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As part of the recently initiated research project, we are in the process of studying in detail the geodynamic behavior of the Carboneras fault (CF) in the SE Betics in Spain. Specifically, we plan to quantify the geodetic and geologic slip rates for the on-land section of the fault, as well as getting some insight on the state of locking of the fault. As a result of our previous GPS observations, we have been able to illustrate the continuing tectonic activity of the Carboneras fault, expressed mainly as a left-lateral strike slip motion of 1.3±0.2 mm/yr, with a less significant compression of 0.4±0.2 mm/yr (Echeverria et al., 2015). To reveal how the deformation is partitioned between different structures, in the last years 2 new continuous GPS points were established along the fault-perpendicular profile. In addition, we have conducted several surveys of the nearby CuaTeNeo and IGN Regente points and established and measured several new geodetic points in the vicinity of the Carboneras fault. The updated horizontal geodetic slip rates for the CF are 1.1±0.2 and 0.4±0.3 mm/yr in fault parallel and perpendicular directions, respectively. These estimates are somewhat smaller than previously published results, although considering the uncertainties, are statistically equivalent.The above-mentioned geodetic, short-term, slip rates deduced from GNSS observations, are in good agreement with the estimates of geologic slip rates based on paleoseismic and geomorphologic studies, which indicate a minimum strike-slip rate of 1.3 mm/yr and dip-slip rate of 0.05 mm/yr since 110.3 ka (Moreno et al. 2015). In the coming years we plan to conduct further geodetic surveys and paleoseismic trenching surveys. These new data, should significantly improve the reliability of the existent deformation data and therefore, contribute to better understanding of the seismic hazard posed by the Carboneras fault in the SE Betics.Project NSOURCES (PID2020-119772RB-I00) financed by MCIN/AEI/10.13039/501100011033

It is known that the VLF/LF radiation existing prior to large earthquakes is recorded in several seismically active countries of the world. The networks of this radiation consist of stationary transmitters and receivers. However, there are cases of large earthquakes, when existing networks cannot detect relevant EM radiation. In the present paper we focus on the optimal option of a mobile VLF/LF electromagnetic radiation network arrangement to ensure a detection of the upcoming earthquake precursor. We discuss new possibilities of arrangement of the VLF/LF mobile network based on certain physical considerations, which is relatively simplified and completely different from the existing stationary networks. The suggested design, will significantly increase the number of detected/ predicted earthquakes with the relevant EM emissions receivers, strategically placed in the regions of the increased tectonic and seismic activity.

The Eastern Betics, located on the SE of Spain, is one of the areas with the highest seismic activity within the Iberian Peninsula. The Eastern Betic Shear Zone (EBSZ) is comprised by a set of active, slow-moving faults, which are partially absorbing the ~5 mm deformation caused by the convergence between the Eurasian and Nubian plates. The precise kinematics of these faults remains unclear to this date, due to their slow slip rates and the distributed strain across the region. Over the past years, several studies have focused on this area, especially after the devastating 2011 Lorca earthquake (Mw 5.1). However, there is a lack of precise GNSS observations in the central area of the EBSZ. Therefore, we present here an updated GNSS velocity field of the central EBSZ, which includes all the available continuous stations in the area, as well as continuous and campaign observations carried out under the GeoActiva project (CGL2017-83931-C3-3-P). Additionally, we discuss alternative deformation sources affecting the GNSS observations (other than those of tectonic origin), such as the human-induced subsidence in the Guadalentín River Basin. We use Sentinel-1 SAR images to identify the affected areas and to quantify the impact on the GNSS velocities.This work has been developed in the framework of GeoActiva project (CGL2017-83931-C3-3-P, funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”) and e-Shape project (H2020 programme, Grant Agreement 820852), as well us under Grant FPU19/03929 (funded by MCIN/AEI/10.13039/501100011033 and by “FSE invests in your future”).

