G3.4

G3 EDI

The study of the deformation processes in the interior and boundaries of oceanic and continental plates relies strongly on geodetic surveys. The recent development of dense GNSS networks and Interferometric Synthetic Aperture Radar (InSAR) satellite missions with higher spatio-temporal resolution data, and seafloor geodesy experiments (pressure monitoring, acoustic ranging, GNSS-Acoustic positioning...) has significantly enhanced the level of observations and analysis of numerous active deformation areas, and the understanding of geodynamics of lithospheric plates. Interplate and intraplate tectonic domains may also expose striking examples of crustal deformation including large or moderate earthquakes. Such great wealth of new data allows us to tackle fundamental questions to understand strain-partitioning in present-day active zones, the kinematics of crustal tectonic blocks and its relationship with seismogenic fault sources, and between lithospheric processes and surface deformation. Such new knowledge will be greatly benefited from comparisons with theoretical and experimental models, or joint inversion efforts including sea-land- or space-based geophysical and geochemical surveys.
In this session, we seek contributions using geodetic, geophysical, geologic and seismotectonic data analysis in continental and oceanic active deformation zones, including intraplate volcanic provinces. In particular, studies with multidisciplinary approaches using geodesy, seismology, tectonics and geophysics that bring new constraints on the strain distribution, plate kinematics and lithospheric deformation. Our aim is to discuss new geodetic results and show how they contribute to our understanding of the geodynamics of the lithosphere.

Co-sponsored by IUGG
Convener: Pablo J. Gonzalez | Co-conveners: Lavinia TuniniECSECS, Pierre SakicECSECS, Mustapha Meghraoui, Takuya Nishimura
Presentations
| Tue, 24 May, 13:20–18:20 (CEST)
 
Room D3

Presentations: Tue, 24 May | Room D3

Chairpersons: Pierre Sakic, Takuya Nishimura, Pablo J. Gonzalez
13:20–13:30
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EGU22-9748
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solicited
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Highlight
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Virtual presentation
Heidrun Kopp, Dietrich Lange, Morelia Urlaub, Florian Petersen, and Anna Jegen

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.

13:30–13:37
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EGU22-1652
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ECS
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Presentation form not yet defined
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Yuto Nakamura, Tadashi Ishikawa, Shun-ichi Watanabe, and Yusuke Yokota

The Japanese Islands lie along subduction zones where the Pacific Plate and the Philippine Sea Plate subduct, making the islands one of the most seismically active zones in the world. Japan, prone to earthquake disasters throughout its history, has constructed numerous seismic and geodetic observation networks to elucidate the mechanism of catastrophic megathrust earthquakes that occur along the plate boundary near the subduction zones.

The Hydrographic and Oceanographic Department of the Japan Coast Guard (JCG) is one of the government branches that conduct geodetic observations to advance megathrust earthquake research. JCG conducts seafloor geodetic observation using the GNSS-Acoustic ranging combination technique (GNSS-A). GNSS-A enables us to measure the global coordinates of a seafloor reference point in precision of centimeters by simultaneously conducting GNSS observation of a sea surface platform (i.e., survey vessel, buoy, autonomous vehicle…) and trilateration of seafloor benchmarks using acoustic ranging. As of now, JCG regularly conducts GNSS-A observations at 27 seafloor sites along the Japan Trench and the Nankai Trough, named the Seafloor Geodetic Observation Array (SGO-A).

JCG has been conducting GNSS-A seafloor geodetic observation since 2000, and numerous technological advancements have been made in the past 20 years, significantly improving the observation frequency and positioning precision. The observation system currently operated by the JCG using survey vessels enables us to measure 3-4 times per year per seafloor site (Ishikawa et al. 2020, Front. Earth Sci.). Recently, we have developed an open-source GNSS-A analysis software named “GARPOS”, which simultaneously estimates sound speed perturbation and seafloor benchmark positions using empirical Bayesian inversion (Watanabe et al. 2020, Front. Earth Sci.).

Our regular observation at the SGO-A sites along the Japan Trench has revealed co- and postseismic processes of the 2011 Tohoku-oki Earthquake (Watanabe et al. 2021, EPS). Along the Nankai Trough, we have elucidated heterogeneous interplate coupling (Yokota et al. 2016, Nature) and shallow slow slip events (Yokota and Ishikawa 2020, Sci. Adv.). In this presentation, we review our observation and analysis methods, tectonic phenomena revealed from our observation, and the latest observation results at our SGO-A sites.

How to cite: Nakamura, Y., Ishikawa, T., Watanabe, S., and Yokota, Y.: Overview of the seafloor geodetic observation conducted by the Japan Coast Guard using the GNSS-Acoustic ranging combination technique, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1652, https://doi.org/10.5194/egusphere-egu22-1652, 2022.

