Depth corrections to surface-wave magnitudes for intermediate and deep earthquakes in the regions of North Eurasia

摘要

This paper reports a study of surface wave M_(S,MOS) magnitudes from the seismological catalog derived from teleseismic stations of the Geophysical Survey of the Russian Academy of Sciences (GS RAS) with aim of determination of depth corrections to M_S and subsequent standardization of the catalogs with regard to M_S. Unlike the M_S reported by major international centers, such as National Earthquake Information Center of United States Geological Survey (NEIC USGS) and the International Seismological Centre (ISC), for earthquakes occurring at shallow and crustal depths up to 50–60 km, M_(S,MOS) is also determined for intermediate-depth and deep earthquakes. The analysis of depth corrections to M_S was based on M_(S,MOS) from the GS RAS Seismological Catalog and M_W from the ISC-GEM (Global Earthquake Model) Catalogue for 736 earthquakes of North Eurasia with M_W ≥ 5.5 for the period 1988 through 2014. It was found that the decrease in M_(S,MOS) with increasing depth becomes noticeable for h > 40 km. For the earthquakes of h > 40km, we found two increasing log linear relations for the correction of M_(S,MOS) as function of depth: ΔM_(S,MOS)(h) = 1.71·log(h) ? 2.726 for h = 40–90 km and ΔM_(S,MOS)(h) = 0.556·lg(h)? 0.508 for h > 90 km. We applied these corrections to M_(S,MOS) and found a substantially better correlation and lower standard errors in the M_(S,MOS) vs M_W relation. Applying the corrections to M_(S,MOS) of the Okhotsk Sea earthquake on May 24, 2013, h = 617 km showed a good agreement between the corrected M_(S,MOS) = 8.4 and M_W = 8.3.