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The interplay between tectonics and surface processes defines the evolution of mountain belts. However, correlating these processes through the evolution of natural orogens represents a scientific challenge. Analog models can be used for analyzing and interpreting the effect of such interaction. To fulfill this purpose it is necessary to understand how the imposed boundary conditions affect analog models' evolution in time and space. We use nine analog models characterized by different combinations of imposed regional slope and rainfall rates to investigate how surface processes respond to the presence of tectonically built topography (imposed slope) under different climatic conditions (rainfall rate). We show how the combination of these parameters controls the development of drainage networks and erosional processes. We quantify the morphological differences between experimental landscapes in terms of a proposed Se/R ratio, accounting for both observables and boundary conditions. We find few differences between analog models and natural prototypes in terms of parametrization of the detachment-limited stream power law. We observe a threshold in the development of channelization, modulated by a tradeoff between applied boundary conditions. [ABSTRACT FROM AUTHOR]

The interplay between tectonics and surface processes defines the evolution of mountain belts. However, correlating these processes through the evolution of natural orogens represents a scientific challenge. Analogue models can be used for analyzing and interpreting the effect of such interaction. We use nine analog models characterized by different combinations of imposed regional slope and rainfall rates to investigate how a small scale orogen evolves in response to tectonics and surface processes. We show how the combination of these parameters control the development of drainage networks and erosional processes. We quantify the different morphological expression of analogue landscapes in terms of a proposed Ae number that accounts for both observables and boundary conditions. We find few differences between analogue models and natural prototypes, in terms of parametrization of the detachment-limited stream power law. We observe a threshold in the development of channelization, modulated by a tradeoff between applied boundary conditions. [ABSTRACT FROM AUTHOR]

Tectonics and erosion–sedimentation are the main processes responsible for shaping the Earth's surface. The link between these processes has a strong influence on the evolution of landscapes. One of the tools we have for investigating coupled process models is analog modeling. Here we contribute to the utility of this tool by presenting laboratory-scaled analog models of erosion. We explore the erosional response of different materials to imposed boundary conditions, trying to find the composite material that best mimics the behavior of the natural prototype. The models recreate conditions in which tectonic uplift is no longer active, but there is an imposed fixed slope. On this slope the erosion is triggered by precipitation and gravity, with the formation of channels in valleys and diffusion on hillslope that are functions of the analog material. Using digital elevation models (DEMs) and a laser scan correlation technique, we show model evolution and measure sediment discharge rates. We propose three main components of our analog material (silica powder, glass microbeads and PVC powder; PVC: polyvinyl chloride), and we investigate how different proportions of these components affect the model evolution and the development of landscapes. We find that silica powder is mainly responsible for creating a realistic landscape in the laboratory. Furthermore, we find that varying the concentration of silica powder between 40 wt% and 50 wt% (with glass microbeads and PVC powder in the range 35 wt% –40 wt% and 15 wt% –20 wt% , respectively) results in metrics and morphologies that are comparable with those from natural prototypes. [ABSTRACT FROM AUTHOR]

