Fault Slip Rates Research Articles

Along‐strike variation of fault slip rate of a transform plate boundary in Tierra del Fuego (South Patagonia)

AbstractThe Magallanes–Fagnano Fault is an active strike‐slip structure accommodating the relative displacement between South America and the Scotia Plate. The Chilean portion of the fault is poorly studied because most of it runs below the sea level in the Strait of Magellan. Our tectonic geomorphological study is focused on a rare onshore fault section, along which streams horizontally deflected by hundreds of metres since the last main deglaciation are compatible with a dominant left‐lateral fault kinematics and yield a slip rate of 15.7 ± 2.4 mm/year. This rate is between 2 and 3 times higher than the one estimated on the Argentinian portion of the fault over the same period. This spatial variation may be due to both glacial unloading on the fault zone and/or structural factors. These results point out the need to study strike‐slip faults on several portions to unravel behaviour changes related to internal or external forcing.

Dynamical Modeling of Fault Slip Rates at the New Zealand Plate Boundary Indicates Fault Weakness

AbstractWe construct a thin‐sheet dynamical model of the New Zealand plate boundary that includes faults. Our model fits fault slip rates, style of distributed deformation, and is constrained by relative plate boundary motion. We assume a pseudo‐plastic rheology and achieve a best fit to slip rate observations with a deviatoric stress magnitude of 20 MPa. Modeled local forces are significant at Puysegur and Hikurangi subduction zones, and smaller forces are related to mantle downwelling beneath South Island and Havre Trough mantle upwelling. Modeled tractions on faults are mostly 5–20 MPa, similar to or slightly smaller than stress magnitudes adjacent to faults. Modeled shear tractions are generally 2–10 MPa, comparable to stress drops during earthquakes. Modeled stress orientations and fault dips suggest that many faults are not optimally oriented for their style of faulting. Notably small traction magnitudes of <5 MPa and shear tractions of <0.5 MPa are modeled for faults in the central North Island Dextral Fault Belt (NIDFB), which we infer to be very poorly oriented. Friction coefficients on faults (ratio of shear stress to effective normal stress) are in the range 0.1–0.3 for major crustal faults such as the Alpine Fault and Marlborough faults, but subduction zones and the NIDFB have values <0.1. We propose that low values of long‐term fault strength, shear stress resolved onto the fault, and overall magnitudes of deviatoric stress in the crust are a consequence of dynamic weakening of faults during fault slip.

Shallow crustal deformation in the Yunnan-Myanmar and surrounding areas by regionally weighted interpolation of GPS measurements data

Yunnan-Myanmar and its surrounding areas are the areas directly affected by the collision of the Eurasian Plate and the Indian Plate. In view of the uneven distribution of GPS stations in Yunnan and Myanmar, this paper employs the method of regionally weighted interpolation. In areas with a high concentration of GPS stations, a combination of Voronoi cell weighting function and Gaussian function weighting is utilized, while in regions with sparse GPS coverage, a combination of Voronoi cell weighting function and quadratic function weighting is employed. Utilizing the rigid-body movement uniform strain model, we calculate the horizontal strain rates of the crust in Yunnan-Myanmar and adjacent areas, followed by an in-depth analysis of model performance and the activity of primary faults. The results show that: (1) We found that Yunnan Myanmar strain has obvious boundary characteristics. (2) Upon scrutinizing the model, it was ascertained that the model delineated in this study possesses an expansive search range, enabling it to yield more precise outcomes, particularly in regions characterized by the disparate distribution of GPS stations; (3) Through the analysis of the profiles of horizontal GPS velocity field and maximum shear strain rates of the main faults in the study area, we found that the direction of the maximum shear strain rate is consistent with the direction of the main faults in the study area, and that the slip and maximum shear strain rate of the major faults increase and decrease along the tectonic direction.

