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Most Cited Geodesy and Geodynamics Articles

The most cited articles published since 2015, extracted from Scopus.

GNSS receiver autonomous integrity monitoring (RAIM) algorithm based on robust estimation

Volume 7, Issue 2, March 2016, Pages 117-123
Yuanxi Yang | Yuanxi Yang | Yuanxi Yang | Junyi Xu

© 2016 Institute of Seismology, China Earthquake Administration. Integrity is significant for safety-of-life applications. Receiver autonomous integrity monitoring (RAIM) has been developed to provide integrity service for civil aviation. At first, the conventional RAIM algorithm is only suitable for single fault detection, single GNSS constellation. However, multiple satellite failure should be considered when more than one satellite navigation system are adopted. To detect and exclude multi-fault, most current algorithms perform an iteration procedure considering all possible fault model which lead to heavy computation burden. An alternative RAIM is presented in this paper based on multiple satellite constellations (for example, GPS and BeiDou (BDS) etc.) and robust estimation for multi-fault detection and exclusion, which can not only detect multi-failures, but also control the influences of near failure observation. Besides, the RAIM algorithm based on robust estimation is more efficient than the current RAIM algorithm for multiple constellation and multiple faults. Finally, the algorithm is tested by GPS/BeiDou data.

Performance of GPS slant total electron content and IRI-Plas-STEC for days with ionospheric disturbance

Volume 7, Issue 1, January 2016, Pages 1-10
Feza Arikan | Seymur Shukurov | Hakan Tuna | Orhan Arikan | T. L. Gulyaeva

© 2016 Institute of Seismology, China Earthquake Administration. Total Electron Content (TEC) is an important observable parameter of the ionosphere which forms the main source of error for space based navigation and positioning systems. Since the deployment of Global Navigation Satellite Systems (GNSS), cost-effective estimation of TEC between the earth based receiver and Global Positioning System (GPS) satellites became the major means of investigation of local and regional disturbance for earthquake precursor and augmentation system studies. International Reference Ionosphere (IRI) extended to plasmasphere (IRI-Plas) is the most developed ionospheric and plasmaspheric climatic model that provides hourly, monthly median of electron density distribution globally. Recently, IONOLAB group (www.ionolab.org) has presented a new online space weather service that can compute slant TEC (STEC) on a desired ray path for a given date and time using IRI-Plas model (IRI-Plas-STEC). In this study, the performance of the model based STEC is compared with GPS-STEC computed according to the estimation method developed by the IONOLAB group and includes the receiver bias as IONOLAB-BIAS (IONOLAB-STEC). Using Symmetric Kullback-Leibler Distance (SKLD), Cross Correlation (CC) coefficient and the metric norm (L2N) to compare IRI-Plas-STEC and IONOLAB-STEC for the month of October 2011 over the Turkish National Permanent GPS Network (TNPGN-Active), it has been observed that SKLD provides a good indicator of disturbance for both earthquakes and geomagnetic storms.

Water storage variations in the Poyang Lake Basin estimated from GRACE and satellite altimetry

Volume 7, Issue 2, March 2016, Pages 108-116
Yang Zhou | Yang Zhou | Shuanggen Jin | Robert Tenzer | Jialiang Feng

© 2016 Institute of Seismology, China Earthquake Administration. The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides a unique opportunity to quantitatively study terrestrial water storage (TWS) variations. In this paper, the terrestrial water storage variations in the Poyang Lake Basin are recovered from the GRACE gravity data from January 2003 to March 2014 and compared with the Global Land Data Assimilation System (GLDAS) hydrological models and satellite altimetry. Furthermore, the impact of soil moisture content from GLDAS and rainfall from the Tropical Rainfall Measuring Mission (TRMM) on TWS variations are investigated. Our results indicate that the TWS variations from GRACE, GLDAS and satellite altimetry have a general consistency. The TWS trends in the Poyang Lake Basin determined from GRACE, GLDAS and satellite altimetry are increasing at 0.0141 km3/a, 0.0328 km3/a and 0.0238 km3/a, respectively during the investigated time period. The TWS is governed mainly by the soil moisture content and dominated primarily by the precipitation but also modulated by the flood season of the Yangtze River as well as the lake and river exchange water.

