JGR–Solid Earth

(Ultra)high-pressure metamorphic rocks provide valuable insights into the properties of slab-derived fluids. Here, we report CH4-rich fluid inclusions in garnet of a metapelite from the Zermatt-Saas ophiolite, western Alps. Two types of metapelite, a CH4-bearing pelitic schist and a calcareous pelitic schist, were investigated to unravel favorable P-T-fO2 conditions for preservation of CH4 in high-pressure metapelite. In the CH4-bearing pelitic schist, CH4-rich fluid inclusions exclusively occur in the core of garnet (GrtI) rather than the rim (GrtII). GrtI records P-T conditions of ∼2.85 GPa and ∼555°C, whereas GrtII records a prograde P-T path from ∼1.75 GPa at 510°C to ∼2.0 GPa at 530°C. Compositional profile of garnet in the calcareous pelitic schist reflects a prograde metamorphic path from ∼1.9 GPa at 510°C to ∼2.12 GPa at 545°C. CH4-rich fluid formation may primarily rise from graphite reduction at high-pressure reduced conditions (ΔFMQ −3.5 to −4, 2.85 GPa, ∼550°C), while graphite and carbonates stabilize in a relatively oxidized environment (ΔFMQ ∼0, 2.12 GPa, 545°C). The initial redox budget of subducted sediments is primarily controlled by the amount of sedimentary carbonate and organic carbon, which plays the most important role in deciding the carbon speciation at different subduction depths. CH4 formation in COH fluids could primarily be attributed to the reduction of graphite. Subducted metasediments act as conduits for transporting non-oxidized fluids to arc magmas, which provides crucial evidence to support the heterogeneity for slab-derived COH fluids and offers new insights into the deep carbon cycle.

No abstract is available for this article.

Coseismic rupture and aftershock development on a fault plane are complex and heterogeneous processes. The M w 6.1 L’Aquila 2009 normal faulting earthquake is a perfect case to explore how fault geometry and rheology influence the rupture process and aftershocks distribution. In this study, we use for the first time a dense set of earthquake data to obtain enhanced images of the causative normal fault structure to the kilometer scale. The hypocenter of the emergent onset of the mainshock took place within a low V p/V s volume, while the large coseismic slip occurred a few kilometers above, as the rupture propagated through a high V p and high V p/V s fluid-filled rock volume. The increase of V p/V s in the fault hanging wall during the sequence suggests a strong dehydration in the earthquake asperity, with an upward fluid pressure migration along the fault toward the host rock volume. We propose that the localization of deformation on the fault plane is favored by high fluid pressure, while the spreading of aftershocks on a wide volume around the fault is driven by the depletion of fluids from the slipped portion of the fault plane and migration to small segments within the fault host rocks.

In crustal faults dominated by granitoid gouges, the frictional-viscous transition marks a significant change in strength constraining the lower depth limit of the seismogenic zone. Dissolution-precipitation creep (DPC) may play an important role in initiating this transition, especially within polymineralic materials. Yet, it remains unclear to what extent DPC contributes to the weakening of granitoid gouge materials at the transition. Here we conducted sliding experiments on wet granitoid gouges to large displacement (15 mm), at an effective normal stress and pore fluid pressure of 100 MPa, at temperatures of 20–650°C, and at sliding velocities of 0.1–100 μm/s, which are relevant for earthquake nucleation. Gouge shear strengths were generally ∼75 MPa even at temperatures up to 650°C and at velocities >1 μm/s. At velocities ≤1 μm/s, strengths decreased at temperatures ≥450°C, reaching a minimum of 37 MPa at the highest temperature and lowest velocity condition. Microstructural observations showed that, as the gouges weakened, the strain localized into thin, dense, and ultrafine-grained (≤1 μm) principal slip zones, where nanopores were located along grain contacts and contained minute biotite-quartz-feldspar precipitates. The stress sensitivity exponent n decreased from a large number at 20°C to ∼2.2 at 650°C at the lowest velocities. These findings suggest that high temperature, slow velocity and small grain sizes promote DPC-accommodated granular flow over cataclastic frictional granular flow, leading to the observed weakening and strain localization. Field observations together with extrapolation suggest that DPC-induced weakening occurs at depths of 7–20 km depending on geothermal gradient.