It has long been recognized that sediments subducting along the megathrust influence the occurrence of giant (Mw ≥ 8.5) megathrust earthquakes. However, the limited observation span and the concurrent influence of multiple parameters on megathrust behavior prevent us from understanding how sediments affect earthquake size and frequency. Here, we address these limitations by using two‐dimensional, visco‐elasto‐plastic, seismo‐thermo‐mechanical numerical models to isolate how sediment thickness affects subduction geometry and seismicity. Our results show that increasing sediment thickness on the incoming plate results in a decrease of the slab dip, as the trench retreats due to the seaward growth of the sedimentary wedge that also unbends the slab. This decrease in megathrust dip results in a wider seismogenic zone, so that the maximum magnitude of megathrust earthquakes increases. Concurrently, the recurrence time of characteristic events increases and partial ruptures are introduced. The maximum magnitude estimated for subduction segments with the thickest sediment input (Makran, West‐Aegean, and Calabria) is distinctly higher than the instrumentally recorded magnitude. These segments may thus experience larger than as of yet observed earthquakes, albeit infrequently. Increasing sediment thickness also decreases megathrust normal stresses, as the seismogenic zone is more shallow and overlain by a lighter forearc structure. Thicker incoming plate sediments also favor more splay fault activity, whereas we observe more outer rise events for low sediment thickness. Finally, we demonstrate that modeling long‐term subduction dynamics and sediment subduction is crucial for understanding and quantifying megathrust seismicity and seismic potential of subduction zones. Key Points: Thick sediments reduce slab dip and increase seismogenic zone width and maximum earthquake magnitudeThick sediments also favor splay over outer rise faulting and partial over complete megathrust rupturesSimulation of long‐term subduction dynamics and sediments significantly increases the estimated maximum magnitude of the megathrust [ABSTRACT FROM AUTHOR]

The magnitude of great subduction megathrust earthquakes is controlled mainly by the number of adjacent asperities failing synchronously and the resulting rupture length. Here we investigate experimentally the long‐term recurrence behavior of a pair of asperities coupled by static stress transfer over hundreds of seismic cycles. We statistically analyze long (c. 500 ka) time series of M8‐9 analogue earthquakes simulated using a seismotectonic scale model approach with two aims: First, to constrain probabilistic measures (frequency‐size distribution, variability) useful for hazard assessment and, second, to relate them with geometric observables (coseismic slip pattern, locking pattern). We find that the number of synchronized asperity failures relative to the number of individual asperity failures as well as the coefficients of variation of recurrence intervals and seismic moment scale with the logarithm of stress coupling between the asperities. Accordingly, tighter packed asperities tend to recur more periodically and with a more characteristic magnitude while more distant asperities show clustering of more variable sized events. The probability of synchronized failures seems to be controlled to first order by geometrical relations (i.e., spacing and offset of asperities). The effects of rheological properties are evident but it remains to be explored to which extent they vary in nature and how sensitive the system is to those. Key Points: We tested geometric controls on asperity interaction and subduction earthquake recurrence behavior using seismotectonic scale modelingSimulated analogue earthquake sequences mimic long‐term behavior of a system of two asperities coupled by static stress transferThe degree of synchronization and intrinsic variability is controlled by the asperity distribution [ABSTRACT FROM AUTHOR]

The roughness of the subduction interface is thought to influence seismogenic behavior in subduction zones, but a detailed understanding of how such roughness affects the state of stress along the subduction megathrust is still debated. Here, we use seismotectonic analogue models to investigate the effect of subduction interface roughness on seismicity in subduction zones. We compared analogue earthquake source parameters and slip distributions for two roughness endmembers. Models characterized by a very rough interface have lower integrated fault strength and lower interseismic coupling than models with a smooth interface. Overall, ruptures in the rough models have smaller rupture area, duration, and mean displacement. Individual slip distributions indicate a segmentation of the subduction interface by the rough geometry. We propose that flexure of the overriding plate is one of the mechanisms that contribute to a heterogeneous stress distribution, responsible for the observed seismic behavior. Plain Language Summary: The largest and most destructive earthquakes on Earth occur along the plate contact in subduction zones, the region where an oceanic plate dives below another plate. The roughness of the downgoing plate, which is a result of the seafloor topography on that plate, is thought to play a role in the occurrence of large subduction earthquakes. With analogue models that include a 3‐D‐printed seafloor, we test the effect of two types of seafloor roughness on the occurrence of earthquakes: a very rough versus a very smooth seafloor. We observe that the rough seafloor geometry generally hinders the occurrence of large earthquakes along the subduction interface. This finding helps us to highlight where large future earthquakes are more likely to occur. Key Points: We perform analogue models to investigate the effect of subduction interface roughness on megathrust earthquakesModels with a very rough subduction interface are characterized by lower integrated fault strength and lower interseismic couplingRuptures in models with a very rough subduction interface are generally smaller in terms of rupture area, duration, and mean displacement [ABSTRACT FROM AUTHOR]