Water storage changes and balances in Africa observed by GRACE and hydrologic models

Volume 7, Issue 1, January 2016, Pages 39-49
Ayman Hassan | Shuanggen Jin

© 2016 Institute of Seismology, China Earthquake Administration. Continental water storage plays a major role in Earth's climate system. However, temporal and spatial variations of continental water are poorly known, particularly in Africa. Gravity Recovery and Climate Experiment (GRACE) satellite mission provides an opportunity to estimate terrestrial water storage (TWS) variations at both continental and river-basin scales. In this paper, seasonal and secular variations of TWS within Africa for the period from January 2003 to July 2013 are assessed using monthly GRACE coefficients from three processing centers (Centre for Space Research, the German Research Centre for Geosciences, and NASA's Jet Propulsion Laboratory). Monthly grids from Global Land Data Assimilation System (GLDAS)-1 and from the Tropical Rainfall Measuring Mission (TRMM)-3B43 models are also used in order to understand the reasons of increasing or decreasing water storage. Results from GRACE processing centers show similar TWS estimates at seasonal timescales with some differences concerning inter-annual trend variations. The largest annual signals of GRACE TWS are observed in Zambezi and Okavango River basins and in Volta River Basin. An increasing trend of 11.60 mm/a is found in Zambezi River Basin and of 9 mm/a in Volta River Basin. A phase shift is found between rainfall and GRACE TWS (GRACE TWS is preceded by rainfall) by 2-3 months in parts of south central Africa. Comparing GLDAS rainfall with TRMM model, it is found that GLDAS has a dry bias from TRMM model.

Influence of higher-order ionospheric delay correction on GPS precise orbit determination and precise positioning

Volume 7, Issue 5, September 2016, Pages 369-376
Zhimin Liu | Zhimin Liu | Yangyang Li | Jinyun Guo | Jinyun Guo | Fei Li

© 2016 Institute of Seismology, China Earthquake Administration At present, Global Navigation Satellite Systems (GNSS) users usually eliminate the influence of ionospheric delay of the first order items by dual-frequency ionosphere-free combination. But there is still residual ionospheric delay error of higher order term. The influence of the higher-order ionospheric corrections on both GPS precision orbit determination and static Precise Point Positioning (PPP) are studied in this paper. The influence of higher-order corrections on GPS precision orbit determination, GPS observations and static PPP are analyzed by neglecting or considering the higher-order ionospheric corrections by using a globally distributed network which is composed of International GNSS Service (IGS) tracking stations. Numerical experimental results show that, the root mean square (RMS) in three dimensions of satellite orbit is 36.6 mm–35.5 mm. The maximal second-order ionospheric correction is 9 cm, and the maximal third-order ionospheric correction is 1 cm. Higher-order corrections are influenced by latitude and station distribution. PPP is within 3 mm in the directions of east and up. Furthermore, the impact is mainly visible in the direction of north, showing a southward migration trend, especially at the lower latitudes where the influence value is likely to be bigger than 3 mm.

Variations in China's terrestrial water storage over the past decade using GRACE data

Volume 6, Issue 3, May 2015, Pages 187-193
Qian Zhao | Weiwei Wu | Weiwei Wu | Yunlong Wu

