We present a comprehensive review of the status and changes in glacier length (since the 1850s), area and mass (since the 1960s) along the Himalayan-Karakoram (HK) region and their climate-change ...context. A quantitative reliability classification of the field-based mass-balance series is developed. Glaciological mass balances agree better with remotely sensed balances when we make an objective, systematic exclusion of likely flawed mass-balance series. The Himalayan mean glaciological mass budget was similar to the global average until 2000, and likely less negative after 2000. Mass wastage in the Himalaya resulted in increasing debris cover, the growth of glacial lakes and possibly decreasing ice velocities. Geodetic measurements indicate nearly balanced mass budgets for Karakoram glaciers since the 1970s, consistent with the unchanged extent of supraglacial debris-cover. Himalayan glaciers seem to be sensitive to precipitation partly through the albedo feedback on the short-wave radiation balance. Melt contributions from HK glaciers should increase until 2050 and then decrease, though a wide range of present-day area and volume estimates propagates large uncertainties in the future runoff. This review reflects an increasing understanding of HK glaciers and highlights the remaining challenges.
New satellite missions (e.g., the European Space Agency's Sentinel‐1 constellation), advances in data downlinking, and rapid product generation now provide us with the ability to access ...space‐geodetic data within hours of their acquisition. To truly take advantage of this opportunity, we need to be able to interpret geodetic data in a prompt and robust manner. Here we present a Bayesian approach for the inversion of multiple geodetic data sets that allows a rapid characterization of posterior probability density functions (PDFs) of source model parameters. The inversion algorithm efficiently samples posterior PDFs through a Markov chain Monte Carlo method, incorporating the Metropolis‐Hastings algorithm, with automatic step size selection. We apply our approach to synthetic geodetic data simulating deformation of magmatic origin and demonstrate its ability to retrieve known source parameters. We also apply the inversion algorithm to interferometric synthetic aperture radar data measuring co‐seismic displacements for a thrust‐faulting earthquake (2015 Mw 6.4 Pishan earthquake, China) and retrieve optimal source parameters and associated uncertainties. Given its robustness and rapidity in estimating deformation source parameters and uncertainties, our Bayesian framework is capable of taking advantage of real‐time geodetic measurements. Thus, our approach can be applied to geodetic data to study magmatic, tectonic, and other geophysical processes, especially in rapid‐response operational settings (e.g., volcano observatories). Our algorithm is fully implemented in a MATLAB®‐based software package (Geodetic Bayesian Inversion Software) that we make freely available to the scientific community.
Key Points
We present a Bayesian approach for the inversion of geodetic data and demonstrate successful applications to synthetic and real data
Our approach allows rapid estimates of source parameters and uncertainties and is well suited for rapid‐response and operational settings
We have implemented our approach in a MATLAB®‐based software package (GBIS) that is made freely available to the scientific community
The present study elucidates velocity of the Indian plate from 2013 to 2016 with the help of six continuously operating permanent Global Positioning System (GPS) stations and tracks the crustal ...motion and direction directly by means of space-based geodetic measurements. The GPS derived velocity estimates were computed with respect to 2008 International Terrestrial Reference Frame (ITRF 08) and carried out almost all along the arc in the Indian Himalayan Region (IHR). The velocity vectors indicate that the Indian plate is moving towards the NE direction (average velocity of 46.95 ± 0.23 mm/yr) with higher movement towards the eastward direction (36.11 ± 0.17 mm/yr) compared to the northward direction (29.02 ± 0.16 mm/yr). Variations in the plate motion between IISC and permanent GPS stations suggest that presently, the convergence rate is about 8.06 ± 0.28 mm/yr and 5.71 ± 0.17 mm/yr for Higher Himalaya and Lesser Himalaya respectively. In addition, the deformation rate was also calculated on the basis of baseline shortening between IGS stations (IISC and LHAZ) and permanent GPS stations. The results suggest that the deformation is about 11.68 ± 1.32 mm/yr above the Main Central Thrust (MCT) and 6.74 ± 1.20 mm/yr above the Main Boundary Thrust (MBT) with respect to the Indian plate (IISC), while it is 20.60 ± 1.76 mm/yr above the MCT and 11.42 ± 1.21 mm/yr above the MBT with respect to Eurasian plate (LHAZ). The strain rate through GPS measurement reveals that the maximum strain is accumulated in the central part of the Himalaya between the MBT and MCT, indicating vulnerability of the central Indian Himalaya for future earthquakes.