Abstract: The role of seafloor roughness on the seismogenic behavior of subduction zones has been increasingly addressed over the past years, although their exact relationship remains unclear. Do subducting features like seamounts, fracture zones, or submarine ridges act as barriers, preventing ruptures from propagating, or do they initiate megathrust earthquakes instead? We address this question using a global approach, taking into account all oceanic subduction zones and a 117‐year time window of megathrust earthquake recording. We first compile a global database, SubQuake, that provides the location of a rupture epicenter, the overall rupture area, and the region where the largest displacement occurs (the seismic asperity) for MW ≥ 7.5 subduction interplate earthquakes. With these data, we made a quantitative comparison with the seafloor roughness seaward of the trench, which is assumed to be a reasonable proxy for the subduction interface roughness. We compare the spatial occurrence of megathrust ruptures, seismic asperities, and epicenters, with two roughness parameters: the short‐wavelength roughness RSW (12–20 km) and the long‐wavelength roughness RLW (80–100 km). We observe that ruptures with MW ≥ 7.5 tend to occur preferentially on smooth subducting seafloor at long wavelengths, which is especially clear for the MW > 8.5 events. At both short and long wavelengths, seismic asperities show a more amplified relation with smooth seafloor than rupture segments in general. For the epicenter correlation, we see a slight difference in roughness signal, which suggests that there might be a physical relationship between rupture nucleation and subduction interface roughness. [ABSTRACT FROM AUTHOR]

The majority of the largest subduction megathrust earthquakes share the common characteristic of rupturing more than one asperity along strike of the margin. Understanding the factors that control coseismic failure of multiple asperities, and thus maximum magnitude, is central for seismic hazard assessment. To investigate the role of asperities size and spacing on maximum magnitude, seismicity rate, and percentage of synchronized ruptures, we use analog models simulating along-strike rupture behavior of megathrust earthquakes. We found negative correlations between the barrier-to-asperity length ratio Db/Da and maximum magnitude and seismicity rate. Db/Da also controls the process of asperities synchronization along the megathrust. A permanent barrier behavior is observed for Db/Da > 0.5. Comparing our experimental results to the Nankai Trough historical seismicity, we propose that the distribution of megathrust frictional heterogeneities likely explains the diversity of earthquakes which occurred there. [ABSTRACT FROM AUTHOR]

Earth deformation is a multi-scale process ranging from seconds (seismic deformation) to millions of years (tectonic deformation). Bridging short- and long-term deformation and developing seismotectonic models has been a challenge in experimental tectonics for more than a century. Since the formulation of Reid's elastic rebound theory 100 years ago, laboratory mechanical models combining frictional and elastic elements have been used to study the dynamics of earthquakes. In the last decade, with the advent of high-resolution monitoring techniques and new rock analogue materials, laboratory earthquake experiments have evolved from simple spring-slider models to scaled analogue models. This evolution was accomplished by advances in seismology and geodesy along with relatively frequent occurrences of large earthquakes in the past decade. This coincidence has significantly increased the quality and quantity of relevant observations in nature and triggered a new understanding of earthquake dynamics. We review here the developments in analogue earthquake modelling with a focus on those seismotectonic scale models that are directly comparable to observational data on short to long timescales. We lay out the basics of analogue modelling, namely scaling, materials and monitoring, as applied in seismotectonic modelling. An overview of applications highlights the contributions of analogue earthquake models in bridging timescales of observations including earthquake statistics, rupture dynamics, ground motion, and seismic-cycle deformation up to seismotectonic evolution. [ABSTRACT FROM AUTHOR]

Tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency-magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg-Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude Mw = 4.2 and Mw = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the Ml > 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been 'passive' features, with small fault patches failing on largely locked faults, or may have been accompanied by an 'active', largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area. [ABSTRACT FROM AUTHOR]

