Continuous GPS Measurements Research Articles

Combining SAR interferometric phase and intensity information for monitoring of large gradient deformation in coal mining area

Coal mining usually causes drastic large gradient deformation in the earth's surface in a short period, which leads to the formation of collapse basin or collapse pit. The drastic deformation renders the generation of dense fringes in interferogram, leading to difficulties in the phase unwrapping step. In this paper we propose using intensity tracking technique to monitor large gradient deformation in the subsidence center. To obtain the small deformation information around the basin and collapse pit, we use Small Baseline Subset (SBAS) interferometry technique to monitor the small deformation, after which we integrate the results under the two methods to obtain complete monitoring results. We take Daliu Tower mining of Shanxi Province in China as an example, using Terra SAR-X satellite data of 13 scenes spanning from 21/11/2012 to 02/04/2013 to conduct deformation monitoring experiment. The experiment result shows that the proposed method has the capability to detect and measure the large gradient deformation, meanwhile, small deformation information is preserved. Moreover, by comparing the experiment monitoring results to continuous GPS measurements, we estimate that the accuracy of deformation monitor is about 8 cm in the range direction.

UP-25 口永良部島火山山頂部のGPSによる地殻変動観測と噴気・地中温度観測(緊急学術セッション(ポスター))

UP-25 口永良部島火山山頂部のGPSによる地殻変動観測と噴気・地中温度観測(緊急学術セッション(ポスター))

A geodetic plate motion and Global Strain Rate Model

We present a new global model of plate motions and strain rates in plate boundary zones constrained by horizontal geodetic velocities. This Global Strain Rate Model (GSRM v.2.1) is a vast improvement over its predecessor both in terms of amount of data input as in an increase in spatial model resolution by factor of ∼2.5 in areas with dense data coverage. We determined 6739 velocities from time series of (mostly) continuous GPS measurements; i.e., by far the largest global velocity solution to date. We transformed 15,772 velocities from 233 (mostly) published studies onto our core solution to obtain 22,511 velocities in the same reference frame. Care is taken to not use velocities from stations (or time periods) that are affected by transient phenomena; i.e., this data set consists of velocities best representing the interseismic plate velocity. About 14% of the Earth is allowed to deform in 145,086 deforming grid cells (0.25° longitude by 0.2° latitude in dimension). The remainder of the Earth's surface is modeled as rigid spherical caps representing 50 tectonic plates. For 36 plates we present new GPS-derived angular velocities. For all the plates that can be compared with the most recent geologic plate motion model, we find that the difference in angular velocity is significant. The rigid-body rotations are used as boundary conditions in the strain rate calculations. The strain rate field is modeled using the Haines and Holt method, which uses splines to obtain an self-consistent interpolated velocity gradient tensor field, from which strain rates, vorticity rates, and expected velocities are derived. We also present expected faulting orientations in areas with significant vorticity, and update the no-net rotation reference frame associated with our global velocity gradient field. Finally, we present a global map of recurrence times for Mw=7.5 characteristic earthquakes.

Coseismic and postseismic motion of a landslide: Observations, modeling, and analogy with tectonic faults

AbstractWe document the first time series of a landslide reactivation by an earthquake using continuous GPS measurements over the Maca landslide (Peru). Our survey shows a coseismic response of the landslide of about 2 cm, followed by a relaxation period of 5 weeks during which postseismic slip is 3 times greater than the coseismic displacement itself. Our results confirm the coseismic activation of landslides and provide the first observation of a postseismic displacement. These observations are consistent with a mechanical model where slip on the landslide basal interface is governed by rate and state friction, analogous to the mechanics of creeping tectonic faults, opening new perspectives to study the mechanics of landslides and active faults.

Modeling of coseismic crustal movements initiated by the May 24, 2013, M w = 8.3 Okhotsk deep focus earthquake

The Okhotsk deep focus earthquake (M w = 8.3), the largest in the history of instrumental seismology, occurred on May 24, 2013, at 05:45 UTC in the Sea of Okhotsk near the western coast of the Kamchatka Peninsula. For the first time we have succeeded in catching the field of horizontal and vertical coseismic offsets generated by a strong deep seismic event, and investigating its characteristics using continuous GPS measurements. Based on these data and taking into account the seismological information, we have developed a dislocation model of the Okhotsk deep focus earthquake.

