Surface Offsets Research Articles

Characteristic Slow‐Slip Events on the Superstition Hills Fault, Southern California

AbstractThe Superstition Hills Fault (SHF) exhibits a rich spectrum of slip modes, including M 6+ earthquakes, afterslip, quasi‐steady creep, and both triggered and spontaneous slow slip events (SSEs). Following 13 years of quiescence, creepmeters recorded 25 mm of slip during 16–19 May 2023. Additional sub‐events brought the total slip to 41 mm. The event nucleated on the northern SHF in early‐May and propagated bi‐laterally at rates on the order of kilometers per day. Surface offsets reveal a bi‐modal slip distribution, with slip on the northern section of the fault being less localized and lower amplitude compared to the southern section. Kinematic slip models confirm systematic variations in the slip distribution along‐strike and with depth and suggest that slip is largely confined to the shallow sedimentary layer. Observations and models of the 2023 SSE bear a strong similarity to previous slip episodes in 1999, 2006, and 2010, suggesting a characteristic behavior.

Deciphering the Biophysical Impact of Permafrost Greening on Summer Surface Offset

AbstractSatellite observations have shown widespread greening during the last few decades over the northern permafrost region, but the impact of vegetation greening on permafrost thermal dynamics remains poorly understood, hindering the understanding of permafrost‐vegetation‐climate feedbacks. Summer surface offset (SSO), defined as the difference between surface soil temperature and near‐surface air temperature in summer (June‐August), is often predicted as a function of surface thermal characteristics for permafrost modeling. Here we examined the impact of leaf area index (LAI), detected by satellite as a proxy to permafrost vegetation dynamics, on SSO variations from 2003 to 2021 across the northern permafrost region. We observed latitude‐ and biome‐dependent patterns of SSO changes, with a pronounced increase in Siberian shrublands and a decrease in Tibetan grasslands. Based on partial correlation and sensitivity analyses, we found a strong LAI signal (∼30% of climatic signal) on SSO with varying elevation‐ and canopy height‐dependent patterns. Positive correlations or sensitivities, that is, increases in LAI lead to higher SSO, were distributed in relatively cold and wet areas. Biophysical effects of permafrost greening on surface albedo, evapotranspiration, and soil moisture (SM) could link the connection between LAI and SSO. Increased LAI substantially reduced surface albedo and enhanced evapotranspiration, influenced energy redistribution, and further controlled interannual variability of SSO. We also found contrasting effects of LAI on surface SM, consequently leading to divergent impacts on SSO. The results offer a fresh perspective on how greening affects the thermal balance and dynamics of permafrost, which is enlightening for improved permafrost projections.

The 2022 Mw 6.6 Menyuan earthquake: An early-terminated runaway rupture by the complex fault geometry

The 2022 Mw 6.6 Menyuan earthquake, which caused unexpectedly large surface offsets (about 2.6–3.5 m) relative to the moment magnitude of this event, is one of the best-recorded strike-slip events in the northeastern Tibetan plateau. Although previous studies have revealed many kinematic features of this event, the mechanism and rupture dynamic characteristics underlying unexpectedly large surface dislocations need to be clarified. In this study, based on the grid search method, we conducted 61 dynamic rupture simulations considering terrain relief to screen out a preferred dynamic model that fits the geodetic, seismic, and geological observations well. The results show that the average stress drop of the nucleation part is relatively high (11 MPa), which could provide high initial rupture energy and give this event a chance to develop into a large earthquake. However, the rupture propagating eastward is slowed and terminated by two consecutive fault bends of about 10° each, and the westward propagating one might concentrate at a shallow depth (< 3 km) on the south secondary fault after it jumps over the stepover. These results imply that the complex fault geometry (the fault bend and stepover) might terminate the rupture early so that the observed magnitude of this event (Mw 6.6) is smaller than the estimated magnitude (Mw 7.1–7.2) based on the surface offsets. Our study again shows that, due to advances in computational power and observations (coverage and quality), physics-based dynamic rupture simulations have entered an era where it is possible to fit the observed data well, which is vital for further understanding the mechanisms of earthquakes.

Surface deformations of the 6 February 2023 earthquake sequence, eastern Türkiye.