This paper describes a geomorphological map representing a sector of the Ionian coastal belt, located in north-eastern Calabria, between the catchments of the Trionto and Colognati Rivers. The landforms have been distinguished according to their origin into: a) structural and tectonic-controlled landforms; b) gravity-induced landforms; c) landforms formed by running water; d) coastal and transitional landforms; e) anthropic landforms, using as support a simplified topographic map on scale 1:20,000. The geomorphological map provides information about the long-term evolution of the landscape and identifies the geomorphic processes presently active. Therefore, the map could be used in developing land management and planning guidelines. [ABSTRACT FROM AUTHOR]

Despite the growing spatio-temporal density of geophysical observations at subduction zones, our understanding of the rupture limits of earthquakes (with respect to supposed asperity locations) and the timing of ruptures still remains poorly understood. Here, we contribute to improving this understanding by simulating multiple seismic cycles in a laboratory-scale analogue model of subduction. The experiment includes two asperities on the megathrust interface and creates full or partial ruptures on either both or a single asperity for each seismic cycle. We show that the apparent slip deficit accumulated since the last earthquake weakly correlates with the slip of the subsequent earthquake along the whole margin while within the slip area the correlation is generally high. The extents (and, in turn, the magnitude) of ruptures are thus not predictable from estimates of recent slip deficit alone. Next we test the predictive potential of Machine Learning (in particular Gradient Boosting Regression Trees GBRT) to predict analog earthquake recurrence and magnitude. We use 94 features extracted from the displacement field measured at the models surface with digital image correlation technique. This method allows for the discretization of the surface deformation with > 1000 interrogation windows that are analogs of "synthetic GPS stations" homogeneously distributed over the whole margin (including the generally offshore seismogenic zone). Impressively, GRBT is able to decipher the slow deformation accumulating in the analog tectonic plates during the periods in-between earthquakes and successfully predicts the timing and size of laboratory earthquakes. These results promise substantial progress in real earthquake forecasting, as they suggest that patterns in the motion recorded by geodesists at subduction zones might be diagnostic of earthquake imminence. [ABSTRACT FROM AUTHOR]

Subduction zones are complex dynamic systems hosting two of the most dangerous geo-hazards: mega- earthquakes and tsunamis. The scientific community is making great efforts to instrument and monitor these areas in order to illuminate, with improved resolution, the spatial and temporal features of subduction zone earthquakes. A very important aspect is the spatial relation between the interseismic degree of locking and the co-seismic slip distribution along the subduction interface, and thus the seismic cycle of megathrusts. This is particularly relevant for the intermediate-shallow part of megathrusts, where ruptures can occur and more easily produce devastating tsunamis, as demonstrated by the 2010 Maule and the 2011 Tohoku events. Another significant aspect is the range of transient signals that we might observe as the non-steady state interseismic period evolves towards the next co-seismic rupture. There are numerous examples of late-interseismic transients for recent large ruptures (e.g. Tohoku Mw 9.0, Iquique Mw 8.1, Illapel Mw 8.3), some of which were only subtly recorded by onshore GPS, but captured more clearly with analysis of repeating events.One major challenge is that interseismic locking is most often estimated using onland GNSS instruments, but the trench is so far offshore that we struggle to obtain enough model resolution in the updip regions of the plate interface. Accordingly, specific efforts are currently dedicated to the configuration and installation of geodetic sensors, specifically on the seafloor.Here, we use a novel analog model, that is a simplified scale reproduction of a subduction zone, to simulate hundreds of seismic cycles in a reasonable experimental time and observe the seismic behaviour of the megathrust for a given asperities configuration on a timescale of 10-100 kyr. Material properties (both elasticity and friction) and subduction geometry in the model are well defined, whereby specific configurations of asperities can be implemented a-priori. We exploit top-view monitoring with a videocamera and digital image cross correlation analysis to measure the velocity field of the model surface, discretized in a large number (i.e. thousands) of interrogation windows that ideally play the role of a set of homogeneously distributed "synthetic geodetic stations" above the whole model surface.Our preliminary results analyse the relation between the spatial distribution of geodetic sensors (both offshore and inland) and the resolution to which velocities can be imaged, hence indirectly the slip and interseismic locking and other potential transient signals along the subduction interface. [ABSTRACT FROM AUTHOR]

