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Regeneration after landslides is how an ecosystem recovers itself following a landslide event. Natural systems can recover and regenerate over time. The main objective of the current work is to identify and characterise the regeneration pattern after a great landslide event in 2013 in the Guerrero state (Mexico) using remote sensing, geographic information system (GIS), and machine learning techniques. Remarkably, the authors consider normalised difference vegetation index (NDVI) as a proxy of part of this "regeneration" in the present work. A first methodology attempt presented here was to monitor and characterise the "regeneration" after severe landslide events. First, the authors calculated and identified the (1) losses, (2) speed and (3) recovery time through a continuous change detection and classification algorithm (CCDC) in Google Earth Engine (GEE) from a NDVI-Landsat time series (from 1984 to 2021). Second, these three factors were introduced as variables in a not supervised machine-learning model to get 5 clusters that characterise the different regeneration patterns followed from 2013 to 2021 in the landslide zones. Finally, we studied 16 variables like elevation, slope, or soil pH. The authors included those variables in a supervised machine learning classification to find the most important main drivers related to the NDVI regeneration of the landslide areas. The results showed that the cluster called Group 0 had a low loss of NDVI value, speed and medium recovery time. Group 1 showed a medium–high loss, high speed and low recovery time. Group 2 reached a high loss, a low speed, and an increased recovery time. Group 3 with a medium loss, a medium speed, and a low recovery time. Finally, Group 4 with a high loss of NDVI, a medium speed, and a medium recovery time. Distance to the edge of the landslide, precipitation, land cover type and lithology are highlighted as the main drivers in landslide regeneration. [ABSTRACT FROM AUTHOR]

Earthquakes with magnitudes greater than 4.5–5 induce massive rockfalls close to the fault rupture zone. Driven by seismic shaking, the blocks collapse through the hillslope, which yields a fresh surface that is unbeatable for new lichen colonization. The lichenometric technique involves dating lichens developed on the surfaces of rockfall blocks induced by earthquakes. This study is focused on Cejo de Cano (Lorca, Spain), which is an earthquake-prone landslide scarp, as shown after the 2011 Lorca shaking (Mw 5.2). After this event, the possibility that the rocky volume at the foot of its slope could have a seismic origin started to be considered. In this research, lichenometry is used to date lichens on rock surfaces and test a possible correlation with the cataloged historical earthquakes. This research is important because of the large number of rockfall earthquakes found at this site by applying lichenometry compared to other studies in the literature. This technique allows us to extend the regional seismic catalog because the oldest lichens are older than the documented catalog of historical earthquakes. An oriented rockfall pattern that correlates with the location of epicenters is observed. In addition, the parallel and oblique previous fracturing of Cejo de Cano makes this scarp a suitable place to test whether the fracturing direction of the scarp could control a greater volume of rockfalls. This research opens up a new field of study to evaluate this correlation in larger areas. [ABSTRACT FROM AUTHOR]

The unprecedented and long-lasting seismicity of Triacastela (over 25 years) attracted the interest of the research community on this stable continental region (SCR), particularly after the anomalously high 5.1 and 4.9 Mw earthquakes compared to the regional standards. The high rainfall and tide rates of this region compared to the rest of the Iberian Peninsula, in addition to the recognized existence of thermal springs and crustal fluids, motivated us to test these sources of hydroseismicity as a potential trigger mechanism for the observed seismicity in Triacastela. Based on network upgrades, we have gathered the seismic catalog in two periods for analysis (before and after year 2002). Before 2002, neither a diffusion-type earthquake migration nor any significant statistical correlation between the seismicity rates and rainfall or tides is found. After 2002, some clusters migrate to the south, suggesting the presence of fluid migration during earthquake swarms, but no diffusion-type migration is observed on longer time scales. Furthermore, we find correlation coefficients close to zero, indicating that rainfall and tides can be excluded as driving mechanisms. However, the seismic upward migration, a high b-value (1.2), and a low aftershock-productivity parameter (α = 0.9) observed in this period support the hypothesis of upward fluid migration through fracture zones. The presence of Mantellic helium-3 along the seismogenic faults and the increase of geochemical precursors in the groundwater previously to 1995 and 1997 mainshocks further support deep fluids as a source for the observed induced fluid migration seismicity in Triacastela. [ABSTRACT FROM AUTHOR]

