The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian plate and surrounding regions in the Middle East

A detailed study was made of the consequences of the Arabian plate convergence against Eurasia and its effects on the tectonics of Anatolia and surrounding regions of the eastern Mediterranean. A primary source of information is time rates of change of baseline lengths and relative heights determined by repeated SLR measurements. These SLR observations are augmented by a network of GPS stations in Anatolia, Aegea, and Greece, established and twice surveyed since 1988. The existing SLR and GPS networks provide the spatial resolution necessary to reveal the details of ongoing tectonic processes in this area of continental collision. The effort has involved examining the state of stress in the lithosphere and relative plate motions as revealed by these space based geodetic measurements, seismicity, and earthquake mechanisms as well as the aseismic deformations of the plates from conventional geodetic data and geological evidence. These observations are used to constrain theoretical calculations of the relative effects of: (1) the push of the Arabian plate; (2) high topography of Eastern Anatolia; (3) the geometry and properties of African-Eurasian plate boundary; (4) subduction under the Hellenic Arc and southwestern Turkey; and (5) internal deformation and rotation of the Anatolian plate

Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

Intracontinental deformation occurrence and the processes and physical parameters that control the rates and styles of deformation were examined. Studies addressing specific mechanical aspects of deformation were reviewed and the studies of deformation and of the structure of specific areas were studied considering the strength of the material and the gravitational effect

The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

The long term objective of this project is to interpret NASA's Crustal Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of relative plate motions and intraplate deformation. The approach is to combine realistic modeling studies with an analysis of available geophysical and geological observations to provide a framework for interpreting NASA's measurements. This semi-annual report concentrates on recent results regarding the tectonics of Anatolia and surrounding regions from ground based observations. Also briefly reported on is progress made in using GPS measurements to densify SLR observations in the Eastern Mediterranean

The Interpretation of Crustal Dynamics Data in Terms of Plate Interactions and Active Tectonics of the Anatolian Plate and Surrounding Regions in the Middle East

During the past 6 months, efforts were concentrated on the following areas: (1) Continued development of realistic, finite element modeling of plate interactions and associated deformation in the Eastern Mediterranean; (2) Neotectonic field investigations of seismic faulting along the active fault systems in Turkey with emphasis on identifying seismic gaps along the North Anatolian fault; and (3) Establishment of a GPS regional monitoring network in the zone of ongoing continental collision in eastern Turkey (supported in part by NSF)

Finite-Difference Simulations of Time Reversed Acoustics in a Layered Earth Model

Traditionally an earthquake is located by using the arrival times of P and S phases. This uses only a limited portion of the information on a seismogram. A large part of the information carried by the waveform is not used. In this study we investigate the applicability of the Time Reversed Acoustics (TRA) technique, and thus the whole waveform of the recorded signal, for earthquake locations and source characterization. The basic concept involved in TRA is the fundamental symmetry of time reversal invariance. Injecting the recorded signal, with time running backwards, reconstructs the whole wave field within the medium and can focus the wave field to the source. TRA has emerged as an important technique in acoustics with applications to medicine, underwater sound, and many other disciplines. The objective of this paper is to demonstrate the feasibility of applying TRA to seismological data by means of simulating the relevant features using a finite-difference approach. The following subjects are investigated: (1) Locating the earthquake hypocenter; (2) finding the source space-time function; and (3) characterizing the direction of fault rupture during an earthquake. The results show that the TRA technique can focus back to the source reasonably well in a layered earth model and can recover the source time function. The results also show that TRA has a good tolerance to noise. For efficient applications, calculation time can be reduced by generating a medium response library. The source location and source time function can then be determined by convolving the medium response library with the time-reversed signals recorded at the seismic stations.Massachusetts Institute of Technology. Earth Resources Laborator

Scattering Characteristics In Heterogeneous Fractured Reservoirs From Waveform Estimation

Offset-dependent characteristics of seismic scattering are useful in the interpretation of fractured reservoirs. Synthetic seismograms generated by a 3-D finite difference modeling are used to study elastic wave propagation and scattering in heterogeneous fractured reservoirs. We use two models having different background medium properties and different azimuthal AVO responses and build heterogeneous fracture density realizations through stochastic modeling. Gas-saturated fractured reservoirs and waveforms ill fracture normal and strike directions are considered in this paper. The multiple signal classification (MUSIC) frequency estimator is used in waveform estimation to provide frequency domain attributes related to seismic wave scattering by fractures. Our results indicate that the strength of the scattered field increases with increasing fracture scatter density and decreasing correlation length of spatial variations of fracture density. It is also a function of the background medium. The strength of the scattering field is stronger in model 1 which has smaller property contrasts in the background medium than model 2. The scattering characteristics for both models are different at the top and the base of the fractured reservoir. Our results show that the scattered field is weak at the top of a fractured reservoir. The first order results are dominated by velocity anisotropy of a mean crack density field. However, the base of the fractured reservoir corresponds to a strong scattered field on which fracture heterogeneity has a larger effect.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation ConsortiumUnited States. Dept. of Energy (Grant DE-82066-223II-1

