Permanent GPS Stations Research Articles

Accuracy of Deformation Rates from Campaign GPS Surveys Considering Extended Observation Session and Antenna Set-Up Errors

GPS campaign measurements are still in use in the monitoring of ground deformation. Campaign measurements are frequently referred to because installing permanent stations are costly, and they cannot be installed at the desired density. Using the data from the International Global Navigation Satellite Systems (GNSS) Service (IGS) permanent GPS stations, the duration, sampling interval, etc. of the campaign measurements can be simulated. Thus, the contribution of the campaign data to the monitoring of the ground deformation can be evaluated. In this study, we carried out an experiment with the aim of determining the deformation of tectonic plates at the selected IGS stations more accurately considering by extending the observation duration to a full 24 h length. We also made an attempt to take into consideration the antenna set up errors developing a scenario referring to the information available in the literature. We have decimated the continuous data of 40 globally scattered IGS stations into monthly intervals between 2012 and 2016 and estimated the deformation rates at the IGS stations from a continuous time series of four years. The continuous time series solutions for those stations were produced by the Jet Propulsion Laboratory (JPL), NASA. We compare velocities (i.e., the deformation rates) determined from GPS campaigns (in which the sampling was performed monthly and four-monthly) with those of the continuous data. The major conclusion of this study is that the vertical velocity estimation accuracy of the GPS campaign measurements had been improved by about 85% by extending the session duration to 24 h. The repetition interval of GPS campaign measurements as per one observation every four months produced only slightly coarser accuracy (i.e., on the average 8% poorer) than those of the measurements repeated once every month.

Historical Duration of Base Triangulation Network of Turkey

After establishing National Horizontal and Vertical Control Networks and Turkish National Fundamental GPS Network (TUTGA) for Turkey's geodetic infrastructure, governmental institutes that produce maps and map info like HGK (General Command of Mapping), TKGM (General Directorate of Land Registration and Cadastral of Turkey) and IKU (Istanbul Kultur University) established CORS-TR system in order to execute Turkey's defensive, developmental and scientific works with technological developments. CORS-TR, that has 146 permanent GPS stations across Turkey, enables users to calculate Real Time Kinematic positions with correction data. Therefore, in Turkey, mapping facilities are being done more rapidly, more economically and more easily. Keywords : TUTGA, CORS-TR, GNSS, ED50, ITRF96, TUT54, TC-91, GRS80, TG-99, OPUS. DOI : 10.7176/JSTR/5-2-23

New estimation of Nile Delta subsidence rates from InSAR and GPS analysis

Increase of water level in most of the world’s oceans and seas, including the Mediterranean, due to global warming may have a serious impact on the Nile Delta. The Nile Delta is considered as one of the most important regions in Egypt as more than 50% of the Egyptians are living there. To study the thread of a potentially sinking and flooding of the Nile Delta, here, we estimate present vertical motion by use of the Persistent Scatterer InSAR (PSI) analysis in addition to the available GPS stations in the Nile Delta. The subsidence rate of the Nile Delta is estimated by applying the PSI processing for all archived Envisat SAR data from the descending tracks 207 and 436. From these tracks, 36 and 37 SAR scenes were collected, respectively. Moreover, the results of a time series analysis for six GPS permanent stations in the Nile Delta were used to validate the estimated subsidence rates from PSI analysis. The PSI and GPS solutions show that the estimated ground deformation is strongly localized at the big cities. From time series for selected PS pixels from Cairo, Tanta, Mahala, Mansoura, Damietta, and Port Said, the estimated subsidence rates from Envisat scenes are around − 6.4 ± 0.4 mm/year, − 4.0 ± 0.6 mm/year, − 4.8 ± 1.0 mm/year, − 10.0 ± 1.2 mm/year, − 10.3 ± 1.6 mm/year, and − 4.9 ± 1.6 mm/year, respectively. The localization of subsidence rates at big cities implies that the detected signals may be due to human activities, such as ground water pumping, and that the Delta as a whole presently is not subsiding.