GNSS imaging coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake

The coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake is imaged using the geodetic modeling method. Further, the spatio-temporal evolution of afterslip and aftershocks (0–60 days) is also investigated based on the postseismic deformations captured by Global Navigation Satellite System (GNSS) sites in this study. The coseismic slip is mainly concentrated at depths of 20–50 km with a maximum of 3.92 m. After this earthquake, a significant afterslip can be observed in the shallow region, which is distributed around the coseismic rupture region. Afterslip is primarily accumulated at depths of 10–30 km, and the maximum reaches 1.29 m, which is located at a longitude of 157.19°W, latitude of 55.09°N, and depth of 21.80 km. The spatio-temporal properties of afterslip indicate that the spatial extent and magnitude of afterslip continuously increase during the 60 days after the earthquake, and the fault activity in the first seven days is significantly strong. Meanwhile, the fault slip rate during the time span of 0–7 days is the largest with a maximum of 0.054 m/day. The fault slip rate gradually decreases with time, implying that the fault activity is slowly weakening. The Coulomb Failure Stress (CFS) distribution suggests that afterslip and most aftershocks are located at the southeastern region of the hypocenter, which is covered by positive CFS. Moreover, in addition to coseismic rupture effects, afterslip may be a possible triggering mechanism of early aftershocks as evidenced by the fact that the spatial distributions of afterslip and aftershocks are highly consistent.

Combining geomorphological and kinematic models to analyze tectonic deformation rates: A case study of the Bayin anticline in the eastern Tian Shan Mountains

Quantitatively characterizing the geometry, kinematics, and deformation rate of fold-thrust belts in intermontane basins is the key to understanding strain partitioning within the Tian Shan range. This work focuses on the Bayin anticline in the Youludusi Basin, a typical intermontane basin located within the eastern Tian Shan. The Kaidu River cuts through the Bayin anticline and has developed three levels of terraces (T1–T3) across the structure. By using cosmogenic nuclide and optically stimulated luminescence dating methods, the formation ages of terraces T1 and T3 are constrained to 11.54 ± 0.55 ka and 42 + 7.0/−7.1 ka, respectively. When applying a listric thrust fault model to the Bayin anticline and using terraces as references, the vertical displacements are estimated to be 16.45 + 6.46/−3.19 m (T1), 32.08 + 12.85/−6.19 m (T2), and 95.93 + 38.94/−18.6 m (T3), and the shortening amounts are 10.56 + 8.33/−5.04 m (T1), 20.46 + 16.68/−9.64 m (T2), and 61.24 + 50.22/−28.93 m (T3). Based on this listric thrust fault model and terrace T1–T3 ages, the rate of fault slip controlling the growth of the Bayin anticline is determined to be 1.6 ± 1.0 mm/yr, and the crustal shortening rate of the anticline is 1.0 + 0.7/−0.6 mm/yr. The estimated crustal shortening deformation of the Bayin anticline accounts for ~12 % of the total deformation in the Youludusi Basin. In terms of the entire orogenic belt, the crustal shortening absorbed in the southern, central, and northern parts accounts for 24 %–56 %, 46 %–71 %, and 19 %–74 %, respectively, of the total strain across the eastern Tian Shan. Therefore, we believe that the Eastern Tianshan undergoes uniform deformation.

Resolving the slip-rate inconsistency of the northern Dead Sea fault.

Reported fault slip rates, a key quantity for earthquake hazard and risk analyses, have been inconsistent for the northern Dead Sea fault (DSF). Studies of offset geological and archeological structures suggest a slip rate of 4 to 6 millimeters per year, consistent with the southern DSF, whereas geodetic slip-rate estimates are only 2 to 3 millimeters per year. To resolve this inconsistency and overcome limited access to the northern DSF in Syria, we here use burst-overlap interferometric time-series analysis of satellite radar images to provide an independent slip-rate estimate of ~2.8 millimeters per year. We also show that the high geologic slip rate could, by chance, be inflated by earthquake clustering and suggest that the slip-rate decrease from the southern to northern DSF can be explained by splay faults and diffuse offshore deformation. These results suggest a microplate west of the northern DSF and a lower earthquake hazard for that part of the fault.

Prediction of fractures by using the stress field in medium to deep shale gas reservoirs: A case study of Late Ordovician–early Silurian shale gas reservoirs in the Nanchuan region, South China

