Abstract
Evaluation of fluid content in deep earth reservoirs or of fluid contaminants in shallow earth environments has necessitated the use of various geophysical imaging methods such as seismic reflection prospecting. Interpretation of seismic velocities and amplitudes is based on theories of fluid-saturated and partially-saturated rocks that have been available since the 1950's. A new synthesis of these same physical concepts uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply, yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution. The key idea revolves around the fact that the density and the first Lamé elastic constant (lambda) are the only two parameters determining seismic velocities that also contain information about fluid saturation. (At low enough frequencies, Gassmann's well-known equations show that the shear modulus is independent of the fluid saturation level.) We use these facts to construct saturation-proxy plots from seismic velocity data. This method is more robust that AVO (amplitude versus offset) since it does not require reflectivity data, although it can use these data when available. The method therefore applies to a wide range of source-receiver configurations, including seismic reflection profiling (surface-to-surface), vertical seismic profiling (well-to-surface), wireline data (single well), and crosswell seismic transmission tomography (well-to-well)---since measurement of both compressional and shear wave speeds is the main requirement.

Biography
Jim Berryman completed his education with a PhD in physics from the University of Wisconsin, Madison, in 1975, having written a thesis on heterogeneous materials. After a post-doc in applied math on nonlinear waves and inverse problems, he joined CONOCO as a research geophysicist in 1976. His first day on the job he was handed a stack of geophysics-related papers to read. The top two papers in the stack were the 1956 papers of M. A. Biot on waves in poroelastic media, and the third paper was the one by Geertsma and Smit from Geophysics attempting to simplify and explain these two papers of Biot. Since this introduction, Jim has continued working on inverse problems, heterogeneous media, and poroelasticity at the Courant Institute (NYU), at Bell Labs (Whippany), and at the Lawrence Livermore National Laboratory, where he has been a physicist since 1981. He has also been a consulting professor in geophysics at Stanford since 1992.

Abstract
Land-based, shallow seismic reflection profiling is a technique that has become technologically viable and more widely applied during the last 20 years. Processed seismic sections are used to delineate the structure of the shallow subsurface (10's to 100's m depth), with potential vertical resolution on the metre scale. In glaciated terrain, shallow seismic reflection surveys have been shown to be an effective means of delineating the thickness, two-dimensional structure, and lateral continuity of different units of a sequence of unconsolidated sediments and also of mapping the depth to, and nature of, the bedrock surface. Such information is critical in any 3D mapping program, especially in areas where overburden materials are thick (many 10s of metres) and waterwell or borehole control is sparse. Examples of the application of shallow seismic methods to resource and hazard studies in different geological areas from across Canada demonstrate the potential (as well as some of the limitations) of this technique.

Biography
Susan Pullan received her B.Sc. in geophysics from the University of Western Ontario, London, Ontario, and her Ph.D. from the Australian National University, Canberra, Australia. She joined the Geological Survey in Canada (GSC) as a research scientist in 1982. Her particular research interests are in the development of shallow seismic techniques and their application to near-surface problems. She is a founding member and past-president of the Environmental and Engineering Geophysical Society (EEGS) and a long-standing member of the Society of Exploration Geophysics (SEG). She is currently Acting Chief, Hazards and Environmental Geology Subdivision at the GSC.

Abstract
The shallow subsurface of the earth is an extremely important zone that yields much of our water resources, supports our agriculture, serves as the repository for most of our wastes and contaminants, and supports our infrastructure. As safe and effective use of the near-surface environment is a major challenge facing our society, there is a great need to improve our understanding of the shallow subsurface. Conventional sampling techniques for characterizing the shallow subsurface can be costly, time-consuming, and invasive, potentially causing disturbance of the in-situ conditions and human exposure to contaminants. Conventional measurements are typically sparse and are often associated with a support scale that does not capture field-scale variability. With poor subsurface characterization, water resource managment or remediation schemes are unnecessarily expensive or ineffective.

