The GPS velocity field of the Aegean. New observations, contribution of the earthquakes, crustal blocks model

2021 ◽  
Author(s):  
Pierre Briole ◽  
Athanassios Ganas ◽  
Panagiotis Elias ◽  
Dimitar Dimitrov
Keyword(s):  
Time Series ◽  
Kinematic Model ◽  
Relaxation Times ◽  
North Anatolian Fault ◽  
Postseismic Deformation ◽  
Boundary Line ◽  
Localized Deformation ◽  
Series Length ◽  
North West ◽  
The North

Summary We calculate and analyse the coordinate time series of 282 permanent GPS stations located in Greece and 47 in surrounding countries. The studied period is 2000–2020. The average GPS time series length is 6.5 years. The formal velocity uncertainties are rescaled to be consistent with the velocity scatters measured at 110 pairs of stations separated by less 15 km. We remove the effect of the crustal earthquakes of Mw ≥ 5.3. We quantify and model the postseismic deformations. Two relaxation times are usually needed, one short of some weeks, one long of one year or more. For the large Mw = 6.9 events of Samothraki 2014 and Methoni 2008, the postseismic deformation equals or exceeds the coseismic one. We detect at three stations a deformation transient in May 2018 that may correspond to a slow earthquake beneath Zakynthos and north-west Peloponnese, with equivalent magnitude 5.8. The density and accuracy of the velocities make it possible to better quantify several characteristics of the deformation in the Aegean, in particular: (a) the transition from the Anatolian domain, located in the south-east, to the European domain through the western end of the North Anatolian fault; (b) the north-south extension in the western Aegean; (c) the east-west extension of the western Peloponnese; (d) the clockwise rotation of the Pindos; (e) the north-south extension in central Macedonia. Large parts of the central Aegean, eastern Peloponnese and western Crete form a wide stable domain with internal deformation below 2 nstrain yr−1. We build a kinematic model comprising ten crustal blocks corresponding to areas where the velocities present homogeneous gradients. The block boundaries are set to fit with known localized deformation zones, e.g. the rift of Corinth, the North Anatolian fault, the Katouna fault. When the velocities steps are clear but not localized, e.g. through the Peloponnese, the boundary line is arbitrary and represents the transition zone. The model fits the velocities with a root mean square deviation of ± 0.9 mm yr−1. At the boundaries between blocks we compare the predicted and observed deformations. We find shear rates of 7.4 and 9.0 mm yr−1 along the Movri and Katouna faults, 14.9 and 8.7 mm yr−1 along the North Anatolian fault near Lemnos and near Skopelos respectively, extension of 7.6, 1.5 and 12.6 mm yr−1 across the Gulf of Patras, the Trichonis Lake and the Ambracian Gulf. The compression across western Epirus is 3.7 mm yr−1. There is a dextral transtensional movement of 4.5 mm yr−1 between the Amorgos and Astypalea islands. Only the Ionian Islands region shows evidence of coupling along the subduction interface.

Coincident changes in four components of the North Sea ecosystem

1999 ◽  
Vol 79 (1) ◽  
pp. 183-185 ◽  
Author(s):  
K.F. Pearce ◽  
C.L.J. Frid
Keyword(s):  
Time Series ◽  
Species Composition ◽  
North Sea ◽  
Food Chain ◽  
Demersal Fish ◽  
North West ◽  
The North ◽  
The North Sea ◽  
Chain Links ◽  
Single Set

An analysis of species composition of the zooplankton, macrobenthos (two stations) and demersal fish from Northumberland (north-west North Sea) are reported. The four time-series show synchronous changes in species composition. While some of these changes coincide with changes in climateological variables, others do not. The degree of synchrony implies that either all the time-series are responding to a single set of extraneous forcing factors, or that food chain links, rapidly translate the signal through all ecosystem components.

