References

Comprehensive Subsurface Solution

SeisOpt™ ReMi©

The ReMi method uses refraction microtremor recordings from standard refraction equipment to estimate 30 m (100 ft) average shear wave velocities. Design ready outputs are created for one- and two-dimensional shear wave profiles down to depths of 100 m with 5%-15% accuracy.

Faster, Better: Shear-Wave Velocity to 100 Meters Depth From Refraction Microtremor Arrays

Current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites. They require large sources to be effective in noisy urban settings, or specialized independent recorders laid out in an extensive array. This work shows that microtremor noise recordings made on 200-m-long lines of seismic refraction equipment can estimate shear velocity with 20% accuracy, often to 100 m depths. The combination of commonly available equipment, simple recording with no source, a wavefield transformation data processing technique, and an interactive Rayleigh-wave dispersion modeling tool exploits the most effective aspects of the microtremor, spectral analysis of surface wave (SASW), and multichannel analysis of surface wave (MASW) techniques. The slowness-frequency wavefield transformation is particularly effective in allowing accurate picking of Rayleigh-wave phase-velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities, higher-mode Rayleigh waves, body waves, air waves, and incoherent noise. Read More…

Applying the Refraction Microtremor Shear Wave Technique to Geotechnical Characterization

The refraction microtremor (ReMi) technique provides a simplified characterization of relatively large volumes of the subsurface in 1-dimensional vertical (depth) profiles. Field data can be collected using seismic refraction equipment; ReMi and seismic refraction data can be collected using the same geophone array setups. Surface wave energy sources for ReMi can be ambient noise or range from jogging for short arrays to field vehicle for long arrays. ReMi profiles can be performed effectively in urban areas with considerable activity using ambient noise as the
energy source. Read More…

Blind Shear-Wave Velocity Comparison of ReMi and MASW Results with Boreholes to 200 m in Santa Clara Valley

Multichannel analysis of surface waves (MASW) and refraction microtremor (ReMi) are two of the most recently developed surface acquisition techniques for determining shallow shear-wave velocity. We conducted a blind comparison of MASW and ReMi results with four boreholes logged to at least 260 m for shear velocity in Santa Clara Valley, California, to determine how closely these surface methods match the downhole measurements. Average shear-wave velocity estimates to depths of 30, 50, and 100 m demonstrate that the surface methods as implemented in this study can generally match borehole results to within 15% to these depths. Read More…

Charecterizing Potential "Bridging Ground" Conditions Using the Refraction Microtemor (ReMi) Surface Seismic Technique

The refraction microtremor (ReMi) technique provides a simplified characterization of relatively large volumes of the subsurface in 1-dimensional vertical (depth) profiles. ReMi can characterize a lower velocity horizon underlying a higher velocity horizon (velocity reversal) condition that is missed using standard seismic refraction. In a situation where more competent ground is bridging over a weaker zone due to subsidence or collapse of underlying geologic materials or abandoned spaces, ReMi has the capability to detect the weaker underlying material s-wave velocity. Read More…

Determination of 1-D Shear Wave Velocities Using the Refraction Microtremor Method

Current commonly used techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use in most urban areas. They require large sources to be effective in noisy urban settings, or specialized independent recorders laid out in an extensive array. The refraction microtremor (ReMi) method (Louie, 2001) overcomes these problems by using standard P-wave recording equipment and ambient noise to produce average one-dimensional shear-wave profiles down to 100m depths. Read More…

SeisOpt™ ReMi© and SeisOpt™ @2D Combined Research

These papers include a combination of SeisOpt™ ReMi© and SeisOpt™ @2D to analyze both S- and P- Wave velocities. The combination of these two methods allow for additional information on the geologic layers, liquefaction analysis, and many more applications.

