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Reply to comment by P. Rydelek et al. on “Earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records”
Author(s) -
Zollo Aldo,
Lancieri Maria,
Nielsen Stefan
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl030560
Subject(s) - magnitude (astronomy) , seismology , amplitude , geology , waveform , moment magnitude scale , geodesy , coda , seismic moment , displacement (psychology) , peak ground acceleration , strong ground motion , ground motion , physics , fault (geology) , mathematics , geometry , quantum mechanics , astronomy , scaling , psychology , voltage , psychotherapist
[1] Based on the analysis of Mediterranean, near-source, strong motion records Zollo et al. [2006] (hereinafter referred to as ZLN) showed that peak displacement amplitudes of initial Pand S-wave seismic signals scales with the earthquake size in the moment magnitude range 4 6.1. [9] In Figure 1 we report data distribution vs. magnitude and hypocentral distance. Note that the distance distribution of analyzed events for Japan (Figure 1) is clearly different from that for the Mediterranean (MED) earthquakes given by ZLN. Whereas most of MED records occur at an HD 40 km. [10] At odds with RWH, we did not apply any cut-off at M = 5.5 on hypocentral distance for small and moderate events; indeed this may introduce a bias on the estimation of attenuation law parameters retrieved from both small and large earthquakes records. We follow the ZLN procedure involving among others sensitivity correction, P and S phase identification, double integration, filtering in a frequency band (0.075, 3 Hz). Peaks are read on the modulus of displacement expressed in meters. Starting from the Pwave and S-wave picked arrivals, we measure peaks within a 2 second window. For the P arrival, we also test the method with 4 second windows. [11] The distance attenuation effect is corrected for by assuming a simple log-linear model [Wu and Zhao, 2006; ZLN]; the amplitudes are normalized to a reference distance of 10 Km (i.e., the same as for ZLN in the Mediterranean study, to facilitate comparison). Though RWH show data normalized at a distance of 20 km (ZLN, Figures 2a and 2b), the use of a different normalization distance does not change the slope of the log(peak) vs Magnitude relationships and thus does not alter the graphical interpretation. [12] In Figure 2 we show the relation between the logarithm of distance normalized, peak displacement for P and S waves in different time windows vs final magnitude of the events (following ZLN, statistical significance was GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L20303, doi:10.1029/2007GL030560, 2007 Click Here for Full Article