Containing representative shale gas reservoirs, the Wufeng–Longmaxi Formations in the Nanchuan region in South China have been modified by three compressional tectonic movements (in the Late Jurassic to Early Cretaceous, Late Cretaceous, and Cenozoic to present). These movements formed deeply buried reservoirs with complex in situ stresses and rapid directional changes, influencing the state of shale gas reservoirs fractures. Numerical modeling applied to model the stress field in the three periods showed that the maximum compressive horizontal principal stress (σHmax), strain rate, and fault slip rate regimes transformed from a thrust and strike-slip regime to a thrust and strike-slip regime to a thrust regime. The σHmax direction changed from NW–SE and WNW–ESE to WNW–ESE and nearly E–W and then to multiple directions. The magnitude of strain rate changed from -16 ∼ -15 to -17.7 ∼ -15.6 to -18.8 ∼ -15.8. The fault slip rate changed from 0 to 0.029 mm/a to 0–0.0026 mm/a to 0–0.0012 mm/a. These data strongly agree with data from drilled wells and outcrops and show that the present-day stress field is the superposed effect of multistage movements. Semiquantitative research was conducted on shale gas fracture openness and fracture development. Fracture openness is favorable when the angle between the σHmax direction and nearby faults is ≤45° and the distance from the fault is >2 km, and fracture development is favorable when the magnitude of the strain rate is <-17.6 and the fault slip rate is <0.00036 mm/a. Accordingly, we predicted fractured shale gas reservoirs.

Definitions, Classification Schemes for Active Faults, and Their Application

Active faults are generally defined as faults that have moved in the past and will continue to be active in the future. They are expected to cause deformation and potential disasters if they are localized close to human activities. The definition and classification of active faults are important bases for evaluating the risk. This paper summarizes and compares the history, status, and progress of their definition and classification schemes used in representative countries and regions, as well as in some relevant standards, in active fault mapping, in the construction of spatial databases, and in some other aspects. It is concluded that the current geodynamic setting, existing technical means, geological operability, application purpose, and social acceptability of active faulting hazard in a specific area comprehensively determine the selection of the definition and classification. The key parameter in defining active faults is the time limit. It usually involves four time scales, i.e., Neotectonic (post-Neogene), Quaternary, Late Quaternary, and Holocene. The definition using a short time scale, such as Late Quaternary and Holocene, is usually suitable for the plate boundary zone, which has a high strain rate, but active faults in the intraplate deformation region and stable continental region should be defined with a long time scale, such as the Quaternary and Neotectonics. In addition, the magnitude standard can determine the activity intensity of active faults, which most generally includes three classes, namely, M ≥ 5.0 damaging earthquakes, M ≥ 6.0 strong earthquakes, and M ≥ 6.5 earthquakes that may produce surface displacement or deformation. The M ≥ 5.0 earthquake is generally applicable to regional earthquake prevention and risk mitigation in many countries or regions, but the M ≥ 6.5 earthquake magnitude benchmark is generally used as the standard in rules or regulations regarding active fault avoidance. The most common classification schemes in many countries or regions are based on fault activity, which is reflected mainly by the fault slip rate and fault recurrence interval (FRI), as well as by the last activation time. However, when determining the specific quantitative parameters of the different activity levels of faults, it is necessary to comprehensively consider the differences in activity and ages of the faults in the study region, as well as the amount and validity of existing data for the purpose of classifying different active levels of faults effectively.

Robust Imaging of Fault Slip Rates in the Walker Lane and Western Great Basin From GPS Data Using a Multi‐Block Model Approach

AbstractThe Walker Lane (WL) in the western Great Basin (GB) is an active plate boundary system accommodating 10%–20% of the relative tectonic motion between the Pacific and North American plates. Its neotectonic framework is structurally complex, having hundreds of faults with various strikes, rakes, and crustal blocks with vertical axis rotation. Faults slip rates are key parameters needed to quantify seismic hazard in such tectonically active plate boundaries but modeling them in complex areas like the WL and GB is challenging. We present a new modeling strategy for estimating fault slip rates in complex zones of active crustal deformation using data from GPS networks. The technique does not rely on prior estimates of slip rates from geologic studies, and only uses data on the surface trace location, dip, and rake. The iterative framework generates large numbers of block models algorithmically from the fault database to obtain many estimates of slip rates for each fault. This reduces bias from subjective choices about how discontinuous faults connect and interact to accommodate strain. Each model iteration differs slightly in block boundary configuration, but all models honor geodetic and fault data, regularization, and are kinematically self‐consistent. The approach provides several advantages over bespoke models, including insensitivity to outlier data, realistic uncertainties, explicit mapping of off‐fault deformation, and slip rates that are more objective and independent of geologic slip rates. Comparisons to the U.S. National Seismic Hazard Model indicate that ∼80% of our geodetic slip rates agree with their geologic slip rates to within uncertainties.