Geophysical methods hold promise for rapid, minimally-destructive, and vastly improved characterization of the shallow subsurface. Although many geophysical advances have been made in the last decade, several obstacles still hinder the routine use of geophysics for hydrogeological characterization. The multi-disciplinary research area of hydrogeophysics strives to overcome these obstacles, and to rigorously reconcile information obtained using both hydrogeological and geophysical approaches for an improved understanding of subsurface parameters or processes. This presentation will review the state-of-the-discipline of hydrogeophysics, followed by hydrogeological-geophysical data fusion examples. Case studies will be presented that focus on how we have used hydrogeophysical data to characterize the shallow subsurface and to monitor system transformations that occurred during biostimulation at the DOE Bacterial Transport Site near Oyster, Virginia.

Biography
Susan's educational background includes a B.S. in geology from UC Santa Barbara, an M.S. in geophysics from Virginia Tech, and a Ph.D. in groundwater from the Civil and Environmental Engineering Department of UC Berkeley. She has worked as a geologist for the USGS, as an exploration geophysicist within the petroleum industry, and is now a staff scientist in the Earth Science Division of the Lawrence Berkeley National Laboratory in Berkeley, California. Susan's research interests focus on the integratino of hydrogeological and geophysical data for environmental site characterization, remediation monitoring, and ecosystem studies. She is an Associate Editor for Water Resources Research, the United States representative for the International Associate of Hydrological Sciences 2020 Working Group, the chair of the AGU Hydrogeophysics Technical Committee, and a member of AGU, SEG, EEGS, and IAHS.

http://esd.lbl.gov/people/shubbard/vita/webpage/hubbard_cv.html

Abstract
Modern airplanes, especially the latest generation of jet aircraft, are designed to operate in environments free from dust and corrosive gases. Explosive volcanic eruptions such as the 1989-90 eruptions of Redoubt Volcano in Alaska and the 1991 eruptions of Mount Pinatubo, Philippines, inject large amounts of very small rock fragments, known as volcanic ash, and corrosive gases into the troposphere and lower stratosphere where commercial jet airplane traffic occurs. Such explosive eruptions occur somewhere on Earth about 10 times per year. Many of these explosive volcanoes are found around the rim of the Pacific Ocean in the "Ring of Fire" and have a direct impact on air routes, airports, and flight operations.

In the past 20 years, more than 100 jet aircraft have been damaged as a result of inadvertent encounters with drifting clouds of volcanic ash that have contaminated air routes and airport facilities. Most of these encounters involved large commercial jet airliners, seven of which experienced in-flight loss of engine power. The repair and replacement costs associated with airplane-ash cloud encounters during the past 20 years exceed $200 million. In addition to the high economic cost of these encounters, the potential human cost is very high: more than 1,500 passengers aboard the seven airliners were put at risk. Compounding the problem is the fact that volcanic ash clouds are not detectable by the present generation of radar instrumentation aboard aircraft. Complete avoidance of volcanic ash clouds is the only way to prevent damage to aircraft by volcanic ash.

Volcanic ash clouds may drift for hundreds to thousands of miles from their sources and can contaminate large volumes of airspace. Ash clouds may drift over several countries and into different Flight Information Regions (FIRs) and Air Traffic Control (ATC) jurisdictions. At times, ash from a single eruption can contaminate a heavily used airspace region. This causes flights to be diverted, delayed, or canceled. Given the nature of today's long range flight operations, a single eruption can have a global effect on air traffic operations.

Biography
Tom Casadevall became Regional Director of the U.S. Geological Survey's 15 state Central Region in January 2000. As regional director, he is responsible for helping to lead the nation's largest water, earth, and biological science and civilian mapping agency in its mission to provide the scientific data that enable decision-makers to create sound policies for a changing world.

From February 1998 through November 1998, Dr. Casadevall was Acting Director of the USGS and from April 1996 to January 1998, he was the Western Region Director of the USGS in Menlo Park, California. From 1978 to 1996, he was a geologist with the USGS Volcano Hazards Program, stationed at the Hawaiian Volcano Observatory, the Cascades Volcano Observatory, as Advisory Volcanologist to the Government of Indonesia, and in Denver, Colorado. As project chief of the Volcanic Hazards and Avaiation Safety Project 1990-1996, he coordinated USGS activities with other Federal agencies and non-governmental groups in the area of aviation safety and he was instrumental in organizing the First International Symposium on Volcanic Ash and Aviation Safety, in 1991. In 1977-1978 he was a faculty member o the Escuela Politecnica Nacional in Quito, Ecuador. In 1976, he was a National Research Council post-doctoral research fellow with the USGS. From 1969 to 1972, he worked for Bear Creek Mining Compnay as a geologist exploring for base metals in the western United States and in 1974 as a production geologist in the Sunnyside gold mine, Colorado.

