G3.4

The ocean floor is the outer solid shell for over 70% of our planet, which is continuously moved and deformed in the course of global plate tectonics. These processes lead to tectonic stresses building up in the seafloor, which over long periods of time become so large that they suddenly and usually (still) unexpectedly discharge in an earthquake. In the marine environment, the seafloor cannot be studied with the established tools of tectonic geodesy, as water is not a suitable medium for geodetic systems that depend on the relatively unperturbed transmission of electromagnetic waves. During the past three decades, advances made by using space geodetic systems, such as GPS and InSAR, have revolutionized our ability to precisely track actively deforming areas onshore in high spatial and temporal resolution. Offshore, seafloor geodesy aims at precise underwater measurements of interstation distances, absolute positions, water depth, and tilt. Seafloor displacement occurs in the horizontal (x,y) and vertical direction (z) as a function of time (t). The vertical displacement is measured by monitoring pressure variations at the seafloor. Horizontal seafloor displacement can be measured either using an acoustic/GPS combination to provide absolute positioning or by long-term acoustic telemetry between different beacons fixed on the seafloor to determine relative distances by using the travel time observations to each other, which is the technique used in the framework of the GeoSEA project (Geodetic Earthquake Observatory on the SEAfloor) with the aim to record deformation directly on the seafloor. Acoustic direct path measurements by the GeoSEA Array were conducted across the North Anatolian Fault in the Sea of Marmara, on the flank of Mt Etna in the Ionian Sea, and on the North-Chilean subduction zone in the eastern Pacific. The goal of these observations is to be able to directly measure the stress buildup and use it to refine estimates of the hazard situation. Since the expected deformation rates are low (a few cm/year at most), the stations have to remain on the seafloor for several years, where they measure autonomously in water depths up to 5,500 m with a precision of 5 mm, allowing for precise measurements of strain build-up in the seafloor. The results from the different campaigns reveal the range and degree of coupling as well as the distribution of deformation, ranging from fully locked to slow-slip movement.

How to cite: Kopp, H., Lange, D., Urlaub, M., Petersen, F., and Jegen, A.: In-situ monitoring of strain on the seafloor: an overview and results of the GeoSEA projects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9748, https://doi.org/10.5194/egusphere-egu22-9748, 2022.

The birth of a new volcano offshore the eastern coast of Mayotte, one of the oldest volcanic island in the Comoros archipelago rose questions about the origin of the volcanism in this area. The volcano-tectonic context of this region is poorly known mainly because high-resolution marine data was missing. Here we present new marine geophysical data (bathymetry, backscatter and seismic reflexion data) acquired between December 23 2020 and February 11 2021 during the SISMAORE cruise (Thinon et al., 2021) in the framework of the French ANR COYOTES project. The high-resolution multibeam bathymetric and backscatter data reveal the existence of two submarine volcanic provinces we named N’Droundé and Mwezi (Thinon et al., 2022). In these provinces, we identified faults scarps, volcanic structures, lava flows and flat-top sedimentary domes on the seafloor. Those volcanic and tectonic features are very well preserved in the morphology and very reflective in the backscatter attesting that they are recent and probably active. Several seismic reflection profiles crosscut those structures. They reveal that the sedimentary layers are cut by faults and intruded by sills and dykes. We showed that the recent deformations of the seafloor such as flat-topped domes and grabens are promoted by those intrusions. The recent deformation of the sediments accommodating the magmatic intrusions are used as indirect markers to establish a relative chronology of magmatic activity in the two volcanic provinces. We showed that the magmatism is older in the N’Droundé volcanic province, near Grande Comore than in Mwezi’s, North-East of Anjouan. We also showed from the analysis of sills and dykes in the sedimentary cover that the magmatism intruded during two non-concurring episodes.

Those volcano-tectonic features align in a mean NW-SE direction and may have likely emplaced in a NE-SW extensional stress field. At a smaller spatial scale, some diking-induced graben form swarms of different directions implying local perturbation of the regional stress field by volcanic intrusions.

