The WEGENER initiative was started in 1981 with the aim of creating an interdisciplinary forum supporting geodynamic studies by means of space and terrestrial geodetic techniques. Therefore, WEGENER promotes the establishment of a consistent framework leading from data acquisition, to data analysis, modeling and interpretation of the results. These activities provide key information to a broad range of phenomena that have critical implications for society, particularly in the field of natural hazards and climate change using techniques such as GNSS, InSAR, LiDAR, space/air/terrestrial gravimetry and ground-based geodetic observations.
In this session, we seek contributions that improve our understanding of geodynamical processes and crustal deformations at the local-to-global scale by means of geodetic techniques and innovative modeling approaches. Contributions showing the benefit of integrating geodetic and complementary geophysical, hydrological, geological, oceanographical and climatological information are also welcome. Relevant submissions may focus on the earthquake cycle, volcanic processes, sea-level changes, fluid redistributions and near surface motions such as landslides and subsidence. We also encourage contributions discussing the realization and outcomes of Supersites in the frame of the GEO initiative, as well as reports of the establishment of new geodetic networks in tectonically active areas.
Among other activities, the WEGENER will contribute to the joint IAG-IASPEI sub-commission on Seismo-Geodesy.

Co-organized by GD10/SM2
Convener: Sara BruniECSECS | Co-conveners: Takuya Nishimura, Jean-Mathieu Nocquet, Haluk Ozener, Susanna Zerbini
| Attendance Thu, 07 May, 14:00–15:45 (CEST)

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Chat time: Thursday, 7 May 2020, 14:00–15:45

D1713 |
| solicited
Jianghui Geng, Qiang Wen, and Qijin Chen

High-rate GNSS receivers, sampling satellite signals at over 1-Hz rate, can record strong ground motions and directly in the form of displacements instead of velocities or accelerations. In this case, broadband displacement waveforms down to 0 Hz can be obtained nominally; the benefit is that static offsets can be identified accurately from high-rate displacements with minimal contamination by the very early postseismic signals. The drawback of high-rate GNSS, however, consists in its orders of magnitude higher noise than that of seismometers, almost on all frequency bands concerning seismic studies. Combining collocated high-rate GNSS and accelerometers can be a remedy and produces broadband seismogeodetic displacements. However, accelerometer data must be heavily downweighted due to their baseline errors originating primarily in instrument rotations, and therefore their contribution to seismogeodetic displacements is seriously underestimated. We further introduced a gyroscope into this classic seismogeodesy to mitigate baseline errors and formulated advanced six-degree-of-freedom (6-DOF) seismogeodesy without undervaluing accelerometer data. A shake table holding one GNSS antenna, four accelerometers, and one gyroscope was used to simulate waveforms from the 2010 Mw 7.2 El Mayor-Cucapah earthquake. We found that the displacements derived from the 6-DOF seismogeodesy were up to 68% more accurate than those from the classic seismogeodesy over 0.04–0.4 Hz. Moreover, broadband rotations containing the permanent components were also generated, which were unachievable by integrating gyroscope data. We believe that the 6-DOF seismogeodesy is capable of improving both source rupture studies of large earthquakes and high-rise monitoring under strong seismic waves.

How to cite: Geng, J., Wen, Q., and Chen, Q.: Six-degree-of-freedom seismogeodesy by combining collocated high-rate GNSS, accelerometers and gyroscopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1568, https://doi.org/10.5194/egusphere-egu2020-1568, 2020.

D1714 |
| Highlight
Jesus Piña-Valdés, Anne Socquet, Céline Beauval, Pierre-Yves Bard, Marie-Pierre Doin, and Zhengkang Shen

Probabilistic Seismic Hazard Assessment demands the development of reliable earthquake recurrence models, which are usually based on time and spatial distribution of the past seismicity contained on earthquake catalogs. This usually generate models rather well constrained on seismically active regions where large historical catalogs are available. But in low to moderate seismicity regions, where data is scarce, establishing earthquake recurrence from past events is a major challenge. On those regions, geodetic measurements can provide useful information for deriving alternative recurrence models based on strain rate.

The impact of the crust deformation on the processes that control the seismic activity is still controversial. The seismic activity is usually thought to be associated to the active tectonic deformation as estimated from the horizontal displacements field. But in regions with low horizontal deformation, getting the horizontal strain rates is difficult since the displacements field can be dominated by the noise of the geodetic data. Additionally, non-tectonic processes such as the Glacial Isostatic Adjustment (GIA) can exist, and may impact the seismicity rate of those regions. Then seismicity rates derived from the horizontal velocity fields might not adjust the observed seismicity rates on such regions.

We propose a methodology to build a combined GNSS velocity field dataset for Europe, that could be used for the development of earthquake recurrence models. For this, 5 different GNSS velocity field solution for Europe are considered. Using the velocity solutions of common stations, the different datasets are converted to a common reference frame. Based on the comparison of the velocity values, a methodology is established to generate a combined velocity field, considering the uncertainty of each independent solution. A criterion for automatic identification and outliers removal is implemented, as well an adaptive smoothing scheme that depends on the station density, the noise and the local tectonic deformation rate.

We propose a methodology to obtain strain rate maps from GNSS data based on the VISR software [Shen et al., 2015], not only considering the horizontal velocity field, but including also the vertical velocity field for Europe, considering the effects of flexure of the crust on regions where important GIA signals are observed.

Finally, earthquake recurrence models are derived and compared with catalog-based models in Europe to evaluate their mutual agreement, comparing also the results obtained on regions with significant tectonic deformation versus regions where important GIA signals are observed.

How to cite: Piña-Valdés, J., Socquet, A., Beauval, C., Bard, P.-Y., Doin, M.-P., and Shen, Z.: Toward the Development of Earthquake Recurrence Models from 3D GNSS Velocity Field in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19808, https://doi.org/10.5194/egusphere-egu2020-19808, 2020.

