Global Positioning System Deformation Research Articles

Fault slip distribution of the 2015 Mw7.8 Gorkha (Nepal) earthquake estimated from InSAR and GPS measurements

Inversion of the coseismic slip distribution is important for understanding seismogenic mechanisms. In this study, the geometric parametersand uncertainties for the 2015 Gorkha earthquake in Nepal were inverted using a Bayesian approach. The coseismic fault slip distribution was inverted based on triangular dislocations from interferometrc synthetic aperture radar (InSAR) and Global Positioning System (GPS) surface displacement measurements. The inversion results show that the rupture propagated southeast for approximately 140 km, with most of the slip constrained within 30 - 40 km along the dip direction. There are two peak slips in the slip distribution: a ∼5.9 m slip located ∼50 km southeast of the epicenter at a depth of 10.2 km, and a ∼6.32 m slip located ∼100 km southeast of the epicenter at a depth of 10 km. Near the Mw7.3 aftershock, the rupture propagated to the north and southeast. The gap in slip formed between the mainshock and the Mw7.3 aftershock is similar to the shape of a “crocodile with an open mouth”. The results of the triangular dislocation model can explain the GPS-based coseismic displacements and the InSAR deformation field when compared with a classic rectangular dislocation, with a 10.6 cm reduction in the average residual of the InSAR data and a 2 cm reduction in the average residual of the GPS deformation. Compared to the geometry of a ramp—flat—ramp structure, we postulate that both a single-segment and multiple-segments are possible near Kathmandu.

Method for determining weight matrix for resolving three-dimensional surface deformation using Multi-LOS D-InSAR technology

Three-dimensional surface deformation is resolved using deformations obtained from multiple line of sight differential interferometry synthetic aperture radar (multi-LOS D-InSAR). However, the random model is susceptible to both accidental errors (such as errors due to noises) and system errors (such as orbital errors and topographic errors). To solve this problem, we present a weight-determining method based on high-precision global positioning system (GPS) observations. Specifically, the precision of multi-LOS D-InSAR deformation observations is evaluated based on high-precision GPS deformation observations from the same period. Then, by considering the influence of system errors and accidental errors on the deformation of a pixel observed by multi-LOS D-InSAR, a combined fitting model associated with the positions and elevations of a pixel is built. Finally, the precision of deformations from multi-LOS D-InSAR is evaluated pixel-by-pixel by using the built model. As a result, the weights of observations in the model for resolving three-dimensional surface deformation using multi-LOS D-InSAR can be determined. We verify the feasibility and precision of the weight-determining method through a simulation experiment and a real data experiment, respectively. The verification results show that the proposed weight-determining method based on high-precision GPS observations provides higher reliability for the resolved three-dimensional surface deformation.

GPS Recovery of Daily Hydrologic and Atmospheric Mass Variation: A Methodology and Results From the Australian Continent

AbstractWe present a methodology to invert a regional set of vertical displacement data from Global Positioning System (GPS) to determine the surface mass redistribution. It is assumed that GPS deformation is a result of the Earth's elastic response to the surface mass load of hydrology, atmosphere, and/or ocean. We develop an algorithm to estimate the spectral information of displacements from “regional” GPS data through regional spherical (Slepian) basis functions and apply the load Love numbers to estimate the mass load. The same approach is applied to determine global mass changes from “global” geopotential change data of Gravity Recovery and Climate Experiment (GRACE). We rigorously examine all systematic errors caused by various truncations (spherical harmonic series and Slepian series) and the smoothing constraint applied to the GPS inversion. We demonstrate the technique by processing 16 years of daily vertical motions determined from 114 GPS stations in Australia. The GPS‐inverted surface mass changes are validated against GRACE data, atmosphere and ocean models, and a land surface model. Seasonal and interannual terrestrial mass variations from GPS are in good agreement with GRACE data and the water storage models. The GPS recovery compares better with the water storage model around the smaller coastal basins than two different GRACE solutions. The submonthly mass changes from GPS provide meaningful results agreeing with atmospheric mass changes in central Australia. Finally, it is suggested to integrate GPS and GRACE data to draw a comprehensive picture of daily mass changes on different continents.

