Advances in Biology & Earth Sciences

The seismicity of eastern Java is controlled by the subduction of the Australian Plate beneath the Sunda arc, yet the processes governing intermediate-depth intraslab earthquakes in this region remain poorly understood. In April-May 2021, a damaging earthquake sequence south of Malang (Mw 6.0 mainshock and subsequent Mw 5.1 and Mw 5.9 aftershocks) highlighted the hazard potential of intraslab events, which occurred at depths exceeding 80 km. To investigate the geodynamic processes responsible for this sequence, we analyzed 3,380 earthquakes recorded by the BMKG network between 2008 and 2022, relocated them using a newly derived 1D P-wave velocity model and inverted full-waveform moment tensors for the mainshock and two largest aftershocks. The mainshock exhibited a thrust-faulting mechanism consistent with slab-parallel compression, whereas the aftershocks ruptured deeper within the slab along different fault orientations. Static stress transfer modeling indicates that the mainshock promoted failure on adjacent structures at depths exceeding 100 km, consistent with triggering under fluid-assisted weakening. Combined with seismotectonic cross-sections and stress field analysis, our results support slab dehydration embrittlement as the primary mechanism enabling rupture at intermediate depths, while also explaining the distinct focal mechanisms of the aftershocks. These findings provide new insight into the dynamics of the Java subduction system, highlight the importance of slab-related processes in generating damaging earthquakes and underscore the seismic hazard posed by intraslab events in eastern Java. In other hand, the three-year average vulnerability pattern highlights persistent area that require prioritization in local disaster management strategies. These findings show the critical value of integrating seismic observations with spatial vulnerability metrics to understand post-earthquake risk trajectories and to guide resilience-oriented planning in seismically active regions.