Continuous Global Positioning System Network Research Articles

Slip Rate for the Rose Canyon Fault through San Diego, California, Based on Analysis of GPS Data: Evidence for a Potential Rose Canyon–San Miguel-Vallecitos Fault Connection?

ABSTRACT The Rose Canyon fault is the southern extension of the larger Newport–Inglewood–Rose Canyon fault system, which represents a major structural boundary in the Inner Continental Borderland (ICB) offshore of southern California. Ten to fifteen percent of total plate boundary motion in southern California is thought to be accommodated by the faults of the ICB, but the exact distribution of slip is uncertain. With an onshore segment, the Rose Canyon fault offers an opportunity to measure the slip rate using traditional geodetic methods. In this study, we use Global Positioning System (GPS) surface velocities from a combined campaign and continuous GPS network to constrain elastic models of the Rose Canyon fault. We then compare the observed surface velocities with proposed conceptual models of regional fault connections that facilitate the transfer of slip into the Rose Canyon fault to assess how well the observations are explained by the models. The results of elastic half-space models suggest that the Rose Canyon fault may be slipping toward the higher end of geologic estimates, with the preferred model indicating a slip rate of 2.4 ± 0.5 mm/yr. Although limited in terms of near-fault benchmarks, we find an improved model fit using an asymmetrical elastic half-space model and a higher slip rate, suggesting a potential rheological contrast across the Rose Canyon fault, similar to observations from the northern Newport–Inglewood fault segments. Observed GPS surface velocities, background seismicity, and gravity anomalies south of San Diego Bay point toward a more easterly trace for the Rose Canyon fault, suggesting a possible connection with the San Miguel–Vallecitos fault system. Such a connection could increase the potential rupture lengths of future earthquakes and have important consequences for regional seismic hazards.

Slow slip events and the 2016 Te AraroaMw7.1 earthquake interaction: Northern Hikurangi subduction, New Zealand

AbstractFollowing a sequence of three Slow Slip Events (SSEs) on the northern Hikurangi Margin, between June 2015 and August 2016, aMw7.1 earthquake struck ~30 km offshore of the East Cape region in the North Island of New Zealand on the 2 September 2016 (NZ local time). The earthquake was also followed by a transient deformation event (SSE or afterslip) northeast of the North Island, closer to the earthquake source area. We use data from New Zealand's continuous Global Positioning System networks to invert for the SSE slip distribution and evolution on the Hikurangi subduction interface. Our slip inversion results show an increasing amplitude of the slow slip toward the Te Araroa earthquake foreshock and main shock area, suggesting a possible triggering of theMw7.1 earthquake by the later stage of the slow slip sequence. We also show that the transient deformation following the Te Araroa earthquake ruptured a portion of the Hikurangi Trench northeast of the North Island, farther north than any previously observed Hikurangi margin SSEs. Our slip inversion and the coulomb stress calculation suggest that this transient may have been induced as a response to the increase in the static coulomb stress change downdip of the rupture plane on the megathrust. These observations show the importance of considering the interaction between slow slip events, seismic, and aseismic events, not only on the same megathrust interface but also on faults within the surrounding crust.

Investigation of GPS positioning accuracy during the seasonal variation

The aim of this study is to investigate the accuracy of GPS (Global Positioning System) positioning determined by GPS measurements carried out during the seasonal variations. The observations have been analyzed to determine how the accuracy of derived relative positions of GPS stations depends on the baseline length, the duration of observing session and the seasonal variations.For this purpose, we selected three days of each month in 2009 from the GPS observations made in the Marmara Continuous GPS Network (MAGNET). The GPS observations were processed in the ITRF 2005 reference frame using the Bernese 5.0GPS software. The baseline length varies between 6km and 237km, session duration varies between 4h and 24h. Seasonal variation effects on the accuracy of coordinate components were analyzed. Our results showed that seasonal variation is a significant factor for determining the accuracy of GPS measurements. Also, increasing the observation period hardly improves the horizontal positioning accuracy while improving the vertical positioning accuracy.

Assessment of Pseudorange Multipath at Continuous GPS Stations in Mexico

We conducted a study to quantify the amount of pseudorange multipath at continuous Global Positioning System (CGPS) stations in the Mexican territory. These CGPS stations serve as reference stations enabling rapid high-precision three-dimensional positioning capabilities, supporting a number of commercial and public safety applications. We studied CGPS data from a large number of publicly available networks spanning Mexico. These include the RGNA (National Active Geodetic Network) administered by INEGI (National Institute of Statistics and Geography), the PBO network (Plate Boundary Observatory) funded by the National Science Foundation (NSF) and operated by UNAVCO (University NAVstar Consortium), the Southern California Integrated GPS Network (SCIGN), which is a collaboration effort of the United States Geological Survey (USGS), Scripps Institution of Oceanography and the Jet Propulsion Laboratory (JPL), the UNAM network, operated by the National Seismological System (SSN) and the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), the Suominet Geodetic Network (SNG) and the CORS (Continuously Operating Reference Station) network, operated by the Federal Aviation Administration (FAA). We evaluated a total of 53 CGPS stations, where dual-frequency geodetic-grade receivers collected GPS data continuously during the period from 1994 to 2012. Despite carefully selected locations, all GPS stations are, to some extent, affected by the presence of signal multipath. For GPS network users that rely on pseudorange observables, the existence of pseudorange multipath could be a critical source of error depending on the time scale of the application. Thus, to identify the most and the least affected GPS stations, we analyzed the averaged daily root mean square pseudorange multipath variations (MP1-RMS and MP2-RMS) for all feasible satellites tracked by the CGPS networks. We investigated the sources of multipath, including changes associated with hardware replacement (i.e., receiver and antenna type) and receiver firmware upgrades.

Monitoring of the ionosphere TEC variations during the 17th August 1999 Izmit earthquake using GPS data

In this paper, we aim to determine a snapshot of previously unstudied ionospheric variations which were recorded in a two-week interval before and after a large earthquake of M 7.6 occurred on 17 August, 1999, in the Marmara region of Turkey. We detected ionospheric perturbations before the earthquake occurred using Global Positioning System (GPS) data received from the Marmara Continuous GPS Network (MAGNET). Pre-seismic ionospheric total electron content (TEC) anomalies were observed three days before the earthquake at sets of stations near the earthquake location, while post-seismic traveling ionospheric disturbances could not be detected. The ionospheric variability had a negative sign with an enhancement of about 8–10 TECU (1 TECU = 1016 electrons/m2) relative to the non-distributed state of the ionosphere. The results show that this method will be a useful addition to the already-available continuous monitoring techniques in the region.

Estimates of ocean tide loading displacements and its impact on position time series in Hong Kong using a dense continuous GPS network

Three-dimensional ocean tide loading (OTL) displacements of eight diurnal and semidiurnal constituents at 12 sites in Hong Kong were estimated using 3–7 years of continuous global positioning system (GPS) observations. OTL displacements were estimated using the precise point positioning (PPP) technique on a daily basis and then combined. The OTL displacements obtained by GPS were compared with predictions using seven recent global ocean tide models. The effect of OTL displacements on GPS position time series was also investigated. The study shows that the GPS-derived OTL displacements (excluding K1 and K2 constituents) agree best with those predicted by the GOT4.7 and NAO99b models. The GPS/model agreement is generally at the sub-millimeter level, except for S2, K1, and K2 constituents with relatively large errors. After systematic biases between the GPS and model values are removed, the misfits of all sites for M2, S2, N2, O1, P1, and Q1 are less than 0.5 and 1.0 mm in the horizontal and vertical components, respectively, while larger misfits (within 2.5 mm) are observed for K1 and K2. Integer ambiguity fixing slightly improves the east component of OTL displacement estimates. The study also finds that GPS-derived OTL corrections, instead of model predicts, can be used in daily data processing with the exception of K1 and K2. Including K2 corrections, a secular vertical rate of up to 1 mm/year in position time series can be induced, which needs to be confirmed by further studies.

