The rupture mechanisms of intraslab earthquakes: A multiscale review and re-evaluation

The initiation of intraslab earthquakes and their location depend on multiple factors such as slab heterogeneity, pre-subduction anisotropy, thermal parameters and the metamorphic history of the lithosphere slab. As a result, these failures occur over a range of temperature-pressure conditions through different mechanisms. Therefore, to unravel the intricacy of intraslab seismicity, it is crucial to investigate the details of failure mechanisms using multiple datasets, at different scales. Details on rupture mechanisms are now accessible through advanced, highresolution seismologic approaches. However, seismologic archives are limited to events of the past few decades. Further, quasi-synchronous multiple-source mechanisms can be challenging to distinguish from seismic data only. Alternatively, the geologic records of intraslab seismicity, preserved in pseudotachylytes, provide a higher spatiotemporal resolution than seismic data, resulting in direct insight into the rupture triggering mechanisms.. These fault rocks also inform, over the geologic timescale, on the integrated deformation history of the slab. Despite this fact, only a handful of natural exposures have been investigated, and these include localities in Corsica, Italy, Zambia, and Japan. In addition, despite some strain rate limitations, deformation experiments, conducted using a wide range of starting materials and over broad pressure-temperature conditions, may further constrain the causes of intraslab rupture. These experiments, being intrinsically performed on relatively small rock volumes cannot capture large scale aspects of intraslab deformation. Finally, numerical modelling may overcome some of the above limitations as long as accurate and realistic parameters are chosen. Ultimately, our review shows that to fill the gap in our knowledge of intraslab seismicity, we need a multiscale-multimethod approach that integrates seismologic, geologic, experimental and numerical perspectives.