© 2015 The Authors Variations in China's terrestrial water storage from March 2003 to February 2013 were determined using data from the Gravity Recovery and Climate Experiment (GRACE) monthly gravity field model provided by the Center for Space Research. The results were compared with the variations in surface water estimated using the Global Land Data Assimilation System (GLDAS) hydrological model. The results indicated a decline in terrestrial water storage in the Shanxi and Xinjiang Tianshan regions over the past decade with a downward trend that reached −7.76 ± 0.71 mm/a and −5.8 ± 0.67 mm/a, respectively. Anthropogenic activities were considered to be the major cause of this terrestrial water loss (especially groundwater) in these regions. In contrast, the intersection of the Xinjiang and Tibet Autonomous Regions and the Qinghai Province showed an upward trend in the terrestrial water storage at a rate of 9.06 ± 0.37 mm/a, which is closely related to the high-quality local ecological environment and lack of human activities. At the intersections between the Chongqing, Guizhou, and Hunan Provinces and between the Jiangxi, Zhejiang, and Fujian Provinces, the terrestrial water storage increased at rates of 7.86 ± 0.9 and 8.68 ± 0.8 mm/a, respectively. These two regions received abundant annual precipitation; moreover, there was no considerable variation in the amount of groundwater storage over the past decade. In addition, the empirical orthogonal function (EOF) method used in this study could eliminate correlated errors in the GRACE monthly gravity field model more effectively than the traditional polynomial fitting method, and it did not generate false signals.

Sea level change along the Black Sea coast from satellite altimetry, tide gauge and GPS observations

Volume 7, Issue 1, January 2016, Pages 50-55
Nevin B. Avsar | Shuanggen Jin | Shuanggen Jin | Hakan Kutoglu | Gokhan Gurbuz

© 2016 Institute of Seismology, China Earthquake Administration. Sea level change affects human living conditions, particularly ocean coasts. However, sea level change is still unclear along the Black Sea coast due to lack of in-situ measurements and low resolution satellite data. In this paper, sea level change along the Black Sea coast is investigated from joint satellite altimetry, tide gauge (TG) and Global Positioning System (GPS) observations. The linear trend and seasonal components of sea level change are estimated at 8 TG stations (Amasra, Igneada, Trabzon-II, Sinop, Sile, Poti, Tuapse, and Batumi) located along the Black Sea coast, which are compared with Satellite Altimetry and GPS. At the tide gauge stations with long-term records such as Poti (about 21 years) and Tuapse (about 19 years), the results obtained from the satellite altimetry and tide gauge observations show a remarkably good agreement. While some big differences are existed between Satellite Altimetry and TG at other stations, after adding vertical motion from GPS, correlation coefficients of the trend have been greatly improved from 0.37 to 0.99 at 3 co-located GPS and TG stations (Trabzon-II, Sinop and Sile).

Mechanism of crustal extension in the Laxmi Basin, Arabian Sea

Volume 6, Issue 6, November 2015, Pages 409-422
Anju Pandey | Dhananjai K. Pandey

© 2015 The Authors Continental rifting and magmatism has been extensively studied worldwide as it is believed that continental rifting, break up of continents and associated magmatism lead to genesis of new oceanic crust. However, various regions of the world show that these processes may lead to genesis of other types of crust than the oceanic crust. Laxmi Basin in the western continental margin of the India is one such region with an enigmatic crust. Due to its extreme strategic significance for the palaeogeographic reconstruction of continents during Cretaceous continental breakup of India, this basin has attracted various workers for more than two decades. However, still the issue of nature of crust in the basin remains controversial. In this contribution, in order to identify nature of crust, mechanism of continental extension in the Laxmi Basin has been studied for the first time through newly acquired seismic data from the basin. Here, we propose a plausible mechanism of crustal extension in the Laxmi Basin which eventually constrains the nature of crust of the Laxmi Basin. We have demonstrated that the crust in the Laxmi Basin can be categorised in two zones of stretched and transitional crust. In the stretched zone several fault bounded horst and graben structures are identified which preserve syn- and post-rift sediments along with different periods of hiatus in sedimentations as unconformities. These faults are identified as listric faults in the upper crust which sole out in the detachment faults. Detachment faults decouples the upper brittle and lower ductile crust. The transitional crust is identified as heavily intruded by sills and basaltic volcanic which were emplaced due to melting of subcontinental mantle (SCM) after hyper-stretching of crust and serpentinisation of the SCM. Panikkar Ridge is proposed to be one such basaltic volcanic body derived from melting of lower part of the SCM.