Accuracy Analysis of Relative Positions of Permanent GPS Stations in the Marmara Region, Turkey

The accuracy of GPS (Global Positioning System) derived relative positions of stations depends on several factors. Besides the baseline length and duration of observation session, the methodology and the software used influence the results. In this paper, the observations made in the Marmara Continuous GPS Network (MAGNET) have been analysed to determine how the accuracy of derived relative positions of GPS stations depends on the baseline length and the duration of the observing session. Seven days of GPS observations in the MAGNET collected in 2002 were processed in the ITRF 2000 reference frame using Bernese 4.2 software. The baseline length varies between 6 km and 340 km, the session duration varies between 4h and 24h. The independent baseline components have been analysed.

Estimation of the time-dependent crustal movements of the İzmit Earthquake

The 17 August 1999 İzmit earthquake significantly deformed the earth's crust in the Marmara Region, especially in the Gölcük–Sapanca Zone, Turkey. It broke a 150-km long segment of the northern branch of North Anatolian Fault Zone. The geodetically determined moment magnitude was Mw=7.5. Global Positioning System (GPS) sites, which are a small subset of the Marmara Continuous GPS Network (MAGNET), and survey sites in the region were studied to estimate coseismic and postseismic deformations, using different methodologies with linear, quadratic and exponential kinematic models. Six GPS epochs for these sites, which were carried out before and after the 17 August 1999 İzmit earthquake, were used to define the kinematic models. The quadratic deformation model was also applied to determine the time-dependent crustal movement parameters (velocity and acceleration) of the sites, using the Kalman filter technique. In order to show the differences between the models, the estimated deformation fields on the last epoch were compared. In all models, as expected, the faults near the sites show large coseismic displacements with fault parallel direction, whereas the far sites show small coseismic displacements due to the effects of the İzmit earthquake. Each kinematic model, fitted to the epochs after the earthquake, shows different behaviour. While the linear model shows insufficient results, the nonlinear models (quadratic and exponential) give the best fitted to the postseismic deformations. As a result of Kalman filter analysis, the fault near-sites shows significant velocities with fault parallel direction, whereas the far sites have insignificant velocities. All stations have insignificant accelerations in the last epoch.

DISCUSSION ON STANDARD AND ROBUST KALMAN FILTERS, USING POST-EARTHQUAKE DATA SET OF 17 AUGUST 1999 IZMIT EARTHQUAKE

We discuss on the performances of standard and robust Kalman filters to estimate the post-seismic deformation field produced by the 17 August 1999 lzmit, Turkey, earthquake. The data set covers a subset of the Marmara Continuous GPS (Global Positioning System) Network (MAGNET) and other available survey stations in the region. The results of the models suggest that the standard Kalman filter estimate is not optimal due to serious bias that occurs between epochs. The bias, however, can be detected and removed using a robust Kalman filter.

Integrated satellite interferometry: Tropospheric noise, GPS estimates and implications for interferometric synthetic aperture radar products

Interferometric synthetic aperture radar (INSAR), like other astronomic and space geodetic techniques, is limited by the spatially and temporally variable delay of electromagnetic waves propagating through the neutral atmosphere. Statistical analysis of these variations, from a wide variety of instruments, reveals a power law dependence on frequency that is characteristic of elementary (Kolmogorov) turbulence. A statistical model for a major component of the delay fluctuations, the “wet” component, has previously been developed by Treuhaft and Lanyi [1987] for very long baseline interferometry. A continuous Global Positioning System (GPS) network is now in place in southern California that allows estimation of, along with geodetic parameters, the total delay due to the atmosphere above each site on a subhourly basis. These measurements are shown to conform to the Treuhaft and Lanyi (TL) statistical model both temporally and spatially. The TL statistical model is applied to the problem of INSAR and used to produce the covariance between two points separated in time and/or space. The error, due to the atmospheric variations, for SAR products such as topography and surface deformation is calculated via propagation of errors. There are two methods commonly cited to reduce the effect of atmospheric distortion in products from SAR interferometry, stacking and calibration. Stacking involves averaging independent interferograms to reduce the noise. Calibration involves removing part (or all) of the delay using data from an independent source such as total zenith delay estimates from continuous GPS networks. Despite the relatively poor spatial density of surface measurements, calibration can be used to reduce noise if the measurements are sufficiently accurate. Reduction in tropospheric noise increases with increasing number of measurement points and increasing accuracy up to a maximum of √N, where N is the number of points. Stacking and calibration are shown to be complementary and can be used simultaneously to reduce the noise to below that achievable by either method alone.