Two powerful earthquakes struck Türkiye on 6 February 2023. The initial rupture was on the Dead Sea fault zone, yet maximum displacements and energy release [moment magnitude (Mw) 7.8] occurred 24 seconds later when rupture transferred to the East Anatolian fault zone (EAFZ). More than 7 hours later, a Mw 4.5 aftershock at the junction of the EAFZ with the east-west striking Çardak-Sürgü fault was followed 86 minutes later by the second large (Mw 7.5) earthquake, suggesting a causal relationship. We provide quantitative ground and aerial documentation of surface offsets and kinematics from the slipped faults, providing important data on surface deformation during large continental strike-slip earthquakes, rupture propagation mechanisms, and how slip may be transferred between complex fault systems. We also provide insight into how slip along linked fault systems accommodates global plate motions.

Ransiki earthquakes, northeastern Bird’s Head Peninsula, northwestern New Guinea, Indonesia: Deformation partitioning in oblique plate convergence

The plate boundary between the Pacific-Caroline and Australian plates in northwestern New Guinea is associated with a geographic concentration of earthquakes developed in the Ransiki region of the northeastern Bird’s Head Peninsula (West Papua, northwestern New Guinea) at the intersection of the Ransiki and Yapen faults. We examine these earthquakes based on regional geomorphological and lithostratigraphical frameworks, field observations of surface ruptures and liquefaction phenomena, and focal mechanisms of historical earthquakes. The Ransiki earthquakes are a set of 29 earthquakes from the Global Centroid Moment Tensor catalogue in the period 1977–2019 (magnitudes of Mw4.9 to Mw7.5). In the east, focal mechanisms show sinistral movement along the east-west trending Yapen Fault including the Mw6.7 earthquake on 21 April 2012. The largest earthquake was on 10 October 2002 (Mw7.5) and along with other earthquakes mainly in the southwest were associated with dextral movement indicated by focal mechanism solutions on the northwest trending Ransiki Fault south of its intersection with the Yapen Fault. The southern part of the Ransiki Fault therefore indicates local north-northeast compression that is also evident in the newly recognised Wainoei Fault south of Yapen Island. The two largest earthquakes (10 October 2002, 21 April 2012) show ground effects associated with liquefaction, indicated by surface offsets, open fissures, and sand blows, that all occurred in saturated sediments of the Ransiki delta. Earthquakes in the Ransiki region show that west-southwest oblique plate convergence between the Australian and Pacific-Caroline plates is partitioned into east-west sinistral strike-slip motion along the Yapen Fault and north-northeast compression associated with the Ransiki Fault.

The Destructive Earthquake Doublet of 6 February 2023 in South-Central Türkiye and Northwestern Syria: Initial Observations and Analyses

AbstractOn 6 February 2023, two large earthquakes with magnitude 7.8 and 7.6 rocked south-central Türkiye and northwestern Syria. At the time of writing, the death toll exceeded 50,000 in Türkiye and 7200 in Syria. The epicenter of the first mainshock was located ∼15 km east of the east Anatolian fault (EAF), the second large earthquake (9 hr later) initiated ∼90 km to the north on the east–west-trending Sürgü fault. Aftershocks delineate fault lengths of ∼350 and ∼170 km, respectively. Using satellite and seismic data for first-order analyses of surface-fault offsets, space–time rupture evolution, and recorded ground motions, our study sheds light on the reasons for the extensive destruction. The first event ruptured the EAF bilaterally, lasted for ∼80 s, and created surface fault offsets of over 6 m. The second event also ruptured bilaterally with a duration of ∼35 s and more than 7 m surface offsets. Horizontal ground accelerations reached locally up to 2g in the first mainshock; severe and widespread shaking occurred in the Hatay-Antakia area with values near 0.5g. Both earthquakes are characterized by directivity effects and abrupt rupture cessation generating stopping phases that contributed to strong seismic radiation. Shaking was further aggravated locally by site-amplification effects.