13:37–13:44
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EGU22-2138
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Highlight
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Virtual presentation
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Motoyuki Kido, Chie Honsho, Fumiaki Tomita, Yusaku Ohta, Ryota Hino, and Takeshi Iinuma

Following the 2011 Tohoku Earthquake, we constructed seafloor geodetic benchmarks for GNSS-Acoustic measurement at twenty sites along the Japan trench in September 2012 and have started repeating surveys since then. Reliable horizontal displacement rates were obtained to date for a sufficiently long period of surveys, which revealed the coexistence of viscoelastic relaxation and after slips from place to place. Further analysis to estimate vertical motion, we preliminary exposed regions of uplift and subsidence, although the expected errors were still significant. However, the pattern of vertical motion gives independent information from the horizontal ones for verifying viscoelastic models and evaluating the extent of after slips.

We introduced an unmanned autonomous vehicle, called Waveglider (WG), as a surface platform instead of a ship, which overcomes the deficiency in ship-time in the sense of budget and human resources. Actually, data obtained by WG bear comparison with that by shipboard survey, and even the onboard-processed data can be transmitted to the onshore station via satellite system nearly in realtime. Moreover, significantly intensive use of WG helps increase the survey frequency, which can have a chance to identify slow slip events; for instance, marine seismometers have revealed the existence of slow events off the Sanriku region near our survey sites. 

The WG deficit is sometimes trapped against sea current even along the Japan trench, typically when over 2 knots, and fails into low power conditions depending on weather, season, and solar culmination altitude. Well-organized planning and operation may reduce such deficit. More practically, the slower speed of WG prevents efficient moving survey over a transponder array, especially for deep (>5000m) sites having a large footprint of the array, which is typical for our sites. Insufficient moving survey degrades the accuracy in vertical crustal movement, the importance of which increases to monitor the afterslip distribution as noted above. Then we solve this problem using a different approach that utilizes different incident angles even in point survey by employing two concentric triangles of different sizes for a six transponder site or a triangle with a centered one for a four transponder site.

If WG operation would become more common and can be appropriative, a fully continuous survey will be realized at a specific site without a moored buoy. This will be valuable not only for detecting temporal phenomena like slow slip events but also for disaster mitigation to monitor offshore fault failure in realtime. In addition, such prompt measurement just after a large earthquake reveals rapid postseismic deformation in an early stage. Long-term continuous operation requires particular battery specifications and operational fashion for seafloor transponders. We are also designing such transponders at this moment.

How to cite: Kido, M., Honsho, C., Tomita, F., Ohta, Y., Hino, R., and Iinuma, T.: Impact of employing a waveglider on GNSS-Acoustic survey along the Japan trench, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2138, https://doi.org/10.5194/egusphere-egu22-2138, 2022.

13:44–13:51
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EGU22-11454
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ECS
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Highlight
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Presentation form not yet defined
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Pierre Sakic, Clémence Chupin, Valérie Ballu, Thibault Coulombier, Pierre-Yves Morvan, Paul Urvoas, Mickael Beauverger, Edgar Lenhof, and Jean-Yves Royer

Precise underwater geodetic positioning remains a challenging operation. Measurements combining surface positioning (GNSS) with underwater acoustic positioning are usually performed from research vessels. We present an alternative approach using a small Unmanned Surface Vehicle (USV) equipped with a compact GNSS/Acoustic experimental configuration, which is more cost-effective and easier to deploy. The positioning system included a GNSS receiver mounted above an Ultra Short Baseline (USBL) module integrated with an inertial system (INS) to correct the USV movements. The experiment conducted in the shallow waters (40 m) of the Bay of Brest, France, provided a data set to derive the coordinates of individual transponders from two-way-travel times and direction of arrival (DOA) of acoustic rays from the transponders to the USV. We tested different acquisition protocols (box-in circles around transponders and two static positions of the USV). Using a least-squares inversion, we show that DOAs improve single transponder positioning both in box-in and static acquisitions. From a series of short positioning sessions (20 min) over two days, we achieved repeatability of ~5 cm in the locations of the transponders. Post-processing of the GNSS data also significantly improved the two-way-travel times' residuals compared to the real-time solution.

How to cite: Sakic, P., Chupin, C., Ballu, V., Coulombier, T., Morvan, P.-Y., Urvoas, P., Beauverger, M., Lenhof, E., and Royer, J.-Y.: Contribution of Direction-of-Arrival Observations for Geodetic Seafloor Positioning Using an Unmanned Surface Vehicle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11454, https://doi.org/10.5194/egusphere-egu22-11454, 2022.

13:51–13:58
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EGU22-3758
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Virtual presentation
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Lenhof Edgar, Royer Jean-Yves, Ballu Valérie, Sakic Pierre, Poitou Charles, Beauverger Mickaël, Coulombier Thibault, Dausse Denis, Jamieson Gregor, Morvan Pierre-Yves, and Gutscher Marc-André

The FOCUS project funded by the European Research Council aims at monitoring deformation across an active submarine fault with an optical fiber using laser reflectometry. To calibrate the measured strains in an absolute reference frame, such as the International Terrestrial Reference Frame (ITRF), a network of eight seafloor geodetic stations was deployed on both sides of the cable and fault. The fault (North Alfeo) is located at the foot of Mount Etna collapsing slope, offshore Sicily, and shows evidence of right-lateral strike-slip in the order of 2 cm per year.

