The Western European Alps display measurable surface deformation rates from leveling and GNSS data. Based on the time‐series analysis of 4 years of Sentinel‐1 data, we propose for the first time an ...InSAR‐based mapping of the uplift pattern affecting the Western Alps on a ∼350 × 175‐km‐wide area. This approach provides a denser spatial distribution of vertical motion despite the high noise level inherent to mountainous areas and the low expected deformation signal. Our results show consistency with other geodetic measurements at the regional scale, and reveal smaller‐scale spatial variations in the uplift pattern. Higher uplift rates are found within the external crystalline massifs compared to surrounding areas, in agreement with the variations expected from recent deglaciation and long‐term exhumation data. This work brings the first InSAR‐based geodetic clue of differential uplift within the Alpine belt in response to the surface and deep processes affecting the belt.
Plain Language Summary
The surface of the Earth is constantly moving from about a few millimeters to a few centimeters per year in response to geological processes such as tectonic plate motions and gravitational re‐equilibrium. In the Western European Alps, where the mountain‐building phase of the belt is over, the processes at the origin of surface motions are under debate. Mapping surface displacements at the highest possible resolution is mandatory to better understand the evolution of the Alpine belt. Among other techniques, radar satellites can provide measurements of such displacements. Here, radar images from the recent Sentinel‐1 satellite allow us to improve the spatial resolution of vertical surface displacements in the Western Alps compared to previous techniques. Thanks to the unmatched frequency of acquisitions from this satellite, we are able for the first time in our study area to measure small‐scale spatial variations within the vertical motions. These variations appear correlated to distinct geological units. This brings new insights into the geological processes acting nowadays on the Western Alps.
Key Points
We use four years of Sentinel‐1 radar acquisitions to derive interseismic line‐of‐sight velocities over the Western European Alps
InSAR‐derived velocities are consistent with other geodetic studies and provide increased spatial resolution of surface velocity patterns
Short‐wavelength spatial variations show locally higher velocities localized on crystalline massifs, interpreted as higher uplift rates
SUMMARY
Due to the steady moderate seismicity observed along the Briançon seismic arc, in the south-western French Alps, three temporary GNSS (Global Navigation Satellite System) surveys took place ...in 1996, 2006 and 2011, across a ∼50 × 60 km² wide area, to investigate the surface deformation field. The horizontal velocity field computed from these three surveys showed an east–west extension in the network. A fourth campaign was led in 2016, creating a 20 yr observation span, resulting in measurements which reach a sufficient accuracy to assess whether extension found within the Briançon network is localized onto any particular tectonic feature. Several faults in this area are known to be active normal faults. Assessing the localization of the deformation may lead to a better understanding of the active tectonics of the Alpine belt. To address this issue, a robust velocity field was computed from the combination of the different campaign and permanent GNSS data. Strain rate tensors were derived for the first time in this area on a 0.1 × 0.1 deg grid to assess the distribution of the deformation. The regional deformation appears localized in the Briançon area and reaches up to 20 ± 5 nanostrain yr−1 in the centre of the network. The observed velocities were projected on a profile across the network and compared with modelled interseismic deformation to characterize the behaviour of the major active faults known in the study zone. While a two-fault model provides the best fit to the data, a single fault model has only marginally higher residuals, with parameters which are more consistent with the seismotectonics of the region. The localization of the single modelled fault is consistent with the location of the High Durance Fault (HDF). Therefore, we used the known geological location of this structure as a priori information in a block model to compute a fault slip rate at the interface between the two blocks. The velocities on the interface indicate 0.4–0.5 mm yr−1 of extension, and therefore strain accumulates along the HDF throughout the seismic cycle. The geodetically derived fault slip rate is converted into an equivalent seismic moment release rate, which is consistent within its uncertainty bounds with the known historical and instrumental seismicity of the Briançon area.
