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In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T- axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10E−8/yr (~6.3 10E−16/s)., Scientific Reports, 8, ISSN:2045-2322

Earthquake early warning (EEW) systems’ performance is driven by the trade-off between the need for a rapid alert and the accuracy of each solution. A challenge for many EEW systems has been the magnitude saturation for large events (Mw>7) and the resulting underestimation of seismic moment magnitude. In this study, we test the performance of high-rate (1Hz) GPS, based on seven seismic events, to evaluate whether long-period ground motions can be measured well enough to infer reliably earthquake predominant periods. We show that high-rate GPS data allow the computation of a GPS-based predominant period (τg) to estimate lower bounds for the magnitude of earthquakes and distinguish between large (MW>7) and great (MW>8) events and thus extend the capability of EEW systems for larger events. It is also identified the impact of the different value of the smoothing factor α on the τg results and how the sampling rate and the computation process differentiates τg from the commonly used τp.

Direct observations of vertical movements of the earth's surface are now possible with space-based GPS networks, and have applications to resources, hazards and tectonics. Here we present data on vertical movements of the Earth's surface in New Zealand, computed from the processing of GPS data collected between 2000 and 2015 by 189 permanent GPS stations. We map the geographical variation in vertical rates and show how these variations are explicable within a tectonic framework of subduction, volcanic activity and slow slip earthquakes. Subsidence of >3 mm/yr is observed along southeastern North Island and is interpreted to be due to the locked segment of the Hikurangi subduction zone. Uplift of 1–3 mm/yr further north along the margin of the eastern North Island is interpreted as being due to the plate interface being unlocked and underplating of sediment on the subduction thrust. The Volcanic Plateau of the central North Island is being uplifted at about 1 mm/yr, which can be explained by basaltic melts being injected in the active mantle-wedge at a rate of ∼6 mm/yr. Within the Central Volcanic Region there is a 250 km2 area that subsided between 2005 and 2012 at a rate of up to 14 mm/yr. Time series from the stations located within and near the zone of subsidence show a strong link between subsidence, adjacent uplift and local earthquake swarms.

GPS and strong-motion sensors are broadly used for the monitoring of structural health and Earth surface motions, focusing on response of structures, earthquake characterization and rupture modeling. Most studies have shown differences between the two systems at very long periods (e.g. >100sec). The aim of this study is the assessment of the compatibility of GPS and strong-motion records by comparing the consistency in the frequency domain and by comparing their respective displacement waveforms for several frequency bands. For this purpose, GPS and strong-motion records of 23 collocated sites of the Mw9.0 Tohoku 2011 earthquake were used to show that the consistency between the two datasets depends on the frequency of the excitation, the direction of the excitation signal and the distance from the excitation source., Smart Structures and Systems, 2015

Monitoring surface deformation in real-time help at planning and protecting infrastructures and populations, manage sensitive production (i.e. SEVESO-type) and mitigate long-term consequences of modifications implemented. We present RT-SHAKE, an algorithm developed to detect ground motions associated with landslides, sub-surface collapses, subsidences, earthquakes or rock falls. RT-SHAKE detects first transient changes in individual GPS time series before investigating for spatial correlation(s) of observations made at neighbouring GPS sites and eventually issue a motion warning. In order to assess our algorithm on fast (seconds to minute), large (from 1cm to meters) and spatially consistent surface motions, we use the 1Hz GEONET GNSS network data of the Tohoku-Oki MW9.0 2011 as a test scenario. We show the delay of detection of seismic wave arrival by GPS records is of ~10 seconds with respect to an identical analysis based on strong-motion data and this time delay depends on the level of the time-variable noise. Nevertheless, based on the analysis of the GPS network noise level and ground motion stochastic model, we show that RT-SHAKE can narrow the range of earthquake magnitude, by setting a lower threshold of detected earthquakes to MW6.5-7, if associated with a real-time automatic earthquake location system., Geophysical Journal International, 214 (2), ISSN:0956-540X, ISSN:1365-246X