Geodetic and topographic works determine the necessary information base and of major importance in the design and management of underground construction works (mining, hydrotechnics, roads, etc.). ...The efficiency and safety of these investments with special financial implications depend on their quality. In this context, the geodetic orientation of the underground topographic works was the main and permanent subject of study and analysis on which this scientific paper refers.
The detection of preslip, occurring hours to days before a large earthquake, using geodetic measurements has been a major focus in earthquake prediction research. A recent study claims to have ...detected a preseismic signal interpreted as accelerating slip near the hypocenter of the 2011 great Tohoku‐oki earthquake, starting approximately 2 hr before the mainshock. This claim is based on a stacking procedure using GNSS (Global Navigation Satellite System) data. However, a follow‐up study demonstrated that the signal disappeared when specific GNSS noise was corrected. Here we utilize tiltmeter records, independent on GNSS, to check whether the claimed preseismic signal is detected using a similar stacking procedure. Our results show no acceleration‐like deformation from 2 hr before the mainshock. This indicates that no precursory slip exceeded the noise level of the tilt data, and if any preslip occurred, it was less than 5.0 × 1018 Nm in seismic moment.
Plain Language Summary
The ability to detect large earthquakes before they occur would be invaluable for mitigating damage. Researchers have been searching for precursory signals in crustal deformation data, believing that if precursory slip (fault movement before a major earthquake) is large enough, it could be detected by GNSS or tiltmeters, enabling earthquake prediction. The 2011 Tohoku‐oki earthquake provided a valuable opportunity to study this phenomenon. Extensive data was collected, but previous studies found no significant pre‐earthquake signals on timescales of hours to days. A recent GNSS study claimed an acceleration‐like change 2 hr before the main shock, but another study using the same data disputed this. While reanalysis using the same GNSS data is important, it is also susceptible to the influence of the same noise sources. To avoid this, this study analyzed tiltmeter data, finding no evidence for the precursory deformation suggested earlier. This result indicates no significant precursory slip before the Tohoku‐oki earthquake that causes deformation larger than a noise level of the tiltmeter data. This result can provide constraints on the magnitude of the precursory slip immediately before the mainshock.
Key Points
Tiltmeter records are used to determine whether a preseismic signal of the 2011 great Tohoku‐oki earthquake is detected
No acceleration‐like tilt deformation from about 2 hr before the mainshock is recorded
An upper bound on the size of the preslip immediately before the mainshock can be estimated from the noise level of the observation data
The accuracy of ionospheric models estimated by ground‐based multiple global navigation satellite system ionospheric data over regions with sparse tracking stations is not ideal. To improve the ...accuracy of the estimated ionospheric model, different types of ionospheric data with different combinations were employed for previous studies. However, the ionospheric observational ranges for different types of ionospheric data are not the same. In this study, the accuracy of ionospheric maps generated by ground‐based ionospheric data (ground‐based strategy) and ground‐based ionospheric data combined with data provided by other geodetic measurements normalized by the single‐layer normalization method (multi‐source strategy) were studied. The results showed that the main differences between the ionospheric models estimated by the two strategies occur for data taken over the ocean, which mainly range from −1 to 0 total electron content unit (TECU). When assessed using Jason‐3 vertical total electron content data, the mean root mean square (RMS) value of the ionospheric model estimated by the multi‐source strategy was 5.03 TECU, which is approximately 15% smaller than that estimated by the ground‐based strategy. The maximum reduction in results using the multisource strategy was approximately 25% over different latitudes compared with that of the ground‐based strategy. Furthermore, the self‐consistency evaluation method was employed for evaluation. The results showed that the RMS of the ionospheric model estimated by the multi‐source strategy was 2.41 TECU, which is 3.60% better than that of the ground‐based strategy. The maximum reduction was 15% on different days.
