Pulse Peak Migration during the Outburst Decay of the Magnetar SGR 1830-0645: Crustal Motion and Magnetospheric Untwisting

Magnetars, isolated neutron stars with magnetic-field strengths typically ≳1014 G, exhibit distinctive months-long outburst epochs during which strong evolution of soft X-ray pulse profiles, along with nonthermal magnetospheric emission components, is often observed. Using near-daily NICER observations of the magnetar SGR 1830-0645 during the first 37 days of a recent outburst decay, a pulse peak migration in phase is clearly observed, transforming the pulse shape from an initially triple-peaked to a single-peaked profile. Such peak merging has not been seen before for a magnetar. Our high-resolution phase-resolved spectroscopic analysis reveals no significant evolution of temperature despite the complex initial pulse shape, yet the inferred surface hot spots shrink during peak migration and outburst decay. We suggest two possible origins for this evolution. For internal heating of the surface, tectonic motion of the crust may be its underlying cause. The inferred speed of this crustal motion is ≲100 m day−1, constraining the density of the driving region to ρ ∼ 1010 g cm−3, at a depth of ∼200 m. Alternatively, the hot spots could be heated by particle bombardment from a twisted magnetosphere possessing flux tubes or ropes, somewhat resembling solar coronal loops, that untwist and dissipate on the 30–40 day timescale. The peak migration may then be due to a combination of field-line footpoint motion (necessarily driven by crustal motion) and evolving surface radiation beaming. This novel data set paints a vivid picture of the dynamics associated with magnetar outbursts, yet it also highlights the need for a more generic theoretical picture where magnetosphere and crust are considered in tandem.

Age of the Jurassic hemipelagic sediments from the Ljubiš area (Zlatibor Mt., SW Serbia)

The type section of the Ljubiš Formation, (Djokov Potok, Zlatibor area, western Serbia) is characterized by abundant poorly-to-moderately preserved radiolarians. The lower part of the type section is characterized by Middle Jurassic (?Bajocian to Bathonian) radiolarian assemblages with Japonocapsa fusiformis (YAO), Takemuraella weghae (GRILL & KOZUR), Eoxitus hungaricus KOZUR, E. baloghi KOZUR, Helvetocapsa matsuokai (SASHIDA), Quarkus japonicus (YAO), Hexasaturnalis suboblongus (YAO), H. tetraspinus (YAO). Taking into account previous data from the upper part of the Ljubiš Formation, the age of the formation can be estimated to be in the interval from the ?Bajocian to Bathonian-Oxfordian. The new biostratigraphic data clearly show the onset of tectonic motion in the Middle Jurassic, documented by the presence of mass transport deposits intercalated in the radiolarite successions. This suggests a Middle Jurassic onset of ophiolite obduction which triggered the rapid deepening of the Adria margin, documented by the abrupt change from carbonate to radiolarite deposition.

Detecting recent creeping landslide activity in central Taiwan by multi-temporal InSAR technique

<p>The main objective of this study is to present the progress and state-of-the-approaches of PSInSAR with Sentinel-1 radar images to detect the creeping activity of the potential large landslides revealed by LiDAR in the mountainous area of the slate belt in central Taiwan. We choose Qingjing and Lushan area to process the Multi-Temporal InSAR (MTI) to capture the signals the creeping activity associated with the heavy rainfall events. First, we carry out the feasibility analysis to predict whether the MTI analysis is suitable for detecting the potential persistent scatterers (PS) and test the sensitivity with the effect of layover and shadowing resulted from mountainous topography in central Taiwan. In addition, we also take the effect of land cover on PS distributions into account. Second, we set a threshold of LOS (line of sight) velocity of creeping activity to assess the state of activity. Then we make a Vslope for projection of the LOS velocity along the down-slope direction for steep slope located in the potential landslide area. Furthermore, both the ascending and descending orbits are used to get two LOS velocities which allows us to resolve the E–W and vertical velocity components in order to compare with the tectonic motion due to the mountain building process in slate belt. Finally, the analysis in time series of PSInSAR is carried out for the evolution of creeping events in study area. In this study, we also want to improve the efficiency of remote sensing products for operational monitoring with integration of SAR/InSAR products with numerical and analytical geotechnical models for stability analysis of large potential landslide area detected by geomorphological features from LiDAR-derived DEM.</p>

Towards computing a new kinematic coordinates transformation parameters for Egypt

ITRF (International Terrestrial Reference Frame) determines the origin, alignment of the system ’s fundamental planes or axes, scale, physical constants, and models such as the size, shape, and alignment of the reference ellipsoid. The ITRF is regularly updated to take into account the Earth’s dynamics and is now sufficiently re-fined to ensure that the change between successive ITRF versions is in the order of 1-2 cm. The Egyptian Survey Authority (ESA) established the Egyptian’s HARN (High Accuracy Reference Network) and linked it to the international frame (ITRF1994 epoch1996) as a static frame. As this datum is static, coordinates of stations do not change with time, ignoring both the tectonic motion and the different definitions for all following ITRF realizations. With the continuous increasing progress of using the IGS and CORS stations as well as the merging of the concept of tectonic plate motion, and the Precise Point Positioning technique has a well know precise technique, there were offset in the current coordinates of the HARN network about 40 cm, so a set of simple transformation parameters (T x , T y , T z ) calculated. In the current study, Plate Motion Models (PPM) and Egyptian Deformation Model (EGY-DM) were investigated based on ITRF2008 epoch2015.4 to choose the best model in calculating the computed parameters. The evaluation process of the computed transformation parameters on chosen points of HARN & NACN (Notational Agricultural Cadastral network) demonstrates that the estimated transformation parameters by EGY-DM give the lowest horizontal and vertical differences 16 mm and 17mm, respectively, and with standard deviation does not exceed 2 cm, except one station due to deficiency of observation time.

