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Past studies indicate that landscape evolution on various timescales is influenced by vegetation cover. However, the linkages between vegetation, type, and species distribution and erosion processes and their relationships between landscape steepness and climate are not well understood. In this study, we focus on the active tectonic setting of the East-African Rift System and its complex climatic and biotic environment to explore linkages between millennial-scale denudation rates and landscape steepness, climate, and vegetation. We specifically focus on spaceborne vegetation-height and biomass measurements that may better reflect the impact of vegetation on geomorphic processes when compared to generally used vegetation cover measurements. We present 12 new in situ 10Be catchment-averaged denudation rates from the tectonically active Chew Bahir area in southern Ethiopia. The sampled catchments comprise a range of denudation rates over one order of magnitude from 0.01 to 0.1 mm/y and largely correlate with rainfall-weighted landscape steepness. We analyze the rates in comparison to previous studies (a) that evaluated the drier central and northern areas of the Kenya Rift to the south of Chew Bahir and (b) that measured denudation rates in the wetter, densely vegetated Rwenzori mountains in Uganda to the west. Rock-strength values between the sites are comparable, although the Rwenzori mountains have undergone rapid Miocene-Pliocene exhumation processes that may have been aided by ubiquitous fractured bedrock. Importantly, we observe a clear impact of biomass on denudation rates. For example, catchments with the same denudation rate and erosional integration timescale but higher biomass can sustain steeper fluvial channels as indicated by their river-steepness indices. We argue that high vegetation heights characterized by deep root structures lead to a stabilization of hillslopes and ultimately allow the formation of steeper channels. This in turn results in lower denudation rates comparable to less vegetated terrain where hillslopes destabilize more rapidly. We analyze the spatial distribution of hillslopes, river-steepness, rainfall, and vegetation biomass within catchments to elucidate their relative impact. This allows us demonstrate the usefulness of vegetation height and biomass measurements for assessing impacts on erosion rates and we explore different weighting schemes for digital elevation model analysis.

The Cyprus Arc is one of the major sources of earthquakes in the Eastern Mediterranean Region. There is limited large-magnitude earthquake activity during the instrumental period. Still, archeoseismological data imply the occurrence of large-magnitude earthquakes that hit the island and gave rise to casualties and destructions. Nevertheless, these data are insufficient to give information about the source of the earthquakes. In this study, we focussed on coastal geomorphology to unravel paleoseismic activity, at least generated by near offshore faults, that released sufficient seismic energy to deform the shoreline in Holocene.We mapped coseismically uplifted abrasion platforms, tidal notches, fish tanks and a surface rupture implying active near offshore faults in Holocene. The elevation of paleo shorelines varies between 0.4 m to 3 m above sea level, indicating multiple occurrences of paleo earthquakes. Our radiocarbon 14C ages from biological markers (algal rims, etc) indicate that the coseismic uplift of the shoreline starts from 4,5 ka to 1.2 ka BP.The ages of the paleoearthquakes display non-uniform spatial distribution and show migration of paleoearthquakes from west to east, especially along the island's northern coast. This study is supported by Istanbul Technical University Research Fund (Project No: 37548) and Alexander von Humboldt Foundation, Germany.

We deployed a dense geodetic and seismological network in the Atacama seismic gap in Chile. We derive a microseismicity catalog of >30,000 events, time series from 70 GNSS stations, and apply a transdimensional Bayesian inversion to estimate interplate locking degree. We identify two highly locked regions of different sizes whose geometries appear to control seismicity patterns. Interface seismicity concentrates beneath the coastline just downdip of the highest locking. A region of lower interplate locking around 27.5ºS coincides with higher seismicity levels, a high number of repeating earthquakes and events extending further towards the trench. Having shown numerous signs of aseismic deformation (slow-slip events and earthquake swarms), this area is situated where the Copiapó Ridge is subducted. While these findings suggest that the structure of the downgoing oceanic plate prescribes patterns of interplate locking and seismicity, we note that the Taltal Ridge further north lacks a similar signature.

Time-dependent earthquake forecast depends on the frequency and number of past events and time since the last event. Unfortunately, only a few past events are historically documented along subduction zones where forecasting relies mostly on paleoseismic catalogs. We address the role of dating uncertainty and completeness of paleoseismic catalogs on probabilistic estimates of forthcoming earthquakes using a 3.6-ka-long catalog including 11 paleoseismic and 1 historic (Mw≥8.6) earthquakes that preceded the great 1960 Chile earthquake. We set the clock to 1940 and estimate the conditional probability of a future event using five different recurrence models. We find that the Weibull model predicts the highest forecasting probabilities of 44% and 72% in the next 50 and 100 yr, respectively. Uncertainties in earthquake chronologies due to missing events and dating uncertainties may produce changes in forecast probabilities of up to 50%. Our study provides a framework to use paleoseismic records in seismic hazard assessments including epistemic uncertainties.