Slip-deficit estimation with a 3D fault model of the North Anatolian Fault by using InSAR time series

2021 ◽  
Author(s):  
Alison Seidel ◽  
Henriette Sudhaus
Keyword(s):  
Time Series ◽  
Crustal Deformation ◽  
Time Series Data ◽  
Fault Model ◽  
North Anatolian Fault ◽  
Series Data ◽  
The North ◽  
Slip Deficit ◽  
Finite Fault ◽  
Finite Fault Model

<p>Crustal earthquakes are events of sudden stress release throug­h rock failure, for example as a consequence of continuous and long-term stress buildup at tectonic faults that eventually exceeds the strength of rock. Before failure, under increasing stress at a fault, the surrounding crust is slowly deforming. The amount and pattern of crustal deformation carries information about location and potential magnitude of future earthquakes.</p><p>Time series of space-borne interferometric Synthetic Aperture Radar (InSAR) data can be used to precisely measure the surface motion, which corresponds to the crustal deformation, in the radar line-of-sight and across large areas. These observations open the opportunity to study fault loading in terms of location, size of locked parts at faults and their slip deficit. Here we study the North Anatolian Fault (NAF), a major right-lateral strike-slip fault zone of about 1500 km length in the north of Turkey and we create its first large-scale 3D finite-fault model based on InSAR data.</p><p>We use the InSAR time series of data recorded by ESA’s Envisat SAR satellite between 2002 and 2010 (Hussain et al., 2018 and Walters et al., 2014).<!-- Das ist nicht ganz eindeutig formuliert. rigid motion darf nicht auf die InSAR Daten bezogen werden. --> We represent the fault with several vertical, planar fault segments that trace the NAF with reasonable resolution. The medium model is a layered half space with a viscoelastic lower crust and mantle. Several GNSS velocity measurements are used to apply a trend correction and calibrate the InSAR time series data to an Eurasia-fixed-reference frame. We use the plate motion difference of the Anatolian and the Eurasian plates calculated through an Euler pole to set up a back-slip finite-fault model. We then optimize the back-slip as the slip deficit, the width and the depth of the locked fault zone at each segment to achieve a good fit to the measured surface motion.</p><p>We find shallow locking depths and small slip deficits in the eastern and westernmost regions of the NAF, while the central part shows both deeper locking depths and larger slip deficits for the observation period. <!-- So wie es jetzt ist sind es zu viele Wörter, wenn man diesen erklär-Satz rausnehmen würde, würde es gerade so passen. Für die Erdbebenaktivität im Osten hab ich bis jetzt für den Zeitraum auch noch kein entsprechendes Paper gefunden, da suche ich aber noch. -->For both parameters the trends are in an overall agreement to earlier studies. There, InSAR-time series data have been used to calculate slip deficits at the North Anatolian fault with 2D models and/or assuming a homogeneous and purely elastic medium.<!-- Passt vom flow jetzt besser hier hin, denke ich. --> Local modeled differences therefore might be connected to differences in the modeling approaches, but also remain subject to further investigations and discussions.</p><p>Our model provides a very suitable basis for future time-dependent modeling of the slip deficit at the NAF that includes also more recent InSAR time series based on data from the Sentinel-1 radar satellite mission of ESA.</p>

A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault

2020 ◽  
Author(s):  
Jorge Jara ◽  
Alpay Ozdemir ◽  
Angelique Benoit ◽  
Romain Jolivet ◽  
Ziyadin Çakir ◽  
...  
Keyword(s):  
Time Series ◽  
Ground Deformation ◽  
North Anatolian Fault ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Central Section ◽  
Slow Slip Events ◽  
The North ◽  
Aseismic Deformation ◽  
Over Time

<p>Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.</p><p>We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.</p>

scholarly journals The Sub-Polar Gyre Index – a community data set for application in fisheries and environment research

2016 ◽  
Author(s):  
Barbara Berx ◽  
Mark R. Payne
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Marine Ecosystem ◽  
Series Length ◽  
Data Set ◽  
The North ◽  
Community Data ◽  
Definition Of ◽  
Index Time Series

Abstract. Scientific interest in the sub-polar gyre of the North Atlantic Ocean has increased in recent years. The sub-polar gyre has contracted and weakened, and changes in circulation pathways have been linked to changes in marine ecosystem productivity. To aid fisheries and environmental scientists, we here present a time series of the Sub-Polar Gyre Index (SPG-I) based on monthly mean maps of sea surface height. The established definition of the SPG-I is applied, and the first EOF and PC are presented. Sensitivity to the spatial domain and time series length are explored, but found not to be important factors. Our time series compares well with indices presented previously. The SPG-I time series is freely available online (doi:10.7489/1806-1) and we invite the community to access, apply and publish studies using this index time series.