Volcanoes may erupt dominantly at their summit or on their flanks, depending on edifice shape, magma composition, tectonic setting. At calderas, which lack a summit to focus ascending magma, past eruptive vents are often scattered within or around the caldera rim, distributed in patterns that may show shifts during the history of the volcanic complex. Volcanic hazards may thus affect vast areas of such systems, making forecasting of future vents difficult to asses. Here we show that magma pathways, and thus future vent locations, may be forecasted by combining the physics of magma transport by dyking, whose propagation direction is controlled by stresses, with a Monte Carlo inversion scheme for the stress history of the volcano, constrained by the location of past vents. We apply our new approach on Campi Flegrei (Italy). We find that shifts in vent patterns are controlled by a delicate balance between regional/local stresses and the stresses induced by surface loads (including topography and volcanic deposits), which at most volcanoes varies in time due to eruptive activity. The resulting stress balance governs the curvature of the trajectories of ascending dykes and thus the location of future vents. Our method offers a mechanical explanation for the vent clustering and migration observed over the successive eruptive epochs at Campi Flegrei. We also show how vent opening probability maps may be calculated based on a parametric stress model for the volcano. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present the results of an integrated geomorphological, pedological and stratigraphical study carried out along the Ionian coast of northern Calabria (southern Italy). This area is characterised by the occurrence of five orders of alluvial terraces that are striking features of the landscape, where large and steep catchments debouch from the mountain front to the hilly coastal belt. Field investigations indicate that the deposits of all five terraces are suggestive of shallow gravel-bed braided streams. On the basis of the age of the Pleistocene substratum and morphostratigraphic correlation with marine terraces cropping out in the nearby areas, each order has been associated to specific marine oxygen isotope stages. Consequently, we focused on the interplay of allocyclic factors influencing stream aggradation/degradation. Soil features and other climatic proxies suggest that climate didn''t play an important role with respect to tectonic and base-level changes in controlling fluvial dynamics. In particular, we recognised that during the middle Pleistocene the study area experienced a period of subaerial landscape modelling, as suggested by the thick and complex alluvial sequence of the highest terrace (T1). The onset of regional uplift marks a change in the geomorphic scenario, with tectonic and eustatically driven changes in base-level working together in causing switches in fluvial aggradational/erosional phases (T2–T5 terraces). Because of the uplift, river dissection occurred during phases of sea level fall, whereas aggradation phases occurred during periods of climate amelioration (sea level rise) just before highstands were attained. As a consequence, the stepped terraces in the study area reflect the interplay between tectonics (uplift) and sea level changes, in which terraces define episodes of relative sea level fall during the late Quaternary. [Copyright &y& Elsevier]

Tectonic earthquake swarms (TES) often coincide with aseismic slip and sometimes precede damaging earthquakes. In spite of recent progress in understanding the significance and properties of TES at plate boundaries, their mechanics and scaling are still largely uncertain. Here we evaluate several TES that occurred during the past 20 years on a transform plate boundary in North Iceland. We show that the swarms complement each other spatially with later swarms discouraged from fault segments activated by earlier swarms, which suggests efficient strain release and aseismic slip. The fault area illuminated by earthquakes during swarms may be more representative of the total moment release than the cumulative moment of the swarm earthquakes. We use these findings and other published results from a variety of tectonic settings to discuss general scaling properties for TES. The results indicate that the importance of TES in releasing tectonic strain at plate boundaries may have been underestimated. [ABSTRACT FROM AUTHOR]