Shelton, CT, United States
Shelton, CT, United States

Time filter

Source Type

Obando E.A.,Lund University | Park C.B.,Park Seismic LLC | Ryden N.,Lund University | Ulriksen P.,Lund University
Soil Dynamics and Earthquake Engineering | Year: 2010

In order to maintain lateral resolution while maximizing investigation depth in a multichannel surface wave method, it is beneficial to implement the walk-away approach by using a relatively short receiver spread. Combined walk-away records, however, normally suffer from time-shift inaccuracies that adversely influence the subsequent dispersion imaging process. Time-shift inaccuracies produce phase discontinuities which can generate false apparent higher modes in the dispersion images misleading the correct interpretation of the dispersion curve. To minimize these adverse effects, we present a phase-scanning approach that searches for an optimum phase shift to correct the phase shift generated by the walk-away method. Results obtained from synthetic and real-world field data show that for the specific case of a single dominating mode the proposed approach reduces the distortions in the dispersion image caused by the walk-away approach. The proposed method is especially efficient in the presence of ambient random noise. © 2010 Elsevier Ltd.


Nasseri-Moghaddam A.,Inspec Sol Inc. | Park C.B.,Park Seismic LLC.
Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP | Year: 2010

The effect of source offset distance and the geophone array length on the dispersion curves are discussed in this paper. The source offset distance was changed systematically at sites with various subsurface conditions to investigate its effect on quality of data and the corresponding dispersion curves. Further, tests were carried out at same locations with various geophone intervals to evaluate the effect of the array length on the quality of the data and dispersion curves. Active and passive data were collected and the dispersion images were combined for possible improvement in dispersion image with enhanced multimodal delineation over a broadened bandwidth. It is observed that source offsets in the range of 25% to 45% of the array length provide dispersion curves with reasonable quality. Further, collecting data with different geophone intervals (same array mid station) improves the resolution of the obtained dispersion image. Multi geometry technique is suggested to obtain better quality field data. In this approach two (or more) different geophone intervals are used with same mid station. Passive and active data at two or more offset distances are collected for each of the array geometries. Stacking the obtained dispersion images can also result in a better quality dispersion curve.


Carnevale M.,Hager GeoScience Inc. | Park C.B.,Park Seismic LLC
Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP | Year: 2010

Since its inception as a subsurface imaging technique, the multichannel analysis of surface waves (MASW) seismic method has been used in a variety of environmental and geotechnical applications. One of the more interesting applications is performing subsurface imaging in a beach environment. Although the loose and dry ground surface appears to present a formidable obstruction to the application of MASW for deep imaging, there could be an anonymous unexploited source of energy to make it happen. We look at the possibility that low frequency energy from ocean wave fronts can be introduced into seismic recordings made during MASW surveys along a beach or shoreline. Seismic data from MASW beach and shoreline surveys in Massachusetts will be examined for possible evidence of constructive or destructive interference from energy produced by ocean waves. The possible relationships of MASW survey geometry and the geography of the project settings are also examined. This study aims at evaluating the possible exploitation of ocean energy for deep MASW surveys in beach and shoreline environments.


Park C.B.,Park Seismic LLC | Taylor C.,GeoView Inc.
Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP | Year: 2010

By running three parallel and one crossing lines of conventional 2D MASW surveys followed by normal 1-D MASW inversions, a 3D characterization was attempted as a pilot study over an area of a known sinkhole 10-40 ft deep with lateral dimension smaller than 50 ft. Shear-velocity (Vs) data sets from each line were then used as constraints to calculate a cubic grid data in x (east-west), y (southnorth), and z (depth) directions by using a 3D inverse-distance-weighted (IDW) interpolation scheme. When displayed in depth-stripping mode at 5-ft depth intervals, velocity anomalies of substantially lower values than those in the ambient are recognized in the surface and depth locations that correlate fairly well with those identified in a geologic cross section previously compiled from other methods of well drilling, CPT, and GPR surveys. Properly selecting offset range during data acquisition and subsequent dispersion analysis seems critically important for the successful detection of a sinkhole.


