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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 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

We report on the first single crystal study of SrTm2O4. Magnetization measurements along the crystallographic axes of a nearly stoichiometric Sr1.07(3)Tm2.07(6)O4.00(2) sample show either a positive or a negative Curie–Weiss temperature indicative of a competition between antiferromagnetic and ferromagnetic couplings. The field-dependent magnetization suggests an effective Zeeman splitting of the high-level J-multiplets above ∼8.3 T and that the paramagnetism may originate from only one of the two inequivalent Tm3+ crystallographic sites. Our single-crystal polarized neutron scattering and powder unpolarized neutron diffraction data show no evidence for either long- or short-range magnetic order even down to ∼65 mK. We reveal two TmO6 octahedral distortion modes, i.e., one distortion is stronger than the other especially at low temperatures, which is attributed to different crystal fields of the two inequivalent octahedra. Therefore, the compound SrTm2O4 is unique and different from its brethren in the family of frustrated SrRE2O4 (RE = rare earth) magnets. We propose that crystal field anisotropy may dominate over weak dipolar spin interactions in SrTm2O4, thereby leading to a virtually non-ordered magnetic state.

A new continuous GPS network was installed under the umbrella of a research project called "Geociencias en Iberia: Estudios integrados de topografía y evolución 4D (Topo-Iberia)", to improve understanding of kinematic behavior of the Iberian Peninsula region. Here we present a velocity field based on the analysis of the 4 years of data from 25 stations constituting the network, which were analyzed by three different analysis groups contributing to the project. Different geodetic software packages (GIPSY–OASIS, Bernese and GAMIT) as well as different approaches were used to estimate rates of present day crustal deformation in the Iberian Peninsula and Morocco. In order to ensure the consistency of the velocity fields determined by the three groups, the velocities obtained by each analysis center were transformed into a common Eurasia Reference Frame. After that, the strain rate field was calculated. The results put in evidence more prominent residual motions in Morocco and southernmost part of the Iberian Peninsula. In particular, the dilatation and shear strain rates reach their maximum values in the Central Betics and northern Alboran Sea. A small region of high shear strain rate is observed in the east-central part of the peninsula and another deformation focus is located around the Strait of Gibraltar and the Gulf of Cadiz, This research has been funded by the Spanish Government through the research project "Geosciences in Iberia: Integrated studies on topography and 4-D evolution" (CSD2006- 00041).

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.

SUMMARY The Pyrenees mountain belt, which separates the Iberian Peninsula from the rest of the European continent, is part of the Alpine–Himalayan orogenic belt, formed as a result of a collision between the African and Eurasian Plates. Although the instrumental seismicity in the Pyrenees is moderate, in the past centuries a number of destructive earthquakes have occurred, which could indicate continuing tectonic activity of the area. We analyse GPS observations spanning 3.5 yr from 35 continuous stations in the Pyrenees region and find significant on-going extension perpendicular to the range at 2.5 ± 0.5 nstrain yr–1, with the possibility of higher strain rates concentrated in the westernmost part of the range. This finding is in agreement with the predominantly normal faulting focal mechanisms of earthquakes that occur in the area and suggests a recurrence time for magnitude 6.5 earthquakes of 2200–2500 yr.

The coseismic superficial deformation at the region of Lorca (Murcia, southeastern Spain) due to the Mw 5.1 earthquake on 11 May 2011 was characterized by a multidisciplinary team, integrating information from DInSAR, GPS and numerical modelling techniques. Despite the moderate magnitude of the event, quantitative information was obtained from the interferometric study of a pair of TerraSAR-X images. The DinSAR results defined the trace of the fault plane and evidenced uplift of the hanging wall block in agreement with the estimated deformation obtained through an elastic rupture dislocation numerical model. Meanwhile for the footwall block, interferometric results showed that tectonic deformation is masked by an important subsidence related to groundwater extraction previously identified at the area of study. Horizontal crustal deformation rates and velocity vectors, obtained from GPS stations existent at the area, were also coherent with the tectonic setting of the southern margin of the Iberian Peninsula and with the focal mechanism calculated for the Lorca event. The analysis of a continuous GPS site in Lorca showed good agreement with the horizontal N–S direction component relative to the numerical model and tectonics of the region. This is the first time at this seismic active area that a multi-technique analysis has been performed immediately after the occurrence of a seismic event, comparing the existing deformation data with a theoretical numerical model based on estimated seismic rupture dislocation.