We show that high-rate GPS can have a vital role to play in near real-time monitoring of potentially destructive earthquakes. We do this by investigating the potential of GPS in recording strong ground motions from earthquakes in Switzerland and Japan. The study uses finite-fault stochastic ground motion simulation based on Fourier amplitude spectra and duration models previously developed for both countries, allowing comparisons in terms of both Fourier and time domain characteristics (here the Peak Ground Velocity, PGV). We find that earthquakes of magnitude Mw>5.8 can be expected to be recorded by GPS in real-time at 10 km distance, i.e. their Fourier spectrum exceeds the noise of the instruments enough to be used in strong motion seismology. Post-processing of GPS time series lowers the noise and can improve the minimum observable magnitude by 0.1-0.2. As GPS receivers can record at higher rates (> 10 sps), we investigate which sampling rate is sufficient to optimally record earthquake signals and conclude that a minimum sampling rate of 5 sps is recommended. This is driven by recording events at short distances (below 10 km for magnitude 6 events and below 30 km for magnitude 7 events). Furthermore, the Maximum Ground Velocity derived from GPS is compared to the actual PGV for synthetic signals from the stochastic simulations and the 2008 Mw=6.9 Iwate earthquake. The proposed model, confirmed by synthetic and empirical data, shows that a reliable estimate of PGV for events of about magnitude 7 and greater can be basically retrieved by GPS in real-time and could be included for instance in ShakeMaps for aiding post-event disaster management.

Reduced near-infrared reflectance observed in September 1973 in Skylab images of the western flank of Mt. Etna has been interpreted as an eruption precursor of the January 1974 eruption. Until now, it has been unclear when this signal started, whether it was sustained and which process(es) could have caused it. By analyzing tree-ring width time-series, we show that the reduced near-infrared precursory signal cannot be linked to a reduction in annual tree growth in the area. However, comparing the tree-ring width time-series with both remote sensing observations and volcano-seismic activity enables us to discuss the starting date of the pre-eruptive period of the 1974 eruption., Scientific Reports, 7, ISSN:2045-2322

© 2015 IEEE. We evaluate the potential of troposphere models derived from ground meteorological data (pressure, temperature, and relative humidity) and Global Positioning System (GPS) data to improve InSAR measurements and models derived from them. We test this approach on an ERS-2/Envisat data set collected during a transient surface deformation episode that occurred from January to July 2005 in the San Gabriel Valley, southern California, USA. We find that the interferometric phase change observed over the corresponding period cannot be solely attributed to hydrological uplift associated with rising groundwater levels but also includes a significant contribution from differential tropospheric delay due to differing quantities of water vapor in the troposphere on the two SAR observation dates. We show that, if the tropospheric phase contribution is mistakenly interpreted as the range change associated with changes in groundwater storage, both the surface displacement and the groundwater storage coefficient may be overestimated by up to 30%. This method could be applied in real time where meteorological measurements are available near one or more GPS permanent site(s).

International audience; Relying on densely spaced GPS data collected between 1996 and 2007 and on InSAR data spanning the 1992–2001 time period, we explore the effects of lateral rheological heterogeneities across the San Andreas Fault near Point Reyes on the interseismic velocity field. We evaluate heterogeneous elastic dislocation models, including an asymmetric model with contrasting rigidities on either side of the San Andreas Fault and models with a narrow compliant fault zone that lead to high near-fault strain rates. We show that we cannot resolve a compliant zone from interseismic surface displacement measurements unless independent constraints on the locking depth exist. We infer an 18 ± 1 mm yr− 1 slip rate on the San Andreas Fault with a 10 ± 2 km locking depth and a 40% higher rigidity to the SW of the fault. At Bodega Bay, GPS and EDM data suggest a compliant zone on the SAF with a 50-to-60% rigidity decrease, but 25 km further south we find no evidence for a weak fault zone. This suggests substantial variability in fault zone properties along the San Andreas Fault.

Broadband seismic data enable us to test whether Ultra Long Period (ULP) signals can be used to investigate magma chamber pressure state and to monitor volcanic eruptions. By systematically investigating seismic signals at GEOSCOPE station RER, we find ULP signals associated with volcanic events, during the last 2 decades. We tentatively propose to interpret these signals as events highlighting the activity of the upper magma feeding system of the Piton de la Fournaise volcano and as being related to the deep magma chamber. Some of these unusual signals were previously detected and usually interpreted in term of tilt [Battaglia, J., Aki, K., Montagner, J.-.J.-P. Tilt signals derived from a GEOSCOPE VBB station on the Piton de la Fournaise volcano, Geophys. Res. Lett. 27 (5) (2000) 605–608.]. They are detected using STS1 seismometers sensitive in the bandwidth 10 −3 to 10 −2 Hz. This alternative model enables to quantify each event in terms of a pressure drop in the upper magma reservoir of the volcano. Two kinds of seismic waveforms can be associated with two types of fracturing events. The first one is related to the fast rise of a magma batch coming from the deep magma chamber and the second is the result of a slow rise in pressure inside a shallow reservoir. In both cases, we are able to detect these events on very long period seismic data. The interpretation of these signals supports the idea of a single magma source at the sea level. Thus, we propose to classify all the eruptions occurring during the last two decades into two groups, corresponding to the two primary pressure states of the magma chamber. © 2007 Elsevier B.V. All rights reserved.

