Permanent Global Positioning System Stations Research Articles

Enhanced neural network model for regional ionospheric modeling and evaluation under different solar-geomagnetic conditions

Monitoring spatiotemporal variations of ionospheric vertical total electron content (VTEC) is crucial for space weather and satellite positioning. In the present study, an enhanced neural network (ENN) model is proposed to capture the changing characteristics of ionospheric VTEC and compared with the traditional mathematical models, i.e. the POLYnomial (POLY) model, generalized trigonometric series function and spherical harmonic function (SHF) model. The ionospheric VTEC data obtained from 31 permanent global positioning system stations in the southwest region of China on 26 August and 8 September, 2017, were used to test the performance of the mentioned models under different Solar-geomagnetic conditions. The ENN model is derived from the ensemble learning method, and the disadvantage that simple backpropagation neural network learners that are not robust enough is weakened by the ENN model. After statistical analysis and single-frequency precise point positioning (SF-PPP) experiments, it is demonstrated that the ENN model is superior to the above three mathematical models, regardless of the solar-geomagnetic conditions. In terms of mean absolute error, root mean square error, standard deviation, and mean absolute percentage error, the ENN model outperforms the SHF model, which is the best mathematical model in the analysis, by 40.7%, 30.20%, 29.88%, 38.04% under quiet solar-geomagnetic conditions, and by 37.66%, 29.93%, 30.96%, 32.01% under active solar-geomagnetic conditions. In addition, the accuracy of the SF-PPP is greatly affected by the error caused by ionosphere. In the static SF-PPP experiment of this study, the ENN model can better correct ionospheric error. Under quiet and active solar-geomagnetic conditions, the SF-PPP accuracy can be improved by 85.1% and 85.2% with the ionosphere delay correction from the ENN model.

Dependence of epoch-wise two-way nested ANOVA estimates of variances of unmodeled effects present in relative GPS positioning on satellite elevation cutoff angle and PDOP mask

Impact of satellite elevation cutoff angle and position dilution of precision (PDOP) mask change on epoch-wise variance components of unmodeled effects that accompany relative Global Positioning System (GPS) positioning is presented herein. Data used for this study refer to the winter and summer periods of the years with minimal (2008) and maximal (2013) solar activity. These data were collected every 30 s in static mode, at two permanent GPS stations located in Montenegro, establishing a medium-distance (116-km-long) baseline with a height difference of approximately 760 m between its endpoints. The study showed that changing satellite elevation cutoff angle, with a fixed PDOP mask, affects epoch-wise two-way nested ANOVA estimates of variances related to the ‘far-field’ multipath (considered as the nested factor herein) and the combined unmodeled effect of tropospheric and ionospheric refraction (considered as the nesting factor herein). However, changing of PDOP mask, with a fixed satellite elevation cutoff angle, doesn't affect epoch-wise two-way nested ANOVA estimate of variance of the combined unmodeled effect of tropospheric and ionospheric refraction, but, generally, affects the estimate of variance of the ‘far-field’ multipath (possibly mixed with a part of a ‘shorter-term’ ionospheric refraction), which is especially pronounced for the summer period. It should also be noted that there is a significant influence of satellite elevation cutoff angle change on both epoch-wise horizontal and vertical position accuracy, only for the summer period, especially in the presence of maximal solar activity, while there is no significant impact of PDOP mask change on epoch-wise positional accuracy.

Cost-Effective, Single-Frequency GPS Network as a Tool for Landslide Monitoring.

The constant monitoring of active landslides, particularly those located in the proximity of populated areas or touristic places, is crucial for early warning and risk-management purposes. The commonly used techniques deploy expensive instrumentation that can be hardly afforded, especially by small mountain communities in which landslide events often occur repeatedly. In recent years, the scientific community, as well as the private sector, have devoted growing effort to reducing the costs of monitoring systems. In this work, we present a monitoring network based on single-frequency Global Positioning System (GPS) sensors that have been activated to monitor an active landslide in the Carnic Alps, North-Eastern Italy. The system, which was composed of 12 single-frequency GPS stations, one seismometric station coupled with a single-frequency GPS instrument for real-time monitoring, and one permanent dual-frequency GPS station located in a stable area, provided daily reports of the landslide motion to the local authorities and administration. We show that this system is a valuable, flexible, and cost-effective tool for quick landslide characterization, and has high potential to be used as a landslide early warning system in case of emergency situations.