Studies on earthquake precursors in China: A review for recent 50 years

Volume 8, Issue 1, January 2017, Pages 1-12
Fuqiong Huang | Mei Li | Yuchuan Ma | Yanyan Han | Lei Tian | Wei Yan | Xiaofan Li

© 2017 Institute of Seismology, China Earthquake Administration Since the 1960s, China has been conducting a persistent and systematic observation and monitoring experiment to falsify the hypothesis of premonitory anomalies and the predictability of earthquakes and the application of the assessment of time-dependent seismic hazard to the reduction of earthquake disaster risk. Such an endeavor, with cases of both successes and failures, provided lessons which are heuristic for the studies in earthquake science and social sustainability. This paper provides the background information of such an endeavor, discussing on the achievements and space for improvements of this long lasting and continuing effort.

Comparison and analysis of unmodelled errors in GPS and BeiDou signals

Volume 8, Issue 1, January 2017, Pages 41-48
Zhetao Zhang | Bofeng Li | Yunzhong Shen

© 2016 Institute of Seismology, China Earthquake Administration In Global Navigation Satellite Systems (GNSS) positioning, one often tries to establish a mathematic model to capture the systematic behaviors of observations as much as possible. However, the observation residuals still exhibit, to a great extent, as (somewhat systematic) signals. Nevertheless, those systematic variations are referred to as the unmodelled errors, which are difficult to be further modelled by setting up additional parameters. Different from the random errors, the unmodelled errors are colored and time correlated. In general, the larger the time correlations are, the more significant the unmodelled errors. Hence, understanding the time correlations of unmodelled errors is important to develop the theory for processing the unmodelled errors. In this study, we compare and analyze the time correlations caused by unmodelled errors of Global Positioning System (GPS) and BeiDou signals. The time correlations are estimated based on the residuals of double differenced observations on 11 baselines with different lengths. The results show that the time correlation patterns are different significantly between GPS and BeiDou observations. Besides, the code and phase data from the same satellite system are also not the same. Furthermore, the unmodelled errors are affected by not only the baseline length, but also some other factors. In addition, to make use of the time correlations with more efficiency, we propose to fit the time correlations by using exponent and quadratic models and the fitting coefficients are given. Finally, the sequential adjustment method considering the time correlations is implemented to compute the baseline solutions. The results show that the solutions considering the time correlations can objectively reflect the actual precisions of parameter estimates.

Source rupture process of the 2015 Gorkha, Nepal Mw7.9 earthquake and its tectonic implications

Volume 7, Issue 2, March 2016, Pages 124-131
Lifen Zhang | Lifen Zhang | Jinggang Li | Jinggang Li | Wulin Liao | Qiuliang Wang

© 2016 Institute of Seismology, China Earthquake Administration. On 25 April, 2015, an Mw7.9 earthquake occurred in Nepal, which caused great economic loss and casualties. However, almost no surface ruptures were observed. Therefore, in order to interpret the phenomenon, we study the rupture process of the earthquake to seek answers. Inversion of teleseismic body-wave data is applied to estimate the rupture process of the 2015 Nepal earthquake. To obtain stable solutions, smoothing and non-negative constraints are introduced. 48 teleseismic stations with good coverage are chosen. Finite fault model is established with length and width of 195 km and 150 km, and we set the initial seismic source parameters referring to CMT solutions. Inversion results indicate that the focal mechanism of this earthquake is a thrust fault type, and the strike, dip and rake angle are in accordance with CMT results. The seismic moment is 0.9195 × 1021Nm (Mw7.9), and source duration is about 70 s. The rupture nucleated near the hypocenter and then propagated along the dip direction to the southeast, and the maximum slip amounts to 5.2 m. Uncertainties on the amount of slip retrieved by different inversion methods still exist, the overall characteristics are inconsistent. The lack of shallow slip during the 2015 Gorkha earthquake implies future seismic hazard and this region should be paid more attention to.