Surface Geophysics as Tools for Characterizing Existing Bridge Foundation and Scour Conditions

Assessing foundation and scour conditions at existing bridges frequently requires geotechnical characterization of the subsurface. Characterization may be needed either to verify subsurface conditions as reported in the original bridge design investigations or to identify and characterize changes in subsurface conditions due to scour events. Sometimes, previous subsurface characterization for scour at older bridges has not been performed, cannot be located or was incomplete or inadequate for current design criteria. Surface geophysical methods provide economical means to profile relevant subsurface information, including depth to and competency of more dense or cohesive alluvial horizons and bedrock. Read More…

Integrating Seismic Refraction and Surface Wave Data Collection and Interpretation for Geotechnical Site Characterization

Recent advances in surface wave measurement capabilities now permit collection of both seismic refraction compressional wave (p-wave) and Rayleigh surface wave (for s-wave) data using the same physical field equipment and geophone arrays. Typical energy sources include sledge hammer for pwave data and field vehicle, jogging or background ambient noise for refraction microtremor (ReMi) data. Read More…

SeisOpt™ @2D: Seismic Refraction

Seismic refraction is a method used to identify rock properties, geological structures, and much more. Once the data is collected and analyzed, it produces a 2D tomographic image displaying velocity contrast, i.e. geological boundaries.

A Generalized Simulated-Annealing Optimization for Inversion of First-Arrival Times

We employ a Monte Carlo-based optimization scheme called generalized simulated annealing to invert first-arrival times for velocities. We use “dense” common depth point (CDP) data having high multiplicity, as opposed to traditional refraction surveys with few shots. A fast finite-difference solution of the eikonal equation computes first arrival travel times through the velocity models. We test the performance of this optimization scheme on synthetic models and compare it with a linearized inversion. Our tests indicate that unlike the linear methods, the convergence of the simulated-annealing algorithm is independent of the initial model. In addition, this scheme produces a suite of  “final” models having comparable least-square error. These allow us to choose a velocity model most in agreement with geological or other data. Exploiting this method’s extensive sampling of the model space, we can determine the uncertainties associated with the velocities we obtain. Read More…

Seismic Refraction Analysis of Landslides

Seismic refraction has proven a useful geophysical tool for investigating landslides. The velocity structure of a landslide mass, the depth to the failure surface, and the lateral extent of a landslide are variables that may be estimated using seismic refraction. Data obtained using refraction can aid in determining appropriate mitigation and maintenance practices involving landslides. One method used to interpret seismic refraction data, the General Reciprocal Method (GRM), calculates refractor depths using overlapping refraction arrival times from both forward and reverse shots. Read More…

Seismic Refraction Interpretation with Velocity Gradient and Depth of Investigation

Traditional interpretation of seismic refraction data has used a concept of layered horizons or zones where each horizon has a discrete a seismic velocity. Software packages are now available that analyze and present seismic velocity as a continuously varying gradient across a grid or mesh. Such packages may utilize optimizing methods coupled with finite element or finite difference concepts to achieve interpretations. The resulting velocity gradient style of interpretation presents very different representations of the subsurface compared to traditional interpretations. These differences include advantages, disadvantages and conceptual challenges in utilizing the results. Read More…

The Northern Walker Lane Refraction Experiment: P Arrivals and the Northern Sierra Nevada Root

In May 2002, we collected a new crustal refraction profile from Battle Mountain, Nevada across western Nevada, the Reno area, Lake Tahoe, and the northern Sierra Nevada Mountains to Auburn, CA. Mine blasts and earthquakes were recorded by 199 Texan instruments extending across this more than 450-km-long transect. The use of large mine blasts and the ultra-portable Texan recorders kept the field costs of this profile to less than US$10,000. Read More…

Ground Penetrating Radar (GPR)

GPR is a non-invasive method that uses electromagnetic waves in the microwave band (UHF/VHF frequencies) of the radio spectrum to detect subsurface materials. GPR is applicable in a variety of environments including rock, soil, water, pavement, and ice.

Utility of Ground-penetrating Radar in Near-surface, High-resolution Imaging of Lansing-Kansas City (Pennsylvanian) Limestone Reservoir Analogs

High-resolution ground-penetrating radar (GPR) is a subsurface imaging tool that can extend results gained from studies of reservoir-analog outcrops and add detailed information about reservoir analogs that is unavailable from either seismic data or well control alone. Read More…

Mapping of Sewer Lines Using GPR: A Case Study in Tunisia

Many infrastructure enhancement projects require underground utility mapping before starting any excavation processes, especially in urban areas. In fact, mapping of an area provides a general overview of the infrastructure above and underground. This mapping can be done by Ground Penetrating Radar (GPR), which is commonly used as a Non-Destructive Testing (NDT) technique that allows, among others, the detection and localization of buried utilities without any damage to the surface. Read More…

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