Interseismic slip distribution and locking characteristics of the mid-southern segment of the Tanlu fault zone

In this paper, we employ the block negative dislocation model to invert the distribution of fault coupling and slip rate deficit on the different segments of the Tanlu fault zone, according to the GPS horizontal velocity field from 1991 to 2007 (the first phase) and 2013 to 2018 (the second phase). By comparing the deformation characteristics results, we discuss the relationship between the deformation characteristics with the 3.11 earthquake in Japan. The results showed that the fault couping rate of the northern section of Tancheng in the second phase reduces compared with that in the first phase, but the results of the two phases showed that the northern section of Juxian still has high coupling rate, the deep blocking depth, and the dextral compressive deficit, which is the unrupture section of the 1668 Tancheng earthquake. At the same time, the area strain results show that the strain rate of the central and eastern regions of the second phase is obviously enhanced compared with that of the first phase. The occurrence of the great earthquake in Japan has played a certain role in alleviating the strain accumulation in the middle and south section of the Tanlu fault zone. The results of the maximum shear strain show that the shear strain in the middle section of Tanlu fault zone in the second phase is weaker than that in the first phase, and the maximum shear strain in the southern section is stronger than that in the first phase. The fault coupling coefficient of the south Sihong to Jiashan section is high, and it is also the unruptured section of historical earthquakes. At the same time, small earthquakes in this area are not active and easy to accumulate stress, so the future earthquake risk deserves attention.

Inverting Geodetic Strain Rates for Slip Deficit Rate in Complex Deforming Zones: An Application to the New Zealand Plate Boundary

AbstractThe 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.

Evidence for a Constant Slip Rate Over the Last ∼40 ka Along the Mt. Morrone Fault System in Central Apennines

AbstractLocated in the easternmost portion of the Central Apennines, the Mt. Morrone normal fault system is one of the highest seismic hazards in Italy. Previous geological and geomorphological observations revealed the presence of a ∼22 km‐long NW‐SE right‐lateral en echelon fault system made of two parallel faults affecting Quaternary deposits. Our analysis focused on the westernmost fault, which bounds the Sulmona Basin. Cumulative offsets were identified and quantified using high‐resolution Digital Elevation Models derived from LiDAR, Satellite Pleiades images, and drone acquisition at the three sites. Morphological markers displaced from a few to tens of meters were dated using 36Cl exposure dating. The results would be suggesting a fault slip rate of 0.2–0.4 mm/a. The deformed markers that dated at 36–44 ka consist of alluvial terraces emplaced by the main streams flowing down from Mt. Morrone to the Sulmona Basin, subsequently incised, and preserved when the fluvial base level dropped because of the former Sulmona lake fluctuations. The yielded ages for these markers fit well with the last major aggradational event associated with the 35–40 ka Heinrich event described and dated to other fluvial basins in the Apennines. Furthermore, the estimated rate agrees with the values obtained in previous studies over shorter and longer periods (105−6 years) and within similar uncertainties. This might then suggest that the period recovered by this study encompasses the entire seismic cycle.

Comparison of geodetic slip-deficit and geologic fault slip rates reveals that variability of elastic strain accumulation and release rates on strike-slip faults is controlled by the relative structural complexity of plate-boundary fault systems

Comparison of geodetic slip-deficit rates with geologic fault slip rates on major strike-slip faults reveals marked differences in patterns of elastic strain accumulation on tectonically isolated faults relative to faults that are embedded within more complex plate-boundary fault systems. Specifically, we show that faults that extend through tectonically complex systems characterized by multiple, mechanically complementary faults (that is, different faults that are all accommodating the same deformation field), which we refer to as high-Coefficient of Complexity (or high-CoCo) faults, exhibit ratios between geodetic and geologic rates that vary and that depend on the displacement scales over which the geologic slip rates are averaged. This indicates that elastic strain accumulation rates on these faults change significantly through time, which in turn suggests that the rates of ductile shear beneath the seismogenic portion of faults also vary through time. This is consistent with models in which mechanically complementary faults trade off slip in time and space in response to varying mechanical and stress conditions on the different component faults. In marked contrast, structurally isolated (or low-CoCo) faults exhibit geologic slip rates that are similar to geodetic slip-deficit rates, regardless of the displacement and time scales over which the slip rates are averaged. Such faults experience relatively constant geologic fault slip rates as well as constant strain accumulation rate (aside from brief, rapid post-seismic intervals). This suggests that low-CoCo faultsd "keep up" with the rate imposed by the relative plate-boundary condition, since they are the only structures in their respective plate-boundary zone that can effectively accommodate the imposed steady plate motion. We hypothesize that the discrepancies between the small-displacement average geologic slip rates and geodetic slip-deficit rates may provide a means of assessing a switch of modes for some high-CoCo faults, transitioning from a slow mode to a faster mode, or vice versa. If so, the differences between geologic slip rates and geodetic slip-deficit rates on high-CoCo faults may indicate changes in a fault's behavior that could be used to refine next-generation probabilistic seismic hazard assessments.