D1715 |
Mustapha Meghraoui, Frederic Masson, Nejib Bahrouni, Abdelilah Tahayt, Mohamed Saleh, and Salem Kahlouche

The Maghrebian tectonic domain in North Africa is here examined in the light of the recent GPS and seismotectonic results. The region includes the plate boundary in the western Mediterranean previously characterized by transpression and block rotation. The crustal deformation is documented along the Atlas Mountains in terms of the displacement field, with strain partitioning largely controlled by plate motions. The tectonic and seismotectonic analysis is based on our published data on shortening directions of Quaternary faulting and folding compared with present-day seismotectonic characteristics (earthquake moment tensors) of significant seismic events that allow an estimate of local and regional deformation rates in North Africa. Shortening directions oriented NE-SW to NW-SE for the Pliocene and Quaternary, respectively, and the S shape of the Quaternary anticline axes are in agreement with the 2°/Myr to 4°/Myr clockwise rotation obtained from paleomagnetic results on small tectonic blocks in the Tell Atlas. The continuous GPS data and results are obtained from the network in Morocco operative 1999 to 2006, the REGAT network in Algeria since 2007, and the network in Tunisia with data collected from 2014 to 2018. In addition, we add the most recent GPS results in southern Spain and southern Italy. The NW-SE to NNW-SSE 5 ±1.5 mm/yr convergence velocity and strain distribution of the Maghrebian tectonic domain is controlled by crustal block tectonics driven by E-W trending right-lateral faulting and NE-SW thrust-related folding. The correlation between the active transpression tectonic structures and velocity field shows a geodynamic framework consistent with the oblique plate convergence of Africa towards Eurasia. 

How to cite: Meghraoui, M., Masson, F., Bahrouni, N., Tahayt, A., Saleh, M., and Kahlouche, S.: Constraint of active deformation and transpression tectonics along the plate boundary in North Africa , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4835, https://doi.org/10.5194/egusphere-egu2020-4835, 2020.

D1716 |
Nicola D'Agostino and William C. Hammond

One way for the continental lithosphere to extend is to increase its regional elevation, yet the mechanism for the formation of high-topography in actively extending continental settings (e.g., Tibet, Basin and Range, southwestern Balkans, Apennines) is still uncertain. It has been suggested that active extension in the Apennines Mountain chain in Italy is intimately related with regional topographic elevation. We use a newly updated GPS dataset and the GPS Imaging technique to show that the dynamic relief of the Apennines is currently increasing along its entire length by ~1 mm/yr. We image positive uplift along the entire length of the Apennine crest including the northern Apennines, Calabria and northern Sicily. The maximum rate is geographically aligned with the highest elevations and the topographic drainage divide. Relief is increasing in a ~120 km wide zone with a profile similar to the long wavelength topography, but not similar to the shorter wavelength topography generated by active faulting and erosion. A zone of minor active uplift is aligned with areas having restive volcanic fields and high geothermal potential west of the Apennines: e.g., Campi Flegrei, Alban Hills, and Lago Bolsena. However, the primary uplift axis aligns with the topography and zone of extension accommodating east-northeast translation of the Adriatic microplate relative to the Tyrrhenian Basin. Broad uplift occurs despite that the expected consequence of extension is crustal thinning and subsidence.   Anomalies in free-air gravity and deep seismic wavespeed suggest that elevation gain is driven by forces originating in the mantle. We use these results to address the hypothesis that these forces result from upward flow of asthenospheric mantle beneath the Apennines, possibly related to a sinking and detached slab previously attached to the Adriatic microplate, or from extensional flank flexure across the axis of the Apennine rift.

How to cite: D'Agostino, N. and Hammond, W. C.: GPS Imaging of Mantle Driven Uplift of the Apennines, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13278, https://doi.org/10.5194/egusphere-egu2020-13278, 2020.

D1717 |
Fateme Khorrami, Andrea Walpersdorf, Zahra Mousavi, Erwan Pathier, Hamid Nankali, Reza Sa'adat, Richard Walker, Marie-Pierre Doin, Farokh Tavakoli, and Yahya Djamour

The enigmatic 600 km long E-W trending left-lateral Doruneh fault in eastern Iran is certified to be active by its well preserved geomorphological features all along its trace, but it is lacking recent seismic activity that could be attributed to its motion. Instead, the high seismogenic potential of the study zone is highlighted by the two M=7 earthquakes on the left-lateral E-W trending Dasht-e-Bayaz fault just south of Doruneh, in 1968 and 1979. Therefore, it remains important to understand the role of the Doruneh fault in the kinematics of the Arabia-Eurasia collision that takes place inside Iran’s political boundaries.

Many different slip-rates have been estimated for the left-lateral motion of the Doruneh fault: 2.5 mm/yr by geomorphological marker offset dating, 1 mm/yr from preliminary GNSS measurements, and 5 mm/yr from a local InSAR study.  These rather local estimates on the 600 km long fault highlight either temporal or spatial variability of the Doruneh present-day behavior. The spatial variability of the fault slip is still badly constraint as the western half of the fault is located in the Great Kavir desert. The analysis of satellite radar images was supposed to provide good constraints on the inter-seismic deformation with a full spatial coverage of the fault, especially thanks to the favorable E-W orientation of the Doruneh fault and the arid Iranian climate. However, decorrelation due to sand dunes and unexpected large tropospheric noise prohibited precise results from a first large-scale ENVISAT study, yielding an upper limit of the slip rate of 4 mm/yr. The high resolution SENTINEL-1 constellation (operational since 2014) is predicted to provide constraints on inter-seismic velocities down to 2 mm/yr from 2020 on. In complement, a dense GNSS survey has been conducted in 2012 and 2018 on a temporary network of 18 sites around a large part of the fault. This network densifies and completes the 17 permanent GNSS stations in up to 200 km distance to the fault trace situated mostly in the eastern, more populated part of the fault.

