Observed characteristics of regional seismic phases and implications
for P/S discrimination in the European Arctic
Pure and Applied Geophysics, 159 (4):
701--719 (Feb 1, 2002)DOI: 10.1007/s00024-002-8655-5
Abstract
- In this paper, we use data from seismic stations operated by NORSAR,
the Kola Regional Seismological Centre (KRSC) and IRIS to study the
characteristics of regional phases in the European Arctic, with emphasis
on the P/S ratio discriminant. While the detection and location capability
of the regional station network is outstanding, source classification
of small seismic events has proved very difficult. For example, the
m<SUB>b</SUB>=3.5 seismic event near Novaya Zemlya on 16 August,
1997 has been the subject of extensive analysis in order to locate
it reliably and to classify the source type. We consider the application
of the P/S discriminant in the context of this event and other events
observed at regional distances in the European Arctic. We show that
the P/S ratios of Novaya Zemlya nuclear explosions measured in the
1-3Hz filter band scale with magnitude, indicating a need for caution
and further research when applying P/S discriminants. Using mainly
data from the large NORSAR array, we note that observed P/S amplitude
ratios in the European Arctic show large variability for the same
source type and similar propagation paths, even when considering
closely spaced observation points. This effect is most pronounced
at far regional distances and relatively low frequencies (typically
1-3Hz), but it is also significant on closer recordings (around 10
degrees) and at higher frequencies (up to about 8Hz). Our conclusion
from this study is that the P/S ratio at high frequencies (e.g.,
6-8Hz) shows promise as a discriminant between low-magnitude earthquakes
and explosions in the European Arctic, but its application will require
further research, including extensive regional calibration and detailed
station-source corrections. Such research should also focus on combining
the P/S ratio with other short-period discriminants, such as complexity
and spectral ratios.