The 2016 implementation of the EU Flood Directive in Spain defines within the flood-prone zones the Preferential Flow Zone (Zona de Flujo Preferente, ZFP). This zone includes a) broadly, the area where the floods flow is concentrated; b) for the 100 years return period flood, the intensive drainage waterway and the zone dangerous to persons. The ZFP is usually defined for the 100 years flood applying hydraulic modelling. However, the calculation of the 100 years flood poses multiple limitations. For instance, different probability distributions produce different results for the same data series, or for rainfall and discharge data, depending on the time interval considered in the calculation, the results are also different. Regarding rainfall, the meteorological radar data are still too new to extrapolate to 100 years. The destruction of meteorological and gauging stations during storms and floods is not rare; hence, a lack of data on major events in the data series can deeply affect the calculations. Furthermore, similar rainfall can produce different discharges due to differences in the antecedent conditions or to land use changes. All the above and the climate change, question the hypothesis of stationarity at the base of the floods return period concept1 and, thus, its calculation reliability.Since the middle of the 20th century, significant socio-economic and land use changes occurred in the western Mediterranean region, resulting in changes in the morphology of rivers (e.g., reduced channel section, entrenchment). The record of these morphological changes, including the effects of major floods, can provide insights to define the high-energy flow zone or ZFP. This work contributes to determine the flash flood effects and, therefore, to define the ZPF, through multitemporal geomorphological analysis applied to a case study of the upper basin of the Francolí river in Catalonia, Spain. It was affected by several major floods in 1874, 1930, 1994 and 2019, where the first and the last events were the largest and of quite similar, centenial magnitude. Different reaches of the river are studied and compared to validate the analysis: reaches where 1994 and 2019 flood were similar and reaches where these floods were of very different magnitude; reaches where all the basic dataset is available (1946, 1956, 1995 post flood, pre and post 2019 orthophotos; 2003 detailed DTM; stereo photographs, post 2019 flood field data and GNSS-RTK data of river cross sections) and reaches with lack of some data (especially of the 1995 post flood image). Historical information (water levels attained by the past floods and the calculated discharges) are also used to complement and validate the geomorphological analysis results.With this work we test whether the main geomorphic effects of the 2019 flood could have been predicted using the multitemporal geomorphological analysis. The ZFP can be reasonably determined for major floods in this Mediterranean river. This multitemporal geomorphological analysis appears as a good complementary tool to inform flood risk.1 Sofia, G., E. I. Nikolopoulos, L. Slater (2020), It’s time to revise estimates of river flood hazards, Eos, 101, https://doi.org/10.1029/2020EO141499. 16 March 2020.

Seismic sensors installed in areas prone to rockfalls provide a continuous record of the phenomenon, allowing real-time detection and characterization. Detection of small scale rockfalls (< 0.001 m3), that might be precursors of larger events, can be worthwhile for early warning systems of rockfalls. However, seismic signals are closely dependent on the characteristics of the event and on the geotechnical characteristics of the ground, making the detection of small rockfalls complex and requiring detailed in-situ analyzes. For this reason, an experiment was carried out on the UB experimental site (Puigcercós Cliff, Catalonia, NE Spain) on 6th-7th of June 2013, where 21 rocks with volumes ranging from 0.0015 m3 to 0.0004 m3 were thrown from the top of the cliff (200 m long and 27 m high) and the seismic signals were registered with three 3D short period seismic sensors located at different distances from the rock wall: 57 m, 67 m, and 107 m.The recorded seismic signals have a frequency content between 10-30 Hz, and the duration of the peak amplitudes varied between 0.3 and 0.6 s. Based on these characteristics, different phases of the dynamics of the rockfalls were identified, including main impacts, rebounds, flights, rolling and final stop of the events. The furthest station recorded the lowest frequency and amplitude values, limiting our ability to detect those blocks smaller than 0.0015 m3. Comparing the results with the nearest station, seismic attenuation phenomena is detectable even at distances of 50 m.After the experiment, a permanent seismic station was installed in the area, at 107 m from the cliff. Using LiDAR and 2D imagery monitoring, two naturally triggered rockfalls were identified on 30th and 31st August 2017 (0.28 m3 and 0.25 m3 respectively). Based on the results from the experiment and an automatic detection system, these main events and prior minor events have been found in the continuous seismic records of this permanent station. The characteristics of these natural detachments differ partially from the artificially triggered rockfalls during the experiment, since the geometry of the seismic signals is different. The observed shapes of the natural detachments are similar to that of granular flows, much more continuous than the sharp shapes that were observed in the isolated blocks of the experiment. This shows the possibility of incorporating seismic stations for the automatic detection and initial characterization of rockfalls and its effectiveness in detecting frequencies of occurrence.In order to evaluate the possibility of estimating rockfall volumes, diverse energy ratios (Es/Ep) were calculated. However, precise volume estimation is not possible. Nevertheless, the combination of seismic data with LiDAR and photographic techniques allows accurate new volume calculations of rockfalls to be incorporated progressively into the study of rockfalls.ACKNOWLEDGMENTS: The authors would like to acknowledge the financial support from CHARMA (CGL2013-40828-R) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) projects, Spanish MINEICO. We are also thankful to Origens UNESCO Global Geopark.

The Republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and the Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of up to 20 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The main objective of the given work is to monitor a millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.

On October 22, 2019, intense rains took place in Catalonia (292,6 mm in 24 hours at Prades), associated with a meteorological isolated depression at high atmospheric level (DANA in Spanish language). These rains caused a sudden discharge increase and a major flash-flood in the Francolí river (Tarragona, Catalonia, Spain). As a result, the river swept along a large quantity of vegetation, crops and infrastructures, such as bridges, roads, and houses. Unfortunately, the flood caused a considerable economic damage (exceeding 100 million euros), and a loss of six human lives. This area was also affected by the 1994 flood, which produced 10 fatalities and losses worth 17,000 million euros.The Francolí river watershed has an area of 853 km2 and a length of 59 km. The study area stretches for ~20 km along the upper basin, without regulatory infrastructures. It covers the localities of Vimbodí, L´Espluga de Francolí, Montblanc and Vilaverd, with a population of 12,463 people. Downstream Vilaverd, the river crosses the strait of La Riba at the west of the Prades mountains. The Francolí River has low water levels much of the year and a strong seasonal regime. It presents high sediment mobility and large transportation capacity.Orthophotographs, LiDAR and field work data, including GNSS-RTK data of river sections, are fundamental for this hydro-geomorphic analysis. It is performed mostly through classical and stereo-anaglyph photo-interpretation and comparison of the 2019 (post-flood event), 2016 (pre-flood event), 1995 (after the 1994 flood) and 1945-56 orthophotographs (provided by the Geological and Cartographic Institute of Catalonia). The main effects considered are: a) channel migration, cuts or changes in the sinuosity of meanders; b) significant bank erosion; c) pull up and dragging of vegetation; d) channel widening and braiding; e) development of secondary active channels during the flood; f) significant erosive and sedimentary morphologies; g) extension of the flooded areas through ephemeral evidence. From the geomorphological effects of the 2019 and 1994 floods, the Active Band is determined and mapped. This characterization highlights that the Francolí river is, geomorphologically, very active. In consequence, when defining flood hazard zones, hydraulic modelling would not be able to capture the complexity of this system and would produce biased results.Once the Active Band is determined and with the estimation of peak flows in crucial localities, the Preferential Flow Zone (PFZ) can be defined. PFZ is the envelope of the areas where the flow concentrates during major floods or, also, the most frequently flooded areas in minor floods. This zoning allows us to discriminate areas with high and low flow energies, and to identify the margins most prone to erosion. Accordingly, varying levels of flood hazard can be mapped, and flood areas classified.This combined analysis of indicators allows us to characterize the flood hazard more precisely in the studied stretch. The method can serve to better understand and predict the flash-floods associated hydro-geomorphic hazards in these kind of geomorphologically active rivers.The authors thank the financial support from PROMONTEC project (CGL2017-84720-R AEI/FEDER, UE), Spanish MINEICO.

The republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of 18 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The principle objective of the given work is to monitor millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults. This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.