Improved Hydrological Loading Models in South America: Analysis of GPS Displacements Using M-SSA

Environmental loading, in particular from continental water storage changes, induces geodetic station displacements up to several centimeters for the vertical components. We investigate surface deformation due to loading processes in South America using a set of 247 permanent GPS (Global Positioning System) stations for the 2003–2016 period and compare them to loading estimates from global circulation models. Unfortunately, some of the hydrological components, and in particular surface waters, may be missing in hydrological models. This is especially an issue in South America where almost half of the seasonal water storage variations are due to surface water changes, e.g., rivers and floodplains. We derive river storage variations by rerouting runoffs of global hydrology models, allowing a better agreement with the mass variations observed from GRACE (Gravity Recovery and Climate Experiment) mission. We extract coherent seasonal GPS displacements using Multichannel Singular Spectrum Analysis (M-SSA) and show that modeling the river storage induced loading effects significantly improve the agreement between observed vertical and horizontal displacements and loading models. Such an agreement has been markedly achieved in the Amazon basin. Whilst the initial models only explained half of the amplitude of GPS, the new ones compensate for these gaps and remain consistent with GRACE.

GPS derived crustal velocity, tectonic deformation and strain in the Indian Himalayan arc

The present study elucidates velocity of the Indian plate from 2013 to 2016 with the help of six continuously operating permanent Global Positioning System (GPS) stations and tracks the crustal motion and direction directly by means of space-based geodetic measurements. The GPS derived velocity estimates were computed with respect to 2008 International Terrestrial Reference Frame (ITRF 08) and carried out almost all along the arc in the Indian Himalayan Region (IHR). The velocity vectors indicate that the Indian plate is moving towards the NE direction (average velocity of 46.95 ± 0.23 mm/yr) with higher movement towards the eastward direction (36.11 ± 0.17 mm/yr) compared to the northward direction (29.02 ± 0.16 mm/yr). Variations in the plate motion between IISC and permanent GPS stations suggest that presently, the convergence rate is about 8.06 ± 0.28 mm/yr and 5.71 ± 0.17 mm/yr for Higher Himalaya and Lesser Himalaya respectively. In addition, the deformation rate was also calculated on the basis of baseline shortening between IGS stations (IISC and LHAZ) and permanent GPS stations. The results suggest that the deformation is about 11.68 ± 1.32 mm/yr above the Main Central Thrust (MCT) and 6.74 ± 1.20 mm/yr above the Main Boundary Thrust (MBT) with respect to the Indian plate (IISC), while it is 20.60 ± 1.76 mm/yr above the MCT and 11.42 ± 1.21 mm/yr above the MBT with respect to Eurasian plate (LHAZ). The strain rate through GPS measurement reveals that the maximum strain is accumulated in the central part of the Himalaya between the MBT and MCT, indicating vulnerability of the central Indian Himalaya for future earthquakes.

Surface Mass Variations from GPS and GRACE/GFO: A Case Study in Southwest China

Surface mass variations inferred from the Global Positioning System (GPS), and observed by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) complement each other in terms of spatial and temporal coverage. This paper presents an analysis of regional surface mass variations inverted from GPS vertical displacements under different density distributions of GPS stations, and compares the GPS-derived mass variations with GRACE/GFO inversion results in spatial and temporal domains. To this end, GPS vertical displacement data from a total of 85 permanent GPS stations of the Crustal Movement Observation Network of China (CMONOC), the latest GRACE/GFO RL06 spherical harmonic (SH) solutions and GRACE RL06 mascon solutions are used to investigate surface mass variations in four regions or basins, including the Yunnan Province (YNP), Min River Basin (MRB), Jialing River Basin (JLRB), and Wu River Basin (WRB) in Southwest China. Our results showed that the spatial distributions and seasonal characteristics of GPS-derived mass change time series agree well with those from GRACE/GFO observations, especially in regions with relatively dense distributions of GPS stations (e.g., in the YNP and MRB), but there are still obvious discrepancies between the GPS and GRACE/GFO results. Scale factor methods (both basin-scaled and pixel-scaled) were employed to reduce the amplitude discrepancies between GPS and GRACE/GFO results. The results also showed that the one-year gap between the GRACE and GFO missions can be bridged by scaled GPS-derived mass change time series in the four studied regions, especially in the YNP and MRB regions (with relatively dense distributions of GPS stations).