Step-like displacements of a deep seated gravitational slope deformation observed during the 2016–2017 seismic events in Central Italy

Deep Seated Gravitational Slope Deformations are characterized by low deformation rates although they can experience partial-collapse phases or more rapid movements, especially in presence of active tectonic structures. In the Central Italy, considering the high seismicity rate, seismic activity must be considered to be an important trigger of deep slope movements. We aim to contribute to the research in this field by reporting the results of a monitoring program on a Deep Seated Gravitational Slope Deformation in this region that involves marly calcareous rocks. We documented the pre-earthquakes evolution of the phenomenon and measured its displacements during the seismic sequence in 2016 and 2017 in Central Italy, which largest events were Mw 5.0-to-6.5.A multidisciplinary approach that combines a field geomorphological survey, installation of permanent GPS stations, and InSAR elaborations was adopted for this study.The average ground motion rate of the slope deformation before the earthquakes was very low (<3 mm/y) and not spatially homogenous, as detected by GPS and InSAR. In detail, the uppermost area of the slope instability likely moves faster than the lowest sector.On the other hand, GPS and InSAR recorded significant step-like movements, one to ten times higher than the normal activity rate, triggered by the Mw 5.0-to-6.5 earthquakes. In detail, the movement mainly depended on the magnitude of the earthquake and the distance from the epicenter, and only secondarily on the number of larger magnitude earthquakes on a given day.In conclusion, we furnished monitoring data on the activity rate of a Deep Seated Gravitational Slope Deformation in seismic context, we indicated two sectors of the investigated deformation that resulted more unstable and we proved that the combination of InSAR and GPS data is a useful monitoring system for earthquake-activated, slow-moving slope instabilities.

Present‐Day Deformations of the Jura Arc Inferred by GPS Surveying and Earthquake Focal Mechanisms

AbstractThis study presents a compilation of more than 40 years of seismotectonic data, including 54 computed focal mechanisms, combined with 15 years of GPS data coming from a dense network of 35 permanent GPS stations within the Jura arc and its vicinity. These data are compared to previous available geomorphological, geophysical, and structural studies in order to discuss the 3D distribution of the deformation within the Jura arc. GPS data show coherent schemes in terms of velocities and allowed to discriminate between two provinces (NE of the belt and in its front/foreland). They also constrain a low but significant overall strain tensor with a NNW‐SSE shortening of 2.16 nanostrain/year associated with an ENE‐WSW extension of 0.44 nanostrain/year. The seismotectonic approach is based on a data set of 2,400 events and 54 focal mechanisms. Inversions of the focal mechanisms both globally and in homogeneous sectors highlight a general strike‐slip deformation regime, with sigma1 oriented NW‐SE and sigma3 oriented NE‐SW. We discriminate two different sectors in terms of basement/cover (un)coupling: (1) potentially decoupled deformation between the basement and the sedimentary cover in the NE part; and (2) coupled deformation in the sedimentary cover and its basement in the Jura foreland.

Houston16: A stable geodetic reference frame for subsidence and faulting study in the Houston metropolitan area, Texas, U.S.

Houston, Texas, is one of the earliest regions to employ continuous GPS technology for land subsidence monitoring. Currently, there are over 200 permanent GPS stations located in the greater Houston area. The need for a consistent and stable reference frame to precisely interpret local ground deformation has become critically important since the 1990s, because of the significant spreading of subsidence. We have established a stable Houston reference frame, designated Houston16, using publicly available GPS observations (>5 years) from 15 Continuously Operating Reference Stations (CORS) located outside of the greater Houston area. Applications of the reference frame in subsidence and faulting studies are demonstrated in this article. Houston16 is aligned in origin and scale with the International GNSS Reference Frame of 2008 (IGS08). A 7-parameter method was employed to transform the GPS-derived positional time series from IGS08 to Houston16. The primary product of this study is the seven parameters for transforming Earth-Centered-Earth-Fixed XYZ coordinates from IGS08 to Houston16. The frame stability of Houston16 is approximately 1 mm/year. Houston16 will be updated every few years to mitigate degradation of the frame's stability with time and to synchronize with future updates of the IGS reference frame.

