11/7/2023 0 Comments Moment magnitude scale chart![]() Both the Arabia–Eurasia continentalĬollision and the subduction of the African Plate beneath Eurasia started in Geodynamically active areas because of the deformation among the Eurasian,Īfrican, and Arabian plates (Fig. 1). This study focuses on earthquakes in Turkey. In the last two decades, the studies on unifying earthquake magnitudes and generating improved catalogues have been carried out for different regions on the Earth (i.e. Grünthal et al., 2009 Chang et al., 2016 Manchuel et al., 2018 Rovida et al., 2020). Therefore, a homogenized catalogue with a unified magnitude scale becomes essential. One common magnitude scale should be used to standardize analyses in the studies based on the parametric data such as hazard mitigation. As a result, there is more than one reported magnitude value for an event with known and unknown calculation errors. These small moment magnitudes are obviously determined by using an empirical relationship without using waveform data. However, a few institutes report M w for small events to the international catalogues ( M w<3.0, i.e. 25 January 1999 at 13:06 UTC M w=1.8 by Cyprus Geological Survey Department 29 May 2014 at 01:14 UTC M w=1.8 by the Earthquake Research Center, Ataturk University, Turkey). M w is determined using waveform modelling for events ( M w≥3.5–4.0) with a high signal-to-noise ratio. Table 1Symbols for different magnitude scales in the priority order ofĪnother issue picked out in this study is the reported moment magnitudes ( M w) in the catalogues. Therefore, institutions may report different magnitudes for an event. Consequently, the average magnitude is closely related to several factors such as the number of stations, the standard deviation of the average, amplification or attenuation due to the geological structure beneath the station, and the radiation pattern that depends on the azimuthal distribution of stations. The median is also preferred to exclude the magnitude outliers (Havskov and Ottemöller, 2010). ![]() Generally, the average magnitude for all stations is calculated to minimize the effect of the radiation pattern. Different amplitudes are observed for an event because of the source radiation pattern. Magnitudes, except m d, are calculated using the waveform amplitudes at each station for an event. ![]() Values for the Californian earthquakes (i.e. for local magnitude by Richter,ġ935 Hutton and Boore, 1987) are widely used. Although the coefficients must be specific for a regionīecause of seismic wave attenuation in the crust and mantle, the calculated Both amplitude and distance coefficients in the magnitude equations are The equations coefficients, seismic network structures, human-made mistakes,Įtc. ![]() There are several unknowns in magnitude calculations by institutions due to The relief model is generated with the ETOPO1 model (Amante and Triangles indicate the direction of vergence or subduction. Sea Fault Zone EAFZ: East Anatolian Fault Zone and NAFZ: North Anatolian Fault Contrary to the limitedĮarthquake parameters in the previous catalogues for Turkey, the 45 parameters of ∼378 000 events are presented in this study.įigure 1Simplified tectonic map of the eastern Mediterranean. Median of the observed magnitudes for each event. It contains not only M w * but also the average and The final catalogue is not declustered or truncated using a threshold magnitude in order to be a widely usable catalogue. The magnitude of completeness is 2.7 M w *. The equivalent moment magnitudes ( M w * ) for the entire catalogue are calculated using the magnitude relations to homogenize the catalogue. The 95 % confidence intervals are estimated using the bootstrap method with 1000 samples. New conversion equations between moment magnitude and the other scales ( m d, M L, m b, M s, and M) are determined using the general orthogonal regression method to build up a homogeneous catalogue, which is the essential database for seismic hazard studies. The earthquake parameters are obtained from the Bulletin of International Seismological Centre that was fully updated in 2020. A new homogenized earthquake catalogue for Turkey is compiled for the period 1900–2018.
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