Complex 3‐D Surface Deformation in the 1971 San Fernando, California Earthquake Reveals Static and Dynamic Controls on Off‐Fault Deformation

AbstractThe shallow 1971 MW6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non‐planar geometry, and is notable for having a higher component of left‐lateral surface slip than expected from seismic source models. We extract its 3‐D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and fault trace‐parallel components of distributed deformation along strike. The results confirm the significant left‐lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off‐fault deformation averaging 69% in both the fault trace‐parallel and vertical components. However, the magnitude and width of off‐fault deformation behave differently between the vertical and fault trace‐parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.

Probing the Upper End of Intracontinental Earthquake Magnitude: A Prehistoric Example From the Dzhungarian and Lepsy Faults of Kazakhstan

AbstractThe study of surface ruptures is key to understanding the earthquake occurrence of faults especially in the absence of historical events. We present a detailed analysis of geomorphic displacements along the Dzhungarian Fault, which straddles the border of China and Kazakhstan. We use digital elevation models derived from structure‐from‐motion analysis of Pléiades satellite imagery and drone imagery from specific field sites to measure surface offsets. We provide direct age constraints from alluvial terraces displaced by faulting and indirect dating from morphological analysis of the scarps. We find that the southern 250 km of the fault likely ruptured in a single event in the last 4,000 years, with displacements of 10–15 m, and potentially up to 20 m at one site. We infer that this Dzhungarian rupture is likely linked with a previously identified paleo‐earthquake rupture on the Lepsy Fault through a system of splays in the intervening highlands. Though there are remaining uncertainties regarding consistency in age constraints between the two fault ruptures, most of the sites along the two faults are consistent with a most recent event 2,000–4,000 years ago. Rupture on the Dzhungarian Fault alone is likely to have exceeded Mw 8, and the combined Lepsy‐Dzhungarian rupture scenario may have been up to Mw 8.4. Despite being at the upper end of known or inferred continental earthquake magnitudes, our proposed scenario combining the 375 km of the Dzhungarian and Lepsy ruptures yields a slip‐to‐length ratio consistent with global averages and so do other historical intracontinental earthquakes in Central Asia.

Long-term morpho-structural development of major normal fault zones, Gran Sasso area, Central Apennines (Italy)

Although the Central Apennines of Italy are frequently struck by earthquakes related to normal faulting, so far, no detailed regional study into long-term development and mode of normal faulting exists. In this study, we focus on the Assergi fault zone (AFZ) and the Campo Imperatore fault zone (CIFZ) in the Gran Sasso area.Both fault zones are S-dipping and ~ 20 km in length. Range front faults with ~1 km of footwall topography are associated with basins in the hanging wall. To create footwall relief, long-term throw rates of >0.6 mm/a are required. We compared geologic throw with morphologic markers, such as range and triangular facet height, drainage basin size, spacing between drainage basin outlets, and surface offsets. The morphologic analysis allows to distinguish fault sectors that share morphological characteristics but typically include several mapped fault segments. The history of faulting of the CIFZ indicates that normal fault segments first acquire offset at a constant length until reaching a threshold, and then link with neighbouring fault segments into longer fault zones.Our study of the fault zones suggests the following general concept for long-term development of range-front fault morphology and associated slopes: (1) Surface offset by active faulting is followed, or accompanied, by incision of numerous small alluvial-fan catchments with narrow outlet spacing into the fault footwall. (2) Upon further fault growth, large triangular facets separated by gullies develop. By headward and lateral erosion the small fan catchments merge into fewer and larger catchments with larger outlet spacing. (3) During fault dormance, fault scarps degrade to lower-dipping slopes typically veneered by scree. On these slopes, scarps excavated by differential erosion expose Riedel shears of the main faults.

Hypocentral dependent shallow slip distribution and rupture extents along a strike-slip fault

Natural faults feature heterogeneities in geometry, material properties, and stress distributions, posing great challenges in predicting fault slip behaviors. Among these factors, the stress on the fault is poorly understood due to the lack of direct measurements. Here, we estimate stress distribution from interseismic locking models and derive earthquake scenarios along the Anninghe fault in Sichuan, China, by conducting dynamic rupture simulations. The predicted rupture segmentation and moment magnitudes (Mw 6.9 – 7.3) are well consistent with historical earthquakes. Besides, we have observed models accompanied by continuous surface rupture, with surface offsets comparable to the values identified in field surveys of historical earthquakes. In addition, the surface rupture and the shallow slip deficit (SSD) vary drastically among models with different hypocenters, demonstrating that the earthquake process is indeterministic. The coseismic moment predicted in our models is ∼50% of what was anticipated from the static locking model. Our results highlight that those rupture scenarios derived from the locking-based heterogeneous stress can further contribute to the seismic hazard assessment.

