Joint Correction of Tropospheric and Orbital Errors in SAR Differential Interferograms

Synthetic Aperture Radar (SAR) satellite imagery is a source of data widely employed in the quantification and analysis of an earthquake coseismic displacement. However, due to the signal path along the atmosphere and to other sources, the interferometric phase becomes compromised. In this work, a methodology for the correction of tropospheric and orbital errors in the differential interferogram is presented. This methodology was applied to a couple of Sentinel-1A data. The phenomenon studied was the 11th November 2018 Zeribet el Oued earthquake, Mw. 5.2 (The state of Biskra, South East of Algeria). It was possible to correct both tropospheric and orbital errors, where the dominant one was the tropospheric delay, a displacement error of 4 cm was added to the differential interferogram by this noise source. The correction of orbital error led to a better interpretation of the coseismic displacement.

Assessment of the Feasibility of PPP-B2b Service for Real-Time Coseismic Displacement Retrieval

Traditional coseismic displacement retrieval generally uses real-time kinematic (RTK) and precise point positioning (PPP) services. However, both RTK and real-time PPP need a network link to transmit the corrected data. Although the network link may be interrupted when an earthquake happens, the PPP-B2b service broadcasted by geostationary orbit (GEO) satellites will not be affected. Its service range mainly covers China and the surrounding areas. In this research, the PPP method with PPP-B2b service based on constrained coordinates is proposed and overcomes the limitation of the network link and long convergence time. First, the accuracy of orbits and clock offsets for the PPP-B2b service is evaluated and compared with real-time service (RTS). Then, the simulated experiments are carried out using the PPP method with PPP-B2b service based on constrained coordinates, which tests the accuracy by calculating the coordinate displacement of the measurement station. The results show that the accuracy of PPP-B2b orbits in the radial direction is within 0.1 m. Moreover, regarding the accuracy of clock offsets, the PPP-B2b service is no more than 3.5 cm. This validates the feasibility of replacing RTS products with PPP-B2b. In the 15 min simulated experiments, the root mean square (RMS) of horizontal and vertical directions is maintained within 3 cm.

GNSS TIME SERIES ANALYSIS RELATED TO EARTHQUAKE OF THE Mw 6.2 PETRINJA

<p>A devastating earthquake (Mw 6.2) occurred on December 29, 2020,  near the town of Petrinja, in Croatia, a few kilometers north of the Bosnian border with Croatia. The earthquake affected Bosnia and Herzegovina as well, and many buildings in northwestern Bosnia and Herzegovina were severely damaged. The main earthquake impact was preceded by two strong for-shocks, which shows a great resemblance to the Banja Luka earthquake of 1969. Seismic activity at the end of December 2020 and January 2021 was manifested through the occurrence of a large number of seismic events, namely: one earthquake of magnitude 6.2, two earthquakes of magnitude between 5.0 and 6.0, twenty-two earthquakes of magnitude between 4.0 and 5.0, sixty-six earthquakes of magnitude 3.0 and 4.0 and two hundred and seventy-seven earthquakes of magnitude between 2.0 and 3.0. This earthquake is a consequence of the movement of the Adriatic microplate and its interaction with the Eurasian tectonic plate. Its movement results in the creation of current seismicity in Croatia, Bosnia and Herzegovina, Italy, Montenegro, Serbia, Slovenia.</p><p>Today, analysis of the deformations of the Earth's crust plays an important role in research related to the entire seismic cycle. The phases of seismic cycles can be reliably estimated using time series of daily coordinates from continuously operating stations of the Global Navigation Satellite System (GNSS).</p><p>In this study, we used five time-series GNSS positions (Sarajevo, Poreč, Ljubljana, Požega, and Zadar), daily resolutions (24 hours) in the IGS14 reference frame, taken from Nevada Geodetic Laboratory through the website. We determined the coseismic displacement field of the Mw 6.2 Petrinja mainshock using downloaded the GNSS time-series as well as coseismic displacement field for all earthquakes of magnitude over 4. We processed data for the GNSS time series for the period from January 2016 to December 2020. GNSS stations are located at distances ~100 km to the ~250 km distances the epicenter of the Petrinja earthquake, of which the Poreč station is the closest. JavaScript Object Notation (JSON) text format was used for processing all earthquakes in our study. JSON offset file is created based on the data downloaded from USGS (U.S. Geological Survey).</p><p>This paper, apply interactive processing in tectonics and seismology, presented offset in time series as a consequence of earthquakes. We have concluded that the cumulative movement of the Earth's crust is not only a consequence of large earthquakes but also the cause of many smaller accumulated movements caused by smaller earthquakes. The paper presents the contribution in the field of application of satellite positioning methods in geodynamic research and defines an approach that enables objective quantification of deformations of the Earth's crust in cases of seismic events. The earthquake occurred in a fault that extends approximately in the northwest-southeast direction and passes through Pokuplje near Petrinja and Glina. This fault is the boundary between two very different tectonic blocks, the Dinarides and the Pannonian Basin. Therefore, it can be said that the different stresses and displacements in these blocks are compensated through these blocks.</p>