Analysis and Comparison of GPS Precipitable Water Estimates between Two Nearby Stations on Tahiti Island.

Since Bevis first proposed Global Positioning System (GPS) meteorology in 1992, the precipitable water (PW) estimates retrieved from Global Navigation Satellite System (GNSS) networks with high accuracy have been widely used in many meteorological applications. The proper estimation of GNSS PW can be affected by the GNSS processing strategy as well as the local geographical properties of GNSS sites. To better understand the impact of these factors, we compare PW estimates from two nearby permanent GPS stations (THTI and FAA1) in the tropical Tahiti Island, a basalt shield volcano located in the South Pacific, with a mean slope of 8% and a diameter of 30 km. The altitude difference between the two stations is 86.14 m, and their horizontal distance difference is 2.56 km. In this paper, Bernese GNSS Software Version 5.2 with precise point positioning (PPP) and Vienna mapping function 1 (VMF1) was applied to estimate the zenith tropospheric delay (ZTD), which was compared with the International GNSS Service (IGS) Final products. The meteorological parameters sourced from the European Center for Medium-Range Weather Forecasts (ECMWF) and the local weighted mean temperature () model were used to estimate the GPS PW for three years (May 2016 to April 2019). The results show that the differences of PW between two nearby GPS stations is nearly a constant with value 1.73 mm. In our case, this difference is mainly driven by insolation differences, the difference in altitude and the wind being only second factors.

Evaluation of the GPS Precise Point Positioning technique during the 21 July 2017 Kos-Bodrum (East Aegean Sea) Mw 6.6 earthquake

Precise Point Positioning (PPP) algorithms have been widely used in the Global Positioning System (GPS)-based applications. A PPP technique with a single receiver provides effective solutions where accurate absolute positioning is required. This paper provides the performance assessment of GPS PPP for detecting the displacements caused by an earthquake. For this purpose, the earthquake that occurred on 21 July 2017 at Kos-Bodrum with the impact of Mw 6.6 was investigated by analyzing the data of the permanent GPS stations located around the related region with the PPP technique. The location distances of these GPS stations range from 10 to 89 km to the epicenter of this earthquake. GPS data provided from seven permanent stations from the Continuously Operating Reference Stations-Turkey (CORS-TR) and local Bodrum CORS networks were processed to determine the co-seismic displacements during the earthquake. The data of these stations for days of year (DOYs) 200, 201, 202, and 203 were analyzed with post-process static PPP and kinematic PPP methods. GIPSY-OASIS II v6.4 was used for processing the data and all of the solutions were performed in the ITRF2008 reference frame. Two strategies were followed on the post-process static solutions. In the first strategy, 4-day data with 24-h observations were separately analyzed day by day. In the second strategy, the 24-h data were divided into 3-h duration, which is the minimum duration for optimum PPP solutions, and then the analyses were performed. When the displacements between DOYs 200 and 203 are considered in the 24-h data analysis, significant displacements have been observed through northwest direction in the northern stations whereas MUG1 is excluded. Moreover, there is significant displacement through the southeast direction in the station DATC located in the south of the epicenter. When the 3-h solutions are examined, displacements, especially on n and e directions, are observed starting from the solutions, which include Mw 6.6 earthquake. According to the kinematic PPP solutions, the effects of the Mw 6.6 earthquake can be seen clearly in the stations DATC, ORTA, TRKB, and YALI. Considering all outcomes, the PPP technique with both static and kinematic solutions provides effective results for detecting the displacements during the earthquake.

Predicting TEC in China based on the neural networks optimized by genetic algorithm

