Studying the Sensitivity of Satellite Altimetry, Tide Gauge and GNSS Observations to Changes in Vertical Displacements

Tide gauge observations provide sea level relative to the Earth’s crust, while satellite altimetry measures sea level variations relative to the centre of the Earth’s mass. Local vertical land motion can be a significant contribution to the measured sea level change.Satellite altimetry was traditionally used to study the open ocean, but this technology is now being used over inland seas too.The difference of both observations can be used to estimate vertical crustal movement velocities along the sea coast. In this paper, vertical crustal movement velocities were investigated at tide gauge sites along the Adriatic Sea coast by analyzing differences between Tide Gauge (TG) and Satellite Altimetry (SA) observations. Furthermore, the estimated vertical motion rates were compared with those from nearby GNSS measurements.The study determines the practical relationships between these vertical crustal movements and those determined from unrelated data acquired from the neighbouring GNSS stations. The results show general consistence with the present geodynamics in the Adriatic Sea coastal zone.

Decaying Post-Seismic Deformation Observed on the Korean Peninsula Following the 2011 Tohoku-Oki Earthquake

We investigated decaying post-seismic deformation observed on the Korean Peninsula associated with the 2011 Mw 9.0 Tohoku-Oki earthquake using Global Navigation Satellite System (GNSS). The GNSS velocity vectors were estimated in five periods from 2005 to 2019. A co-seismic offset of the Korean Peninsula caused by the 2011 earthquake was inversely proportional to epicentral distances. According to the temporal variations of two components (magnitude and direction) of the GNSS velocity vector with the epicentral distance, the difference between the eastern and western regions for the two components becomes smaller over time. For approximately nine years after the 2011 event, the direction for the crustal movement in South Korea showed a recovery pattern returning to the pre-earthquake motion. In addition, the recovery patterns of the crustal movement were observed differently with the regional geologic structure (e.g., the crustal thickness) and each period. Our estimates of the decay in post-seismic deformation of the Korean Peninsula suggest that post-seismic relaxation will be complete within 5–20 years after the 2011 earthquake. The results suggest that the crustal movement on the Korean Peninsula is gradually recovering to its pre-earthquake motion.

Analysis of Crustal Movement and Deformation in Mainland China Based on CMONOC Baseline Time Series

In this paper, we propose a method for the analysis of tectonic movement and crustal deformation by using GNSS baseline length change rates or baseline linear strain rates. The method is applied to daily coordinate solutions of continuous GNSS stations of the Crustal Movement Observation Network of China (CMONOC). The results show that: (a) The baseline linear strain rates are uneven in space, which is prominent in the Tianshan, Sichuan-Yunnan, Qinghai-Tibet Plateau, and Yanjing areas, with a maximum value of 1 × 10−7 a−1, and about two orders smaller in the South China block, the Northeast block, and the inner area of the Tarim basin, where the average baseline linear strain rates are 1.471 × 10−9 a−1, 2.242 × 10−9 a−1, and 3.056 × 10−9 a−1, respectively; (b) Active crustal deformation and strong earthquakes in the Xinjiang area are mainly located in the north and south sides of the Tianshan block; the compression deformations both inside the Tarim block and in the southern Tianshan fault zone are all increasing from east to west, and the Tarim block is not a completely “rigid block”, with the shrinkage rate in the west part at about 1~2 mm/a; (c) The principal directions of crustal deformation in the Xinjiang, Tibet, and Sichuan-Yunnan regions are generally in the north—south compression and east—west extension, indicating that the collision and wedging between the Indian and Eurasian plates are still the main source of tectonic movements in mainland China.

GIA effects of Holocene rapid ice thinning on the observed geodetic signals along the coast of Lützow-Holm Bay in East Antarctica