In this work, we will point out our recent GNSS, InSAR and tectonic studies on the present-day characteristics of the Doruneh fault, to better understand the mechanism of this major fault in the kinematics of the Arabia-Eurasia collision, and to contribute to a better assessment of the seismic hazard in eastern Iran.

How to cite: Khorrami, F., Walpersdorf, A., Mousavi, Z., Pathier, E., Nankali, H., Sa'adat, R., Walker, R., Doin, M.-P., Tavakoli, F., and Djamour, Y.: How to reveal the present-day mechanism of the 600 km long Doruneh fault in eastern Iran ?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11110, https://doi.org/10.5194/egusphere-egu2020-11110, 2020.

D1718 |
Yukitoshi Fukahata, Angela Meneses-Gutierrez, and Takeshi Sagiya

In general, there are three mechanisms causing crustal deformation: elastic, viscous, and plastic deformation. The separation of observed crustal deformation to each component has been a challenging problem. Meneses-Gutierrez and Sagiya (2016, EPSL) have successfully separated inelastic deformation from observed geodetic data from the comparison of GNSS data before and after the 2011 Tohoku-oki earthquake in the northern Niigata-Kobe tectonic zone (NKTZ), central Japan. In this study, we further succeed in separating plastic deformation as well as viscous deformation in the northern NKTZ using GNSS data before and after the 2011 Tohoku-oki earthquake, under the assumptions that elastic deformation is principally caused by the plate coupling along the Japan trench and that plastic deformation ceased after the Tohoku-oki earthquake due to the stress drop caused by the earthquake. The cease of plastic deformation can be understood with the concept of stress shadow used in the field of seismic activity. The separated strain rates are about 30 nanostrain/yr both for the plastic deformation in the preseismic period and for the viscous deformation in both the pre- and post-seismic periods, which means that the inelastic strain rate in the northern NKTZ is about 60 and 30 nanostrain/yr in the pre- and post-seismic periods, respectively. This result requires the revision of the strain rate paradox in Japan. The strain rate was exceptionally faster before the Tohoku-oki earthquake due to the effect of plastic strain, and the discrepancy between the geodetic and geologic strain rates is much smaller in usual time, when the plastic strain is off. In oder to understand the onset timing of plastic deformation, the information on stress history is essentially important.


How to cite: Fukahata, Y., Meneses-Gutierrez, A., and Sagiya, T.: Detection of Plastic Strain Using GNSS Data of Pre- and Post-Seismic Deformation of the 2011 Tohoku-oki Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12803, https://doi.org/10.5194/egusphere-egu2020-12803, 2020.

D1719 |
Megan Miller and Cathleen Jones

California’s Central Valley is the site of a complex heterogeneous aquifer system composed of alternating layers of coarse sediments and fine-grained confining material. Confined and semi-confined aquifer systems experience groundwater fluctuations coupled with elastic and inelastic land surface deformation. Data from the UAVSAR L-band synthetic aperture radar acquired between May 29, 2013 and November 27, 2018 were used to generate a high resolution deformation time series, and identify and track the development of a small subsidence feature that developed immediately adjacent to the California Aqueduct. By the end of the time series, the feature surface area that subsided 10 cm or more was 4452 hectares. The California Aqueduct supports Central Valley agriculture and large urban populations in Southern California, and a 10.5+ km segment of the aqueduct subsided 10 cm or more due to this one subsidence feature.  The Central Valley experienced a persistent drought starting in 2012, followed abruptly by a wet period from December 2016 to February 2018. The data were analyzed for the drought period in conjunction with hydraulic head level data from nearby wells to solve for aquifer storage parameters and volume storage loss.  We found the inelastic volume storage loss was 7.1x106 m3, or an average rate of 7x103 m3/day.

Compared to satellite SARs, UAVSAR has a higher spatial resolution (<2 m ground resolution) and signal-to-noise ratio. Because of these factors along with spatial averaging to reduce phase noise, accuracy is increased and temporal decorrelation is reduced, so a greater proportion of the scene produces useful measurements while maintaining a spatial resolution of 7mx7m. The resolution achieved with UAVSAR time series processing allows for modeling and monitoring localized subsidence features affecting the aqueduct that were not previously observed by satellite. The data, analysis, model, and results are described in this presentation.  It is notable that UAVSAR is a prototype for the L-band SAR to be launched on the NASA-ISRO SAR Mission (NISAR) in 2022.  In that context, we also discuss and compare the expected performance of the two instruments and highlight how these technologies can be used to study aquifer properties in areas where water level data are sparse in both space and time.

How to cite: Miller, M. and Jones, C.: Drought-induced rapid subsidence in the Central Valley and its impact on the California Aqueduct, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10733, https://doi.org/10.5194/egusphere-egu2020-10733, 2020.

