Intraplate Velocities Research Articles

Practical Application of a Horizontal Intraplate Velocity Field Model for the Territory of Bulgaria

The Republic of Bulgaria is situated on the edge of the Eurasian tectonic plate. This is defined by active tectonic and seismic activity, which is an issue in the implementation of the official coordinate reference system in the country - the ETRS89, as far as precise solutions are concerned. The reason is that the intraplate, relative to Eurasia, tectonic movements south of Stara Planina are about 5 times larger than those north of it. Over a period of time (about 10 years), the coordinate errors of the points from a static network become bigger than the uncertainties of GNSS measurements and thus limit their potential. Thanks to the presence of networks of continuously operating reference GNSS stations (CORS networks), and advanced methods of processing and analysis of the results, it is possible to monitor the crustal deformations with sufficient precision. A model of horizontal intraplate velocities was developed based on measurements from different epochs of the CORS networks operating on the territory of Bulgaria. Precise coordinates and velocities of the stations were estimated using the Bernese GNSS Software v5.2, and the deformation modeling was performed using a method of determining parameters of local deformation and Euler poles of distinctive tectonic blocks to which the country is divided according to the authors. This paper presents the practical applicability of this model for interpolation the velocities of stations from static networks and verification of the official results for the points of the National GPS Network. The results are encouraging for the practical realization of ETRS89 on the territory of Bulgaria.

Quantitative impact of structural inheritance on present-day deformation and seismicity concentration in intraplate deformation zones

Structural inheritance (i.e. paleo-tectonic) areas, acting as weakened domains, appear to be a key element localizing the seismicity in intraplate deformation zones. However, the impact of structural inheritance on the observed present-day seismicity and strain rate concentration remains to be quantified. In this study, we quantify through 2D numerical modeling the localization and amplification factor of upper crustal strain rates induced by structural inheritance. Our 2D models are constrained by intraplate velocity boundary conditions and include rheology laws that accounts for inherited strain weakening in both the brittle and ductile layers of the lithosphere. The role of structural inheritance is investigated for different localization of the weakened domain in the lithosphere. For an average intraplate geotherm (Moho temperature ca. 500°C), brittle weakening (i.e. inherited faults) alone induces a limited amplification factor of upper crustal strain rates of ca. 4. Ductile weakening can increase the amplification factor to ca. 7 when localized in the lower crust, but has no effect when localized in the lithospheric mantle. Overall, the amplification factors of upper crustal strain rates vary between 1 and 27 depending on the location of the weakened area in the lithosphere and on the different possible net driving forces, crustal strengths, amounts of weakening, and geotherms. These model amplification factors are in reasonable agreement with those derived from GPS and seismicity data over large spatial scale (several hundreds of kilometers) in North America.

Application of PPP with ambiguity resolution in earth surface deformation studies: a case study in eastern Canada

Earth surface deformations are commonly studied by processing observations of continuously operating GPS (CGPS) stations located in the deformation area using differential methods. In this study, we assessed the performance of precise point positioning (PPP) with and without ambiguity resolution (AR) to recover station velocities. Using 37 CGPS stations mostly located in eastern Canada over a 10-year period, the PPP-derived velocities were compared with the official velocities of Natural Resources Canada obtained from differential processing using the Bernese GNSS Software. The estimated horizontal and vertical velocities of the three solutions (PPP, PPP-AR and differential) were in good agreement, and show the overall rotation and vertical uplift/subsidence of the study region. The same consistency was observed by comparing intraplate horizontal velocities. Ambiguity fixing abilities in PPP showed substantial improvement in the east component compared to the float solution. PPP was also found to considerably reduce computational load by processing each station independently, taking approximately 2.2 seconds per station on a desktop computer. The results of this study confirmed that PPP-AR can provide position and velocity accuracy comparable to a global differential solution, and can be used for identifying intraplate velocities.

Comparison of the historic seismicity and strain-rate pattern from a dense GPS-GNSS network solution in the Italian Peninsula

We present a dense crustal velocity field and corresponding strain-rate pattern computed using Global Positioning System (GPS)- Global Navigation Satellite System (GNSS) data from several hundred permanent stations in the Italian Peninsula. GPS data analysis is based on the GAMIT/GLOBK 10.6 software, which was developed and maintained mainly by Massachusetts Institute of Technology (MIT), using tools based on the distributed-sessions approach implemented in this package. The GPS data span the period from January 2008 to December 2012 and come from several different permanent GPS networks in Italy. The GLOBK package implemented in the last version of the GAMIT package is used to compute the position time-series and velocities registered in the International Terrestrial Reference Frame (ITRF) 2008. The resulting high-density intra-plate velocity field provides indications of the tectonics of the Mediterranean region. A computation of the strain-rate pattern from GPS data is performed and compared with the map of the epicentral locations of historical earthquakes that occurred in the last 1000 years in the Italian territory, showing that, in general, higher crustal deformation rates are active in regions affected by seismicity of greater magnitude.

ESTIMATING EULER POLE PARAMETERS FOR EASTERN CANADA USING GPS VELOCITIES

Eastern Canada is characterized by many intraplate earthquakes mostly concentrated along the Saint Lawrence River and Ottawa River valleys. After the rigid plate rotation of North America, the glacial isostatic adjustment (GIA) is by far the largest source of geophysical signal in eastern Canada. We estimate a set of Euler pole parameters for this area using a velocity field of 19 continuously operating GPS stations out of 112, and show that they are different from the overall rotation of the North American plate. This difference potentially reflects local stresses in this seismic region, and the difference in intraplate velocities between the two flanks of the Saint Lawrence River valley accumulate stress along the river.

Irregular variations in GPS time series by probability and noise analysis

The character of the topocentric components in ETRF2000(R08) from the Polish ASG-EUPOS system was analysed using skewness and kurtosis derived from the data probability density function. The data from 115 permanent GPS stations with a time span of more than 5 years were used. The main goal of this research was to show that any unmodelled systematics can disrupt the results. The obtained median values of skewness and kurtosis clearly indicate the discrepancies between the assumed normality of the GPS time series distribution and the reality, mainly due to stochastic and/or deterministic parts that are still present in the data. The quadratic relationship between skewness and kurtosis was developed with the empirically determined constants. The noise analysis with the Maximum Likelihood Estimation was also performed with the assumptions of white and white plus power-law noise. The estimated spectral indices for power law noises are close to −1 (flicker noise). The uncertainties of the intraplate velocities with white and white plus power law noise assumptions were calculated. It was shown that these uncertainties can be underestimated up to 5 mm/year. Additionally we made 1000 simulation which were aimed at showing how the values of skewness and kurtosis are changed when some mismodelled part of the data remains in the time series. We assumed different values of trend (1 and 6 mm/year), seasonal amplitudes (1 and 6 mm) and offsets (3 and 10 mm) with flicker noise of 1 mm amplitude to see how the metrics we use are biased.

Interplate coupling off northeastern Japan before the 2011 Tohoku‐oki earthquake, inferred from seafloor geodetic data

AbstractSeafloor crustal movements off Miyagi and Fukushima Prefectures, northeastern Japan, observed for about 9 years before the 2011 Tohoku‐oki earthquake (M9.0) with the GPS/acoustic geodetic technique, revealed the spatiotemporal variation of interplate coupling in this region. Off Miyagi Prefecture, temporal variations of the crustal movements are characterized as a strain accumulation‐release process in relation to the 2005 Miyagi‐oki earthquake (M7.2). The intraplate velocity since December 2006, when the strain accumulation seemed to have restarted, is 4–5 cm/yr relative to the North American plate, which is significantly lower than that before the 2005 event, 6–7 cm/yr. This suggests that interplate coupling off Miyagi Prefecture since around 2007 is weaker than that before the 2005 event. On the other hand, off Fukushima Prefecture, a westward crustal movement at a constant rate of about 2 cm/yr relative to the North American plate has been observed for the interseismic period from 2002 to 2008. The interplate coupling off Fukushima Prefecture is significantly weak compared with that off Miyagi Prefecture. This is consistent with the observed coseismic displacements associated with the 2011 event, which are much smaller off Fukushima Prefecture than off Miyagi Prefecture.

Modelling the Velocity Field in a Regular Grid in the Area of Poland on the Basis of the Velocities of European Permanent Stations

The paper presents the results of testing the various methods of permanent stations’ velocity residua interpolation in a regular grid, which constitutes a continuous model of the velocity field in the territory of Poland. Three packages of software were used in the research from the point of view of interpolation: GMT (The Generic Mapping Tools), Surfer and ArcGIS. The following methods were tested in the softwares: the Nearest Neighbor, Triangulation (TIN), Spline Interpolation, Surface, Inverse Distance to a Power, Minimum Curvature and Kriging. The presented research used the absolute velocities’ values expressed in the ITRF2005 reference frame and the intraplate velocities related to the NUVEL model of over 300 permanent reference stations of the EPN and ASG-EUPOS networks covering the area of Europe. Interpolation for the area of Poland was done using data from the whole area of Europe to make the results at the borders of the interpolation area reliable. As a result of this research, an optimum method of such data interpolation was developed. All the mentioned methods were tested for being local or global, for the possibility to compute errors of the interpolated values, for explicitness and fidelity of the interpolation functions or the smoothing mode. In the authors’ opinion, the best data interpolation method is Kriging with the linear semivariogram model run in the Surfer programme because it allows for the computation of errors in the interpolated values and it is a global method (it distorts the results in the least way). Alternately, it is acceptable to use the Minimum Curvature method. Empirical analysis of the interpolation results obtained by means of the two methods showed that the results are identical. The tests were conducted using the intraplate velocities of the European sites. Statistics in the form of computing the minimum, maximum and mean values of the interpolated North and East components of the velocity residuum were prepared for all the tested methods, and each of the resulting continuous velocity fields was visualized by means of the GMT programme. The interpolated components of the velocities and their residua are presented in the form of tables and bar diagrams.