Tom graduated from Beloit College, Wisconsin, with a Bachelor of Arts degree (1969); he earned a Master of Arts degree in geology (1974) and a Ph.D. in geochemistry (1976) from Pennsylvania State University.

Abstract
Models of processes in the alpine snow cover fundamentally depend on the spatial distribution of the surface energy balance. For this reason, we want to estimate the spectral albedo of the snow, along with other properties such as grain size, contaminants, temperature, liquid water content, and depth or water equivalence. In the optical part of the spectrum, the retrievable properties include albedo, grainsize, contaminants, liquid water, and temperature.

Biography
Jeff Dozier's research and teaching interests are in the fields of snow hydrology, Earth system science, remote sensing, and information systems. In addition, he has played a role in development of the educational and scientific infrastructure. He founded UCSB's Donald Bren School of Environmental Science and Management and served as its first dean for six years. He was the senior project scientist for NASA's Earth Observing System in its formative stages when the configuration for the system was established. He helped found the MEDEA group, which investigates the use of classified data for environmental research, monitoring, and assessment.

Jeff received his B.A. from California State University, Hayward in 1968 and his Ph.D. from the University of Michigan in 1973. He has been a faculty member at UC Santa Barbara since 1974. He is a Fellow of the American Geophysical Union, the American Association for the Advancement of Science, and the UK's National Institute for Environmental Science. He is also an Honorary Professor of the Chinese Academy of Sciences and a recipient of the NASA Public Service Medal.

Abstract
For many years geophysicists have tried to achieve a means to interpret multiple geophysical data sets. These attempts have been called by many names (data fusion, data integration, etc.), and used numerous technical approaches (statistical, mathematical combinations, empirical comparisons, etc.). We have developed an approach that we call integrated active interpretation. This approach is a purely visual approach that utilizes a three dimensional display to interpret several data sets simultaneously. The approach uses well-established principles of interpretation, with the 3D display used as an interactive tool. The colors and opacities on each data set can be manipulated independently so that optimum images can be achieved for each type of geophysical data. The 2D data sets can be displayed as color contours, or as pseudo-relief maps. The 3D data sets (GPR or seismic) are displayed in 3D space-time, as they are usually displayed. The power of this interpretation scheme lies in the fact that the colors, relative amplitudes, and opacities of the individual data sets can be manipulated independently. This allows the interpreter to directly compare the locations of individual anomalies on each data set, and determine the locations of mutually coincident anomalies for the different geophysical data types. This approach is not restricted to geophysical data sets. Geophysical model responses, geologic hydrologic, and chemical data can also be incorporated into an active integrated interpretation using this 3D real-time approach.

Biography

Jeffrey J. Daniels is currently a professor at The Ohio State University. He received B.S. and M.S. degrees in geology from Michigan State University and a Ph.D. in geophysical engineering from the Colorado School of Mines. He worked for the U.S. Geological Survey in Denver from 1974-1985. He joined the faculty of OSU in 1985. His current research focus is on the integration of geophysical methods through visualization and numerical fusion, and hydrogeophysics. He is a member of the American Geophysical Union (AGU), the Society of Exploration Geophysicists (SEG), the Society of Professional Well Log Analysts, the Environmental and Engineering Geophysical Society (EEGS), and Sigma Xi. He was the founding president of EEGS, and he is a member of the Science Advisory Board for SEDP. He is an author of over 90 professional publications.

Abstract
According to the International Committee of the Red Cross in Geneva, land mines around the world claim a victim every twenty minutes. The United Nations estimates it will take $33 billion and 1, 100 years to clear all of the mined areas in the world using the current technology.

All methods to detect land mines rely on a contrst of some physical property of the land mine and the surrounding soil. Some of these methods are not sensitive enough or are too sensitive, causing many false alarms. Also, most methods require contact with the surface, which increases the risk of accidental detonation. The Physical Acoustics Laboratory (PAL) at the Colorado School of Mines, in collaboration with New England Research (NER), proposes the investigation of a new, non-contacting, acousto-optic method for land mine detection.

