Time-domain source parameter estimation of Mw 3-7 earthquakes in Japan
from a large database of moment-rate functions
Abstract
Time-domain analyses of seismic waveforms have revealed diverse source
complexity in large earthquakes (Mw>7). However, source
characteristics of small earthquakes have been studied by assuming a
simple rupture pattern in the frequency domain. This study utilized
high-quality seismic network data from Japan to systematically address
the source complexities and radiated energies of Mw 3β7 earthquakes in
the time domain. We first determined the apparent moment-rate functions
(AMRFs) of the earthquakes using the empirical Greenβs functions. Some
of the AMRFs showed multiple peaks, suggesting complex ruptures at
multiple patches. We then estimated the radiated energies (πΈπ
) of 1736
events having more than ten reliable AMRFs. The scaled energy (ππ
=πΈπ
/π0)
did not strongly depend on the seismic moment (π0), focal mechanisms, or
depth. The median value of ππ
was 3.7Γ10-5, which is comparable to those
of previous studies; however, ππ
varied by approximately one order of
magnitude among earthquakes. Additionally, we measured the source
complexity based on the radiated energy enhancement factor (π
πΈπΈπΉ). The
values of π
πΈπΈπΉ differed among earthquakes, implying diverse source
complexity. The values of π
πΈπΈπΉ did not show strong scale dependence for
Mw 3β7 earthquakes, suggesting that the source diversity of smaller
earthquakes is similar to that of larger earthquakes at their
representative spatial scales. Applying a simple spectral model (e.g.,
the Ο2-source model) to complex ruptures may produce substantial
estimation errors of source parameters.