Overall, those observations are crucial to improve our knowledge of the geodynamics in the area and to constrain boundary conditions for future numerical modeling of deformation at lithospheric scale.

How to cite: Boymond, P., Feuillet, N., Thinon, I., Scholtès, L., Leroy, S., Rusquet, A., Masquelet, C., and Jacques, E. and the SISMAORE team: Volcano-tectonic interactions within two recently discovered submarine volcanic fields: Implication for geodynamics in the Comoros, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10160, https://doi.org/10.5194/egusphere-egu22-10160, 2022.

Earthquake swarms are generally interpreted as phenomena related to external stress perturbation including slow slip events and magma intrusion or weakening of fault strength due to pore pressure increase. Extensive swarm activities accompanying geodetically detectable deformation are often observed along plate boundary faults and volcanic areas. However, an extensive seismic swarm started in December 2021 at the northern tip of the Noto Peninsula, central Japan, which is a non-volcanic/geothermal area far from the major plate boundaries. We present a preliminary report of observed seismicity, crustal deformation, and their interpretation. The swarm activity started with several episodic earthquake bursts in the first several months and turned to be a continuous activity. The number of M≥1 earthquakes has been roughly constant at ~120 per week since July 2021, as of January 2022. The largest M5.1 earthquake occurred on September 16, 2021. Focal mechanisms of large earthquakes including the largest one suggest reverse faulting with a compressional axis of NW-SE. The focal depth ranges between 10-18 km. Transient displacements are observed at three permanent GNSS stations operated by the Geospatial Information Authority of Japan within 30 km from the epicentral region of earthquake swarms. The annual observed displacement from December 2021 suggests inflation with up to 12 mm of horizontal displacement and 30 mm of uplift. We installed four new GNSS stations near the epicentral area in September 2021 and found rapid extensional deformation around the epicentral area. Assuming a spherical inflation (Mogi) source, we estimated an annual volumetric increase of ~2.5 x 10⁷ m³ at a depth of ~12 km. We speculate the volumetric increase is caused by upwelling water originally dehydrated from the subducted Pacific plate. Although the estimated source predicts to increase of the Coulomb stress in the epicentral area, the temporal evolution of crustal deformation and earthquake activity is not always synchronized. It may suggest fault weakening due to pore fluid migration into the fault zone.

How to cite: Nishimura, T., Nishikawa, T., Sato, D., Hiramatu, Y., and Sawada, A.: Ongoing crustal deformation and earthquake swarm in the Noto Peninsula, central Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10652, https://doi.org/10.5194/egusphere-egu22-10652, 2022.

Volcanic reservoirs are usually the main source of freshwater on volcanic islands. On Tenerife Island, groundwater extraction occurs by drilling horizontal water tunnels. This has resulted in a sustained extraction due to the hundreds of water tunnels that have been drilled since around 1900 for agriculture, industry and freshwater supply. The extraction is exceeding the natural recharge, leading to groundwater table decline, locally up to 200+ m of down drop. Since 2000, satellite radar interferometry (InSAR) applied to measure surface deformation has located several subsidence bowls (e.g., Fernandez et al., GRL 2009). The localized surface deformation patterns have been correlated with water table changes and hence aquifer compaction. By overlapping InSAR data time series with Global Navigation Satellite Systems (GNSS) we hope to better understand the compaction processes around volcanic aquifers and explain the observed surface deformation.  This knowledge could help make decisions about water management policies.

To investigate the compaction processes affecting the volcanic rock aquifers of Tenerife, we utilize simultaneous geodetic observations using Global Navigation Satellite Systems time series (GNSS) and satellite radar interferometry over the period October 2014 to December 2021. The GNSS network is composed of 10 GNSS sites and it was processed by the Nevada Geodetic Laboratory (Blewitt et al., 2018; http://geodesy.unr.edu/NGLStationPages/gpsnetmap/GPSNetMap.html). The satellite radar interferometry time series were computed using Sentinel-1 ascending and descending orbits with ID tracks 060 and 096, respectively. Finally, we analyzed the spatio-temporal behaviour using statistical methods to identify distinct regions more or less affected by the underlying aquifer mechanical processes. 

Blewitt, G., W. C. Hammond, and C. Kreemer (2018), Harnessing the GPS data explosion for interdisciplinary science, Eos, 99,https://doi.org/10.1029/2018EO104623.

Fernandez, J., et al. (2009), Gravity-driven deformation of Tenerife measured by InSAR time series analysis, Geophys. Res. Lett., 36, L04306, doi:10.1029/2008GL036920.

How to cite: Jones, M., Gonzalez, P. J., Charco, M., Marrero, R., and Eff-Darwich, A.: Characterizing spatio-temporal changes in volcanic rock aquifer compaction using satellite-based geodetic measurements (GNSS and InSAR), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4565, https://doi.org/10.5194/egusphere-egu22-4565, 2022.

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”).

How to cite: Portela Fernández, J. J., Staller, A., Béjar-Pizarro, M., and Khazaradze, G.: Updating the GNSS velocity field in the Eastern Betics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-208, https://doi.org/10.5194/egusphere-egu22-208, 2022.

GPS measurements within the transform Caribbean–North American plate boundary in Hispaniola, Greater Antilles, with five additional years of data at continuous sites and additional campaign measurements, significantly improve the resulting velocities of earlier works. In a Caribbean-fixed frame, velocities at sites located along the island's southern coast are small (< 2 mm/yr), indicating that the offshore active faults mapped south of Haiti are currently slipping at very low rates. In the Southern Peninsula, velocities are oriented westward, parallel to the Enriquillo fault zone, consistent with strain accumulation on that left-lateral strike-slip fault. North of the Southern Peninsula, including the Gonâve island, velocities are consistently trending SW to WSW, oblique to the east-west direction of the plate boundary. This difference in velocity trend between the Southern Peninsula and areas to the north indicates regional shortening north of the southern Peninsula with an amplitude of 6-7 mm/yr of plate boundary-normal shortening. Geologic and high-resolution seismic data show that this shortening is likely taking place just at the northern coast of the Southern Peninsula, localized on a north-verging reverse fault system offshore the north coast of the Southern Peninsula of Haiti. This reverse fault system extends westward a similar fault system previously described on the southern edge of the Cul-de-Sac Plain, together delineating what we call the "Jérémie-Malpasse" reverse-fault system. This fault zone marks the boundary between the Caribbean Large Igneous Province to the south (CLIP), an oceanic plateau outcropping in the Southern Peninsula, and terranes of island arc crust to the north, a rare case of ongoing obduction in a transform context. This setting, consistent with the source mechanisms of the Mw7.0 January 2010 and Mw7.2 August 20121 earthquakes in southern Haiti, has significant implications in terms of regional seismic hazard.

How to cite: Calais, E., Symithe, S., and Mercier de Lépinay, B.: Geodetic evidence for a significant component of shortening along the northern Caribbean strike-slip plate boundary in southern Haiti, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10329, https://doi.org/10.5194/egusphere-egu22-10329, 2022.

Part of the 5-km high Tibetan plateau is undergoing eastward extension and crustal thinning, which might be the signature of a waning orogeny. However, the actual extent of such processes throughout the high plateau remains uncertain. Here, we examine the impact of tectonic, geodynamic, and climate-related surface processes on the vertical deformation monitored since 2007 by continuous Global Positioning System (GPS) across the East Kunlun Shan (EKS), the largest relief inside the Tibetan plateau. GPS measurements reveal 1-2 mm/yr uplift of the EKS relative to the 2-km-lower Qaidam Basin. However, the range-perpendicular shortening is limited at most to ~1 mm/yr, which is not adequate to drive the observed vertical motion. Instead, (1) the isostatic response to erosion and regional deglaciation since the last glacial period likely accounts for a significant fraction, up to 40%, of our GPS derived vertical rate, and (2) the EKS and its surrounding region to the south are probably still rising at ~1 mm/yr, rather than subsiding. Thus, our results show that this part of the northern Tibetan plateau is rising, demonstrating that the Tibetan Plateau is still actively growing, in contrast with previous models proposing the passive demise of the high plateau due to erosion and gravitational collapse.

How to cite: Liu, S., Nocquet, J.-M., Xu, X., Jónsson, S., Chen, G., Tan, X., and Klinger, Y.: Present-day uplift of the East Kunlun Shan, Northern Tibetan Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10281, https://doi.org/10.5194/egusphere-egu22-10281, 2022.

It is typically assumed that the relative plate motions are not affected by temporal stress changes occurring during the seismic cycle, which comprises a phase of slow buildup of stress (interseismic phase) followed by a phase of sudden release of stress accompanied by rapid fault slip (coseismic phase). However, small- to medium-sized tectonic plates experience a reduced viscous resistance at their base, making the torques necessary to change their motions comparable to those generated by large earthquakes.

Here we explore whether the motions of medium-size tectonic plates experience temporal variations associated with earthquake-cycle stresses. In particular, we focus on the kinematics of the Nazca plate (NZ) in relation to the most recent M_w>8 megathrust earthquakes occurring across the Chilean trench (e.g., 2010 Maule and 2015 Illapel earthquakes). We utilise available GNSS time series to explore links between the recent (i.e., past two decades) plate kinematics and the seismic cycle of megathrust earthquakes occurring along the Chilean subduction zone. Our approach differs from classical studies on the earthquake-cycle induced deformation of the plate boundary region in that it focuses on the potential impact of large earthquakes onto rigid whole-plate kinematics.

How to cite: Martin de Blas, J., Iaffaldano, G., Tassara, A., Melnick, D., and Moreno, M.: Linking the Nazca plate rigid motions to the megathrust earthquakes occurring along the Chilean subduction zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4642, https://doi.org/10.5194/egusphere-egu22-4642, 2022.

The Lisbon Metropolitan Area, in the southern sector of the Lusitanian basin, SW Portugal, has been affected by relevant seismicity. Known destructive earthquakes affecting the region range in time from 1344 to 1969, and include catastrophic occurrences in 1356, 1531, 1909 and 1755. Modern instrumental data are available for the M7.8 Cadiz Gulf earthquake of 1969 only, which reached EMS-98 intensity 5 to 6 in the study area. While several of these earthquakes nucleated offshore, the 1909 earthquake, with estimated magnitude in the range M6.0-M6.5, had a clear intraplate nature, and it is widely accepted that the M7 1531 earthquake also nucleated onshore, in the active structures of the Lower Tagus Valley. The relative importance of the contributions of onshore versus offshore sources to seismic hazard in Portugal is largely debated. On one hand, in view of the modest NW Africa – SW Iberia convergence rate (~4 mm/yr in a NW-SE direction), it has been argued that most of the cumulated crustal deformation is fully released by 1969-type offshore earthquakes of the Gulf of Cadiz, implying that intraplate faults account for very small slip-rates. It follows that destructive intraplate earthquakes are deemed very rare events with limited contribution to the probabilistic hazard. This view is supported by very low intraplate slip-rate estimates of 0.005 to 0.3-0.5 mm/yr derived from geological studies. However, seismic hazard disaggregation studies indicate that the dominant scenario is the rupture of an intraplate fault.

