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Full-Text Articles in Physical Sciences and Mathematics
A Modified Delay-Time Method For Statics Estimation With The Virtual Refraction, T. Dylan Mikesell, Kasper Van Wijk, Elmer Ruigrok, Andrew Lamb, Thomas E. Blum
A Modified Delay-Time Method For Statics Estimation With The Virtual Refraction, T. Dylan Mikesell, Kasper Van Wijk, Elmer Ruigrok, Andrew Lamb, Thomas E. Blum
CGISS Publications and Presentations
Topography and near-surface heterogeneities lead to traveltime perturbations in surface land-seismic experiments. Usually, these perturbations are estimated and removed prior to further processing of the data. A common technique to estimate these perturbations is the delay-time method. We have developed the “modified delay-time method,” wherein we isolate the arrival times of the virtual refraction and estimate receiver-side delay times. The virtual refraction is a spurious arrival found in wavefields estimated by seismic interferometry. The new method removes the source term from the delay-time equation, is more robust in the presence of noise, and extends the lateral aperture compared to the …
Extension Of The Spatial Autocorrelation (Spac) Method To Mixed-Component Correlations Of Surface Waves, Matthew M. Haney, T. Dylan Mikesell, Kasper Van Wijk, Hisashi Nakahara
Extension Of The Spatial Autocorrelation (Spac) Method To Mixed-Component Correlations Of Surface Waves, Matthew M. Haney, T. Dylan Mikesell, Kasper Van Wijk, Hisashi Nakahara
CGISS Publications and Presentations
Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations …
A Feasibility Study Of Time-Lapse Seismic Monitoring Of Co2 Sequestration In A Layered Basalt Reservoir, Murari Khatiwada, Ludmila Adam, Michael Morrison, Kasper Van Wijk
A Feasibility Study Of Time-Lapse Seismic Monitoring Of Co2 Sequestration In A Layered Basalt Reservoir, Murari Khatiwada, Ludmila Adam, Michael Morrison, Kasper Van Wijk
CGISS Publications and Presentations
We investigate the potential of scattered seismic waves to remotely sense geological sequestration of CO2 in basalt. Numerical studies in horizontally layered models suggest that strong scattering quickly complicates the wave fields, but also provides a sensitive tool to monitor physical changes in and around the reservoir. These results go hand-in-hand with recent laboratory work and rock-physics modeling that has shown significant changes in the seismic properties of a reservoir undergoing CO2 sequestration, due to fluid substitution and mineral precipitation.
Scanning For Velocity Anomalies In The Crust And Mantle With Diffractions From The Core-Mantle Boundary, Elmer Ruigrok, T. Dylan Mikesell, Kasper Van Wijk
Scanning For Velocity Anomalies In The Crust And Mantle With Diffractions From The Core-Mantle Boundary, Elmer Ruigrok, T. Dylan Mikesell, Kasper Van Wijk
CGISS Publications and Presentations
A novel method, based on differential arrival times of diffractions from the core-mantle boundary, swiftly scans for seismic velocity anomalies in the crust and mantle below an array of seismometers. The method is applied to data from the USArray and the large-scale structural features in the western United States are resolved. High lateral resolution is achieved, but structure is averaged over depth. As such, this method is complementary to surface-wave and tomographic body-wave methods, where averaging takes place in the lateral sense. Processing and data-volume requirements involved are minimal. Therefore, this method can be applied during the early stages of …
The Emergence And Future Of Near-Surface Geophysics, William E. Doll, Richard D. Miller, John Bradford
The Emergence And Future Of Near-Surface Geophysics, William E. Doll, Richard D. Miller, John Bradford
CGISS Publications and Presentations
Over the past 30 years, geophysical methods have assumed a much more prominent and integral role in many investigations where subsurface features have environmental and engineering importance. In fact, the field once referred to as "environmental and engineering geophysics" has broadened to include other applications (e.g., archeology, forensics), and is now commonly referred to more generally as "near-surface geophysics." It is difficult to precisely define near-surface geophysics, and the definition will likely depend on whom you ask. However, we define it as the use of geophysical methods to investigate the zone between the surface and hundreds of meters into the …
Three-Dimensional Stochastic Estimation Of Porosity Distribution: Benefits Of Using Ground-Penetrating Radar Velocity Tomograms In Simulated-Annealing-Based Or Bayesian Sequential Simulation Approaches, Baptiste Dafflon, Warren Barrash