More than a century ago, the Puigcercós village located in the region of Pallars Jussà (Catalonia, Spain), suffered a large-scale landslide that occurred on January 13th, 1881. More than 5 million m3 of sediments and rocks were displaced and a 200 m long and 25 m high rock scarp was formed. Luckily, during the main event, the nearby village was not affected, and due to a prompt evacuation and re-location of the entire village, no casualties were reported. Nevertheless, consequent retreat of the main scarp did destroy the big part of the old village, which confirmed not only the necessity for its relocation, but also gave one of the first clearly described and confirmed examples of a successful geologic risk prevention.During the last decade, the members of the RISKNAT-UB group have chosen this site to conduct pilot studies of rockfalls and landslides using a multidisciplinary approach. The utilized observational techniques include Terrestrial Laser Scanner (TLS), photogrammetry, GPS, seismic monitoring and geophysical prospecting techniques. The work presented here is an overview of these activities, including the main milestones of the ongoing research. Special emphasis will be given to the use of geodetic techniques for investigating changes on the depositional area of the landslide and around the crown cracks at the upper level of the main scarp. As a result of the GPS observations, for the first time, 130 years after the occurrence of the event, it was possible to observe a continuing geomorphological activity of the depositional zone of this historical landslide, Currently, the RISKNAT-UB group operates cost-effective, high-resolution and low-cost photogrammetric instruments and seismic continuous records at the site, in order to monitor the evolution of the Puigcercós rock scarp. The correlation of the seismic and the photogrammetric data and intermittently obtained LiDAR images enables us to monitor and characterize frequent rockfalls and premonitory deformations occurring at the site. These observations have allowed quantifying the rate of retreat of the rock scarp at a rate of 10 to 11 cm/yr and a slow motion of the depositional zone up to 6 mm/yr. Since the geologic risk at the study area is not significant, due to the absence of population and/or infrastructures, this site is an ideal natural laboratory for developing new observational techniques, which can be used to develop early warning systems for rockfalls and landslides.The authors would like to acknowledge a financial support from CHARMA (CGL2013-40828-R) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) projects, financed by the Spanish MINEICO. We are also thankful to UNESCO Global Geopark Conca de Tremp-Montsec for their support.

On the 22nd and 23rd of October 2019 a severe rainfall produced floods in the basins of the Catalan Coastal Range-Ebro Depression border (Francolí, Set, Femosa rivers) that affected various towns such as L'Espluga de Francolí, Montblanc, l'Albi, Vinaixa, among others, causing 6 deaths and material damages that exceeded 100 million euros. According to historical records, this rainfall episode would exceed the maximum rainfall estimates expected for 500 years in this region and the maximum heights reached by the water are comparable to, or exceed, those of the remembered Santa Tecla flash flood on September 1874, which would have a recurrence of more than 250 years.This rain was caused by a S-SE warm and wet Mediterranean air mass over the Catalan Coastal System (Prades and Llena Ranges). The area of maximum rainfall was located at the headwaters of the rivers Set, Francolí and Montsant rivers, with rain depths above 200 mm. The hourly distribution at El Vilosell and Prades rain gauges shows 50 mm from 6 to 14 UTC and maximum intensity of 10 to 15 mm h-1, followed by a second pulse of 180-220 mm from 16 to 01 UTC and maximum intensity of 65 mm h-1 (maximum 3.1 mm min-1). Soil moisture content was low at the time of the rain after a dry summer. Early precipitation saturated the topsoil, therefore the soil surface was very wet at the beginning of the second rainfall event and it generated a hortonian overland flow. The highest rainfall intensity occurred around 19 UTC and the peak flow response was immediate, around an hour later, depending on the location.Despite the similarity of rainfall and initial soil moisture conditions, the hydrological response in the two analyzed basins was markedly different. The flows generated in the Set River basin at l'Albagès reservoir produced a peak flow of 245 m3 s-1 (1.5·m3·s-1·km-2) and a very low flood runoff ratio of only 8%. In the basin of the Francolí River, at L'Espluga de Francolí, the peak flow was 1,300 m3 s-1 (13 m3·s-1·km-2) and the runoff ratio was of the order of 70%. The Set river basin is basically agricultural with terraced slopes that retained much of the precipitation, only released after the flood as baseflow. The Francolí river basin has steeper slopes and channels and is dominated by an extensive tree cover but very poorer soils that caused little water retention, giving rise to a major hydrological response, an order of magnitude larger than that of the Set River.

The sensitive mountain catchment of Portain&eacute, (Eastern Pyrenees, Iberian Peninsula) has recently experienced a significant change in its torrential dynamics due to human disturbances. The emplacement of a ski resort at the headwaters led to the surpassing of a geomorphological threshold, with important consequences during flood events. Consequently, since 2008, channel dynamics have turned into sediment-laden, highly destructive torrential flows. In order to assess this phenomenon and to acquire a holistic understanding of the catchment&rsquo, s behaviour, we carried out a field work-based multidisciplinary study. We considered the interaction of the various controlling factors, including bedrock geology, geomorphological evolution, derived soils and coluvial deposits, rainfall patterns, and the hydrological response of the catchment to flood events. Moreover, anthropogenic land-use changes, its consequential hydrogeomorphic effects and the role of vegetation were also taken into account. Robust sedimentological and geomorphological evidence of ancient dense debris flows show that the basin has shifted around this threshold, giving rise to two different behaviours or equilibrium conditions throughout its history: alternating periods of moderate, bedload-laden flows and periods of high sediment-laden debris flow dynamics. This shifting could have extended through the Holocene. Finally, we discuss the possible impact of climate and global change, as the projected effects suggest future soil and forest degradation, this, jointly with more intense rainfalls in these mountain environments, would exacerbate the future occurrence of dense sediment-laden flows at Portain&eacute, but also in other nearby, similar basins.

International audience; The Pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity. To quantify its deformation field, we present the velocity field estimated from a GPS survey of the Pyrenees spanning 18 yr. The PotSis and ResPyr networks, including a total of 85 GPS sites, were installed and first measured in 1992 and 1995–1997, respectively, and remeasured in 2008 and 2010. We obtain a deformation field with velocities less than 1 mm yr−1 across the range. The estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence. Even so, we estimate a maximum extensional horizontal strain rate of 2.0 ± 1.7 nanostrain per year in a N–S direction in the western part of the range. We do not interpret the vertical displacements due to their large uncertainties. In order to compare the horizontal strain rates with the seismic activity, we analyse a set of 194 focal mechanisms using three methods: (i) the ‘r’ factor relating their P and T axes, (ii) the stress tensors obtained by fault slip inversion and (iii) the strain-rate tensors. Stress and strain-rate tensors are estimated for: (i) the whole data set, (ii) the eastern and western parts of the range separately, and (iii) eight zones, which are defined based on the seismicity and the tectonic patterns of the Pyrenees. Each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike-slip in the west of the range. Although the horizontal components of the strain-rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the GPS velocity field, they are consistent within the 2σ uncertainties. Furthermore, the orientations of their principal axes agree with the mapped active faults.

vol.162, 216-229., Torrential floods are hazardous hydrological phenomena that produce significant economic damage worldwide. Flood reconstruction is still problematic in ungauged mountainous areas due to the lack of systematic data, so indirect techniques are required. This paper presents an integrated palaeoflood study of a Pyrenean stream that combines fluvio-torrential geomorphology, dendrogeomorphology, palaeoflood discharge estimation and flow hydraulics. The use of a total station and airborne LiDAR data allows detailed topography for geomorphological mapping and running a one-dimensional hydraulic model. Based on the height of scars on several damaged trees, we obtained palaeodischarges of 316 m3 s−1 and 314 m3 s−1 for the 2008 and 2010 floods. The hydraulic parameters were related to the geomorphic position of trees, showing a positive relation between most energetic geomorphic elements and both flow depth and velocity values. The most affected trees are located in intermediate energy geomorphic positions. Analysing variation in scar height and flow stage differences, we suggest that most reliable trees for peak discharge estimation correspond to those in areas related with fluvio-torrential processes of intermediate energy. This multidisciplinary palaeohydrological study relates flood hydrodynamics with the damage to trees and their geomorphological characteristics, focusing on the hydraulic parameters of the peak flow (depth, velocity and unit stream power), which has never been performed before. The proposed approach shows strong potential for palaeoflood analysis in ungauged mountain catchments with scarce nonsystematic data., Geomodels Research Institute, Departament d'Geodinàmica i Geofísica, Universitat de Barcelona, España, Área de Riesgos Naturales, Instituto Geológico y Minero de España, España, Departamento de Sistemas y Recursos Naturales, Universidad Politécnica de Madrid, España