Full-waveform Based Complete Moment Tensor Inversion and Stress Estimation from Downhole Microseismic Data for Hydrofracture Monitoring

Downhole microseismics has gained increasing popularity in recent years as a way to characterize hydraulic fracturing and to estimate in-situ stress state. Conventional approaches only utilize part of the information contained in the microseismic waveforms such as the P/S far-field amplitudes to determine the focal mechanisms and infer stress state. The situation becomes more serious for downhole monitoring where only limited azimuthal coverage is available. In this study, we developed a full-waveform based approach to invert for complete moment tensor. We use the discrete wavenumber integration method as the fast forward modeling tool to calculate the full wavefield in the layered medium. By matching the waveforms across the array, a stable moment tensor solution can be obtained without imposing additional constraints. We show that by using full waveforms, the resolution of the full seismic moment tensor is improved even with data from a single monitoring well. We also determine the stress drop from the S-wave displacement spectrum. We test our method using a downhole microseismic dataset from hydraulic fracturing treatments in East Texas. The results indicate the existence of non-double-couple components in the moment tensor. The derived fracture plane direction also agrees with that derived from multiple event location.Halliburton Compan

Effects of tool eccentricity on wave dispersion properties in borehole acoustic logging while drilling

In this paper, a finite element approach is applied to study the dispersion properties of non-leaky acoustic waves inside boreholes with off-centered LWD (logging while drilling) tools. Both soft and hard formation cases are studied with focus on phase velocity dispersions of Stoneley, dipole and quadrupole modes. When an LWD tool is off-centered, the dispersion curve of the Stoneley mode shifts to the lower phase velocity compared with that of a centered-tool condition. Meanwhile, the dipole dispersion curve splits into two curves with different phase velocities. This splitting phenomenon is also observed with the quadrupole mode. The splitting and shifting of the dipole mode are greater than those of the quadrupole mode. These new observations are important for interpreting acoustic LWD data accurately.Massachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Effective Conductivity Modeling of a Fluid Saturated Porous Rock

The microstructure of a porous medium and physical characteristics of the solid and the fluids that occupy the pore space determine the macroscopic transport properties of the medium. The computation of macroscopic properties from the rock microtomography is becoming an increasingly studied topic. The transport properties are especially difficult to determine at the microscopic scale. In this paper, we will focus on modeling the electric conductivity from the X-ray CT microtomograhpy of a 1mm3 Fontainbleau Sandstone sample. To accomplish this, we modified the finite difference Laplace solver developed at NIST (National Institute of Standards and Technology, Gaithersburg, MD 20899-8621, U.S.A). Our modified finite difference code can calculate the effective conductivity of random materials with different levels of conductivity contrasts. The effective conductivity and the current density distribution of gas, oil and different salinity brine saturated Fontainbleau Sandstone are calculated using a two-phase model. When we compare our numerical results with experimental results from previous studies, the numerically resolved conductivity is almost 100% lower than the experimental data. This is the case for all of the previous work on the numerical computation of electric conductivity from digital images of rocks. Our explanation for this large discrepancy is due to the exclusion of the surface conductivity in the electric double layer (EDL) at the rock-electrolyte interface. Thus, we develop a three phase conductivity model to include the surface conductivity and determine the effective conductivity of the numerical grids containing the EDL from the Waxman-Smits equation. By adding the surface conductivity into our numerical modeling, the calculated conductivity from rock microtomography is much closer to the experimental data.Massachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Seismoelectric And Seismomagnetic Measurements In Fractured Borehole Models

Seismoelectric and seismomagnetic fields generated by acoustic waves in fluid-saturated fractured borehole models are experimentally investigated with an electrode and a Halleffect sensor. In a borehole with a horizontal fracture, the Stoneley and flexural waves induce seismoelectric and seismomagnetic fields on the borehole wall and an electromagnetic wave propagating with light speed at the horizontal fracture. In a borehole with a vertical fracture, the acoustic field generated by a monopole or dipole source is similar to that in a borehole without a vertical fracture. However, the acoustic wave propagating along the vertical fracture induces seismoelectric and seismomagnetic fields, whose apparent velocities are equal to that. of a Stoneley wave. Experimental results show that two different kinds of electric and magnetic fields are generated by acoustic waves in borehole models with horizontal and/or vertical fractures. One is an electromagnetic wave propagating with light speed. The second is a stationary or localized seismoelectric and seismomagnetic field. Seismoelectric and seismomagnetic measurements might be a new logging technique for exploring fractures in a borehole.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu