JGR–Solid Earth

Numerous studies have reported the occurrence of aseismic slip or slow slip events along faults induced by fluid injection. However, the underlying physical mechanism and its impact on induced seismicity remain unclear. In this study, we develop a numerical model that incorporates fluid injection on a fault governed by rate-and-state friction to simulate the coupled processes of pore-pressure diffusion, aseismic slip, and dynamic rupture. We establish a field-scale model to emulate the source characteristics of induced seismicity near the Dallas-Fort Worth Airport (DFWA), Texas, where events with lower-stress drops have been observed. Our numerical calculations reveal that the diffusion of fluid pressure modifies fault criticality and induces aseismic slip with lower stress drop values (<1 MPa), which further influence the timing and source properties of subsequent seismic ruptures. We observe that the level of pore-pressure perturbation exhibits a positive correlation with aseismic-stress drops but a reversed trend with seismic-stress drops. Simulations encompassing diverse injection operations and fault frictional parameters generate a wide spectrum of slip modes, with the scaling relationship of moment (M 0) with ruptured radius (r 0) following an unusual trend, M0∝r04.4 ${M}_{0}\propto {r}_{0}^{4.4}$, similar to M0∝r04.7 ${M}_{0}\propto {r}_{0}^{4.7}$ observed in the DFWA sequence. Based on the consistent scaling, we hypothesize that the lower-stress-drop events in the DFWA may imply less dynamic ruptures in the transition from aseismic to seismic slip, located in the middle of the broad slip spectrum, as illustrated in our simulations.

The slow spreading Reykjanes Ridge overlies the Iceland hotspot and has undergone well ordered changes in crustal segmentation. Previous studies have attributed these changes to varying mantle plume thermal effects, rendering the lithosphere ductile or brittle. Here we use seafloor spreading magnetic anomalies to show that crustal accretion has been focused throughout its spreading history and to determine the detailed evolution of Reykjanes Ridge segments. By ∼53 Ma, organized spreading had developed on an orthogonally spreading linear axis following continental breakup. After a plate motion change at ∼38 Ma, orthogonally spreading offset ridge segments formed by ridge propagation forming varying length fracture zones. From then to the present, the offset segments diachronously migrated back to the original linear geometry from north to south replacing orthogonal with oblique spreading as the axis became linear again. Fracture zones were not terminated, however, simply by reducing segment offsets even to zero. Their termination involved the axial propagation of buoyant upwelling instabilities across the discontinuities, correspondingly extending V-shaped crustal ridges southward. This evolution was guided by a persistent linear deep damp mantle melting interval maintained by the episodic propagation of buoyant upwelling instabilities. Our study indicates that at slow spreading ridges, where buoyant upwelling instabilities govern crustal segmentation, spatial gradients in mantle melting properties may direct the behavior of the instabilities. Where ridges overlie regional hotspot gradients in mantle melting, buoyant instabilities may propagate systematically, and plate boundary evolution may follow an organized pattern.

We develop a 3-D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land-based seismographs to investigate along-strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land-based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high-velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from VS reduction and VP/VS are larger than those determined using VP reduction in prior studies, likely due to water in cracks affecting VS more than VP. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments.

Models of near-field tsunamis and an extreme hurricane provide further evidence for a great precolonial earthquake along the Puerto Rico Trench. The models are benchmarked to brain-coral boulders and cobbles on Anegada, 125 km south of the trench. The models are screened by their success in flooding the mapped sites of these erratics, which were emplaced some six centuries ago. Among 25 tsunami scenarios, 19 have megathrust sources and the rest posit normal faulting on the outer rise. The modeled storm, the most extreme of 15 hurricanes of category 5, produces tsunami-like bores from surf beat. In the tsunami scenarios, simulated flow depth is 1 m or more at all the clast sites, and 2 m or more at nearly all, given either a megathrust rupture 255 km long with 7.5 m of dip slip and M8.45, or an outer-rise rupture 130 km long with 11.4 m of dip slip and M8.17. By contrast, many coral clasts lie beyond the reach of simulated flooding from the extreme hurricane. The tsunami screening may underestimate earthquake size by neglecting trees and shrubs that likely impeded both the simulated flows and the observed clasts; and it may overestimate earthquake size by leaving coastal sand barriers intact. The screening results broadly agree with those from previously published tsunami simulations. In either successful scenario, the average recurrence interval spans thousands of years, and flooding on the nearest Caribbean shores begins within a half-hour.