The Carpathian belt is one of Europe's major metallogenic provinces, where magmatic ore mineralization is associated with the past subduction environment. The upper crust is mapped for the first time in the Northeast Carpathian Volcanic Arc using magnetotelluric data inversion. The obtained 3-D electrical resistivity model is interpreted in conjunction with geological information and magnetic anomaly data. The model illustrates the deep magmatic plumbing system including kilometer-scale plutonic bodies at a depth of 2–7 km. The model implies that the transport of magma and fluids in the uppermost crust was controlled by pre-existing faults and décollement horizons. Present ore mineralization, mined since historical times, can be attributed to an electrically conductive conduit that is mapped from the surface to a depth of about 30 km. It is suggested that this conduit connected a shallow magmatic chamber to a deep source region in the southeast during late Miocene time. An observed northwest deflection of the deep magmatic conduit at a depth of more than 10 km may explain the spatial gap in the distribution of the Miocene volcanic activity along the Eastern Carpathians.

Fluid-induced seismicity has been a particularly emphasized mechanism over the last few years, especially after fluid-related, moderate-to-large earthquakes have been observed in several locations around the globe. Several studies suggest that the relationships between seismicity and fluid presence are related to variations in the stress state of rocks, due to the increase or drop of the pore fluid pressure. In this scenario, the Val d’Agri represents a precious case study where fluid-induced seismicity is observed. In this area, two seismic clusters are observed in the Apulian Carbonate Platform, caused by (a) wastewater reinjection that reactivated the Costa Molina Fault blind thrust, and (b) seasonal water loading from the Pertusillo reservoir. The mechanisms behind these reactivated faults' evolution are still uncertain, especially in the compressive/extensional tectonic setting characterizing the area's evolution. Consequently, the distribution of the seismic potential in the region is largely unconstrained. We constructed a numerical thermo-mechanical model to identify the main mechanisms that promoted the Val d’Agri present-day tectonic setting and to assess the seismic hazard characterizing this region. We show that deformation within the Sedimentary Cover and the Crystalline Basement decoupled along a major décollement layer, represented by the Triassic Burano Formation. We also estimate the Coulomb stress (σ C ) in the region, assessing the crust's potential to generate earthquakes. Our results suggest that σ C  > 0 in a large part of the crust, and therefore that fluid injection may be particularly effective for the reactivation of buried structures, especially at a depth between ≃2 and ≃6 km.

Temperature serves as a critical yet elusive factor impacting the mechanical properties of deep rocks. In this work, we shall develop a new micro-thermomechanical model for rocks based on the Mori-Tanaka homogenization scheme. Free energy and thermodynamic forces are deduced within the framework of irreversible thermodynamics, including the local stress applied on the mesocracks, damage driving force, macroscopic stress, and entropy. The salient innovation of this study lies in formulating subtle physically based temperature-dependent friction and damage laws, considering the influence of ambient temperature on the mesocracking in rocks. Through a coupled friction-damage analysis, a temperature-dependent quasi-static strength criterion and analytical stress-strain-damage relations are then derived. Physical implications and calibration methods of each parameter in the proposed model are meticulously presented. Furthermore, a semi-implicit plasticity damage decoupled procedure (SIPDDC) integration algorithm is employed for the numerical implementation of the proposed model. Subsequently, numerical simulations are conducted to obtain the mechanical response of Jinping marble, Beibei sandstone, and Gongjue granite under various real-time temperature-confining pressure coupling conventional triaxial compression tests (TP-CTC). The congruence of stress-strain curves between model predictions and experimental data validates the robust performance and potential applicability of the proposed model.

The seismic data recorded at 48 broadband stations on an 1,800-km-long linear array have been used to image the deep structure and deformation in the intra-continental collision between the Tarim Basin and the Northern Tibetan Plateau (NTP). Common Conversion Point (CCP) stacking imaging along the linear array and joint inversion of receiver function and surface wave dispersion defined the crustal and upper mantle structure, indicating that the Tarim block underthrusts the Altyn Tagh Range–Qaidam Basin. Whereas Moho is flattened, the lithospheric mantle beneath the Qaidam Basin has unusually low velocity, which is thought to be the consequence of the delamination in the lower crust and mantle lithosphere. Strong positive phase occurring at depths of 150–200 km on the CCP stacking imaging is likely to be associated to the remnant subducted oceanic lithospheric slab or the underthrusting Tianshan lithospheric slab beneath the collision zone. The removal of the Altyn Tagh Range–Qaidam Basin orogenic root may be due to convection-driven delamination underneath it and subsequent underthrusting of the Tarim block. The spatial variation of the SKS splitting is manifested as the large-scale pattern of lithospheric deformation and local abrupt changes, transitioning from pure shear on the NTP to simple shear in the Altyn Tagh Range. A comprehensive analysis of SKS splitting and GPS data reveals a simple shear pattern of vertical coherent deformation in the Altyn Tagh Range and its adjacent areas, which is evidence of the lithospheric shear zones.