We propose to investigate the feasibility of fully non-contacting mine detection based on a novel combination of laser and ultrasonic methods. The idea is to excite the ground with a parametric acoustic array, using a narrow beam of ultrasound and the nonlinear interaction of the ultrasound with air, to focus low-frequency sound into the ground. Ground motion causes the land mine to scatter acoustic energy that is detected with a vibrometer with sub-millimeter to centimeter wavelengths. Characteristic resonance patterns of the land mine, as well as spatial characteristics of the wave field, may allow us to separate scattering from land mines from other inhomogeneities in the sub-surface.

I will illustrate the acoustic response of a near-surface scatterer (such as a land mine) with a scaled acousto-optic experiment from the Physical Acoustics Laboratory.

Biography

Kasper van Wijk is a Ph.D. candidate in the Department of Geophysics at the Colorado School of Mines. He earned a M.S. in geophysics from Utrecht University, The Netherlands. He works on wave propagation in disordered media with Professor John Scales in the Physical Acoustics Laboratory (PAL).

Abstract
Seismic reflection events are typically catalogued as primary or multiple depending on whether the arriving energy at the receiver has in its history experienced one or more upward reflections, respectively. We can trace the evolution of progress and effectiveness in seismic processing by folowing the physics used to describe what the wave experiences between source and reciever. More realism and comjpleteness in the physics, when applied appropriately, has an associated improvement in prediction and reduction in risk. Hence, there is alignment between providing step-change improvement in seismic effectiveness and a central need of the petroleum industry. We classify three types of step-changes that occur when: (1) the dimension of the physics moves up-1D to 2D, 2D to "3D", "3D" to 3D to match the dimension of subsurface variation, ("3D" here refers to current typical 3D acquisition); two other step-changes occur within a given dimension when; 9(2) the theory, and algorithms, for propagation and reflection are expanded to accommodate further significant, prioritized and relelvant phenomena, (e.g., including rapid lateral heterogeneous velocity variations and curved, dipping, and diffractive reflectors with large contrast in earth properties, and; (3) the language and associated mathematics for describing the experiences and history of therecorded wave-field allows for coding an decoding (i.e., processing), or raveling and unraveling, in terms of approximate achievable rather than inaccessible precise subsurfce information. It is much simpler to provide a precise description of an event in terms of accurate rather than approximate subsurface information-and the former is the assumption behind all current leading-edge depth imaging and subsequent amplitude analysis. The problem is if the forward description is in terms of, e.g., actualvelocity, the reverse or processing of those events within that picture requires actual velocity, as well. While the precise desciprtion of events in terms of approximate information is more comoplicated, and hence, the processing algorithms more computer intensive, the benefits can be not only cost-effective, but often without peer-especially under complex geologic conditions. Seismic methods that derive from the inverse-scattering series provide the opportunity to realize step-3 change. They produce currently used algorithms that predict and subtract free-surface and internal multiples with only reflection data and no subsurface inforamtion whatsoever. Regarding primaries, the requirements on adequate velocity information to achieve accurate imaging at depth can often be an unattainable demand under complex geologic conditions, e.g., sub-salt, sub-basalt and sub-karsted sediments, and can cause our current leading-edge imaging techniques to produce sub-optimal of unacceptable results. In response, the inverse series provides the conceptual possibility of imaging and inverting large contrast complex targets directly in terms of reflection data and an inadequate velocity model of the overburden. The promise of step-3 change in the evolution of processing is to relax or lower the demand on subsurfce information for processing multiples/primaries, especially under complex geologic conditions, while maintaining or raising processing objectives, (e.g., the removal of multiples and imaging-inversion of primaries in depth) and to broaden the 3D physics of propagation and reflection. Step-3 places increased demands on the definition, (e.g., the source signature) and completeness of acquisition, and higher computer costs. However, the requirement that we can access inaccessible subsurface information is lifted and the burden shifts up to the surface of the earth, to assumptions and demands on acqusition and computers where intelligence and money can influence effectiveness. It represents an enormous empowerment, where those willing to pay more (for acquisition and compute time) have the opportunity to achieve more. Computers get faster and chaper. Furthermore, these added costs pale in comparison to the economic risk, potential benefit and technical challenges faced, for example, in deep-water E&P. We kjnow that bringing multiples through that step-3 wasn't easy, and considerable conceptual and practical hurdles were faced and overcome. We anticipate that in bringing primaries to a similar state we will face higher hurdles yet, but the research efforts are underway, and enthusiasm, courage, and the sense of adventure are on our side.