Cyprus is located right on the plate boundary where the African Plate subducts beneath the Anatolian Microplate. Although subduction zones are earthquake-prone areas, the seismicity of the Cyprus and adjacent areas are not very active during the instrumental period. Nevertheless, archaeological and historical data indicate casualties and destructions within the island because of strong tremors and tsunamigenic waves. None of these data gives information about the source faults of these earthquakes. Are they far-field earthquakes (e.g., AD 365 Crete) or near-field earthquakes that occurred nearshore of the island? We focused on the island’s coast and mapped geomorphological, sedimentological, biological, and archaeological strain markers to answer these questions. Our geomorphological observations reveal the presence of at least three major Holocene abrasion platform levels uplifted coseismically. The presence of biological markers such as reef rims provides a dateable material to quantify these events. We also observed archaeological fish tanks as evidence of coseismic uplift of the shoreline during the historical periods. Radiocarbon 14C dating results indicate a temporal clustering of earthquakes within the 1300-1700 yr BP, 2000-2200 yr BP, and 4500 yr BP, which indicate overlapping of 4th and 6th-century historical earthquakes and also older earthquakes beyond the historical records.

Assessing seismic and tsunami hazards commonly relies on historical accounts of past events, but aside from limitations where such chronicles are too short to account for variability in earthquake size, rupture style, tsunamigenesis and the existence of supercycles, even where long written histories exist, records may be biased by temporal gaps due to historical circumstances. We demonstrate that this is the case for the area affected by the magnitude 9.5 1960 Chile earthquake. Historical records document four great earthquakes (M8+) in the last 450 years in this region, but while devastating tsunamis are known to have accompanied earthquakes in 1575, 1837 and 1960 CE, there is no such record of inundation in 1737. The lack of reports of tsunami inundation from the 1737 south-central Chile earthquake has been attributed to either civil unrest or a small tsunami due to deep fault slip below land. Here we cross-check the historical record using a coastal sedimentary record from Chaihuín, a tidal marsh 15 km southwest of Valdivia, close to the region of maximum 1960 slip. Tidal marshes are low energy intertidal settings that may preserve evidence for abrupt co-seismic changes in land level and inundation by extreme waves. We conduct sedimentological and diatom analyses of tidal marsh sediments within the 1737 rupture area and find evidence for a locally-sourced tsunami consistent in age with this event. The evidence is a laterally-extensive sand sheet coincident with abrupt, decametric-scale subsidence. Coupled dislocation-tsunami models place the causative fault slip mostly offshore rather than below land, as had previously been assumed from the absence of historical accounts of a tsunami. Whether associated or not with the 1737 earthquake, our findings reduce the average recurrence interval of tsunami inundation derived from historical records alone, highlighting the importance of combining geological and historical records in order to obtain robust long-term patterns to inform seismic and tsunami hazard assessment.

The tectonically active western coast of South America is characterized by the accumulation of deformation that contributes to permanent uplift of the Andean forearc at glacial-cycle timescales. However, the individual mechanisms responsible for long-term coastal uplift are still debated, mostly because analyses at continental-scale have not been carried out as yet. In coastal realms, permanent deformation is often estimated from marine terraces, which depict the interplay between wave erosion, tectonic uplift, and sea-level changes. Based on ~2000 elevation measurements of last interglacial marine terraces, we performed wavelength analyses using fast Fourier transforms. We compared the resulting uplift-rate signal with various tectonic processes and subduction parameters associated with the accumulation of permanent deformation. We detected a constant background signal of uplift along the South American margin (median rate: 0.22 mm/yr), which is disturbed by short-, intermediate- and long-wavelength changes between ~20 and ~800 km wavelengths, with the most prominent wavelengths at scales of ~500 km. Similarities between the wavelength spectra of uplift rate and signals from tectonic parameters suggest potential correlations, although multiple individual mechanisms usually contribute to a larger wavelength peak or to a certain range of wavelengths. For instance, crustal faulting is responsible for short-wavelength deformation (W>7.5) mostly cover wavelength ranges from ~100 to 200 km, despite reaching wavelengths over 600 km as well. The subduction of bathymetric anomalies and the extent of interseismic locking correlate with intermediate wavelengths (~200 to ~500 km), whereas residual gravity anomalies, basal friction, and background seismicity correlate with long-wavelength deformation (>500 km). We suggest that the constant background signal of uplift rate results from two possible mechanisms: (a) a combination of multiple processes acting at different wavelengths, times and locations over millennial timescales or (b) a single unidentified process acting homogeneously along the western South American margin. With this study, we highlight the application of novel signal analysis approaches to elucidate the mechanisms driving surface deformation in subduction zones on different spatial and temporal scales.