D1720 |
Sujata Dhar, Nagarajan Balasubramanian, and Onkar Dikshit

India extends from 8° 4’ N to 37° 6’ N latitude and 68° 7’ E to 97° 25’ E longitude. It lies largely on the Indian plate. Major earthquakes generally happen along tectonic plate boundaries. But, Indian subcontinent has experienced some of the largest earthquakes, with magnitude more than 7, within it. This directs the possibility of significant intraplate movement in the Indian plate. Narmada river flows through the central part of India and is considered as the boundary between northern and southern India. It is tectonically active, which is not found in other river basins. Geophysical studies in the Son Narmada Fault (SNF) zone reveal that this is a zone of intense deep-seated faulting which has been reactivated and hence, this is the cause of major earthquakes and various tectonically induced landforms in that region recently. Estimates of intraplate strain across Narmada Son Lineament (NSL) from early campaign-mode GPS data and geological studies suggested movement of 2-3 mm per year. The Indian Plate is currently moving northeast at 5 cm/year, while the Eurasian Plate is moving northeast at only 2 cm/yr. Most of the research has been done with geological studies to determine the rate of the movement along NSL. We are considering Global Navigation Satellite System (GNSS) data for around 16 continuously operating and well distributed sites in India. We are using BERNESE and GAMIT software’s for GNSS data processing. Both are scientific GNSS processing software with single differencing for ambiguity resolution. This is the first time in India that movement across NSL, with ITRF14 reference frame, will be determined from any space geodetic technique dominantly. In this study, several continuous GNSS stations in India along with nearby IGS sites from 2013 to 2018 are used to examine the distribution and magnitude of intraplate movement across the active SNF.

Keywords: Indian plate, Son Narmada Fault, GNSS, BERNESE, GAMIT, ITRF14

How to cite: Dhar, S., Balasubramanian, N., and Dikshit, O.: Study of Intra-plate Movement in the Indian Subcontinent along Narmada Son Lineament by Baseline Processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1158, https://doi.org/10.5194/egusphere-egu2020-1158, 2020.

D1721 |
Luca Tavasci, Miriana Di Donato, Maddalena Errico, Stefano Gandolfi, and Susanna Zerbini

Permanent GNSS stations have become fundamental for geodynamic studies thanks to their capability of providing consistent coordinate time series. The time series analysis is becoming more and more sophisticated and there are several approaches, fully automated or not, helping the users to derive the main parameters of interest such as: trends, periodical signals, discontinuities, types of noises, blunders. Typically, however, the analysis of the time series is still performed considering separately each of the three coordinate components. Actually, this neglects the three-dimensional nature of the GNSS position solutions, which are computed simultaneously, and may have some impact on the analysis. We should also bear in mind that the values of the coordinates time series depend on the reference system orientation. For instance, the time series values expressed in geocentric coordinates (X, Y, Z) are usually different from the same ones represented in a topocentric (E, N, V) reference. Therefore, if the analysis is performed separately on the three coordinate components, results will be different depending on the adopted reference system.
The aim of this work is to address the issue concerning the automated rejection of outliers potentially present in the GNSS time series. This is a fundamental aspect considering the large amount of data that nowadays shall be continuously processed and analyzed, thus requiring procedures as automated as possible. A viable approach is to search for outliers by analyzing the error distribution of the coordinates after having removed trends and signals, assuming that these behave like casual errors and follow a normal density distribution. It is then possible to set a statistical threshold in order to reject iteratively all the solutions with higher residual values. This approach is usually implemented by considering mono-dimensional time series in which the three coordinate components are processed separately. Nevertheless, from a statistical point of view, each GNSS position solution should be considered to be a 3D variable, thus characterized by a probability density function defined in a 3D space. In particular, by considering a chi-square distribution with three degrees of freedom it is possible to consider an ellipsoidal density function that well fit the error distribution of a 3D casual variable such as the GNSS coordinates.
In this work, numerical results obtained from the analysis of real dataset will be presented. In particular, six years of daily position solutions obtained from 12 GNSS permanent stations have been considered. The time series have been analyzed starting from both geocentric and topocentric coordinates using alternatively two different approaches: a classical one, in which the three coordinate components have been processed separately, and the 3D approach that allowed to consider the three coordinates at once. Results show that the second approach is mostly independent from the starting reference system, whereas the classical approach is affected by the orientation of the Cartesian axes used to project the same positions.

How to cite: Tavasci, L., Di Donato, M., Errico, M., Gandolfi, S., and Zerbini, S.: A new 3D approach to automated outliers rejection in GNSS time series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1625, https://doi.org/10.5194/egusphere-egu2020-1625, 2020.

D1722 |
Frédéric Masson, Mustapha Meghraoui, Najib Bahrouni, Mohammed Saleh, Maamri Ridha, Dhaha Faouzi, Patrice Ulrich, and Jean-Daniel Bernard

The plate boundary in the western Mediterranean includes the Tunisian Atlas Mountains. We study the active deformation of this area using GPS data collected from 2014 to 2018. WNW to NNW trending velocities express the crustal motion and geodetic strain field from the Sahara platform to the Tell Atlas, consistent with the African plate convergence. To the south, the velocities indicate a nearly WNW-ESE trending right-lateral motion of the Sahara fault-related fold belt with respect to the Sahara Platform. Further north and northeast, the significant decrease in velocities between the Eastern Platform and Central – Tell Atlas marks the NNW trending shortening deformation associated with local ENE – WSW extension visible in the Quaternary grabens. The velocity field and strain distribution associated with the active E-W trending right-lateral faulting and NE-SW fault-related folds sustain the existence of three main tectonic blocks and related transpression tectonics. The velocity field and pattern of active deformation in Tunisia document the oblique plate convergence of Africa towards Eurasia. 

How to cite: Masson, F., Meghraoui, M., Bahrouni, N., Saleh, M., Ridha, M., Faouzi, D., Ulrich, P., and Bernard, J.-D.: GPS Constraints on the Active Deformation in Tunisia: Implications on the Geodynamics of the Western Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2061, https://doi.org/10.5194/egusphere-egu2020-2061, 2020.