In this study, we used the Pn tomography method to obtain detailed velocity and anisotropy structures of the uppermost mantle beneath Sakhalin–Kuril–Kamchatka region for improving the understanding of plate subduction, arc–arc collision, and volcanism. We found low Pn velocities beneath volcanoes and areas characterized by pronounced tectonic activity and high Pn velocities with strong anisotropy in the subducting plate. Low Pn velocity anomalies beneath southern Sakhalin connected the low-velocity anomalies in the mantle and crust, indicating the ascent of fluid or melt, and may provide a magmatic source for the rear-arc Rishiri volcano. In the absence of plate subduction, low-velocity anomalies and north–south Pn anisotropy manifested beneath northern Kamchatka, revealing the lateral propagation of mantle flow beneath this northern region. We suggest that the eastern boundary of the slab window at the Kamchatka–Aleutian junction is likely to be located near the Komandorsky Islands.

The southeastern margin of the Tibetan Plateau has undergone complex deformation since the Cenozoic, resulting in a high level of seismicity and seismic hazard. Knowledge about the seismic anisotropy provides important insight about the deformation mechanism and the regional seismotectonics beneath this tectonically active region. In this study, we conduct fullwave multi-scale tomography to investigate the seismic anisotropy in the southeastern margin of the Tibetan Plateau. Broadband records at 111 permanent stations in the region from 470 teleseismic events are used to obtain 5,216 high-quality SKS splitting intensity (SI) measurements, which are then inverted in conjunction with 3D sensitivity kernels to obtain an anisotropic model with multi-scale resolution. Resolution tests show that our data set recovers anisotropy anomalies reasonably well on the scale of 1° × 1° horizontally and ∼100 km vertically. Our result suggests that in the southeastern margin of the Tibetan Plateau the deformation in the lithosphere and asthenosphere are decoupled. The anisotropy in the lithosphere varies both laterally and vertically as a result of dynamic interactions of neighboring blocks as well as lithospheric reactivation. The anisotropy in the asthenosphere largely follows the direction of regional absolute plate motion. The SKS splittings observed at the surface are shown to be consistent with the vertical integral of our depth-dependent anisotropy model over lithospheric and asthenospheric depths.

Ambient noise tomography has become a popular method in the past two decades to image the crust and uppermost mantle structure. To date, broadband Rayleigh wave signals can be obtained from ambient noise, which can be utilized to study the earth's interior structure from the surface down to ∼200–300 km depths. However, it is hard to extract intermediate- and long-period (>50 s) Love wave signals from ambient noise using conventional data processing techniques for ambient noise. Array-based data processing techniques can enhance weak signals. In this study, we adopt a modified algorithm of the double-beamforming method to extract broadband Love wave signals from ambient noise. We validate the accuracy of the dispersion curves measured from our method by comparing them to those measured from the conventional method. Then, we use a finite frequency ambient noise tomography method to construct broadband Love wave phase velocity maps across the contiguous USA. These phase velocity maps are consistent with those obtained from conventional methods at short periods (<40 s). Finally, we analyze the resolution of our double-beamforming method based on checkerboard tests and find that the resolution of phase velocity maps based on our method is close to the aperture of the subarrays used in our double-beamforming method.

Ocean bottom seismometers (OBSs) have been used to detect submarine structural and tectonic information for decades. According to signal source controllability, OBS data have generally been classified into active and passive source data categories. The former mainly focuses on the compressional wave (P-wave) velocity inversion and always lacks valid information about the shear wave (S-wave) velocity structure. While the latter provides structural information with limited resolution due to the aperture of the stations. Overcoming the barriers between processing these two data types will allow the reuse of a vast amount of data from active source experiments to explore the submarine S-wave velocity structural properties. Here, we creatively applied ambient noise interferometry to invert the S-wave velocity structure using data from active source OBS deployment conducted in the southernmost Mariana subduction zone, which had already been utilized to detect submarine P-wave velocity structure. Considering the short time duration and relatively low quality of this type of data, a combined method of short-segment cross-correlation and selected time-frequency domain phase-weighted stacking was adopted to obtain stable cross-correlation functions, which were subsequently used to invert S-wave velocity structures. Compared to previous studies using different methods, our result sheds new light on the crust and upper mantle structure of the southernmost Mariana subduction zone. This method could be used to detect more information based on the reutilization of existing active source OBS data.

