A unified seismic catalog for the Iranian plateau (1900-2011)

The first seismograph in Iran was installed in 1959, and this marked the beginning of the national seismic catalog. The seismic network grew with years, but its coverage, the instrumental features, and the details of magnitude calculation changed over time, resulting in a highly heterogeneous national seismic catalog. In this work, we present a unified and homogeneous catalog for the Iranian plateau (Mw ≥4), created by merging data from two local catalogs and seven international agencies, each one covering the magnitude scale and period illustrated in Figure 1. This operation requires the conversion of different magnitudes used by the single agencies to a common type. The moment magnitude (Mw) is chosen as reference for its physical meaning (Kanamori, 1977) and because it does not saturate. In this attempt to convert different magnitude scales to Mw, regression relations that take into account errors on both variables are used, and a specific statistical analysis shows that the region under study (24°N–42°N, 43°W–66°E) is better described when subdivided into two tectonic domains, Zagros and Alborz–Central Iran, characterized by different regression relations. A precedence scheme is then established to select the magnitude value to be preferred when the same event is reported by several catalogs with different magnitude scales and/or values. The resulting unified catalog for the Iranian plateau, spanning 1900–2011, is finally presented also in a declustered form for time-independent seismic hazard estimates.