Vertical Crustal Displacements Research Articles

Detection of extreme hydrological droughts in the poyang lake basin during 2021–2022 using GNSS-derived daily terrestrial water storage anomalies

Poyang Lake is the largest freshwater lake in China, serving as a natural reservoir and playing a paramount role in climate regulation, ecological environment, and water resource management. However, in recent years, Poyang Lake has approached desiccation multiple times, with severe droughts becoming increasingly common. Consequently, precise quantification and analysis of the terrestrial water storage anomalies (TWSA) and drought characteristics of the Poyang Lake basin (PLB) are of profound scientific and practical significance. This paper, for the first time, utilizes data for the period 2021–2022 from 77 newly-established GNSS observation stations in the PLB to precisely determine its vertical crustal displacement, invert daily and monthly TWSA, and investigate extreme hydrological drought. The results reveal the following: 1) The annual amplitude range of vertical surface displacements at GNSS stations in the Poyang Lake basin is from 7 to 14 mm, with the most substantial seasonal vertical displacements occurring during the months of June and July; 2) monthly GNSS-TWSA maintains a commendable consistency with TWSA data obtained from the Gravity Recovery and Climate Experiment (GRACE), the Global Land Data Assimilation System (GLDAS), and precipitation, with correlation coefficients of 0.67, 0.55, and 0.62, respectively; 3) at daily scale, the GNSS-derived Drought Severity Index (GNSS-DSI) accurately recorded the severity and intensity of eight drought events in the PLB during 2021–2022, in particular the period of extensive drought between October 2021 and February 2022, when drought intensity reaching a notable 1.03, which is classified as an extreme and prolonged drought event. Additionally, at local temporal scales, daily GNSS-DSI exhibits heightened sensitivity to drought signals. This study provides novel technological tools and datasets for multi-source satellite-based drought monitoring in the PLB.

On the use of tsunami-source data for high-resolution fault imaging of offshore earthquakes

The source imaging for offshore earthquakes using terrestrial geodetic data has a limited estimation performance due to the low data resolution. One approach to overcome this limitation is the use of seafloor geodetic data. In this study, we focus on tsunami-source data, which is the spatial distribution of vertical crustal displacements above the source area and can be derived from tsunami waveform records. We evaluate how the use of this spatial seafloor geodetic data improves the estimation of a rectangular fault model. Here, the fault model of the 2016 off-Fukushima earthquake in Japan, which was a shallow intraplate earthquake (Mw 7.0), was estimated by three inversions: terrestrial Global Navigation Satellite System (GNSS) data only, tsunami-source data only, and a combination of the GNSS data and tsunami-source data. A Bayesian inversion approach was used to understand the distribution of the estimated fault parameters and their relationship. The results indicated that the terrestrial GNSS data have a low resolution for the analysis of the offshore earthquake, which resulted in a biased solution with large uncertainty. Conversely, the use of tsunami-source data significantly improved the resolution and reliability of source imaging and reduced the dependency among fault parameters. These results suggested that the high-spatial-resolution information of tsunami source is a powerful tool in source imaging of offshore shallow earthquakes. Moreover, the combined use of the two different geodetic data leads to a more robust estimation of fault parameters. We believe that the use of tsunami-source data is useful, not only for the post hoc source analysis, but also for estimating an earthquake rupture area just after a large earthquake, where GNSS data are currently used.Graphical

Characterizing hydrological droughts within three watersheds in Yunnan, China from GNSS-inferred terrestrial water storage changes constrained by GRACE data

SUMMARY The spatiotemporal evolution of drought is often modulated by climate and watershed characteristics. While numerous drought studies using space geodesy have been conducted in Yunnan, the scarcity and limited sensitivity of observation instruments have hindered the development of watershed-scale drought analyses. This study aims to accurately characterize hydrological droughts within three watersheds in Yunnan from 2011 January to 2021 May by a Global Navigation Satellite System (GNSS) inversion constrained by Gravity Recovery and Climate Experiment (GRACE) data. Initially, we employed Variational Bayesian Independent Component Analysis to reconstruct the 3-D crustal deformations at 43 GNSS stations resulting from hydrological loadings. We then computed the time-series of vertical displacements caused by GRACE Mascon water products. Subsequently, utilizing the method of least squares, we derived the scaling factors between the vertical crustal displacements (VCD) obtained from GNSS observations and the synthetic displacements derived from GRACE data. By combing scaling-factor-adjusted VCDs derived from GRACE with the GNSS data, we have obtained accurate estimates of water storage for three Yunnan watersheds. Finally, we identified drought events characterized by abnormal decreases in water storage and used climatological methods to quantitatively describe the severity, extent and recovery of these drought extremes. Additionally, we evaluated the influence of various earth elastic structures on the scaling factors, and demonstrated their advantageous contribution to aligning GNSS and GRACE observations. In conclusion, our study introduces a novel approach to integrate GNSS and GRACE retrievals, allowing for accurate characterization of droughts in data-scarce regions, which cannot be achieved by GNSS or GRACE individually. Moreover, our results underscore the potential benefits of watershed-scale drought monitoring and analysis for effective water resource management.

Deep structure and tectonics of the South Ukrainian monocline in the zone of juncture of the East European platform and the Scythian plate (according to gravimetric data)

In order to investigate the deep structure and tectonics of the central part of the South Ukrainian monocline (SUM), a detailed study of this structure was carried out using a network of gravimetric profiles. It is shown that on the part of the SUM, which belongs to the southern edge of the East European Platform (EEP), the basement is split into separate blocks with different characteristics of the consolidated crust. The crust of the Scythian Plate (SP) within the SUM has undergone considerable changes as a result of tectonic activation and significant complications of its structure. The distribution into the areas with different density characteristics of the basement of EEP and SP does not coincide, indicating that the development of the latter has not been fully inherited from the former. The obtained results, compared with data from other researchers in Prydobrydzha and Crimea, show that the northwestern shelf is an intermediate link between these terranes. A tectonic scheme of the research area based on the hypsometry of the surface of the second layer of the basement was built on the basis of the simulation. It was shown that the southern edge of the platform has undergone rather insignificant transformations, which are manifested in the emergence of an elongated intracrustal graben system along the EEP/SP boundary, divided by sublatitudinal faults into three blocks with different parameters. At the northern margin of the SP within the SUM, in addition to the grabens and horsts in the basement, there are sags and uplifts with boundary faults without vertical crustal displacements along them. Areas of the heterogeneous-heterochronous structure of the crust of the Baikal, Hercynian, and Kimmerian generations have been identified within SUM part of the SP. It has been determined that the Golitsyn fault system and the northern flank of the Karkinit trough were further restructuring during the Alpine tectogenesis phase. A variant of the Scythian Plate origin scenario based on the Mobilist ideas is proposed and substantiated by the results of the conducted studies and the available geological and geophysical information as a discussion.

A copula-supported Bayesian framework for spatial downscaling of GRACE-derived terrestrial water storage flux

The GRACE and GRACE-FO satellite missions provide mass variations as a fundamentally new observation type for a broad spectrum of novel applications in Earth science disciplines, including oceanography, geophysics, hydrology, and hydrometeorology. Despite all the key findings in hydrology, the utility of GRACE-derived Terrestrial Water Storage Anomaly (TWSA) and its time derivative Terrestrial Water Storage Flux (TWSF) have mainly been limited to large catchments due to their coarse spatial resolution. Here, we propose a method to downscale TWSF by incorporating available finer-resolution data. We determine the downscaled TWSF and its uncertainty within a proposed Bayesian framework by incorporating the fine-scale data of TWSF and Soil Moisture Change (SMC) from different available sources. For the Bayesian ingredients, we rely on GRACE data to obtain the prior and rely on copula models to obtain nonparametric likelihood functions based on the statistical relationship between GRACE TWSF with fine-scale TWSF data and SMC. We apply our method to the Amazon Basin and assess the performances of our products from various fine-scale input datasets of TWSFs and SMCs. Given the lack of ground truth for TWSF, we validate our results against space-based Surface Water Storage Change (SWSC) in the Amazon river system and also against the Vertical Crustal Displacements Rate (VCDR) observed by the Global Positioning System (GPS). Overall, the results show that the proposed method is able to estimate a downscaled TWSF, which is informed by GRACE and fine-scale data. Validation shows that our downscaled products are better anticorrelated with VCDR (−0.81) than fine-scale TWSF (−0.73) and show a mean relative RMSE of 26% with SWSC versus 70% for fine-scale TWSF. The proposed methodology can be extended to other coarse scale datasets, which are crucial for hydrological application at regional and local scales.

Characterization of hydrological droughts in Brazil using a novel multiscale index from GNSS

Drought severity is not only related to drought intensity but also depends on drought duration. To accurately characterize short- and long-term droughts and comprehend drought propagation mechanisms, it is essential to ascertain the multiscale features of drought extremes. Here, we estimate terrestrial water storage changes (TWSC) using Global Navigation Satellite System (GNSS) vertical crustal displacement and then develop a novel Multiscale GNSS-based Drought Index (MGDI) to characterize hydrological droughts in Brazil from 2010 to 2021. MGDI is a probability-based drought index, and we employ a normal distribution to fit the TWSC result. The comparisons of temporal variations indicate that the MGDI is similar to other multiscale drought indices (i.e., standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI), and standardized terrestrial water storage index (STI)) at different time scales. Due to the longer response time to meteorological variables, hydrological drought indicators (i.e., MGDI and STI) generally lag behind meteorological drought indicators (i.e., SPI and SPEI) but with less noise on the short scale. The spatial distribution of MGDI-derived drought frequency reveals that hydrological droughts are most frequent in northeastern Brazil and near the Parana River Basin, with a frequency of up to 0.38 (about 55 months) on the 1-month scale. The spatiotemporal evolutions of the 2015–2016 drought event imaged by 3-month MGDI and 12-month SPI are generally consistent, and 3-month MGDI shows good temporal continuity of evolution. Investigation of drought propagation in various basins shows that 1-month MGDI correlates well with SPI on the specific time scales (e.g., 6-month, 11-month, 13-month, and 14-month), with all correlation coefficients above 0.55. In the Amazon Basin, we also find that MGDI on the 1.5–3 years scale is strongly correlated with El Niño-Southern Oscillation (ENSO) events, suggesting hydrological droughts are likely to be modulated by ENSO. Our findings imply that MGDI can characterize hydrological deficits more comprehensively and offer some critical insights for multiscale drought research.

Seismic history of western Anatolia during the last 16 kyr determined by cosmogenic 36Cl dating

Western Anatolia is one of the most seismically active regions worldwide. To date, the paleoseismic history of many major faults, in terms of recurrence intervals of destructive earthquakes, their magnitude, displacement, and slip rates is poorly understood. Regional crustal extension has produced major horst-graben systems bounded by kilometer-scale normal faults locally in carbonates, along which vertical crustal displacements occurred. In this study, we explore the seismic history of western Anatolia using 36Cl exposure dating through study of well-preserved carbonate normal fault scarps. To accomplish this, 36Cl concentrations in 214 samples from fault plane transects on the Rahmiye and Ören fault scarps were measured and compared with existing 36Cl measurements of 370 samples on five fault scraps in western Anatolia. At least 20 seismic events have been reconstructed over the past 16 kyr. The age correlation of the seismic events implies four phases of high seismic activity in western Anatolia, at around 2, 4, 6, and 8 ka. Slips are modeled ranging between 0.6 to 4.2 m per seismic event, but are probably the result of clustered earthquakes of maximum magnitude 6.5 to 7.1. While the average slip rates have values of 0.3 to 1.9 mm/yr, incremental slip rates of the faults range greater than 0.1 to 2.2 mm/yr, showing more activity mostly through late Holocene. Our finding reveals high capability of cosmogenic 36Cl dating to explore seismic behavior of active faults beyond the existing earthquake records.

Hydrological drought characterization based on GNSS imaging of vertical crustal deformation across the contiguous United States

