Marvin L. Johnson

Characterization of spatially varying surface waves in a land seismic survey

Summary We present several methods for analyzing surface waves in a highly sampled 3-C, 3D survey, and report the most important characteristics derived from those analyses. In particular, we demonstrate the spatial variability of surfacewave velocities and polarization properties. We also show that surface-wave velocities are correlated with other seismic and nonseismic properties of the near surface, such as shear-wave statics and surface texture derived from satellite imagery.

High Fidelity Vibratory Seismic (HFVS) I: Enhanced Data Quality

We present here a novel combination of heritage-Mobil and heritage-Exxon vibrator technologies, which improves on both. The following problems with vibratory data are solved or reduced: • first-arrival times difficult to pick • first-arrival times not accurate • well ties poor • pulses ring from correlation sidelobes • noise from harmonic ghosts • vibrator coupling differences In addition, data from multiple vibrators can be separated by 60 dB or more. The advantages of processing separated vibrator data as unique source points are discussed in a second paper (Krohn and Johnson, 2003).

Constrained Polarization Filtering For Surface-wave Mitigation

We present a new method of surface-wave mitigation using polarization filtering. The method evolves from the polarization-analysis technique developed by Diallo et al., (2006) and introduces new constraints to effectively detect and mitigate surface waves without damaging the signal. Straightforward application of polarization filtering without these constraints results in ineffective filtering or damage to the signal, due to the complexity of surface-wave wavetrains. We illustrate the performance of the method with examples from multicomponent seismic data, and demonstrate the superiority of the filtering compared to the unconstrained approach.

Investigations with a Cylindrical Sensor Housing - Implications for OBC Acquisition

A common observation on multicomponent OBC data is the occurrence of high amplitude, shear-like noise as shown in Figure 1. These waveforms typically occur on the vertical component but show characteristics more often associated with waveforms from the horizontal channels. The source of this noise is often attributed to: • Shear energy leaking onto the vertical component primarily from electrical or mechanical cross-coupling of the vertical and horizontal geophones (Gaiser, 1998) • An effect of the geophone gimbal mechanism • Cable strum when OBC cables are stretched taught • Structural effects and shear-wave splitting (Kragh, 2004) • Rocking, rolling, or torque of a cylindrical sensor housing (Gaiser, 1998) Of these proposed mechanisms, the effect of sensor rocking due to seismic-scale motion is the most amenable to laboratory experimentation.