5:15 PM - 6:30 PM
[SSS29-P02] Determination of the coefficients of Mhdd for regional data
Keywords:Magnitude, High frequency energy radiation
Hara (2007, EPS) developed a formula to calculate magnitudes using durations of high frequency energy radiation (HFER) and maximum displacement amplitudes using tele-seismic P waves. Hara (2013, SSJ) referred to a magnitude calculated by this formula as Mhdd. Hara (2014, JpGU) tried to revise the coefficients of the formula by a grid search to reduce the dependences of differences between Mhdd and Mw on epicentral distance and HFER duration. Mhdd calculated by the obtained coefficients were underestimates for larger earthquakes.
Hara (2015, SSJ) investigated the characteristics of Mhdd for tele-seismic data by another grid search, in which the dependence of Mhdd on Mw was taken into account in addition. He proposed a revised formula with small dependences of the differences between Mhdd and Mw on epicentral distance, HFER duration, and Mw allowing a slightly larger RMS of their differences.
In this study, we applied the procedure of Hara (2015) to regional data to determine the coefficients of Mhdd appropriate for regional distance range. We used broadband data recorded at FDSN stations in the epicentral distance range between 10 and 30 degrees for 60 events that occurred in between 1995 and May 2015. We retrieved data from the IRIS DMC. We conducted the grid search for the Mhdd coefficients following Hara (2015) and evaluated the dependences of the differences between Mhdd and Mw on epicentral distance, HFER duration, and Mw. As was observed for tele-seismic data, there is a significant Mw dependence for the set of the coefficients which provides the minimum RMS of the differences between Mhdd and Mw. As Hara (2015) showed for tele-seismic data, when we allow a slightly larger RMS of their differences, it is possible to find a set of the coefficients for regional data for which the dependences of their differences on epicentral distance, HFER duration, and Mw are small.
Hara (2015, SSJ) investigated the characteristics of Mhdd for tele-seismic data by another grid search, in which the dependence of Mhdd on Mw was taken into account in addition. He proposed a revised formula with small dependences of the differences between Mhdd and Mw on epicentral distance, HFER duration, and Mw allowing a slightly larger RMS of their differences.
In this study, we applied the procedure of Hara (2015) to regional data to determine the coefficients of Mhdd appropriate for regional distance range. We used broadband data recorded at FDSN stations in the epicentral distance range between 10 and 30 degrees for 60 events that occurred in between 1995 and May 2015. We retrieved data from the IRIS DMC. We conducted the grid search for the Mhdd coefficients following Hara (2015) and evaluated the dependences of the differences between Mhdd and Mw on epicentral distance, HFER duration, and Mw. As was observed for tele-seismic data, there is a significant Mw dependence for the set of the coefficients which provides the minimum RMS of the differences between Mhdd and Mw. As Hara (2015) showed for tele-seismic data, when we allow a slightly larger RMS of their differences, it is possible to find a set of the coefficients for regional data for which the dependences of their differences on epicentral distance, HFER duration, and Mw are small.