Present‐Day 3D Crustal Deformation of the Northeastern Tibetan Plateau From Space Geodesy

AbstractHigh‐resolution present‐day earth surface deformation maps from satellites provide important data constraints, which help us better understand tectonic processes and analyze seismic hazards. Here, we use Sentinel‐1 Radar images (2014–2020) and accurate positioning measurements (2009–2019) to get a high‐resolution three‐dimensional earth surface velocity map for the northeastern Tibetan Plateau, and we invert the slip rate and coupling ratio of major regional faults. We find ∼4 mm/yr uplift along an arc from the Qilianshan to Lajishan, relative to the neighboring low‐elevation area to the east, which indicates ongoing rapid orogeny. We find transient deformation along the Laohushan and 1920 M8.5 Haiyuan rupture segments of the Haiyuan fault, whereas the western Haiyuan, southern Liupanshan, central Lajishan and central‐western West Qinling faults are essentially locked above 15–20 km, suggesting a potentially high seismic hazard.

Shallow structure and late quaternary slip rate of the Osaka Bay fault, western Japan

The Osaka Bay is situated at a seismically active region north of the Median Tectonic Line and east of Awaji Island in western Japan, known as part of the Kinki Triangle and the Niigata–Kobe Tectonic Zone. Dense distribution of active faults and high geodetic strain rates characterize the region, posing a major seismic hazard potential to the coastal and metropolitan areas of the Kansai region. To investigate the shallow structure and recent deformation history of active faults in the Osaka Bay, we acquired 15 high-resolution seismic profiles using a Mini-GI airgun and a Boomer as active sources, together with multi-beam bathymetry data across the Osaka Bay Fault. Our seismic sections image a ~ 0.1 to 3.7 km-wide asymmetric anticline forelimb above the Osaka Bay Fault at shallow depths, coupled with a ~ 2.6 km-wide syncline to the west, and a broad, ~ 11 km-wide syncline in the footwall to the east. The synclinal axial surface at shallow depths measured in this study ranges 75°–89°. We observe the vertical displacement of the Osaka Bay Fault increasing northwards along strike. The sediment thickness on the hanging wall, however, is variable, modified by non-tectonic processes such as by tidal currents, affecting the geometry of growth strata. The most recent deformation by the Osaka Bay Fault reaches to near the seafloor by active folding, with large vertical offsets of 8–14 m over the last ~ 11 ka, and 5–11 m over the last ~ 5 ka. By combining with previously reported borehole age data, the average uplift rate on the Osaka Bay Fault is estimated to be ~ 1.0 to 1.7 m/ka during the Latest Pleistocene to Holocene. The inferred slip of the Osaka Bay Fault during the Holocene is likely to account for > 5% of the regional geodetic strain accumulation within the Kinki Triangle. Further studies to evaluate the Holocene slip rates of regional faults are necessary to assess the seismic hazards and the internal strain budgets within the Kinki Triangle and the Niigata–Kobe Tectonic Zone.Graphical abstract

Fault activity in the San Gabriel Mountains, southern California, USA: Insights from landscape morphometrics, erosion rates, and fault-slip rates

