Joint traveltime inversion of wide-angle seismic data and a deep reflection profile from the central North Sea

Abstract

We report results from the Seismic Wide‐Angle and Broadband Survey carried out over the Mid North Sea High. This paper focuses on integrating the information from a conventional deep multichannel reflection profile and a coincident wide‐angle profile obtained by recording the same shots on a set of ocean bottom hydrophones (OBH). To achieve this integration, a new traveltime inversion scheme was developed (reported elsewhere) that was used to invert traveltime information from both the wide‐angle OBH records and the reflection profile simultaneously. Results from the inversion were evaluated by producing synthetic seismograms from the final inversion model and comparing them with the observed wide‐angle data, and an excellent match was obtained. It was possible to fine‐tune velocities in less well‐resolved parts of the model by considering the critical distance for the Moho reflection. The seismic velocity model was checked for compatibility with the gravity field, and used to migrate and depth‐convert the reflection profile. The unreflective upper crust is characterized by a high velocity gradient, whilst the highly reflective lower crust is associated with a low velocity gradient. At the base of the crust there are several subhorizontal reflectors, a few kilometres apart in depth, and correlatable laterally for several tens of kilometres. These reflectors are interpreted as representing a strike section through northward‐dipping reflectors at the base of the crust, identified on orthogonal profiles by Freeman et al. (1988) as being slivers of subducted and imbricated oceanic crust, relics of the mid‐Palaeozoic Iapetus Ocean.

Seismic imaging of forearc backthrusts at northern Sumatra subduction zone

“…The velocity just below these reflections is slightly lower (4 km s −1 ) than expected for continental crust, however this could be due to the vertical smoothing. The continental crust underneath the Aceh basin is marked by a high vertical velocity gradient within the first 10 km, similar to high‐velocity gradient observed in upper crystalline crust in other instances (McCaughey et al 2000). Beneath the Aceh basin and forearc ridge, there is a band of reflectivity at ∼25 km depth (11 s), which we interpret as the continental Moho.…”

A crustal seismic velocity model for the UK, Ireland and surrounding seas

“…Although the Moho is generally a continuous surface in crustal models, several refraction profiles show changes in Moho depth over a distance of less than 50 km (the smallest separation in the experimental variograms) (e.g. Aichroth et al 1992; O'Reilly et al 1995; Mjelde et al 1997; McCaughey et al 2000; Raum et al 2002). Such high frequency depth variation is also seen in deep, normal‐incidence reflection profiling (e.g.…”