D1723 |
Xiaoning Su and Guojie Meng

On April 25, 2015, the Nepal MS 8.1 earthquake took place in the Himalayan seismic belt on the southern margin of Tibetan Plateau. After the earthquake, the China Earthquake Administration established Immediately 13 GPS continuous stations in the southern Tibetan region. In this study, such data, the data of China’s crustal movement observation network in the southern Tibet region and the data of GPS continuous stations in Nepal are used to estimate the postseismic deformation of the GPS station. Three postseismic deformation models, i.e., a logarithmic model, an exponential model and an integrated combination, are used for fitting GPS postseismic deformation. The Markov Chain Monte Carlo algorithm, based on a Bayesian framework, is applied to invert model parameters. The results show that the integrated model for the logarithmic model and exponential model can accurately fit the postseismic deformation observed by GPS, indicating that the postseismic deformation observed by GPS may involve two different deformation mechanisms with multi-scale characteristics. Based on the analysis of the spatial-temporal distribution of the postseismic deformation field and its comparison with the coseismic deformation field, it is considered that the afterslip mainly occurs in the deep area where the coseismic rupture extends northward, while the seismic risk in the shallow area where the coseismic rupture is not broken still deserves further attention.

How to cite: Su, X. and Meng, G.: Postseismic deformation of the Ms 8.1 Nepal earthquake in 2015 from GPS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2503, https://doi.org/10.5194/egusphere-egu2020-2503, 2020.

D1724 |
Letizia Elia, Susanna Zerbini, and Fabio Raicich

Time series of GPS coordinates longer than two decades are now available at many stations around the world. The objective of our study is to investigate large networks of GPS stations to identify and analyze spatially coherent signals present in the coordinate time series and, at the same locations, to identify and analyze common patterns in the series of environmental parameters and climate indexes. The study is confined to Europe and the Mediterranean area, where 107 GPS stations were selected from the Nevada Geodetic Laboratory (NGL) archive on the basis of the completeness and length of the data series. The parameters of interest for this study are the stations height (H), the atmospheric surface pressure (AP), the terrestrial water storage (TWS) and the various climate indexes, such as NAO (North Atlantic Oscillation), AO (Artic Oscillation), SCAND (Scandinavian Index) and MEI (Multivariate ENSO Index). The Empirical Orthogonal Function (EOF) is the methodology adopted to extract the main patterns of space/time variability of these parameters. We also focus on the coupled modes of space/time interannual variability between pairs of variables using the singular value decomposition (SVD) methodology. The coupled variability between all the afore mentioned parameters is investigated. It shall be pointed out that EOF and SVD are mathematical tools providing common modes on the one hand, and statistical correlations between pairs of parameters on the other. Therefore, these methodologies do not allow to directly infer the physical mechanisms responsible for the observed behaviors which should be explained through appropriate modelling. Our study has identified, over Europe and the Mediterranean, main modes of variability in the time series of GPS heights, atmospheric pressure and terrestrial water storage. For example, regarding the station heights, the EOF1 explains about 30% of the variance and the spatial pattern is coherent over the entire study area. The SVD analysis of coupled parameters, namely H-AP, TWS-AP and H-TWS, showed that most of the common variability is explained by the first 3 modes. In particular, 70% for the H-AP, 67% for the TWS-AP and 49% for the H-TWS pair. Moreover, we correlated the stations heights with the NAO, AO, SCAND and MEI indexes to investigate the possible influence of climate variability on the height behavior. To do so, the stations heights were represented using the first three EOFs to reduce the potential effect of local anomalies. More than 30 stations, over the total of 107, show significant correlations up to about 0.3 with the AO and SCAND indexes. The correlation coefficients with MEI turn out to be significant and up to 0.5 for about half of the stations.

How to cite: Elia, L., Zerbini, S., and Raicich, F.: PCA study of the interannual variability of GPS heights and environmental parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2616, https://doi.org/10.5194/egusphere-egu2020-2616, 2020.

D1725 |
Majid Abrehdary and Lars Sjöberg

Seismic data are the preliminary information for investigating Earth’s interior structure. Since large parts of the world are not yet sufficiently covered by such data, products from Earth satellite gravity and altimetry missions can be used as complimentary for this purpose. This is particularly the case in most of the ocean areas, where seismic data are sparse. One important information of Earth’s interior is the crustal/Moho depth, which is widely mapped from seismic surveys. In this study, we aim at presenting a new Moho depth model from satellite altimetry derived gravity and seismic data in Fennoscandia and its surroundings using the Vening Meinesz-Moritz (VMM) model based on isostatic theory. To that end, the refined Bouguer gravity disturbance (reduced for gravity of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components by applying so-called stripping gravity corrections) is corrected for so-called non-isostatic effects (NIEs) of nuisance gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA) and plate flexure. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and Moho depth determination from gravity in this area. To do so, the DGIA effect is removed and restored from the NIEs prior to the application of the VMM formula. The numerical results show that the RMS difference of the Moho depth from the (mostly) seismic CRUST1.0 model is 3.6/4.3 km when the above strategy for removing the DGIA effect is/is not applied, respectively. Also, the mean value differences are 0.9 and 1.5 km, respectively. Hence, our study shows that our method of correcting for the DGIA effect on gravity disturbance is significant, resulting in individual changes in Moho depth up to several kilometres.

How to cite: Abrehdary, M. and Sjöberg, L.: A new Moho depth model for Fennoscandia and surroundings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4142, https://doi.org/10.5194/egusphere-egu2020-4142, 2020.

