No abstract

A Subduction‐Transform Edge Propagator (STEP) is the locus of continual lithospheric tearing which enables subduction of one part of a tectonic plate, while the juxtaposed part remains at the surface. A key question is the propagation direction of active STEPs, and we suspect passive margins to play a critical role in steering STEPs. We investigate the role of passive margins (width, orientation, and lateral strength contrast) on the STEP propagation direction through mechanical finite element models. For straight passive margins, we show that STEPs remain parallel to passive margins when within 15° from a trench‐perpendicular geometry. In other cases, where passive margins change strike ahead of the active STEP, STEPs are captured by passive margins for abrupt strike changes (radius of curvature < lithosphere thickness) less than 25° from trench perpendicular. Outside this window, STEPs will propagate in the original direction. If a strike change (>25°) is made through a large radius of curvature (>lithosphere thickness), STEPs will also propagate along the passive margin. A STEP system evolves toward orthogonality, which may explain why STEP faults are approximately perpendicular to trenches in nature. STEP systems are relatively insensitive to small‐scale details (due to large‐scale stresses), propagating as straight features along rugged passive margins. Surprisingly, magnitudes of lithospheric strength variation across the passive margin and subduction history, which determines location and magnitude of density anomalies in the mantle, are less relevant for the STEP propagation direction.

The Mediterranean region displayed transient behavior throughout the last 30 Myrs, with ephemeral fault activity and strong variation in deformation intensity. This suggests that the tectonic forces changed rapidly as well, both in time and space. The main forces are associated with the large-scale Miocene to Quaternary processes: 1) slow Africa-Eurasia plate convergence (∼5 mm/yr), and 2) slab rollback, with the trench and the Calabrian block moving mainly towards the SE, resulting in a migrating Aeolian volcanic arc and opening of the Tyrrhenian back-arc basin.

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;The 2018 &lt;em&gt;M&lt;sub&gt;w&lt;/sub&gt;&lt;/em&gt; 7.5 Palu earthquake is a remarkable strike-slip event due to its nature as a shallow supershear&amp;#160;fault rupture across several segments and a destructive tsunami that followed co-seismic deformation.&amp;#160;GPS offsets in the wake of the 2018 earthquake display a transient in the surface motions of northwest&amp;#160;Sulawesi. A Bayesian approach identifies (predominantly a-seismic) deep afterslip on and below the co-seismic rupture plane as the dominant physical mechanism causing the cumulative, post-seismic, surface&amp;#160;displacements whereas viscous relaxation of the lower crust and poro-elastic rebound contribute&amp;#160;negligibly. We confirm a correlation between shallow supershear rupture and post-seismic surface&amp;#160;transients with afterslip activity in the zone below an inter-seismically locked fault plane where the slip&amp;#160;rate tapers from zero to creeping.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

The 2018 Mw7.5 Palu earthquake is a remarkable strike‐slip event due to its nature as a shallow supershear fault rupture across several segments and a destructive tsunami that followed coseismic deformation. GPS offsets in the wake of the 2018 earthquake display a transient in the surface motions of northwest Sulawesi. A Bayesian approach identifies (predominantly aseismic) deep afterslip on and below the coseismic rupture plane as the dominant physical mechanism causing the cumulative, postseismic, surface displacements whereas viscous relaxation of the lower crust and poro‐elastic rebound contribute negligibly. We confirm a correlation between shallow supershear rupture and postseismic surface transients with afterslip activity in the zone below an interseismically locked fault plane where the slip rate tapers from zero to creeping.