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Large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water-limited environments. We examine growth and photosynthetic responses of Pine plantations to the Maule M-w 8.8 earthquake in headwater catchments of Chile's Coastal Range. We combine high-resolution wood anatomic (lumen area) and biogeochemical (delta 13C of wood cellulose) proxies of daily to weekly tree growth sampled from trees on floodplains and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree trees on valley floors had increased lumen area and decreased delta 13C, while trees on hillslopes had a reverse trend. Our results indicate a control of soil water on this response, largely consistent with models that predict how enhanced postseismic vertical soil permeability causes groundwater levels to rise on valley floors, but fall along the ridges. Statistical analysis with boosted regression trees indicates that streamflow discharge gained predictive importance for photosynthetic activity on the ridges, but lost importance on the valley floor after the earthquake. We infer that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short-lived signals that we identified, however, show that such responses are only valid under water-limited, rather than energy-limited tree, growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality.
Seafloor spreading at slow rates can be accommodated on large-offset oceanic detachment faults (ODFs), that exhume lower crustal and mantle rocks in footwall domes termed oceanic core complexes (OCCs). Footwall rocks experience large rotation during exhumation, yet important aspects of the kinematics-particularly the relative roles of solid-block rotation and flexure-are not clearly understood. Using a high-resolution numerical model, we explore the exhumation kinematics in the footwall beneath an emergent ODF/OCC. A key feature of the models is that footwall motion is dominated by solid-block rotation, accommodated by the nonplanar, concave-down fault interface. A consequence is that curvature measured along the ODF is representative of a neutral stress configuration, rather than a "bent" one. Instead, it is in the subsequent process of "apparent unbending" that significant flexural stresses are developed in the model footwall. The brittle strain associated with apparent unbending is produced dominantly in extension, beneath the OCC, consistent with earthquake clustering observed in the Trans-Atlantic Geotraverse at the Mid-Atlantic Ridge.
The wetland cover is defined as the spatially homogenous region of a wetland attributed to the underlying biophysical conditions such as vegetation, turbidity, hydric soil, and the amount of water.
Here, we present a novel method to derive the wetland-cover types (WCTs) combining three commonly used multispectral indices, NDVI, MNDWI, and NDTI, in three large Ramsar wetlands located in different geomorphic and climatic settings across India. These wetlands include the Kaabar Tal, a floodplain wetland in east Ganga Plains, Chilika Lagoon, a coastal wetland in eastern India, and Nal Sarovar in semi-arid western India.
The novelty of our approach is that the derived WCTs are stable in space and time, and therefore, a given WCT across different wetlands or within different zones of a large wetland will imply similar underlying biophysical attributes.
The WCTs can therefore provide a novel tool for monitoring and change detection of wetland cover types.
We have automated the proposed WCT algorithm using the Google Earth Engine (GEE) environment and by developing ArcGIS tools. The method can be implemented on any wetland and using any multispectral imagery dataset with visible and NIR bands.
The proposed methodology is simple yet robust and easy to implement and, therefore, holds significant importance in wetland monitoring and management.
The Alpine mountains in central Europe are characterized by a heterogeneous crust accumulating different tectonic units and blocks in close proximity to sedimentary foreland basins. Centroid moment tensor inversion provides insight into the faulting mechanisms of earthquakes and related tectonic processes but is significantly aggravated in such an environment. Thanks to the dense AlpArray seismic network and our flexible bootstrap-based inversion tool Grond, we are able to test different setups with respect to the uncertainties of the obtained moment tensors and centroid locations. We evaluate the influence of frequency bands, azimuthal gaps, input data types, and distance ranges and study the occurrence and reliability of non-double-couple (DC) components. We infer that for most earthquakes (M-w >= 3.3) a combination of time domain full waveforms and frequency domain amplitude spectra in a frequency band of 0.02-0.07 Hz is suitable. Relying on the results of our methodological tests, we perform deviatoric moment tensor (MT) inversions for events with M-w > 3.0. Here, we present 75 solutions for earthquakes between January 2016 and December 2019 and analyze our results in the seismotectonic context of historical earthquakes, seismic activity of the last 3 decades, and GNSS deformation data. We study regions of comparably high seismic activity during the last decades, namely the Western Alps, the region around Lake Garda, and the eastern Southern Alps, as well as clusters further from the study region, i.e., in the northern Dinarides and the Apennines. Seismicity is particularly low in the Eastern Alps and in parts of the Central Alps. We apply a clustering algorithm to focal mechanisms, considering additional mechanisms from existing catalogs. Related to the N-S compressional regime, E-W-to-ENE-WSW-striking thrust faulting is mainly observed in the Friuli area in the eastern Southern Alps. Strike-slip faulting with a similarly oriented pressure axis is observed along the northern margin of the Central Alps and in the northern Dinarides. NW-SE-striking normal faulting is observed in the NW Alps, showing a similar strike direction to normal faulting earthquakes in the Apennines. Both our centroid depths and hypocentral depths in existing catalogs indicate that Alpine seismicity is predominantly very shallow; about 80% of the studied events have depths shallower than 10 km.