Many studies use landscape form to determine spatial patterns of tectonic deformation, and these are particularly effective when paired with independent measures of rock uplift and erosion. Here, we use morphometric analyses and 10Be catchment-averaged erosion rates, together with reverse slip rates from the Sierra Madre−Cucamonga fault zone, to reveal patterns in uplift, erosion, and fault activity in the range front of the San Gabriel Mountains in southern California, USA. Our analysis tests two prevailing hypotheses: (1) the range front of the San Gabriel Mountains is at steady state, in which rock uplift balances erosion and topographic elevations are stable throughout time, and (2) that west-to-east increases in elevation, relief, erosion rate, and stream-channel steepness across the interior of the massif reflect a parallel reverse-slip rate gradient on the range-bounding Sierra Madre−Cucamonga fault zone. We show that although deviations from steady state occur, the range-front hillslopes and stream channels are typically both well-connected and adjusted to patterns in Quaternary uplift driven by motion on the range-front fault network. Accordingly, landscape morphometrics, 10Be erosion rates, and model erosion rates effectively image spatial and temporal patterns in uplift. Interpreted jointly, these data reveal comparable peak slip rates on the Sierra Madre−Cucamonga fault zone and show that they do not monotonically increase from west to east. Thus, the eastward-increasing gradients developed within the interior of the massif are not solely related to reverse slip on the range-front faults. Evaluated on shorter length scales (&amp;lt;10 km), morphometric data corroborate earlier descriptions of the Sierra Madre−Cucamonga fault zone as multiple individual faults or fault sections, with slip rates tapering toward fault tips. We infer that these patterns imply the predominance of independent fault or fault section ruptures throughout the Quaternary, though data cannot rule out the possibility of large, connected Sierra Madre−Cucamonga fault zone ruptures. Deeper in the hanging wall of the Sierra Madre−Cucamonga fault zone, secondary faults accommodate range-front uplift. Motion on these faults may contribute to active uplift of the highest topography within the massif, in addition to partly reconciling differences between geologic and geodetic Sierra Madre−Cucamonga fault zone reverse-slip rates. This study provides a new, unified perspective on tectonics and landscape evolution in the San Gabriel Mountains.

Current active fault distribution and slip rate along the middle section of the Jiali-Chayu fault from Sentinel-1 InSAR observations (2017–2022)

The Jiali-Chayu fault, situated on the eastern side of the eastern Himalayan syntaxis, is the southeastern margin of the large strike-slip fault zone of the Jiali Fault. The study of the distribution and activity within this fault zone is imperative for a comprehensive understanding of the tectonic movement patterns in the southeastern Tibetan Plateau. Previous studies have established that the kinematic characteristic of the Jiali-Chayu fault diverges significantly from that of other segments within the Jiali fault. Nonetheless, the current tectonic characteristics, including the slip sense, slip rate, and geometric deformation of this fault, are still not well resolved, leading to divergent interpretations regarding its contemporary activity intensity. This paper introduced an optimized time-series InSAR method with phase compensation designed for regions characterized by low coherence and exhibiting slow deformation. Using Sentinel-1 SAR data from both ascending and descending orbits spanning the period between 2017 and 2022, we successfully derived deformation rates for the middle part of the Jiali-Chayu fault at a spatial resolution of 150 m. The slip and dip rates of active faults are determined by considering the fault movement rates from two different observation angles, in conjunction with strike angle and the assumed dip angle of the fault. The results show that the deformation rates of the three branches are very different, with F2-1 and F2-2 exhibiting notable activity, while other areas exhibit relatively weaker activity. The strike-slip rates for F2-1 and F2-2 faults range between 3.6 and 5.3 mm/a and 3.05 to 5.13 mm/a, respectively, while their respective dip-slip rates fall within the range of 1.1–2.7 mm/a and 2.99–5.02 mm/a. In accordance with the fault slip directions, we classify the F2-1 fault as a sinistral (left-lateral) strike-slip fault and the F2-2 fault as a dextral (right-lateral) strike-slip fault. This study addresses a gap in remote sensing methods for detecting active fault activity in this region, providing a systematic foundation for identifying weak activity characteristics within the fault zone.Graphical

Investigating paleoseismicity using high-resolution airborne LiDAR data - A case study of the Huangxianggou fault in the northeastern Tibetan plateau

