Crustal Faults Research Articles

Lineament Domain Analysis to Unravel Tectonic Settings on Planetary Surfaces: Insights from the Claritas Fossae (Mars)

Linear geo-textures are widely recognized on synthetic scaled images of planetary surfaces and consist of elongated alignments of tonal contrasts. When these linear patterns are clustered in azimuthal sets and organized in domains occurring on specific terranes, they reflect the structural grain of the crust and provide clues on the stress trajectories. In this way, the geostatistical analysis of lineament domains represents a useful tool to highlight the geotectonic settings of planetary surfaces. In this work, we applied a lineament domain analysis to better frame the tectonic evolution of the Claritas Fossae (CF) area on Mars, the origin of which is still debated, and both dip–slip and strike–slip tectonics have been described in the literature. A twofold approach was followed that included the identification of a linear pattern with manual and automatic approaches. The automatic method confirmed and validated the results of the manual detection. The statistical analysis of the identified lineaments showed their clustering in two domains that persisted on different terranes separated by the regionally sized scarp associated with the CF. This scarp is the surface manifestation of the CF crustal fault. The spatial distribution of the two domains and their constant angular relationship of about 30° allowed relating one domain to the main CF fault and the other domain to the extensional deformation associated with the fault kinematics. Our results suggest that the CF frames well within a regional setting characterized by right–lateral kinematics with about 20% transtension. Temporal constraints derive from the ages of the terrains where the two domains develop. On this basis, we propose that a first tectonic event occurred in the Noachian age followed by a reactivation occurring after the emplacement of the Late Hesperian lavas.

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Seismicity under a Dormant Volcano: Unveiling Active Crustal Faulting beneath Piton des Neiges, La Réunion

ABSTRACT Volcanic environments are commonly associated with seismic activity. The two prominent shield volcanoes of La Réunion island—Piton des Neiges and Piton de la Fournaise, exhibit sustained seismic activity. Whereas the seismicity at Piton de la Fournaise is tied to its volcanic activity, the seismic activity beneath Piton des Neiges, which has been dormant for 27,000 yr, remains poorly understood. The occurrence of earthquakes under the north flank of Piton des Neiges, often felt by the population, led to the deployment of several seismic stations in the area since 2012. In this study, we employ template matching and double-difference relocation techniques to construct a high-resolution catalog of the region. Our results reveal that the seismicity observed under Piton des Neiges is primarily concentrated on a northeast-dipping fault located in the oceanic crust beneath the volcanic edifice. Analysis of focal mechanisms indicates that this structure operates as a reverse fault. In the vicinity of this primary fault, we also identify secondary seismicity clusters with similar orientation and focal mechanisms. The region has experienced continuous seismicity since 1999, with occasional periods of increased swarmlike activity in 2011 and 2018. These fluctuations in seismicity rate do not correlate with markers of deep magma transfers often observed before eruptions at the Piton de la Fournaise volcano. Beyond the crustal faults highlighted in this study, it is noteworthy that the majority of earthquakes in northern La Réunion island exhibit consistent reverse focal mechanisms. These observations suggest that seismic events may not be driven by deep magmatic activity but, rather, result from regional tectonic stress and edifice loading on pre-existing faults.

Regional structural control on the Mont-Dore Plio-Quaternary volcanism (France)