Application of Low-Cost GPS Tools and Techniques for Landslide Monitoring: A Review

The main goal of our ongoing research is to design a low-cost continuous monitoring system for landslide investigation using the Reverse RTK (RRTK) technique. The main objectives of this paper are to review the existing Global Positioning System (GPS) tools and techniques used for landslide monitoring, and to propose a novel low-cost landslide monitoring technique using Reverse RTK GPS. A general overview of GPS application in landslide monitoring is presented, followed by a review of GPS deformation monitoring systems and some of the factors used for their categorization. Finally, the concept, principles and advantages of the proposed new landslide monitoring system are discussed.

Wavelet based multi-step filtering method for bridge health monitoring using GPS and accelerometer

Effective monitoring, reliable data analysis, and rational data interpretations are challenges for engineers who are specialized in bridge health monitoring. This paper demonstrates how to use the Global Positioning System (GPS) and accelerometer data to accurately extract static and quasi-static displacements of the bridge induced by ambient effects. To eliminate the disadvantages of the two separate units, based on the characteristics of the bias terms derived from the GPS and accelerometer respectively, a wavelet based multi-step filtering method by combining the merits of the continuous wavelet transform (CWT) with the discrete stationary wavelet transform (SWT) is proposed so as to address the GPS deformation monitoring application more efficiently. The field measurements are carried out on an existing suspension bridge under the normal operation without any traffic interference. Experimental results showed that the frequencies and absolute displacements of the bridge can be accurate extracted by the proposed method. The integration of GPS and accelerometer can be used as a reliable tool to characterize the dynamic behavior of large structures such as suspension bridges undergoing environmental loads.

Geologic versus geodetic deformation adjacent to the San Andreas fault, central California

We combine geologic and global positioning system (GPS) data to characterize the style and magnitude of off-fault deformation across the San Andreas fault system in central California. Geologic structures record ∼12 km of both fault-parallel and fault-perpendicular displacements across creeping and locked portions of the San Andreas fault. Analysis of 150 GPS site velocities suggests that the borderlands record 4–6 mm/yr of fault-parallel and 3–5 mm/yr of fault-perpendicular motion alongside the creeping segment, where elastic strain is minimized. The distribution of both long-term geologic and short-term geodetic deformation is affected by basement type, where more deformation is concentrated northeast of the San Andreas fault on Franciscan basement. We suggest that at least half the fault-parallel GPS deformation measured by GPS bordering the creeping segment must be accommodated by geologic structures; this permanent deformation needs to be incorporated into dynamic models of the fault system. Elastic modeling of the San Andreas fault in central California, which incorporates its well-known transition from locked to creeping behavior near Parkfield, predicts first-order variations in the GPS velocity field along the fault and corresponding variations in dilatational strain rates. The strain rate pattern is dominated by a large contractional region northeast of the transition from locked to creeping behavior and a large extensional region southwest of the transition. The former coincides with the Coalinga and Kettleman Hills anticlines, the growth and development of which seem to have occurred under at least two kinematic conditions. We suggest that the onset of fault creep in central California promoted the growth of these folds. By implication, fault creep has been active over geologic time scales.

A new GPS deformation monitoring algorithm applied to Donghai Bridge

A real-time, long-round global positioning system (GPS) bridge-deformation monitoring technology was proposed, which processes the carrier phase of multiple GPS receivers in an operation center. It was demonstrated an extended Kalman filter with triple differential ionospheric-free measurement (EKF-TIF) which can eliminate the ionospheric delay, whiten the TIF noise and optimize the results of EKF, consequently, achieves a better performance than existing real time kinematic (RTK) solution. An experiment, which takes an active ionosphere condition into consideration, proves the feasibility of this system by comparing its records to that of a traditional RTK solution, practically, the system installed on the Donghai Bridge has survived a non-break running for five months. The analysis to the monitoring records shows the system achieves the designed accuracy and reliability.

Temporal stability of deformation rates: Comparison of geological and geodetic observations, Hikurangi subduction margin, New Zealand

We examine how well contemporary horizontal velocity fields from Global Positioning System (GPS) geodetic measurements describe long-term deformation rates. Million-year rates of extension, shortening, strike slip and vertical-axis rotations are compared with modelling of GPS velocities from the last 10–15 years in the Hikurangi subduction margin, New Zealand. Within measurement uncertainties of mainly ≤ 50%, the rates of deformation and vertical-axis rotations for each time interval are usually indistinguishable. The comparable deformation rates are consistent with the notion of near-constant rates since ∼ 1.5 Ma. During this time oblique relative plate motion was partitioned, with the majority (85%) of margin-normal motion accommodated on the plate interface, and most (≥ 60%) margin-parallel motion by strike-slip faulting and vertical-axis rotations in the upper plate. Prior to ∼ 1.5 Ma GPS velocities cannot be reliably used to describe deformation and rotations of the Hikurangi margin because, at this time, the Taupo Rift commenced opening, the boundary between Raukumara and Wairoa rotational domains was abandoned and the rates of upper-plate shortening increased. The broad compatibility of GPS and geological deformation and rotation rates since ∼ 1.5 Ma suggests that the build up of contemporary elastic strains in the North Island, measured by GPS, is largely uniform for much of the duration of each seismic cycle. The good agreement between the GPS and geological deformation rates in the North Island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large-magnitude earthquakes.