Two adjacent groundwater wells on the North China Platform are used to study how earthquakes impacted aquifers. We use the response of water level to solid Earth tides to document changes after earthquakes and how aquifer and fracture properties recovered to pre-earthquake properties. We consider two models for the phase and amplitude of water level response to the lunar diurnal (O1) and semidiurnal (M2) tides: a leaky aquifer model, and a model in which fracture orientation determines the response. In the leaky aquifer model, changes arise from changes in permeability and storage; in the fracture model, changes are due to changes in apparent orientation of transmissive fractures. Responses in one well are best explained by the leaky aquifer model, and can explain the large amplitude coseismic water level and permeability changes and the non-recoverable changes after the largest earthquake. Responses in the other well are consistent with the fracture model and show little coseismic change in water level but changes in apparent fracture orientation. Larger ground motions lead to larger coseismic water level changes and longer recovery times. We propose that the well in the more permeable and shallow aquifer has less variable pore-pressures around the well. Larger coseismic strains from water level changes may enable longer-lasting changes in aquifer properties. We conclude that relatively high permeability aquifers are less susceptible to impacts from seismic waves, and thus have small changes in water levels and hydrogeological properties.

Deformation experiments on hematite characterize its slip-rate dependent frictional properties and deformation mechanisms. These data inform interpretations of slip behavior from exhumed hematite-coated faults and present-day deformation at depth. We used a rotary-shear apparatus to conduct single-velocity and velocity-step experiments on polycrystalline specular hematite rock (∼17 μm average plate thickness) at slip rates of 0.85 μm/s to 320 mm/s, displacements of primarily 1–3 cm and up to 45 cm, and normal stresses of 5 and 8.5 MPa. The average coefficient of friction is 0.70; velocity-step experiments indicate velocity-strengthening to velocity-neutral behavior at rates <1 mm/s. Scanning electron microscopy showed experimentally generated faults develop in a semi-continuous, thin layer of red hematite gouge. Angular gouge particles have an average diameter of ∼0.7 μm, and grain size reduction during slip yields a factor of 10–100 increase in surface area. Hematite is amenable to (U-Th)/He thermochronometry, which can quantify fault-related thermal and mechanical processes. Comparison of hematite (U-Th)/He dates from the undeformed material and experimentally produced gouge indicates He loss occurs during comminution at slow deformation rates without an associated temperature rise required for diffusive loss. Our results imply that, in natural fault rocks, deformation localizes within coarse-grained hematite by stable sliding, and that hematite (U-Th)/He dates acquired from ultracataclasite or highly comminuted gouge reflect minor He loss unrelated to thermal processes. Consequently, the magnitude of temperature rise and associated thermal resetting in hematite-bearing fault rocks based on (U-Th)/He thermochronometry may be overestimated if only diffusive loss of He is considered.

We discuss the tectonic structure, seismic stratigraphy and evolution of the NW Sulu Sea using reprocessed 2D reflection profiles. The NW Sulu Sea is located between the Palawan continental shelf and the Cagayan Ridge and represents the northern part of the Sulu Sea, a marginal sea resulting from Paleogene extension and subsequent Neogene contraction due to convergence between the Palawan and the Philippine blocks. The basin consists of six seismo-stratigraphic units overlying crystalline basement. Syn-orogenic depocenters contain calibrated Middle Miocene to, possibly, Lower Miocene units, while rift-related depocenters consist of uncalibrated but tentatively dated Paleogene to Lower Miocene units. Thickness and depth maps of the main units and bounding horizons differentiate the Piedra-Blanca and the Rasa domains, separated by the NW-Sulu-Break major tectonic structure. Fault-bounded rift-related depocenters are strongly segmented. We interpret that NW-SE and NE-SW trending zones accommodate shape and trend variations of these depocenters. We suggest that these zones may link rift segments, recording different extensional deformation. Miocene thrusting and folding in the Piedra-Blanca Domain and mudflow with associated gravitational structures in the Rasa Domain influenced the deposition of syn-orogenic units. Rift structures inherited from rift segmentation may have conditioned the style and distribution of contractional deformation during the subsequent incipient reactivation during contraction. In the context of SE Asia, our results support that the timing of rifting of the NW Sulu Sea overlaps with the opening of the South China Sea and the North Palawan margin, which may indicate a common geodynamic driving force triggering extension.