Instantaneous deformation and kinematics of the India-Australia Plate

SUMMARY Active intraplate deformation of the India‐Australia Plate is now being captured by far-field global positioning system (GPS) measurements as well as measurements on a few islands located within the deforming zone itself. In this paper, we combine global and regional geodetic solutions with focal mechanisms of earthquakes to derive the present-day strain field of the India‐Australia Plate. We first compile an updated catalogue of 131 Indian intraplate earthquakes (M > 5) spanning the period between the two Asian mega earthquakes of Assam 1897 and Sumatra 2004. Using Haines and Holt’s numerical approach applied to a fully deformable India‐Australia Plate, we show that the use of GPS data only or earthquakes data only has severe drawbacks, related, respectively, to the small number of stations and the incompleteness of the earthquakes catalogue. The combined solution avoids underestimation of the strain inherent to the Kostrov summation of seismic moments and provides details that cannot be reached by pure GPS modelling. We further explore the role of heterogeneity of the India‐Australia Plate and find that the best model, in terms of geodetic vectors fit, relative distribution of strain, style and direction of principal strain from earthquakes, is obtained using the surface heat-flow as a proxy for rheological weakness of the oceanic lithosphere. The present-day deformation is distributed around the Afanasy Nikitin Chain in the Central Indian Basin (CIB)—where it is almost pure shortening—and within the Wharton Basin (WB) off Sumatra—where it is almost pure lateral strike-slip. The northern portion of NinetyEast ridge (NyR) appears as a major discontinuity for both strain and velocity. The new velocity field gives an India/Australia rotation pole located at 11.3 ◦ S, 72.8 ◦ E( −0.301 ◦ Myr −1 )o verlapping with previous solutions, with continental India moving eastward at rates ranging from 13 mm yr −1 (southern India) to 26 mm yr −1 (northern India) with respect to Australia. Taking into account the intraplate velocity field in the vicinity of the Sumatra trench, we obtain a convergence rate of 46 mm yr −1 towards N18 ◦ Ea tthe epicentre of the 2004 Aceh megaearthquake. The predicted instantaneous shortening in the CIB and WB and extension near Chagos-Laccadive are in good agreement with the finite deformation measured from plate reconstructions and seismic profiles, suggesting a continuum of deformation since the onset of intraplate deformation around 7.5‐8 Ma. Since no significant change in India convergence is detected at that time, we suggest that the intraplate deformation started with the trenchward acceleration of Australia detaching from India along a wide left-lateral oceanic shear band activating the NyR line of weakness as well as north‐south fracture zones east of it. The predicted total amount of left lateral finite strain along these faults is in the range 110‐140 km.

Present crustal movement and strain distribution in Central Europe inferred from GPS measurements

In 1992, an international collaboration was initiated to study the present‐day geodynamics of Central Europe. The primary tool of this research is the Global Positioning System (GPS) therefore the Central European GPS Geodynamic Reference Network was established in 1994. The network extends from the south in the Eurasian‐African plate boundary zone to the East European Pre‐Cambrian Platform in the northeast. During the first phase of the project four GPS campaigns were organized between 1994 and 1997. Analysis of GPS data provided RMS repeatabilities around 2 mm in the horizontal and 5–6 mm in the vertical component for each campaign. The velocities of GPS sites situated on the Eurasian plate were compared with those predicted by the NNR‐NUVEL‐1A plate velocity model. The intraplate velocity field shows that the northern part of Central Europe seems generally stable with velocities under 2 mm/yr. However, the southern sites close to the plate boundary zone show higher values and abrupt changes of velocities indicating the existence of narrow deformation zones. The primary feature revealed by the strain calculation in the Alpine‐Pannonian‐Dinaric system is the dominant north‐south contraction resulting from the collision of the African and Eurasian plates transmitted by the Adriatic microplate. However the direction of contraction in the Alpine‐Pannonian‐Dinaric junction zone changes from NW‐SE at the northeastern boundary of the Adriatic microplate to NE‐SW toward the Bohemian Massif. The magnitudes of these strain rates are similar, −8.0±5.3 ppb/yr and −8.6±2.5 ppb/yr, respectively over ∼200×350 km subnetworks. We observe E‐W oriented (93°±13°) right‐lateral shear (12±5 ppb/yr), between the Alpine‐North Pannonian unit and the southernmost sites in the Dinarides and Southern Alps, along with left‐lateral shear (97°±7°; 10±2 ppb/yr) relative to the stable Bohemian Massif in the north. Both the strain field and the intraplate velocities presented show that the Alpine‐North Pannonian unit is presently crushed out to the east with 2 mm/yr velocity on average along two main fault zones as a consequence of the compression caused by the Adria‐Alpine collision.