Previous studies pointed out that the hydraulic aperture (b h) is solely dependent on the geometric features of a fracture, independent of fluid inertia effects. Here we present an inertial hydraulic aperture (b ih) that considers the fluid inertial effect and fracture geometry effect by massive direct numerical simulations of fluid flow in real and artificial 3-D fractures. Simulation results indicate that with an increase in Reynolds number (Re), the evolution eddy volume ratio exhibits three distinct stages: stable stage (Re < 1), fluctuating stage (1 ≤ Re ≤ 10), and increasing to stable stage (Re > 10). These stages correspond to the transition of flow regimes from the viscous Darcy regime to the weak inertia regime, and further developing into the strong inertia regime. Among them, Re = 1 can be considered as the critical point for the onset of the non-Darcy flow. Furthermore, As Re increases, the evolution of b ih exhibits four stages influenced by fluid inertia effects and main flow width in the fracture: stability, slight increase, slight decrease, and rapid increase. Then, based on 892 sets of simulation results (Re ≥ 1), the expression of b ih was obtained using Gene Expression Programming. Compared to the four existing empirical models of b h, the present b ih exhibits the highest accuracy and the lowest errors (R 2 = 0.994, MAE = 0.008, RMSE = 0.013). Finally, the proposed b ih is further employed to modify the Forchheimer equation. This study enhances the understanding of hydraulic conductivity in 3-D rough single fractures.

In response to the need for high-resolution imaging of shallow crustal structure, we present a linear array double-difference (DD) adjoint tomography method, using DD Rayleigh wave traveltime measurements for enhanced spatial resolution. This method, validated through synthetic experiments, improves velocity anomaly detection with fewer iterations compared to absolute traveltime measurements. Applied to data from four linear seismic arrays in the central Tanlu fault zone (TLFZ) in the eastern China, our approach integrated both DD and absolute difference (AD) of adjoint traveltime measurements. We performed cluster analysis for data quality control, reducing data outliers and increasing reliability, particularly in suppressing cycle skipping for short-period measurements. The resulting high-resolution S-wave velocity profiles in the shallow crust well delineate geological structures, revealing a continuous low-velocity anomaly beneath the eastern branch of TLFZ. Our comparative analysis with the southern segment of TLFZ further highlights the segmented nature of the fault zone structure. These variations might suggest a dominant influence of deep magmatic processes due to destruction of the North China Craton. Our study links shallow structural features to deeper geodynamic activities, emphasizing the role of TLFZ as a critical tectonic boundary.

The structure of fault zones and the ruptures they host are inextricably linked. Fault zones are narrow, which has made imaging their structure at seismogenic depths a persistent problem. Fiber-optic seismology allows for low-maintenance, long-term deployments of dense seismic arrays, which present new opportunities to address this problem. We use a fiber array that crosses the Garlock Fault to explore its structure. With a multifaceted imaging approach, we peel back the shallow structure around the fault to see how the fault changes with depth in the crust. We first generate a shallow velocity model across the fault with a joint inversion of active source and ambient noise data. Subsequently, we investigate the fault at deeper depths using travel-time observations from local earthquakes. By comparing the shallow velocity model and the earthquake travel-time observations, we find that the fault's low-velocity zone below the top few hundred meters is at most unexpectedly narrow, potentially indicating fault zone healing. Using differential travel-time measurements from earthquake pairs, we resolve a sharp bimaterial contrast at depth that suggests preferred westward rupture directivity.