A new PC control software for ZLS-Burris gravity meters

Volume 9, Issue 3, May 2018, Pages 210-219
H. Richard Schulz

© 2017 The Author The previous operation of the ZLS-Burris gravity meter using a PDA already provides a significant improvement of the operation of a metal spring gravity meter. But in the practical field work the observer usually wishes more information about the measurement and the collected data. This situation suggested an improvement of the software and computer hardware. The goal was to develop a small useful PC tool that eliminates these deficits. However, it resulted in a very extensive application software, which was developed during 2011–2015. Along the way, some unwanted effects of the original control circuit were detected. Therefore as a last step a complete new control circuit for the feedback system was developed. This new circuit is fast and smooth and without resonance effects to the system. The algorithm parameters can be specifically adapted to the specific gravity meter. The software has a security system that ensures the user, depending on his level of knowledge, a limited access to the software options. Furthermore, a customer project management system is integrated. The observer, the gravity meters, the projects and maps can be assigned. Several ZLS Burris gravity meters can be managed. A large station data management is integrated. Every station has up to more than twenty parameters, such as the mandatory coordinates or supplementary pictures of the station. External storage and documentation of the measurements are possible with extra modules. In addition the maintenance of the gravity meter system is significantly improved. The motor control of the early ZLS Burris gravity meter is also improved. The complete rotation is displayed on the screen. Finally, two survey examples show the advantages of the software related to the accuracy and the time needed for a measurement.

Influence of ocean tidal loading on InSAR offshore areas deformation monitoring

Volume 8, Issue 1, January 2017, Pages 70-76
Mengfei Lei | Qijie Wang | Xiaoli Liu | Bing Xu | Hongqiang Zhang

© 2016 Institute of Seismology, China Earthquake Administration The ocean tide can cause the redistribution of the seawater mass, resulting in earth's surface deformation, namely ocean tidal loading (OTL). OTL vertical displacement may reach several centimeters, especially in coastal areas, so its effect in the field of high precision geodesy must be considered. This study concentrates on the influences of OTL on InSAR deformation measurements. We improve the osu.chinasea.2010 regional model and then compare the improved regional model with other regional models. It turns out that the improved regional model can achieve higher precision. Then we use it to replace the offshore part of the global model to generate the present model. We find that the displacement observed by the present model is 2–3 mm larger than that of other models on some sites. Finally, the present model is used to correct the deformation observed by InSAR of Shanghai and Los Angeles. A comparison between the displacements of IGS station with the corrected data shows that the OTL correction can improve the accuracy of InSAR deformation results by about 20%.

Evaluation of ocean tide loading effects on GPS-estimated precipitable water vapour in Turkey

Volume 7, Issue 1, January 2016, Pages 32-38
Gurbuz Gokhan | Shuanggen Jin | Shuanggen Jin

© 2016 Institute of Seismology, China Earthquake Administration. Global Positioning System (GPS) has been widely used to estimate the total zenith tropospheric delay (ZTD) and precipitable water vapour (PWV) for weather prediction and atmospheric research as a continuous and all-weather technique. However, estimations of ZTD and PWV are subject to effects of geophysical models with large uncertainties, particularly imprecise ocean tide models of inland seas in Turkey. In this paper, GPS data from Jan. 1, 2010 to Dec. 31, 2011 are processed using GAMIT/GLOBK at four co-located GPS stations (ISTN, ERZR, SAMN, and IZMI) with Radiosonde from the Turkish Met-Office together with several nearby IGS stations. Four widely used ocean tide models are adopted to evaluate their effects on GPS-estimated PWV, such as IERS recommended FES2004, NAO99b, CSR4.0 and GOT00. Five different strategies are taken without ocean tide model and with four ocean tide models, respectively, which are used to evaluate ocean tide models effects on GPS-estimated PWV through comparing with co-located Radiosonde. Results showed that ocean tide models have greatly affected the estimation of the precipitable water vapour at stations near coasts. The ocean tide model FES2004 gave the best results when compared to Radiosonde with ±2.12 mm in PWV at stations near coastline. While other ocean tides models agree each other at millimeter level in PWV. However, at inland GPS stations, ocean tide models have less effect on GPS-estimated PWV.

GRACE-based estimates of water discharge over the Yellow River basin

Volume 7, Issue 3, January 2016, Pages 187-193
Qiong Li | Bo Zhong | Bo Zhong | Zhicai Luo | Zhicai Luo | Chaolong Yao

© 2016 Institute of Seismology, China Earthquake Administration As critical component of hydrologic cycle, basin discharge is a key issue for understanding the hydrological and climatologic related to water and energy cycles. Combining GRACE gravity field models with ET from GLDAS models and precipitation from GPCP, discharge of the Yellow River basin are estimated from the water balance equation. While comparing the results with discharge from GLDAS model and in situ measurements, the results reveal that discharge from Mosaic and CLM GLDAS model can partially represent the river discharge and the discharge estimation from water balance equation could reflect the discharge from precipitation over the Yellow River basin.

A regional GNSS-VTEC model over Nigeria using neural networks: A novel approach

Volume 7, Issue 1, January 2016, Pages 19-31
Daniel Okoh | Oluwafisayo Owolabi | Christopher Ekechukwu | Olanike Folarin | Gila Arhiwo | Joseph Agbo | Segun Bolaji | Babatunde Rabiu

© 2016 Institute of Seismology, China Earthquake Administration. A neural network model of the Global Navigation Satellite System - vertical total electron content (GNSS-VTEC) over Nigeria is developed. A new approach that has been utilized in this work is the consideration of the International Reference Ionosphere's (IRI's) critical plasma frequency (foF2) parameter as an additional neuron for the network's input layer. The work also explores the effects of using various other input layer neurons like disturbance storm time (DST) and sunspot number. All available GNSS data from the Nigerian Permanent GNSS Network (NIGNET) were used, and these cover the period from 2011 to 2015, for 14 stations. Asides increasing the learning accuracy of the networks, the inclusion of the IRI's foF2 parameter as an input neuron is ideal for making the networks to learn long-term solar cycle variations. This is important especially for regions, like in this work, where the GNSS data is available for less than the period of a solar cycle. The neural network model developed in this work has been tested for time-varying and spatial performances. The latest 10% of the GNSS observations from each of the stations were used to test the forecasting ability of the networks, while data from 2 of the stations were entirely used for spatial performance testing. The results show that root-mean-squared-errors were generally less than 8.5 TEC units for all modes of testing performed using the optimal network. When compared to other models, the model developed in this work was observed to reduce the prediction errors to about half those of the NeQuick and the IRI model.

Gravity variations before the Menyuan Ms6.4 earthquake

Volume 7, Issue 4, July 2016, Pages 223-229
Weifeng Liang | Guoqing Zhang | Yiqing Zhu | Yunma Xu | Shusong Guo | Yunfeng Zhao | Fang Liu | Lingqiang Zhao

© 2016 Institute of Seismology, China Earthquake Administration In order to study the relationship between gravity variation and Menyuan Ms6.4 earthquake, gravity variation characteristics in mid-eastern of Qilian Mountain were analyzed based on the 2012–2015 relative gravity datasets. The results indicated that the gravity changes in mid-eastern of Qilian Mountain increased gradually, while gravity changes around Menyuan remarkably. Besides, great positive-negative gravity changing gradients appeared along the Lenglongling Fault which was located at the north of Menyuan, and the 2016 Menyuan Ms6.4 earthquake occurred near the junction of positive and negative gravity changes.

