|詳細||Widespread slow slip events triggered at the Hikurangi subduction zone by the M7.8 Kaikoura earthquake, New Zealand|
|詳細||With the recent discovery of slow transient deformation at the roots of plate boundaries, there are many new fundamental questions about how these slow slip phenomena modify our understanding of how tectonic convergence is accommodated along plate interfaces. Geodetic data have been able to directly constrain the largest slow slip events, suggesting a slow rupture that is smooth in both time and space. On the other hand, seismology provides indirect observations of slow slip in the form of tectonic tremor and repeating low-frequency earthquakes that highlight a rough and intermittent evolution of slip on the plate interface. I will show here how to reconcile these contradictory observations by exploiting the time history of this slow seismicity to uncover new geodetic constraints that force us to reconsider the consensus model of slow deformation dynamics.
First, I will describe how GPS records between previously identified slow slip events do not represent continuous convergent motion and can in fact be decomposed into two distinct regimes of tectonic loading and release. This intermittent slip that was previously hidden within the noise demonstrates that the plate boundary where slow slip occurs can be as strongly coupled as the seismogenic zone and undergoes cyclic stress build-up and release over a wide range of time scales. I will then investigate the short-period dynamics at the plate interface during a large slow slip event. I show that while the long-period surface displacements as recorded by GPS suggest a six month duration, motion in the direction of tectonic release only sporadically occurs over <60 days and its surface signature is attenuated by rapid relocking of the plate interface. These results demonstrate that our current conceptual model of slow and continuous rupture is outdated and is an artifact of low-resolution geodetic observations of a superposition of small, clustered slip events.|