Continuous Global Navigation Satellite System (GNSS) measurements allow us to track subtle elastic crustal deformation in the response to hydrological mass variations and provide an additional tool to independently characterize hydrological extremes (e.g., droughts and floods). In this study, we develop a time-varying GNSS imaging strategy that depends on the principal component analysis of GNSS-sensed vertical crustal displacement (VCD) in 2006–2020 and the monthly images of hydrology-induced deformation are generated for drought characterization across the contiguous United States. The first 12 principal components are selected in our time-varying imaging system, which account for 85% of the data variance. Considering that surface water loads are inversely correlated with the induced elastic vertical motions, we reverse the signs of the GNSS-imaged time series in all grids in subsequent studies (referred to as negative VCD (NVCD)). The GNSS-NVCD data generally correlate well with the water estimates from the Gravity Recovery and Climate Experiment (GRACE) and North American Land Data Assimilation System (NLDAS). Using the GNSS-imaged gridded NVCD products, we produce a GNSS-based drought severity index (GNSS-DSI) based on the climatological methodology, which is implemented by standardizing the GNSS NVCD anomalies that deviate from climatological normal. In most regions, strong linear correlations are accessible for GNSS-DSI relative to GRACE-DSI and the self-calibrating Palmer Drought Severity Index (scPDSI). The new drought monitoring tool, which is based solely on GNSS-measured vertical positions, is used for hydrological drought characterization (onset, end, duration, magnitude, intensity, and recovery); it succeeds in identifying well-documented historical droughts from the US drought monitor (USDM). Our study presents a new drought characterization framework using solely GNSS-measured hydrological loading displacements from a dense GNSS network, which has great potential to strengthen operational drought monitoring and assessment.

Co-Seismic Ionospheric Disturbances Following the 2016 West Sumatra and 2018 Palu Earthquakes from GPS and GLONASS Measurements

The study of ionospheric disturbances associated with the two large strike-slip earthquakes in Indonesia was investigated, which are West Sumatra on 2 March 2016 (Mw = 7.8), and Palu on 28 September 2018 (Mw = 7.5). The anomalies were observed by measuring co-seismic ionospheric disturbances (CIDs) using the Global Navigation Satellite System (GNSS). The results show positive and negative CIDs polarization changes for the 2016 West Sumatra earthquake, depending on the position of the satellite line-of-sight, while the 2018 Palu earthquake shows negative changes only due to differences in co-seismic vertical crustal displacement. The 2016 West Sumatra earthquake caused uplift and subsidence, while the 2018 Palu earthquake was dominated by subsidence. TEC anomalies occurred about 10 to 15 min after the two earthquakes with amplitude of 2.9 TECU and 0.4 TECU, respectively. The TEC anomaly amplitude was also affected by the magnitude of the earthquake moment. The disturbance signal propagated with a velocity of ~1–1.72 km s−1 for the 2016 West Sumatra earthquake and ~0.97–1.08 km s−1 for the 2018 Palu mainshock earthquake, which are consistent with acoustic waves. The wave also caused an oscillation signal of ∼4 mHz, and their azimuthal asymmetry of propagation confirmed the phenomena in the Southern Hemisphere. The CID signal could be identified at a distance of around 400–1500 km from the epicenter in the southwestern direction.

Effects and Correction of Atmospheric Pressure Loading Deformation on GNSS Reference Stations in Mainland China

Atmospheric pressure loading (APL) deformation is one component of nontectonic deformation for Global Navigation Satellite System (GNSS) time series and is a kind of deformation response caused by a redistribution of atmospheric pressure. In this paper, we present an atmospheric data processing strategy to compute the APL based on a spherical harmonic expansion of the global atmosphere pressure changes. We also provide a sample model to describe the relativity between the global atmosphere pressure changes and APL vertical deformation. The results show that the variation of air mass has a major impact on the north-eastern area of East China, the eastern area of North China, and Northeast China, and the vertical crustal displacement caused by the atmosphere changes in these regions can reach about 20 mm. The correction of APL for vertical time series of GNSS reference stations in different regions indicates that the arid area of the Northwest China, Northeast China, Central China, and North China are greatly affected by APL. While for the station located in Sichuan-Yunnan region, the amplitude and period change are small after correction of APL for vertical time series of GNSS reference stations, which reveals that the area is seriously affected by tectonic movement and water migration loading. The correlation between atmospheric pressure changes and crustal deformation is analyzed, which shows that APL has a serious impact on the north-eastern area of North China, the Northeast China, and the eastern area of Central China when the variations in atmospheric pressure in mainland China are the same. The research results of this paper will provide some reference value for the study of crustal structural deformation and the establishment of geodetic datum.