Application of Multipath Template Technique to Real-Time Ionospheric Delay Estimation Using Global Positioning System Measurements

When global positioning system (GPS) signals propagate through the ionosphere, they experience an extra time delay. The ionospheric delay can be estimated using L1/L2 GPS measurement. In order to mitigate the pseudorange multipath effect on real-time ionospheric delay estimation, the multiday multipath template technique has been developed. The algorithm permits the pseudorange multipath error for a specific day to be corrected using the generated multipath template. Data from National Chengchi University, in Taiwan was used to test the application of the multipath template to real-time ionospheric delay estimation. Test results indicate that: (1) The performance of the various 5 day multipath templates is better than that of other multiday multipath templates and (2) the multipath template technique is an effective method to mitigate the GPS pseudorange multipath and should be implemented at reference stations within local-area differential GPS, wide-area differential GPS, and wide-area augmentation system networks, GPS deformation monitoring networks, etc.

GPS deformation in a region of high crustal seismicity: N. Cascadia forearc

We estimate the rate of crustal deformation in the central and northern Cascadia forearc based on a combination of existing global positioning system (GPS) velocity data along the Cascadia subduction zone. GPS strain rates and velocities show that the northwestern Washington–southwestern British Columbia region is currently shortening at 3–3.5 mm yr −1 in a N–S direction, in good agreement with inference from crustal earthquake statistics. On the long-term, the shortening rate is 5–6 mm yr −1, providing that the subduction-related interseismic loading of the margin is purely elastic. Compared to the velocity of the Oregon forearc with respect to North America (∼7 mm yr −1), this indicates that most of the forearc motion is accommodated in the Puget–Georgia basin area, corresponding to the main concentration of crustal seismicity. The difference between the current and long-term shortening rates may be taken up during subduction megathrust earthquakes. Thus, these events could produce a sudden increase of N–S compression in the Puget sound region and could trigger major Seattle-fault-type crustal earthquakes.

Transient and permanent deformation of central Japan estimated by GPS

Abstract Deformation of central Japan can be divided into two main components: elastic deformation due to the interseismic locking of subduction thrusts and deformation associated with intra-arc tectonics. In a companion paper [Henry et al., Earth Planet. Sci. Lett. (2000) this issue], we estimated an elastic deformation field based on the modeling of global positioning system (GPS) strain rates. In this study, we show that the corrected field (GPS minus predicted elastic deformation) is consistent with geological and seismological observations and should represent long-term plastic deformation. We use this corrected GPS deformation field to describe the kinematics of partitioning of the Philippine Sea plate/Amurian plate (AMU) convergence, in relation with the Izu-Bonin arc collision. About one third of the relative Philippine Sea/Amur motion is transferred to the central Japan crust, north of the collision front. This transfer induces high strain rates in southern Kanto and in the northern Japanese Alps. The latter region corresponds to the eastern boundary of the AMU. We propose that the independent motion of central Japan results from the delamination and the underthrusting of the Izu-Bonin arc lower crust and the upward bent oceanic slab.

The establishment of a GPS deformation network in the ethiopian rift valley

In April and May 1989 the satellite Global Positioning System (GPS) was employed in the establishment of three deformation networks in the Ethiopian Rift Valley. The net E1 consists of 6 points of about 100–270 km interdistances, with two points located on each of the African and the Somalian plate and two points down in the rift. In addition two separate GPS traverses were established: one (E2) runs across the rift, and one (E3) runs about 500 km along the rift. The remeasurement of a 175 km long baseline included in two subcampaigns indicates a repeatability of the GPS observations of the order of 1×10 −7 and 3×10 −7 for slope distance and ellipsoidal height, respectively. Along the E2 traverse GPS/trigonometric levelled geoid undulations and gravimetric geoid undulations agree well, while the discrepancy along the E3 traverse needs further analysis.