Magma transfer in the upper crust including emplacement at the surface of the Earth, have been regarded as largely controlled by the regional tectonic activity. While this relationship is well highlighted for systems like monogenetic, mostly basaltic, volcanic fields, the tectonic control on the transfer and emplacement of magmas in complex, polygenetic, volcanic systems, remains poorly documented in evolving tectonic settings. The Mont-Dore Plio-Quaternary volcanic complex (4.7 to 0.3 Ma) is one of such polygenetic volcanic fields as it is formed of three successive eruptive cycles: The caldera unit (3.3 to 2.2 Ma); The Aiguiller complex (2.5 to 1.5 Ma) and the Sancy stratovolcano unit (1.5 to 0.3 Ma).Analyzing fractures, fault kinematics and regional lineaments in the Variscan basement, together with attitude of dikes and volcanic centers alignments of the three volcanic units, we document the influence of the brittle structuration of the underlying basement on the volcanism distribution over time while regional stress changed. The late-Variscan N02E0, and secondary N160, striking crustal faults were reactivated since the Oligocene and channeled at depth the magma, while similarly oriented faults and fractures triggered the final storage in the shallow crust and spatial distribution of the volcanic vents. This fault system continued to act from the Miocene to the present-day uplift, associated with new N020E striking, flat-lying, fractures. An exception arises during the upper Miocene while N060E and N135E striking faults enabled the development of the caldera unit in a NW-SE extensional context.The emplacement of the three units from the mid-Pliocene to the end of the Pleistocene while a change in regional stress field conditions emerged at about 2.5 Ma exemplify the control of the brittle Variscan basement on the magmatic activity of the Mont-Dore Plio-Quaternary volcanic complex.

Unraveling the Complex Interplay: Exploring the Relationships between Seismic and Volcanic Activities in the Colca River Area Using the Coulomb Stress Transfer

Abstract The Colca River area is affected by shallow small-to-moderate earthquakes due to the activity of normal and strike-slip crustal faults on the overriding South American plate. In addition, volcanic activity from the Sabancaya volcano has been recorded. However, the complex relationship between seismic and volcanic activities and the factors that trigger them are poorly understood. To better understand the factors that influence seismic and volcanic activity and their potential connection, it is crucial to characterize the interactions between subsequent earthquakes and assess the impact of magmatic inflation on seismic events. In this study, we analyzed the static Coulomb stress transfer caused by the selected largest earthquakes from 1991 to 2022. We focused on both the assumed source faults and the receiver faults. Furthermore, we examined the Coulomb stress change due to magmatic inflation in 2013–2022 on nodal planes of the selected earthquakes. The results confirm the tectonic source for most earthquakes in the Colca region. Commonly, the magmatic source enhanced the stress change induced by the tectonic source. Although the Coulomb stress change caused by the significant earthquakes had a greater impact than the one resulting from the magmatic inflation, the Coulomb stress transfer seems not to be a dominant factor determining the occurrence and location of earthquakes in this area. The results indicate that most source faults of the analyzed earthquakes were not brought closer to failure due to a positive Coulomb stress transfer caused by seismic activity or magmatic inflation.

Qualitative study of a geodynamical rate-and-state model for elastoplastic shear flows in crustal faults

The Dieterich–Ruina rate-and-state friction model is transferred to a bulk variant and the state variable (aging) influencing the dissipation mechanism is here combined also with a damage influencing standardly the elastic response. As the aging has a separate dynamics, the overall model does not have a standard variational structure. A one-dimensional model is investigated as far as the steady-state existence, localization of the cataclastic core, and its time response, too. Computational experiments with a damage-free variant show stick-slip behavior (i.e. seismic cycles of tectonic faults) as well as stable slip under very large velocities.

Empirical Earthquake Source Scaling Relations for Maximum Magnitudes Estimations in Central America

ABSTRACT Central America is a seismically active region where six tectonic plates (North America, Caribbean, Cocos, Nazca, Panama, and South America) interact in a subduction zone with transform faults and two triple points. This complex tectonic setting makes the maximum magnitude—Mmax—estimation a challenging task, with the crustal fault earthquakes being the most damaging in the seismic history of Central America. The empirical source scaling relations (ESSR) allow the Mmax of faults to be determined from rupture parameters. In this study, we use a dataset of well-characterized earthquakes in the region, comprising 64 events from 1972 to 2021 with magnitudes between Mw 4.1 and 7.7. The dataset incorporates records of rupture parameters (length, width, area, slip, and magnitude) and information on the faults and aftershocks associated. This database is an important product in itself, and through its use we determine which global relations fit best to our data via a residual analysis. Moreover, based on the best-quality records, we develop scaling relations for Central America (CA-ESSR) for rupture length, width, and area. These new relations were tested and compared with recent earthquakes, and logic trees are proposed to combine the CA-ESSR and the best-fit global relations. Therefore, we estimate the Mmax for 30 faults using the logic tree for rupture length, considering a total rupture of the fault and multifault scenarios. Our results suggest that in Central America rupture areas larger than other regions are required to generate the same magnitudes. We associate this with the shear modulus (μ), which seems to be lower (∼30% less) than the global mean values for crustal rocks. Furthermore, considering multifault ruptures, we found several fault systems with potential Mmax≥Mw 7.0. These findings contribute to a better understanding of regional seismotectonics and to the efficient characterization of fault rupture models for seismic hazards.

Delineation of an exhumed intermediate‐depth crustal fault in a collisional setting: An example from the Himalaya

AbstractThe regionally prominent main boundary thrust (MBT) of the Himalayan fold‐thrust belt in northwest India is typically defined by the presence of Proterozoic rocks in the hanging wall and Cenozoic rocks in the footwall. The present study focuses on identifying the MBT contact across Gambar River section in Himachal Pradesh, India, using alternative methodologies, such as the meter‐scale litho‐structural mapping, followed by detrital zircon U–Pb geochronology to precisely identify the thrust contact and provide insights on the deformation history of the MBT zone. We have identified a sharp change in the age (from ~600 to ~61 Ma) of the sedimentary units along a narrow zone in the study area by detrital zircon U–Pb geochronology using LA‐ICP‐MS. The sharp change in the detrital zircon U–Pb age data thus delineate the MBT occurring in the area along a < ~1 m thickness. The lithological assemblage and the age data indicate the unified maximum depositional age from ~700 to ~600 Ma for the hanging wall rocks, which have been equated with the Krol Group of the Lesser Himalayan Sequence (LHS). In comparison, the footwall rocks exhibit the maximum depositional age of ~61 Ma and have been equated with the Cenozoic Subathu Formation of the Sub‐Himalayan Sequence (SHS).

Fault structure and slip mechanics of the 2022 Mw 6.7 Menyuan earthquake revealed by coseismic rupture observations

Large and shallow strike-slip earthquakes produce striking ground ruptures, damaging roads and infrastructure but providing great opportunities for examining the fault's structure. After the 2022 Mw 6.7 Menyuan earthquake, we observed abundant surface fractures by a combination of optical remote sensing, radar offset and unmanned aerial vehicle measurements. These fractures reveal a complex fault structure including apparent bending geometries and bifurcating branches, which are essential to understanding the mechanisms of faulting. In this paper, we used triangular dislocations to construct the fault geometry that reflected the distribution of measured strike changes but avoided unexcepted discontinuities and overlaps where the fault bent. The modeled fault geometry revealed an extensional releasing bend which was responsible for the southward branching of the fault rupture at its western edge. Our results also demonstrated the potential to explain the occurrence of aftershock clusters and to infer their fault geometries through the correlation analysis of the aftershock distribution and the slip induced stress field. The triangular dislocation model also enabled the calculation of the fault plane roughness and its spatial variation which directly controlled the fault slip magnitude and rupture termination. These analyses reveal an unprecedented level of detail of the fault structure and slip mechanics and, to some extent, offer insights into the physical processes and structural properties of crustal faults in the Earth's shallow crust.

Capturing Directivity in Probabilistic Seismic Hazard Analysis for New Zealand: Challenges, Implications, and a Machine Learning Approach for Implementation