Park C.B.,Park Seismic LLC
Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP | Year: 2010

In a roadside passive surface-wave survey under a typical urban setting with relatively heavy traffic and a complicated network of roads, a field record usually contains surface wave events generated from multiple source points scattered around the survey location. It is, however, those dominating energy events coming from one common surface point on the road that are used as signal in most advanced dispersion analysis methods based on the 2-D wavefield transformation. Events from other locations interfere adversely with signal events during the analysis if they take comparable energy or are largely ignored in the case of insignificant energy. A long record (e.g., 120 sec) is divided into many subsets of much shorter time of a proper length (e.g., 1 sec) and are treated as independent records of only one (or none) of a dominating event. By utilizing an advanced technique to detect fairly accurately the source location of the event, subsets are processed for their own dispersion images by using the scheme commonly used in the active MASW survey. Multiple data sets of the dispersion image are then stacked to result in an image of the highest signal-to-noise ratio (S/N) ever possible. This is demonstrated by using a field record acquired with a linear receiver array deployed along a busy street that contains events from complex source points and therefore could not be processed for any interpretable dispersion image using other methods currently available.


Yaede J.R.,Brigham Young University | McBride J.H.,Brigham Young University | Nelson S.T.,Brigham Young University | Park C.B.,Park Seismic LLC | And 6 more authors.
Geosphere | Year: 2015

Estimates of the thickness variation in lateritic weathering profiles (LWPs) are important in tropical areas underlain by young basalt lavas like those found in Hawaii. Seismic shear-wave velocity data were obtained by a new application of multichannel analysis of surface waves (MASW) to map variations in the LWP and to derive the downward rate of advance of the weathering front in basaltic lavas. The MASW technique proved highly capable of imaging the internal structure and base of the critical zone, as confirmed by borehole data and direct field measurements. Profile thickness thus obtained, rapidly and without drilling, has applications to engineering and geochemical studies. The rate of advance of the weathering front derived from MASW in Oahu ranged from 0.010 m/ka to 0.026 m/ka in mesic zones (~1500 mm/a rainfall), whereas an area with ~800 mm/a revealed rates from 0.005 m/ka to 0.011 m/ka. These rates are comparable to those derived from recent solute-based mass balance studies of ground and surface water. Conventional P-wave seismic reflection did not perform as well for detecting boundaries due to a gradational seismic velocity structure within the weathering profile. Shear-wave velocity models showed internal variations that may be caused by textural differences in parental lava flows. Limitations in imaging depth were overcome by innovative experiment designs. Increasing source-receiver offsets and merging surface-wave dispersion curves allowed for a more objective derivation of velocity-frequency relations. Further improvements were made from a recently developed form of the combined active and passive source technique. These advances allowed for more detailed and deeper imaging of the subsurface with greater confidence. Velocity models derived from MASW can thus describe the LWP in terms of depth and variability in stiffness. © 2015 Geological Society of America.


Park C.,Park Seismic LLC
Leading Edge | Year: 2013

Multichannel anaylsis of surface waves (MASW) is a seismic surface-wave technique developed specifically for near-surface applications at depths usually shallower than a few tens of meters (Park et al., 1999). Since its introduction in the late 1990s, use of the technique has rapidly increased for two reasons: (1) it provides the shear-wave velocity (VS) of ground materials, which is one of the most important geotechnical parameters in civil engineering, and (2) it is easier to use than other common seismic approaches (e.g., refraction, reflection, and surface-wave surveys). © 2013 © 2013 by The Society of Exploration Geophysicists.