To locate the acoustic beacons relative to the ITRF, we use a GNSS/Acoustic positioning method. Its principle is to jointly acquire positions of a surface platform relative to the GNSS and, acoustically, relative to the beacons on the seafloor. Positioning a set of beacons over the years should yield their absolute displacement. The optical cable and geodetic stations were deployed in October 2020 at a depth of ~1850m. The first set of GNSS/A data was acquired in August 2021. The next set will be collected in July 2022.

GNSS/A positioning of acoustic beacons on the seafloor within 1 cm is a challenge. The lever arm between the GNSS and acoustic antennas on the surface platform must be precisely known; the motion of the platform (i.e. antennas) must be precisely monitored. Then, in addition to reducing the uncertainties in GNSS positioning, an acquisition strategy must be designed to minimize the uncertainties in the acoustic ranging data, due to the unknown sound-speed field in the water column and its variability during the ranging sessions (5-6 hours).

To address these challenges, we used an Autonomous Surface Vehicle (ASV) equipped with a GNSS antenna, an ultra-short acoustic baseline (USBL) transponder coupled with an inertial system (INS). The ASV (3m x 1.60m) has the advantage of being very maneuvrable, acoustically silent (electric power), and compact (reduced lever-arm between antennas). Instead of positioning a single beacon (e.g. boxin), we positioned the ASV relative to several beacons at once and tested different trajectories: quasi-static stations of the ASV (within few meters) at the barycenter of 3 beacons, or series of straight profiles equidistant to pairs of beacons. In addition, while the ASV was acquiring GNSS/A data, a series of vertical temperature/pressure/salinity (CTD) profiles was acquired from the support vessel (R/V Tethys II) to monitor changes in the sound-speed.

Here we discuss the first results in processing these data and the ensuing uncertainty on the positioning. The GNSS data are reprocessed using Precise Point Positioning (PPP) with Ambiguity Resolution (AR). The improved navigation is then reprocessed with the INS data to obtain a precise position of the USBL center of mass. Then the acoustic ranging data can be merged with the sound-speed information to locate the beacon barycenter, using a least-squares inversion.

How to cite: Edgar, L., Jean-Yves, R., Valérie, B., Pierre, S., Charles, P., Mickaël, B., Thibault, C., Denis, D., Gregor, J., Pierre-Yves, M., and Marc-André, G.: GNSS/Acoustic positioning of acoustic beacons on the seafloor using an autonomous surface vehicle. Example from the FOCUS experiment offshore Sicily (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3758, https://doi.org/10.5194/egusphere-egu22-3758, 2022.

13:58–14:05
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EGU22-10160
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ECS
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Highlight
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Presentation form not yet defined
Pierre Boymond, Nathalie Feuillet, Isabelle Thinon, Luc Scholtès, Sylvie Leroy, Anaïs Rusquet, Charles Masquelet, and Eric Jacques and the SISMAORE team

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.

14:05–14:12
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EGU22-8264
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Virtual presentation
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Jean-Yves Royer, Edgar Lenhof, Charles Poitou, Valerie Ballu, Thibault Coulombier, Denis Dausse, Pierre Sakic, Gregor Jamieson, Pierre-Yves Morvan, and Marc-André Gutscher

In the framework of the European Research Council (ERC) funded project – FOCUS, testing laser reflectometry in a fiber optic cable to detect movement across an active submarine fault in real time, an array of eight acoustic beacons has been set up for monitoring motions across the fault and calibrating the observation from the fiber optic cable (see Gutscher et al. abstract in session SM2.1). The two experiments jointly started in October 2020. The selected North-Alfeo Fault is located at the foot of Mount Etna and shows evidence of right-lateral strike-slip motion.

The geodetic array forms a triangular web of 28 baselines, 16 of which cross the fault and 4 of which are parallel to the sections of fiber-optic cable cutting the fault.  Beacon depths range from 1910 to 1806m.  Each baseline, 400 to 1800 m long, is measured 4 times a day in both directions. Additional sensors simultaneously monitor the temperature (at ±0.001˚C) and pressure (at ±0.01dbar), so that sound-speed can be derived, and acoustic ranging (at ±1 microsecond) converted into distances. Inclinometers monitor the stability of the beacons (at ±0.05˚), mounted on 3m-high tripods, which, so far, have remained stable on the seabed.

The collected data (Jan. 2022) show transient and inhomogeneous environmental changes, due to cold bottom-water flows or mixing that last from days to weeks, and hence causing transient changes in the sound-speed and measured acoustic flight-times between beacons. Sound-speed (SSP) varies up to 0.1 m/s, inducing changes up to 25 microsecondes in one-way flight-times (equivalent to a 4-cm displacement at a constant SSP). Unfortunately, such an episode occurred when the optic fiber detected a significant elongation (20 - 40 microstrain) at two fault crossings, between 19 and 21 November 2020. Further processing is underway to extract possible actual displacements from the first 14 months of continuous acoustic ranging.

How to cite: Royer, J.-Y., Lenhof, E., Poitou, C., Ballu, V., Coulombier, T., Dausse, D., Sakic, P., Jamieson, G., Morvan, P.-Y., and Gutscher, M.-A.: Active Strike-Slip Fault Monitoring Using Marine Geodesy, Offshore Mt Etna, Sicily (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8264, https://doi.org/10.5194/egusphere-egu22-8264, 2022.

14:12–14:19
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EGU22-9770
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ECS
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On-site presentation
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Florian Petersen, Morelia Urlaub, Felix Gross, Alessandro Bonforte, and Heidrun Kopp

The Earth’s ocean floor deforms continuously under the influence of tectonic and non-tectonic processes. In the recent decade, the installation of seafloor geodetic instruments to accurately monitor fault displacement and strain accumulation has greatly improved our understanding of seafloor deformation and our knowledge of associated offshore hazards. In particular, the application of acoustic direct-path ranging networks allows the detection of displacement and strain accumulation of faults in millimeter-level precision.

On-land geodetic networks revealed that the Southeast flank of Mount Etna slides seawards at a rate of ~3 cm/yrs. The highest rates are observed near the coast and the volcano flank extends far into the Ionian Sea. The long-term deformation is superimposed by frequent slow-slip events with up to ~3 cm displacement. Our first acoustic ranging measurements between 2016 and 2018 confirmed offshore active deformation and seafloor displacement by detecting a slow-event of up to ~4 cm with a right-lateral offset. Thus, the application of direct-path ranging transponders has proven to be a promising tool to monitor horizontal and vertical displacement of such strike-slip fault zones. However, the observation of long-term deformation, as observed on onshore faults, is lacking. Therefore, we conducted a second acoustic geodetic deployment at the same site offshore Mount Etna between September 2020 and November 2021 and used a different network design. The new data set shows an indication for slow long-term seafloor deformation, which had not been resolved in the first deployment. By comparing the different configurations of the acoustic direct-path networks we were able to improve data processing to achieve millimeter-level precision. We have learned that longer-distance measurements over a sharp fault favor the detection of slow-slip events, but impede the observation of slow long-term deformation. In order to resolve the latter movement, very short baselines close to the fault trace are ideal. Therefore, a trade-off between long and short-distance measurements might be the key for compressive deformation monitoring. Our results prove that the direct-path acoustic ranging technique is well-suited to detect different styles of fault slip at faults with sharp surface traces.

How to cite: Petersen, F., Urlaub, M., Gross, F., Bonforte, A., and Kopp, H.: How to detect slow slip and long-term seafloor deformation? Lessons from two acoustic ranging campaigns on the submerged flank of Mt Etna, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9770, https://doi.org/10.5194/egusphere-egu22-9770, 2022.

14:19–14:26
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EGU22-1564
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Virtual presentation
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Yusuke Yokota, Tadashi Ishikawa, Shun-ichi Watanabe, and Yuto Nakamura

The GNSS-A seafloor geodetic observation array (SGO-A) has been operated in about 20 years by the Japan Coast Guard [Ishikawa et al., 2020]. It has become possible to measure interplate coupling condition and shallow slow slip events along the Nankai Trough in recent years [Yokota et al., 2016; Yokota and Ishikawa, 2020], and it has become possible to interpret the time change of postseismic deformation following the 2011 Tohoku-oki earthquake [Watanabe et al., 2021]. For understanding the detail physical process of the plate boundary (e.g., SSE), it is necessary to understand the accuracy of the GNSS-A system and study the quantification and attenuation of the error source.

SGO-A data is very useful for this purpose. This dataset is located in the SGO-A site, and basic analysis software GARPOS is also open to the public [Watanabe et al., 2020]. The format is also defined, and a lot of information necessary for error analysis is published.

For example, using the estimation result of SGO-A data by GARPOS, the relationship between the vertical movement and the sound speed structure’s disturbance can be investigated from the residual of the vertical movement and the estimated sound speed structure. In addition, the existence of unexpected errors and their effects can be considered by examining the correlation with the position of the seafloor station.

It is also possible to understand the disturbance in the ocean from the estimated disturbance of the sound speed structure. Recently, the theoretical background for this estimation has been organized and made easier to handle. Considering this result and the comparison of the ocean fields that are likely to occur in reality, it was also found that the observation accuracy is expected to be improved depending on the observation points. In this presentation, we introduce the interpretation method of GNSS-A data that is being developed in recent years.

 

SGO-A data: https://www1.kaiho.mlit.go.jp/KOHO/chikaku/kaitei/sgs/datalist_e.html

GARPOS: https://doi.org/10.5281/zenodo.4522027

How to cite: Yokota, Y., Ishikawa, T., Watanabe, S., and Nakamura, Y.: Development of a method to analyze the error factor of GNSS-A system using SGO-A data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1564, https://doi.org/10.5194/egusphere-egu22-1564, 2022.

