Estimation of broadband source time functions of seismic slow earthquakes

We propose a method for estimating broadband source time functions of seismic slow earthquakes, which can reproduce observed seismograms at both bands of very low frequency earthquake and tectonic tremor. In our method, we assume the broadband characteristics of seismic slow earthquakes (e.g., Ide et al., 2008; Masuda et al., 2020).

In our method, first, we estimated source time functions of very low frequency earthquakes using filtered seismograms at frequencies below 0.1 Hz via the simulated annealing method (e.g., Takemura et al., 2022ab). To achieve broadband source time function, we added random temporal fluctuations into obtained smooth source time function of very low frequency earthquakes. This approach is similar to previous studies for regular earthquakes (e.g., Koyama, 1985; Hisada, 2000). We assumed that fluctuations of source time function can be characterized by a von-Kármán autocorrelation function. A decay rate parameter of a von-Kármán autocorrelation function can model various decay rates at high-frequency ranges.

We confirmed the validity of our method using synthetic seismograms, which were made from Green’s function datasets using a 1D velocity model and the Brownian-walk source time function model (e.g., Ide, 2008; Ide & Maury, 2018). Our estimation well reproduced target seismograms of synthetic seismic slow earthquakes.

In our presentation, we will introduce our methodology and applications at shallow plate boundary in Nankai.