The magnitude of earthquakes on continental normal faults rarely exceeds 7.0 Mw. However, because of their vicinity to large population centers they can be highly destructive.
Long recurrence time, relatively small deformations, and limited observations hinder our understanding of the deformation patterns and mechanisms controlling the magnitude of events.
Here, this problem is addressed with 2D thermomechanical modeling of normal fault seismic cycles.
The 2020 Samos, Greece Mw7.0 earthquake is used as an example as it is one of the largest and most studied continental normal fault earthquakes. The modeling approach employs visco-elasto-plastic rheology, compressibility, free surface, and a rate-and-state friction law for the fault.
Modeling of the Samos earthquake suggests the pore fluid pressure ratio on the fault ranges from 0 to 0.7. The model demonstrates that most of the deformation during interseismic and coseismic periods, besides on the fault, occurs in the hanging wall and footwall below the seismogenic part of the fault. The largest vertical surface displacement during the earthquake is the subsidence of the hanging wall in the vicinity of the fault, while the uplift of the footwall and remote part of the hanging wall is significantly smaller.
Modeling of the seismic cycles on normal faults with different setups shows the dependency of the magnitude on the thermal profile and dipping angle of the fault; low heat flow and low dipping angle are favorable conditions for the largest events, while steep normal faults in the areas of high heat flow tend to have the smallest magnitudes.
In a warming Arctic, permafrost-related disturbances, such as retrogressive thaw slumps (RTS), are becoming more abundant and dynamic, with serious implications for permafrost stability and bio-geochemical cycles on local to regional scales. Despite recent advances in the field of earth observation, many of these have remained undetected as RTS are highly dynamic, small, and scattered across the remote permafrost region. Here, we assessed the potential strengths and limitations of using deep learning for the automatic segmentation of RTS using PlanetScope satellite imagery, ArcticDEM and auxiliary datasets. We analyzed the transferability and potential for pan-Arctic upscaling and regional cross-validation, with independent training and validation regions, in six different thaw slump-affected regions in Canada and Russia. We further tested state-of-the-art model architectures (UNet, UNet++, DeepLabv3) and encoder networks to find optimal model configurations for potential upscaling to continental scales. The best deep learning models achieved mixed results from good to very good agreement in four of the six regions (maxIoU: 0.39 to 0.58; Lena River, Horton Delta, Herschel Island, Kolguev Island), while they failed in two regions (Banks Island, Tuktoyaktuk). Of the tested architectures, UNet++ performed the best. The large variance in regional performance highlights the requirement for a sufficient quantity, quality and spatial variability in the training data used for segmenting RTS across diverse permafrost landscapes, in varying environmental conditions. With our highly automated and configurable workflow, we see great potential for the transfer to active RTS clusters (e.g., Peel Plateau) and upscaling to much larger regions.
The formation of the Central Andes dates back to similar to 50 Ma, but its most pronounced episode, including the growth of the Altiplano-Puna Plateau and pulsatile tectonic shortening phases, occurred within the last 25 Ma.
The reason for this evolution remains unexplained. Using geodynamic numerical modeling we infer that the primary cause of the pulses of tectonic shortening and growth of the Central Andes is the changing geometry of the subducted Nazca plate, and particularly the steepening of the mid-mantle slab segment which results in a slowing down of the trench retreat and subsequent increase in shortening of the advancing South America plate.
This steepening first happens after the end of the flat slab episode at similar to 25 Ma, and later during the buckling and stagnation of the slab in the mantle transition zone. Processes that mechanically weaken the lithosphere of the South America plate, as suggested in previous studies, enhance the intensity of the shortening events.
These processes include delamination of the mantle lithosphere and weakening of foreland sediments.
Our new modeling results are consistent with the timing and amplitude of the deformation from geological data in the Central Andes at the Altiplano latitude.
Plain Language Summary
The Central Andes is a subduction-type orogeny that formed as a result of the interaction between the Nazca oceanic plate and the South American continental plate over the last 50 million years. Growth of the Andes is primarily the result of crustal shortening. Nevertheless, "geological" data compiled from previous studies have shown that phases of drastic pulsatile shortening occur at 15 and 5 Ma.
In this study, we used high-resolution 2D numerical geodynamic simulations to investigate the link between oceanic and continental plate dynamics and their interaction. We find that when the oceanic plate steepens in the mantle transition zone, the trench retreat is hindered. Coupled with the weakening of the continental plate through the slab flattening and subsequent delamination of the lithospheric mantle, this leads to pulsatile shortening phases of a magnitude equivalent to that suggested by the data.
Magma-filled dikes may feed erupting fissures that lead to alignments of craters developing at the surface, yet the details of activity and migrating eruptions at the crater row are difficult to monitor and are hardly understood.