Using a dense GNSS dataset coupled with PSInSAR analysis, we characterize the style of crustal deformation in the Lisbon Metropolitan Area and estimate the associated fault slip rates. We provide evidence of sinistral simple shear driven by a NNE-SSW first-order tectonic lineament. PSInSAR vertical velocities corroborate qualitatively the GNSS strain-rate field, showing uplift/subsidence where the GNSS data indicate contraction/extension. We propose the presence of a small block to the W of Lisbon moving independently towards the SW with a relative velocity of 0.96±0.20 mm/yr. Comparison between geodetic and seismic moment-rates indicates a high seismic coupling. We conclude that the contribution of intraplate faults to the seismic hazard in the Lisbon Metropolitan Area is more important than currently assumed.

How to cite: Fonseca, J., Palano, M., Falcão, A., Hrysiewicz, A., and Férnandez, J.: Crustal deformation near Lisbon, Portugal, from GNSS and PSInSAR data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1351, https://doi.org/10.5194/egusphere-egu22-1351, 2022.

The Central part of the Greater Caucasus, as a part of the Alpine-Himalayan mobile belt, is a zone of complex tectonics associated with the interaction of the two major tectonic plates, Arabian and Eurasian. This work presents the strain rate and spatial distribution in the Central part of the Greater Caucasus. The assessments have been done based on long-term observations on the regional GNSS network, which currently consists of 7 continuous stations and 59 campaign sites. 45 IGS stations were used as the fiducial stations in the data analysis. The strain-rate tensor is calculated using the Shen method.

The results of our study show that, in general, this region is in the state of tectonic compression over which there are some features characteristics of particular structures of the region. The Main Caucasian Ridge and the trough of the southern slope are in the state of not only submeridional compression, but also sublatitudinal extension, which leads to an intensive dilatant expansion of the eastern segment of this area. The strain pattern of the northern part of the region differs from the southern one. The northern slope of the Main Caucasian Ridge zone and the foothill trough, including the Vladikavkaz fault zone, are in the state of compression with moderate intensity. At the same time, an analysis of the distribution of earthquake epicenters has shown that the Northern branch is currently aseismic in the central and eastern parts of the Vladikavkaz fault. This geodynamic feature indicates the high seismic potential of the Vladikavkaz Fault Zone.

This work is supported by the State assignment of the Vladikavkaz Scientific Center RAS, and partly by the Russian Foundation for Basic Research, grant no. 21-55-45007.

How to cite: Milyukov, V., Milronov, A., Steblov, G., Drobishev, V., and Hubaev, H.: Geodynamic features of the Central part of the Greater Caucasus according to GNSS observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2951, https://doi.org/10.5194/egusphere-egu22-2951, 2022.

Assessing the distribution of seismic hazard in the continents requires an understanding of how much deformation is accommodated by major faults. In one view, upper-crustal seismogenic faults respond passively to continuous viscous deformation of the underlying lithosphere; the alternative model is that lithospheric-scale faults control the distribution of deformation and hazard. We combine InSAR data derived from automatic (COMET-LiCSAR) processing of Sentinel-1 data (2015-2021) with a compilation of velocities from GNSS stations to produce the first high-resolution surface velocity field for the Tibetan plateau, where the collision of rigid Indian lithosphere with Eurasia has created the largest deforming region on the planet. We tie the reference frame of InSAR line-of-sight velocities to Eurasia using a joint inversion for surface velocities on a triangular mesh and reference frame adjustment parameters following the approach described in Wang and Wright 2012. We use the referenced InSAR data to invert for high-resolution East-West and Vertical velocities. The results show that the internal deformation of the Tibetan plateau can be described as a combination of distributed deformation and focused strain on a few major faults (Altyn Tagh, Kunlun, Haiyuan, Xianshuihe). We also observe continued postseismic transients associated with earthquakes that occurred within 20 years of the observations, including the 2001 Kokoxili and 1997 Manyi earthquakes. The highest elevations of the Tibetan plateau show dilatation, demonstrating the importance of internal buoyancy forces in continental tectonics. We present a new dynamic model that can explain the key features of the observations.