Automated Burris gravity meter for single and continuous observation

Volume 9, Issue 3, May 2018, Pages 204-209
Gerhard Jentzsch | Richard Schulz | Adelheid Weise

© 2018 The Authors The Burris Gravity Meter™ manufactured by ZLS Corporation, Austin/Texas, USA, is based on the invention of L&R (L. LaCoste and A. Romberg): The ZLS (zero-length spring). A digital feedback system (range of about 50 mGal) is used to null the beam. Now, more than 120 gravity meters of this make exist worldwide and are used successfully in exploration, volcanology, geodetic work and surveying. The sensor is made of the well-known (L&R) metal-alloy zero-length spring providing a low drift characteristic. The drifts observed are comparable to L&R gravimeters and are less than 0.3 mGal per month, which is much lower than the drifts known for the fused quartz sensors. The dial is calibrated every 50 mGal over the entire 7000 mGal meter range. Since the gravity value is determined at these points, there are no periodic errors. By a fourth heater circuit temperature effects are totally avoided. The gravity meter is controlled via Bluetooth®either to a handheld computer (tablet) or a notebook computer. The feedback responds with high stability and accuracy. The nulling of the beam is controlled by the UltraGrav™ control system which incorporates an inherently linear PWM (pulse-width modulated) electrostatic feedback system. In order to improve the handling of the gravimeter we have developed two Windows based programs: AGESfield for single measurements and AGEScont for continuous readings.

Scintrex CG5 used for superconducting gravimeter calibration

Volume 9, Issue 3, May 2018, Pages 197-203
Bruno Meurers

© 2017 The Author The scale factor accuracy of superconducting gravimeters (SG) can be largely improved by a high repetition rate of calibration experiments. At stations where the availability of absolute gravimeters is limited, carefully calibrated spring gravimeters can be used for providing the reference signal assuming the irregular drift is properly adjusted. The temporal stability of the SG scale factor is assessable by comparing the temporal variations of M2 tidal parameters observed at neighboring SG sites or from synthetic tide models. Combining these methods reduces the SG scale factor error to a few 0.1‰. The paper addresses the particular procedure required for evaluating the calibration experiments based on spring gravimeters and presents results obtained at Conrad observatory (Austria). Comparing the M2 amplitude factor modulation helped to reveal a SG scale factor offset of about 0.2‰ due to re-installation.

Non-tidal tilt and strain signals recorded at the Geodynamic Observatory Moxa, Thuringia / Germany

Volume 9, Issue 3, May 2018, Pages 229-236
Th Jahr

© 2018 The Author Since end of the 90s of the last century the seismological station Moxa was extended and developed into the modern Geodynamic Observatory. It comprises also the new installation of borehole-tilt meters in front of the observatory building and laser-strain meters in the gallery. The question arises how non-tidal signals are displayed in the measured time series. The investigation of such signals which can be caused naturally or man-made, can result in different sensitivities for the various tilt- and strainmeter systems, e.g. regarding barometric pressure impacts and hydrological induced pore pressure effects.

Geodynamics of the Calabrian Arc area (Italy) inferred from a dense GNSS network observations

Volume 7, Issue 1, January 2016, Pages 76-86
Giuseppe Casula

© 2016, Institute of Seismology, China Earthquake Administration, etc. The tectonics and geodynamics of the Calabria region are presented in this study. These are inferred by precise computation of Global Navigation Satellite Systems (GNSS) per-manent station velocities in a stable Eurasian reference framework. This allowed computation of the coordinates, variance and covariance matrixes, and horizontal and vertical velocities of the 36 permanent sites analyzed, together with the strain rates, and using different techniques. Interesting geodynamic phenomena are presented, including compressional, and deformational fields in the Tyrrhenian coastal sites of Calabria, extensional trends of the Ionian coastal sites, and sliding movement of the Crotone Basin. Conversely, on the northern Tyrrhenian side of the network near the Cilento Park area, the usual extensional tectonic perpendicular to the Apennine chain is observed. The large-scale pattern of the GNSS height velocities is shown, which is characterized by general interesting geodynamic vertical effects that appear to be due to geophysical movement and anthropic activity. Finally, the strain-rate fields computed through three different tech-niques are compared.