14:26–14:33
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EGU22-3274
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ECS
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Virtual presentation
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Shun-ichi Watanabe, Tadashi Ishikawa, Yuto Nakamura, and Yusuke Yokota

For the seafloor geodesy, the GNSS-A is an only tool to directly solve the global positions with the precision of centimeters. Different from the terrestrial GNSS observations, the GNSS-A has a lot of difficulties both in the observation operation and the error corrections. For the latter issue, the researchers should take care that the GNSS-A solutions strongly affected by the underwater sound speed perturbation because it uses acoustic waves for ranging between the sea-surface and seafloor instruments. To solve this issue, the authors had developed the GNSS-A analysis software named “GARPOS” (Watanabe et al., 2020, Front. Earth Sci.), which simultaneously solves the seafloor positions and the perturbation effects based on the empirical Bayes (EB) approach. It can search the appropriate strength of smoothness constraint to the temporal change of perturbation field using the statistical criterion, to avoid the overfitting of the travel-time residuals. This software provided the sufficiently stable solutions to discuss the time-dependent crustal deformation (e.g., Watanabe et al., 2021, Earth Planets Space). Meanwhile, to provide the information on the variance of estimated positions as the joint posterior probability, the probability distributions of hyperparameters should be accounted. Therefore, we developed the program for sampling from the full-Bayesian (FB) posterior probability, based on the Markov-Chain Monte Carlo (MCMC). In this presentation, we introduce the methodology of GARPOS and its expansion to the MCMC mode. We will also show the MCMC results for the GNSS-A data obtained at sites of the Seafloor Geodetic Observation Array (SGO-A) operated by the Japan Coast Guard, to discuss the difference between the EB-based and FB-based solutions.

How to cite: Watanabe, S., Ishikawa, T., Nakamura, Y., and Yokota, Y.: Full-Bayesian GNSS-A seafloor positioning solution derived by the Markov-Chain Monte Carlo method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3274, https://doi.org/10.5194/egusphere-egu22-3274, 2022.

14:33–14:40
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EGU22-10652
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Virtual presentation
Takuya Nishimura, Tomoaki Nishikawa, Daisuke Sato, Yoshihiro Hiramatu, and Akihiro Sawada

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.

14:40–14:47
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EGU22-4565
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Presentation form not yet defined
Mireia Jones, Pablo J. Gonzalez, Maria Charco, Rayco Marrero, and Antonio Eff-Darwich

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.

Coffee break
Chairpersons: Lavinia Tunini, Mustapha Meghraoui, Pablo J. Gonzalez
15:10–15:20
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EGU22-208
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ECS
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solicited
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Virtual presentation
Juan J. Portela Fernández, Alejandra Staller, Marta Béjar-Pizarro, and Giorgi Khazaradze

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.

15:20–15:27
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EGU22-3882
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Virtual presentation
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Andrea Magrin, Lavinia Tunini, David Zuliani, and Giuliana Rossi

North-Eastern Italy is a region of particular interest in tectonics because it is located on the northernmost edge of the convergent margin between Eurasia and the Adria microplate with consequences on the regional deformation and seismicity. The FReDNet (Friuli Venezia Giulia Deformation Network) GNSS network was established in 2002 to monitor the crustal deformation in NE-Italy and it is currently counting 19 permanent GNSS stations. In order to place the regional deformation in a broader tectonic context, we processed the data from FReDNet and other geodetic networks covering northern Italy and surrounding areas (including some sites in Slovenia and Austria) in the period 2002-2021. We used the GAMIT-GLOBK software ver10.71 to process multi-satellite data and to calculate the position and velocity for each station. We processed the whole dataset by using Galileo and G100 CINECA HPC clusters.  

In this study, we will show the processing strategies and analyze the GNSS time-series of NE-Italy stations, as well as the outcoming deformation field. The preliminary results  confirm the decrease in the velocity module from the Friuli plain toward the Alps, suggesting a possible deformation accrual in the latter.

This research was supported by OGS and CINECA under HPC-TRES program award number 2020-11. We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support (IscraC IsC83_GPSIT).

How to cite: Magrin, A., Tunini, L., Zuliani, D., and Rossi, G.: Adria-Eurasia collision front: insights from GNSS time series in NE Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3882, https://doi.org/10.5194/egusphere-egu22-3882, 2022.

15:27–15:34
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EGU22-10329
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Presentation form not yet defined
Eric Calais, Steeve Symithe, and Bernard Mercier de Lépinay

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.

15:34–15:41
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EGU22-10281
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ECS
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On-site presentation
Shaozhuo Liu, Jean-Mathieu Nocquet, Xiwei Xu, Sigurjón Jónsson, Guihua Chen, Xibin Tan, and Yann Klinger

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.

15:41–15:48
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EGU22-6216
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ECS
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On-site presentation
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Hugo Boulze, Luce Fleitout, Emilie Klein, and Christophe Vigny

Spatial geodesy through GNSS allows to measure with a millimetric precision the displacement of the lithosphere during the seismic cycle. The post-seismic part of this cycle can last for decades, traduced by long-lasting surface deformations. One of the main physical processes involved in the postseismic deformation is the viscoelastic relaxation in the asthenosphere. However, a long term debate persists about the involved rheology of the asthenosphere:  Is the viscosity highly variable from one region to the next and is effective viscosity Newtonian (linear) or non-Newtonian (non linear)? 

To investigate these questions, we compare the horizontal post-seismic deformations induced by three Chilean megathrust earthquakes: Maule Mw8.8 (2010), Illapel Mw8.3 (2015) and Iquique Mw8.1 (2014). For each earthquake, we select permanent GPS stations along profiles perpendicular to the trench, extending as far as 1400 km. We calculate the ratio of the cumulative post-seismic (post) over 5 years and the coseismic (co) displacements for each station. Remarkably, at a given distance to the trench, the post/co ratios from the three earthquakes differ only slightly.