This paper illustrates the application of neural networks (NN) in developing a regional prediction model for the ionospheric total electron content (TEC) over China. To avoid the ‘local minimum’ effect caused by the traditional NN-based model, genetic algorithm (GA) is utilized to optimize the initial weights of NN. In this study, the NN has 19 input parameters which are known to cause variations in the ionospheric parameters. These parameters relate to the ionospheric diurnal variations, seasonal information, solar cycle, geomagnetic activities, geographic coordinates, and declination. The output parameter is the daily hourly vertical TEC (VTEC) measured from 43 permanent GPS (Global Positioning System) stations in China. Datasets for 2012–2014 are used to train the network, and datasets for 2015 are selected as the test data to verify the model’s performance. Predictions from the GA-based NN (GA-NN) model, back propagation-based NN (BP-NN) model, and International Reference Ionosphere 2012 (IRI2012) model are then compared with the observed TEC from 12 GPS stations in China. According to the numerical analysis, the root-mean-square error (RMSE) of GA-NN model ranges from 5.2140 to 8.4756 TECU, the corresponding percent deviation (PD) is 8.78–12.30%, and the correlation coefficient falls within the range of 0.8069–0.9583. The BP-NN model’s RMSE varies between 6.2962 and 12.1468 TECU, PD is between 10.17% and 14.16%, and the correlation coefficient lies in the range of 0.7192–0.9348. For the IRI2012 model, the corresponding ranges are 6.5513–11.7937 TECU, 11.01–14.07%, and 0.7292–0.9129, respectively. This, combined with the comparison of diurnal variations of TEC, suggests that the GA-NN model greatly outperforms the BP-NN and IRI2012 models. Furthermore, the variation of seasonal and local characteristics are also validated by the GA-NN model. The results indicate that the GA-NN model is very promising for applications in ionospheric studies.

Precipitable water vapour estimation using the permanent single GPS station in Zanjan, Iran

ABSTRACTMeteorological investigations using the global positioning system (GPS) are based on expensive permanent networks and they are not developed globally on the Earth. In this study it is confirmed that single station GPS meteorology is feasible where there is no possibility for development of a sophisticated dense GPS network. Since 1 January 2011 a GPS station has been installed in the Institute for Advanced Studies in Basic Sciences in the province of Zanjan, Iran, where upper air meteorological data are not available. The GPS data were processed in order to estimate the zenith total delay (ZTD) of GPS signals due to the troposphere. The estimated ZTD was then transformed to precipitable water vapour (PWV) using the ERA‐Interim globally available humidity and temperature vertical profiles. Three kinds of validation were applied to the estimated PWV and all of them reasonably proved the validity of the GPS results: (1) the measured surface water vapour pressure and dew point temperature show 87.8 and 86.6% correlation respectively with the estimated PWV; (2) the PWV measured using radiosondes in three neighbouring cities of Zanjan (Tabriz, Tehran and Kermanshah) with nearly the same climatic regime show 81.1, 71.7 and 66.4% correlation respectively with the GPS PWV time series, and (3) the global reanalysis datasets for Zanjan show 89.2% correlation with the GPS results. These validations indicate that, in the absence of permanent GPS networks, if proper data processing strategies are adopted the low cost single station GPS meteorology can be considered as a possibility for meteorological monitoring.

Cost-effective monitoring of land subsidence in developing countries using semipermanent GPS stations: a test study over Houston, Texas

We present a cost-effective method for monitoring land subsidence in developing countries using measurements from semipermanent global positioning system (GPS) stations and interferometric synthetic aperture radar (InSAR) observations. The cost of maintaining a network of permanent GPS stations to monitor subsidence in developing countries might be implausible due to the high cost of maintenance. Hence, semipermanent GPS stations could be an alternative method, which densifies a GPS network with relatively inexpensive costs. We used three statistical methods to estimate the subsidence. We investigated the optimum time intervals for semipermanent GPS measurements based on the similarities of subsidence magnitudes and curve patterns with the permanent GPS measurements. In addition, we assessed the open source GPS processing tools based on the data quality of different session durations. Among the three models, the smoothing spline model showed the best estimation of subsidence. Among the different time interval data, 10- or 30-day time interval data were optimum for semipermanent GPS stations. Finally, we compared the GPS results to the InSAR-derived subsidence result, and both methods show that the northwestern Houston area subsides by about 1.5 to 2.0 cm/year. We anticipate that our method can be applied to other cities experiencing subsidence in developing countries.

GPS geodetic infrastructure for natural hazards study in the Puerto Rico and Virgin Islands region

