12:00 PM - 12:15 PM
[SCG46-21] The flat 410 and 660 discontinuities below the subducting Pacific slab beneath northeastern Japan
Keywords:sub-slab, plume, receiver function
Recent seismic tomography studies have shown that the sub-slab low-velocity anomalies exist in many subduction zones and these anomalies are interpreted as a hot mantle plume from the lower mantle. However, details are still unclear. Here, we estimated the horizontal temperature variation by the determination of the depth variation of 410 and 660 discontinuities.
We applied an instrumental response correction (Maeda et al., 2011) to waveform data and calculated RFs with a water level of 0.001 in a frequency range of 0.1-0.5Hz. For the RF calculation, we used the tele-seismic waveform data of magnitude 5.5 or greater that occurred during a period from April 2005 to March 2023 and epicentral distances between 30°-90°. These waveforms are obtained at 455 Hi-net stations provide by National Research Institute for Earth Science and Disaster Resilience. We discarded RFs with <3 signal-to-noise ratios, and finally used a total of about 216,414 RFs from 1086 events. RFs were migrated into space-domain using the iasp91 1D velocity model (Kennett and Engdahl 1991). Employing CCP (common conversion point) stacking, and we gathered Ps amplitudes within 100 km radius of each grid and produced a transect with a 10 km (distance) × 2 km (depth) grid.
We observed almost flat planes of the 410 and 660 discontinuities. In addition, there are no correlations between the 410 and 660 topography and S-wave velocity perturbation, which suggests that the sub-slab low-velocity anomaly cannot be explained by the temperature change only. Therefore, the cause of low-velocity anomaly may not be temperature, but other factors such as hydration, composition or anisotropy.
We applied an instrumental response correction (Maeda et al., 2011) to waveform data and calculated RFs with a water level of 0.001 in a frequency range of 0.1-0.5Hz. For the RF calculation, we used the tele-seismic waveform data of magnitude 5.5 or greater that occurred during a period from April 2005 to March 2023 and epicentral distances between 30°-90°. These waveforms are obtained at 455 Hi-net stations provide by National Research Institute for Earth Science and Disaster Resilience. We discarded RFs with <3 signal-to-noise ratios, and finally used a total of about 216,414 RFs from 1086 events. RFs were migrated into space-domain using the iasp91 1D velocity model (Kennett and Engdahl 1991). Employing CCP (common conversion point) stacking, and we gathered Ps amplitudes within 100 km radius of each grid and produced a transect with a 10 km (distance) × 2 km (depth) grid.
We observed almost flat planes of the 410 and 660 discontinuities. In addition, there are no correlations between the 410 and 660 topography and S-wave velocity perturbation, which suggests that the sub-slab low-velocity anomaly cannot be explained by the temperature change only. Therefore, the cause of low-velocity anomaly may not be temperature, but other factors such as hydration, composition or anisotropy.