Determining seasonal displacements of Earth\u2019s crust in South America using observations from space-borne geodetic sensors and surface-loading models

There are small pieces of evidence, suggesting that South America’s hydrological cycle is changing, which impacts its water availability and, consequently, the Earth’s surface due to its elastic response to the surface mass loading/unloading. Therefore, we analyzed 3 to 15 years of vertical crustal displacements (VCDs) due to mass loadings using 292 Global Positioning System (GPS) stations in South America, which are essential for studies related to tectonic phenomena, for example. Thus, we investigated whether the intra-annual variabilities of the displacements could be reduced using modeled VCDs and inverted displacements from Gravity Recovery and Climate Experiment (GRACE) harmonic solutions (Release 06). The modeled VCDs come from the combination of nontidal atmospheric and ocean loadings with the hydrological loadings from the land-surface model (GLDAS) and reanalysis (MERRA). We found that the highest amplitudes of VCDs of the annual signals are concentrated mainly over the Amazon Rainforest and Brazilian Highlands. However, the results also show different behavior throughout other physiographic provinces of South America, which shows low water capabilities as “sensed” by GRACE and described by the GLDAS and MERRA models. Accordingly, when we disregard the stations over the Andes Mountains and Patagonia in the analysis, the highest reduction in the variability of GPS-observed VCDs is achieved while using GRACE (79% of the sites), MERRA (75% of the sites), and GLDAS (74% of the sites). For these stations, the amplitudes (and phases) of the annual signals depicted by the geodetic sensors generally agree, while those from GLDAS and MERRA explain only approximately 50% of the deformation. However, in the southwest region of South America (between the latitude bands of − 40° to − 30°), GPS annual signals, which reached up to 11 mm, are much larger than those from GRACE and the models due to the existence of lakes that are not resolved in global analysis. These inconsistencies between GPS-observed VCDs and those derived from GRACE and the other models require further investigation, specifically for Chile.

Akaike's Bayesian Information Criterion for the Joint Inversion of Terrestrial Water Storage Using GPS Vertical Displacements, GRACE and GLDAS in Southwest China.

Global navigation satellite systems (GNSS) techniques, such as GPS, can be used to accurately record vertical crustal movements induced by seasonal terrestrial water storage (TWS) variations. Conversely, the TWS data could be inverted from GPS-observed vertical displacement based on the well-known elastic loading theory through the Tikhonov regularization (TR) or the Helmert variance component estimation (HVCE). To complement a potential non-uniform spatial distribution of GPS sites and to improve the quality of inversion procedure, herein we proposed in this study a novel approach for the TWS inversion by jointly supplementing GPS vertical crustal displacements with minimum usage of external TWS-derived displacements serving as pseudo GPS sites, such as from satellite gravimetry (e.g., Gravity Recovery and Climate Experiment, GRACE) or from hydrological models (e.g., Global Land Data Assimilation System, GLDAS), to constrain the inversion. In addition, Akaike’s Bayesian Information Criterion (ABIC) was employed during the inversion, while comparing with TR and HVCE to demonstrate the feasibility of our approach. Despite the deterioration of the model fitness, our results revealed that the introduction of GRACE or GLDAS data as constraints during the joint inversion effectively reduced the uncertainty and bias by 42% and 41% on average, respectively, with significant improvements in the spatial boundary of our study area. In general, the ABIC with GRACE or GLDAS data constraints displayed an optimal performance in terms of model fitness and inversion performance, compared to those of other GPS-inferred TWS methodologies reported in published studies.

An Improved GPS-Inferred Seasonal Terrestrial Water Storage Using Terrain-Corrected Vertical Crustal Displacements Constrained by GRACE