It is typically assumed that the relative plate motions are not affected by temporal stress changes occurring during the seismic cycle, which comprises a phase of slow buildup of stress (interseismic phase) followed by a phase of sudden release of stress accompanied by rapid fault slip (coseismic phase). However, small- to medium-sized tectonic plates experience a reduced viscous resistance at their base, making the torques necessary to change their motions comparable to those generated by large earthquakes.Here we explore whether the motions of medium-size tectonic plates experience temporal variations associated with earthquake-cycle stresses. In particular, we focus on the kinematics of the Nazca plate (NZ) in relation to the most recent Mw>8 megathrust earthquakes occurring across the Chilean trench (e.g., 2010 Maule and 2015 Illapel earthquakes). We utilise available GNSS time series to explore links between the recent (i.e., past two decades) plate kinematics and the seismic cycle of megathrust earthquakes occurring along the Chilean subduction zone. Our approach differs from classical studies on the earthquake-cycle induced deformation of the plate boundary region in that it focuses on the potential impact of large earthquakes onto rigid whole-plate kinematics.

The tsunami associated with the giant 9.5 M-w 1960 Chile earthquake deposited an extensive sand layer above organic-rich soils near Queule (39.3 degrees S, 73.2 degrees W), south-central Chile. Using the 1960 tsunami deposits, together with eye-witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960-4520 and 5930-5740 cal BP. This >4500-year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south-central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea-level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past >4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment. Puget Sound Energy Graduate Fellowship at Central Washington University; Earthquake Hazards Program of the U.S. Geological Survey; Chilean National Fund for Development of Science and Technology (FONDECYT)Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)CONICYT FONDECYT [1190258, 1181479]; Millennium Scientific Initiative (ICM) of the Chilean government [NC160025]; National Science Foundation (NSF)National Science Foundation (NSF)National Research Foundation of Korea [EAR-1624533, EAR-1624542]; ANID PIA Anillo [ACT192169] Published version Puget Sound Energy Graduate Fellowship at Central Washington University; Earthquake Hazards Program of the U.S. Geological Survey; Chilean National Fund for Development of Science and Technology (FONDECYT), Grant/Award Numbers: 1190258, 1181479; Millennium Scientific Initiative (ICM) of the Chilean government, Grant/Award Number: NC160025; National Science Foundation (NSF), Grant/Award Numbers: EAR-1624533, EAR-1624542; ANID PIA Anillo, Grant/Award Number: ACT192169 Public domain – authored by a U.S. government employee

We present evidence of land-level change resulting from the 2016 Mw 7.6 Chiloe earthquake from tidal wetlands along the southern coastline of Isla de Chiloe, Chile, to test criteria for the detection of low-level

The structural evolution of calderas in rifts helps to characterize the spatiotemporal relationships between magmatism, long wavelength crustal deformation and the formation of tectonic deformation zones along the rift axis. We document the structural characteristics of the c. 36 ka old Menengai Caldera located within a young zone of extension in the central Kenya Rift. Field mapping and high-resolution digital surface models show that NNE-striking Holocene normal faults perpendicular to the regional ESE–WNW extension direction dominate the interior sectors of the rift. Inside the caldera, these structures are overprinted by post-collapse doming and faulting of the magmatic centre, resulting in obliquely slipping normal faults bounding a resurgence horst. Radiocarbon dating of faulted units as young as 5 ka cal BP and the palaeo-shorelines of a lake formed during the African Humid Period in the Nakuru Basin indicate that volcanism and fault activity inside and in the vicinity of Menengai must have been sustained during the Holocene. Our analysis confirms that the caldera is located at the centre of an extending rift segment and suggests that other magmatic centres and young zones of faulting along the volcano-tectonic axis of the Kenya Rift may constitute nucleation points of faulting that ultimately foster future continental break-up. Supplementary material:40Ar/39Ar radiometric dating data table is available at: https://doi.org/10.6084/m9.figshare.c.4647818

Subaqueous landslides are common features at active and passive ocean margins, in fjords and lakes. They can develop on very gentle slope gradients (