ABSTRACT The proximity of fast-slipping crustal faults to urban areas may result in pulse-like ground motions from rupture directivity, which can contribute to increased levels of damage even for engineered structures. Systematic modeling of directivity within probabilistic seismic hazard analysis (PSHA) remains challenging to implement at the regional scale, despite the availability of directivity models in the literature. In the process of developing the 2022 National Seismic Hazard Model for New Zealand (2022 NSHM), we explored the feasibility and impact of modeling directivity for PSHA at a national scale using the previous generation 2010 NSHM. The results of this analysis allowed us to quantify the impact of directivity on the resulting seismic hazard maps for New Zealand and gain insights into the factors that contribute to the expected increases (and decreases) in ground-motion level. For the 2022 NSHM, the earthquake rupture forecast (ERF) seismogenic source models introduced enormous challenges for directivity modeling due to the abundance of large multisegment or multifault ruptures with complex geometries. To overcome these challenges, we applied a machine learning-based strategy to “overfit” an artificial neural network to capture the distributions of directivity amplification and its variability for each unique rupture in the earthquake rupture forecast. This produces a compact representation of the spatial fields of amplification that are computationally efficient to generate within a complete PSHA calculation for the 2022 NSHM. This flexible and reproducible framework facilitates the implementation of directivity in PSHA at a regional scale for complex ERF source models and opens up the possibility of more complex characterization of epistemic uncertainties for near-source ground motion in practice.

A Comprehensive Fault-System Inversion Approach: Methods and Application to NSHM23

ABSTRACT We present updated inversion-based fault-system solutions for the 2023 update to the National Seismic Hazard Model (NSHM23), standardizing earthquake rate model calculations on crustal faults across the western United States. We build upon the inversion methodology used in the Third Uniform California Earthquake Rupture Forecast (UCERF3) to solve for time-independent rates of earthquakes in an interconnected fault system. The updated model explicitly maps out a wide range of fault recurrence and segmentation behavior (epistemic uncertainty), more completely exploring the solution space of viable models beyond those of UCERF3. We also improve the simulated annealing implementation, greatly increasing computational efficiency (and thus inversion convergence), and introduce an adaptive constraint weight calculation algorithm that helps to mediate between competing constraints. Hazard calculations show that ingredient changes (especially fault and deformation models) are the primary driver of hazard changes between NSHM23 and UCERF3. Updates to the inversion methodology are also consequential near faults in which the slip rate in UCERF3 was poorly fit or was satisfied primarily using large multifault ruptures that are now restricted by explicit b-value and segmentation constraints.

Geodetic slip rate partitioning in the central Anninghe and Daliangshan faults: Effects of fault geometry, elastic heterogeneity, and viscoelastic rheology

Geodetic measurements can be employed to estimate the secular slip rates and locking depths of crustal faults, two key parameters which influence assessment of long-term seismic hazard presented by a fault. However, this process requires making assumptions about the rheological properties of the Earth's crust and lithosphere, as well as the fault geometry at depth. Previous geodetic studies have inferred widely varying slip rates and locking depths for the central Xianshuihe-Xiaojiang Fault System, located along the southeastern margin of the Tibetan plateau. In this study, we use updated GNSS measurements, including 13 new velocities, to explore the effects of assumed rheology and fault geometry on the inferred slip rates and locking depths of the subparallel Anninghe (ANH) and Daliangshan (DLS) faults in this region. We demonstrate that only models taking into account the viscoelastic relaxation of the lower crust can resolve the apparent discrepancies. Models assuming a fully elastic rheology suggest very deep locking depths (∼35 km) and a lower slip rate on the ANH fault (∼5 mm/yr) than the DLS fault (∼7 mm/yr). Neither the relative slip rates nor the locking depths agree with seismic or geologic observations. We also consider models assuming a heterogeneous elastic rheology, but find they are indistinguishable from the homogeneous models. Modifying the fault geometry can impact the relative slip rates of the two faults but does not produce a reasonable locking depth either. In contrast, viscoelastic models accounting for seismic cycle effects indicate a faster ANH slip rate (∼5–7 mm/yr), a slower DLS rate (∼4–5 mm/yr), and a shallower locking depth for both faults (∼18 km), all of which are more consistent with independent seismic and geological observations. Our study suggests that steady long-term motion on these faults is modulated by long-lasting viscoelastic effects over a relatively broad region.