The Puerto Rico and Virgin Islands (PRVI) are located within the complex plate boundary zone between the North American and Caribbean plates. This region faces multiple natural hazards, such as earthquakes, tsunamis, landslides, hurricanes, and flooding. The islands are part of the Greater Antilles island chain, which is one of the earliest places that employed Global Positioning System (GPS) technology in plate tectonics and natural hazards studies. A dense Continuously Operating Reference Stations (CORS) network with 24 permanent GPS stations is currently operated by a joint effort of academic, government, and local land surveying communities. This region has been regarded as one of the densest CORS coverage regions worldwide. This article summarized the current GPS geodetic infrastructure in the PRVI region, which includes three components: a dense CORS network that is open to the public, a stable local reference frame that is updated in time, and sophisticated software packages for GPS data processing that are freely available to the academic and research community. This article focused on establishing a local reference frame, the stable Puerto Rico and Virgin Islands reference frame of 2014 (PRVI14), which is essential for precisely delineating local ground deformation over space and time. Applications of the geodetic infrastructure for precise faulting, landslide, and sea-level monitoring were illustrated in this study. According to this study, the St. Croix Island is moving away from the Puerto Rico and Northern Virgin Islands toward southeast with a steady velocity of 1.7 mm/year; the Lajas Valley in southwestern of Puerto Rico may be experiencing a north–south direction extension (1.5 mm/year) and a minor right-lateral strike slip (0.4 mm/year) with respect to the PRVI14 reference frame; the current absolute sea-level rise rate in the PRVI coastal region is about 1.6–2.0 mm/year.

Rescue of the historical sea level record of Marseille (France) from 1885 to 1988 and its extension back to 1849–1851

This paper describes the historical sea level data that we have rescued from a tide gauge, especially devised originally for geodesy. This gauge was installed in Marseille in 1884 with the primary objective of defining the origin of the height system in France. Hourly values for 1885–1988 have been digitized from the original tidal charts. They are supplemented by hourly values from an older tide gauge record (1849–1851) that was rediscovered during a survey in 2009. Both recovered data sets have been critically edited for errors and their reliability assessed. The hourly values are thoroughly analysed for the first time after their original recording. A consistent high-frequency time series is reported, increasing notably the length of one of the few European sea level records in the Mediterranean Sea spanning more than one hundred years. Changes in sea levels are examined, and previous results revisited with the extended time series. The rate of relative sea level change for the period 1849–2012 is estimated to have been \(1.08\pm 0.04\) mm/year at Marseille, a value that is slightly lower but in close agreement with the longest time series of Brest over the common period (\(1.26\pm 0.04\) mm/year). The data from a permanent global positioning system station installed on the roof of the solid tide gauge building suggests a remarkable stability of the ground (\(-0.04\pm 0.25\) mm/year) since 1998, confirming the choice made by our predecessor geodesists in the nineteenth century regarding this site selection.

Geodetic evidence on segmentation of Cascadia subduction zone based on episodic tremors and slips using multivariate harmonic analysis of GPS time series

Episodic tremor and slip (ETS) events with different recurrence intervals have been observed in abundance all along the Cascadia subduction zone margin. Analysis of seismic records as well as Global Positioning System (GPS) time series of the Pacific Northwest Geodetic Array (PANGA) has suggested three distinct coherent zones for the occurrence of these events. In this paper multivariate harmonic estimation has been deployed for further analysis of the segmentation in this area. Raw time series of 43 permanent GPS stations have been used for this purpose. The GPS stations have been geographically divided into three distinct groups including those in the northern, middle and southern parts of the study area. After the reduction of time series for the linear trend as well as annual and semiannual effects, the data series of each group has been analyzed using the multivariate harmonic estimation technique. Subsequently, different combinations of GPS stations including the stations located in the southern, northern and middle zones have been analyzed. Furthermore, the northern and middle, southern and middle as well as the northern and southern zone pair combinations have also been analyzed. The statistical measure devised for identifying the significant frequencies suggests common periods that are consistent with the recurrence intervals of the ETS events already reported for each of the above three geographic zones. Moreover, the method can provide geodetic evidence, in addition to geophysical ones, on the segmentation of ETSs, provided that the adopted time series are of a sufficient length. The geodetic evidence obtained in this research is consistent with the recurrence intervals as well as the boundaries obtained by the analysis of seismic records. Contrary to univariate harmonic estimation, multivariate approach using spatio-temporal correlation of the GPS time series is capable to detect those ETSs whose impacts on the time series are weak.

