Characterisation of ground motion recording stations in the Groningen gas field

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity (VS). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ VS values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed VS profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent VS information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative VS profiles at the accelerograph station sites. The measured VS profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the VS profile and the observed amplification from vertical array stations is also excellent

Inguinal hernia surgery in the Netherlands: are patients treated according to the guidelines?

Purpose In 2003, a dedicated Dutch committee developed vidence-based guidelines for the treatment of nguinal hernia (IH) in children and adults. The aim of this tudy was to describe trends in hernia care before and after he publication of the guidelines on IH surgery in the etherlands. ethods Originally, a retrospective baseline analysis of H surgery in 90 Dutch hospitals was performed among atients treated for IH in 2001. The results of this baseline nalysis were compared with a recently performed second nalysis of patients treated for IH in 2005. esults In children\\4 years of age, the study showed a ignificant decrease of contralateral explorations. In adults, he study showed that significantly more patients were reated with a mesh-based repair in 2005 (95.9 vs. 78.8%, <0.01eover, there was an increase of patients ith bilateral hernia treated with an endoscopic technique 41.5 vs. 22.3%, P<0.01) and more patients were treated n day surgery (53.5 vs. 38.6%, P<0.01). Lastly, a decline n operations performed for recurrent IH in adults was bserved (10.9 vs. 13.3%, P<0.01). onclusion This study showed that most patients with IH n the Netherlands were treated according to the main ecommendations of the Dutch evidence-based guidelines