Radon Hazard of the Zhurinsky Fault for the Population in the Kuznetsk Coal Basin: Primary Results

The aim of this study is the primary assessment of radon hazard of the Zhurinsky fault of the Kuznetsk coal basin, in the territory of the Salair–Altai–Irtysh fold. Soil radon content, radon flux densities, their spatial characteristics and correlations with each other and with other factors were evaluated. We found that soil radon concentration varies within the range of 3599 to 14,413 Bq/m3 (mean value 8766 ± 569.8 Bq/m3), and radon flux density ranges from 23 to 147 mBq·m−2·s−1 with a mean value of 67.19 ± 1.31 mBq·m−2·s−1. A correlation with air temperature, pressure and humidity was found, which decreases with the depth of the measurements. All studied parameters in space are clustered (p ≤ 0.1). At the same time, the whole studied area in the vicinity of the tectonic disturbance should be classified as radon-hazardous, and residential structures located within its boundaries as potentially hazardous. Our study contributes to understanding the radon hazard of crustal faults.

Quantifying drainage divide migration in active orogens: Insights from the eastern margin of the Tibetan Plateau

Landscape of active orogens results from a competition balance between tectonic rock uplift and erosion. Drainage divide migration is a useful approach for quantifying the landscape evolution and the underpinning drivers, because the fluvial networks adjust their geometry in response to spatiotemporal changes in rock uplift, climate and lithology. Many quantitative geomorphological metrics, such as χ-anomaly, Gilbert metrics, have been proposed to analyze the drainage divide migration. However, their interpretations often yield inconsistent results, especially in tectonically active orogens with spatial changes in rock uplift. The highly elevated and tectonically active eastern margin of the Tibetan Plateau has been studied by multiple methods of different time-scales, producing abundant structural and erosion rates determinations needed for evaluating the landscape stability and evolution. Here, we evaluated the effectiveness of χ- and Gilbert metrics in quantifying the stability of the Longmenshan-Minshan divide parallel with the plateau margin, by comparing with erosion rate data of different time scales, rock uplift predicted by upper crustal structures, bedrock lithology, precipitation. Our analyses reveal that the divide has reached dynamic steady state, as shown by the consistent cross-divide Gilbert metrics and consistent spatial changes of short, medium and long-term erosion rates, indicating the overall balance between the erosion and rock uplift. The spatial changes in rock uplift underpinned by reverse faulting along a listric upper crustal fault also explains the development of cross-divide χ-anomaly that cannot be used as an index for divide migration in regions with spatially nonuniform rock uplift. The formation of the long-term stable drainage divide in the EMTP serves as a natural laboratory for studying the divide formation and evolution in response to a phase of non-uniform rock uplift. We infer that in regions of this kind, drainage divide forms and evolves from uplift-driven to erosion-driven migration, via an intervening stable state.

Exploring the Connection of XVI‐Century Major Historical Earthquakes in the Eastern Betic Cordillera, Spain: Insights From Viscoelastic Relaxation of the Lithosphere

AbstractUnderstanding the crustal fault interaction and connection between earthquakes in areas with slow tectonic deformation, such as Betic Cordillera (South Spain), is challenging. When seismic rates are low and large destructive earthquakes happen less frequently, it is necessary to resort to historical or paleoseismic records. This study investigates the postseismic viscoelastic relaxation mechanism as a potential explanation for the occurrence of three historical earthquakes (IEMSVIII‐IX) in the Eastern Betic Shear Zone during the XVI‐century, all of which occurred within a span of 13 years: 1518 Vera Mw6.2, 1522 Alhama de Almeria Mw6.5, and 1531 Baza Mw6.2 associated with the Palomares, Carboneras, and Baza faults, respectively. The results strongly suggest a sequential stress‐triggering connection between the three events. The northern NS‐oriented section of the Baza fault is found to have experienced a larger positive ΔCFS and, indeed, more prone to rupture in 1531. The study also examines whether the cumulative ΔCFS had influenced the occurrence of further significant earthquakes (≥Mw6.0) in the region. A triggering connection between the cascade and the 1658 Almeria Mw6.2 earthquake is suggested, whereas no indications of similar linkage to the 1674 Lorca Mw6.0 or the 1804 Dalias Mw6.4 events are found. The stress triggering impact of the cascade over nearby active faults is noteworthy. It is expected that this analysis could have future applications for studying other important historical events, and improving seismic hazard analysis in complex fault settings of the Betic Cordillera.

