3:45 PM - 4:00 PM
[SIT22-08] Waveform inversion for localized 3-D shear velocity structure in the lowermost mantle
beneath Caroline hotspot
Keywords:Caroline hotspot, waveform inversion, S-velocity structure, lowermost mantle
The result of checkerboard test shows that the resolution of 300-400 km above the CMB is improved as compared with that of Konishi et al. (2014). The inferred structure has two features: (1) two low-velocity anomalies immediately above the CMB, which merge into one low-velocity anomaly (about 6%) at 100 km above the CMB and is continuous up to at least 400 km above the CMB. The location of low-velocity anomaly is consistent with that of Konishi et al. (2014). (2) about 3% high velocity anomaly from 150 to 400 km above the CMB to about 1000 km northwest of the low velocity anomaly. We interpret these features as: (1) the ‘tower shaped’ low-velocity anomaly indicates upwelling flows from the two separated low-velocity roots immediately above the CMB. The location of the prominent low-velocity anomaly is consistent with the location of the Caroline hotspot. (2) Suppose the velocity anomalies are due to the thermal effects, this high-velocity anomaly indicates colder materials than its surroundings. Since the location of the high-velocity anomaly is consistent with the paleo-subduction of the Izanagi plate in 200 Ma (Matthews et al. 2016), this high-velocity anomaly could be a remnant of the subducted Izanagi plate.