High nonlinear urban ground motion in Manila (Philippines) from 1993 to 2010 observed by DInSAR: Implications for sea-level measurement

In coastal low-lying urban areas, vertical ground motions can significantly exacerbate the hazards related to sea-level rise. However, their spatial extent, their temporal evolution, and even sometimes their existence are often poorly known. This study aims to monitor variable urban ground motion (uplift and subsidence) from 1993 to 2010 in the metropolitan area of Manila, Philippines. Because high subsidence rates have been reported in this city in previous studies, conventional Differential SAR Interferometry (DInSAR) was applied with an adapted stacking procedure to the archive of ERS and Envisat satellite images to produce surface deformation-velocity maps for different periods. The results showed that the city is locally affected by vertical ground motions on the order of 15cm/yr. Moreover, the spatio-temporal evolution of the ground-motion phenomena is highly nonlinear. These results are in good agreement with previous studies focused on groundwater use in Manila and in the Marikina Fault Valley, suggesting a plausible interpretation of the processes causing surface motion. Incidentally, the ground motions are affecting the locations of several geodetic instruments, including a tide gauge with sea-level records starting in 1902, two permanent GPS (Global Positioning System) stations, and a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) station. A major implication of those large and locally variable ground motions is that they impede the use of the nearby GPS and DORIS data to correct the tide-gauge records and to derive robust sea-level trends associated with climate change.

A stable reference frame for landslide monitoring using GPS in the Puerto Rico and Virgin Islands region

Global Positioning System (GPS) technologies have been frequently applied for the purpose of landslide monitoring. A local stable reference frame is essential for precisely interpreting landslide movements derived from GPS observations. In this study, we define a stable reference frame using over 5 years of continuous GPS data collected from eight permanent GPS stations in the Puerto Rico and Virgin Islands (PRVI) region. The realization of the Stable Puerto Rico and Virgin Islands Reference Frame (SPRVIRF) is defined in terms of a 14-parameter Helmert transformation from the International Global Navigation Satellite System (GNSS) Service Reference Frame of 2008 (IGS08). SPRVIRF is aligned with the IGS08 at epoch 2013.0. The GIPSY/OASIS (V6.2) software package, which employs the precise point positioning (PPP) with single receiver phase ambiguity resolution, was used to calculate position coordinates within IGS08. Through the combined use of the PPP post-processing method and SPRVIRF, it is practical and easy to conduct millimeter accuracy landslide monitoring by a single technician with a single GPS unit. SPRVIRF provides a precise common reference frame in the PRVI region that can be used for a broad range of research applications, such as delineating long-term landslide creeping, studying ground deformation associated with subsidence, fault creep, hydrologic loading and microplate motions, and monitoring long-term deformation of critical structures, such as dams, high-rise buildings, and long-span bridges.

Analysis of the displacement of geodetic stations during the Emilia seismic sequence of May 2012

<span style="font-family: Times New Roman; font-size: small;"> </span><span style="font-family: Times New Roman;"><span style="font-size: small;"><span style="font-family: Calibri; font-size: x-small;"> </span></span><p>The two events of Mw 6.11 and 5.96 [EMERGEO Working Group 2012, this volume] that took place on May 20 and 29, 2012, respectively, in the Po Plain, and the associated seismic sequence, represent the response of the brittle upper crust (hypocentral depth ca. 10 km) to the compressive stress in the outer Apennine Arc. Kinematically, the motion of the Apennines that has led to a compressional regime in the Po Plain can be represented as a counterclockwise rotation, as demonstrated by the shortening of the transalpine baselines, with a rate that decreases going west [Caporali and Martin 2000]. The compressive stress field is known from borehole breakout data [Pierdominici and Heidbach 2012] and it agrees with the principal directions of the strain rate derived from global positioning system (GPS) data. The geodetic strain rate for seismic zone 912 (Dorsale Ferrarese, according to Meletti et al. [2008]) is 92.86 ±0.04 nstrain/yr, which is a relatively high value [Caporali et al. 2011]. On a more local scale, the Mirandola fault is described in the Database of Individual Seismic Sources (DISS; http://diss.rm.ingv.it/) under the ID ITIS107 as a possible individual source, and it has a position, strike, dip, size and expected maximum magnitude [Burrato et al. 2003, Carminati et al. 2010, Scrocca et al. 2007] that are very close to the main events of the 2012 sequence. Several permanent GPS stations were in activity in the area. Using ultrarapid international Global Navigation Satellite Systems (GNSS) Service (IGS) orbits and the Bernese BSW 5.0 software [Dach et al. 2007] at our computing facility, a fast solution for the coseismic displacement was published on the May 21, 2012, and on the May 30, 2012, for the events of May 20 and 29, 2012, respectively. The largest signal was about 2 cm in the North direction at the station SGIP (San Giovanni in Persiceto), which was relatively consistent with the fault-plane solution [Devoti 2012, this volume]. In this study, we present more detailed estimates of the coseismic offsets at several other stations in the area, including a kinematic solution at 30 s temporal resolution. The coseismic displacements are inverted using the Okada [1985] model and a preliminary model of the two faults is obtained for each of the two main events, taking into account the available synthetic aperture radar (SAR) data. […]</p><p class="MsoNormal" style="margin: 0cm 0cm 10pt; text-align: justify; line-height: normal;"><span style="font-family: Calibri; font-size: x-small;"><br /></span></p><span style="font-size: small;"> </span></span>