D1726 |
Shaozhuo Liu, jean-Mathieu Nocquet, Yann Klinger, Xiwei Xu, Guihua Chen, Guihua Yu, and Sigurjón Jónsson

GPS observations across active mountain ranges provide essential constraints on uplift rates, which sheds light on the underlying physical processes contributing to the development of topography. The Kunlun Shan (KLS) mountain range bounds the topographic high of the northern Tibetan Plateau. The elevation across the range sharply decreases from >4000 m in the interior of the plateau to ~2700 m in the Qaidam Basin. The mechanism responsible for its formation is debated with several models proposed on the basis of seismological and geological data. Here we consider data constraints from a cGPS profile that runs across the KLS and was installed in 2007. Our GPS time series reveal direct mechanical response to the crustal thickening across the KLS and therefore provide a promising dataset against which some geodynamical models can be tested.  Based on the GPS time series, we estimate rates of tectonic uplift and evaluate the impacts originating from reference frame drifts, common mode errors, some non-tectonic signals (e.g., hydrological loading), time-correlated noise, and postseismic transients of recent large earthquake. The GPS-derived uplift rate is ~1 mm/yr at the KLS. We find that ~2 mm/yr deep slip on a low- or intermediate-angle south-dipping thrust fault can explain the GPS-derived uplift rate. The possibility of a high-angle thrust fault, as has been proposed for the Longmen Shan (southeastern Tibetan Plateau), does not appear to be likely in the KLS case.

How to cite: Liu, S., Nocquet, J.-M., Klinger, Y., Xu, X., Chen, G., Yu, G., and Jónsson, S.: Contemporary uplift of the Kunlun Shan, Northern Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6011, https://doi.org/10.5194/egusphere-egu2020-6011, 2020.

D1727 |
Takuya Nishimura

The Kanto region, central Japan situated in the complex tectonic region where two oceanic plates subducts from the Japan trench and Sagami trough. Although many previous studies clarified repeated Mw~6.6 Slow Slip Events (SSEs) with a duration of a week in an offshore region of the Boso Peninsula along the Sagami trough, the number of the detected SSEs are limited and overall activity of SSEs have not been fully understood in these regions. We, here, applied our SSE detection in these regions to the whole available GNSS dataset for a quarter century spanning from 1994 to 2019 and clarify the relation between SSE and tremor distribution.

We use daily coordinates at 291 GNSS stations using a precise point positioning strategy of the GIPSY 6.4 software. We apply the method of Nishimura et al. (2013) and Nishimura (2014) to detect a jump associated with short-term SSEs in GNSS time-series and estimate their fault models from observed displacements. A rectangular fault on the Philippine Sea or the Pacific plates is assumed for each SSE. The stacking of GNSS time-series based on the displacement predicted by the fault model [Miyaoka and Yokota, 2012] enable us to estimate duration of SSEs.

  We detected ≥ 150 possible SSEs along both the Japan trench and Sagami trough but we here focus on SSEs along the southernmost part of the Japan trench. Total slip distribution of the detected possible SSEs shows that large slip (≥ 0.3 m) is limited near the trench. A comparison with low-frequency tremors (LFTs) along the Japan trench (Nishikawa et al., 2019) suggests SSEs occur in the same depth range (10-20 km) of LFTs but their distribution is rather complimentary whereas a minor tremor activity exists at the edge of the SSE total slip. This complimentary distribution is contrast to overlapping distribution of SSEs and LFTs observed in a deep episodic and tremor region in the other subduction zones including southwest Japan. Another distinctive feature is that SSEs continuously occur from the trench to a depth of ~60 km only at ~ 35.5ºN. Because the subducted seamounts locate at this latitude, geometry of plate interface may control a genesis of SSEs in these regions.

How to cite: Nishimura, T.: Short-term SSEs in the Kanto region, central Japan using GNSS data for a quarter century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8182, https://doi.org/10.5194/egusphere-egu2020-8182, 2020.

D1728 |
Yurii Gabsatarov, Irina Vladimirova, Grigory Steblov, Leopold Lobkovsky, and Ksenia Muravieva

Kuril subduction zone is one of the most active continental margins due to the high plate convergence rate. Latest oceanographical, seismological and geological studies show a block structure of the Kuril island arc. In 2006-2008 Kuril GNSS network was installed along the island arc to provide information on the dynamics of the continental margin. Proper geodetic characterization of surface deformations in Kuril region is necessary for studies of regional geodynamical processes associated with seismic cycles and the evolution of the subduction zone. Since Kuril network has some disadvantages such as small amount of continuous stations (cGNSS) and its near-linear arrangement, special attention must be paid to correct processing of the GNSS data to exclude miscalculations that can affect further modeling of regional geodynamical processes.

We use regression analysis of time series of cGNSS stations displacements to distinguish components which are related to: 1) long-term accumulation of elastic stresses (secular velocity); 2) almost instant release of substantial part of accumulated stresses during main shock (coseismic offsets); 3) transient processes following large subduction eartquakes. The main advantages of the proposed regression analysis algorithm are: 1) an automatic process for detecting coseismic displacements, based on direct modeling of surface deformations using a dislocation model, 2) an automatic process for identifying transient processes; 3) taking into account the realistic GNSS noise model in calculating errors.

Since most of the GNSS stations were deployed only after large 2006-2007 Simushir earthquakes their time series were affected by intense and long-term postseismic transient processes such as afterslip and viscoelastic relaxation in the upper mantle. We use our direct models of these postseismic processes to construct residual time series, which allows us to estimate magnitudes of seasonal periodic signal and to calculate realistic errors.

We use correlation-based clustering algorithm to identify the influence of block structure of island arc on observed deformation patterns during interseismic, coseismic and postseismic stages of the seismic cycle. We also check our processing of GNSS data by constructing model of slip distribution in the source of 2006 Simushir earthquake on the basis of our estimates of coseismic offsets and by comparing our model with previous ones obtained on the basis of satellite geodetic data. The performed analysis of continuous GNSS observations shows that different parts of Kuril island arc are at different stages of seismic cycle.

How to cite: Gabsatarov, Y., Vladimirova, I., Steblov, G., Lobkovsky, L., and Muravieva, K.: Revealing of surface deformations induced by geodynamic processes in the Kuril island arc from GNSS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8952, https://doi.org/10.5194/egusphere-egu2020-8952, 2020.