Elastic period of vibration calculated experimentally in buildings hosting permanent GPS stations

During the earthquake in Emilia (Italy) of 2012, ca. 30 permanent GPS stations were in operation within a radius of about 100 km from the epicenter, each equipped with an antenna rigidly fixed to the host building and sampling the GPS signal at a high rate (> 1 Hz). From the recording of the GPS measurements, the instantaneous displacements s(t) in the North- South and East-West directions of the phase centers of the single GPS antennas at each permanent station during the most important seismic sequences were calculated in kinematic mode. Subsequently, for each of the two displacements considered as two distinct external forces, the elastic response spectra of the building were determined and from them the two periods of vibration T along two orthogonal directions coinciding with the walls of the building were extracted. The experimentally obtained periods of vibration were compared with those inferable from the technical literature. In this way, a sufficiently large sample was obtained per building type, geometry (square, rectangular, regular or irregular planimetry), height (from a minimum of 4 to a maximum of 20 m) and materials (masonry, reinforced concrete, etc.). From the computational point of view, the study confirmed that GPS is an emerging tool for monitoring dynamic displacements and the experimentally estimated value of T is always lower than the one estimated with the formulae reported in the literature. The limitations of the study lie in the impossibility to choose a priori the geometry and/or structural type of the building hosting the GPS station.

Experimental Calculation of the Damping Ratio In Buildings Hosting Permanent GPS Stations During the Recent Italian Earthquakes

Experimental Calculation of the Damping Ratio In Buildings Hosting Permanent GPS Stations During the Recent Italian Earthquakes

Analysis of Seasonal Signal in GPS Short-Baseline Time Series

Proper modeling of seasonal signals and their quantitative analysis are of interest in geoscience applications, which are based on position time series of permanent GPS stations. Seasonal signals in GPS short-baseline ( 5 m) or type of the monument. For comparison, we also processed an approximately zero baseline with a distance of 0.4 mm in the horizontal direction are observed in five short-baselines, and the amplitudes exceed 1 mm in four of them. These horizontal seasonal signals are likely related to the propagation of daily/sub-daily TEM displacement or other signals related to the site environment. Mismodeling of the tropospheric delay may also introduce spurious seasonal signals with annual amplitudes of ~ 5 and ~ 2 mm, respectively, for two short-baselines with elevation differences greater than 100 m. The results suggest that the monument height of the additional part of a typical GPS station should be considered when estimating the TEM displacement and that the tropospheric delay should be modeled cautiously, especially with station pairs with apparent elevation differences. The scheme adopted in this paper is expected to explicate more seasonal signals in GPS coordinate time series, particularly in the vertical direction.

Cansiglio Karst Plateau: 10 Years of Geodetic–Hydrological Observations in Seismically Active Northeast Italy

Ten years’ geodetic observations (2006–2016) in a natural cave of the Cansiglio Plateau (Bus de la Genziana), a limestone karstic area in northeastern Italy, are discussed. The area is of medium–high seismic risk: a strong earthquake in 1936 below the plateau (Mm = 6.2) and the 1976 disastrous Friuli earthquake (Mm = 6.5) are recent events. At the foothills of the karstic massif, three springs emerge, with average flow from 5 to 10 m3/s, and which are the sources of a river. The tiltmeter station is set in a natural cavity that is part of a karstic system. From March 2013, a multiparametric logger (temperature, stage, electrical conductivity) was installed in the siphon at the bottom of the cave to discover the underground hydrodynamics. The tilt records include signals induced by hydrologic and tectonic effects. The tiltmeter signals have a clear correlation to the rainfall, the discharge series of the river and the data recorded by multiparametric loggers. Additionally, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence with the river level. The fast water infiltration into the epikarst, closely related to daily rainfall, is distinguished in the tilt records from the characteristic time evolution of the karstic springs, which have an impulsive level increase with successive exponential decay. It demonstrates the usefulness of geodetic measurements to reveal the hydrological response of the karst. One outcome of the work is that the tiltmeters can be used as proxies for the presence of flow channels and the pressure that builds up due to the water flow. With 10 years of data, a new multidisciplinary frontier was opened between the geodetic studies and the karstic hydrogeology to obtain a more complete geologic description of the karst plateau.

