Estimation of τ_c, τ^max_c and P_d, Earthquake Early Warning Parameters, for Northwest of Iran

Abstract

The ability to rapidly estimate earthquake magnitude based on the first few seconds after P-wave’s arrival is essential for establishing an Earthquake Early Warning (EEW) system. In this study, vertical components of velocity records at the first three seconds of the P wave were used to obtain the magnitude scaling relation of EEW parameters (${\tau }_{\mathrm{c}}$, ${\tau }_{\mathrm{p}}^{\mathrm{max}}$ and ${P}_{\mathrm{d}}$) in Tabriz region, located in northwestern Iran. A data set, including 1045 events between 2006 and 2014 with $2.5\le {M}_{\mathrm{w}}\le 6.5$ and epicentral distance less than 200 km was selected to estimate EEW parameters. Magnitude scaling relations were analyzed at three different signal-to-noise ratios (signal-to-noise ratio (SNR) greater than 15, 30, and 50). To obtain a more accurate magnitude scaling relation, the estimated magnitude was compared with the reference magnitude (${M}_{\mathrm{w}}$). The average absolute magnitude errors ($\left|{M}_{\mathrm{est}}-{M}_{\mathrm{obs}}\right|$) based on ${\tau }_{\mathrm{c}}$, ${\tau }_{\mathrm{p}}^{\mathrm{max}}$ and ${P}_{\mathrm{d}}$ Methods were $\pm 0.4$ $\pm 0.3$ and $\pm 0.6$ magnitude units, respectively. Furthermore, an additional test was carried out to check the validity of the obtained results using acceleration data from the November 12, 2017, M7.3 Sarpol-E Zahab, June 22, 2002, M6.5 Changureh-Avaj, and December 26, 2003, M6.6 Bam earthquakes. It was suggested that the magnitudes estimated using ${\tau }_{\mathrm{p}}^{\mathrm{max}}$ method yielded more reliable results as compared with other methods, especially for M ≥ 5. It can be concluded that the lack of further large earthquakes and stations plays an essential role in the level of uncertainty associated with these methods. So, it can be supposed that the combination of the consequence on global observations would result in more accurate and applicable magnitude scaling relations, especially for more significant earthquakes.