International audience; The Azores archipelago is located near the triple junction between the Nubian (NU), North America (NA), and Eurasia (EU) plates. It is characterized by a relatively strong seismicity and active volcanism. The best estimate of the current plate velocities in the area over geologic timescales comes from the NUVEL1-NNR model (DeMets et al.) . At the geodetic timescale, plate motion models (Altamimi et al., Sella et al.) including GPS, DORIS, SLR and VLBI data currently do not yet include data from the Azores. In the framework of a research project focused on the seismotectonics and volcanotectonics of São Miguel island, we have analysed GPS data collected there in 1993, 1994, 1997, 2000 and 2002. Our analysis determines both the velocity in the REVEL (Sella et al.) reference frame of São Miguel and its internal deformation. The comparison of the 2000 and 2002 coordinates indicates that São Miguel accommodates moderate WNW-ESE extension at a rate slower than 5 mm yr-1.

Tectonophysics, 599, ISSN:0040-1951, ISSN:1879-3266

On Mt. Etna (Italy), an enhanced Normalized Difference in Vegetation Index (NDVI) signature was detected in the summers of 2001 and 2002 along a distinct line where, in November 2002, a flank eruption subsequently occurred. These observations suggest that pre-eruptive volcanic activity may have enhanced photosynthesis along the future eruptive fissure. If a direct relation between NDVI and future volcanic eruptions could be established, it would provide a straightforward and low-cost method for early detection of upcoming eruptions. However, it is unclear if, or to what extent, the observed enhancement of NDVI can be attributed to volcanic activity prior to the subsequent eruption. We consequently aimed at determining whether an increase in ambient temperature or additional water availability owing to the rise of magma and degassing of water vapour prior to the eruption could have increased photosynthesis of Mt. Etna's trees. Using dendro-climatic analyses we quantified the sensitivity of tree ring widths to temperature and precipitation at high elevation stands on Mt. Etna. Our findings suggest that tree growth at high elevation on Mt. Etna is weakly influenced by climate, and that neither an increase in water availability nor an increase in temperature induced by pre-eruptive activity is a plausible mechanism for enhanced photosynthesis before the 2002/2003 flank eruption. Our findings thus imply that other, yet unknown, factors must be sought as causes of the pre-eruption enhancement of NDVI on Mt. Etna. ISSN:1932-6203

International audience; [1] We have processed thirty Global Positioning System (GPS) campaigns carried out at Etna from 1994 to early 2001 between the last two main flank eruptions of the Mt. Etna (Sicily, Italy). This rest period allowed us to investigate the deep magma plumbing system of the Mt. Etna. The temporal dynamics of twenty-three points observed three times or more were analyzed. All the time series show a first-order linear trend during the five years period. It suggests that the volcano was continuously deformed by the action of a deep source while a discrete activity of the volcano was observed at the summit. We have interpreted the residual deformation field as the result of an major eastward motion of the eastern flank of the volcano.

We present a comparison of long‐period (30 T M w 8.3) with both very broadband seismograms and synthetic waveforms. We show that GPS provides valuable waveform data between 40 and 160 s periods, especially in the near field of the earthquake where seismograms are saturated. There are no long‐period broadband seismic data available in the near field of large earthquakes (∼100 km for earthquakes M w >7 and ∼500 km for earthquakes M w >8). The comparison with synthetic seismic displacement waveforms shows that the GPS waveforms are performing well at periods of 40–80 s at epicentral distances between 150 and 600 km and at periods of 80–160 s at epicentral distances between 150 and 400 km. At longer periods and larger epicentral distances, the amplitudes do not always exceed the noise level (∼2–3 mm), but we still observe at selected GPS sites that the phase and the amplitude of the surface waves are of good quality, up to ∼1200 km. We conclude that GPS waveforms in the near field of a large event can be used for seismological applications. In this article, we recover the focal mechanism of the Tokachi‐Oki event by inverting the GPS data recorded within 300 km of the epicenter.