The compound hazard effects of multiple process cascades severely affect Chilean river systems and result in a large variety of disturbances on their ecosystems and alterations of their hydromorphologic regimes leading to extreme impacts on society, environment and infrastructure. The acute, neo-tectonically pre-determined susceptibility to seismic hazards, the widespread volcanic activity, the increasing glacier retreat and the continuous exposure to forest fires clearly disturb entire riverine systems and concur to trigger severe floods hazards. With the objective to refine the understanding of such cascading processes and to prospect feasible flood risk management strategies in such a rapidly changing environment we first classify the large river basins according to a set of disturbances (i.e. volcanic eruptions, earthquakes, glacier lake outburst floods, wild fires and mass movements). Then, we describe emblematic cases of process cascades which affected specific Chilean drainage basins and resulted in high losses as tangible examples of how the cascading processes may unfold in other river basins with similar characteristics. As an attempt to enrich the debate among management authorities and academia in Chile, and elsewhere, on how to sustainably manage river systems, we: a) highlight the pivotal need to determine the possible process cascades that may profoundly alter the system and b) we suggest to refine hazard and risk assessments accordingly, accounting for the current and future exposure. We advocate, finally, for the adoption of holistic approaches promoting anticipatory adaptation which may result in resilient system responses.

Tectonically active coasts are dynamic environments characterized by the presence of multiple marine terraces formed by the combined effects of wave-erosion, tectonic uplift, and sea-level oscillations at glacial-cycle timescales. Well-preserved erosional terraces from the last interglacial sea-level highstand are ideal marker horizons for reconstructing past sea-level positions and calculating vertical displacement rates, which can be subsequently compared to short-term coastal deformation patterns associated with the earthquake cycle. We carried out an almost continuous mapping of the last interglacial marine terrace along ~5,000 km of the western coast of South America between 1°N and 40°S. We used quantitatively replicable approaches constrained by published terrace-age estimates to ultimately compare elevations and patterns of uplifted terraces with tectonic and climatic parameters in order to evaluate the controlling mechanisms for the formation and preservation of marine terraces, and crustal deformation. Uncertainties were estimated on the basis of measurement errors and the distance from referencing points. Overall, our results indicate a median elevation of 30.1 m, which would imply a median uplift rate of 0.22 m/ka averaged over the past ~125 ka. The patterns of terrace elevation and uplift rate display high-amplitude (~100–200 m) and long-wavelength (~102 km) structures at the Manta Peninsula (Ecuador), the San Juan de Marcona area (central Peru), and the Arauco Peninsula (south-central Chile). Medium-wavelength structures occur at the Mejillones Peninsula and Topocalma in Chile, while short-wavelength (< 10 km) features are for instance located near Los Vilos, Valparaíso, and Carranza, Chile. We interpret the long-wavelength deformation to be controlled by deep-seated processes at the plate interface such as the subduction of major bathymetric anomalies like the Nazca and Carnegie ridges. In contrast, short-wavelength deformation may be primarily controlled by sources in the upper plate such as crustal faulting, which, however, may also be associated with the subduction of topographically less pronounced bathymetric anomalies and varying distances to the trench. Latitudinal differences in climate additionally control the formation and preservation of marine terraces. Based on our synopsis we propose that increasing wave height and tidal range result in enhanced erosion and morphologically well-defined marine terraces in south-central Chile. Conversely, river incision and lateral scouring in areas with high precipitation may degrade marine terraces. Our study emphasizes the importance of using systematic measurements and uniform, quantitative methodologies to characterize and correctly interpret marine terraces at regional scales, especially if they are used to unravel tectonic and climatic forcing mechanisms of their formation.

Tectonically active coasts are dynamic environments characterized by the presence of multiple marine terraces formed by the combined effects of wave erosion, tectonic uplift, and sea-level oscillations at glacial-cycle timescales. Well-preserved erosional terraces from the last interglacial sea-level highstand are ideal marker horizons for reconstructing past sea-level positions and calculating vertical displacement rates. We carried out an almost continuous mapping of the last interglacial marine terrace along ∼ 5000 km of the western coast of South America between 1∘ N and 40∘ S. We used quantitatively replicable approaches constrained by published terrace-age estimates to ultimately compare elevations and patterns of uplifted terraces with tectonic and climatic parameters in order to evaluate the controlling mechanisms for the formation and preservation of marine terraces and crustal deformation. Uncertainties were estimated on the basis of measurement errors and the distance from referencing points. Overall, our results indicate a median elevation of 30.1 m, which would imply a median uplift rate of 0.22 m kyr−1 averaged over the past ∼ 125 kyr. The patterns of terrace elevation and uplift rate display high-amplitude (∼ 100–200 m) and long-wavelength (∼ 102 km) structures at the Manta Peninsula (Ecuador), the San Juan de Marcona area (central Peru), and the Arauco Peninsula (south-central Chile). Medium-wavelength structures occur at the Mejillones Peninsula and Topocalma in Chile, while short-wavelength (