In this study, we revisit the shear-wave velocity structure of the lithosphere and asthenosphere surrounding the Hawaiian hotspot and Hawaiian swell using Rayleigh wave data spanning periods of 20–125 s from the PLUME project. A primary goal of this investigation is to probe the origin of the Hawaiian swell and the mechanism that elevates the topography, providing insights into mantle dynamics beneath hotspot swells. In the shear velocity model, the 30–70 km depth range is largely featureless with weak and local anomalies, indicating that the elevation of the Hawaiian swell cannot be attributed to upper lithospheric reheating or replacement. In contrast, at 80–150 km depth, a pronounced region of anomalously low velocities is well-resolved, with the lowest velocities found beneath the Hawaii-Maui-Molokai part of the island chain. Minimum shear velocities are approximately 4.0 km/s at 100–120 km depth, which is an ∼8%-10% velocity decrease relative to the surrounding velocities away from the swell. This pattern suggests that hot, buoyant mantle from deeper plume sources laterally spread out near the top of the normal oceanic asthenosphere. We find that the low-velocity pattern in the asthenosphere exhibits a strong correlation with the overall shape of the Hawaiian swell topography. Assuming that density anomalies are proportional to shear velocity anomalies, we demonstrate that the anomalous elevation of the swell can be explained by the uplift of a 30-km-thick elastic plate loaded from below by this buoyant, low-seismic-velocity layer in the asthenosphere.

Metal complexation and speciation is the primary process responsible for metal transport and circulation in hydrothermal systems, during which stable and soluble metal complexes play a pivotal role. Here, we investigate the speciation of Os and the thermodynamic stability of Os(IV)-Cl complexes in chloride-bearing solutions at temperatures ranging from 150 to 600°C and pressure of 100 MPa through hydrolysis experiments. The results show that the dominant species of Os is OsCl6 2− at temperatures between 150 and 450°C and 100 MPa, gradually converting into Os(IV)-OH-Cl and Os(II)-Cl complexes over 450°C. The equilibrium constant (ln K) (K = [HCl]4 ⨯ [Cl−]2/[OsCl6 2−]) between OsCl6 2− and water molecule is determined as ln K = (50.43 ± 4.633) − (54223 ± 2525.6)/T, and Δ r H m Θ and Δ r S m Θ are inferred to be (450.8 ± 21.00) kJ · mol−1 and (419.3 ± 38.52) J · mol−1 · K−1. Furthermore, the formation constant (ln β) of OsCl6 2− exhibits a change from −0.097 to −0.104 as temperatures increase from 150 to 400°C, while the change values in standard Gibbs free energy (Δ r G m Θ ) for the hydrolysis reactions decrease with rising temperature, suggesting a temperature-dependent thermodynamic stability of OsCl6 2−. Geochemical modeling further demonstrates that high solubility of OsCl6 2− could exist in low-temperature and acidic fluids (≤300°C and pH < 5), or relatively high-temperature and acidic-neutral fluids (>300°C and pH < 7), primarily influenced by the Cl concentration. Acidic and near-neutral fluids with high Cl concentration venting in the mid-ocean ridge, back-arc, and sediment-hosted systems contribute more to dissolving and transporting Os from the lithosphere to the hydrosphere, thereby impacting the global ocean dissolved Os budget.

Systematical investigation of deep mantle structure beneath the Pamir Plateau, western Tian Shan and their surroundings is of great significance to understand dynamics of continental collision, intracontinental orogenesis and deformation in response to the Indo-Eurasian collision. In this research, we imaged the mantle transition zone (MTZ) structure beneath these regions using 42,560 P-wave receiver functions obtained from 352 seismic stations and 6,173 teleseismic events. Our results reveal significant 15–20 km depression of the 410-km discontinuity (d410) mainly beneath the southern Kazakh Shield, which is consistent with the low-velocity anomaly in tomographic models and thus attributed to the mantle upwelling from the MTZ, providing evidence for the fossil Tian Shan plume responsible for the Late Cretaceous-Paleocene basaltic magmatism (74–52 Ma) at the western Tian Shan. Considering that the d410 is slightly depressed by ∼8 km beneath the western Tian Shan, deep subduction of the Tarim lithosphere is likely excluded and its subhorizontal indentation into the Tian Shan is preferred. As a result, segments of thickened Tian Shan lithosphere delaminated and accumulated near the 660-km discontinuity (d660), which induce small-scale upwelling across the d410 there. The d410 is depressed by ∼10–15 km beneath Tarim, which is interpreted to be caused by the mantle upwelling originating from beneath the d410. The d660 below the central Hindu Kush is extremely depressed by 25–30 km, providing direct evidence for the deep subduction of Indian lithosphere into the bottom of the MTZ and suggesting different mechanisms for continental collision between the Hindu Kush and Pamir Plateau.

