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The increasing density of geodetic measurements makes it possible to map surface strain rate in many zones of active tectonics with unprecedented spatial resolution. Here we show that the strain tensor rate calculated from GPS in the India–Asia collision zone represents well the strain released in earthquakes. This means that geodetic data in the India–Asia collision zone region can be extrapolated back in time to estimate strain buildup on active faults, or the kinematics of continental deformation. We infer that the geodetic strain rates can be assumed stationary through time on the timescale needed to build up the elastic strain released by larger earthquakes, and that they can be used to estimate the probability of triggering earthquakes. We show that the background seismicity rate correlates with the geodetic strain rate. A good fit is obtained assuming a linear relationship (⁠|$\dot{N} = \lambda \ \cdot \dot{\epsilon }$|⁠ , where |$\dot{N}$| is the density of the rate of M w ≥ 4 earthquakes, |$\dot{\epsilon }$| is strain rate and λ = 2.5 ± 0.1 × 10−3 m−2), as would be expected from a standard Coulomb failure model. However, the fit is significantly better for a non-linear relationship (⁠|$\dot{N} = \gamma _1 \cdot \dot{\epsilon }^{\gamma _2}$| with γ1 = 2.5 ± 0.6 m−2 and γ 2 = 1.42 ± 0.15). The b -value of the Gutenberg–Richter law, which characterize the magnitude–frequency distribution, is found to be insensitive to the strain rate. In the case of a linear correlation between seismicity and strain rate, the maximum magnitude earthquake, derived from the moment conservation principle, is expected to be independent of the strain rate. By contrast, the non-linear case implies that the maximum magnitude earthquake would be larger in zones of low strain rate. We show that within areas of constant strain rate, earthquakes above M w 4 follow a Poisson distribution in time and and are uniformly distributed in space. These findings provide a framework to estimate the probability of occurrence and magnitude of earthquakes as a function of the geodetic strain rate. We describe how the seismicity models derived from this approach can be used as an input for probabilistic seismic hazard analysis. This method is easy to automatically update, and can be applied in a consistent manner to any continental zone of active tectonics with sufficient geodetic coverage. [ABSTRACT FROM AUTHOR]

The article offers information about the slow earthquakes result from unstable frictional slip. It characterizes the system dynamics using embedding theory and extreme value theory, along with information on the analysis reveals a low-dimensional nonlinear chaotic system rather than a stochastic system.

The accuracy, reliability and best practises of Tiin- quartz thermobarometry (TitaniQ) in greenschist facies rocks have not been established. To address these issues, we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from the Hsüehshan range, Taiwan. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~100-200 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1-10 ppm) relative to detrital porphyroclasts (Ti ~0.1-200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10-20 μm) has a further restricted Ti concentration peaking at 0.8-2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Unlike previously documented examples, Ti concentration in the quartzite is inversely correlated with blue cathodoluminescence. Deformation was associated with a minimum grain boundary diffusivity of Ti on the order of 10-22 m2 s-1. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250-350 °C and 300-410 °C, respectively, with lithostatic pressure of 3- 4 kbar (assuming a geothermal gradient of 25° km-1), and with hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure and these temperatures, the Thomas et al. (2010) calibration yields Ti concentrations within error of concentrations measured by SIMS. If fluid pressure is instead used, predicted temperatures are ~30-40 °C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 °C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted. [ABSTRACT FROM AUTHOR]

The variation of stress on faults is important for our understanding of fault friction and the dynamics of earthquake ruptures. However, we still have little observational constraints on their absolute magnitude, or their variations in space and in time over the seismic cycle. Here we use a new geodetic imaging technique to measure the 3D coseismic slip vectors along the 2019 Ridgecrest surface ruptures and invert them for the coseismic stress state. We find that the coseismic stresses show an eastward rotation that becomes increasingly transtensional from south‐to‐north along the rupture, that matches the known background stress state. We find that the main fault near the Mw 7.1 mainshock hypocenter was critically stressed. Coseismic slip was maximum there and decreased gradually along strike as the fault became less optimally oriented due its curved geometry. The variations of slip and stress along the curved faults are used to infer the static and dynamic fault friction assuming Mohr‐Coulomb failure. We find shear stresses of 4–9 MPa in the shallow crust (∼1.3 km depth) and that fault friction drops from a static, Byerlee‐type, value of 0.61 ± $\pm $ 0.14 to a dynamic value of 0.29 ± $\pm $ 0.04 during seismic slip. These values explain quantitatively the slip variations along a transpressional fault bend. Plain Language Summary: Understanding the orientation and magnitude of stresses within the crust are important because they can affect the location, size and spatial extent of earthquake rupture. However, measuring the absolute magnitude and orientation of stresses as well as the frictional properties of the fault surface (i.e., how strongly the fault resists the applied driving forces) is very difficult. Here we use optical images acquired by satellites to measure how the surface deformed in 3D during the 2019 Ridgecrest event. These 3D measurements allow us to extract the direction of fault slip movement along the entire rupture length which we use to estimate the direction of stresses by assuming the shear stress is parallel to the direction of the observed fault slip motion. We find that the main fault near the mainshock epicenter was the most optimally aligned for failure, which could be one contributing reason for the location of rupture initiation. By deriving a relation between how much a fault slips with how well aligned it is to the stress field we can estimate the absolute magnitude of stresses, the frictional resistance at initial fault sliding (finding a static friction = 0.61) and during sliding (a dynamic friction = 0.29). Key Points: Inverting surface coseismic slip vectors show a variable stress state that matches the background stresses constrained by seismicityFaults at the mainshock epicenter were the most critically stressed; we find slip increases linearly as faults become more optimally alignedWe find absolute stress magnitudes of 8–26 MPa in the upper crust, a static frictional coefficient of 0.61 and a dynamic value of 0.29 [ABSTRACT FROM AUTHOR]