Rupture and Afterslip Controlled by Spontaneous Local Fluid Flow in Crustal Rock

AbstractShear rupture and fault slip in crystalline rocks like granite produce large dilation, impacting the spatiotemporal evolution of fluid pressure in the crust during the seismic cycle. To explore how fluid pressure variations are coupled to rock deformation and fault slip, we conducted laboratory experiments under upper crustal conditions while monitoring acoustic emissions and in situ fluid pressure. Our results show two separate faulting stages: initial rupture propagation, associated with large dilatancy and stabilized by local fluid pressure drops, followed by sliding on the newly formed fault, promoted by local fluid pressure recharge from the fault walls. This latter stage had not been previously recognised and can be understood as fluid‐induced afterslip, co‐located with the main rupture patch. Upscaling our laboratory results to the natural scale, we expect that spontaneous fault zone recharge could be responsible for early afterslip in locally dilating regions of major crustal faults, independently from large‐scale fluid flow patterns.

Volcanic debris avalanche deposits and their significance in the architecture and evolution of the Miocene-Quaternary Călimani-Gurghiu-Harghita volcanic range (Eastern Transylvania, Romania)

The Călimani-Gurghiu-Harghita volcanic range (CGH) represents the surface manifestation of the post-collisional magmatism that followed the docking of its basement, the Dacia Mega Unit, onto the East European margin. Between ca. 11 and 0.3 Ma, detachment of subducted slab, magma generation, and volcanic activity in CGH propagated south-southeastward, sub-parallel with the collisional Eastern Carpathian Orogen, resulting in the construction of a series of mostly composite volcanoes dominated by calc-alkaline lavas and pyroclastic products. The generally well-preserved axial row of the CGH volcanic edifices is accompanied by voluminous volcaniclastic deposits of which sources and emplacement history persist as a matter of debate. In the standard view reflected in regional scale geologic maps, these deposits represent products of complete erosion of hypothetical earlier volcanoes. Other interpretation, however, suggest that they are at least partially constituted by voluminous volcanic debris avalanche deposits (VDADs).By combining evidence from field observation and GIS analysis with published and new data from petrography, bulk-rock geochemistry, and K/Ar geochronology, here we demonstrate that VDADs vastly dominate these volcanoclastic deposits. In addition to two previously identified VDADs (Western Călimani and Vârghiş), we show that further six VDADs (Eastern Călimani, Fâncel-Lăpuşna, Ostoroş, Ivo-Cocoizaş, Luci, and Pilişca) were generated due to the sector failure of a series of CGH volcanoes, most of which still preserve well-distinguishable collapse scars. Based on our estimates, debris avalanches with volumes between <1 km3 and > 100 km3 displaced 0.4–39% of the source edifices, transferring nearly a third of their cumulated volcanic output to the observed volcaniclastic deposits.K/Ar age constraints suggest VDAD formation closely followed in space and time the migrating volcanic activity between ca. 7.8 and 1.5 Ma. Relying on this age pattern, collapse scar orientations, and VDAD runout directions, we propose that regional scale deformation of the Dacia lithosphere imposed by progressive detachment of the underlying subducted slab, manifested on the surface as a transient subsidence–uplift couple traveling along CGH as well as opening of intramountain basins at the eastern flank of the range, was responsible for basement tilting and faulting that destabilised the CGH volcanic edifices. Seismic activity associated with slab detachment and shallow crustal fault system as well as explosive volcanic eruptions may have triggered the collapse of these edifices, leading to the generation of the VDADs.