Geodetic observations and modeling of time-varying deformation at Taal Volcano, Philippines

We investigate active crustal deformation patterns associated with magmatic activity at Taal Volcano, an active tholeiitic volcano located in southwestern Luzon, Philippines. We present comparisons of elastic and combined elastic–viscoelastic modeling results with deformation observed by continuous GPS measurements on and near the volcano. Continuous dual-frequency and single-frequency (L1) GPS data between 1998 and 2005 provide evidence for smoothly transitioning periods of inflation and deflation centered under the volcano. Within deformation phases that typically last 3–9months (with rates exceeding 200mmyr−1), prominent inflationary phases were observed in February–November 2000 and June 2004–March 2005. The 2000 period of inflation was characterized by up to 145mmyr−1 surface extension and 220mmyr−1 of uplift of the center of Volcano Island relative to the northern caldera rim, while the 2005 inflation was characterized by as much as 116mmyr−1 horizontal extension of the volcanic edifice and 180mmyr−1 uplift. Inversions of observed surface deformation to determine the source location points to a relatively stable spherical source, situated under Volcano Island's central crater, at depths of ~5km (based on the preferred Mogi model). Using this source geometry, we develop axisymmetric finite element models with annuli of concentric shells around the magma reservoir, embedded within a multi-layered elastic lithosphere. Using simply varying pressure histories as input, a variety of forward models are fit to the time history of continuously observed deformation for GPS stations located on Volcano Island. Though the inferred source geometry, volume and near-source rheological properties are non-unique, they represent more physically appropriate material properties than those assumed in simple elastic half-space models. The sources inferred using viscoelastic shell models suggest simpler pressure histories and reduced overall pressure changes, relative to equivalent elastic half-space models.

Kinematic interpretation of present-day crustal deformation in central Greece from continuous GPS measurements

We processed 30-s GPS data from continuous GPS stations in central Greece using the Kalman filtering approach and accounting for time-correlated noise content obtaining a velocity field in the ITRF2008 and the Eurasian-fixed reference frame. The station distribution allowed us to compute 1D strain through rates of baseline length changes as well as to construct the image of the 2D strain and rotation rate fields. The obtained baselines range in length from 11 to 132km and show rates from −1.95mm/yr up to 14.14mm/yr (estimated uncertainties from 0.3 to 0.8mm/yr), while the calculated 1D strain rate ranges from −27ns/yr up to 226ns/yr (average uncertainty ∼15ns/yr). Largest extension (192–226ns/yr) is observed in the western and central part of the Corinth rift while similar extension rates (80–120ns/yr) are obtained for the eastern part of the Corinth rift and its continuation in the south Viotia–south of Evia region and across the Sperchios–Kammena Vourla rift. The coherent picture of the velocity pattern for Attica and north-eastern Peloponnese (Corinth) stations indicates that these areas belong to the same crustal block, separating by the Viotia region by a nearly E–W crustal discontinuity along the Kaparelli–Asopos valley faults. However, some internal strain is present within Attica's crust as well as across the Saronic Gulf resulting in extension rates of the order of 25ns/yr. We also find extension (54–71ns/yr) across “rigid” Peloponnese taken by normal faults in the greater Kalavryta region.

Measuring GNSS ionospheric total electron content at Concordia, and application to L-band radiometers

<p>In the framework of the project BIS - Bipolar Ionospheric Scintillation and Total Electron Content Monitoring, the ISACCO-DMC0 and ISACCO-DMC1 permanent monitoring stations were installed in 2008. The principal scope of the stations is to measure the ionospheric total electron content (TEC) and to monitor the ionospheric scintillations, using high-sampling-frequency global positioning system (GPS) ionospheric scintillation and TEC monitor (GISTM) receivers. The disturbances that the ionosphere can induce on the electromagnetic signals emitted by the Global Navigation Satellite System constellations are due to the presence of electron density anomalies in the ionosphere, which are particularly frequent at high latitudes, where the upper atmosphere is highly sensitive to perturbations coming from outer space. With the development of present and future low-frequency space-borne microwave missions (e.g., Soil Moisture and Ocean Salinity [SMOS], Aquarius, and Soil Moisture Active Passive missions), there is an increasing need to estimate the effects of the ionosphere on the propagation of electromagnetic waves that affects satellite measurements. As an example, how the TEC data collected at Concordia station are useful for the calibration of the European Space Agency SMOS data within the framework of an experiment promoted by the European Space Agency (known as DOMEX) will be discussed. The present report shows the ability of the GISTM station to monitor ionospheric scintillation and TEC, which indicates that only the use of continuous GPS measurements can provide accurate information on TEC variability, which is necessary for continuous calibration of satellite data.</p>

An Improved Persistent Scatterer Interferometry for Subsidence Monitoring in the Tehran Basin