A method to determine the dissipated seismic energy into the ground by a down going avalanche is presented. Evaluation of the seismic energy is useful for avalanche size classification, model validation, and for characterization and better understanding of the avalanche evolution as it propagates downhill along the changing slope. The method was applied to two different type avalanches that were released artificially on 2004/02/28 and 2005/04/15 at Ryggfonn (Norway) avalanche experimental site, operated by the Norwegian Geotechnical Institute (NGI). The analysed seismic data were recorded by the University of Barcelona seismic instruments consisting of two three-component wide-range seismometers located respectively, in the middle and on the side of the avalanche path. The energy determination requires a priori seismic characterization of the site and the knowledge of the avalanche front speed. In this paper a seismic characterization (surface wave phase velocity and amplitude attenuation factor) of the Ryggfonn site is presented. This characterization will serve for subsequent studies. We attribute the main source of seismic signals for the studied events to basal friction and ploughing occurring at the avalanche front and related to the changing slope in the propagation path, which causes high seismic energy dissipation. A comparative study of the evolution of the dissipated seismic energy with the energy generated by a simple sliding block model of constant mass was performed. The observed differences highlight the importance of ploughing and basal friction and the specific characteristics of the avalanches, such as their length and type. The difference between the calculated total dissipated seismic energy for the two similar size avalanches reflects their different flow type. As expected, the dry/mixed event dissipates a smaller amount of energy (not, vert, similar 1.2 MJ) than the dry/dense event (not, vert, similar 2.8 MJ).

SummaryWe interpret Global Positioning System (GPS) measurements in the northwestern United States and adjacent parts of western Canada to describe relative motions of crustal blocks, locking on faults and permanent deformation associated with convergence between the Juan de Fuca and North American plates. To estimate angular velocities of the oceanic Juan de Fuca and Explorer plates and several continental crustal blocks, we invert the GPS velocities together with seafloor spreading rates, earthquake slip vector azimuths and fault slip azimuths and rates. We also determine the degree to which faults are either creeping aseismically or, alternatively, locked on the block-bounding faults. The Cascadia subduction thrust is locked mainly offshore, except in central Oregon, where locking extends inland. Most of Oregon and southwest Washington rotate clockwise relative to North America at rates of 0.4–1.0 ° Myr−1. No shear or extension along the Cascades volcanic arc has occurred at the mm/yr level during the past decade, suggesting that the shear deformation extending northward from the Walker Lane and eastern California shear zone south of Oregon is largely accommodated by block rotation in Oregon. The general agreement of vertical axis rotation rates derived from GPS velocities with those estimated from palaeomagnetic declination anomalies suggests that the rotations have been relatively steady for 10–15 Ma. Additional permanent dextral shear is indicated within the Oregon Coast Range near the coast. Block rotations in the Pacific Northwest do not result in net westward flux of crustal material—the crust is simply spinning and not escaping. On Vancouver Island, where the convergence obliquity is less than in Oregon and Washington, the contractional strain at the coast is more aligned with Juan de Fuca—North America motion. GPS velocities are fit significantly better when Vancouver Island and the southern Coast Mountains move relative to North America in a block-like fashion. The relative motions of the Oregon, western Washington and Vancouver Island crustal blocks indicate that the rate of permanent shortening, the type that causes upper plate earthquakes, across the Puget Sound region is 4.4 ± 0.3 mm yr−1. This shortening is likely distributed over several faults but GPS data alone cannot determine the partitioning of slip on them. The transition from predominantly shear deformation within the continent south of the Mendocino Triple Junction to predominantly block rotations north of it is similar to changes in tectonic style at other transitions from shear to subduction. This similarity suggests that crustal block rotations are enhanced in the vicinity of subduction zones possibly due to lower resisting stress.