Performance Evaluation of Different SAR-Based Techniques on the 2019 Ridgecrest Sequence

We evaluated the performances of different SAR-based techniques by analyzing the surface coseismic displacement related to the 2019 Ridgecrest seismic sequence (an Mw 6.4 foreshock on July 4th and an Mw 7.1 mainshock on July 6th) in the tectonic framework of the eastern California shear zone (Southern California, USA). To this end, we compared and validated the retrieved SAR-based coseismic displacement with the one estimated by a dense GNSS network, extensively covering the study area. All the SAR-based techniques constrained the surface fault rupture well; however, in comparison with the GNSS-based coseismic displacement, some significant differences were observed. InSAR data showed better performance than MAI and POT data by factors of about two and three, respectively, therefore confirming that InSAR is the most consolidated technique to map surface coseismic displacements. However, MAI and POT data made it possible to better constrain the azimuth displacement and to retrieve the surface rupture trace. Therefore, for cases of strike-slip earthquakes, all the techniques should be exploited to achieve a full synoptic view of the coseismic displacement field.

Real-Time Coseismic Displacement Retrieval Based on Temporal Point Positioning with IGS RTS Correction Products

With the rapid development of the global navigation satellite system (GNSS), high-rate GNSS has been widely used for high-precision GNSS coseismic displacement retrieval. In recent decades, relative positioning (RP) and precise point positioning (PPP) are mainly adopted to retrieve coseismic displacements. However, RP can only obtain relative coseismic displacements with respect to a reference station, which might be subject to quaking during a large seismic event. While PPP needs a long (re)convergence period of tens of minutes. There is no convergence time needed in the variometric approach for displacements analysis standalone engine (VADASE) but the derived displacements are accompanied by a drift. Temporal point positioning (TPP) method adopts temporal-differenced ionosphere-free phase measurements between a reference epoch and the current epoch, and there is almost no drift in the displacement derived from TPP method. Nevertheless, the precise orbit and clock products should be applied in the TPP method. The studies in recent years are almost based on the postprocessing precise orbits and clocks or simulated real-time products. Since 2013, international GNSS service (IGS) has been providing an open-access real-time service (RTS), which consists of orbit, clock and other corrections. In this contribution, we evaluated the performance of real-time coseismic displacement retrieval based on TPP method with IGS RTS correction products. At first, the real-time precise orbit and clock offsets are derived from the RTS correction products. Then, the temporal-differenced ionosphere-free (IF) combinations are formed and adopted as the TPP measurements. By applying real-time precise orbit and clock offsets, the coseismic displacement can be real-timely retrieved based on TPP measurements. To evaluate the accuracy, two experiments including a stationary experiment and an application to an earthquake event were carried out. The former gives an accuracy of 1.8 cm in the horizontal direction and 4.1 cm in the vertical direction during the whole period of 15-min. The latter gives an accuracy of 1.2 cm and 2.4 cm in the horizontal and vertical components, respectively.

Empirical Relationship for Assessing the Near-Field Horizontal Coseismic Displacement Using GPS Seismology Data

In this research, a data set of horizontal GPS coseismic displacement in the near-field has been assembled around the world in order to investigate a potential relationship between the displacement and the earthquake parameters. Regression analyses have been applied to the data of 120 interplate earthquakes having the magnitude (Mw 4.8-9.2). An empirical relationship for prediction near-field horizontal GPS coseismic displacement as a function of moment magnitude and the distance between hypocenter and near field GPS station has been established using the multi regression analysis. The obtained relationship allows assessing the coseismic displacements associated with some large historical earthquakes occurred along the Dead Sea fault system. Such a fair relationship could be useful for assessing the coseismic displacement at any point around the active faults.