The Southwestern Tehran basin is covered primarily by agricultural fields and is subjected to significant levels of land subsidence phenomena. Conventional SAR interferometry cannot extract deformation information from the available SAR images due to large spatial baselines and temporal de-correlation. Moreover, the proper Persistent Scatterer interferometry method for a rural area (StaMPS, Stanford method for Persistent Scatterer) cannot efficiently operate in areas with high deformation, such as the Tehran basin, because of unwrapping error caused by temporal aliasing of the signal. Therefore, in this work, a method based on StaMPS is developed to address the unwrapping error in the Tehran basin. In the proposed method, the estimated deformation rate from the wrapped phase and the periodogram approach are used to reduce the likelihood of aliasing, and StaMPS is subsequently applied to the residual phase. The method is applied to ENVISAT ASAR images captured between 2003 and 2008, and the mean precision of the estimated deformation is approximately 2.5 mm/yr. A comparison of the results obtained from the proposed method with those from continuous GPS and leveling measurements demonstrates its efficiency.

The coseismic displacements of the 2013 Lushan Mw6.6 earthquake determined using continuous global positioning system measurements

Abstract: Based on Continuous GPS (CGPS) observation data of the Crustal Movement Observation Network of China (CMONOC) and the Sichuan Continuous Operational Reference System (SCCORS), we calculated the horizontal coseismic displacements of CGPS sites caused by the 2013 Lushan Mw 6. 6 earthquake. The results indicate that the horizontal coseismic deformations of CGPS stations are consistent with thrust-compression rupture. Furthermore, the sites closest to the epicenter underwent significant coseismic displacements. Three network stations exhibited displacements greater than 9 mm (the largest is 20. 9 mm at SCTQ), while the others were displaced approximately 1–4 mm.

Investigation of correlation of the variations in land subsidence (detected by continuous GPS measurements) and methodological data in the surrounding areas of Lake Urmia

Abstract. Lake Urmia, a salt lake in the north-west of Iran, plays a valuable role in the environment, wildlife and economy of Iran and the region, but now faces great challenges for survival. The Lake is in immediate and great danger and is rapidly going to become barren desert. As a result, the increasing demands upon groundwater resources due to expanding metropolitan and agricultural areas are a serious challenge in the surrounding regions of Lake Urmia. The continuous GPS measurements around the lake illustrate significant subsidence rate between 2005 and 2009. The objective of this study was to detect and specify the non-linear correlation of land subsidence and temperature activities in the region from 2005 to 2009. For this purpose, the cross wavelet transform (XWT) was carried out between the two types of time series, namely vertical components of GPS measurements and daily temperature time series. The significant common patterns are illustrated in the high period bands from 180–218 days band (~6–7 months) from September 2007 to February 2009. Consequently, the satellite altimetry data confirmed that the maximum rate of linear trend of water variation in the lake from 2005 to 2009, is associated with time interval from September 2007 to February 2009. This event was detected by XWT as a critical interval to be holding the strong correlation between the land subsidence phenomena and surface temperature. Eventually the analysis can be used for modeling and prediction purposes and probably stave off the damage from subsidence phenomena.

Present kinematics of the Tjornes Fracture Zone, North Iceland, from campaign and continuous GPS measurements

Present kinematics of the Tjornes Fracture Zone, North Iceland, from campaign and continuous GPS measurements

Monitoring of active tectonic deformations in the Longitudinal Valley (Eastern Taiwan) using Persistent Scatterer InSAR method with ALOS PALSAR data

This paper presents new observation of the interseismic deformation along the Longitudinal Valley (Eastern Taiwan) that represents a major tectonic boundary of the Taiwan collision zone. We investigate the southern part of the Valley from Rueisuei to Taitung (latitude 23.5°N–22.7°N), which is the part of the Valley where interseismic surface creep has already been observed at some points of the Longitudinal Valley Fault (LVF). A Persistent Scatterer SAR interferometry approach (StaMPS) is applied using ten L-band SAR images from ALOS satellite acquired over the period 2007–2010. Interferograms from L-Band data show a dramatic improvement of coherence in comparison to previous studies using C-Band ERS data. The density of measurement resulting from StaMPS processing is the highest achieved so far in the area (about 40–55 points per km2 for a total of 77,000 points) allowing a continuous view of the deformation along the Valley and also giving information on its borders (Central Range and Coastal Range). The most striking feature of the resulting mean velocity map is a clear velocity discontinuity localized in a narrow band (0.1–1km) along the LVF and responsible for up to 3cm/yr velocity offset along the radar line of sight, which is attributed to shallow interseismic creep. InSAR results are in good agreement with continuous GPS measurements over the same period (0.3cm/yrrms). The density of measurement allows us to improve fault trace map along the creeping section of the LVF (with accuracy of about 100m) and to find new field evidences of the fault activity. In some places, our trace differs significantly (hundreds of meters) from previous published traces. The creep rate shows significant variations along the fault. At the southern end of the valley the deformation is distributed on several structures, including the Luyeh Strand, and drops significantly south of the Peinanshan. However there are discrepancies with previous studies made from ERS data over the period 1993–1999 that remain to be investigated. The mean velocity for each point of measure and the improved faults' trace are provided as Supplementary data.