How to cite: Wright, T., Elliott, J., Fang, J., Hooper, A., Houseman, G., Lazecky, M., Maghsoudi, Y., Ou, Q., Parsons, B., Rollins, C., Styron, R., Wang, H., and Zheng, G.: The Dynamics of the India-Asia collision revealed by Geodetic Imaging of the Tibetan plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1675, https://doi.org/10.5194/egusphere-egu22-1675, 2022.

The 2017 Mw 7.3 Sarpol-e Zahab earthquake is the largest instrumentally recorded event to have ruptured in the Zagros Fold-thrust belt. In this study, we perform multi-temporal interferometry analysis using Sentinel-1 SAR data to investigate changes in postseismic ground deformation at the Earth’s surface and interpret this change in terms of various models including kinematic afterslip, stress-driven afterslip and viscoelastic response. We show that the kinematic afterslip model can explain the postseismic deformation spatiotemporally, while the stress-driven afterslip model tends to underestimate the earlier deformation in the western part of the postseismic deformation field. The viscoelastic response, however, is negligible with the best-fitting viscosity which is on the order of 10¹⁹ Pa s. By an integrated analysis of geodetic inversion results, geological cross-section data, regional stratigraphic column and local structures, we infer that the spatial heterogeneity of frictional property of fault plane and/or more complex geological structures may explain the underfitting between the earlier postseismic deformation and the corresponding stress-driven afterslip models. Because the coseismic rupture propagated along a basement-involved fault while the postseismic slip was more likely activated the frontal structures and/or shallower detachments in the sedimentary cover, the 2017 Sarpol-e Zahab earthquake may be evidence of a typical event which contributes both of the thick- and thin-skin shortening of Zagros in both seismic and aseismic way.

How to cite: Guo, Z., Motagh, M., Hu, J.-C., Xu, G., Haghighi, M. H., Bahroudi, A., and Fathian, A.: Transient aseismic slip and crustal shortening following 2017 Iran-Iraq (Sarpol-e Zahab) Mw 7.3 Earthquake Inferred from 3 years of InSAR Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2737, https://doi.org/10.5194/egusphere-egu22-2737, 2022.

In order to improve our understanding of the present-day  continental deformation in the Iranian-Turkish plateau we map the surface motions across the Iranian-Turkish boundary between Ardabil (NW Iran) and Van (E Turkey) using Sentinel-1 satellites’ TOPSAR data between 2014 and 2021 on descending (6, 79, 152) and ascending (101, 174 and 72) tracks. Interferograms generated with GMTSAR are used to calculate PS-InSAR time series with the multi-temporal InSAR analysis tools of the StaMPS software. Mean line of sight (LOS) velocity fields reveal a dominant right-lateral shear zone between Tabriz and Van acting as a boundary between Eurasian and Arabian plates. The Tabriz-Van shear zone (TVSZ) comprises the North Tabriz, Kotur, Ozalp and Ercis faults. We model the LOS velocity fields using TDEFNODE, a fortran package for block modelling and estimate slip rates and locking depthes along the TVSZ. The best fitting model suggests a 9±2 km of looking depth and a westward increasing slip rate from 7 to 10±2 mm/yr, consistent with GNSS observations. To the west the TVSZ appears to join with Karliova Triple Junction (KTJ). This dextral slip fault zone accommodates a part of motion resulting from the Arabia–Eurasia collision and has experienced a westward migration in M > 5 events since the 18th century including the 18th and 19th century M > 7 events along the North Tabriz Fault. 

How to cite: Nozadkhalil, T., Çakir, Z., Ergintav, S., and Özakin, A.: Interseismic Strain Accumulation Along The Tabriz-Van (Iran-Turkey) Shear Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7131, https://doi.org/10.5194/egusphere-egu22-7131, 2022.