The Mw 6.4 right‐lateral Petrinja earthquake (2020, Croatia) is one of the largest continental earthquakes of central Europe for decades. The slip pattern of such events is usually difficult to ...retrieve with terrestrial geodesy due to limited monitoring means. This study takes advantage of a unique data set of dense measurements of coseismic displacement in the epicentral area, obtained by repeated measurements of benchmark networks designed for civilian purposes, and supplemented by far‐field continuous GNSS measurements. Elastic modeling of these data shows two coseismic slip patches that extend over a 15 × 10 km rupture plane, locally reaching the surface, and that a right‐lateral sub‐parallel secondary fault in the central part of the rupture likely accommodated part of the coseismic deformation. This study demonstrates that rapid re‐measurement of pre‐existing civilian networks offers unique coseismic constrains in the near‐field where InSAR or optical image correlation may decorrelate.
Plain Language Summary
The magnitude 6.4 Petrinja earthquake that stroke Croatia on 29 December 2020, is one of the largest earthquakes registered for decades in continental Europe. Large damage and surface ruptures were observed, suggesting that the earthquake occurred at a very shallow depth. The slip pattern for such moderate magnitude earthquakes is usually difficult to retrieve with terrestrial geodesy because of limited monitoring means and small deformations. In this study, we use a unique data set made of dense coseismic displacement estimates in the epicentral area obtained by repeated positioning measurements of benchmark networks designed for civilian purposes. The inversion of this displacement field completed by far‐field continuous GNSS measurements shows that the coseismic slip on the Petrinja‐Pokupsko fault is limited to depths no greater than 10 km and has reached the surface locally. A single‐fault model explains well the data, but the fit is largely improved with a sub‐parallel secondary fault in the central part of the rupture. This study demonstrates that quick remeasurement of pre‐existing civilian networks can offer unique constrains on the coseismic deformation and the associated fault geometry when spatial techniques such as InSAR or optical correlation may decorrelate.
Key Points
Real Time Kinematics measurements of civilian networks capture near‐field coseismic displacements of the 2020 strike‐slip Petrinja earthquake
Time‐series from regional continuous GNSS stations constrain coseismic deformation in the far‐field
Elastic modeling argues for two slip patches on the main fault and for significant slip on a parallel secondary fault
Ebola and Marburg viruses are the only members of the Filoviridae family (order Mononegavirales), a group of viruses characterized by a linear, non-segmented, single-strand negative RNA genome. They ...are among the most virulent pathogens for humans and great apes, causing acute haemorrhagic fever and death within a matter of days. Since their discovery 50 years ago, filoviruses have caused only a few outbreaks, with 2317 clinical cases and 1671 confirmed deaths, which is negligible compared with the devastation caused by malnutrition and other infectious diseases prevalent in Africa (malaria, cholera, AIDS, dengue, tuberculosis…). Yet considerable human and financial resourses have been devoted to research on these viruses during the past two decades, partly because of their potential use as bioweapons. As a result, our understanding of the ecology, host interactions, and control of these viruses has improved considerably.
Large earthquakes produce crustal deformation that can be quantified by geodetic measurements, allowing for the determination of the slip distribution on the fault. We used data from Global ...Positioning System (GPS) networks in Central Chile to infer the static deformation and the kinematics of the 2010 moment magnitude (M(w)) 8.8 Maule megathrust earthquake. From elastic modeling, we found a total rupture length of ~500 kilometers where slip (up to 15 meters) concentrated on two main asperities situated on both sides of the epicenter. We found that rupture reached shallow depths, probably extending up to the trench. Resolvable afterslip occurred in regions of low coseismic slip. The low-frequency hypocenter is relocated 40 kilometers southwest of initial estimates. Rupture propagated bilaterally at about 3.1 kilometers per second, with possible but not fully resolved velocity variations.
SUMMARY
Quito, the capital city of Ecuador hosting ∼2 million inhabitants, lies on the hanging wall of a ∼60-km-long reverse fault offsetting the Inter-Andean Valley in the northern Andes. Such an ...active fault poses a significant risk, enhanced by the high density of population and overall poor building construction quality. Here, we constrain the present-day strain accumulation associated with the Quito fault with new Global Positioning System (GPS) data and Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) analysis. Far field GPS data indicate 3–5 mm yr–1 of horizontal shortening accommodated across the fault system. In the central segment of the fault, both GPS and PS-InSAR results highlight a sharp velocity gradient, which attests for creep taking place along the shallowest portion of the fault. Smoother velocity gradients observed along the other segments indicate that the amount of shallow creep decreases north and south of the central segment. 2-D elastic models using GPS horizontal velocity indicate very shallow (<1 km) locking depth for the central segment, increasing to a few kilometres south and north of it. Including InSAR results in the inversion requires locking to vary both along dip and along strike. 3-D spatially variable locking models show that shallow creep occurs along the central 20-km-long segment. North and south of the central segment, the interseismic coupling is less resolved, and data still allows significant slip deficit to accumulate. Using the interseismic moment deficit buildup resulting from our inversions and the seismicity rate, we estimate recurrence time for magnitude 6.5 + earthquake to be between 200 and 1200 yr. Finally, PS-InSAR time-series identify a 2 cm transient deformation that occurred on a secondary thrust, east of the main Quito fault between 1995 and 1997.