Efforts to include geological and geodetic observations in the assessment of earthquake activity in Denmark

Assessment of earthquake hazard is improved if geological and geodetic data are included in addition to seismological data. In earthquake regions like Japan and California, palaeoseismology combines data from geology and seismology, and networks of permanent GPS (global positioning system) stations situated on bedrock supplement the networks of seismographs. A combination of seismographs and GPS stations on ice is also used in current studies of glacial earthquakes in Greenland. In Denmark only broad-scale geodetic coverage is available (Khan et al. 2005) and only a few examples of geological input are found in the literature. However, more thorough geodetic evaluations of deformations are currently made in Nordic co-operation projects and we are looking forward to learn about the results. Also the number of permanent GPS stations in Denmark has recently been increased from 3 to 13. The geological input is limited but may hold some potential, and the aim of this article is to evaluate this. We also discuss new investigations of recent geological movements, both in projects on post-glacial uplift (and accompanying horizontal deformation) of Scandinavia, and more locally of geological indicators of uplift in selected areas. As seismologists, we are interested in a homogeneous evaluation of geological indicators in all of Denmark and its neighbouring areas.

Pre-seismic anomalies in seismicity and crustal deformation: case studies of the 2007 Noto Hanto earthquake of M6.9 and the 2007 Chuetsu-oki earthquake of M6.8 after the 2004 Chuetsu earthquake of M6.8

SUMMARY If aseismic slip occured on a fault or its deeper extension, both seismicity and crustal deformation around the source would be affected. Such anomalies are determined from earthquake occurrence data and geodetic records during the periods leading up to the 2007 March Noto Hanto earthquake of M6.9 and the 2007 July Chuetsu-oki earthquake of M6.8, which successively occurred after the 2004 October Chuetsu earthquake of M6.8 on the Japan Sea coast. Assuming such aseismic slips, seismic zones corresponding to negative and positive increments of the Coulomb failure stress show seismic quiescence and activation, respectively, relative to the rate predicted by the epidemic type aftershock sequence model. These interpretations are further supported by transient crustal movements around the sources preceding the ruptures, for example, the time-series of baseline distances between permanent Global Positioning System stations deviated from their long-term linear trends in a manner that is consistent with the assumed slip. In particular, this paper emphazes on the investigation of the interacting tectonic processes within such a narrow area and a short period, considering the precursory slow slips on the focal faults or their downdip extensions based on the observed anomalies in seismicity and crustal movement.

Active tectonics in northern Victoria Land (Antarctica) inferred from the integration of GPS data and geologic setting

A semipermanent Global Positioning System (GPS) network of 30 vertices known as the Victoria Land Network for Deformation Control (VLNDEF) was set up in the Austral summer of 1998 in northern Victoria Land (NVL), including Terra Nova Bay (TNB), Antarctica. The locations were selected according to the known Cenozoic fault framework, which is characterized by a system of NW‐SE regional faults with right‐lateral, strike‐slip kinematics. The TNB1 permanent GPS station is within the VLNDEF, and following its installation on a bedrock monument in October 1998, it has been recording almost continuously. The GPS network has been surveyed routinely every two summers, using high‐quality, dual‐frequency GPS receivers. In this study we present the results of a distributed session approach applied to the processing of the GPS data of the VLNDEF. An improved reference frame definition was implemented, including a new Euler pole, to compute the Antarctic intraplate residual velocities. The projection of the residual velocities on the main faults in NVL show present‐day activities for some faults, including the Tucker, Leap Year, Lanterman, Aviator, and David faults, with right‐lateral strike‐slip kinematics and local extensional and compressional components. This active fault pattern divides NVL into eight rigid blocks, each characterized by its relative movements and rigid rotations. These show velocities of up to several millimeters per year, which are comparable to those predicted by plate tectonic theory at active plate margins.