Travel-times and attenuation relations for regional phases in the
Barents Sea region
Pure and Applied Geophysics, 161 (1):
1--19 (Jan 1, 2004)DOI: 10.1007/s00024-003-2437-6
Abstract
A database containing 45 events in the Barents Sea region has been
compiled and analyzed with the aim of evaluating crustal models,
travel-times and attenuation relations in the context of performing
regional detection threshold monitoring of this region. The 45 events
are mostly located around the circumference of the study area due
to the virtually aseismic nature of the Barents Sea itself. Regional
P n and S n phases were observable for most events in the database,
while P g and L g phases were only observable for events with raypaths
that do not cross the tectonic structures in the Barents Sea. This
corroborates a number of previous observations of L g-wave blockage
within the Barents Sea. Three existing velocity models were evaluated,
with a model having slightly lower S velocities than earlier assumed
in the upper mantle giving the overall best fit to the observed arrivals.
In order to estimate magnitudes, short-term average (STA) and spectral
amplitude values were calculated in several frequency bands for all
phase arrivals in the database. There were no significant differences
between spectral and STA amplitudes, so the latter were used as this
parameter is more efficient to calculate in real-time processing.
An inversion was performed in order to determine an attenuation relation
specific for this region. The resulting magnitudes based on P n,
P g, S n and L g phases gave an internally consistent, reasonably
stable set of values, which can be calibrated towards any existing
global or regional scale.