Key Points
The single‐layer normalization method is employed to make multi‐source data have the same observational range compared with those of ground‐based global navigation satellite system data
The distribution of multi‐source data has better coverage, especially over the oceanic region
The main differences between the ionospheric models estimated by the ground‐based strategy and the multi‐source strategy occur over the ocean
Oblique convergence across the northern Qilian Shan is accommodated by sub‐parallel strike‐slip and thrust faults that ruptured simultaneously in the Mw 8 Gulang earthquake in 1927. We investigate ...the kinematics of fault loading in the northern Qilian Shan and provide insights into the conditions necessary for generating multi‐fault earthquakes. We perform Bayesian inversions for the geometry and creep rate on the fault network. We infer that all of the thrust faults are locked north of the Qilian‐Haiyuan strike‐slip fault and are accumulating elastic strain. Multi‐fault earthquakes may occurr in this fault system because the faults are simultaneously loaded by the same source of deformation and are linked together by locked fault segments. The interseismic velocity field alone can not contain the location or activity of individual faults visible in the geomorphology, therefore the short‐term geodetic measurements may not reliably indicate the long‐term behavior of the fault system.
Plain Language Summary
This study aims to understand the earthquake hazard in the northern Qilian region of China. We use measurements of ground deformation between earthquakes to infer how the faults are being loaded in the region. We find that the ground deformation can be explained by a simple model with a single, slowly creeping fault at depth that loads all of the overlying faults. Large earthquakes that were caused by slip on many different faults at the same time have occurred in this region before. We suggest these so‐called “multi‐fault” earthquakes may occur because all of the faults are being simultaneously loaded by the same source of stress.
Key Points
Oblique convergence in the northern Qilian Shan is accommodated by sub‐parallel thrust and strike‐slip faulting
The short‐term geodetic measurements do not constrain the thrust fault kinematics in the northern Qilian Shan over geological timescales
Multi‐fault earthquakes may be common in the region as all of the shallow thrust faults are linked together by locked fault segments
We demonstrate the feasibility of detecting very weak deformation in the shallow crust with high temporal resolution by monitoring the relative changes in seismic wave velocity (dv/v) using dense ...arrays of seismometers. We show that the dv/v variations are consistent between independent measurements from two seismic arrays. Dominant peaks in the observed dv/v spectrum suggest that tides and temperature changes are the major causes of daily and subdaily velocity changes, in accordance with theoretical strain modeling. Our analysis illustrates that dv/v perturbations of the order of 10−4, corresponding to crustal strain changes of the order of 10−8, can be measured from ambient seismic noise with a temporal resolution of 1 hr. This represents a low‐cost technique for high precision and high time‐resolution monitoring of crustal deformation that is complementary to existing geodetic measurements and is instrumental in both the detection and understanding of low‐amplitude precursory processes of natural catastrophic events.
Plain Language Summary
Theoretical and laboratory studies have shown that the onset of earthquakes, landslides, and volcanic eruptions is often preceded by a so‐called initiation phase. Detecting such a precursory phenomenon will help in the prediction, early warning, or assessment of catastrophic geological events. The time scale and amplitude of these precursory evolutions are not well known, however, and their detection and characterization require monitoring techniques with both high precision and high temporal resolution. We present here an approach to monitor the elastic properties of crustal rocks using continuous recordings of ambient seismic noise by networks of dense autonomous sensors. We show that this technique allows the monitoring at a temporal resolution of 1 hr for crustal strain variations of the order of 10−8, namely, the deformation associated with tides. This technique can be used in concert with existing geodetic techniques for understanding and detecting transient crustal deformation.