Calculation of Surface Offset Gathers Based on Reverse Time Migration and Its Parallel Computation with Multi-GPUs

As an important method for seismic data processing, reverse time migration (RTM) has high precision but involves high-intensity calculations. The calculation an RTM surface offset (shot–receiver distance) domain gathers provides intermediary data for an iterative calculation of migration and its velocity building. How to generate such data efficiently is of great significance to the industrial application of RTM. We propose a method for the calculation of surface offset gathers (SOGs) based on attribute migration, wherein, using migration calculations performed twice, the attribute profile of the surface offsets can be obtained, thus the image results can be sorted into offset gathers. Aiming at the problem of high-intensity computations required for RTM, we put forth a multi-graphic processing unit (GPU) calculative strategy, i.e., by distributing image computational domains to different GPUs for computation and by using the method of multi-stream calculations to conceal data transmission between GPUs. Ultimately, the computing original efficiency was higher relative to a single GPU, and more GPUs were used linearly. The test with a model showed that the attributive migration methods can correctly output SOGs, while the GPU parallel computation can effectively improve the computing efficiency. Therefore, it is of practical importance for this method to be expanded and applied in industries.

From Interseismic Deformation With Near‐Repeating Earthquakes to Co‐Seismic Rupture: A Unified View of the 2020 Mw6.8 Sivrice (Elazığ) Eastern Turkey Earthquake

AbstractThe East Anatolian Fault (EAF) is a left‐lateral transform fault accommodating the relative motion between the Anatolian and Arabian plates. On January 24, 2020, Mw6.8 Sivrice (Elazığ) earthquake is the largest event that occurred along the EAF since the nineteenth century. The earthquake provides a unique opportunity to capture a critical stage of the seismic cycle from the interseismic deformation to co‐seismic rupture. In this study, we examine the relationship between the interseismic fault activity and co‐seismic behavior of the earthquake. A kinematic model of the earthquake obtained from strong‐motion, GNSS and teleseismic waveforms along with static displacements from GNSS and InSAR data shows that the mainshock ruptured only 45 km of the 95 km long Sivrice‐Pütürge segment. Rupture initiated adjacent to the interseismically weakly coupled northeastern section and propagated unilaterally toward southwest with a rupture velocity of ∼2.5 km/s, stopping ∼30 km before the southwestern segment boundary. The earthquake did not generate any surface offsets. We identified 4 long‐term near‐repeating earthquake clusters beneath the highest co‐seismic slip zone adjacent to the northeastern creeping section. The mainshock was dynamically triggered by a M ∼ 5.4 foreshock located within the zone of near‐repeating earthquakes. We suggest that creep along the weakly coupled section of the fault loaded the neighboring locked section leading to the repeating earthquakes below the locked zone. The earthquake partially ruptured a fault segment characterized by high rate of diffuse seismicity, structural complexities and heterogeneous coupling, leading to a source characterized by a complex source time function with relatively slow rupture velocity.

Local events-based fast RTM surface-offset gathers via dip-guided interpolation

Reverse Time Migration (RTM) Surface Offset Gathers (SOGs) are demonstrated to deliver more superior residual dip information than ray-based approaches. It appears more powerful in complex geological settings, such as salt areas. Still, the computational cost of constructing RTM SOGs is a big challenge in applying it to 3D field data. To tackle this challenge, we propose a novel method using dips of local events as a guide for RTM gather interpolation. The residual-dip information of the SOGs is created by connecting local events from depth-domain to time-domain via ray tracing. The proposed method is validated by a synthetic experiment and a field example. It mitigates the computational cost by an order of magnitude while producing comparable results as fully computed RTM SOGs.

