Precursors to P'P' and upper mantle discontinuities

In this paper the origin of precursors to P' P' with lead times greater than 50 s is investigated. Good NORSAR records of P'650P' and P'400P' for these arrivals as well as corresponding slowness estimates are presented. These phases are interpreted as done by others in terms of underside reflections from discontinuities or sharp transition zones in the upper mantle. An extensive search of 5 years of NORSAR records did not produce any significant evidence on P' P' precursor arrivals with lead times greater than 50 s other than those mentioned above.           ARK: https://n2t.net/ark:/88439/y030873 Permalink: https://geophysicsjournal.com/article/255 &nbsp

Criteria for Selecting and Adjusting Ground-Motion Models for Specific Target Regions: Application to Central Europe and Rock Sites

International audienceA vital component of any seismic hazard analysis is a model for predicting the expected distribution of ground motions at a site due to possible earthquake scenarios. The limited nature of the datasets from which such models are derived gives rise to epistemic uncertainty in both the median estimates and the associated aleatory variability of these predictive equations. In order to capture this epistemic uncertainty in a seismic hazard analysis, more than one ground-motion prediction equation must be used, and the tool that is currently employed to combine multiple models is the logic tree. Candidate ground-motion models for a logic tree should be selected in order to obtain the smallest possible suite of equations that can capture the expected range of possible ground motions in the target region. This is achieved by starting from a comprehensive list of available equations and then applying criteria for rejecting those considered inappropriate in terms of quality, derivation or applicability. Once the final list of candidate models is established, adjustments must be applied to achieve parameter compatibility. Additional adjustments can also be applied to remove the effect of systematic differences between host and target regions. These procedures are applied to select and adjust ground-motion models for the analysis of seismic hazard at rock sites in West Central Europe. This region is chosen for illustrative purposes particularly because it highlights the issue of using ground-motion models derived from small magnitude earthquakes in the analysis of hazard due to much larger events. Some of the pitfalls of extrapolating ground-motion models from small to large magnitude earthquakes in low seismicity regions are discussed for the selected target region