Three-Dimensional Stochastic Estimation Of Porosity Distribution: Benefits Of Using Ground-Penetrating Radar Velocity Tomograms In Simulated-Annealing-Based Or Bayesian Sequential Simulation Approaches, Baptiste Dafflon, Warren Barrash
CGISS Publications and Presentations
Estimation of the three-dimensional (3-D) distribution of hydrologic properties and related uncertainty is a key for improved predictions of hydrologic processes in the subsurface. However it is difficult to gain high-quality and high-density hydrologic information from the subsurface. In this regard a promising strategy is to use high-resolution geophysical data (that are relatively sensitive to variations of a hydrologic parameter of interest) to supplement direct hydrologic information from measurements in wells (e.g., logs, vertical profiles) and then generate stochastic simulations of the distribution of the hydrologic property conditioned on the hydrologic and geophysical data. In this study we develop and …
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, Kasper Van Wijk, Matthew M. Haney, John H. Bradford, Hans-Peter Marshall, Joel T. Harper
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, Kasper Van Wijk, Matthew M. Haney, John H. Bradford, Hans-Peter Marshall, Joel T. Harper
CGISS Publications and Presentations
Sliding glaciers and brittle ice failure generate seismic body and surface wave energy characteristic to the source mechanism. Here we analyze continuous seismic recordings from an array of nine short-period passive seismometers located on Bench Glacier, Alaska (USA) (61.033°N, 145.687°W). We focus on the arrival-time and amplitude information of the dominant Rayleigh wave phase. Over a 46-hour period we detect thousands of events using a cross-correlation based event identification method. Travel-time inversion of a subset of events (7% of the total) defines an active crevasse, propagating more than 200 meters in three hours. From the Rayleigh wave amplitudes, we estimate …
A Field Proof-Of-Concept Of Aquifer Imaging Using 3-D Transient Hydraulic Tomography With Modular, Temporarily-Emplaced Equipment, Michael Cardiff, Warren Barrash, Peter K. Kitanidis
A Field Proof-Of-Concept Of Aquifer Imaging Using 3-D Transient Hydraulic Tomography With Modular, Temporarily-Emplaced Equipment, Michael Cardiff, Warren Barrash, Peter K. Kitanidis
CGISS Publications and Presentations
Hydraulic tomography is a field scale aquifer characterization method capable of estimating 3-D heterogeneous parameter distributions, and is directly sensitive to hydraulic conductivity (K), thus providing a useful data source for improving flow and transport models. We present results from a proof-of-concept field and modeling study in which we apply 3-D transient hydraulic tomography (3DTHT) to the relatively high-K and moderately heterogeneous unconfined aquifer at the Boise Hydrogeophysical Research Site. Short-duration (20 min) partially penetrating pumping tests, for which observed responses do not reach steady state, are used as the aquifer stimulation. To collect field data, we utilize a system …
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
CGISS Publications and Presentations
Greater understanding of variations in firn densification is needed to distinguish between dynamic and melt-driven elevation changes on the Greenland ice sheet. This is especially true in Greenland’s percolation zone, where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt. We used georadar to investigate firn density variations with depth along a ~70 km transect through a portion of the accumulation area in western Greenland that partially melts. We estimated electromagnetic wave velocity by inverting reflection traveltimes picked from common midpoint gathers. We followed a procedure designed to find the simplest velocity …
Near-Surface Imaging Of A Hydrogeothermal System At Mount Princeton, Colorado Using 3d Seismic, Self-Potential, And Dc Resistivity Data, Andrew P. Lamb, Lee M. Liberty, Kasper Van Wijk, André Revil, Chuck Diggins
Near-Surface Imaging Of A Hydrogeothermal System At Mount Princeton, Colorado Using 3d Seismic, Self-Potential, And Dc Resistivity Data, Andrew P. Lamb, Lee M. Liberty, Kasper Van Wijk, André Revil, Chuck Diggins
CGISS Publications and Presentations
The Upper Arkansas Valley in the Rocky Mountains of central Colorado is the northernmost extensional basin of the Rio Grande Rift(Figure 1). The valley is a half graben bordered to the east and west by the Mosquito and Sawatch ranges,respectively. The Sawatch Range is home to the Collegiate Peaks,which include some of the highest summits in the Rocky Mountains. Some Collegiate Peaks over 4250 m (14,000 ft) from north to south include Mount Harvard, Mount Yale, Mount Princeton,and Mount Antero. The Sawatch range-front normal fault strikes north-northwest along the eastern margin of the Collegiate Peaks and is characterized by a …