D1729 |
Jean-Mathieu Nocquet, Takuya Nishimura, Sara Bruni, Susanna Zerbini, and Haluk Ozener

Thanks to both technological evolution and analysis improvement in the past decades, space geodesy can now monitor crustal movements of a few millimeters over time opening new prospects for the study of earthquakes. However, fully exploiting the potential of geodetic measurements is subject to their further integration with seismological analysis and requires the development of a multidisciplinary approach. The new joint IAG-IASPEI sub-commission on Seismogeodesy aims to facilitate the cooperation between the geodetic and the seismological communities in order to improve our current understanding of the different processes leading to earthquakes.

The new Seismogeodesy sub-commission will focus on both observational challenges and theoretical aspects. Particular effort will be dedicated to identifying gaps of knowledge and opportunity for progress. Specifically, the sub-commission will:
* actively encourage the cooperation between all geoscientists studying the plate boundary deformation zones, by promoting the exploitation of synergies between different fields;
*  work to reinforce collocated and integrated geodetic and seismological monitoring of seismically active areas, inland and off-shore by increasing and/or developing infrastructures dedicated to broadband observations from the seismic wave band to the permanent displacement;
* be a reference group for the integration of the most advanced geodetic and seismological techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;
* act as a forum for discussion and scientific support for international geoscientists investigating the kinematics and mechanics of the plate boundary deformation zone;
* promote the use of standard procedures for geodetic data acquisition, quality evaluation, and processing, particularly GNSS data and InSAR data;
* promote earthquake geodesy, the study of seismically active regions with large earthquake potential, and geodetic application to early warning system of earthquakes and tsunamis for hazard mitigation;
* promote the role of geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on faults.
* facilitate and stimulate the integrated exploitation of large data sets, using Machine Learning and Data Mining
* support the organization of periodic workshops, meetings, summer schools with special emphasis on interdisciplinary research and interpretation and modeling issues
* help to the emergence of a new generation of researchers in Seismogeodesy worldwide

We invite any researcher interested in Seismogeodesy to join us and have a fruitful discussion in front of our poster.  

How to cite: Nocquet, J.-M., Nishimura, T., Bruni, S., Zerbini, S., and Ozener, H.: A new joint IAG-IASPEI sub-commission for Seismogeodesy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11112, https://doi.org/10.5194/egusphere-egu2020-11112, 2020.

D1730 |
Juan José Portela Fernández, Alejandra Staller Vázquez, and Marta Béjar Pizarro

The Central Valley, Costa Rica, is subject to moderate seismicity, related to the Central Costa Rica Deformation Belt: a region with diffuse deformation, where Caribbean, Cocos and Nazca Plates, as well as the Panama Micro-plate, interact.  The Eastern part of the valley is dominated by the Aguacaliente-Navarro fault system. The city of Cartago was destroyed by an earthquake Ms 6.4 in 1910, associated with the rupture of the Aguacaliente fault. Volcanic unrest –mainly in Turrialba Volcano, with recent activity reported- is present in the area, thus resulting in a very complex interaction zone, where seismic hazard studies are crucial.

In this context, we process GNSS observations from five different campaigns -2012, 2014, 2016, 2018 and 2020- in 13 stations in the area, in order to estimate their Caribbean-fixed velocities, hence the regional cumulative strain. Additionally, we use both InSAR and GNSS data to measure volcanic deformation, aiming to refine the computed velocities by removing volcanic deformation from the tectonic signal.

The refined velocities allow us to asses a more precise cumulative strain for the Aguacaliente-Navarro fault system, which is useful to improve seismic hazard assessment in Cartago, one of the most important cities in the region.

How to cite: Portela Fernández, J. J., Staller Vázquez, A., and Béjar Pizarro, M.: Cortical deformation in the Aguacaliente-Navarro fault system (Central Valley, Costa Rica) from Geodetic data (GNSS and InSAR) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12015, https://doi.org/10.5194/egusphere-egu2020-12015, 2020.

D1731 |
Juan Ignacio Martin de Blas, Giampiero Iaffaldano, and Eric Calais

It is typically assumed that the occurrence of large earthquakes along the margins of tectonic plates does not impact on their rigid motions. However, for tectonic units of small size (i.e. for microplates), the viscous resistance at the plate base, and thus the torques needed to change their rigid motions, are significantly smaller than those needed for medium/large-size plates. In fact, a recent study that makes use of numerical simulations of synthetic microplates indicates that it is theoretically possible to link the temporal evolution of geodetically-observed microplate motions to the buildup and release of stresses associated with the earthquake cycle.

Here, we focus on the motion of the Anatolian microplate. We extract its rigid motion from GPS time series spanning the time around the 1999 MW = 7.5 Izmit earthquake. We select those GPS stations that are sufficiently away from plate boundaries, such as the North Anatolian Fault, the East Anatolian Fault and the Western Anatolia Extensional Province. Then, we attempt linking the temporal evolution of the Anatolian microplate rigid motion to the stresses associated with the 1999 MW = 7.5 Izmit earthquake rupture. The novelty of our approach lies in the fact that, in contrast to current models of the earthquake cycle, we connect earthquake stresses to changes in plate rigid motions and not to the crustal deformation in the vicinity of earthquake-prone faults.

How to cite: Martin de Blas, J. I., Iaffaldano, G., and Calais, E.: Linking the Anatolian microplate rigid motions to the 1999 Mw = 7.5 Izmit earthquake rupture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13627, https://doi.org/10.5194/egusphere-egu2020-13627, 2020.

