[SSS11-P15] Adjoint tomography beneath the Kanto region using broadband seismograms
Keywords:Seismic wave-speed model, Adjoint tomography, Broadband seismogram
The revisions were following three. (1) I re-determined centroid time. I basically used the parameters of MT solutions provided by the NIED F-net as initial source parameters. Although the synthetics are similar with the observation, the synthetic was faster than the observation on almost seismograms due to significant rupture duration. I estimated the centroid time using the differential time between observation and synthetic estimated by phase correlation for a packet of P-waves. (2) I considered attenuation effect in the forward modeling. I assumed attenuation structure depending on S-wave structure (Olsen et al. 2003). (3) I broaden the period band toward shorter periods. I used four period bands between 5 and 30 sec in the iteration. I started the inversion from the waveforms in the period band of 20 - 30 sec, and finally 5 - 30 sec in order to avoid cycle skipping.
One iteration involved forward modeling, estimation of misfit, calculation of misfit kernel using adjoint method, and model update using Hessian kernels. I obtained the preferred model after 16 iteration. Initial model was the tomographic model based on ray theory (Matsubara and Obara 2011). The main results are as follows: (i) the synthetic waveforms improved 20 % based on the amplitude misfit between observation and synthetics in the period of 5 - 30 sec. The new model reproduced the waveforms of both inversion data and extra data well. (ii) As for average wave-speeds in each depth, the average S-wave speed is not changed basically, while the P-wave speed model was slightly slower than that of the initial model. (iii) I detected the extreme low wave-speed areas at a depth of 5 km and 40 km. These low wave-speed areas are consistent with geological and tectonic features pointed out by the previous researches (e.g. Suzuki 1996; Kamiya and Kobayashi 2000).
Acknowledgements: We thank to the NIED F-net for providing seismological data, and the Computational Infrastructure for Geodynamics (CIG) for providing SPECFEM3D_Cartesian code. This work was supported by JSPS KAKENHI (Grant Number 16K21699) and MEXT KAKENHI (Grant number 15H05832).