Active subduction and strain partitioning in western Myanmar revealed by a dense survey GNSS network

The active tectonics of the Myanmar (formerly Burma) microplate in central Myanmar are caused by the oblique collision between the Sunda and Eurasia plates to the east and the Indian plate to the west. The kinematics of this plate boundary zone remain a subject of controversy, due in part to limited geodetic and seismic observations in the region. Here, we report 41 new and 67 updated survey-mode and continuous Global Navigation Satellite System (GNSS) velocities spanning central and western Myanmar, between 15 – 23°N and 93 – 98°E. For the first time, our network allows us to directly observe the occurrence of active convergence along the central Rakhine coast in a manner consistent with active subduction and kinematic coupling of the megathrust, at a rate of 15 – 20 mm/yr. The data also establish a nearly constant strike-slip rate of 20 – 23 mm/yr along the entire length of the Sagaing fault. Using an elastic block-modeling approach, we examine several proposed models for the partitioning of oblique convergence into strike-slip and thrust motion across the Indo-Myanmar Ranges and the Myanmar Central Basin. We find evidence for shortening perpendicular to local topography throughout the Indo-Myanmar Ranges, indicating active convergence and nearly complete strain partitioning between thrust and transform faults north of 19°N, and estimate a rate of moment-deficit accumulation along the megathrust of 0.8−1.5×1019 N m/yr, equivalent to one MW 9.0 earthquake every 250 to 450 years, assuming all elastic strain is released seismically. We also find that a relatively small set of major active crustal faults can explain much of the data, though the data cannot resolve smaller faults that may be active at rates lower than a few mm/yr. Our results have important implications for earthquake and tsunami preparedness across the region, and indicate areas for future study where the geodetic observations remain ambiguous about ongoing fault activity and seismic hazard, particularly within the densely populated Ayeyarwady Delta region and along the southern Rakhine coast.

Deciphering Permanent Uplift Along the Pacific Coast of South America Through Signal Analysis of Various Tectonic Processes

AbstractThe tectonically active South American margin is characterized by the accumulation of deformation contributing to uplift of the Andean forearc at millennial time scales. However, the mechanisms responsible for permanent coastal uplift are debated, mainly because methodologically consistent, continental‐scale analyses of uplifted terraces have not yet been carried out for South America. Uplifted marine terraces are generally used to infer permanent coastal deformation and uplift; we used almost 2,000 measurements of last‐interglacial marine terraces to calculate an uplift‐rate signal on which we performed a wavelength analysis. The same spectral analysis was applied to tectonic and subduction parameters associated with accumulation of permanent deformation to detect possible links with the uplift‐rate signal. The uplift‐rate signal displays a constant background‐uplift rate along the margin, perturbed by changes at variable wavelengths. Similarities between its wavelength spectrum and the spectra of tectonic parameters suggest potential correlations pointing toward underlying processes. For example, crustal faulting is mainly responsible for short‐wavelength deformation; intermediate‐wavelength to long‐wavelength tectonic features indicate various extents of locked areas on the megathrust that relate to its long‐term seismotectonic segmentation. We suggest that moderate, long‐term background uplift is caused by major, deep earthquakes near the Moho, although records of such events are sparse. Due to their disparate occurrence, we infer accumulation of permanent deformation over millennial time scales through multiple, distinct uplift phases that are spatially and temporally distributed. Our study highlights the application and utility of a signal‐analysis approach to elucidate the mechanisms driving surface deformation in subduction zones at a continental scale.

Complex Crustal Deformation Controlled by the 3D Geometry of the Chile Subduction Zone

ABSTRACT The Chilean subduction zone hosts Mw&amp;gt;8 earthquakes, which could trigger earthquakes on crustal faults located along the plate margin. Using synthetic earthquakes from a quasi-dynamic boundary element method model, we obtain traction fields and perform a slip tendency analysis to obtain synthetic faults, which we compare with existing potentially seismogenic crustal faults. With our results, we find geometric patterns of the highest slip tendency planes with deformations induced by synthetic subduction events, such that north of the rupture area of each event, correlate with normal N20°W–50°W/N60°SW fault planes, and to the south, correlate with normal N30°E–80°E/N60°NW faults planes. These observations agree with observed fault traces in central and northern Chile, and past observations of crustal fault reactivation.