Based on a geophysical model for elastic loading, the application potential of Global Positioning System (GPS) vertical crustal displacements for inverting terrestrial water storage has been demonstrated using the Tikhonov regularization and the Helmert variance component estimation since 2014. However, the GPS-inferred terrestrial water storage has larger resulting amplitudes than those inferred from satellite gravimetry (i.e., Gravity Recovery and Climate Experiment (GRACE)) and those simulated from hydrological models (e.g., Global Land Data Assimilation System (GLDAS)). We speculate that the enlarged amplitudes should be partly due to irregularly distributed GPS stations and the neglect of the terrain effect. Within southwest China, covering part of southeastern Tibet as a study region, a novel GPS-inferred terrestrial water storage approach is proposed via terrain-corrected GPS and supplementary vertical crustal displacements inferred from GRACE, serving as "virtual GPS stations" for constraining the inversion. Compared to the Tikhonov regularization and Helmert variance component estimation, we employ Akaike’s Bayesian Information Criterion as an inverse method to prove the effectiveness of our solution. Our results indicate that the combined application of the terrain-corrected GPS vertical crustal displacements and supplementary GRACE spatial data constraints improves the inversion accuracy of the GPS-inferred terrestrial water storage from the Helmert variance component estimation, Tikhonov regularization, and Akaike’s Bayesian Information Criterion, by 55%, 33%, and 41%, respectively, when compared to that of the GLDAS-modeled terrestrial water storage. The solution inverted with Akaike’s Bayesian Information Criterion exhibits more stability regardless of the constraint conditions, when compared to those of other inferred solutions. The best Akaike’s Bayesian Information Criterion inverted solution agrees well with the GLDAS-modeled one, with a root-mean-square error (RMSE) of 3.75 cm, equivalent to a 15.6% relative error, when compared to 39.4% obtained in previous studies. The remaining discrepancy might be due to the difference between GPS and GRACE in sensing different surface water storage components, the remaining effect of the water storage changes in rivers and reservoirs, and the internal error in the geophysical model for elastic loading.

Seafloor Crustal Deformation on Ocean Bottom Pressure Records With Nontidal Variability Corrections: Application to Hikurangi Margin, New Zealand

AbstractOcean bottom pressure (OBP) observations are a powerful tool for determining vertical crustal displacements, especially due to earthquakes and slow earthquakes, with centimeter‐level resolution. In these studies, removal of oceanographic noise (tens of centimeters) is required to identify centimeter‐level crustal deformation. We undertake barotropic modeling to remove oceanographic signals from data from an OBP array deployed offshore New Zealand in 2014/2015. We show that removing the nontidal component calculated from a barotropic ocean model reduces the variance in the data by about 66% and provides a feasible means to resolve pressure changes due to crustal deformation during the slow slip events. We also discuss the vertical displacements from slow slip events that occurred in late September to mid‐October 2014, and we outline our procedure for processing OBP data.

Characterizing the Seasonal Crustal Motion in Tianshan Area Using GPS, GRACE and Surface Loading Models

Complex tectonic and non-tectonic movements exist in the Tianshan area. However, we have not acquired good knowledge of such movements yet. In this study, we combine Global Positioning System (GPS), the Gravity Recovery and Climate Experiment (GRACE) and Surface Loading Models (SLMs) data to study the seasonal vertical crustal displacements in the Tianshan area. The results show that all three datasets exhibit significant annual variations at all 26 local GPS stations. Correlation coefficients higher than 0.8 between the GRACE and GPS data were observed at 85% of the stations, and it became 92% when comparing GPS and SLMs. The Weighted Root Mean Squares (WRMS) reductions were 41% and 47% after removing the annual displacements of GRACE and SLMs from the GPS time series, respectively. The consistency between the GPS and SLMs data was higher than that between the GPS and GRACE data, which is mainly due to the dominant position of atmospheric loading in the study area. For the abnormal station XJYN (43°N, 81°E), the GPS time series showed an abnormal uplift from early 2013 to early 2015, but this not shown in the GRACE and SLMs results. We attribute this discrepancy to groundwater variations, which are not resolvable by GRACE and SLMs for small-scale regions.

Annual variations of monsoon and drought detected by GPS: A case study in Yunnan, China

The Global Positioning System (GPS) records monsoonal precipitable water vapor (PWV) and vertical crustal displacement (VCD) due to hydrological loading, and can thus be applied jointly to diagnose meteorological and hydrological droughts. We have analyzed the PWV and VCD observations during 2007.0–2015.0 at 26 continuous GPS stations located in Yunnan province, China. We also obtained equivalent water height (EWH) derived from the Gravity Recovery And Climate Experiment (GRACE) and precipitation at these stations with the same period. Then, we quantified the annual variations of PWV, precipitation, EWH and VCD and provided empirical relationships between them. We found that GPS-derived PWV and VCD (positive means downward movement) are in phase with precipitation and GRACE-derived EWH, respectively. The annual signals of VCD and PWV show linearly correlated amplitudes and a two-month phase lag. Furthermore, the results indicate that PWV and VCD anomalies can also be used to explore drought, such as the heavy drought during winter/spring 2010. Our analysis results verify the capability of GPS to monitor monsoon variations and drought in Yunnan and show that a more comprehensive understanding of the characteristics of regional monsoon and drought can be achieved by integrating GPS-derived PWV and VCD with precipitation and GRACE-derived EWH.