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.

En este trabajo presentamos el campo de deformacion cortical de la peninsula Iberica y norte de Marruecos, basado en el analisis de observaciones continuas de GPS (CGPS) de los ultimos cinco anos, combinado con observaciones de campanas (SGPS) de la red CuaTeNeo en las Beticas Orientales. Las estaciones CGPS analizadas provienen de varias redes GNSS nacionales y regionales, con variedad de disenos y estabilidad de los monumentos. Cuatro campanas de la red CuaTeNeo se realizaron con un intervalo aproximado de 4 anos, desde 1997 hasta 2011. Aunque el campo de deformacion es complejo, se pueden identificar facilmente algunas caracteristicas esperables. Teniendo en cuenta el sistema de referencia de Eurasia, las velocidades con valores mas altos, como era de esperar, se observan en Marruecos, donde las velocidades alcanzan 4.7±0.2 mm/ano. En el sur de Espana, las estaciones situadas al oeste de Almeria, presentan una tendencia del movimiento hacia el oeste, con valores de hasta 3.2±0.1 mm/ano en la estacion SFER. La orientacion de estos vectores, nos hace pensar que la principal fuerza impulsora de las deformaciones observadas no puede atribuirse unicamente a la convergencia entre Africa-Eurasia, sino que debe ser debida a procesos geodinamicos mas profundos relacionados con la subduccion de la laja Betico-Alboran.

The analysis of 3 years of continuous data from 7 permanent GPS stations along the western Washington section of the Cascadia Subduction Zone indicates that the direction of the observed horizontal velocities (with respect to station DRAO, nominally representing the stable North American continent) is roughly parallel to the relative plate convergence direction of the Juan de Fuca and North America plates and that their magnitude decreases away from the trench. Most of this deformation can be attributed to inter-seismic strain accumulation due to the locking of the thrust interface. When the dislocation model predictions are subtracted from the observed velocities, there is evidence for an additional N-S oriented contraction at a rate of ∼4 mm/yr over a distance of 250 km. This signal presumably represents a more long-term deformation pattern than the periodic accumulation and release of elastic strain connected with subduction earthquakes and is most likely related to the occurrence of shallow earthquakes in western Washington that are characterized by predominantly N-S oriented maximum principal stress.

On May 11 th of 2011, a seismic series occurred near the city of Lorca (Murcia). The main earthquake of magnitude Mw 5.2 has been attributed to the Alhama de Murcia Fault, one of the most active faults in the SE Iberian Peninsula. We analyzed data from 5 GPS campaigns of the CuaTeNeo network conducted between 1997 and 2011. The velocities of the stations closest to the Alhama de Murcia Fault show the reverse and strike-slip direction of motion. Stations located on the southeastern side of the fault have the maximum velocities in the area (between 1.4 and 1.8 mm/yr), oriented towards NNW direction, obliquely to the trace of the fault. The kinematics of the fault and the strain rate directions obtained from the CuaTeNeo network GPS measurements matches the calculated focal mechanism of Lorca earthquake. Detailed analysis of the time-series from the continuous GPS station at the Lorca city allows the detection of co-seismic offset of ~6 mm to the North.

