Abstract
The relation between earthquake size (radiated energy or seismic moment) and duration of faulting (predominant period or corner frequency) was investigated from a waveform analysis of shallow earthquakes with a seismic moment between 1010 and 1025 dynebcm. The earthquakes analyzed were observed at relatively short focal distances where anelastic attenuation had no serious effect on their waveforms. The waveforms are characterized by their simplicity and relative lack of coda.We found that the radiated energy of the P and S wave is proportional to the fifth power of the period of P and S wave velocity seismograms, respectively, and that the relation between the seismic moment (M0) and the corner frequency of the P wave (i0) is given by M0pi0-4. The above two relations are consistent with each other. The relation M0pi0-3 which is generally accepted for large earthquakes (M0>1025 dynebcm) does not hold true for smaller earthquakes (M0>1025 dynebcm), possibly because, for smaller earthquakes, slip velocity does not exceed a critical level owing to small rupture velocity and because effective stress is not constant and independent of seismic. moment.The relation between M0 and the fault length (L) was estimated as M0pL2.5-L3.2 from aftershock distributions ranging from a microearthquake to moderate earthquakes. By combining this relation with the M0-f0 relation, we have come to the conclusion that average rupture velocity and slip velocity decrease with the decreasing seismic moment. We have also concluded that the deviations of data from the relation M0pf0-3 are not attributed to small stress drop but small rupture velocity and slip velocity.
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