We report the first detection of unrest at Socompa, Northern Chile, a stratovolcano which has recorded no eruptions since ~7,200 years ago. We measure deformation at and around Socompa using Interferometric Synthetic Aperture Radar (InSAR) observations between Jan 2018 and Oct 2021. We find that, whilst initially inactive, Socompa shows a steady uplift (17.5 mm/yr) from Dec 2019, independently recorded by near-field continuous Global Positioning System (GPS) data. The data can be fit with pressure increase in an ellipsoidal source region stretching from 1.9 to 9.5 km, with a volume change rate of ~5.8×106 m3/yr. Our observations of the onset of uplift preclude the possibility that a nearby Mw 6.8 deep intraslab earthquake on 3rd June 2020 triggered the unrest. The deformation signal we detect indicates the initiation of unrest at Socompa, after at least two decades without measurable deformation, and many thousands of years without volcanic activity.

Cosmogenic exposure data can be used to calculate time-varying fault slip rates on normal faults with exposed bedrock scarps. However, the method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to determine the slip rate of a fault. Here we show that by applying strict sampling criteria and using geologically informed modelling parameters in a Bayesian-inference Markov chain Monte Carlo method, similar patterns of slip rate changes can be modelled at multiple sites on the same fault. Consequently, cosmogenic data can be used to resolve along-strike fault activity. We present cosmogenic 36Cl concentrations from seven sites on two faults in the Italian Apennines. The average slip rate varies between sites on the Campo Felice Fault (0.84 0.23 to 1.61 0.27 mm yr ^-1), and all sites experienced a period of higher than average slip rate between 0.5 and 2 ky and a period of lower than average slip rate before 3 ky. On the Roccapreturo fault, slip rate in the centre of the fault is 0.550.11 and 0.350.05 mm yr ^-1 at the fault tip near a relay. The estimated time since the last earthquake is the same at each site along the same fault. These results highlight the potential for cosmogenic exposure data to reveal the detailed millennial history of earthquake slip on active normal faults.

Interferometric Synthetic Aperture Radar (InSAR) is used to measure deformation rates over whole continents to constrain tectonic processes. The resulting velocity measurements are only relative, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. However, these ambiguities mostly cancel when using spectral diversity to estimate along-track motion, allowing measurements to be made with respect to a global reference frame. Here, we calculate along-track velocities for a partial global dataset of Sentinel-1 acquisitions and find good agreement with ITRF2014 model values. We include corrections for solid-earth tides and gradients of ionospheric total electron content. By combining data from ascending and descending orbits we are able to estimate north and east velocities with average precision of 4 and 20 mm/year, respectively. Although we have calculated these over large 250x250 km areas, such measurements can also be made at much higher resolution, albeit with lower accuracy. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation, where GNSS measurements are sparse.

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 M$_{\mathrm{w}}=7.5$ Palu earthquake (Sulawesi, Indonesia). With a predominantly strike-slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake-induced landslides. In this study we examine the tsunami potential of the co-seismic deformation. To this end, we present a novel geodetic dataset of GPS and multiple SAR-derived displacement fields to estimate a 3D co-seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co-seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co-seismic uplift (~2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co-seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video-derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co-seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic dataset constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike-slip faults in transtensional basins.

InSAR measurements of ground displacement are relative, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. However, these ambiguities mostly cancel when using spectral diversity to estimate along-track (azimuth) velocities allowing measurements to be made with respect to a terrestrial reference frame. Here, we calculate along-track velocities for a partial global dataset of Sentinel-1 acquisitions as processed by the COMET LiCSAR system, and find good agreement with model values from ITRF2014 plate motion model. We include corrections for solid-Earth tides and gradients of ionospheric total electron content based on a moderate resolution model IRI2016. Application of tidal corrections improves the average velocity precision from 23 to 11 mm/yr. Ionospheric corrections, however, have significant effect only in near-equatorial regions. The median difference between along-track velocities and values predicted by ITRF2014 is 3 mm/yr. A preliminary study using reprocessed precise orbit determination products in a limited dataset shows significant improvement in both precision and accuracy. By combining data from ascending and descending orbits we are able to estimate north-south (N-S) and east-west (E-W) velocities with an average precision of 3 and 16 mm/yr, respectively. Although we have calculated these estimates over large 250 x 250 km areas, such measurements can also be made at much higher resolution, albeit with lower precision. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation, where GNSS measurements are sparse. We will also investigate large-scale averages of across-track (range) pixel offsets, which are most sensitive to E-W and vertical displacements, and perform a comparison to a GNSS network in selected areas.

Processes that facilitate the transition between continental rifting and sea-floor spreading remain unclear. Variations in the spatial distribution of extension through Afar and into the Red Sea are indicative of temporal evolution of the rift. We develop a time series of Sentinel-1 interferometric synthetic aperture radar (InSAR) observations of ground deformation covering the whole Afar Rift from 2014-2019, to study the distribution of extension across all magmatic segments. By incorporating GNSS observations, we resolve 3D average velocities in the vertical, rift-perpendicular, and rift-parallel directions. Results show the spatial distribution of long-term plate motions over the rift, as well as deformation at individual volcanic centres, including Dallol, Nabro, and Erta ’Ale. We find that in northern and central Afar, the majority of extension is accommodated within +/- 15-30 km of magmatic spreading centres. In southern Afar, near the Nubia-Arabia-Somalia triple-junction, extension is distributed over 90-180 km, which may indicate an increase in rift focussing with rift maturity. We also observe rapid surface uplift and rift-perpendicular extension at the Dabbahu-Manda-Hararo segment with velocities of 33 +/- 4 mm/yr and 37 +/- 4 mm/yr respectively. These are higher than the background extension rate of 18-20 mm/yr, but have decreased by 55-70 % since 2006-10. The data suggests that this is due to an on-going long-lived response to the 2005-10 rifting episode, with potential continued processes below the segment including a lower-crustal viscous response and magma movement. Continued long-term observations of surface deformation provide key constraints on tectono-magmatic processes in Afar.