What can be the interpretation of this observation in terms of rheology of the asthenosphere? First we can analyse the response of the asthenosphere in the case of homothetic earthquakes of different magnitude. The post/co ratio obeys simple analytical relationships: For a Newtonian rheology, it is simply a function of the (time/viscosity) ratio. For a non-Newtonian viscosity with a stress exponent n=3, the timescale becomes inversely proportional to M**2, where M is the moment of the earthquake. We show that these relationships are only slightly modified when the earthquakes are no longer homothetic and that the post/co ratio is a good proxy to quantify the strain-rate and stress ratio in the underlying asthenosphere. As a conclusion, the post-seismic deformation following the three Chilean earthquakes reveals very similar viscosity. In particular, a Newtonian, rather than a non-Newtonian, effective viscosity is required to explain the post-seismic deformation process.

How to cite: Boulze, H., Fleitout, L., Klein, E., and Vigny, C.: Comparison of horizontal post-seismic deformations induced by Maule, Iquique, and Illapel megathrust earthquakes: A clue to a linear asthenospheric viscosity?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6216, https://doi.org/10.5194/egusphere-egu22-6216, 2022.

15:48–15:55
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EGU22-11691
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ECS
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Presentation form not yet defined
On the cause of enhanced landward motion in adjacent segments of subduction zones after megathrust earthquakes
(withdrawn)
Mario D'Acquisto, Matthew Herman, Riccardo Riva, and Rob Govers
15:55–16:02
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EGU22-4642
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ECS
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On-site presentation
Juan Martin de Blas, Giampiero Iaffaldano, Andrés Tassara, Daniel Melnick, and Marcos Moreno

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 Mw>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.

16:02–16:09
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EGU22-6189
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ECS
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Presentation form not yet defined
Parameter estimation for interseismic surface deformation using data assimilation
(withdrawn)
Celine P. Marsman, Femke C. Vossepoel, Ylona van Dinther, and Rob Govers
16:09–16:16
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EGU22-11401
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ECS
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Virtual presentation
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Juliette Cresseaux, Anne Socquet, Mathilde Radiguet, Marie-Pierre Doin, David Marsan, Mathilde Marchandon, Flora Huiban, and Rémi Molaro-Maqua

Large earthquakes are followed by a post-seismic period during which the stresses induced by the co-seismic phase are relaxed through different processes. This post-seismic phase participates to the redistributions of stresses in the earth, and understanding its mechanism is a key to understand interactions between earthquakes at different spatial and temporal scales. In subduction zones the most important terms are the afterslip and the visco-elastic relaxation. It is generally considered that the two mechanisms affect different spatial and temporal scales: the afterslip is prevalent the first months in the surrounding of the fault, while the visco-elastic relaxation process affects a larger area and lasts a longer time. The time-space pattern of the measured deformation can help to characterize the rheology of the underlying structure.

In this work we look at the processes involved after the Iquique earthquake.

 

To explore the processes driving the post-seismic deformation, we use a finite element model (FEM) (2D model, using the FEM software Pylith) that is constrained with InSAR and GNSS data. The GPS time series (processed with GipsyX) include 83 stations located in North Chile, Peru and Bolivia. The post-seismic signal is isolated using a trajectory model. The InSAR data consist in two Sentinel-1 time series (ascending and descending tracks) processed with the NSBAS chain, they include 514 interferograms, starting 7 months after the earthquake up to the end of 2019. In the model we impose a co-seismic displacement on the plate interface and explore the influence of the structure and the rheology on the predicted surface displacement.

 

Our tests reveal that the viscosity in the continental and the oceanic mantle both have an impact on the displacement produced at the surface. The difference between these viscosities controls the movements allowed at depth. The crust thickness and the presence of a cold nose have a clear impact on the wavelength and the location of the maximum of amplitude, respectively.

The afterslip is the major contribution at short time. At longer time, it affects weakly the near trench displacements. To fit the long-term data, we show that visco-elastic relaxation is needed. After 7 months, the InSAR data show a clear spatial wavelength with a strong signal 150 to 300 km from the trench which can be explained by the visco-elastic process.

We pointing out that these is a trade-off between the contribution of afterslip and visco-elastic relaxation. However, both processes affect different space and time, and the comparison with GNSS data and two InSAR tracks allows to strongly constrain the model and reduce the range of plausible models.

How to cite: Cresseaux, J., Socquet, A., Radiguet, M., Doin, M.-P., Marsan, D., Marchandon, M., Huiban, F., and Molaro-Maqua, R.: Modelling the post-seismic deformations measured by GNSS and InSAR, following the 2014 Iquique earthquake, Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11401, https://doi.org/10.5194/egusphere-egu22-11401, 2022.

16:16–16:23
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EGU22-1351
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Presentation form not yet defined
João Fonseca, Mimmo Palano, Ana Falcão, Alexis Hrysiewicz, and José Férnandez

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.

16:23–16:30
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EGU22-2951
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Presentation form not yet defined
Vadim Milyukov, Alexey Milronov, Grigory Steblov, Valery Drobishev, and Hariton Hubaev

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.