Fast magnitude determination using a single seismological station record implementing machine learning techniques

Volume 9, Issue 1, January 2018, Pages 34-41
Luis H. Ochoa | Luis F. Niño | Carlos A. Vargas

© 2017 Universidad Nacional de Colombia In this work a Support Vector Machine Regression (SVMR) algorithm is used to calculate local magnitude (Ml) using only five seconds of signal after the P wave onset of one three component seismic station. This algorithm was trained with 863 records of historical earthquakes, where the input regression parameters were an exponential function of the waveform envelope estimated by least squares and the maximum value of the observed waveform for each component in a single station. Ten-fold cross validation was applied for a normalized polynomial kernel obtaining the mean absolute error for different exponents and complexity parameters. The local magnitude (Ml) could be estimated with 0.19 units of mean absolute error. The proposed algorithm is easy to implement in hardware and may be used directly after the field seismological sensor to generate fast decisions at seismological control centers, increasing the possibility of having an effective reaction.

Recent developments in seismological geodesy

Volume 7, Issue 3, March 2016, Pages 157-164
Caijun Xu | Caijun Xu | Caijun Xu | Zheng Gong | Jieming Niu

© 2016 Institute of Seismology, China Earthquake Administration With the advanced development of the modern geodetic techniques, the geodetic observations have been proved to be more powerful to uncover the geophysical phenomena, especially the seismic one, than that in the past time. The recent developments and achievements in the seismological geodesy are summarised here. Several popular geodetic techniques, such as high-rate GNSS, InSAR and Satellite Gravimetry, are introduced first to present their recent contributions in studying the seismic deformations. The developments of the joint inversion of the seismic source parameters from multiple observations are then highlighted. Some outlooks in seismological geodesy are presented in the end.

Coseismic and postseismic slip ruptures for 2015 Mw 6.4 Pishan earthquake constrained by static GPS solutions

Volume 7, Issue 5, September 2016, Pages 323-328
Ping He | Ping He | Qi Wang | Kaihua Ding | Kaihua Ding | Jie Li | Rong Zou

© 2016 Institute of Seismology, China Earthquake Administration On 3 July 2015, a Mw 6.4 earthquake occurred on a blind fault struck Pishan, Xinjiang, China. By combining Crustal Movement Observation Network of China (CMONOC) and other Static Global Positioning System (GPS) sites surrounding Pishan region, it provides a rare chance for us to constrain the slip rupture for such a moderate event. The maximum displacement is up to 12 cm, 2 cm for coseismic and postseismic deformation, respectively, and both the deformation patterns show a same direction moving northeastward. With rectangular dislocation model, a magnitude of Mw6.48, Mw6.3 is calculated based on coseismic, postseismic deformation respectively. Our result indicates the western Kunlun range is still moving toward Tarim Basin followed by an obvious postseismic slip associated with this earthquake. To determine a more reasonable model for postseismic deformation, a longer GPS dataset will be needed.

Carrier phase-based ionospheric observables using PPP models

Volume 8, Issue 1, January 2017, Pages 17-23
Yan Xiang | Yang Gao | Junbo Shi | Chaoqian Xu

© 2017 Institute of Seismology, China Earthquake Administration The ionosphere is one of the major error sources in Global Navigation Satellite System (GNSS) positioning, navigation and timing. Estimating the ionospheric delays precisely is of great interest in the GNSS community. To date, GNSS observables for ionospheric estimation are most commonly based on carrier phase smoothed code measurements. However, leveling errors, which affect the performance of ionospheric modeling and differential code bias (DCB) estimation, exist in the carrier phase smoothed code observations. Such leveling errors are caused by the multipath and the short-term variation of DCB. To reduce these leveling errors, this paper investigates and estimates the ionospheric delays based on carrier phase measurements without the leveling errors. The line-of-sight ionospheric observables with high precision are calculated using precise point positioning (PPP) techniques, in which carrier phase measurements are the principal observables. Ionosphere-free and UofC PPP models are applied and compared for their effectiveness to minimize the leveling errors. To assess the leveling errors, single difference of ionospheric observables for a short baseline is examined. Results show that carrier phase-derived ionospheric observables from PPP techniques can effectively reduce the leveling errors. Furthermore, we compared the PPP ionosphere estimation model with the conventional carrier phase smoothed code method to assess the bias consistency and investigate the biases in the ionospheric observables.

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