The eastern Betic Cordillera, Spain, is the most seismically active area within the Iberian Peninsula. We present a Global Positioning System (GPS)-derived horizontal crustal deformation obtained from five occupations of the CuaTeNeo GPS network (1997, 2002, 2006, 2009 and 2011) that clearly shows continuing tectonic activity in the SE Betics. The most prominent feature of the GPS velocity field is the NW oriented motion of the majority of the stations at rates ranging from 2 mm/yr near the coast to 0.5 mm/yr inland. This type of deformation indicates that the main driving force responsible for the observed velocities is related to the on-going convergence between Nubia and Eurasia plates. The calculated deformation field shows evidence for localized deformation related to active faults within the area. Most of the deformation is concentrated on the Alhama de Murcia fault, the source of the 2011 Lorca earthquake (M w 5.2). We estimate a reverse-sinistral geodetic slip rate of 1.5 ± 0.3 mm/yr for this fault. Our crustal deformation field and analyses are important contributions to estimating seismic hazard for the eastern Betics, since it is the first time crustal deformation rates at this scale are presented.

We present a new method to determine the average propagation speed of avalanches using seismic techniques. Avalanche propagation speeds can reach 70 m/s and more, depending on a wide range of factors, such as the characteristics of the avalanche track (e.g. topography) and the snowpack properties (e.g. density). Since the damage produced by the avalanche depends primarily on the size and on the speed of the avalanche, the knowledge of the latter is therefore crucial for estimating avalanche induced hazard in inhabited mountain areas. However, our knowledge of this basic physical parameter is limited by the difficulty of conducting various measurements in the harsh winter weather conditions that often accompany this natural phenomenon. The method of avalanche speed determination presented in this paper is based on cross-correlation and time-frequency analysis techniques. The data used in this study come from the Ryggfonn (Norway) avalanche experimental site operated by the Norwegian Geotechnical Institute (NGI), and recorded by an array of 6 geophones buried along the main avalanche path during the 2003-2004 and 2004-2005 winter seasons. Specifically, we examine the speeds of 11 different events, characterized by size and snow type. The results obtained are compared with independent speed estimates from CW-radar and pressure plate measurements. As a result of these comparisons our method was validated and has proved to be successful and robust in all cases. We detected a systematic behaviour in the speed evolution among different types of avalanches. Specifically, we found that whereas dry/mixed type flow events display a complex type of speed evolution in the study area with a gradual acceleration and an abrupt deceleration, the speed of the wet snow avalanches decreases with distance in an approximately linear fashion. This generalization holds for different size events. In terms of time duration and maximum speed of the studied events, dry/mixed type avalanches lasted between 8 to 18 s and reached speeds up to 50 m/s, whereas the duration of wet avalanches ranged between 50 and 80 s and their maximum speeds were 10 m/s.

As part of the South American Geodynamic Activities project we observed the present day deformation field in the territories of Chile and Argentina using the Global Positioning System. The results clearly show that the earthquake cycle dominates the contemporary surface deformation of the central and southern Andes. Compared to geological timescales, the transient elastic deformation related to subduction earthquakes presents a short-term signal which can be explained by interseismic, coseismic, and postseismic phases of interplate thrust earthquakes. We constructed the Andean Elastic Dislocation Model (AEDM) in order to subtract the interseismic loading from the observed velocities. The estimated parameters of the AEDM, and the amount and depth of coupling between the subducting Nazca and overriding South American Plates, represent long-term features and show that the seismogenic interface between both plates is fully locked and that the depth of coupling increases from north to south. The prominent signals in the residual velocity field (i.e. observed velocities minus AEDM) are obviously due to postseismic relaxation processes; they are visible in the area of the 1995 Mw 8.0 Antofagasta earthquake and in the area of the 1960 Mw 9.5 Valdivia earthquake. Although postseismic deformations, compared to geologic timescales, are short-term signals, those signals are valuable constraints on important long-term features of Andean evolution, i.e., the viscosity of the upper mantle and lower crust. The observed surface data are best fitted with a three-dimensional finite element model in which we incorporate a mantle viscosity of 4 × 1019 Pa s. The most obvious long-term deformation signal is manifested in the back-arc of the subduction zone where the Brazilian Shield thrusts beneath the Subandean zone. The style and amount of backarc shortening changes along strike of the orogen, increasing from zero in the south (latitude < −38° S) to values in the order of 10 mm yr−1 close to the Bolivian Orocline. In the fore-arc, whilst we see indications for long-term E-W extension, we did not find any apparent slip partitioning. In addition to this long-term signal, we suggest that the asymmetry of interseismic and coseismic deformation may lead to tectonic structures in the fore-arc. If the coseismic deformation does not release all of the accumulated deformation, then, over many earthquake cycles, part of the interseismic deformation may be transformed into permanent long-term plastic deformation.