The southern margin of the Central Anatolian Plateau (CAP) records a strong uplift phase after the early Middle Pleistocene, which has been related to the slab break‐off of the subducting Arabian plate beneath the Anatolian microplate. During the last 450 kyr the area underwent an uplift phase at a mean rate of ~3.2 m/kyr, as suggested by Middle Pleistocene marine sediments exposed at ~1,500 m above sea level. These values are significantly higher than the 1.0–1.5 m/kyr estimated since the Late Pleistocene, suggesting temporal variations in uplift rate. To estimate changes in uplift rate during the Pleistocene we studied the marine terraces along the CAP southern margin, mapping the remnants of the platforms and their associated deposits in the field, and used the TerraceM software to identify the position and elevation of associated shoreline angles. We used shoreline angles and the timing of Quaternary marine sedimentation as constrains for a Landscape Evolution Model that simulates wave erosion of an uplifting coast. We applied random optimization algorithms and minimization statistics to find the input parameters that better reproduce the morphology of CAP marine terraces. The best‐fitting uplift rate history suggests a significative increase from 1.9 to 3.5 m/kyr between 500 and 200 kyr, followed by an abrupt decrease to 1.4 m/kyr until the present. Our results agree with slab break‐off models, which suggest a strong uplift pulse during slab rupture followed by a smoother decrease., Key Points: The marine terrace evolution modeling allowed the reconstruction of the Quaternary uplift trend. The uplift trend describes a bell‐shaped path in the last 500 kyr, with a peak in uplift rates at MIS7 (3.4–3.8 m/kyr). Results are in agreement with numerical models that relate strong uplift pulses to slab break‐off., MIUR‐Italy Dipartimenti di Eccellenza, Millennium Scientific Initiative (ICM), DEUTSCHES GEOFORSCHUNGSZENTRUM POTSDAM Blended DEAL

In seismically-active regions, mapping capable faults and estimating their recurrence time is the first step to assess seismic hazards. Fault maps are commonly based on geologic and geomorphic features evident at the surface; however, mapping blind faults and estimating their seismic potential is challenging because on-fault diagnostic features are absent. Here, we study the Pichilemu Fault in coastal Chile, unknown until it generated a M7.0 earthquake in 2010. The lack of evident surface faulting suggests a partly-hidden blind fault. Using off-fault deformed marine terraces, we estimate a slip-rate of 0.42 ± 0.04 m/ka, which when integrated with deformation estimated from satellite geodesy during the 2010 earthquake suggests a 2.5 ± 0.25 ka recurrence time for M6.6-6.9 extensional earthquakes. We propose that extension is associated with stress changes during megathrust earthquakes and accommodated by sporadic slip during upper-plate earthquakes. Our results have implications for assessing the seismic potential of cryptic faults along seismically-active coasts.

Great subduction earthquakes rupture similar regions of the megathrust during successive events separated by centuries. Mapping these regions (asperities) and their boundaries (barriers) is importa...

We present a comprehensive relative sea-level (RSL) database for north, central, and south-central Chile (18.5 degrees S - 43.6 degrees S) using a consistent, systematic, and internationally comparable approach. Despite its latitudinal extent, this coastline has received little rigorous or systematic attention and details of its RSL history remain largely unexplored. To address this knowledge gap, we re-evaluate the geological context and age of previously published sea-level indicators, providing 78 index points and 84 marine or terrestrial limiting points spanning from 11 ka to the present day. Many data points were originally collected for research in other fields and have not previously been examined for the information they provide on sea-level change. Additionally, we describe new sea-level data from four sites located between the Gulf of Arauco and Valdivia. By compiling RSL histories for 11 different regions, we summarise current knowledge of Chilean RSL. These histories indicate mid Holocene sea levels above present in all regions, but at highly contrasting elevations from similar to 30 m to