16:30–16:37
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EGU22-10716
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ECS
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On-site presentation
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Mohammad M. Aref, Bodo Bookhagen, and Manfred R. Strecker

Slow-moving landslides pose significant natural hazards to humans and infrastructure.  Analysis of Interferometric Synthetic Aperture Radar (InSAR) time series provide the opportunity to monitor unstable hillslopes in difficult to access terrains at large spatial scales.

The geological conditions and land cover of the eastern Central Andes in northwestern Argentina ranges from densely vegetated areas in the low elevation foreland at around 1000 metres to arid, vegetation free conditions at high elevations at about 6000 metres. The land cover has a significant impact on the spatial and temporal InSAR signal decorrelation and deformation estimation. In our study, we extract InSAR time series from Sentinel-1 ascending and descending data acquired between 2014 and 2021 using both linear small baseline technique and non-linear phase inversion techniques to have a better understanding of deformation rate estimation techniques for landslide detection in complex areas. We identified several landslides including three main translational bodies with areas exceeding 1 km2 and downslope deformation rates in excess of 5-10 cm/yr. 

Our study is influenced by ionospheric total electron content variation for the C band Sentinel-1 ascending phase observations. We applied the split range-spectrum technique to minimize the ionospheric contribution on the phase measurements. The tropospheric signal was estimated using both statistical approaches based on topography and weather models to reduce the effects of atmospheric water vapor during South American Monsoon activity. We explore the impact of topographic relief on tropospheric phase delay. We compared our deformation-rate estimates with a double-differencing time series with local and regional spatial filters to mitigate tropospheric noise and unwrapping problems in the time series. We take advantage of connected component analysis and hierarchical clustering approaches on the mean velocity from the double-difference time series and vertical component derived from the 3D decomposition of InSAR time series to map landslides with similar characteristics. Our results highlight the importance of the several processing parameters during InSAR time-series analysis and their sensitivity toward slow-moving landslide detection.

How to cite: M. Aref, M., Bookhagen, B., and R. Strecker, M.: Kinematics Characterization of Slow-Moving Landslide using InSAR Time Series Analysis in the South-Central Andes of NW Argentina, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10716, https://doi.org/10.5194/egusphere-egu22-10716, 2022.

Coffee break
Chairpersons: Mustapha Meghraoui, Pablo J. Gonzalez, Lavinia Tunini
17:00–17:10
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EGU22-1675
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solicited
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Highlight
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Presentation form not yet defined
Tim Wright, John Elliott, Jin Fang, Andrew Hooper, Greg Houseman, Milan Lazecky, Yasser Maghsoudi, Qi Ou, Barry Parsons, Chris Rollins, Richard Styron, Hua Wang, and Gang Zheng

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.

17:10–17:17
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EGU22-1709
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ECS
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On-site presentation
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Manon Dalaison, Romain Jolivet, and Laetitia Le Pourhiet

The Chaman plate boundary between India and Eurasia is a wide faulted region in Pakistan and Afghanistan, hosting distributed seismicity. Along the western edge of the deforming region, the Chaman fault currently accommodates less than 15 mm/yr of slip, while the differential left-lateral motion between both tectonic plates is close to 30 mm/yr. In the past century, significant earthquakes have ruptured structures east of the Chaman fault, including the 1931 Mach earthquake and 1935 Quetta earthquake with magnitudes (Mw) greater than seven. We aim to identify where strain focuses so that active structures likely to rupture in large earthquakes are outlined. We use ground velocities computed from 6 years-long InSAR time series in ascending and descending line of sights to map gradients of deformation in the Kirthar ranges. InSAR data reveals that most of the current plate boundary strain focuses east of the Chaman and Ghazaband fault in the central axis of the ranges. We model velocities along profiles across the plate boundary as the surface expression of left-lateral slip on several vertical faults: the Chaman fault, the subparallel Ghazaband fault, the Hoshab fault and one to three unknown faults to the east. We localise strain in the continuation of the Ornach Nal in the south and along the Quetta-Kalat fault which is thought to have hosted the 1935 Quetta earthquake (Mw 7.7). Three discrete portions of the Ghazaband fault slip with rates close to 10 mm/yr. Our description of partitioning matches known seismic ruptures, and makes sense in a geodynamical and geological perspective. We propose a tectonic model of the plate boundary evolution with an eastward migration of strain.

How to cite: Dalaison, M., Jolivet, R., and Le Pourhiet, L.: Mapping the distribution of strain along multiple strike-slip faults in the Chaman fault system from InSAR, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1709, https://doi.org/10.5194/egusphere-egu22-1709, 2022.