Biography

Arthur B. Weglein received his Ph.D. in physics from the City University of New York in 1975 and then spent two years as a Robert Welsh Postdoctoral Fellow at UTD. He entered seismic petroleum research in 1978 and worked at the Cities Service Oil Compnay Research Laboratory in Tulsa from 1978-1981 and then at Sohio Petroleum Company Research Laboratory in Dallas from 1981-85. Weglein joined ARCO in 1985 and spent the next 15 years as a member of its research staff, where he was elected to Research Advisor in 1987 and Senior Research Advisor in 1994. He spent a sabbatical year (1989-90) as Visiting Professor at the Federal University of Bahia in Brazil and three years (1991-94) as Scientific Advisor at Schlumberger Cambridge Research in Cambridge, England. In September 2000, he joined the University of Houston as the Margaret S. and Robert E. Sheriff Endowed Faculty Chair in Applied Seismology. Weglein started the Mission-Oriented Seismic Research Program and industry consortium in January 2001. The goal is to address specific prioritized problems whose solutions would produce the biggest positive step-change in the ability to locate and produce hydrocarbons.

Abstract
Attenuation (1/Q, inverse of quality factor) is a fundamental property of rocks with great potential to discriminate fluids and processes. However, 1/Q is poorly understood due to a lack of reliable data. Almost all the reported 1/Q laboratory measurements are in the megahertz range. The observed loss mechanisms may be completely different from that seen in the seismic frequency range. To address this issue, a low frequency, low-amplitude apparatus was built to measure both seismic velocities and attenuation. Strain gauges bonded directly to the surface of the rock sample allow simultaneous measurement of complex compressional and shear moduli,
giving both velocities and attenuation. Confining pressure, saturation, and pore pressure can all be controlled independently. A sinusoidal stress is applied such that sample strain amplitudes remain below 107, yet phase angles can be resolved to within 0.2 degree. The frequency range is between 25 Hz and 1000 Hz. The low frequencies are thus directly applicable to seismic exploration and the broad bandwidth allows investigation of loss mechanism and velocity dispersion. After calibration, a series of experiments were carried out on Foxhill's, Rim sandstone, Uvalde carbonate and ITF samples concentrating on the role of fluids in determining the frequency-dependent elastic and inelastic responses in the rock-fluid system. As the differential pressure is increased, the attenuation values decrease due to the closing of compliant pores and compaction. Seismic attenuation and velocities were measured at different saturations and differential pressures. It was observed that acoustic velocity drops as the
saturation is increased and then shoots up at full saturation. Attenuation increases with increasing saturation, with shear attenuation being half the compressional attenuation at partial saturation. At full saturation, extensional, compressional and bulk attenuation drops but shear attenuation increases. Clays play an important role as their presence can change the state of the rock by changing the Poisson's ratio. At full saturation, opening and closing the boundary can significantly change the attenuation and velocity values: acoustic velocity drops and attenuation increases. This effect is only observed at low frequencies, which depend on the fluid mobility. At full saturation, the sequence in which attenuation modes increase or decrease changes by opening the boundary, and is also dependent on the frequency. Low frequency shadows beneath amplitude anomalies (bright spots) substantiate the presence of hydrocarbon. The presence of low frequency shadow is due to abnormally high attenuation in a gas reservoir.
It has been argued that these shadows could be due to processing errors (NMO stretching, multiples, improper moveout etc) and in broadband seismic section the shadows cannot be observed. With the help of Instantaneous Spectrum Analysis we can confirm the presence of shadows, but it is very important to understand these observations and give a physical explanation. There are several theoretical models that relate the attenuation and velocity like porosity, permeability, fluid compressibility and viscosity. Viscosity and permeability influence the mobility of a fluid. Laboratory measurements show that velocity dispersion and attenuation are dependent on the above two parameters, and the relaxation frequency shifts towards low or high frequency by decreasing or increasing the fluid mobility respectively.