We develop a three-dimensional viscoelastic finite element model to study postseismic deformation associated with the 1960 great Chile earthquake. GPS observations 35 years after the earthquake show that, while all coastal sites are moving landward, a group of inland sites 200 - 400 km from the trench are moving seaward and that coastal velocities in the 1960 rupture area are distinctly smaller than those to the north. We explain these observations in terms of mantle stress relaxation. The earthquake stretches the upper plate to move seaward, but elastic stresses coseismically induced in the upper mantle resist this motion. Stress relaxation allows seaward motion to take place in the inland area for several decades following the earthquake. With a viscosity of 2.5 × 1019 Pa s for the continental upper mantle, the model well explains the GPS observations. Numerical tests suggest that the continental mantle viscosity value is reasonably well constrained. The model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip. For short rupture and small coseismic slip, the motion will stop very quickly after the earthquake, explaining why this phenomenon is not more commonly observed. With an oceanic mantle viscosity of 1020 Pa s, the model also provides an explanation for tide-gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the Chile subduction fault.

In this study we present the contemporary crustal deformation field along the central and southern Andes (17-42 - S) estimated from four Global Positioning Sys- tem (GPS) campaigns conducted in 1994-97. We find that the majority of the observed crustal deformation field is relatively homogenous: roughly parallel to the plate conver- gence direction with decreasing velocities away from the trench. We attribute this type of deformation pattern to the inter-seismic phase of an earthquake deformation cycle caused by 100% locking of the thrust interface between the subducting Nazca and the overrid- ing South American plates. We have also detected a strong post-seismic deformation sig- nal in the vicinity of the 1995 Mw8.0 Antofagasta (22-26 - S) and 1960 Mw9.5 Chile (38- 43 - S) earthquakes. This type of deformation can be described as short-term in nature compared to geological timescales. The above conclusions are based on the results of the 3-D Andean Elastic Dislocation Model (AEDM). By subtracting the AEDM predicted deformation rates from the observations we obtained a residual velocity field, that high- lights the post-seismic, as well as more long-term deformation eects. For example, we find a strong evidence for the continuing crustal shortening across the back-arc, reach- ing its maximum (4 mm/yr) in the very north of our study area. In addition, between latitudes 29-34 - S, there is an indication of E-W oriented extension within the fore-arc, in accordance with the recent geologic findings for the N-S oriented normal faulting.

With the advent of global positioning system (GPS) technology and its applications to high precision geodesy, earth scientists have gained an unprecedented opportunity to study the kinematics and dynamics of present-day deformation processes along plate boundary zones. However, until now our knowledge of the deformation processes associated with the Andean subduction along the western coast of South America has been limited. Here we present first estimates of present-day crustal deformation rates in the central and southern sections of the Andes, between latitudes 22‡S and 42‡S. We find that the deformation in the central section of our study area is dominated by the interseismic phase of an earthquake deformation cycle, caused by 100% coupling of the thrust interface between the subducting Nazca and the overriding South America plates. The estimated depth of coupling is not uniform along strike: north of 30‡S it is V33 km deep, while south of 35‡S it reaches 50 km depth. In addition, we observed postseismic relaxation effects in the northern part of our network in the area of the 1995 Mw8.0 Antofagasta earthquake. South of 38‡S, we detected a similar deformation pattern as in the Antofagasta area which we attribute to postseismic relaxation effects of the 1960 Mw9.5 Valdivia earthquake. fl 2001 Elsevier Science B.V. All rights reserved.