Geodetic measurements of crustal deformation can provide crucial constraints on a region’s tectonics and seismic hazard. An ideal is for these measurements to be able to directly image deformation well enough (at the surface) that the remaining uncertainty is largely about its depth extent. For this, geodetic measurements need to be five things: spatially dense (on the scale of individual faults), spatially wide-ranging (enough to capture the entirety of strain signals), temporally dense (enough that noise and nuisances can be understood), temporally wide-ranging (enough to bring out gradual interseismic deformation), and accurate. Sentinel-IA InSAR, as processed through large-scale workflows like the COMET-LiCS system and when combined with high-quality GNSS data, is arguably the first geodetic dataset with the potential to be all five. We are using this combination to construct high-resolution maps of crustal deformation and strain across the Alpine-Himalayan Belt. In the Anatolia-Caucasus region, we resolve the large-scale deformation patterns of the North Anatolia and East Anatolian Faults, and a deformation front extending northeastward from their intersection into the Caucasus that is consistent with the locations of large earthquakes. Taking this relationship further, we pair the strain rate map with the Turkish and ISC-GEM seismic catalogues to estimate the recurrence intervals of large, moderate and small earthquakes throughout the Anatolia-Caucasus region assuming conservation of seismic moment. On the North Anatolian Fault, we find that this balance is consistent with the ~250-year recurrence interval between the last two earthquake sequences.

How to cite: Rollins, C., Wright, T., Maghsoudi, Y., Lazecky, M., Hooper, A., and Weiss, J.: Tectonic strain rates in the Anatolia-Caucasus region from Sentinel-I InSAR and GNSS, and their implications for seismic hazard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1948, https://doi.org/10.5194/egusphere-egu22-1948, 2022.

In the current plate tectonics paradigm, relative plate motions remain unperturbed by temporal stress changes occurring during the seismic cycle, whereby the stress slowly built up along tectonic plate boundaries is suddenly released by rapid fault slip during earthquakes. However, the viscous resistance at the base of tectonic units of small size (i.e., microplates), and thus the torques needed to change their rigid motions, are significantly smaller than those needed for large size plates. In fact, a recent study that generates numerical simulations of synthetic microplates indicates that it is theoretically possible to link the temporal evolution of geodetically-observed microplate motions to the stresses associated with the seismic cycle.

Here we show that the rigid motion of the whole Anatolian microplate, measured using space geodetic techniques, was altered by the stress released during the 1999 Izmit-Düzce earthquakes, which ruptured along the North Anatolian Fault. This kinematic change requires a torque change that is in agreement with the torque change imparted upon the Anatolian microplate by the Izmit-Düzce coseismic stress release. This inference holds across realistic ranges of data noise and controlling parameters, and is not hindered by active deformation in western Anatolia. These results suggest the existence of a whole-plate kinematic signal associated with the stress released by large earthquakes.

How to cite: Iaffaldano, G., Martin de Blas, J., and Calais, E.: Have the 1999 Izmit-Düzce earthquakes influenced the motion and seismicity of the Anatolian microplate?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4587, https://doi.org/10.5194/egusphere-egu22-4587, 2022.

Contemporary rigid motions of tectonic plates, which are inferred from geodetic data collected over several years, are commonly assumed to remain steady over the earthquake cycle. Such a tenet is predicated on the notion that stresses associated with the earthquake cycle might not be sufficient to overcome the asthenosphere viscous resistance at the lithosphere base, which counters plate--motion changes. This, however, has never been verified against observations. Here we focus on the Apulia microplate, a rigid tectonic unit located in the buffer zone between the Eurasia and Nubia plates, to show that its rigid motion constrained by Global Positioning System time series has changed in the decade preceding the Mw 6.4, 26 November 2019 Durres (Albania) earthquake. Furthermore, we investigate whether such a change could be the result of the interseismic stress buildup associated with the Durres earthquake cycle. 

How to cite: Í Dali Udbø, B., Iaffaldano, G., and Martin de Blas, J.: Decadal change of the Apulia microplate motion preceding the Mw 6.4, 26 November 2019 Durres (Albania) earthquake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4483, https://doi.org/10.5194/egusphere-egu22-4483, 2022.

