The southeastern part of the Solomon Islands, a highly seismically active area in the southern Pacific, experienced two moderate earthquakes (Mw 6.3 and 6.0) on January 27th and 29th, 2020. The regional seismic network, operational since October 2018, recorded the entire foreshock-main-shock-aftershock sequence, allowing for a new 1D velocity model and relocation of events. Based on the spacial distribution of the foreshock-aftershock sequence, together with focal mechanism data from the Global CMT database, we suggest that there is a near-vertical slab tear at the southern end of the South Solomon subducting slab, abutting a zone of strike-slip faulting that links it to the Vanuatu subduction zone to form a Subduction-Transform Edge Propagator fault. Our new data also indicates that a seismic gap occurs at depths from 25 to 35 km within the southern part of the South Solomon slab.

The Solomon Islands is one of the most seismically active areas in the southern Pacific with high earthquake hazard potential. The regional seismic network, equipped with six broadband seismic stations, was constructed as late as October 2018. On January 27 and 29, 2020, two moderate earthquakes, Mw 6.3 and 6.0, respectively, occurred in the southeastern Solomon Islands. The entire foreshock-main-shock-aftershock sequence was recorded by this seismic network for exploring the seismogenic structures. Based on the spacial distribution of the foreshock-aftershock sequence, the interaction of the subduction and transform zones between the Pacific and the Australia plates could lead to the near-vertical dip-slip tear slab. Confirmed with PREM and the new 1D velocity model for testing the robustness of the earthquake locations, a seismic gap at depths from 25 to 35 km is observed as the “jelly sandwich” rheology of the continental crust of the Australia plate.