High-resolution records of lake-level changes are crucial to elucidate the impact of local and global climatic changes in lacustrine basins. The Late Quaternary evolution of the Dead Sea has been characterized by substantial variability apparently linked with global climatic changes, beign subject of many research efforts since decades. Previous studies have defined two main lake phases, the Lake Lisan and the Dead Sea, the earlier was a highstand period that lasted between ~70 and ~15 ka, the latter was the lowstand period that persisted until the present. Here we focus on the switch between Lake Lisan and Dead Sea studying fossil lake shorelines, a sequence that comprises dozens of levels exposed along the rims of the Dead Sea, containing abundant fossil stromatolites that we dated by mean of radiocarbon and U-decay series. We determined 90 radiocarbon and 35 U-Th ages from stromatolites from almost every shoreline level. We compared U-Th and radiocarbon ages to estimating a radiocarbon reservoir between 0.2 and 0.8 ka, used to correct the remaining radiocarbon ages before calibration. The resulting ages range between ~45 and ~20 ka. Dating was complemented with analysis of stable oxygen and carbon isotopes. Furthermore, we applied a distributed hydrological balance model to constrain past precipitation and temperature conditions. Our results suggest that the duration of the last Lake Lisan highstand was shorter than previously estimated. Taking this at face value, the switch between Lake Lisan and Dead Sea occurred at ~28 ka, ~10 ka earlier than previously suggested. Oxygen and carbon isotopes show a consistent pattern, displaying a switch between wet and dry conditions at ~28 ka. Preliminary results from the hydrological model indicate a much stronger sensitivity of the lake level to precipitation amounts than to air temperature. From our results we can’t observe a clear link between global temperature variations and lake-level changes in the Lisan/Dead Sea lakes. Similar non-linear response to northern hemisphere climatic changes have been also documented in Holocene Dead Sea paleoclimatic records, suggesting that global climatic variations may led to variable lake-level responses. The results of this study adds further complexity to the understanding of factors controlling climate variability in the Dead Sea.

In magmatically active continental rifts, crustal deformation is often accompanied by caldera volcanism along the rift axis. These caldera volcanoes help to characterize the spatiotemporal relationship between regional tectonic extension, the development of normal faults, and the role of magmatism during the long-term evolution of continental rifts. In the Kenya Rift, magmatic activity has been focused at regularly spaced Quaternary volcanoes, each located within an extensional sub-basin of the rift. We document the structural characteristics of the c. 36-ka-old Menengai Caldera and adjacent regions located within such a young zone of extension, to gain insight into the role of regional-scale structures and volcanism in a rift zone subjected to oblique extension, and discuss the role of magmatic centers in the context of advanced stages of rift-basin differentiation.Our field mapping and high-resolution digital surface models in the greater Menengai area located in the Central Kenya Rift show that the interior rift sectors are dominated by NNE-striking Holocene normal faults perpendicular to the regional ESE-WNW extension direction. Inside the caldera, these structures continue, but are overprinted by post-collapse doming and faulting of the magmatic center, resulting in obliquely slipping normal faults bounding a resurgence horst. Radiocarbon dating of faulted units as young as 5 ka cal BP and the paleo-shorelines of a lake formed during the African Humid Period in the Nakuru Basin that we use as strain markers indicate that volcanism and faulting inside and in the vicinity of Menengai must have been sustained during the Holocene.Our analysis confirms that the caldera is located at the center of an extending rift segment that is kinematically linked with adjacent zones of extension; similar volcano-tectonic relationships apply to virtually all larger volcanic centers in the Kenya Rift. These zones of extension in the inner sectors of the rift are arranged in en échelon patterns and are linked by transfer zones. In contrast to punctiform spreading centers in much more advanced extensional regions (e.g., the Red Sea) normal faulting in the Kenya Rift is not focused at these volcanic centers. We suggest that the magmatic centers in the segmented Kenya Rift are precursors of a more evolved rifting stage, where magmatic centers may constitute nucleation points of faulting in future magma-assisted rifting that will ultimately lead to the final stages of continental break-up.

Most of the seismic hazard along subduction zones is posed by great tsunamigenic earthquakes associated with the interplate megathrust fault. However, crustal faults are ubiquitous along overriding continental plates, some of which have been triggered during recent megathrust earthquakes. In Chile, the 2010 Maule earthquake (M8.8) triggered a shallow M7 earthquake on the Pichilemu fault, which had not been mapped and was unknown. In fact, M~7 earthquakes have recently occurred along unknown faults in California and New Zealand, emphasizing the need for better and more detailed mapping initiatives. A first step towards a synoptic assessment of seismic hazards posed by continental faults at the national level is mapping at a homogeneous scale to allow for a systematic comparison of faults and fault systems. Here, we present the first map of active and potentially-active faults in Chile at 1:25,000 scale, which includes published studies and newly-identified faults. All the published faults have been re-mapped using LiDAR and TanDEM-X topography, where available. Using different scaling relations, we estimate the seismic potential of all crustal faults in Chile. For specific faults where we have conducted paleoseismic and tectonic geomorphic field studies (e.g., Liquiñe-Ofqui, El Yolki, Mesamavida, and Pichilemu faults) we provide new estimates of slip rate, recurrence interval, and deformation style. We propose a segmentation model of continental faults systems in Chile, which are associated with distinct morphotectonic units and have predominant kinematics and relatively uniform slip rates. Using stress transfer models, we explore the potential feedbacks between upper-plate deformation and the megathrust seismic cycle.

