A Harmonized Instrumental Earthquake Catalog for Iceland and the
Northern Mid-Atlantic Ridge
Abstract
A comprehensive catalog of historical earthquakes, with accurate
epicenters and homogenized magnitudes is a crucial resource for seismic
hazard mapping. Here we update and combine catalogs from several sources
to compile a catalog of earthquakes in and near Iceland, in the years
1900–2019. In particular the epicenters are based on local information,
whereas the magnitudes are based on teleseismic observations, primarily
from international on-line catalogs. The most reliable epicenter
information comes from the catalog of the Icelandic Meteorological
Office, but this is complemented with information from several technical
reports, scientific publications, newspaper articles, and modified by
some expert judgement. The catalog contains 1272 $M_W
\geq 4$ events and the estimated completeness magnitude
is $M_W$ 5.5 in the first years, going down to $M_W$ 4.5 for
recent years. The largest magnitude is $M_W$ 7.01. Such melting of
local and teleseismic data has not been done before for Icelandic
earthquakes, and the result is an earthquake map with no obviously
mislocated events. The catalog also lists additional 5654 earthquakes on
the Mid-Atlantic Ridge, north of 43\degree, with both
epicenters and magnitudes determined teleseismically. When moment
magnitudes are not available, proxy $M_W$ values are computed with
$\chi^2$-regression, normally on $M_S$, but
exceptionally on $m_b$. All the presented magnitudes have associated
uncertainty estimates. The actual combined seismic moment released in
the Icelandic earthquakes is found to be consistent with the moment
estimated using a simple plate motion model. The catalog is named
ICEL-NMAR and it is available online at
http://dx.doi.org/10.17632/tg67sphksh.1.