Northern Algeria experienced moderate and large earthquakes (with Mw > 6) during the last decades due to the convergence between the African and Eurasian plates. We conduct the joint analysis of multi-temporal SAR-dataset (1995 to 2021), combined with the GPS velocities (2007 to 2018) and seismotectonic studies in the Chlef-El Asnam and Zemmouri Mitidja regions of the Tell Atlas. The multidisciplinary approach adopted in this study has the advantage of integrating the interseismic (paleoseismology, tectonic geomorphology), the coseismic and postseismic (airborne geodesy) crustal deformation. The multi-temporal interferometry is performed using the standard method for persistent scatterers (StaMPS/MTI software) applied to ERS1/2, ENVISAT and Sentinel SAR images, all from C-band dataset on descending and ascending  orbits. The GPS velocities are modeled and re-interpreted  from previous works in order to fit the tectonic block sub-division and related major faulting geometry. The seismicity rate and associated major earthquakes such as the El Asnam in 10/10/1980 (Mw 7.1) and Zemmouri-Boumerdes in 05/21/2003 (Mw 6.8) mark the seismotectonic characteristics of the Tell Atlas. The achieved data analysis and results of the joint InSAR, GPS and seismotectonics reveal that large areas with active deformation undergo uplifting and shortening with a consistent tectonic, geodetic and seismicity rate ranging between 2 and 3 mm/yr.

How to cite: Miloudi, S., Meghraoui, M., Bagdi, S., Hasni, K., and Kahlouche, S.: Crustal deformation along the Tell Atlas of Algeria from joint multi-temporal InSAR, GPS results and seismotectonic analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3210, https://doi.org/10.5194/egusphere-egu22-3210, 2022.

On November 29, 2020 an ~6 Mw earthquake occurred at a depth of almost 10 km (United States Geological Survey) in the Eastern Cordillera in northwestern Argentina. The epicenter was located near the towns of Caspalá and Santa Ana (Salta province) in the Quebrada de Humahuaca, and the maximum surface deformation was measured over the Hornocal syncline. The earthquake was the first recorded in this area in the last three decades. As a consequence, several mass movements were triggered from the nearby slopes composed of mechanically weakened rocks. Fortunately, only damage to buildings and infrastructure were reported.

This research presents the vertical deformation associated with this event relying on Sentinel 1A/1B C-band and ALOS2 L-band data. We generate interferometric time series from the Sentinel data, spanning 2 years prior to the event, on ascending and descending passes and invert to displacement time series. We use ALOS2 (Scansar mode) data on ascending and descending passes, and create interferograms by pairing images acquired before and after the earthquake. We determine the three-dimensional motion components by combining the four view angles. Using the Sentinel-1 data, we analyzed the coherence time series to identify mass movements triggered by the earthquake, thus we present a mass-movement detection approach for SAR coherence data using varying time scales and durations of coherence calculations.

Based on the interferometric time series from the Sentinel data on ascending and descending passes, we measured a maximum cumulative line-of-sight (LOS) displacement of about 10 cm over the Hornocal syncline. We measured similar LOS displacement in interferograms based on ALOS data. We determine that the Hornocal fold subsided and the maximum deformation area was constrained between 65.25° and 65.10° W longitude with 23.31° S as central latitude. Moreover, results based on the coherence time series showed that the maximum concentration of mass movements occurred within the closest 10 km of the epicentre, mainly on the slopes of the Hornocal syncline. Additional mass movement signals were recorded several kilometres from the source. The mass movements triggered by the earthquake exceed the number of mass movements associated with rainfall during the South American Monsoon.

How to cite: Viotto, S., Bookhagen, B., Toyos, G., and Torrusio, S.: The 29th November, 2020 Earthquake in the Eastern Cordillera (NW Argentina): new results on InSAR and coherence time-series analyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5142, https://doi.org/10.5194/egusphere-egu22-5142, 2022.