Key Points
We observe daily and subdaily perturbations of seismic velocity associated with tides and solar heating using ambient seismic noise
This demonstrates that crustal strain changes of the order of 10−8 can be monitored with a time resolution of 1 hr by dense seismic arrays
Passive observations of seismic velocity changes are complementary to surface measurements and theoretical modeling of crustal deformation
The February 2023 Turkey‐Syria Earthquake doublet ruptured multiple segments of the East Anatolian Fault (EAF) Zone. Dominating seismicity focal mechanism shifted dramatically from strike‐slip to ...normal‐faulting after the doublet. To better understand this shift, here we derived a comprehensive 3D co‐seismic displacement field and performed the stress analysis. Abundant space geodetic data were used to generate high‐resolution 3D surface displacement, which provide tight constraints on fault geometry, slip distribution and stress field. Together with stress inversion from aftershock focal mechanisms, we show that the principal stress direction rotation in the region with the most normal‐faulting aftershocks is the staggering 29°. The induced heterogenous stress may explain the shift of the dominant focal mechanism toward normal faulting. We suggest that the extensional horsetail splay faults, likely formed through geologic time scale related to the releasing bend on the EAF, are the hosts of most of the normal faulting aftershocks.
Plain Language Summary
Sudden dislocation of two sides of a fault, or the rupture of rocks, produces an earthquake. The dislocation direction relative to the fault traces reflects the direction of stress that are responsible for the earthquake. When dislocation direction is parallel to the fault strike, the earthquake is termed as strike‐slip type, and termed as normal‐faulting type when they are perpendicular. A remarkable feature for the 2023 Turkey‐Syria Mw7.8 & 7.7 earthquake doublet is that, background seismicity shifted dramatically from strike‐slip to normal type of faulting after the doublet. To unravel the physical process resulted in this feature, we use space geodetic measurements to derive the surface displacements and stress field associated with the doublet. The derived stress field shows a staggering 29° rotation occurred in a horsetail splay fault structure where many normal‐faulting earthquakes happened. The large stress rotation indicates the doublet released considerable stress and may result in a heterogeneous stress field due to the stress change. The combination of the identified horsetail structure and stress rotation can help better explain the occurrence of pervasive normal‐faulting earthquakes.
Key Points
We map the 3D displacements, slip distribution, and stress fields related to the 2023 Turkey‐Syria Earthquake doublet
Dramatic stress rotation occurred after the Earthquake doublet, up to 29°
Stress rotation and horsetail splay fault structure are potentially responsible for normal‐faulting aftershocks
The European Space Agency (ESA) is preparing a satellite mission called GENESIS to be launched in 2027 as part of the FutureNAV program. GENESIS co-locates, for the first time, all four space ...geodetic techniques on one satellite platform. The main objectives of the mission are the realization of the International Terrestrial Reference Frames and the mitigation of biases in geodetic measurements; however, GENESIS will remarkably contribute to the determination of the geodetic parameters. The precise GENESIS orbits will be determined through satellite-to-satellite tracking, employing two GNSS antennas to observe GPS and Galileo satellites in both nadir and zenith directions. In this research, we show results from simulations of GENESIS and Galileo-like constellations with joint orbit and clock determination. We assess the orbit quality of GENESIS based on nadir-only, zenith-only, and combined nadir–zenith GNSS observations. The results prove that GENESIS and Galileo joint orbit and clock determination substantially improves Galileo orbits, satellite clocks, and even ground-based clocks of GNSS receivers tracking Galileo satellites. Although zenith and nadir GNSS antennas favor different orbital planes in terms of the number of collected observations, the mean results for each Galileo orbital plane are improved to a similar extent. The 3D orbit error of Galileo is improved from 27 mm (Galileo-only), 23 mm (Galileo + zenith), 16 mm (Galileo + nadir), to 14 mm (Galileo + zenith + nadir GENESIS observations), i.e., almost by a factor of two in the joint GENESIS + Galileo orbit and clock solutions.
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