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Earthquakes and slow‐slip events interact, however, detailed studies investigating their interplay are still limited. We generate the highest resolution microseismicity catalog to date for the northern Armutlu Peninsula in a ∼1‐year period to perform a detailed seismicity distribution analysis and correlate the results with a local, geodetically observed slow‐slip transient within the same period. Seismicity shows a transition of cluster‐type behavior from swarm‐like to burst‐like, accompanied by an increasing relative proportion of clustered (non‐Poissonian) relative to background (Poissonian) seismicity and gradually decreasing b‐value as the geodetically observed slow‐slip transient ends. The observed slow‐slip transient decay correlates with gradually increasing effective‐stress‐drop values. The observed correlation between the b‐value and geodetic transient highlights the influence of aseismic deformation on seismic deformation and the impact of slow‐slip transients on local seismic hazard., Plain Language Summary: Seismic and aseismic slip on faults can change the stress state in the crust and affect the recurrence time of earthquakes. Observations of how earthquakes and aseismic fault slip influence each other are limited because of the dearth of synchronous high‐resolution seismological and geodetic data. Here we use high‐resolution earthquake data in the northern Armutlu Peninsula along the Marmara seismic gap of the North Anatolian Fault (Turkey) to correlate the earthquake distribution with a local slow‐slip transient that occurred in the same period. We find that the slow‐slip transient modulates the spatiotemporal and frequency‐magnitude evolution of earthquakes, which highlights the influence of slow fault creep on fast fault slip. Our study demonstrates the importance of considering slow‐slip transients for seismic hazard assessment., Key Points: Seismicity analysis suggests that both external and internal forcing drive deformation in the Armutlu Peninsula. Temporal correlation between a slow‐slip transient and seismic b‐value highlights interactions between aseismic and seismic deformation. Slow‐slip transients modulate the frequency‐magnitude and spatiotemporal earthquake distribution., VW momentum grant, Helmotz Association Young Investigator Group http://dx.doi.org/10.13039/501100009318, Helmholtz‐Zentrum Potsdam—Deutsches GeoForschungs Zentrum GFZ, GIPP http://dx.doi.org/10.13039/501100010956

The dynamics of the Alps and surrounding regions is still not completely understood, partly because of a non‐unique interpretation of its upper‐mantle architecture. In particular, it is unclear if interpreted slabs are consistent with the observed surface deformation and topography. We derive three end‐member scenarios of lithospheric thickness and slab geometries by clustering available shear‐wave tomography models into a statistical ensemble. We use these scenarios as input for geodynamic simulations and compare modeled topography, surface velocities and mantle flow to observations. We found that a slab detached beneath the Alps, but attached beneath the Northern Apennines captures first‐order patterns in topography and vertical surface velocities and can provide a causative explanation for the observed seismicity., Plain Language Summary: Present‐day surface deformation, including earthquakes, plate motion, and mass (re)distribution, results from processes operating at the surface and in the interior of the Earth. Understanding these processes and their coupling is of utmost importance in light of the hazard they pose to society. The Alps provide an excellent natural laboratory to understand such coupling. Here, we use seismic tomography models to constrain its upper‐mantle architecture. We further use these models to quantify forces originating from the resolved architecture and their effects on the present‐day surface deformation. The models can reproduce first‐order patterns in the observed topography and vertical surface motions. We found a causative correlation between the presence of a shallow slab attached to the overlying lithosphere in the Northern Apennines and the seismicity in the region. Our results allow us to better understand the transfer of internal forces to the surface, thereby helping to quantify the present‐day mechanical setup of the area., Key Points: Statistical ensemble of S‐wave tomography models is used to infer the Lithosphere‐Asthenosphere Boundary configuration and slab geometries in the Alps. The 3‐D upper‐mantle architecture from the statistics reproduce first‐order patterns in observed topography and Global Navigation Satellite Systems vertical velocities. A shallow/attached slab in the Northern Apennines is consistent with the mantle depth seismicity observed in this region., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, https://doi.org/10.5880/GFZ.4.5.2019.004, https://gfzpublic.gfz-potsdam.de/pubman/item/item_238001, http://ds.iris.edu/ds/products/emc-earthmodels/, https://doi.org/10.5281/zenodo.7071571, https://doi.org/10.5281/zenodo.6538257

In this study, we investigated the phase stability of Al‐free and Al‐bearing superhydrous phase B (shy‐B) up to 55 GPa and 2500 K. In comparison with Al‐free shy‐B, the incorporation of 11.7 wt.% Al2O3 in shy‐B expands the stability by ∼400–800 K at 20–30 GPa. The determined dehydration boundary for Al‐bearing phase D indicates that it could be present even at normal mantle geotherm conditions at 30–40 GPa. Up to 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al‐bearing shy‐B and phase D between 20 and 40 GPa. Results of further experiments indicate that δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite at pressures above 52 GPa. This study shows that the incorporation of Al in dense hydrous magnesium silicates can have a profound impact on our picture of the water cycle in the deep Earth., Plain Language Summary: Constraining the deep cycle of water has a tremendous impact on our picture of the current state of the Earth and the evolution of the Earth's interior. Dense hydrous magnesium silicates (DHMSs) are considered potential H2O carriers in the Earth's mantle. However, the DHMSs can only be present at the relatively cold conditions of subduction slabs due their limited thermal stability. We determined the phase stability of Al‐bearing DHMSs at high pressure and temperature (P‐T) conditions. Our results show that the thermal stability of Al‐bearing shy‐B extends by 400–800 K with respect to its Al‐free counterpart at 600–800 km depth. The incorporation of Al also expands the phase stability of phase D and enhances the likelihood of its occurrence at normal mantle conditions at 800–1100 km. In addition, we observe that 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al‐bearing shy‐B and phase D between 600 and 100 km depth. Furthermore, δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite in the MgO‐SiO2‐Al2O3‐H2O system at pressures above 52 GPa and 1500 K., Key Points: In comparison with Al‐free shy‐B, the incorporation of 11.7 wt.% Al2O3 in superhydrous phase B (shy‐B) expands the stability by ∼400–800 K at 20–30 GPa. Al‐bearing phase D could be present even at normal mantle geotherm conditions at 30–40 GPa. δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite at pressures above 52 GPa., Center for Molecular Water Science, CMWS, https://doi.org/10.5281/zenodo.6320835