Seasonal low-degree changes in terrestrial water mass load from global GNSS measurements

Large-scale mass redistribution in the terrestrial water storage (TWS) leads to changes in the low-degree spherical harmonic coefficients of the Earth’s surface mass density field. Studying these low-degree fluctuations is an important task that contributes to our understanding of continental hydrology. In this study, we use global GNSS measurements of vertical and horizontal crustal displacements that we correct for atmospheric and oceanic effects, and use a set of modified basis functions similar to Clarke et al. (Geophys J Int 171:1–10, 2007) to perform an inversion of the corrected measurements in order to recover changes in the coefficients of degree-0 (hydrological mass change), degree-1 (centre of mass shift) and degree-2 (flattening of the Earth) caused by variations in the TWS over the period January 2003–January 2015. We infer from the GNSS-derived degree-0 estimate an annual variation in total continental water mass with an amplitude of $$(3.49 \pm 0.19) \times 10^{3}$$ Gt and a phase of $$70^{\circ } \pm 3^{\circ }$$ (implying a peak in early March), in excellent agreement with corresponding values derived from the Global Land Data Assimilation System (GLDAS) water storage model that amount to $$(3.39 \pm 0.10) \times 10^{3}$$ Gt and $$71^{\circ } \pm 2^{\circ }$$ , respectively. The degree-1 coefficients we recover from GNSS predict annual geocentre motion (i.e. the offset change between the centre of common mass and the centre of figure) caused by changes in TWS with amplitudes of $$0.69 \pm 0.07$$ mm for GX, $$1.31 \pm 0.08$$ mm for GY and $$2.60 \pm 0.13$$ mm for GZ. These values agree with GLDAS and estimates obtained from the combination of GRACE and the output of an ocean model using the approach of Swenson et al. (J Geophys Res 113(B8), 2008) at the level of about 0.5, 0.3 and 0.9 mm for GX, GY and GZ, respectively. Corresponding degree-1 coefficients from SLR, however, generally show higher variability and predict larger amplitudes for GX and GZ. The results we obtain for the degree-2 coefficients from GNSS are slightly mixed, and the level of agreement with the other sources heavily depends on the individual coefficient being investigated. The best agreement is observed for $$T_{20}^C$$ and $$T_{22}^S$$ , which contain the most prominent annual signals among the degree-2 coefficients, with amplitudes amounting to $$(5.47 \pm 0.44) \times 10^{-3}$$ and $$(4.52 \pm 0.31) \times 10^{-3}$$ m of equivalent water height (EWH), respectively, as inferred from GNSS. Corresponding agreement with values from SLR and GRACE is at the level of or better than $$0.4 \times 10^{-3}$$ and $$0.9 \times 10^{-3}$$ m of EWH for $$T_{20}^C$$ and $$T_{22}^S$$ , respectively, while for both coefficients, GLDAS predicts smaller amplitudes. Somewhat lower agreement is obtained for the order-1 coefficients, $$T_{21}^C$$ and $$T_{21}^S$$ , while our GNSS inversion seems unable to reliably recover $$T_{22}^C$$ . For all the coefficients we consider, the GNSS-derived estimates from the modified inversion approach are more consistent with the solutions from the other sources than corresponding estimates obtained from an unconstrained standard inversion.

Erratum to: The Great Tohoku-Oki Earthquake and Tsunami of March 11, 2011 in Japan: A Critical Review and Evaluation of the Tsunami Source Mechanism