Earthquake surface ruptures on the altiplano and geomorphological evidence of normal faulting in the December 2016 (Mw 6.1) Parina earthquake, Peru

The 2016 Mw 6.1 Parina earthquake ruptured a shallow-crustal normal fault within the high Andes of south Peru. We use high-resolution DEMs and field mapping of the surface ruptures generated by the earthquake, in combination with co-seismic and post-seismic InSAR measurements, to investigate how different features of the geomorphology at Parina are generated by the earthquake cycle on the Parina Fault. We systematically mapped 12 km of NW-SE trending surface ruptures with up to ~27 cm vertical displacement and ~25 cm tensional opening along strike, separated by a gap with no observable surface ruptures. Co- and post-seismic InSAR measurements require slip below this gap in surface ruptures, implying that surface offsets observed in paleoseismic trenches may not necessarily be representative of slip at seismogenic depths, and will typically yield an underestimate of paleo-earthquake magnitudes. The surface ruptures developed along 10–20 m high cumulative scarps cutting through late Quaternary fluvio-glacial deposits and bedrock. The 2016 Parina earthquake did not rupture the full length of the late Quaternary scarps, implying that the Parina Fault does not slip in characteristic, repeat earthquakes. At Parina, and across most of the Peruvian Altiplano, normal faults are most-easily identified from recent scarps cutting late Quaternary moraine crests. In regions where there are no recently-deposited moraines, faults are difficult to identify and lack time constraints to quantify rates of fault slip. For this reason, current fault maps may underestimate the seismic hazard in the Altiplano.

Twenty years of European mountain permafrost dynamics—the PACE legacy

This paper reviews and analyses the past 20 years of change and variability of European mountain permafrost in response to climate change based on time series of ground temperatures along a south–north transect of deep boreholes from Sierra Nevada in Spain (37°N) to Svalbard (78°N), established between 1998 and 2000 during the EU-funded PACE (Permafrost and Climate in Europe) project. In Sierra Nevada (at the Veleta Peak), no permafrost is encountered. All other boreholes are drilled in permafrost. Results show that permafrost warmed at all sites down to depths of 50 m or more. The warming at a 20 m depth varied between 1.5 °C on Svalbard and 0.4 °C in the Alps. Warming rates tend to be less pronounced in the warm permafrost boreholes, which is partly due to latent heat effects at more ice-rich sites with ground temperatures close to 0 °C. At most sites, the air temperature at 2 m height showed a smaller increase than the near-ground-surface temperature, leading to an increase of surface offsets (SOs). The active layer thickness (ALT) increased at all sites between c. 10% and 200% with respect to the start of the study period, with the largest changes observed in the European Alps. Multi-temporal electrical resistivity tomography (ERT) carried out at six sites showed a decrease in electrical resistivity, independently supporting our conclusion of ground ice degradation and higher unfrozen water content.

Impact of user parameters in inversion velocity analysis

ABSTRACTMigration velocity analysis is a method devoted to the evaluation of both reflectivity and background velocity models, associated with the high and low wavenumber components of the model, respectively. Inversion velocity analysis is one of its improved versions, leading to more stable background velocity updates. Still, the impact of the user parameters should be understood for an optimal update of the background velocity. We show that a sign reversal of the background velocity gradient could occur when the selected surface offset range or the space lag range is too small. We derive the theoretical limits and check their consistency through simulations in a simple model with a single interface. These guidelines determine the necessary ranges of surface offsets and space lags for a proper update of the background velocity model. We discuss their applicability on the Marmousi model. Artefacts in the retrieved background velocity model are observed when the guidelines are not satisfied.

Late Quaternary Tectonic Activity of the Udine-Buttrio Thrust, Friulian Plain, NE Italy

The NW-SE trending Udine-Buttrio Thrust is a partly blind fault that affects the Friulian plain southeast of Udine in NE Italy. It is part of a wider fault system that accommodates the northward motion of the Adriatic plate. Although seismic reflection data and morphological evidence show that the fault was active during the Quaternary, comparably little is known about its tectonic activity. We used high-resolution digital elevation models to investigate the surface expression of the fault. Measured vertical surface offsets show significant changes along strike with uplift rates varying between 0 and 0.5 mm/yr. We then analyze a topographic scarp near the village of Manzano in more detail. Field mapping and geophysical prospections (Georadar and Electrical Resistivity Tomography) were used to image the subsurface geometry of the fault. We found vertical offsets of 1–3 m in Natisone River terraces younger than 20 ka. The geophysical data allowed the identification of deformation of the fluvial sediments, supporting the idea that the topographic scarp is a tectonic feature and that the terraces have been uplifted systematically over time. Our findings fit the long-term behaviour of the Udine-Buttrio Thrust. We estimate a post-glacial vertical uplift rate of 0.08–0.17 mm/yr recorded by the offset terraces. Our results shed light on the Late Quaternary behaviour of this thrust fault in the complicated regional tectonic setting and inform about its hitherto overlooked possible seismic hazard.