The information and seismic parameters gained from pre-instrumental earthquakes are essential to improve the seismic catalogs and hazard studies. The earthquake damage (ED) that affected architectonic elements during earthquakes (e.g. fallen walls, conjugated fractures in walls, dropped keystones in arches), and when this earthquake damage is orientated (EDO), can be used to infer seismic parameters of pre-instrumental earthquakes such as epicenter location, seismogenic source or ground motion. However, there is not a common methodology to measure this orientation damage. For example, tilting and fallen walls are some of the most used elements to infer the horizontal ground motion in non-instrumental earthquakes. Nevertheless, according to the shape of the architectonic element (a wall in this case), it has only two degrees of freedom to fall, and therefore, its azimuth does not necessarily fit with the ground motion pulse orientation. In this work, a review of the earthquake damage (ED) and effects described in pre-instrumental earthquakes is carried out. A method is also proposed, considering not only the frequency of damage orientations but also considering the uncertainty angle of each element to be damage. The ED has been classified into five groups according to the angle of uncertainty to record the pulse orientation. This method has been checked taking advantage of recent earthquakes with a good instrumental record of the ground motion pulse, and also tested modeling different scenarios with different pulse orientations. This method, that takes into account the uncertainty angles, is a reliable method to calculate the EDO and back-calculate the ground motion pulse orientation in pre-instrumental earthquakes in absence of more accurate modern instrumental records. This method can also be useful for seismic risk assessment and restoration and protection of historical heritage. [ABSTRACT FROM AUTHOR]

The NW Iberian Peninsula is an intraplate region with significant seismicity, but it has rarely been studied. Despite the increase in seismicity during recent years, which has even forced changes to the building codes, a comprehensive statistical analysis of this seismicity has not been carried out. Thus, this study aims to characterize seismicity clusters on an intraplate region, based on comprehensive qualitative and quantitative analysis. The b value of the Gutenberg–Richter law is estimated and the Epidemic Type Aftershock Sequence model is employed. Additionally, qualitative analysis is carried out using the Mogi classification, and the results of this work are compared with those of other statistical studies in the literature. We identify clustered seismic activity in the NW Iberian Peninsula, which is classified into 18 swarms and eight sequences. A high b value and low efficiency of aftershock generation are characteristic of the swarms. These parameters, along with the similarities to other regions, point to fluid migration as the swarm seismic source mechanism. Earthquakes of higher magnitude than swarms and a b value close to 1 define the sequences of this region. The statistical results in sequences (high k, c, and p values) and the similarity to other regions would indicate a mix of tectonic origin and aseismic processes (such as fluid migration or slow slip events) as the driving force of seismic sequences. The presence of crustal fluids associated with fault activity in the NW Iberian Peninsula also supports the hypothesis of fluid migration as the source of seismic events. [ABSTRACT FROM AUTHOR]

We report the results of a multidisciplinary study of the early Permian (Artinskian–Kungurian) Sotres Formation of northern Spain integrating sedimentology, palaeosols, mineralogy, stable isotopes, palynology, ichnology and tectonics. This continental unit was deposited in the near-equatorial Peri-Tethyan Cantabrian Basin. Having developed in the middle of the Variscan fold belt, it is preserved within the present-day Cantabrian Mountains. Three subunits are recognised in the Sotres Formation based on tectono-stratigraphic and sedimentological data: a lower alluvial subunit, a middle carbonate lacustrine subunit, and an upper palustrine subunit. Multidisciplinary results reveal an upward change in climate from humid-subhumid conditions at the base of the formation (Artinskian) to semi-arid and arid conditions at the top of the formation (Kungurian), which may reflect global deglaciation near the end of the Late Paleozoic Ice Age and a probable northward migration of the Intertropical Convergence Zone. This general upward warming/drying climate trend was interrupted by a short-lived interval of monsoon conditions in mid-Kungurian times, which may have coincided with a pulse of global cooling. Our findings are in agreement with the climate trends reported for other central Pangaean basins. Rising CO2 levels may have been a driving factor for climate transition during this time interval. However, in our study area, which lies within the active central Variscan orogenic belt, tectonic conditions must have also played a role in driving climate change. [ABSTRACT FROM AUTHOR]