Slow slip events along the North Anatolian Fault

2021 ◽  
Author(s):  
Romain Jolivet ◽  
Bertrand Rouet-Leduc ◽  
Jorge Jara ◽  
Manon Dalaison ◽  
Claudia Hulbert ◽  
...  
Keyword(s):  
Time Series ◽  
Fault Plane ◽  
Slip Rate ◽  
North Anatolian Fault ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Temporal Scales ◽  
Slow Slip Events ◽  
Spatial And Temporal Scales ◽  
The North

<p>While some faults remain locked for tens to hundreds of years, some active faults slip slowly, either continuously or episodically. The discovery of slow, generally silent, slip at the turn of the century led to a profound modification of our understanding of the mechanics of faulting, shedding light on the dynamics of fault slip. Such dynamics areis controlled by the past history of stress along the fault plane (i.e. historical ruptures), fluids circulating in the crust and the rheology of the crust and fault plane. Understanding the influence of these different factors requires dense observations, as suggested by the large range of spatial and temporal scales involved in the control of the slip velocity along a fault. Specifically, the smallest scales of slow slip have beenwere inferred by the observation of tremors or low frequency events, interpreted as the chatter of a fault plane while it slips slowly. We are missing direct observations of such kilometer-scale slow slip events and continental creeping faults are an obvious target for such observationsfor such observations.</p><p> </p><p>Aseismic slip along the North Anatolian Fault was recognized in the 1960’s by the observation of offset man-made features without earthquakes recorded. Following these early observations, multiple geodetic studies focused on recording aseismic slip and analyzed the average rate of shallow slow slip in the vicinity of the town of Ismetpasa. GPS, InSAR and creepmeter data all converge toward an aseismic slip rate reaching 1 cm/yr in places, with significant along- strike variations. Furthermore, earlyHowever, creepmeter measurements in the 80’s, confirmed by records from a more recent instrument, suggest aseismic slip is currently episodic, occurring in bursts of slip. Recent InSAR data from the Cosmo-SkyMed constellation captured a month-long slow slip event with a maximum of 2 cm/yr of slip.</p><p> </p><p>We propose to analyze the geodetic record to search for slow slip events over the 2015-2020 period. We take advantage of a dense network of continuous GNSS stations installed in 2017 and of time series of Sentinel 1 SAR data to identify at least 3 slow slip events along the North Anatolian Fault. Thanks to the dense temporal sampling of the GNSS records, we describe faithfullyobserve the onset of slow slip. We use a deep learning algorithm to extract the surface signature of the slow slip events from the InSAR time series, highlighting a slow rupture front propagating along strike. We compare the occurrences of slow slip events with the local fault geometry, the average distribution of kinematic coupling and the historical seismicity. We discuss the mechanical implications of such detailed description of slow slip along an active fault. In conclusion, while slow slip rate averaged over periods longer than 2-3 years seems constant over the last 40 years, identification of slow slip events suggests this apparently constant rate results from slow slip events over multiple spatial and temporal scales.</p>

scholarly journals Test on the Reliability of the Subsurface Fault Geometry Estimated by Deformed River Terraces Along the Bailang River, North Front of the Qilian Shan (North West China)

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaofei Hu ◽  
Xianghe Ji ◽  
Xilin Cao ◽  
Jiuying Chen ◽  
Baotian Pan
Keyword(s):  
Kinematic Model ◽  
Slip Rate ◽  
Seismic Reflection Profile ◽  
Fault Geometry ◽  
North West ◽  
The North ◽  
River Terraces ◽  
Deformation Kinematics ◽  
Kinematic Models ◽  
Crust Deformation

The subsurface fault geometry is the base for understanding a process of crust deformation and mountain building. Based on kinematic models for fault-related folds, a geomorphic method is recently applied to estimate the subsurface fault geometry, while the validation on its reliability is lacking. In this study, we surveyed a suit of river terrace surfaces across an active fold at the north front of the Qilian Shan. According to the deformation geometry of the terraces, the fold deformation is interpreted by a listric fault fold model, and based on this kinematic model, the fault geometry underlying the fold is estimated. In comparison between the estimated fault geometry and a seismic reflection profile, we found that the decollement depth and the back thrust are highly consistent with each other. Although some small fault bends or internal shearing cannot be estimated solely by the terrace deformation, the overall fault geometry is successfully revealed by the terrace deformation. Using this fault geometry and the terrace dating results, the region deformation kinematics are re-evaluated, which suggest that the dip slip (in a rate of 1.8 ± 0.4 mm/a) along the decollement is mainly accommodated by two structures, one is the blind-back-thrust fault within the piggy basin in a dip-slip rate of 0.9 ± 0.3 mm/a and another is the thrust and fold at the west portion of the Yumu Shan range.

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