Low-velocity anomaly around 410 km beneath the Yellow and East China Seas with P wave triplications

Broadband waveform data for one mb6.0 earthquake beneath Honshu,Japan, with focal depth of 167.2 km, recorded by China Digital Seismic Network (CDSN) were retrieved. Through trial-and-error method, the anomalous models beneath the Yellow and East China Seas for the six sub-regions were obtained by matching the theoretical travel-time curves of the P triplications from the modified models for the six sub-regions by using 2-D ray tracing with the observed ones. The local lower velocity anomaly appears around the 410 km discontinuity. Above the discontinuity, the P wave velocity decreases by 4%—5% from 300 km to 410 km and below the discontinuty, the velocity decreases by 4%—7% from 410 km to 460/470 km. Because thermal flow was not observed by former seismic tomographic results, the local low velocity anomaly should be due to the partial-melting caused by the dehydrated water from subducting slab.