The 2021 Tajogaite eruption at the Cumbre Vieja, La Palma (Spain), lasted 85 days and developed a pronounced alignment of craters that may be related to changes within the volcano edifice.
Here, we use COSMO-SkyMed satellite radar data and ground-based time-lapse photographs, offering a high-resolution dataset to explore the locations and characteristics of evolving craters.
Our results show that the craters evolve both gradually and suddenly and can be divided into three main phases. Phase 1, lasting the first 6 weeks of the eruption, was characterized by a NW-SE linear evolution of up to seven craters emerging on the growing cone.
Following two partial collapses of the cone to the northwest and a seismicity increase at depth, Phase 2 started and caused a propagation of the main activity toward the southeastern side, together with the presence of up to 11 craters along this main NW-SE trend. Associated with strong deep and shallow earthquakes, Phase 3 was initiated and continued for the final 2 weeks of the eruption, expressed by the development of up to 18 craters, which became dominant and clustered in the southeastern sector in early December 2021. In Phase 3, a second and oblique alignment and surface fracture was identified.
Our findings that crater and eruption changes coincide together with an increase in seismic activity at depth point to a deep driver leading to crater and morphology changes at the surface.
These also suggest that crater distributions might allow for improved monitoring of changes occurring at depth, and vice versa, such that strong seismicity changes at depth may herald the migration and new formation of craters, which have major implications for the assessment of tephra and lava flow hazards on volcanoes.
The Sea of Marmara is a tectonically active basin that straddles the North Anatolian Fault Zone (NAFZ), a major strike-slip fault that separates the Eurasian and Anatolian tectonic plates. The Main Marmara Fault (MMF), which is part of the NAFZ, contains an approximately 150 km long seismotectonic segment that has not ruptured since 1766. A key question for seismic hazard and risk assessment is whether or not the next rupture along this segment is likely to produce one major earthquake or a series of smaller earthquakes. Geomechanical characteristics such as along-strike variations in rock strength may provide an important control on seismotectonic segmentation. We find that variations in lithospheric strength throughout the Marmara region control the mechanical segmentation of the MMF and help explain its long-term seismotectonic segmentation. In particular, a strong crust that is mechanically coupled to the upper mantle spatially correlates with aseismic patches, where the MMF bends and changes its strike in response to the presence of high-density lower crustal bodies. Between the bends, mechanically weaker crustal domains that are decoupled from the mantle indicate a predominance of creeping. These results are highly relevant for the ongoing debate regarding the characteristics of the Marmara seismic gap, especially in view of the seismic hazard (Mw > 7) in the densely populated Marmara region.
On 12 August 2021, a > 220 s lasting complex earthquake with Mw > 8.2 hit the South Sandwich Trench. Due to its remote location and short interevent times, reported earthquake parameters varied significantly between different international agencies. We studied the complex rupture by combining different seismic source characterization techniques sensitive to different frequency ranges based on teleseismic broadband recordings from 0.001 to 2 Hz, including point and finite fault inversions and the back-projection of high-frequency signals.
We also determined moment tensor solutions for 88 aftershocks. The rupture initiated simultaneously with a rupture equivalent to a M-w 7.6 thrust earthquake in the deep part of the seismogenic zone in the central subduction interface and a shallow megathrust rupture, which propagated unilaterally to the south with a very slow rupture velocity of 1.2 km/s and varying strike following the curvature of the trench.
The slow rupture covered nearly two-thirds of the entire subduction zone length, and with M-w 8.2 released the bulk of the total moment of the whole earthquake.
Tsunami modeling indicates the inferred shallow rupture can explain the tsunami records. The southern segment of the shallow rupture overlaps with another activation of the deeper part of the megathrust equivalent to M-w 7.6. The aftershock distribution confirms the extent and curvature of the rupture. Some mechanisms are consistent with the mainshocks, but many indicate also activation of secondary faults. Rupture velocities and radiated frequencies varied strongly between different stages of the rupture, which might explain the variability of published source parameters.
Plain Language Summary
The earthquake of 12 August 2021 along the deep-sea trench of the South Sandwich Islands in the South Atlantic reached a magnitude of 8.2 and triggered a tsunami. The automatic earthquake parameter determination of different agencies showed very different results shortly after the earthquake and partially underestimated the tsunami potential of the earthquake.
A possible reason was the complex rupture process and that the tsunami was generated by a long and shallow slow slip rupture sandwiched between more conventional fast slip subevents at its northern and southern ends. In addition, the fault surface, which extended over 450 km, was highly curved striking 150 degrees-220 degrees.
We investigated the different components of the seismic wavefields in different frequency ranges and with different methods.
The analysis shows how even complex earthquakes can be deciphered by combining analyzing methods. The comparison with aftershocks and the triggered tsunami waves confirms our model that explains the South Sandwich rupture by four subevents in the plate boundary along the curved deep-sea trench. Here, the depth, rupture velocities, and slip on each segment of the rupture vary considerably.
The method can also be applied to other megathrust earthquakes and help to further improve tsunami warnings in the future.