Abstract:Giant subduction earthquakes (MW 8 to 9) are usually characterized by heterogeneous slip distributions, including regions of very pronounced slip that are commonly known as asperities. However, it is a matter of ongoing debate whether asperities constitute persistent geologic features or if they rather represent transient features related to the release of elastic strain accumulated in areas of seismic gaps. Recent giant earthquakes along the coast of north-central Chile, such as the 2010 Maule (M8.8), 2015 Illapel (M8.3), and 2014 Iquique (M8.2) events, were all associated with the rupture of single or multiple seismic asperities. Here we compare permanent deformation and seismic-cycle deformation patterns and rates along the 2015 Illapel earthquake rupture zone (~30° to 32°S) spanning orbital to decadal time scales. To decipher permanent deformation features manifested in the upper plate of the subduction system we identified and correlated the elevations of Late Pleistocene marine terraces using TanDEM-X digital topography and previously published terrace ages. We focused on terraces related to the Marine Isotope Stages (MIS) 5 and 9 (~124 ka and ~320 ka) due to their excellent preservation and lateral continuity. We furthermore compared deformation rates based on these uplifted terraces and compared them with published co-seismic slip and interseismic locking models of the Illapel earthquake. Uplift rates derived from the MIS-5 marine terraces range between 0.08 and 0.35 m/ka, while uplift rates based on MIS-9 terraces range between 0.38 to 0.96 m/ka. The higher uplift rates are found at the northern part of the Illapel rupture and these areas correlate to crustal structures (e.g. Puerto Aldea Fault). We observed a direct correlation between MIS-5 and MIS-9 uplift rates and co-seismic slip in the northern parts of the rupture while there was no clear correlation in the south at the central and southern parts of the rupture zone. The comparison between the spatial distribution of locked areas and uplift rates provided only a weak correlation for the MIS-9 terraces at the southern part of the rupture. Our results suggest that the northern part of the IIIapel rupture zone may accumulate permanent deformation during megathrust earthquakes. In contrast, accumulation of deformation at the southern part of the rupture may be controlled by activity in the neighboring seismotectonic segment. Broad warping patterns of marine terraces might reflect changes in boundary conditions at interplate depths, such as subduction of seamounts or other oceanic bathymetric features. This analysis highlights the temporal and spatial variability of deformation at convergent plate margins over multiple time scales.

Megathrust earthquakes at subduction zones are one of the most devastating natural phenomena. Understanding the relationships between their temporal recurrence, spatial segmentation and the frictional structure of the megathrust is of primary relevance. We analyzed the common spatial variability of gravity anomalies, geodetic locking and wedge taper basal friction (three independent proxies for megathrust frictional structure) along the Chilean margin. A marked along-strike segmentation has emerged that is organized into three hierarchical levels. At a subcontinental-scale (103 km), we observe a first-order difference between Central (18-32°S) and Southern (32°-46°S) Andes. This is marked by a dominance of positive/negative gravity, high/low locking, high/low friction along the Central/Southern segments. We explain this as mainly reflecting the combined effect on effective normal stress (σeff) of a high/low density forearc and low/high pore pressure along both megathrust segments, in agreement with the geological structure of the forearc, sediment input at the trench and the long-term architecture of the Andes. Inside this large-scale subdivision, we identify a number of segments (102 km) that are limited by marked small-scale (101 km) changes in the first-order tendency of the three proxies coinciding with geological features of both plates. When we compare this against the paleoseismic, historic and instrumental record of past earthquakes in Chile, we note that segments largely coincide with seismic asperities, i.e. those regions of the megathrust concentrating the largest fraction of coseismic slip. Bridging these two scales, the rupture length of giant (Mw 8.5-9.5) earthquakes, which encompassed several asperities, define an intermediate hierarchic level of organization (102-103 km). Considering this segmentation into the conceptual framework of the rate-and-state friction (RSF) law, we infer that asperities inside the rate-weakening seismogenic zone of the Central Andean megathrust are dominantly unstable (i.e. σeff>σc = the critical stress defined by RSF parameters) and therefore prone to initiate and concentrate the coseismic rupture. In contrast, most of the asperities along the Southern mega-segment are likely characterized by a conditionally-stable behavior (σeffc) that allows a rich and complex seismogenic behavior where interseismic creep and locking are both possible and large coseismic slip propagation is dominant. This can explain the apparent difference in the recurrence of giant earthquakes along both mega-segments, since the synchronization of unstable asperities in the Central Andean megathrust (2000-3000 yr recurrence time) is less probable than in the case of conditionally-stable asperities in the Southern segment (300-500 yrs). We will test these hypothesis developing numerical simulations of multiple seismic cycles with setups representing the inferred contrast on the physical properties of the megathrust along the Chilean margin, and we will present preliminary results of this exercise.

