A Slow Rupture Episode during the 2000 Miyakejima Dike Intrusion
Abstract:
The 2000 Miyakejima dike intrusion triggered one of the largest swarms ever recorded, providing a remarkable dataset and a wealth of information regarding the dynamics of dike induced seismicity and faulting. During the months following dike propagation, while the dike continued thickening, seismicity was characterized by several bursts with a duration of less than 24h and propagation along the dike length (Fig. 1). The relative location of the bursts suggests triggering by static stress transfer: each burst starts close to the edge of the previous ones, where the highest stresses are expected.
The largest burst occurred on August 3rd, and it is associated with geodetically recorded surface displacements on the islands of Nijima and Kozushima. We find that the deformation is best explained by a combination of opening on a dike and aseismic slip on the same faults on which seismicity occurred. The geodetic moment of the aseismic slip exceeds both the seismic moment and the opening moment by a factor of 2. Based on these results and on the seismicity bursts as a whole, we suggest that dike-induced faulting occurs largely by intermittent slip episodes with a large aseismic component.
Fig. 1: Detected seismicity bursts in the phase following dike arrest. The insets above the main figure show the migration of earthquakes within individual bursts: both unilateral and bilateral migration are observed.