Synthesized polycrystalline samples composed of enstatite and olivine with different volumetric ratios were deformed in compression under anhydrous conditions in a Paterson gas-medium apparatus at 1150–1300°C, an oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 or 450 MPa (protoenstatite or orthoenstatite fields). Mechanical data suggest a transition from diffusion to dislocation creep with increasing differential stress for all compositions. Microstructural analyses by optical and scanning electron microscopy reveal well-mixed aggregates and homogeneous deformation. Crystallographic preferred orientations measured by electron backscatter diffraction are consistent with activation of the slip systems (010)[100] and (010)[001] for olivine and (100)[001] and (010)[001] for enstatite, as expected at these conditions. Nonlinear least-squares fitting to the full data set from each experiment allowed the determination of dislocation creep flow laws for the different mixtures. The stress exponent is 3.5 for all compositions, and the apparent activation energies increase slightly as a function of enstatite volume fraction. Within the limits of experimental uncertainties, all two-phase aggregates have strengths that lie between the uniform strain rate (Taylor) and the uniform stress (Sachs) bounds calculated using the dislocation creep flow laws for olivine and enstatite. Calculation of the Taylor and Sachs bounds at strain rate and temperature conditions expected in nature (but not extrapolating in pressure) indicates that using the dislocation creep flow law for monomineralic olivine aggregates provides a good estimate of the viscosity of olivine-orthopyroxene rocks deforming by dislocation creep in the deeper lithosphere and asthenosphere.

The start of the Paleoproterozoic supercontinent cycle is typically taken as the initiation of orogenesis at ca. 2.1 Ga leading to the assembly of Earth's first supercontinent, Columbia. However, the dearth of ca. 2.5–2.2 Ga geological records makes it difficult to deduce tectonic factors during the onset of the Paleoproterozoic supercontinent cycle. The petrogenesis of tonalite–trondhjemite–granodiorite (TTG) provides useful proxies for tracing prevailing geodynamic regimes of early continental evolution. However, marked decreases of TTG and other magmatism occurred across the Archean–Paleoproterozoic transition and have previously precluded forming testable hypotheses. Early Paleoproterozoic TTGs have been identified in the North China Craton (NCC) and other cratons, which may represent the last major pulse of TTGs globally. Here we present low δ18O and δ30Si ca. 2.3 Ga TTGs from the NCC, together with thermodynamic modeling and compilation of stable O and Si isotopes for TTGs globally through time. The ca. 2.3 Ga TTGs were derived from the partial melting of Archean basaltic crust and give lighter average zircon δ18O (3.15 ± 0.35‰) and whole-rock δ30Si values (−0.17 ± 0.08‰) than most Archean TTGs. Considering coeval mafic-felsic igneous rocks, and lithospheric thinning since ca. 2.5 Ga based on estimated crustal thickness through the Neoarchean–Paleoproterozoic, we posit the onset of an intraplate rifting consistent with the anomalous low-δ18O magmatism. Continental rifting of Archean cratons/supercratons plausibly hints at the formation of rifts driving subduction initiation as the veritable onset of the Paleoproterozoic supercontinent cycle.

Geodetic methods can monitor changes in terrestrial water storage (TWS) across large regions in near real-time. Here, we investigate the effect of assumed Earth structure on TWS estimates derived from Global Navigation Satellite System (GNSS) displacement time series. Through a series of synthetic tests, we systematically explore how the spatial wavelength of water load affects the error of TWS estimates. Large loads (e.g., >1,000 km) are well recovered regardless of the assumed Earth model. For small loads (e.g., <10 km), however, errors can exceed 75% when an incorrect model for the Earth is chosen. As a case study, we consider the sensitivity of seasonal TWS estimates within mountainous watersheds of the western U.S., finding estimates that differ by over 13% for a collection of common global and regional structural models. Errors in the recovered water load generally scale with the total weight of the load; thus, long-term changes in storage can produce significant uplift (subsidence), enhancing errors. We demonstrate that regions experiencing systematic and large-scale variations in water storage, such as the Greenland ice sheet, exhibit significant differences in predicted displacement (over 20 mm) depending on the choice of Earth model. Since the discrepancies exceed GNSS observational precision, an appropriate Earth model must be adopted when inverting GNSS observations for mass changes in these regions. Furthermore, regions with large-scale mass changes that can be quantified using independent data (e.g., altimetry, gravity) present opportunities to use geodetic observations to refine structural properties of seismologically derived models for the Earth's interior structure.