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

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

ASSESSMENT OF OPTIMUM VALUE FOR DIP ANGLE AND LOCKING RATE PARAMETERS IN MAKRAN SUBDUCTION ZONE

Abstract. Makran subduction zone is one of the convergent areas that have been studied by spatial geodesy. Makran zone is located in the South Eastern of Iran and South of Pakistan forming the part of Eurasian-Arabian plate's border where oceanic crust in the Arabian plate (or in Oman Sea) subducts under the Eurasian plate ( Farhoudi and Karig, 1977). Due to lack of historical and modern tools in the area, a sampling of sparse measurements of the permanent GPS stations and temporary stations (campaign) has been conducted in the past decade. Makran subduction zone from different perspectives has unusual behaviour: For example, the Eastern and Western parts of the region have very different seismicity and also dip angle of subducted plate is in about 2 to 8 degrees that this value due to the dip angle in other subduction zone is very low. In this study, we want to find the best possible value for parameters that differs Makran subduction zone from other subduction zones. Rigid block modelling method was used to determine these parameters. From the velocity vectors calculated from GPS observations in this area, block model is formed. These observations are obtained from GPS stations that a number of them are located in South Eastern Iran and South Western Pakistan and a station located in North Eastern Oman. According to previous studies in which the locking depth of Makran subduction zone is 38km (Frohling, 2016), in the preparation of this model, parameter value of at least 38 km is considered. With this function, the amount of 2 degree value is the best value for dip angle but for the locking rate there is not any specified amount. Because the proposed model is not sensitive to this parameter. So we can not expect big earthquakes in West of Makran or a low seismicity activity in there but the proposed model definitely shows the Makran subduction layer is locked.

GPS Seismology for a moderate magnitude earthquake: Lessons learned from the analysis of the 31 October 2013 ML 6.4 Ruisui (Taiwan) earthquake

The 31 October 2013 M L 6.4 Ruisui earthquake was well recorded by twelve 50-Hz, four 20-Hz and thirteen 1-Hz GPS receivers, and twenty-five strong motion stations located within the epicentral distance of 90 km in eastern Taiwan. Kinematic positioning solutions estimated by four GNSS software (TRACK, RTKLIB, GIPSY, VADASE) are used to derive the seismic waveforms and the co-seismic displacements for this event ; strong motion accelerometers are used to verify the capability of high rate GPS to detect seismic waves generated by this earthquake. Results show that the coordinate repeatability of the GPS displacements time series are ~6 mm and ~20 mm standard deviation in the horizontal and vertical components respectively, after applying spatial filtering. The largest co-seismic displacement derived from high-rate GPS is nearly 15 centimeter at 5 km northeast of the epicenter. S waves and surface waves are successfully detected by motions of high-rate GPS and double-integrated accelerometers within the 15 km epicentral distance. For the first time twelve 50-Hz and four 20 Hz GPS observations for seismological study were used and analyzed in Taiwan; a clear benefit was evidenced with regard to the seismic waves features detection, with respect to the 1-Hz GPS data, so that ultra-high rate (> 1-Hz) observations can compensate the sparse coverage of seismic data, provided proper monuments for the GPS permanent stations are realized. The 2013 Ruisui Taiwan earthquake recorded by the high-rate GPS permanent stations network in Taiwan demonstrates the benefits of GPS Seismology for a moderate size earthquake at a local scale.