D1732 |
Alejandro Pérez-Peña, Alberto Fernández-Ros, Belen Rosado, Amós De Gil, Gonzalo Prates, Jorge Garate, and Manuel Berrocoso

Nowadays, both, the number of observations and the accuracy of satellite-based geodesic measurements, like GNSS, have increased. Therefore, GNSS provides more data as displacement values and velocities. This paper demonstrates that GNSS data analysis is a powerful tool to study geodynamic processes.

In this study, the analyzed GNSS data correspond to continuously recorded GPS (CGPS) stations, what we call the SPINA network. These stations are located in a region called Ibero-Maghrebian which includes the southern areas of the Iberian Peninsula and northern Africa.

The CGPS stations are included in the following organizations: RENEP (National Network of Permanent Stations), RAP (Andalusian Positioning Network), the Murcia Region CGPS Networks, ERVA (Valencian Reference Stations Network), IGN (National Geographic Institute) and the network TOPOIBERIA. The velocity was obtained in two steps: (1) preprocessing position time-series data of daily GPS measurements and (2) applying a combined model using the weighted least-squares method.

The prior knowledge of the crustal strain rate tensor provides a description of geodynamic processes such as the fault strain accumulation.

Based on the distribution of the GNSS stations, several grid sizes were tested to identify the best resolution. A Python script was used to compute the full two-dimensional velocity gradient tensor by means of inverting the GNSS velocities. The tensorial analysis provides different aspects of deformation, such as the maximum shear strain rate, including its direction, and the dilatation strain rate. These parameters can be used to characterize the mechanism of the current deformation.

Based on the computations from the GNSS-data model of components of horizontal deformations, the rates of both principal, values and axes, of the Earth’s crust deformation were found. Deformations measured in the Ibero-Maghrebian region with GPS could be interpreted in terms of either elastic loading or ductile deformation.

How to cite: Pérez-Peña, A., Fernández-Ros, A., Rosado, B., De Gil, A., Prates, G., Garate, J., and Berrocoso, M.: INTEGRATION OF GNSS-GPS NETWORKS (cGPS) FOR OBTAINING STRESS AND STRAIN MODELS FOR THE SPINA REGION (SOUTH OF THE IBERIAN PENINSULA AND NORTH AFRICA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19570, https://doi.org/10.5194/egusphere-egu2020-19570, 2020.

D1733 |
Berrocoso Manuel, Del Valle Arroyo Pablo Emilio, Colorado Jaramillo David Julián, Gárate Jorge, Fernández-Ros Alberto, Pérez-Peña Alejandro, Rosado Moscoso Belén, and Ramírez Zelaya Javier Antonio

The northwest of South America is conformed by the territories of Ecuador, Colombia and Venezuela. Great part of these territories make up the Northern Andes Block (BAN). The tectonic and volcanic activity in the northwest of South America is directly related to the interaction of the South American plate, and the Nazca and Caribbean plates, with the Maracaibo and Panama-Chocó micro plates. The high seismic activity and the high magnitude of the recorded earthquakes make any study necessary to define this complex geodynamic region more precisely. This work presents the velocity models obtained through GNSS-GPS observations obtained in public continuous monitoring stations in the region. The observations of the Magna-eco network (Agustín Codazzi Geographic Institute) are integrated with models already obtained by other authors from the observations of the GEORED network (Colombian Geological Service). The observations have been processed using Bernese software v.52 using the PPP technique; obtaining topocentric time series. To obtain the speeds, a process of filtering and adjustment of the topocentric series has been carried out. Based on this velocity model, regional structures have been defined within the Northern Andes Block through a differentiation process based on the corresponding speeds of the South American, Nazca and Caribbean tectonic plates. Local geodynamic structures within the BAN itself have been established through cluster analysis based on both the direction and the magnitude of each of the vectors obtained. Finally, these structures have been correlated with the most significant geodynamic elements (fractures, faults, subduction processes, etc.) and with the associated seismic activity.

How to cite: Manuel, B., Pablo Emilio, D. V. A., David Julián, C. J., Jorge, G., Alberto, F.-R., Alejandro, P.-P., Belén, R. M., and Javier Antonio, R. Z.: Geodynamic study of the north of the Andes block (Colombia, Panama, Ecuador and Venezuela) through gnss-gps: models of displacements, models of deformation and definition of local and regional geodynamic structures. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21362, https://doi.org/10.5194/egusphere-egu2020-21362, 2020.

D1734 |
Haluk Ozener, Bahadir Aktug, Onur Yilmaz, Asli Sabuncu, Bengisu Gelin, Kaan Alper Uçan, Bulent Turgut, and Maryna Batur

Since 1766, the North Anatolian Fault Zone in the Marmara Sea has not generated a Mw=7.0 earthquake. In the Marmara Sea, three different segments are located having ~25 mm slip rates and ~10 mm slip deficit per year. The faulting mechanism within the Marmara Sea has capability of generating earthquakes larger than Mw7.0. We are continuously monitoring this critical region with more than 30 seismo-geodetic stations equipped with 100 Hz sampling seismographs and 1 Hz sampling GPS receivers, in order to detect fast and slow tectonic motions in and around the Marmara Sea at temporal and spatial scale from milliseconds to years and from centimeters to tens of kilometers.

The data obtained during this study provides us to identify the slip deficit along the fault, the segmentation of fault, the interaction between slip-deficit and background seismicity. Besides, these data also contribute to identify the pre-seismic seismo-geodetic behavior and co-seismic slip when Mw=7.0 type of earthquakes occurs.

How to cite: Ozener, H., Aktug, B., Yilmaz, O., Sabuncu, A., Gelin, B., Uçan, K. A., Turgut, B., and Batur, M.: Investigating the Earthquake Cycle along Marmara Sea Region of North Anatolian Fault by means of seismo-geodetic observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21829, https://doi.org/10.5194/egusphere-egu2020-21829, 2020.