1. We perform a global survey of the 520- and 560-km mantle discontinuity by analyzing SS precursors.
2. Our observations confirm the global existence of the 520-km discontinuity.
3. Depth variations of the 520-km discontinuity correlate with the mid-MTZ temperature.
4. Compositional heterogeneity also contributes to the 520-km discontinuity topography.
5. A 560-km discontinuity is sporadically detected in subduction zones and mantle upwells.
6. The existence of the 560-km discontinuity may imply localized Ca-enrichment in the mid-MTZ possibly related to the recycling of oceanic crust.

1. We present high-precision locations and detailed source information of four small seismic events following North Korea’s 2017 nuclear test.
2. The first event is an on-site collapse 440 m northwest of the test site and best explained by a near vertical single force.
3. The later events are an earthquake swarm located 8.4 km north of the test site with a focal depth of at least 2.4 km.

Although existence of a mushy zone in the Earth’s inner core has been hypothesized several decades ago, no seismic evidence has ever been reported. Based on waveform modeling of seismic compressional waves that are reflected off the Earth’s inner core boundary, here we present seismic evidence for a localized 4–8 km thick zone across the inner core boundary beneath southwest Okhotsk Sea with seismic properties intermediate between those of the inner and outer core and of a mushy zone. Such a localized mushy zone is found to be surrounded by a sharp inner core boundary nearby. These seismic results suggest that, in the current thermo-compositional state of the Earth’s core, the outer core composition is close to eutectic in most regions resulting in a sharp inner core boundary, but deviation from the eutectic composition exists in some localized regions resulting in a mushy zone with a thickness of 4–8 km.