[1] Contemporary crustal deformation of the southern Andean margin shows an interesting feature: While nearly all coastal GPS sites move landward, consistent with inter-seismic deformation near a locked subduction fault, sites 300–400 km landward of the rupture region of the Mw9.5 1960 Chile earthquake are moving in the opposite direction. We attribute the seaward motion of these inland sites to a prolonged crustal deformation due to mantle stress relaxation following the 1960 great earthquake. In order to reproduce the observed seaward motion using a three-dimensional finite element model we need to incorporate a mantle viscosity of about 3 × 1019 Pa s. The possibility that the seaward motion is caused by a silent slip event on the plate interface at large depths cannot be completely excluded, and our analysis provides a working model for future field tests.

After a rockfall event, a usual post event survey includes qualitative volume estimation, trajectory mapping and determination of departing zones. However, quantitative measurements are not usually made. Additional relevant quantitative information could be useful in determining the spatial occurrence of rockfall events and help us in quantifying their size. Seismic measurements could be suitable for detection purposes since they are non invasive methods and are relatively inexpensive. Moreover, seismic techniques could provide important information on rockfall size and location of impacts. On 14 February 2007 the Avalanche Group of the University of Barcelona obtained the seismic data generated by an artificially triggered rockfall event at the Montserrat massif (near Barcelona, Spain) carried out in order to purge a slope. Two 3 component seismic stations were deployed in the area about 200 m from the explosion point that triggered the rockfall. Seismic signals and video images were simultaneously obtained. The initial volume of the rockfall was estimated to be 75 m3 by laser scanner data analysis. After the explosion, dozens of boulders ranging from 10−4 to 5 m3 in volume impacted on the ground at different locations. The blocks fell down onto a terrace, 120 m below the release zone. The impact generated a small continuous mass movement composed of a mixture of rocks, sand and dust that ran down the slope and impacted on the road 60 m below. Time, time-frequency evolution and particle motion analysis of the seismic records and seismic energy estimation were performed. The results are as follows: 1 – A rockfall event generates seismic signals with specific characteristics in the time domain; 2 – the seismic signals generated by the mass movement show a time-frequency evolution different from that of other seismogenic sources (e.g. earthquakes, explosions or a single rock impact). This feature could be used for detection purposes; 3 – particle motion plot analysis shows that the procedure to locate the rock impact using two stations is feasible; 4 – The feasibility and validity of seismic methods for the detection of rockfall events, their localization and size determination are comfirmed.

Seismic methods used in the study of snow avalanches may be employed to detect and characterize landslides and other mass movements, using standard spectrogram/sonogram analysis. For snow avalanches, the spectrogram for a station that is approached by a sliding mass exhibits a triangular time/frequency signature due to an increase over time in the higher-frequency constituents. Recognition of this characteristic footprint in a spectrogram suggests a useful metric for identifying other mass-movement events such as landslides. The 1 June 2005 slide at Laguna Beach, California is examined using data obtained from the Caltech/USGS Regional Seismic Network. This event exhibits the same general spectrogram features observed in studies of Alpine snow avalanches. We propose that these features are due to the systematic relative increase in high-frequency energy transmitted to a seismometer in the path of a mass slide owing to a reduction of distance from the source signal. This phenomenon is related to the path of the waves whose high frequencies are less attenuated as they traverse shorter source-receiver paths. Entrainment of material in the course of the slide may also contribute to the triangular time/frequency signature as a consequence of the increase in the energy involved in the process; in this case the contribution would be a source effect. By applying this commonly observed characteristic to routine monitoring algorithms, along with custom adjustments for local site effects, we seek to contribute to the improvement in automatic detection and monitoring methods of landslides and other mass movements.