Coseismic Rupture Process of the Large 2019 Ridgecrest Earthquakes From Joint Inversion of Geodetic and Seismological Observations

AbstractOn 4 and 6 July 2019, two large strike‐slip earthquakes with W‐phase moment magnitudes MWW 6.5 (foreshock) and MWW 7.1 (mainshock) struck the Eastern California Shear Zone, northeast of Ridgecrest. The faulting geometry and kinematic coseismic slip distribution of both events are determined by jointly inverting seismological and geodetic observations guided by aftershock and surface rupture locations. The foreshock ruptured two orthogonal faults with a prominent L‐shaped geometry with maximum slip of ~1.1 m on the NE‐SW segment. The mainshock faulting extended NW‐SE along several primary fault segments that straddle the foreshock slip. The surface rupture and slip model indicate mostly near‐horizontal strike‐slip motion with maximum slip of ~3.7 m, but there is a localized vertical dip‐slip motion. Both the foreshock and mainshock ruptures terminate in regions of complex surface offsets. High aftershock productivity and low rupture velocity may be the result of rupture of a relatively immature fault system.

Single-year thermal regime and inferred permafrost occurrence in the upper Ganglass catchment of the cold-arid Himalaya, Ladakh, India

Cold-arid regions of the trans-Himalaya in the Indian Himalayan Region (IHR) is suspected to have a significant area of permafrost. However, information on the ground thermal regime of these permafrost areas is so far not available. This study bridge this knowledge gap by analysing the sub-surface thermal regime of selected sites in the Ganglass catchment, Ladakh range. Near surface ground temperature data recorded during September 2016 to August 2017 using 24-miniature temperature data loggers distributed across 12 plots and covering an elevation range of 4700–5612 m a.s.l. are used in this study. Permafrost characteristics including plausible ranges of thermal offset, active-layer thickness and mean annual ground temperature at 10 m depth were estimated by driving a one-dimensional heat conduction model. Two statistical models were used to map first order estimates of permafrost area in this 15.4 km2 catchment. Study suggest permafrost occurrence at all sites above 4900 m a.s.l. with active-layer thickness ranging from 0.1 to 4.2 m and the mean annual ground surface temperature ranging from between −10.0 and −0.85 °C for these sites. MAAT at these sites range from −4.1 to −8.9 °C and the surface offsets vary from −1.1 to 3.9 °C. Estimated thermal offset range from −0.9 to 0 °C. Both statistical models show comparable results and suggest 95% mean permafrost cover in the catchment above 4727 m a.s.l. These results strongly indicate existence of significant permafrost areas across the high elevations of the cold-arid regions of IHR. So far, permafrost processes are not considered for assessing present and future estimates of water and regional climate and as a causative factor for disasters like debris flows and landslides in the region. This study highlight the need for greater research efforts on Himalayan permafrost to have a comprehensive understanding of Himalayan cryosphere.

Half-Space Power Diagrams and Discrete Surface Offsets.

We present an efficient, trivially parallelizable algorithm to compute offset surfaces of shapes discretized using a dexel data structure. Our algorithm is based on a two-stage sweeping procedure that is simple to implement and efficient, entirely avoiding volumetric distance field computations typical of existing methods. Our construction is based on properties of half-space power diagrams, where each seed is only visible by a half space, which were never used before for the computation of surface offsets. The primary application of our method is interactive modeling for digital fabrication. Our technique enables a user to interactively process high-resolution models. It is also useful in a plethora of other geometry processing tasks requiring fast, approximate offsets, such as topology optimization, collision detection, and skeleton extraction. We present experimental timings, comparisons with previous approaches, and provide a reference implementation in the supplemental material.