Active deformation near the Nicoya Peninsula, northwestern Costa Rica, between 1996 and 2010: Interseismic megathrust coupling

We use campaign and continuous GPS measurements at 49 sites between 1996 and 2010 to describe the long‐term active deformation in and near the Nicoya Peninsula, northwestern Costa Rica. The observed deformation reveals partial partitioning of the Cocos‐Caribbean oblique convergence into trench‐parallel forearc sliver motion and less oblique thrusting on the subduction interface. The northern Costa Rican forearc translates northwestward as a whole ridge block at 11 ± 1 mm/yr relative to the stable Caribbean. The transition from the forearc to the stable Caribbean occurs in a narrow deforming zone of ∼16 km wide. Subduction thrust earthquakes take 2/3 of the trench‐parallel component of the plate convergence; however, surface deformation caused by interseismic megathrust coupling is primarily trench‐normal. Two fully coupled patches, one located offshore Nicoya centered at ∼15 km depth and the other located inland centered at ∼24 km depth, are identified in Nicoya with the potential to generate an Mw 7.8 1950‐type earthquake. Another fully coupled patch SE of Nicoya coincides with the rupture region of the 1990 Nicoya Gulf earthquake. Interface microearthquakes, non‐volcanic tremor, low‐frequency earthquakes, and transient slow‐slip events generally occur in the intermediately to weakly coupled regions.

Plate interaction in the NE Caribbean subduction zone from continuous GPS observations

Kinematic similarities between the Sumatra and Puerto Rico Trenches highlight the potential for a mega‐earthquake along the Puerto Rico Trench and the generation of local and trans‐Atlantic tsunamis. We used the horizontal components of continuous GPS (cGPS) measurements from 10 sites on NE Caribbean islands to evaluate strain accumulation along the North American (NA) – Caribbean (CA) plate boundary. These sites move westward and slightly northward relative to CA interior at rates ≤2.5 mm/y. Provided this motion originates in the subduction interface, the northward motion suggests little or no trench‐perpendicular thrust accumulation and may in fact indicate divergence north of Puerto Rico, where abnormal subsidence, bathymetry, and gravity are observed. The Puerto Rico Trench, thus, appears unable to generate mega‐earthquakes, but damaging smaller earthquakes cannot be discounted. The westward motion, characterized by decreasing rate with distance from the trench, is probably due to eastward motion of CA plate impeded at the plate boundary by the Bahamas platform. Two additional cGPS sites in Mona Passage and SW Puerto Rico move to the SW similar to Hispaniola and unlike the other 10 sites. That motion relative to the rest of Puerto Rico may have given rise to seismicity and normal faults in Mona Rift, Mona Passage, and SW Puerto Rico.

Vertical motions in Thailand after the 2004 Sumatra–Andaman Earthquake from GPS observations and its geophysical modelling

Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3*1018Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10cm in the Bangkok area.The post-seismic subsidence makes it difficult to identify other geophysical signals, particularly sea level rise, when observed from tide gauge data and thus there is a need for reliable estimation of subsidence velocities. This phenomenon may also worsen coastal erosion and flooding from sea water and so cause a considerable impact on the socio-economic development of coastal and low-lying areas, especially in the greater Bangkok area.

Improved Ground Subsidence Monitoring Using Small Baseline SAR Interferograms and a Weighted Least Squares Inversion Algorithm

We present the application of a weighted least squares (WLS) method based on image mode interferometric data to monitor the spatiotemporal evolution of land surface subsidence in Mashhad valley, northeast Iran. The technique is based on an appropriate combination of differential interferograms produced by image pairs with small orbital separation to limit the spatial decorrelation phenomena. Our data consist of 17 ASAR single-look-complex images acquired from a descending orbit by the European ENVISAT satellite in image mode (I2), spanning a time interval from June 2004 to November 2007. Fifty-three reliable differential interferograms with relatively little noise and a continuous unwrapped phase are constructed from this data set and are analyzed using a WLS adjustment technique to produce time series of the displacement field. The time-series analysis suggests that the subsidence occurs within a northwest–southeast elongated elliptically shaped bowl along the axis of Mashhad valley. The maximum accumulated subsidence during the 1260-day period reaches approximately 86 cm, located northeast of Mashhad city. The comparison between SAR-interferometry time-series results with continuous Global Positioning System measurements yields an estimated root-mean-square error of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 1.0 cm.