The crystallographic preferred orientation (CPO) of olivine, specifically the type-B characterized by c-axes aligned parallel to lineation and b-axes concentrated perpendicular to foliation, is essential for explaining the trench-parallel seismic anisotropy in the forearc regions of subduction zones. However, its origin remains a subject of ambiguity and controversy. In this study, we present experimental findings on the formation of a type-B olivine CPO through the dehydration of foliated serpentinite under a compressive stress at a pressure of 300 MPa and temperature of 700–750°C. Our results reveal a progressive evolution of olivine CPO, transitioning from a type-C fabric to a type-B fabric, with increasing grain size and dehydration level. The type-B CPO observed in coarse-grained olivine within fully dehydrated samples primarily arises from mechanisms involving anisotropic growth, grain rotation, and oriented coalescence of newly formed, small olivine grains following the decomposition of antigorite under a compressive stress. This study provides the first experimental evidence for a novel, low-temperature dynamic dehydration mechanism, in contrast to the mechanism of high-temperature plastic flow, for explaining the development of type-B olivine CPO in forearc regions. Hence, it contributes significantly to our understanding of the formation of olivine CPO with implications for seismic anisotropy in subduction zone forearcs.

Phlogopite and K-richterite constitute important carrier phases for H and F in Earth's lithosphere and mantle. The relative importance depends on their stabilities at high pressure and temperature, which in turn depends on bulk composition. Most previous experimental studies focused on the thermal stability of phlogopite and K-richterite were conducted using simplified chemical compositions. Here, partial melting experiments on metasomatized and carbonated, OH ± F-bearing near-natural peridotite were performed at high pressures (2 and 5 GPa) and temperatures (1,100–1,350°C) to assess the thermal stability of F-free versus F-bearing phlogopite and K-richterite. Experimental results demonstrate that the thermal stability of F-bearing phlogopite is increased by >55°C/wt.% F, relative to F-free phlogopite, whereas K-richterite is absent in all experiments with significant degrees of melting (>2%). The thermal stability of phlogopite containing several wt.% F exceeds continental and oceanic geotherms within the upper 150 km. Fluorine-rich phlogopite would therefore be stable in virtually all of the continental lithosphere, only to be decomposed during large, regional melting events such as continental break-up, thereby acting as a major long-term sink for F and/or H. This could even be the case for the oceanic asthenosphere, depending on the oceanic geotherm of the area of interest.

The Curie Point Depth (CPD) marks a significant temperature boundary (∼580°C) within the Earth's lithosphere. However, there has been ongoing debate regarding its spatial distribution. In this research, we utilized the Equivalent Source Method (ESM) based on Gauss-Legendre integration and data obtained from the EMM2017 model, along with a five-layer susceptibility model, to generate a 0.5° × 0.5° grid of continental CPD distribution for China and surroundings. The average CPD in the study area is 30.4 km, which is slightly shallower than the average depth of global continental Moho (∼33 km). Notably, stable and cold cratonic basins, such as the Tarim Basin and the Sichuan Basin, exhibit deep CPD of ∼45 km. In contrast, the North China Craton, which has experienced significant tectono-thermal activity since the Late Mesozoic, shows moderate CPD of ∼30 km and a gradual uplift from west to east. The Tuva-Mongol orocline within the Central Asian Orogenic Belt, the Deccan Volcanic Province in the Indian subcontinent and the Eastern Yangtze Craton have shallow CPD of ∼20 km. We estimate the surface heat flow by CPD, and the result is consistent with measurements within a RMSE of 18.1 mW/m2. When comparing the CPD with Moho, we find that the CPD may lie below Moho in stable and cold cratonic areas. In comparison to two recent global CPD models, our regional model demonstrates better alignment with tectonic features.