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.
Collisional mountain belts grow as a consequence of continental plate convergence and eventually disappear under the combined effects of gravitational collapse and erosion. Using a decade of GPS ...data, we show that the western Alps are currently characterized by zero horizontal velocity boundary conditions, offering the opportunity to investigate orogen evolution at the time of cessation of plate convergence. We find no significant horizontal motion within the belt, but GPS and levelling measurements independently show a regional pattern of uplift reaching ~2.5 mm/yr in the northwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhances the vertical response to surface unloading, the summed effects of isostatic responses to erosion and glaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transient glacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In the absence of active convergence, the observed surface uplift must result from deep-seated processes.
Abstract
The NE‐dipping Anghiari normal fault, bounding to the west the Sansepolcro basin in the Upper Tiber Valley (northern Apennines), is thought to be a synthetic splay of the Altotiberina ...low‐angle normal fault (LANF), an active ENE‐dipping extensional detachment whose seismogenic behavior is debated. In order to assess the Anghiari fault capability to break the surface during strong earthquakes and be the source of historical earthquakes, we acquired high resolution topographic data, performed field survey and geophysical investigations (Seismic reflection, Ground Penetrating Radar, Electrical Resistivity Tomography) and dug three paleoseismological trenches across different fault sections of the Anghiari fault. The acquired data reveal for the first time the Late Pleistocene to historical activity of the Anghiari fault, constraining the age of seven paleo‐earthquakes over the last 25 ka, the youngest of which is comparable with one of the poorly constrained historical earthquakes of the Sansepolcro basin. The yielded slip rate is >0.2 mm/yr averaged over the last 25 ka and the recurrence interval is about 2,500–3,200 years. An analysis of the anisotropy of the magnetic susceptibility performed in one of the paleoseismological trenches revealed an extensional stress field, continuously acting during the sedimentation of the entire trenched stratigraphy. Our results confirm the ability of the Anghiari fault to generate surface faulting earthquakes. In addition, if the Anghiari fault does sole at depth into the Altotiberina low‐angle normal fault, this LANF could also be seismogenic and generate
M
> 6.
Plain Language Summary
We analyzed the capability of the Anghiari fault (Upper Tiber Valley, Northern Apennines of Italy) to reach and break the topographic surface during a strong earthquake. This fault may links to the Altotiberina low‐angle normal fault (ATF), a detachment fault accompanied by a system of synthetic splays whose seismogenic behavior is still debated because of a lack of seismological and paleoseismological data. Thanks to geological, morphological, and geophysical analyses, four sites have been selected for paleoseismological investigation. The paleoseismological data revealed the seismic history of the Anghiari fault, assessing its capability to recurrently break the surface during strong earthquakes. In addition, an analysis of the anisotropy of the magnetic susceptibility performed in one of the paleoseismological trenches indicates that the stress field has been extensional, acting continuously during the sedimentation of the entire trenched stratigraphy. Our results suggest that the AF is capable to break the surface during strong earthquakes. This has potential implications for the seismogenic behavior of the ATF low‐angle normal fault, as the strong earthquakes (
M
> 6) may nucleate on the low‐angle fault plane if the AF is soling at depth into that detachment.
Key Points
Revealed the Late Pleistocene—Holocene slip history of the Anghiari fault, considered a synthetic splay of a low‐angle normal fault
The capability of the Anghiari fault to rupture the surface during
M
> 6 earthquakes has been ascertained
The results have potential implications for the activity and seismogenic behavior of a continental low‐angle normal faults
PDF