The article presents a study on the accuracy, reliability and best practices of titanium-in-quartz thermobarometry (TitaniQ) in greenschist facies rocks in the Hsüehshan range, Taiwan. The study measured the Ti concentrations in rutile-bearing samples of recrystallized quartzite and vein quartz from Hsüehshan range. The results showed that TitaniQ has the potential to give accurate predicted temperature (PT) information for dynamic recrystallization of quartz and vein emlplacement.

Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving-implying large sand fluxes-or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar. [ABSTRACT FROM AUTHOR]

We report Global Positioning System (GPS) measurements of postseismic deformation following the 2015 Mw7.8 Gorkha (Nepal) earthquake, including previously unpublished data from 13 continuous GPS stations installed in southern Tibet shortly after the earthquake. We use variational Bayesian Independent Component Analysis (vbICA) to extract the signal of postseismic deformation from the GPS time series, revealing a broad displacement field extending >150 km northward from the rupture. Kinematic inversions and dynamic forward models show that these displacements could have been produced solely by afterslip on the Main Himalayan Thrust (MHT) but would require a broad distribution of afterslip extending similarly far north. This would require the constitutive parameter (a − b)σ to decrease northward on the MHT to ≤0.05 MPa (an extreme sensitivity of creep rate to stress change) and seems unlikely in light of the low interseismic coupling and high midcrustal temperatures beneath southern Tibet. We conclude that the northward reach of postseismic deformation more likely results from distributed viscoelastic relaxation, possibly in a midcrustal shear zone extending northward from the seismogenic MHT. Assuming a shear zone 5–20 km thick, we estimate an effective shear‐zone viscosity of ~3·1016–3·1017 Pa·s over the first 1.12 postseismic years. Near‐field deformation can be more plausibly explained by afterslip itself and implies (a − b)σ ~ 0.5–1 MPa, consistent with other afterslip studies. This near‐field afterslip by itself would have re‐increased the Coulomb stress by ≥0.05 MPa over >30% of the Gorkha rupture zone in the first postseismic year, and deformation further north would have compounded this reloading. Key Points: New GPS data show that postseismic deformation of the 2015 Mw7.8 Gorkha (Nepal) earthquake extended far northward into southern TibetKinematic and dynamic models suggest that the northward reach of deformation likely reflects the influence of viscoelastic relaxationAfterslip likely dominated postseismic deformation in the near field, transferring stress back to the (relocked) Gorkha rupture zone [ABSTRACT FROM AUTHOR]

Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum M w=3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013-2014. The geodetic transient lasted ∼6 months and produced a NW-SE trending extension of ∼5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded. [ABSTRACT FROM AUTHOR]

Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015momentmagnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network. We used GPS and interferometric synthetic aperture radar data to model the earthquake rupture as a slip pulse ~20 kilometers in width, ~6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at ~3.3 kilometers per second over ~140 kilometers. The smooth slip onset, indicating a large (~5-meter) slip-weakening distance, caused moderate ground shaking at high frequencies (>1 hertz; peak ground acceleration, ~16%of Earth's gravity) and minimized damage to vernacular dwellings. Whole-basin resonance at a period of 4 to 5 seconds caused the collapse of tall structures, including cultural artifacts. [ABSTRACT FROM AUTHOR]

Abstract: We use 20 years of Synthetic Aperture Radar acquisitions by the ERS and Envisat satellites to investigate the spatial and temporal variations of strain rates along the 35-km long creeping section of the Haiyuan fault, at the north eastern boundary of the Tibetan plateau. We then use the derived displacements to infer the faultʼs frictional properties and discuss the relationship between creep and the seismic behavior of the fault. Located in between a millennial seismic gap and the 1920 M8 surface rupture trace, this section has an average creep rate of , about the interseismic loading rate. The comparison of average surface velocity profiles derived from SAR interferometry across the creeping section reveals a creep rate increase and/or a creep migration to shallower depth between the 1990s and the 2000s. We apply a smoothed time series analysis scheme on Envisat InSAR data to investigate the creep rate variations during the 2004–2009 time period. Our analysis reveals that the creep rate accelerated in 2007, although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude. Both decadal and short term transient behaviors are coeval with the largest earthquakes along the fault segment in recent years. From the precise mapping of the surface fault trace, we use the fault strike variations and the Mohr circle construction to compute the along-strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate. We find that the creep rate scales logarithmically with the friction coefficient, in agreement with the rate-and-state friction law in a rate strengthening regime. The estimated value of indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segmentʼs creep rate and that the recorded micro seismicity is most likely creep-driven. Finally, given the size and frictional properties of the creeping section, we estimate, based on previous models of dynamic rupture simulations, a 0–20% probability for a rupture to break through this section. Together with the geometrical configuration of the Haiyuan fault, these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation. [Copyright &y& Elsevier]