The great Tohoku-Oki earthquake of March 11, 2011 generated a very destructive and anomalously high tsunami. To understand its source mechanism, an examination was undertaken of the seismotectonics of the region and of the earthquake’s focal mechanism, energy release, rupture patterns and spatial and temporal sequencing and clustering of major aftershocks. It was determined that the great tsunami resulted from a combination of crustal deformations of the ocean floor due to up-thrust tectonic motions, augmented by additional uplift due to the quake’s slow and long rupturing process, as well as to large coseismic lateral movements which compressed and deformed the compacted sediments along the accretionary prism of the overriding plane. The deformation occurred randomly and non-uniformly along parallel normal faults and along oblique, en-echelon faults to the earthquake’s overall rupture direction—the latter failing in a sequential bookshelf manner with variable slip angles. As the 1992 Nicaragua and the 2004 Sumatra earthquakes demonstrated, such bookshelf failures of sedimentary layers could contribute to anomalously high tsunamis. As with the 1896 tsunami, additional ocean floor deformation and uplift of the sediments was responsible for the higher waves generated by the 2011 earthquake. The efficiency of tsunami generation was greater along the shallow eastern segment of the fault off the Miyagi Prefecture where most of the energy release of the earthquake and the deformations occurred, while the segment off the Ibaraki Prefecture—where the rupture process was rapid—released less seismic energy, resulted in less compaction and deformation of sedimentary layers and thus to a tsunami of lesser offshore height. The greater tsunamigenic efficiency of the 2011 earthquake and high degree of the tsunami’s destructiveness along Honshu’s coastlines resulted from vertical crustal displacements of more than 10 m due to up-thrust faulting and from lateral compression and folding of sedimentary layers in an east-southeast direction which contributed additional uplift estimated at about 7 m—mainly along the leading segment of the accretionary prism of the overriding tectonic plate.

COMPARISON OF COSEISMIC IONOSPHERIC DISTURBANCE WAVEFORMS REVISITED: STRIKE-SLIP, NORMAL, AND REVERSE FAULT EARTHQUAKE

Using Total Electron Content (TEC) measurements with Global Positioning System we studied ionospheric responses to three large earthquakes with difference focal mechanism that occurred in the Sumatra Andaman 26 December 2004, North off Sumatra 11 April 2012, and North Japan 7 December 2012. These earthquakes have different focal mechanisms, i.e. high-angle reverse, strike-slip, and normal faulting, respectively. TEC responses to the Sumatra Andaman 2004 and north Japan 2012 events initiated with positive changes. On the other hand, the initial TEC changes in the Sumatra 2012 earthquake showed both positive and negative polarities depending on the azimuth around the focal area. Such a variety may reflect differences in coseismic vertical crustal displacements, which are dominated by uplift and subsidence in the Sumatra 2012 event. This phenomena has same characteristic with 1994 Kuril Arch earthquake. There are three different propagation velocity in the Sumatra 2012 earthquake, within the first 300 km until 430 km, the CID propagation velocity was ~3 km/s, which is equal to the secod sound speed at the height of the ionospheric F-layer. Starting from 380 km until 750 km out from the epicenter, the disturbance seems to divide into two separate perturbations, with each propagating at a different velocity, about 1 km/s for the one and about 0.4 m/s for the other. The apparent velocity in the Sumatra Andaman 2004 and Japan 2012 propagated ~ 1 km/s and ~ 0.3 km/s, consistent with the sound speed at the ionospheric F layer height and internal gravity wave respectively. Resonant oscillation of TEC with a frequency of ~ 3.7 mHZ and ~4.4 mHz have been found in the Sumatra 2012 and Sumatra Andaman 2004 events. Those earthquakes, which occurred during a period of quiet geomagnetic activity, also showed clear preseismic TEC anomalies similar to those before the 2011 Tohoku-Oki and 2007 Bengkulu earthquake. The positive anomalies started 30-60 minutes before the earthquake to the north of the fault region. However, preseismic ionospheric anomalies of the 2012 Japan earthquake could not be observed because moment magnitude of the earthquake is smaller than Mw 8.2

Vertical crustal displacement due to interseismic deformation along the San Andreas fault: Constraints from tide gauges

Interseismic motion along complex strike-slip fault systems such as the San Andreas Fault System (SAFS) can produce vertical velocities that are ~10 times smaller than horizontal velocities, caused by along-strike variations in fault orientation and locking depth. Tide gauge stations provide a long (50–100 year) recording history of sea level change due to several oceanographic and geologic processes, including vertical earthquake cycle deformation. Here we compare relative sea level displacements with predictions from a 3-D elastic/viscoelastic earthquake cycle model of the SAFS. We find that models with lithospheric structure reflecting a thick elastic plate (>50 km) and moderate viscosities produce vertical motions in surprisingly good agreement with the relative tide gauge uplift rates. These results suggest that sea level variations along the California coastline contain a small but identifiable tectonic signal reflecting the flexure of the elastic plate caused by bending moments applied at the ends of locked faults.