THE SAMOTHRACE EARTHQUAKE OF MAY 2014 AND THE DISPLACEMENTS ESTIMATIONS USING PERMANENT GPS STATIONS DATA

The contribution of GPS networks in monitoring seismic events is important because they can provide a direct geometrical information on the Earth's crust using satellite observations In this study position displacements of permanent GPS stations are determined due to intense seismic events in the North Aegean area after the strong earthquake on May 24, 2014. The horizontal coseismic displacements for the Samothrace Island were estimated at 9.4 cm and for Lemnos Island at 5.2 cm respectively. A study period of seven days was enough to show that the deformation evolved into two days.

THE 2014 MW 6.9 NORTH AEGEAN TROUGH (NAT) EARTHQUAKE: SEISMOLOGICAL AND GEODETIC EVIDENCE

A strong earthquake (Mw 6.9) on 24 May 2014 ruptured the North Aegean Trough (NAT) in Greece, west of the North Anatolian Fault Zone (NAFZ). In order to provide unbiased constrains of the rupture process and fault geometry of the earthquake, seismological and geodetic data were analyzed independently. First, based on teleseismic long-period P- and SH- waveforms a point-source solution yielded dominantly right-lateral strike-slip faulting mechanism. Furthermore, finite fault inversion of broad-band data revealed the slip history of the earthquake. Second, GPS slip vectors derived from 11 permanent GPS stations uniformly distributed around the meizoseismal area of the earthquake indicated significant horizontal coseismic slip. Inversion of GPS-derived displacements on the basis of Okada model and using the new TOPological INVersion (TOPINV) algorithm permitted to model a vertical strike slip fault, consistent with that derived from seismological data. Obtained results are consistent with the NAT structure and constrain well the fault geometry and the dynamics of the 2014 earthquake. The latter seems to fill a gap in seismicity along the NAT in the last 50 years, but seems not to have a direct relationship with the sequence of recent faulting farther east, along the NAFZ.

Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review

The Okavango Graben (OG) has been considered as the terminus of the southwestern branch of the East African Rift System (EARS) since the 1970s based on fault morphology and early seismic and geophysical data. Thus it has been assumed to be an incipient rifting zone, analogous to the early stage of mature rifts in the EARS. Recent geodetic data and geophysical studies in the area bring new insights into the local crust and lithosphere, mantle activity and fault activity. In this study, we computed the velocities for three permanent GPS stations surrounding the graben and undertook a review of the new geophysical data available for the area. The northern and southern blocks of the graben show an exclusively low strike-slip displacement rate of about 1mm/year, revealing the transtensional nature of this basin. The seismic record of central and southern Africa was found to be instrumentally biased for the events recorded before 2004 and the OG may not represent the most seismically active area in Botswana anymore. Moreover, no significant lithosphere and crustal thinning is found in the tectonic structure nor any strong negative Bouguer anomaly and surface heat flux. Thus the OG does not match the classical model for a rifting zone. We propose a new geodynamic model for the deformation observed west of the EARS based on accommodation of far-field deformation due to the differential extension rates of the EARS and the displacement of the Kalahari craton relative to the Nubian plate.

Time series analysis of the NOANET CGPS stations

The National Observatory of Athens has begun installing permanent GPS stations on February 2006 including a EUREF permanent station in Attica, NOA1. Currently the National Observatory of Athens operates 20 continuous GPS stations around Greece all sampling at 1-s and transmitting real-time data to Athens. Several stations also sample at 0.2-s (5 Hz) and record the data in the ring buffer for a period of 1-2 days. Their location is carefully selected so that both geological and seismotectonic criteria are fulfilled. All stations are situated close to major seismogenic structures of Greece such as the Cephalonia Transform Fault (CTF) in the Ionian Sea (VLSM, PONT, SPAN, KIPO), and the two North Anatolian Fault branches in the North Aegean Sea (PRKV, LEMN ). We describe the CGPS data archiving and processing procedures, used to combine into a uniform velocity solution the observations of all the NOANET stations, accounting for the seasonal (annual and semiannual) signals, and considering the off-sets in the coordinate time-series.

