Geophone orientation and coupling in three‐component sea‐floor data: a case study

Abstract

We analyse the geophone orientation and coupling in a data set from the North Sea. Based on the polarization of the water‐break on the sea‐floor, we have derived processing algorithms for determining the receiver orientation for gimballed and non‐gimballed geophone systems. For a gimballed system, the problem reduces to a simple horizontal rotation. However, for a non‐gimballed system, where all three geophone axes may vary due to varying acquisition conditions such as dipping sea‐floor, twisting of recording cable, etc., the three orientation angles cannot be found directly from the recorded displacement vectors. Using the data redundancy within a common‐receiver gather, a robust two‐stage method is derived for the non‐gimballed system in which all three orientations can initially be unknown. Testing on the North Sea data set acquired with a gimballed system shows that the three‐component geophones in the data set are orientated satisfactorily within an error of 5°. However, there are some undesirable cross‐couplings between the vertical and horizontal geophones, which results in leakage of shear‐wave energy from the horizontal components to the vertical components.

Where does S‐wave energy on OBC recordings come from?

“…Possible mode conversions (both P-to -S and S-to -P) in the up-going seismic energy were also analyzed. This test was to investigate a phenomenon sometimes observed in OBC data processing (Ebrom et al, 1998;Yuan et al, 1998;Li and Yuan, 1999;: the presence of shear-wave energy on the vertical component while the radial component does not present compressional energy. Perhaps S-wave energy present in the vertical component could be due to some compressional energy converted from shear at shallow sediments, or at the sea bottom.…”

Full Waveform Seismological Advances for Microseismic Monitoring

“…Standard methods are generally based on polarization analysis of body waves (Becquey & Dubesset, 1990;Li & Yuan, 1999). These methods allow to directly estimate the absolute orientation of seismic sensors but on the other hand, as only relying on a small portion of the waveform, may lead to unstable results and are strongly dependent on the signal-to-noise ratio.…”

Vector reconstruction of multicomponent seismic data

“…Traditionally, this is done by rotating components to a reference frame in which the components are linearly independent (Li and Yuan, 1999). At this point, each component can be processed separately with no loss of fidelity.…”