Localized temporal variation of Earth's inner-core boundary from high-quality waveform doublets

The topography of the inner core is crucial to understand its growth process and interaction with the geodynamo. With the accuracy of teleseismic waveform doublets in determining the travel-time shifts between PKPcd and PKPdf inner-core phases, we examined the temporal change of the inner-core boundary sampled by new earthquake doublets that occurred in the Western Pacific and those previously found from the South Sandwich Islands. The receiver stations are those within the distance range of 128°–142° from the hypocenters of the waveform doublets. Our results suggest that temporal changes in PKPcd-PKPdf differential times are very subtle except some isolated regions under central America and Africa. The observations may indicate localized topography of the inner core and/or the inner-core boundary as transient slurry in isolated regions.

Rapid estimation of disaster losses for the M6.8 Luding earthquake on September 5,2022

An M6.8 earthquake occurred in Luding,Sichuan Province,China,on September 5,2022.Since towns and villages in the earthquake-stricken area are densely populated,the earthquake caused severe fatalities and economic losses.Rapid estimation of earthquake intensity and disaster losses is significantly important for post-earthquake emergency rescue,scientific anti-seismic deployment,and the reduction of casualties and economic losses.Therefore,we make a preliminary rapid estimation of the earthquake intensity and disaster losses in the aftermath of the Luding earthquake.The seismic intensity represents the distribution of earthquake disasters and the degree of ground damage and can be directly converted from the peak ground velocity(PGV)map.To obtain a reliable PGV distribution map of this earthquake,we combined the finite-fault model constrained by seismic observations,with the complex three-dimensional(3D)geological environment and topographical features to perform strong ground motion simulation.Then,we compared the consistency between the simulated ground motion waveforms and observations,indicating the plausibility and reliability of simulations.In addition,we transformed the PGV simulation results into intensity and obtained a physics-based map of the intensity distribution of the Luding earthquake.The maximum simulated intensity of this earthquake is IX,which is consistent with the maximum intensity determined from the postearthquake field survey.Based on the simulated seismic intensity map of the Luding earthquake and the earthquake disaster loss estimation model,we rapidly estimated the death and economic losses caused by this earthquake.The estimated results show that the death toll caused by this earthquake is probably 50-300,with a mathematic expectation of 89.Thus the government should launch a Level II earthquake emergency response plan.The economic losses are likely to be 10-100 billion RMB,with a mathematical expectation of 23.205 billion RMB.Such seismic intensity simulations and rapid estimation of disaster losses are expected to provide a preliminary scientific reference for governments to carry out the targeted deployment of emergency rescue and post-disaster reconstruction.