Seasonal speed-up of two outlet glaciers of Austfonna, Svalbard, inferred from continuous GPS measurements

Abstract. A large part of the ice discharge from ice caps and ice sheets occurs through spatially limited flow units that may operate in a mode of steady flow or cyclic surge behaviour. Changes in the dynamics of distinct flow units play a key role in the mass balance of Austfonna, the largest ice cap on Svalbard. The recent net mass loss of Austfonna was dominated by calving from marine terminating outlet glaciers. Previous ice-surface velocity maps of the ice cap were derived by satellite radar interferometry (InSAR) and rely on data acquired in the mid-1990s with limited information concerning the temporal variability. Here, we present continuous Global Positioning System (GPS) observations along the central flowlines of two fast flowing outlet glaciers over 2008–2010. The data show prominent summer speed-ups with ice-surface velocities as high as 240% of the pre-summer mean. Acceleration follows the onset of the summer melt period, indicating enhanced basal motion due to input of surface meltwater into the subglacial drainage system. In 2008, multiple velocity peaks coincide with successive melt periods. In 2009, the major melt was of higher amplitude than in 2008. Flow velocities appear unaffected by subsequent melt periods, suggesting a transition towards a hydraulically more efficient drainage system. The observed annual mean velocities of Duvebreen and Basin-3 exceed those from the mid-1990s by factors two and four, respectively, implying increased ice discharge at the calving front. Measured summer velocities up to 2 m d−1 for Basin-3 are close to those of Kronebreen, often referred to as the fastest glacier on Svalbard.

Seasonal and long‐term vertical deformation in the Nepal Himalaya constrained by GPS and GRACE measurements

We analyze continuous GPS measurements in Nepal, southern side of the Himalaya, and compare GPS results with GRACE observations in this area. We find both GPS and GRACE show significant seasonal variations. Further comparison indicates that the observed seasonal GPS height variation and GRACE‐derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results, for both amplitude and phase. For continuous GPS stations whose observation time span are longer than 3 years, the average WRMS reduction is ∼45% when we subtract GRACE‐derived vertical displacements from GPS observed time series. The comparison for annual amplitudes between GPS observed and GRACE‐derived seasonal displacements also shows consistent correlation. The good seasonal correlation between GPS and GRACE is due to the improved GPS processing strategies and also because of the strong seasonal hydrological variations in Nepal. Besides the seasonal signal, GRACE also indicates a long‐term mass loss in the Himalaya region, assuming no GIA effect. This mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body. We model this effect and remove it from GPS observed vertical rates. With a 2D dislocation model, most GPS vertical rates, especially in the central part of Nepal, can be interpreted by interseismic strain from the Main Himalayan Thrust, and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects.

Present kinematics of Central and Northern Italy from continuous GPS measurements

The geodetic data acquired in the last 10years by a fairly dense network of permanent GPS stations located in Central and Northern Italy are used to reconstruct the present horizontal velocity field in the study area and to evaluate the coseismic and postseismic effects of the recent L’Aquila earthquake (April 6, 2009 Mw=6.3). The distribution of geodetic velocities indicates that during the observation period the outer Adriatic sector of the Central and Northern Apennines has moved faster than the surrounding zones. It is pointed out that this short term kinematic behaviour is compatible with the long term kinematics indicated by the post-early Pleistocene deformation pattern observed in the central Mediterranean area. The short term kinematic pattern in the Central Apennines has been perturbed by the L’Aquila earthquake. The daily position time series of the sites located within 140km from the epicentre show a coseismic offset followed by a non linear time dependent displacement which gradually vanishes in 1–3months, after which the trend of daily positions seems to become linear again. The non linear transient phase has been modelled by a decaying exponential function, possibly connected with postseismic viscoelastic relaxation. The displacements developed during this last phase are rather different from coseismic displacements. Also, the velocities tentatively deduced from the postseismic linear trends (observed for about 17months) show quite different orientations with respect to both coseismic and short term postseismic displacements. This evidence suggests that the tectonic processes which developed in the Central Apennines after the L’Aquila event were complex, possibly related to shallow afterslip, deeper aseismic slip and viscoelastic relaxation of the lower crust and/or uppermost mantle.