Biography

Gautam Kumar received his Bachelor's degree in geosciences from the Indian Institute of
Technology, Kharagpur. He joined CSM in Fall 2001 and is currently pursuing
a Master's degree in geophysics under the supervision of Prof. Mike Batzle
in the Rock Physics group.

Abstract
I will summarize seismic evidence that the conductive cooling of the Pacific lithosphere arrests between ages of about ~70 and ~100 Ma. At ages less than 70 Ma and again between ages of ~100 Ma and ~135 Ma, the average shape of the temperature profile of the Pacific lithosphere changes with age in a way that is consistent with dominantly conductive cooling. This pattern of thermal evolution is also apparent in properly reduced sea floor topography and in the characteristics of subduction in the Western Pacific. The seismic evidence comes from a new data set of broad-band surface wave dispersion measurements across the Pacific. The inversion for a 3-D shear velocity model of the crust and upper mantle includes a physical model of surface wave Fresnel zones and Monte-Carlo inversions based on both seismic and intrinsically thermal parameterizations. I will also briefly discuss a number of conjectures concerning the physical causes that may arrest lithospheric cooling across the Central Pacific. I will argue that the development of lithospheric instabilities (Richter rolls) that set-on at about 70 Ma and drive small-scale convection may play a principal role in the thermal state of the Central Pacific.

Biography

Michael Ritzwoller is a physics professor at the University of Colorado at Boulder. His research interests lie mainly in theoretical and observational normal mode and surface wave seismology. In recent years, his research has concentrated on bridging the gap between the length-scales of traditional global seismic models and the length-scales of tectonic and dynamical processes that operate near the earth's surface. He has also made contributions to studies of the earth's normal modes, helioseismology, aspects of shallow subsurface imaging of relevance to environmental monitoring and hydrocarbon exploration, and the seismic verification of nuclear treaties like the ill-fated nuclear Comprehensive Test Ban Treaty (CTBT).

Abstract
To obtain a good image and an accurate depth estimate of reflectors in the subsurface, it is essential to account for heterogeneity and velocity anisotropy. Existing velocity-analysis algorithms often approximate the subsurface with homogeneous or vertically heterogeneous anisotropic layers or blocks, which is suitable in time imaging. For depth imaging purposes, however, lateral heterogeneity should also be accounted for. If ignored, it may cause significant errors in parameter estimation and distortions in the shape of the imaged reflectors. The present challenge lies in describing lateral and vertical heterogeneity and anisotropy simultaneously. The simplest realistic heterogeneous, anisotropic model is the factorized VTI medium with constant vertical and lateral gradients in vertical velocity. We explore what parameters can be estimated uniquely in such media from surface seismic data, and use that information to develop a robust parameter estimation scheme. By approximating the subsurface with piecewise factorized blocks or layers we attempt to build a spatially varying anisotrooic velocity field for depth imaging.

The parameter estimation algorithm is implemented in the post-migrated domain as a two-step iterative procedure that includes pre-stack depth migration (imaging step) followed by an update of the medium parameters (velocity-analysis step). We find that the move out of events in image gathers can uniquely constrain the vertical velocity gradient, while the lateral gradient is always coupled to the anisotropic parameter d. To decouple the lateral gradient from the anisotropy, apriori information (e.g., vertical velocity at a single point) is required. For simple models with sub-horizontal reflectors, the vertical velocity is also needed to obtain accurate depth estimates. In more complicated models with intermediate dipping interfaces, however, it may be possible to build accurate models in depth without knowledge of the vertical velocity.

Biography

Debashish Sarkar received an INTG.MS (1997) in Geophysics from Indian Institute of Technology, Kharagpur, India, and an MS (1999) in geophysics from the University of Oklahoma. Currently, he is a Ph.D. Candidate in geophysics at the Colorado School of Mines. In 1996 he was employed by Schlumberger in Muscat, Oman, and from 1998 to 2000, he worked for Conoco. At IITT Kharagpur he received the P.K. Bhattacharya Award. He is a member of SEG EAGE, AAPG, and AGU.