Park C.B.,Park Seismic LLC
Journal of Environmental and Engineering Geophysics | Year: 2011

The dispersion imaging scheme for multichannel surface waves involves summation of a given frequency component over all traces in one record, always including wavefields in the fulloffset range in the calculation. The scheme, therefore, does not have any way to take into account near- and far-field effects of surface waves, especially far-field effects, which can result in degraded imaging performance because of low amplitudes in the image space. Far-field effects are caused by noise wavefields dominating at far offsets where source-generated surface waves become relatively weak because of attenuation and geometrical spreading. The adverse influence of far-field effects can be minimized by considering an optimum far offset, which may not be the same as the farthest offset surveyed, but shorter depending on the wavelength being considered. Because the surface wave attenuation is proportional to distance in wavelength, the optimum far offset can be set to a specific number of wavelengths. On the other hand, the geometrical spreading affects all wavelengths equally and this alleviates the need for any other elaborate scheme. In this study, a selective-offset scheme is presented that limits the minimum and maximum offsets used for the imaging to 0.1-1.0 and 3-7 times, respectively, the wavelengths considered. It is shown that a selective-offset scheme can result in dispersion images with improved details, especially at those points dealing with relatively short wavelengths that are vulnerable to attenuation. The common full-offset scheme is explained in more intuitive ways than previously presented and, by extending it, the selective-offset scheme is explained.


Shawver J.B.,Zonge Geosciences Inc. | Fisher A.,FMG Engineering | Park C.,Park Seismic LLC
Geotechnical Special Publication | Year: 2010

The concrete spillway associated with a small dam in Rapid City, South Dakota has evidenced persistent seepage since its construction in the 1970's. Visual inspection appears to indicate signs of worsening seepage. Geotechnical borings from dam pre-construction as well as modern boring logs taken on either side of the spillway have been consulted; however, budgetary, access, and logistical constraints restricted a more in-depth geotechnical boring program. A geophysical investigation was ordered to better define the subsurface stratigraphy. This data would be used to perform seepage/flow net analysis and determine some remedial solutions to mitigate seepage and extend the life of the structure. Seismic surface wave techniques were employed in a shallow marine environment to map depth to bedrock between available boreholes. Hydrophone streamers with 1m and 3m receiver spacing were used as receiver arrays. MASW and microtremor data were collected using various sources located on both the marine (within the river) and land (adjacent the spillway) sides of the rolling receiver arrays. CMP gathers were constructed using data from four different source-receiver array configurations. Geotechnical borings were used to constrain the inverse model and verify interpretation of the geophysical data. A traditional means of collecting 2D MASW data utilizes a "walkaway" test to determine a single optimal source-receiver offset per survey profile. We show that multiple source-receiver offsets, and receiver-receiver spacings, were necessary to generate complete surface wave dispersion curves suitable for modeling total depth of investigation. We present challenges observed during the data collection, modeling of the data, and interpretation caused by using this traditionally land-based method in a marine environment. © 2010 ASCE.


Park C.B.,ParkSeismic LLC | Carnevale M.,Hager GeoScience Inc.
Geotechnical Special Publication | Year: 2010

As an attempt to study systematically on the optimum source offset - the distance between source and the closest receiver - and total receiver spread length with the MASW method, we present our observations with modeling and field data sets indicating that the most accurate analysis of phase velocities can be accomplished only for wavelengths up to one spread length, and subsequent analysis for the longer wavelengths inevitably involves a certain degee of fluctuating inaccuracy that seems to originate from the Gibbs - phenomenon of Fourier transformation. The inaccuracy, however, seems to be within five percentfor those wavelengths shorter than twice the spread length. Also, results from the field data study suggest that importance of the source offset has been previously underestimated and the maximum wavelength can be extended simply by extending the source offset. In addition, they showedthat phase velocities tend to be underestimated if the source offset is smaller than one spread length. The degree of underestimation, however, appears highly site dependent and sometimes becomes negligible even if the source offsetis as short as only one receiver spacing. © 2010 ASCE.

Loading Park Seismic LLC collaborators
Loading Park Seismic LLC collaborators