On May 5th, 2013 a planar rock slide (~450 m3) occurred in the village of La Riba (NE Spain), which forced the closure of the road C-240z for 6 months. This slide left a hanging block (~130 m3) suspended on the slope forcing a controlled blasting, followed by rock slope stabilization works. The volume of rock displaced during the both events was deduced from LiDAR and photogrammetry data following two approaches: subtracting pre- and post-event data and reconstructing the volume by fitting planes on the structural surfaces after a structural analysis of the slope. Information about the natural rock slide was obtained from the records of two permanent broadband seismic stations located 10 km from the site. From these seismic records, the existence of a rock slide was confirmed and its time of occurrence was determined, information that would be otherwise unknown. In addition, despite the small volume displaced during the event, its location was deduced from a single seismic station analysis. The blasting process was recorded with two high-definition (HD) video cameras and by two temporary seismic stations deployed close to the site (10 km). Partially, because only a part of the released energy is transmitted into the ground as seismic energy, and partially because the recorded seismic signal is highly dependent on the event characteristics and the geotechnical conditions of the ground materials. Nevertheless, seismic data is very well suited to detect and characterize in detail both rockfall events of different nature and size. Merging and integrating remote sensing techniques such as LiDAR or photogrammetry with seismic measurements should allow the implementation of rockfall early warning systems.

We present a new 3-D GPS velocity solution for 182 sites for the region encompassing the Western Alps, Pyrenees, and southern France. The velocity field is based on a Precise Point Positioning (PPP) solution, to which we apply a common-mode filter, defined by the 26 longest time series, in order to correct for network-wide biases (reference frame, unmodeled large-scale processes, etc.). We show that processing parameters, such as troposphere delay modeling, can lead to systematic velocity variations of 0.1–0.5 mm yr−1 affecting both accuracy and precision, especially for short (−1 in the horizontal and vertical components, respectively. On average, horizontal residual velocities show a stability of ∼ 0.2 mm yr−1 in the Western Alps, Pyrenees, and southern France. The only significant horizontal strain rate signal is in the western Pyrenees with up to 4 × 10−9 yr−1 NNE–SSW extension, whereas no significant strain rates are detected in the Western Alps (−9 yr−1). In contrast, we identify significant uplift rates up to 2 mm yr−1 in the Western Alps but not in the Pyrenees (0.1 ± 0.2 mm yr−1). A correlation between site elevations and fast uplift rates in the northern part of the Western Alps, in the region of the Würmian ice cap, suggests that part of this uplift is induced by postglacial rebound. The very slow uplift rates in the southern Western Alps and in the Pyrenees could be accounted for by erosion-induced rebound.

The Carboneras fault zone (CFZ) is a prominent onshore–offshore strike–slip fault that forms part of the Eastern Betic Shear Zone (EBSZ), located in SE Spain. In this work, we show for the first time, the continuing tectonic activity of the CFZ and quantify its geodetic slip-rates using continuous and campaign GPS observations conducted during the last decade. We find that the left-lateral motion dominates the kinematics of the CFZ, with a strike–slip rate of 1.3 ± 0.2 mm/yr along the N48° direction. The shortening component is significantly lower and poorly constrained. Recent onshore and offshore paleoseismic and geomorphic results across the CFZ suggest a minimum Late Pleistocene to present-day strike–slip rate of 1.1 mm/yr. Considering the similarity of the geologic and geodetic slip rates measured at different points along the fault, the northern segment of the CFZ must have been slipping approximately at a constant rate during the Quaternary. Regarding the eastern Alpujarras fault zone corridor (AFZ), located to the north of the CFZ, our GPS measurements corroborate that this zone is active and exhibits a right-lateral motion. These opposite type strike–slip motion across the AFZ and CFZ is a result of a push-type force due to Nubia and Eurasia plate convergence, which, in turn, causes the westward escape of the block bounded by these two fault zones.