Abstract
I develop an algorithm for inverting gravity data to construct estimates of the base of salt and investigate the sensitivity of the recovered model to four different sources of errors. The inversion algorithm is based on the approach of Tikhonov regularization, in which I impose an explicit model objective function and incorporate various prior information to constrain the final solution. The prior information is typically the shape and depth of the top salt and a known part of base salt from seismic image. The error in such prior information governs the reliability of the recovered base of salt. It is therefore important to understand the influencing factors of the inversion: (1) input gravity data, (2) top of salt, (3) known part of the base salt, and (4) the background density profile. I use a synthetic model to illustrate the algorithm and find that the recovered model can be a good representation of the true model in the absence of errors. Moderate perturbation in any of these four factors, however, could lead to large errors in the recovered model. Thus one must minimize errors in these input parameters in order for them to improve the reliability of the inverted base of salt. The derived error curves provide an indication of errors to be expected in the inverted base of salt in practical applications, and serve as a guide to data preparation s that the inverted base salt can aid in seismic imaging of base salt, and thereby, the subsalt structure.

Biography
Dongjie Cheng received a BS (1990) in geophysics from the Petroleum University, China. Currently he is a MS candidate in geophysics at the Colorado School of Mines. From 1990-2002, he worked for BGP, China National Petroleum Corporation (CNPC), as analyst of data processing, research programmer and marketing manager. He is a member of SEG and DGS.

Abstract
One of the main tasks of rock physics is predicting the change of properties (like seismic velocity) of a porous rock if the saturating fluid changes or effective pressure is modified. This is directy applicable to Time-lapse (or '4D') seismics: the monitoring of a reservoir over time to ascertain fluid flow in the subsurface and manage the field more efficieintly because of its generality, simple assumptions, and ease of use. Unfortunately, for many of the most interesting cases (for instance, for seismic frequencies), its predictions are often wrong. Extensions like Mavko's Squirt Flow have been developed and work in some cases.

This lecture is about my work in adapting Gassmann's equation for a specific geological area. I will present background material and experimental results in both ultrasonic and low frequency ranges for rocks saturated with different fluids. Interesting fluid effects are obvious. However, much of this work is preliminary, and conclusions may change as further data is collected.

Biography
Han Ecke came to CSM in 1999 from East Germany with a BS in geophysics from Freiberg University of Technology. His research interests are in data processing, numerics, programming and reservoir hydrocarbon properties. He now works with Prof. Mike Batzle in the Rock Physics Lab and is systems administrator and webmaster for the Physical Acoustics Lab. In addition, he maintains the Common Ground database and is rewriting the COOOL project in his spare time.

Abstract
Coda waves are multiply scattered waves. Little attention has been paid to the problem of imaging with coda waves, i.e., localizing changes in the medium. Here, we propose a technique for localizing the temporal change in the medium with multiply-scattered waves. Specifically, we detect changes in the effective medium characterized by strong and random fluctuations of the velocity or slowness.

We take advantage of the fact that the wave transport acquires a diffusive character in a strongly scattering medium to obtain an expression for the mean or average traveltime change of the diffuse wavefield caused by a slowness perturbation. This constitutes the forward problem; the purpose of this work is to test this formalism with synthetic seismograms computed by finite-differences for different perturbations in the slowness. The inverse problem, estimating the temporal change in the slowness given the measured traveltime change between the unperturbed and perturbed wavefield, will be addressed in future work.

Previous formulations of coda wave interferometry make it possible to assess the average change of the medium, but they do not allow for the spatial localization of this change (Gret 2002, Snieder 2002). We present an approach for localizing temporal changes in the medium using strongly scattered waves, and test it with numerical models for 2D scalar waves. Using an integral representation for the diffuse wavefield, we derive an expression for the mean traveltime perturbation due to a small perturbation in the slowness. We validate the theory using synthetic seismograms calculated with a finite-difference algortihm. In general, for localized slowness perturbations, the theory predicts the mean traveltime change of the diffuse wavefield in a multiple-scattering medium. The technique presented here can be used in many applications such as medical imaging, non-destructive testing, and reservoir monitoring, to infer temporal changes of the multiple-scattering medium.

Biography
Carlos Pacheco received a BS in geophysical engineering from the Universidad Simon Bolivar. He then worked as an acquisition geophysicist with PDVSA Exploration and Production, working on the planning and design of land and marine 2D and 3D seismic surveys. Currently, he is a master's candidate in geophysics at the Colorado School of Mines.