Geomagnetic field models over past millennia rely on two main data sources: archeomagnetic data provide snapshots of the geomagnetic field at specific locations, and sediment records deliver time series of the geomagnetic field at specific locations. The limited temporal and spatial coverage of archeomagnetic data necessitates the incorporation of sediment data especially when models go further back in time. When working with sediment data one should consider the post-depositional detrital remanent magnetization (pDRM) process, which can cause delayed and smoothed signals. To address the distortion associated with the pDRM process a Bayesian modeling technique incorporating archeomagnetic data and a class of flexible parameterized lock-in functions has been proposed. In this study, we investigate this method in more detail and apply it to declination and inclination of several lacustrine and marine sediment records. Data-driven results support the hypothesis that the pDRM process can introduce distortions, including offsets and smoothing, in some lacustrine and marine sediment records. We demonstrate a correction approach to minimize the distortion caused by the pDRM process and its impact on geomagnetic field reconstructions. The variability in the results observed across the nine records points to a potential dependence on sedimentological characteristics. To explore this further, we plan to systematically apply our novel method to a larger number of records in future studies.

We develop an inversion procedure for deriving multi-scale velocity models with waveform inversions of earthquake and ambient noise data at multi-frequency bands recorded by regional and dense sensor configurations. The method is applied for the area around the 2019 Ridgecrest earthquake rupture zones, utilizing data recorded by regional stations and dense 2D and 1D arrays with station spacings of ∼5 km and ∼100 m, respectively. Starting with regional Vp, Vs models and locations of Ridgecrest aftershocks, the velocity models and event locations are improved iteratively by inversions of waveforms recorded by regional stations and the 2D array, using a minimum spectral element size of ∼600 m. Waveforms from local events recorded by dense 1D arrays across the M7.1 rupture zone with frequencies of up to 10 Hz are used to resolve small-scale features of the rupture zone and shallow crust with a local spectral element size of 80 m. The refined models provide self-consistent descriptions of the rupture zone and the shallow crust embedded in the regional structures. The results reveal pronounced low Vs and high Vp/Vs in the M6.4 and M7.1 rupture zones coinciding with concentrations of seismicity, and also around the Garlock fault and in several local basins. We also observe clear velocity contrasts across the Garlock fault with polarity reversals along strike and with depth. The obtained multi-scale velocity models can be used to improve derivations of earthquake source properties, simulations of dynamic ruptures and ground motions, and the understanding of fault and tectonic processes in the region.

The accurate assessment of hydraulic transmissivity in rock fractures filled with particles is not only a scientific challenge but also a critical need for various industrial applications. However, the intricate dynamics of particle erosion and pore clogging that govern transmissivity evolution remain largely unexplored. In this study, we experimentally examine the fluid-driven particle migration behavior in filled fractures and its consequent impact on fracture transmissivity under various hydraulic gradients, normal stresses, and fracture apertures. We find that escalating hydraulic gradients not only intensify particle erosion through amplified fluid drag forces and hydro-mechanical coupling effects but also lead to an increase in the size of migrating particles, thereby augmenting pore clogging. The dynamics of erosion and clogging define four distinct migration phases within the filled fractures. Variations in normal stress and initial fracture aperture significantly alter the particle arrangement and the soil structure stability within the fractures, thereby modulating the progress of particle migration in response to hydraulic gradients. The pattern of particle migration in filled fractures dictates the development of the internal pore structure and normal deformation, ultimately affecting fracture transmissivity. We propose an empirical expression to encapsulate the comprehensive evolution of fracture transmissivity across different particle migration patterns. Our research advances the understanding of fluid-driven particle migration within filled fractures and provides a practical tool for the precise determination of hydraulic properties of fractured rocks amidst complex geological settings.

