Spatio-temporal evolution of the June 2007 intrusion and concurrent slow-slip event at Kilauea Volcano, Hawai'i

Rapid changes in ground tilt and GPS positions on Kilauea Volcano, Hawai'i are interpreted as resulting from a shallow, two-segment dike intrusion into the east rift zone that began at 12:17 UTC June 17, 2007 and lasted almost three days. As a result of the intrusion, a very small volume of basalt (about 1,500 m³) erupted on June 19. Northward tilt at a coastal tiltmeter, subsidence of south flank GPS sites, eastward displacements at southwestern flank GPS sites, and a swarm of flank seismicity suggests that a slow slip event occurred on the decollement beneath Kilauea's south flank concurrent with the rift intrusion. To study the spatial and temporal relationships between two shallow, steeply dipping dike segments extending from the surface to about 2 km depth, and decollement slip at 8 km depth, we use 4-minute GPS positions, which include estimates of time-dependent tropospheric gradients, and ground tilt data. We invert for the combined temporal evolution of distributed dike opening and decollement slip in independent inversions at each time step using a non-negative least squares algorithm. Based on these inversions, the intrusion occurred in two stages that correspond spatially and temporally with concentrated rift zone seismicity. The dike opening began just after noon UTC on June 17 on the western of the two segments before jumping to the eastern segment, where the majority of opening accumulated. Dike opening preceded the start of decollement slip offshore of tiltmeter KAE; the latter is indicated by the onset of northward tilt at the coastal tiltmeter KAE. Displacements at southwestern flank GPS sites began about 18 hours later, and are interpreted as resulting from slow slip on the southwestern flank. Additional constraints on the evolution of the intrusion and decollement slip come from an inversion of an ENVISAT interferogram with an ending time of 08:22 UTC on June 18th, 2007, combined with GPS and tilt data up to this time. This inversion shows that up to the time of the ENVISAT acquisition, decollement slip is only required offshore of Kaena point. A similar inversion of the complete event that includes GPS and tilt data up to June 21, and a second ENVISAT interferogram with an end time on June 21 shows that the required decollement slip is spread across the south flank suggesting westward migration of the decollement slip as the event progressed.