No abstract

Key Points:• We present subduction models with varying overriding plate lithosphere • Anisotropic rheology aids in sustained asymmetric subduction from initiation • Overriding plate properties exert a first-order effect on subduction evolution Abstract Geologic and geophysical observations indicate that the thickness, density, and strength of the lithosphere vary on the Earth. However, the role of the overriding plate lithosphere properties on the evolution and morphology of subduction is not well understood. This paper presents time-dependent numerical models of subduction that vary the overriding plate thickness, strength, and density and allow for a plate interface that evolves with time via an anisotropic brittle failure rheology. We examine the effect of these parameters on subduction evolution, in particular, the emergence of (a) asymmetric versus symmetric subduction, (b) trench retreat versus advance, (c) subduction zone geometry, (d) slab stagnation versus penetration into the lower mantle, and (e) flat slab subduction. Almost all of the models presented result in sustained asymmetric subduction from initiation. Trench advance occurs in models with a thick and or strong overriding plate. Slab dip, measured at a depth below the plate boundary interface, has a negative correlation with an increase in overriding plate thickness. Overriding plate thickness exerts a first-order control over slab penetration into the lower mantle, with penetration most commonly occurring in models with a thick overriding plate. Periods of flat slab subduction occur with thick, strong overriding plates producing strong plate boundary interface coupling. The results provide insight into how the overriding plate plays a role in establishing advancing and retreating subduction as well as providing an explanation for the variation of slab geometry across subduction zones on Earth, where similar patterns of evolution are observed.

Accurate and reliable hydrologic simulations are important for many applications such as water resources management, future water availability projections and predictions of extreme events. However, the accuracy of water balance estimates is limited by the lack of large-scale observations, model simulation uncertainties and biases related to errors in model structure and uncertain inputs (e.g., hydrologic parameters and atmospheric forcings). The availability of long-term and global remotely sensed soil moisture offers the opportunity to improve model estimates through data assimilation with complete spatiotemporal coverage. In this study, we assimilated the European Space Agency (ESA) Climate Change Initiative (CCI) derived soil moisture (SM) information to improve the estimation of continental-scale soil moisture and runoff. The assimilation experiment was conducted over a time period 2000-2006 with the Community Land Model, version 3.5 (CLM3.5), integrated with the Parallel Data Assimilation Framework (PDAF) at a spatial resolution of 0.0275 • (∼ 3 km) over Europe. The model was forced with the high-resolution reanalysis COSMO-REA6 from the Hans Ertel Centre for Weather Research (HErZ). The performance of assimilation was assessed against openloop model simulations and cross-validated with independent ESA CCI-derived soil moisture (CCI-SM) and gridded runoff observations. Our results showed improved estimates of soil moisture, particularly in the summer and au-tumn seasons when cross-validated with independent CCI-SM observations. The assimilation experiment results also showed overall improvements in runoff, although some regions were degraded, especially in central Europe. The results demonstrated the potential of assimilating satellite soil moisture observations to produce downscaled and improved high-resolution soil moisture and runoff simulations at the continental scale, which is useful for water resources assessment and monitoring.

Extension of the Earth's crust can result in differing styles of rifting, such as horst-and-graben, half-graben, metamorphic core complexes and areas of distributed crustal thinning. Faulting patterns can range from either being distributed to highly localized. Observations indicate that the factors controlling the extensional deformation, symmetry, and fault spacing include rheological aspects such as the yielding mechanism and strain softening, and physical aspects such as initial heterogeneities and the strength of the lower crust compared to the upper crust. Time-dependent numerical models of extension are presented, which investigate the influence of the yielding mechanism, lower crust strength, strain weakening, and initial heterogeneity in the crust have on (a) the style of rifting, (b) fault spacing, and (c) integrated strength in the upper crust. Models with an anisotropic yielding mechanism result in more realistic lithospheric strength profiles, slip plane angle distributions, and fault interaction than models with an isotropic yielding mechanism. Heterogeneity type and yielding mechanisms have the largest effect on the resulting symmetry of deformation, whereas the amount of strain weakening has the greatest influence on asymmetry. The likelihood of the metamorphic core complex mode occurring is primarily controlled by lower crust strength. Crustal thinning is encouraged by both low amounts of strain weakening and a strong lower crust. Lower crust viscosity exerts the primary control on whether the resulting deformation is distributed or localized. The degree of strain weakening has the largest influence on the average strength of the upper crust and the slope of the strength profile in the upper crust.

No abstract