What Triggers Caldera Ring?Fault Subsidence at Ambrym Volcano? Insights From the 2015 Dike Intrusion and Eruption

Surface deformation accompanying dike intrusions is dominated by uplift and horizontal motion directly related to the intrusions. In some cases, it includes subsidence due associated magma reservoir deflation. When deflation large enough, can form, or reactivate preexisting, caldera ring-faults. Ring-fault reactivation, however, rarely observed during moderate-sized eruptions. On February 21, 2015 at Ambrym volcano in Vanuatu, a basaltic intrusion produced more than 1 m of coeruptive uplift, as measured InSAR, synthetic aperture radar correlation, Multiple Aperture Interferometry. Here, we show that an average ?40 cm slip occurred on normal ring-fault this (VEI < 3) event, which intruded volume ?24 × 106 m3 erupted ?9.3 lava (DRE). Using 3D Mixed Boundary Element Method, explore stress change imposed opening depressurizing passive, frictionless fault. Normal fault promoted when transferred from beneath one Ambrym's main craters. After estimating compressibility, provide upper bound critical fraction (f = 7%) extracted trigger slip. We infer broad calderas may form part hundreds episodes no greater few meters, result extraction