Fault-offset landforms have long been recognized as holding important information about paleoseismic slip. Constructing an along-strike fault slip distribution could help reveal a fault's long-term rupture patterns and facilitate a more precise assessment of its future behavior. In this study, we documented the paleoseismic history of the Huangxianggou Fault, an oblique sinistral-thrust segment of the West Qingling Fault in the northeastern region of the Tibetan Plateau, using LiDAR-derived high-resolution DEM (0.1 m/pixel) and measurement of offset landforms. A total of 46 well-preserved and well-shaped landforms were chosen for horizontal and vertical displacement measurements, and the dense measurement data allow us to generate the cumulative offset probability distribution curves of horizontal and vertical displacements. Statistical analysis revealed at least seven surface-rupturing events, each with similar coseismic horizontal displacements of ∼7.0 m and vertical displacements of ∼0.7 m, in agreement with previous paleoseismic trench results. Using empirical relationships between moment magnitude and horizontal displacement, a plausible moment magnitude range of Mw7.3–7.7 was determined for these paleoearthquakes. Furthermore, by evaluating rupture parameters and fault slip rate, we determined a recurrence interval of 2.7–3.4 kyr for significant surface-rupturing events on this fault. The elapsed time since the last earthquake closely approaches this interval, suggesting a potential seismic risk for the Huangxianggou Fault. Our results emphasizes the importance of high-resolution topographic data in paleoseismic investigations, enabling the identification of numerous offset landforms and precise displacement measurements across faults. Paleoearthquake counts derived from horizontal and vertical displacement analyses were found to be consistent, highlighting the significance of vertical displacements in quantifying paleoearthquakes for strike-slip faults with a thrust component.

Review of Geodetic and Geologic Deformation Models for 2023 U.S. National Seismic Hazard Model

ABSTRACT We review five deformation models generated for the 2023 update to the U.S. National Seismic Hazard Model (NSHM), which provide input fault-slip rates that drive the rate of earthquake moment release. Four of the deformation models use the Global Positioning System-derived surface velocity field and geologic slip-rate data to derive slip-rate estimates (Evans, Pollitz, Shen-Bird, and Zeng), and one model uses geologic data (the “geologic model”). The correlation between the geologic model preferred slip rates and geodetically derived slip rates is high for the Pollitz, Zeng, and Shen-Bird models, and the median of all slip-rate models has correlation coefficient of 0.88. The median geodetic model slip rates are systematically lower than the preferred geologic model rates for faults with slip rates exceeding 10 mm/yr and systematically higher on faults with slip rates less than 0.1 mm/yr. Geodetically derived slip rates tend to the low end of the geologic model range along sections of the San Andreas fault and the Garlock fault, whereas they tend to be higher across north coast California faults. The total on-fault moment rates agree well across models with all rates within 18% of the median. Estimated off-fault strain rate orientations and styles vary considerably across models and off-fault moment rates vary more than on-fault moment rates. Path integrals across the western U.S. accounting for fault-slip rate and off-fault deformation are generally consistent with Pacific-North America plate motion with the median deformation rates recovering about 98% of the plate motion with about 20% of the total plate motion accommodated by off-fault strain rate. The geologic model, which has no off-fault deformation, accounts for about 82% of plate motion with fault slip. Finally, we make a recommendation for relative weighting of the models for the NSHM as well as several recommendations for future NSHM deformation model development.

The Seismicity Rate Model for the 2022 Aotearoa New Zealand National Seismic Hazard Model

ABSTRACT A seismicity rate model (SRM) has been developed as part of the 2022 Aotearoa New Zealand National Seismic Hazard Model revision. The SRM consists of many component models, each of which falls into one of two classes: (1) inversion fault model (IFM); or (2) distributed seismicity model (DSM). Here we provide an overview of the SRM and a brief description of each of the component models. The upper plate IFM forecasts the occurrence rate for hundreds of thousands of potential ruptures derived from the New Zealand Community Fault Model version 1.0 and utilizing either geologic- or geodetic-based fault-slip rates. These ruptures are typically less than a couple of hundred kilometers long, but can exceed 1500 km and extend along most of the length of the country (albeit with very low probabilities of exceedance [PoE]). We have also applied the IFM method to the two subduction zones of New Zealand and forecast earthquake magnitudes of up to ∼Mw 9.4, again with very low PoE. The DSM combines a hybrid model developed using multiple datasets with a non-Poisson uniform rate zone model for lower seismicity regions of New Zealand. Forecasts for 100 yr are derived that account for overdispersion of the rate variability when compared with Poisson. Finally, the epistemic uncertainty has been modeled via the range of models and parameters implemented in an SRM logic tree. Results are presented, which indicate the sensitivity of hazard results to the logic tree branches and that were used to reduce the overall complexity of the logic tree.