ALBERT

Description: We resolve source mechanism and rupture process for the Néon Karlovásion, Samos Mw 7.0 earthquake that struck Greek-Turkish border regions on 30th October 2020 acquired from kinematic joint inversion of teleseismic body-waves and near-field strong ground-motion waveforms. The optimal kinematic finite-fault slip model indicates a planar E-W striking north-dipping normal faulting mechanism with strike ϕ = 270° ± 5°; dip δ = 35° ± 5°; rake λ = −94° ± 5°; centroid depth h = 11 ± 2 km; duration of the source time function STF = 26 s and seismic moment Mo = 3.34 × 1019 Nm equivalent to Mw = 7.0. Our final finite- fault slip models exhibit two main asperities within a depth range from ~20 km to the surface. The dynamic rupture model exposes an initial heterogeneous stress distribution with variations up to 25 MPa. The near-field strong motion waveforms constrained the slip model suggesting up-dip and westward propagation of the bilateral rupture pattern with a maximum slip of 3.2 m, illuminated by back-projection (BP) analysis. The high-frequency (HF) back-projected rupture showed a predominantly E-W striking component (~75%) with directivity of 277° that propagates to the surface along a 60 km long and 24 km wide fault plane in 20 s at a slower speed range of 1.0–2.0 km/s. This well constrains the coseismic slip region where the aftershock sequence confirms distributed deformation. Our back-projection analyses elucidates a dominant HF rupture stage (0–13 s) tracked first on the epicentre area and further along the downdip in the region of maximum coseismic slip indicating ~15 km of persistent rupture. The latter HF emissions (13–20 s) remark a speed of about 3.0 km/s and a westward extension of the rupture up to 30 km from the preceding rupture segment to shorelines at the northeast of the Ikaria Island.

Description: Due to the spectrum congestion of current navigation signals in the L-band, it is difficult to apply for another two proper frequencies in this band for future low earth orbit (LEO)-based navigation augmentation systems. A feasible frequency scheme of using the combined frequencies in the L, S and C bands is proposed. A high-efficiency modulation scheme, termed continuous phase modulation, is adopted to make full use of the very limited spectrums and satisfy the radio frequency compatibility with the existing navigation systems, radio astronomy, and microwave landing systems. The high propagation loss in the S and C bands is absent for LEO, as the power margin owing to the short-distance propagation has compensated the frequency-dependent attenuation. Besides, for high-precision positioning, we consider the specific integer ratios between frequencies and propose a strategy for LEO precise point positioning (PPP) ambiguity resolution (AR) by directly fixing the L + S or L + C dual-band ionospheric-free (IF) ambiguity. Based on the simulated data, the quality of fractional cycle biases (FCBs) and the performance of PPP AR are analyzed. After removing the FCBs, 100.0, 99.7 and 71.7% of the fractional parts are within ± 0.15 cycles for GPS narrow-lane, LEO L + S dual-band IF and LEO L + C dual-band IF float ambiguities. At user stations, the convergence time of GPS PPP in static mode can be significantly shortened from 17.9 to within 2.5 min with the augmentation of 5.44 LEO satellites. Furthermore, compared with ambiguity-float solutions, the positioning accuracy of GPS AR + LEO AR solutions in east, north and up components is improved from 0.008, 0.008 and 0.027 m to 0.002, 0.003 and 0.011 m for 10-min sessions, respectively, and the fixing rate after time to first fix is almost 100%.

Description: This article analyzes the interferometric measurements of ground-based global navigation satellite systems (GNSSs) stations and proposes a novel method for sea surface states detection. The novel technique benefits from a cost-effective data collection from a large number of global GNSS stations. In this study, we extend a traditional GNSS interferometry reflectometry (GNSS-IR) model so that it can be applied to a multilayer surface by considering the surface roughness, total reflectivity, and penetration loss in multilayer situations. Based on this model, the wavelet analysis is used to perform parameterization on the interferometric observations represented by the signal to noise ratio (SNR). An integration factor and power curve are also proposed to characterize the surface state transition. One-year data from an Arctic geodetic GNSS station in the north of Canada are collected for analysis to validate the proposed approach in comparison with the existing methods based on the amplitude and damping factors. The results show that the new method demonstrates good usability and sensitivity to detect surface state transitions, e.g., icing, snowfall, and snow melting. However, the amplitude and damping factor-based methods derived from the single-layer model are only able to detect the pure ice surface and cannot respond to thick snow conditions. Finally, the high-resolution spaceborne images confirm the reliability of this method, exhibiting a great potential for long-term coastal sea surface detection based on the global geodetic GNSS stations and later being expected to be applied to sense cryosphere surface states.