Early signs of geodynamic activity before the 2011–2012 El Hierro eruption

The potential relation between mantle plume dynamics, regional tectonics and eruptive activity in the Canary Islands has not been studied yet through the analysis of long-time series of geophysical observational data. The existence of highly reliable seismic and geodetic data has enabled us to study from 1996 to 2014 the geodynamic evolution of the North Atlantic Azores-Gibraltar region (including the NW African margin) and its relationship with recent volcanic activity in El Hierro (Canary Islands). We compiled a new and unified regional seismic catalog and used long time-series of digital 3D surface displacements recorded by permanent GPS stations in the region. A joint regional- and local-scale analysis based on these data enabled us to identify signs of anomalous tectonic activity from 2003 onwards, whose intensity increased in 2007 and finally accelerated three months before the onset of the volcanic eruption on El Hierro in October 2011. Activity included the occurrence of regional extension and an uplift process affecting the southern Iberian Peninsula, NW Africa, and the Canary Islands. We interpret these observations as early signs of the geodynamic activity, which led to El Hierro eruption and the subsequent episodes of magma intrusion. Results point to the significant contribution of the mantle plume dynamics (i.e. external forces) in this renewed volcanic activity in the Canary Islands and emphasize the role of mantle dynamics in controlling regional tectonics.

Vertical tectonics at an active continental margin

Direct observations of vertical movements of the earth's surface are now possible with space-based GPS networks, and have applications to resources, hazards and tectonics. Here we present data on vertical movements of the Earth's surface in New Zealand, computed from the processing of GPS data collected between 2000 and 2015 by 189 permanent GPS stations. We map the geographical variation in vertical rates and show how these variations are explicable within a tectonic framework of subduction, volcanic activity and slow slip earthquakes. Subsidence of >3 mm/yr is observed along southeastern North Island and is interpreted to be due to the locked segment of the Hikurangi subduction zone. Uplift of 1–3 mm/yr further north along the margin of the eastern North Island is interpreted as being due to the plate interface being unlocked and underplating of sediment on the subduction thrust. The Volcanic Plateau of the central North Island is being uplifted at about 1 mm/yr, which can be explained by basaltic melts being injected in the active mantle-wedge at a rate of ∼6 mm/yr. Within the Central Volcanic Region there is a 250 km2 area that subsided between 2005 and 2012 at a rate of up to 14 mm/yr. Time series from the stations located within and near the zone of subsidence show a strong link between subsidence, adjacent uplift and local earthquake swarms.

Continuous monitoring of surface wave velocity at the Montevecchio earthflow (Forlì-Cesena Province, Northern Apennines)

The Montevecchio landslide is an active earthflow in the province of Forli-Cesena (Northern Apennines of Italy). In the last few years, this landslide reactivated several times. In order to investigate the landslide dynamics, two monitoring systems were installed by combining 3 permanent GPS stations (to measure landslide movement) and 4 geophones (to evaluate surface-wave velocity). In this paper we present the monitoring data collected during the last reactivation of the landslide (24th – 25th of May 2015). The geophones data show a clear relationship between surface-wave velocity (Vr) and displacement rate. In particular, a decrease of Vr value was observed just before an increase of velocity, while higher Vr values were detected when the landslide was slowing down. Moreover, a pressure sensor, buried at low depth beside the geophones, showed an increase in pore water pressure before the failure in correspondence of the critical rainfall event, and while the displacement rate increased the pore water pressure had a positive value (above the ground level), probably due to the undrained compression of the landslide material.