In active tectonic settings dominated by strike-slip kinematics, slip partitioning across subparallel faults is a common feature; therefore, assessing the degree of partitioning and strain localization is paramount for seismic hazard assessments. Here, we estimate a slip rate of 18.8 ± 2.0 mm/year over the past 9.0 ± 0.1 ka for a single strand of the Liquiñe-Ofqui Fault System, which straddles the Main Cordillera in Southern Chile. This Holocene rate accounts for ~ 82% of the trench-parallel component of oblique plate convergence and is similar to million-year estimates integrated over the entire fault system. Our results imply that strain localizes on a single fault at millennial time scale but over longer time scales strain localization is not sustained. The fast millennial slip rate in the absence of historical Mw > 6.5 earthquakes along the Liquiñe-Ofqui Fault System implies either a component of aseismic slip or Mw ~ 7 earthquakes involving multi-trace ruptures and > 150-year repeat times. Our results have implications for the understanding of strike-slip fault system dynamics within volcanic arcs and seismic hazard assessments.

(IF 4.64 [2018]; Q1); International audience; Sequences of uplifted marine terraces are widespread and reflect the interaction between climatic and tectonic processes at multiple scales, yet their analysis is typically biased by the chosen sea-level (SL) curve. Here we explore the influence of Quaternary SL curves on the geometry of marine terrace sequences using landscape evolution models (LEMs). First, we modeled the young, rapidly uplifting sequence at Xylokastro (Corinth Rift

In 2004 migration and mortality for unknown reasons of the herbivorous Black necked swan (Cygnus melancorhyphus (Molina, 1782)) occurred within the Río Cruces wetland (southern Chile), a Ramsar Site and nature sanctuary. Before 2004, this wetland hosted the largest breeding population of this water bird in the Neotropic Realm. The concurrent decrease in the spatial occurrence of the aquatic plant Egeria densa Planch. 1849 - the main food source of swans - was proposed as a cause for swan migration and mortality. Additionally, post-mortem analyses carried out on swans during 2004 showed diminished body weight, high iron loads and histopathological abnormalities in their livers, suggesting iron storage disease. Various hypotheses were postulated to describe those changes; the most plausible related to variations in water quality after a pulp mill located upstream the wetland started to operate in February 2004. Those changes cascaded throughout the stands of E. densa whose remnants had high iron contents in their tissues. Here we present results of a long-term monitoring program of the wetland components, which show that swan population abundance, body weights and histological liver conditions recovered to pre-disturbance levels in 2012. The recovery of E. densa and iron content in plants throughout the wetland, also returned to pre-disturbance levels in the same 8-year time period. These results show the temporal scale over which resilience and natural restoring processes occur in wetland ecosystems of temperate regions such as southern Chile.

Fundamental processes of the seismic cycle in subduction zones, including those controlling the recurrence and size of great earthquakes, are still poorly understood. Here, by studying the 2016 earthquake in southern Chile—the first large event within the rupture zone of the 1960 earthquake (moment magnitude (Mw) = 9.5)—we show that the frictional zonation of the plate interface fault at depth mechanically controls the timing of more frequent, moderate-size deep events (Mw 8.5). We model the evolution of stress build-up for a seismogenic zone with heterogeneous friction to examine the link between the 2016 and 1960 earthquakes. Our results suggest that the deeper segments of the seismogenic megathrust are weaker and interseismically loaded by a more strongly coupled, shallower asperity. Deeper segments fail earlier (~60 yr recurrence), producing moderate-size events that precede the failure of the shallower region, which fails in a great earthquake (recurrence >110 yr). We interpret the contrasting frictional strength and lag time between deeper and shallower earthquakes to be controlled by variations in pore fluid pressure. Our integrated analysis strengthens understanding of the mechanics and timing of great megathrust earthquakes, and therefore could aid in the seismic hazard assessment of other subduction zones. The recurrence time of megathrust earthquakes in Chile may be controlled by frictional contrasts at depth, according to analyses of stress build-up and release related to the December 2016 southern Chile earthquake.