Methane clumped isotope signatures of abiogenesis may be diagnostic of the origin of methane on Earth and other planetary bodies. We performed synthesis of abiogenic methane in hydrothermal conditions between 130 and 300°C and determined δ13C, δD, Δ13CH3D, and Δ12CH2D2. The experiments were performed by heating water in the presence of Fe0 powder and CO. The reduction of water on metallic iron led to the formation of H2. CO was reacted with both H2 and H2O, generating both CH4 and CO2. Methane δ13C values are isotopically depleted by ∼25‰ relative to the CO starting material. This is consistent with carbon isotopic equilibrium between methane, carbon monoxide and carbon dioxide in our experiments. In contrast, D/H ratios are inconsistent with equilibrium isotopic fractionation, as illustrated by δD values of methane fractionated by ∼500‰ relative to starting H2O. This suggests that under our experimental conditions, hydrogen additions to carbon may be governed by kinetics. Δ13CH3D values track experimental temperature, with values between +1.5‰ and +5.0‰ for most samples. In contrast, Δ12CH2D2 values are displaced from equilibrium. We find exclusively negative Δ12CH2D2 values, showing deficits down to 40‰ relative to thermodynamic equilibrium. We interpret the data as evidence for distinct, kinetically induced D/H pools contributing to methane assembly, that is, a combinatorial effect. The cumulative D/H fractionations associated with CO hydrogenation explain the direction and magnitude of Δ12CH2D2 values during abiotic methane formation. We suggest that near equilibrium Δ13CH3D with negative Δ12CH2D2 signatures will help identify methane formed abiotically in nature.

In this study we apply electron tomography to characterize 3D dislocation microstructures in two quartz mylonite specimens from the Moine and Main Central Thrusts, both of which accommodated displacements by dislocation creep in the presence of water. Both specimens show dislocation activity with dislocation densities of the order of 3–4 × 1012 m−2 and evidence of recovery from the presence of subgrain boundaries. 〈a〉 slip occurs predominantly on pyramidal and prismatic planes (〈a〉 basal glide is not active). [c] Glide is not significant. On the other hand, we observe a very high level of activation of 〈c + a〉 glide on the 101‾0 $\left\{10\overline{1}0\right\}$, 101‾1 $\left\{10\overline{1}1\right\}$, 112‾n $\left\{11\overline{2}n\right\}$ (n = 1,2) and even 213‾1 $\left\{21\overline{3}1\right\}$ planes. Approximately 60% of all dislocations show evidence of climb with a predominance of mixed climb, a deformation mechanism characterized by dislocations moving in a plane intermediate between the glide and the climb planes. This atypical mode of deformation demonstrates comparable glide and climb efficiency under natural deformation conditions. It promotes dislocation glide in planes not expected for the quartz structure, probably by inhibiting lattice friction. Our quantitative characterization of the microstructure enables us to assess the strain that dislocations can generate. We show that glide systems indicated by the observed dislocations are sufficient to accommodate any arbitrary 3D strain by themselves. Although historically dislocation glide has been regarded as being primarily responsible for producing strain, activation of climb can also directly contribute to the finite strain. On the basis of this characterization, we propose a numerical modeling approach for attempting to characterize the local stress state that gave rise to the observed microstructure.

Natural fault zones are complex, spatially heterogeneous systems. Rock deformation experimental studies simplify the complexity of natural fault zones either as a surface discontinuity between intact rocks (bare-rock surfaces) or as a few mm-thick gouge layer. However, depending on the simplified fault type and its slip history, the response to applied deformation can vary. In this work, we conduct laboratory experiments for investigating the evolution of mechanical parameters of simulated faults made of calcite gouge subjected to multiple (four) identical seismic slip-rate pulses. We observed that, as the number of applied slip-rate pulses increased, (a) initial friction and steady-state friction remained approximatively constant, (b) peak friction and normalized strength excess increased and, (c) the slip distances to achieve peak and steady-state friction, D a and D c , decreased. The greatest changes occurred between the first and the second slip-rate pulse. From this pulse onward, the dissipated energy of the calcite gouge fault was similar to those obtained in bare-rock surfaces experiments. Microstructural analysis showed that, strain is localized in up to two (recrystallized) principal slip zones (PSZ) with sub-micrometric grain size, surrounded by low porosity sintered and non-sintered comminuted gouge domains. We conclude that previous seismic slip episodes impact on both the structure and the strain localization processes within a fault, contributing to its shear fabric evolution. We highlight that the strain localization process identifies the PSZ, dissipating the least amount of energy within the entire experimental fault zone.