17:17–17:24
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EGU22-11238
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ECS
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Highlight
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On-site presentation
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Xing Li, Sigurjón Jónsson, Zhangfeng Ma, Frédéric Masson, and Yann Klinger

The north-south component of ground deformation remains difficult to derive from InSAR due to the limited sensitivity of standard InSAR observations in that direction. The new approach of burst-overlap interferometry (BOI) exploits swath overlaps of the Sentinel-1 TOPS acquisition mode to retrieve accurate north-south displacements. We applied time-series analysis to such along-track BOI observations of the roughly north-trending Dead Sea fault. Using a large number of Sentinel-1 images acquired from both ascending and descending tracks, we retrieved the horizontal displacement in the burst-overlap areas. Mis-registration errors caused by orbit errors, timing errors, or tropospheric delays are limited in burst-overlap velocities, and ionospheric delays can be reduced through spatial averaging, enhancing the surface displacement estimation. However, interferometric decorrelation is a challenge, as it degrades the co-registration performance in addition leading to fewer observations, particularly near the northern Dead Sea fault. By exploiting hundreds of images, we find a clear and consistent velocity change across different segments of the Dead Sea fault, using coherent distributed scatters optimized by integrating temporal coherence. Modeling of the ascending and descending BOI velocity results suggests that the fault-parallel velocity is in the range 4.2-5.0 mm/yr south of the Lebanese restraining bend, whereas only about half of that to the north of it. The results demonstrate the applicability of BOI time-series analysis in medium-to-low coherence regions with low deformation rates.

How to cite: Li, X., Jónsson, S., Ma, Z., Masson, F., and Klinger, Y.: Measuring interseismic deformation of the Dead Sea fault from along-track Sentinel-1 TOPS interferometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11238, https://doi.org/10.5194/egusphere-egu22-11238, 2022.

17:24–17:31
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EGU22-2737
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ECS
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On-site presentation
Zelong Guo, Mahdi Motagh, Jyr-Ching Hu, Guangyu Xu, Mahmud Haghshenas Haghighi, Abbas Bahroudi, and Aram Fathian

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.

17:31–17:38
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EGU22-7131
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ECS
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Virtual presentation
Tohid Nozadkhalil, Ziyadin Çakir, Semih Ergintav, and Arkadaş Özakin

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.

17:38–17:45
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EGU22-1948
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ECS
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Presentation form not yet defined
Chris Rollins, Tim Wright, Yasser Maghsoudi, Milan Lazecky, Andrew Hooper, and Jonathan Weiss

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.

17:45–17:52
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EGU22-4587
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On-site presentation
Giampiero Iaffaldano, Juan Martin de Blas, and Eric Calais

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.

17:52–17:59
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EGU22-4483
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Presentation form not yet defined
Bjartur Í Dali Udbø, Giampiero Iaffaldano, and Juan Martin de Blas

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.

17:59–18:06
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EGU22-8531
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Virtual presentation
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Marie-Pierre Doin, Marguerite Mathey, Pauline André, Andrea Walpersdorf, Stéphane Baize, and christian Sue

Within the low-deforming western European Alpine belt, GNSS measurements show that uplift is the main signal characterizing current surface deformation in the range, reaching up to 2 mm/yr, while no shortening is observed across the belt. Based on the huge amount of satellite data available today, it now appears possible to constrain new high resolution surface velocities in the western Alps, which is of primary importance to better understand the links between surface deformation and neotectonics processes in this region.

Relying on ~ 170 radar acquisitions from Sentinel-1 satellite over four years, we propose for the first time an InSAR-based mapping of the uplift pattern affecting the Western Alps on a ~350x175 km-wide area. Their processing is challenging due to the high noise level inherent to mountainous areas and the low expected deformation signal. We thus use in this study the NSBAS small baseline approach (Doin et al., 2011) for interferograms corrections, unwrapping, and time-series inversion. Atmospheric corrections are made using ERA5 reanalysis model (Hersbach et al., 2020). We estimate regional line-of-sight (LOS) velocities by correcting the resulting time-series from outliers and by separating seasonal and linear signals through different approaches which all yield similar results, thus highlighting the robustness of the obtained LOS velocity field. Based on several assumptions, we finally convert LOS velocities to uplift rates using local incidence angles.

The corresponding InSAR-derived velocity field is validated by the comparison with GNSS solutions. They both show uplift in the core of the belt, with higher rates in its northern part, and subsidence at its periphery. Our approach however provides a denser spatial distribution of vertical motions compared with GNSS. Higher uplift rates are found within the external crystalline massifs compared with surrounding areas, in agreement with the variations expected from recent deglaciation and long-term exhumation data.

These results bring new insights into active tectonics in the Western Alps. While several distinct wavelength patterns can be identified within the uplift signal throughout the western Alps, we suggest that they may originate from common geodynamic processes, with differential surficial responses explaining their localization. These processes may involve glacial isostatic adjustment, erosion, and/or slab break-off.

How to cite: Doin, M.-P., Mathey, M., André, P., Walpersdorf, A., Baize, S., and Sue, C.: Spatial Heterogeneity of Uplift Pattern in the Western European Alps Revealed by InSAR Time-Series Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8531, https://doi.org/10.5194/egusphere-egu22-8531, 2022.

18:06–18:13
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EGU22-3210
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ECS
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Virtual presentation
Sihem Miloudi, Mustapha Meghraoui, Souhila Bagdi, Kamel Hasni, and Salem Kahlouche

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.

18:13–18:20
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EGU22-5142
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ECS
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On-site presentation
Sofia Viotto, Bodo Bookhagen, Guillermo Toyos, and Sandra Torrusio

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.