Abstract: Erosion is a fundamental player of the interactions existing between internal geodynamics and climate, in particular through its influence on the carbon dioxide budget. However, long term (>1Ma) erosion rates, estimated indirectly from sediment budget, remain poorly constrained. While some studies suggest that worldwide erosion rates increased at the Plio-Pleistocene climatic transition (~4–2Ma), the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins. In the present study, we estimate erosion rates over the last ~9Ma using in situ produced cosmogenic 10Be concentrations measured in magnetostratigraphically dated continental sediments. We focus on an intracontinental endorheic watershed draining the northern Tianshan in Central Asia, a key region regarding the ongoing debate. While erosion rates between 0.1 and 1mm·yr−1 are derived from most of our record, they reach values as high as ~2.5mm·yr−1 from 2.5 to 1.7Ma. Then, after 1.7Ma, recent and modern erosion rates fell below 1mm·yr−1. This temporary increase is correlated with the onset of Quaternary ice ages and suggests that global climate had a significant and transient impact on erosion. [Copyright &y& Elsevier]

Underthrusting of the Indian lithosphere beneath the Himalayas occurs during the Quaternary period along a gently north-dipping main basal detachment (main Himalayan thrust: MHT), from which the southernmost emergent ramp (main frontal thrust: MFT) branches. Historical seismicity shows that slip on the MHT is frequently accommodated through shallow earthquakes, but shows a seismic gap in western Nepal. This absence of major historical earthquakes in western Nepal can be explained either by an aseismic slip on the MHT or a long-lived elastic strain accumulation. To test these hypotheses, the present-day displacement field has been measured for a GPS network formed of 35 sites. The updated solution presented in this paper combines data from 1995, 1997, 1998 and 2000 measurements. The lack of deformation (less than ) through the outer belt does not fit with a regional aseismic slip along the southern part of MHT. A less than 3 mm yr−1 aseismic slip could nonetheless affect restricted areas of the outer belt. In contrast, a strain accumulation of more than is measured south of the Higher Himalayas, in a zone where an intense microseismicity reflects a stress build-up. It is presumably generated by locking of the aseismic creep that occurs along the MHT beneath the Higher Himalayas and Tibet. The displacement field is simulated by a dual-dislocation model that takes into account the pattern of microseismicity, and particularly a segmentation between central and western Nepal. The best fit between the measured and simulated displacement fields is obtained with 19 mm yr−1 thrust and 0–1 mm yr−1 dextral strike-slip components along a 117°NE dislocation locked to a depth of 20–21 km beneath western Nepal, and 19–20 mm yr−1 thrust and 0–2 mm yr−1 dextral strike-slip components along a 108°NE dislocation locked to a depth of 17–21 km beneath central Nepal. The width of the locked zone between the main frontal thrust and the creeping zone is of the same order, but rather greater, in western Nepal than in central Nepal. Therefore it is expected that earthquakes could occur in western Nepal. [ABSTRACT FROM AUTHOR]

Presents research which observed electric potential variations and radon emanations associated with transient deformation events in the French Alps. Precursors for earthquakes; Fluid mechanisms in crustal deformation; Characteristics of deformation events in 1995; Deformation model in which straining induces fluid overpressure and dynamic flow in cracks; Sensitivity of rock transport properties to deformation.

Deformation of the Earth's surface associated with redistributions of continental water mass explains, to first order, the seasonal signals observed in geodetic position time series. Discriminating these seasonal signals from other sources of deformation in geodetic measurements is essential to isolate tectonic signals and to monitor spatio‐temporal variations in continental water storage. We propose a new methodology to identify and extract these seasonal signals. The approach uses a variational Bayesian Independent Component Analysis (vbICA) to extract the seasonal signals and a gravity‐based deformation model to identify which of these signals are caused by surface loading. We test the procedure on two study areas, the Arabian Peninsula and the Nepal Himalaya, and find that the technique successfully extracts the seasonal signals with one or two independent components, depending on whether the load is stationary or moving. The approach is robust to spatial heterogeneities inherent to geodetic measurements and can help extract systematic errors in geodetic products (e.g., draconitic errors). We also discuss how to handle the degree‐1 deformation field present in the geodetic data set but not captured by the gravity‐based model. Key Points: We propose a procedure to isolate seasonal geodetic signals due to surface loads using a GRACE‐based deformation model and an independent component analysisGNSS and GRACE‐derived displacements yield consistent seasonal time evolutions in both the Arabian Peninsula and the Nepal HimalayaThe method is robust to topographic and elastic heterogeneities, simple moving loads and geodetic products errors [ABSTRACT FROM AUTHOR]