Assessment of geodetic velocities using GPS campaign measurements over long baseline lengths

GPS campaign measurements are frequently used in order to determine geophysical phenomena such as tectonic motion, fault zones, landslides, and volcanoes. When observation duration is shorter, the accuracy of coordinates are degraded and the accuracy of point velocities are affected. The accuracies of the geodetic site velocities from a global network of International GNSS Service (IGS) stations were previously investigated using only PPP. In this study, we extend which site velocities will also be assessed, including fundamental relative positioning. PPP-derived results will also be evaluated to see the effect of reprocessed JPL products, single-receiver ambiguity resolution, repeating survey campaigns minimum 3 days at the site, and eliminating noisier solutions prior to the year 2000. To create synthetic GPS campaigns, 18 globally distributed, continuously operating IGS stations were chosen. GPS data were processed comparatively using GAMIT/GLOBK v10.6 and GIPSY-OASIS II v6.3. The data of synthetic campaign GPS time series were processed using a regression model accounting for the linear and seasonal variation of the ground motion. Once the velocities derived from 24 h sessions were accepted as the truth, the results from sub-sessions were compared with the results of 24 h and hypothesis testing was applied for the significance of the differences. The major outcome of this study is that on global scales (i.e. over long distances) with short observation sessions, the fundamental relative positioning produces results similar to PPP. The reliability of the velocity estimation for GPS horizontal baseline components has now been improved to about 85 % of the average for observation durations of 12 h.

Accuracy of geodetic site velocities from repeated GPS measurements: relative positioning over long baselines

Currently, GPS campaign measurements (i.e. repeated GPS measurements) are used frequently in order to determine geophysical phenomena such as tectonic motion, fault zones, landslides, and volcanoes. The coordinates of a new point installed in a study area are usually found either by using relative point positioning or precise point positioning (PPP). Employing observation sessions shorter than 24 h might still be a necessity at times. When observation duration is shorter, the accuracy of coordinates are degraded and also the accuracy of point velocities are affected. The accuracies of the geodetic site velocities from a global network of the International GNSS Service (IGS) stations were previously investigated using only PPP. In this study, we extend that study in which site velocities will also be assessed including fundamental relative positioning. PPP derived results will also be evaluated to see the effect of JPL reprocessed products and single receiver ambiguity resolution. IGS is a good data source for simulation studies and hence globally distributed 18 continuously operating IGS stations were chosen to create synthetic GPS campaigns. GPS data were processed comparatively using GAMIT/GLOBK v10.6 and GIPSY/OASIS II v6.3. The data of synthetic campaign GPS time series were processed using a regression model accounting for the linear and seasonal variation of the ground motion. Once accepting the velocities derived from 24 h sessions as the truth, the results from sub-sessions were compared with the results of 24 h and hypothesis testing was applied for the significance of the differences. The major outcome of this study is that at global scales (i.e. over long distances) with short observation sessions, the fundamental relative positioning produces similar results to PPP. The reliability of the velocity estimation for horizontal components has now been improved to about 85 % on the average for observation durations of 12 h.

THE VALIDATION OF THE TRANSFORMATION BETWEEN AN OLD GEODETIC REFERENCE FRAME AND A MODERN REFERENCE FRAME, BY USING EXTERNAL SPACE TECHNIQUES SITES: THE CASE STUDY OF THE HELLENIC GEODETIC REFERENCE SYSTEM OF 1987

Many of the old geodetic reference frames which realized in the previous decades using classical observations carry biases. These biases are mainly caused due to the problematic observations and/or the tectonic motion. That is the case of the official Greek geodetic reference frame which consists of classical and satellite observations. Herein, we present a rigorous approach of the reconstruction of the Greek official reference frame based on the modern geodetic reference frames and their ability to express the spatial position and the dynamic change of the stations. We applied the rigorous approach to ninety stations located in Greece and we compare it with the officially accepted procedure. We found a consistency at 59.4cm between the rigorous and the officially accepted approaches, respectively. The associated mean bias estimation was estimated at 51.4 cm, indicating the resistance of a rather large amount of systematic effects. In addition, the observed discrepancies between the two approaches show great inhomogeneity all over the country.

DEVELOPMENT OF A TIME-DEPENDENT 3-PARAMETER HELMERT DATUM TRANSFORMATION MODEL: A CASE STUDY FOR MALAYSIA

This paper aims to develop a time-dependent 3-parameter Helmert datum transformation model for Malaysia as a proposed solution to the current non-geocentric issue of the Geocentric Datum of Malaysia 2000 (GDM2000). Methodologically, the datum transformation models is categorised into three parts; firstly, the time-dependent aspect of the datum transformation model is determined using the tectonic motion velocities computed from linear least squares regression of the long-term time series of MyRTKnet stations positions from year December 2004 to 2014; whereby the station positions are obtained from high-precision daily double-difference processing of MyRTKnet and IGS stations via Bernese 5.0. Secondly, the 3 Helmert translation-only parameters, are derived between the original GDM2000 and GDM2000@2013 – the new datum coordinates which refers to ITRF2008 at epoch 3/7/2013 – via Bernese 5.0 software. Thirdly, a distortion model is computed in order to minimise the coordinate residuals between the ‘processed’ and ‘transformed’ new datum. The datum transformation model is then validated to determine the reliability of the model. The validation results show that the datum transformation model is within centimetre-level accuracy, i.e., below 3 cm, over Malaysia for forward transformations to year 2014 and 2015. Therefore, this study anticipates that it will contribute as a feasible solution for the GDM2000 issue with consideration of the core concern: the complex tectonic motion of Malaysia.