<p>Geodetic and geomorphological observations in the Antarctic coastal area generally indicate the uplift trend associated with the Antarctic Ice Sheet (AIS) change since the Last Glacial Maximum (LGM). The melting models of AIS derived from the comparisons between sea-level and geodetic observations and glacial isostatic adjustment (GIA) modeling show the monotonous retreat through the Holocene era (e.g., Whitehouse et al., 2012, <em>QSR</em>; Stuhne and Peltier, 2015, <em>JGR</em>). However, the observed crustal motion by GNSS in some regions of Antarctica cannot be explained as the deformation rates by only glacial rebound due to the last deglaciation of AIS (e.g., Bradley et al., 2015, <em>EPSL</em>). One reason for this mismatch is considered as the control of the uplift induced by the re-advance of AIS following a post-LGM maximum retreat, which was recently reported as the West AIS re-advance in the Ross and the Weddell Sea sectors (e.g., Kingslake et al., 2018, <em>Nature</em>).</p><p>On the other hand, the current crustal motion includes the elastic GIA component due to the present-day surface mass balance of AIS. To reveal the secular crustal movement induced by GIA, the separation of the elastic deformation induced by the current mass balance using GRACE data is essential. In the Lützow-Holm Bay, East Antarctica, GNSS observations have been carried out at several sites on the outcrop rocks since the 1990s to monitor recent crustal movements. Hattori et al. (2019, <em>SCAR</em>) precisely analyzed the GNSS data obtained from this area, which revealed the secular crustal movement by correcting the elastic deformation due to current mass balance. The results indicated the mismatch between secular current crustal motion and GIA calculations based on the previously published ice and viscosity models. Consequently, to represent the observed crustal deformation rates based on the GIA modeling, we must carefully investigate the numerical dependencies of various parameters such as local and global ice history in the AIS.</p><p>Recently, the study of glacial geomorphology and surface exposure dating (Kawamata et al., 2020, <em>QSR</em>) has suggested that the abrupt ice thinning and retreat occurred in Skarvsnes, located at the middle of the Lützow-Holm Bay, during 9 to 6 ka. We obtained the preliminary results related to the GIA effects induced by the abrupt thinning on the geodetic observations in this area. The numerical simulations that we examined are employed for a simple ice model with the thickness change by 400 m during 9 to 6 ka in this area based on the IJ05_R2 model grids (Ivins et al., 2013, <em>JGR</em>). The predictions based on the high-viscosity upper mantle (5x10<sup>20</sup> Pa s) show high uplift rates (~ +4.0 mm/yr), whereas the calculated uplift rates for the weaker viscosity (2x10<sup>20</sup> Pa s) show low value (~ +1.0 mm/yr). These results suggest that the viscoelastic relaxation due to the abrupt ice thinning in the mid-to-late Holocene may influence the current crustal motion and highly depend on the upper mantle viscosity profile. We will discuss the influences on the GIA-calculated crustal movement by AIS retreat history and mantle viscosity structure.</p>

The chloroplast genome sequencing of two important annual Trifolium species T. alexandrinum and T. resupinatum and comparative analysis with other congeneric species

Background: Chloroplast (cp) genome of most plant species has two typical inverted-repeats (IRs) regions. However, in some species this IR structure is lost for unknown reasons and the consequence still needs to be revealed . Here, we present whole cp genome sequencing of Trifolium alexandrinum (Egyptian clover) and T. resupinatum (Persian clover) from the IR lacking clade (IRLC) . Results: Global aligning of T. alexandrinum and T. resupinatum to other eight Trifolium species revealed a large amount of rearrangement and repetitive events in these ten species. We found that IR lacking species have lower GC content and higher percentage of repetition than IR containing species. Abundant single nucleotide polymorphisms (SNPs) and insertions/deletions (In/Dels) were discovered between those two species. As hypothetical cp open reading frame (ORF) and RNA polymerase subunits severally, two genes ycf1 and rpoC2 in the cp genomes, which both contain vast repetitive sequences and high Pi values (0.6656, 0.455) between T. alexandrinum and T. resupinatum , possessed highly variation among ten Trifolium species. Thus they could greatly influence evolutionary process of Trifolium species. In addition, IR containing and IR lacking Trifolium species were estimated to split during the upper Cretaceous period, which was potentially related to the violent crustal movement and sea-land changes. Conclusions: Cp genomes of T. alexandrinum and T. resupinatum, which belong to IRLC were sequenced and annotated in present study, and compared with cp genomes of other eight Trifolium species reported previously. This valuable information will provide insight into the evolution of IR lacking species. Nevertheless, further investigating of the detailed reason of IR lacking is still challenging, but it may be related to the violent crustal movement and sea-land changes of the Cretaceous period presented in this study.