Concentrically zoned pyrite aggregates (CZPA) are common in sediment-hosted massive sulfide (SHMS) deposits and have been widely used to interpret the ore-forming processes. There is considerable uncertainty, however, over the formation of aggregates that are oscillatorily zoned and contain randomly-orientated pyrite microcrystals. Guided by the results of examination of the micro-textures of CZPA and in-situ chemical analyses, we conducted a quantitative diffusion-reaction simulation to assess the mechanism of CZPA formation. Our study shows that oscillatory zoning results from the feedback between the diffusion of reactants and the nucleation-growth of Fe-sulfides. Externally derived Fe2+ diffuses into the early diagenetic sediments containing decomposing organic matter (2CH2O + SO4 2− = 2HCO3 − + H2S) and reacts with H2S to form a pyrite layer via an intermediate pathway (Fe2+ + H2S → FeS + 2H+, FeS + H2S → FeS2 + H2). This growth of pyrite layers depletes the local concentration of reactants and suppresses nucleation until the diffusive reaction front advances and another layer is formed. Intermediate phases, for example, mackinawite, nucleate instead of pyrite, because of their greater ease of nucleation due to the low surface tension, and lead to the domination of nucleation over growth. The nucleation of mackinawite and occurrence of siderite in the CZPA are consistent with a low temperature, high pH, anoxic early diagenetic environment. Our study demonstrates that CZPA in SHMS deposits are formed by intrinsic self-organizational processes rather than by extrinsic changes of ore-forming fluids. The CZPA in SHMS deposits are thus indicative of their diagenetic origin with Fe2+ infiltrated and diffused from hydrothermal fluids into the sediments.

Several negative C isotope excursions (CIEs) occurred at the end of the Neoproterozoic era which have been generally attributed to the oxidation of organic carbon using sulfate as the terminal electron acceptor and the subsequent release of 13C-depleted dissolved inorganic C (DIC). Based on new analyses from the Doushantuo Formation in South China, we observe a negative C isotope excursion right after the well-known Shuram excursion. This excursion is equivalent to the ∼550 Ma negative CIE which is globally expressed within several continental margins. However, the origins of this CIE in the termination of Ediacaran remain unresolved. Here, we hypothesize that this post-Shuram negative CIE was caused by a localized manganese cycling that began with the oxidation of hydrothermal Mn(II) in a water column to insoluble Mn(IV)-oxide, followed by accumulation of Mn(IV)-oxide to the seafloor and its subsequent dissolution via Mn(IV) reduction leading to the release of dissolved Mn(II) and 13C-depleted DIC into ambient seawaters. This ultimately led to the precipitation of particulate Mn(II)-carbonate characterized by low δ13Ccarb values ranging from −11.1‰ to −2.8‰. The presence of microbial fabrics in association with the Mn(II)-carbonate further suggests that Mn(II)-carbonate precipitation took place at the seafloor in shallow sun-lit waters rather than in the deeper sediment pile, which archived ambient seawater C isotopic signal. Although most Ediacaran negative CIEs were generally attributed to sulfate reduction, our findings suggest that at a local level, Mn cycling can also lead to negative CIE in the Neoproterozoic, and potentially at other times in Earth's history.

The potential for future earthquakes on faults is often inferred from inversions of geodetically derived surface velocities for locking on faults using kinematic models such as block models. This can be challenging in complex deforming zones with many closely spaced faults or where deformation is not readily described with block motions. Furthermore, surface strain rates are more directly related to coupling on faults than surface velocities. We present a methodology for estimating slip deficit rate directly from strain rate and apply it to New Zealand for the purpose of incorporating geodetic data in the 2022 revision of the New Zealand National Seismic Hazard Model. The strain rate inversions imply slightly higher slip deficit rates than the preferred geologic slip rates on sections of the major strike-slip systems including the Alpine Fault, the Marlborough Fault System and the northern part of the North Island Fault System. Slip deficit rates are significantly lower than even the lowest geologic estimates on some strike-slip faults in the southern North Island Fault System near Wellington. Over the entire plate boundary, geodetic slip deficit rates are systematically higher than geologic slip rates for faults slipping less than one mm/yr but lower on average for faults with slip rates between about 5 and 25 mm/yr. We show that 70%–80% of the total strain rate field can be attributed to elastic strain due to fault coupling. The remaining 20%–30% shows systematic spatial patterns of strain rate style that is often consistent with local geologic style of faulting.