsource radiation in attenuative anisotropic media 
Perturbation raytheory allows us to compute asymptotic Green's function in attenuative, anisotropic media. As a "byproduct" of this method, we obtain approximations for the complexvalued slowness vector. The complexvalued slowness vector (bivector) describes the orientation of the planes of constant phase and constant amplitude. I will show some numerical examples which gives us a qualitative description of the behaviour of the complexvalued slowness vector. I will then describe some analytical methods to evaluate the slowness vector. 

10/31/12 
No seminar. 

11/7/12 
SEG 

11/14/12 
Roundtable discussion about anisotropyrelated talks at the SEG. 

11/21/12 
Thanksgiving break 

11/28/12 
Pengfei Cai 
Joint migration velocity analysis of PP and PSwaves for Volve OBC data 
I will first briefly review the methodology of joint MVA of PP and PSwaves, which consists of applying PP+PS=SS method, flattening PP and SS CIGs and codepthing. Then some synthetic models will be shown to test joint MVA. At last, I will show some results from a 2D line of the Volve 3D OBC dataset. 

12/05/12 
Bharath Shekar 
Pointsource radiation in attenuative media. 
We will discuss/prove the following: 1. In viscoacoustic media, waves from a pointsource propagate with a zero inhomogeneity angle (I have seen this stated as a "fact" in many papers, but I have not seen a proof.) 2. Saddlepoint condition for evaluating the wavefield from point sources in viscoelastic media. Although this has been investigated in a few papers, the saddlepoint condition was derived from a geometric argument. Therein, the interpretation of the saddlepoint condition was erroneous. We will provide an alternative derivation and carefully interpret the saddlepoint condition. 3. The behaviour of the inhomogeneity angle visàvis velocity and attenuation anisotropy.

