Fault-slip Analysis Research Articles

The landform Deformation at the Iraq-Iran Border due to Earthquakes in the Period (2017-2018)

The study targets to assess the potential of Interferometric Synthetic Aperture Radar (InSAR) in detecting ground distortion caused by earthquakes. The inSAR technique integrates Synthetic Aperture Radar (SAR) and interferometry to reveal the slightest changes on the earth's surface through a specified period, impregnable to climate or time of day. The research analyses some scholarly articles to demonstrate the interest of InSAR in examining earthquakes and their outcome. These articles demonstrate the practical application of InSAR in enhancing fault slip analysis, ground deformation assessment, and early post-seismic changes in earthquakes. InSAR is beneficial with measurements from other tools, such as GPS and time series analysis, but it still offers valuable insights into earthquake characteristics and associated effects. The insights from these methodologies can help devise solutions to mitigate the impacts of earthquakes. In addition, the paper presents information about three earthquake swarm events and their corresponding fault types. The first event occurred on November 12th, 2017, while the second happened on November 25th, 2018. Despite their differences in magnitude and location, the second event was associated with a strike-slip fault. InSAR provides extensive practical applications, from natural hazard monitoring to infrastructure projects and topographic mapping.

Kinematic and dynamic fault slip analyses: Implications from the surface rupture of the 2023 Elbistan (Kahramanmaraş) (Mw7.6) earthquake, Türkiye

On 6 February 2023, the Elbistan (Kahramanmaraş) (Mw7.6) earthquake produced a strike-slip type coseismic surface rupture zone, involving the sinistral slip of the Doğanşehir Fault (DF) and Çardak Fault (ÇF). Fault slickenlines and seismic slickenlines were included in the inversion as part of the dynamic analysis. The inversion of fault slickenlines collected from nine outcrops along the surface rupture following the earthquake, many of which developed during the event and are referred to as coseismic slickenlines, reveals a strike-slip stress regime (σ2 = σv) characterized by a NE-SW (mean azimuth: N045°E) σ1 (maximum) axis. Relict slip planes adjacent to main slip surfaces were found to host slickenlines that appear much older than the most recent earthquake, referred to as paleoslip slickenlines. Inversion of the paleoslip slickenline collected from four outcrops reveals an extensional stress regime (σ1 = σv) characterized by a NE-SW σ3 (min) axis, consistent with previously published studies. To define a significant stress tensor concerning present-day faulting within the investigated area, the inversion method was applied to the seismic slickenlines of shallow earthquakes in the surface rupture area. The inversion of sixty selected nodal planes reveals a strike-slip stress regime (σ2 = σv) characterized by an NNE–SSW (N10°E) σ1 (max) axis. Besides, the moment tensor summation analysis using displacement vectors inferred from visible field markers offset during the earthquake was applied to the seismic slickenlines as part of the kinematic analysis. The shortening and extension results for the moment tensor summation are 044/36 and 307/11 indicating NE-SW compression. Results of the moment tensor summation (weighted by fault displacement) agree broadly with the inversion of seismic slickenlines results, indicating an NE orientation for shortening and an SE orientation for extension.

Evolution of tensile fractures in feldspar porphyroclast and its implication in paleostress estimation

Fractures are ubiquitous brittle features of the upper crust. Syntectonic granites are often replete with fractures of various attitudes, cross-cutting each other, which develop under the prevalent states of stress. In this article, we study the origin and mechanism of formation of tensile fractures restricted within rectangular alkali feldspar porphyroclasts found in Closepet granite (Dharwar Craton, India), and venture on the possibility of using them as potential paleostress marker. The study is conducted using finite-element-method (FEM) to assess the distribution of induced stresses within the porphyroclasts considering the geometry and varying mechanical properties of the porphyroclast and the embedding matrix. We infer that fractures in the porphyroclast develop due to amplification and concentration of far-field stresses within it. The direction of maximum principal compressive stress as indicated by the fractured porphyroclasts lies in close proximity to the paleostress direction derived from fault-slip analysis of adjacent bodies such as Chitradurga Schist Belt and Koppal syenite (Dharwar craton). Therefore, we advocate that fractured feldspar porphyroclasts are a reliable indicator of paleostress orientations.

Induced Seismicity Hazard Assessment for a Potential CO2 Storage Site in the Southern San Joaquin Basin, CA

California’s Central Valley offers vast opportunities for CO2 storage in deep saline aquifers. We conducted an induced seismicity hazard assessment for a potential injection site in the southern San Joaquin Basin for 18 years of injection at 0.68 MtCO2/yr and 100 years of monitoring. We mapped stress, faults, and seismicity in a 30 km radius around the site to build a geomechanical model and resolve the stresses on major faults. From a 3D hydromechanical simulation of the CO2 plume, we calculated the change in pressure over time on these faults and determined the conditions for safe injection. Lacking any subsurface imaging, we also conducted a probabilistic fault slip analysis using numerous random distributions of faults and a range of geomechanical parameters. Our results show that the change in probability of fault slip can be minimized by controlling the size, migration, and magnitude of the pressure plume. We also constructed a seismic catalog for the last 20 years around the site and characterized the natural patterns of seismicity. We use these results to establish criteria for evaluating potential-induced events during the storage period and to develop a traffic light response system. This study represents a first-order procedure to evaluate the seismic hazards presented by CO2 storage and incorporate uncertainties in hydrological and geomechanical parameters.

Kinematic analysis of the mesozoic - Early Cenozoic deformation in the paipote basin (27°10′S)

An integrated structural and kinematic study focused on the characterization of an Andean Mesozoic basin was carried out in the upper stream of the Paipote Creek, in the western limit of the Southern Puna, Fault slip data analysis (n = 80) and structural observations at different scales were collected from Triassic to Upper Cretaceous volcanic and sedimentary units to constrain the structural architecture and the kinematic evolution of the area. Regional observations provide evidence for syntectonic extensional deposition during the Triassic - Jurassic and positive tectonic inversion from at least the Late Jurassic. Extensional features such as growth strata, harpoon structures and roll-over anticlines, helped to infer two main depocenters controlled by west dipping listric faults. E-W extension directions have been recognized in Triassic - Jurassic units, linked to an extensional basin architecture, and mixed contraction directions were related to compressional and strike-slip deformation in the area. A forward model is proposed based on the interpreted architecture in depth of the basin, defining two major depocenters that, together, define the Paipote basin. A shortening estimate of 21% (5,44 km) was calculated for the basin, wich corresponds to the lowest shortening values reported for the Triassic-Jurassic basins in the Atacama region. The strike-slip deformation can be associated previously with recognized NW-SE strike-slip faults, and aids in proposing the Paipote basin as a transitional zone between the Lautaro basin to the south and the Potrerillos basin to the north.

3D in situ stress state modelling and fault reactivation risk exemplified in the Ruhr region (Germany)

Throughout the 700-yearlong coal exploration period in the Ruhr region, an abundance of geological, geophysical, seismic, and in situ stress data was obtained from the Carboniferous strata. In this study, we take advantage of this unique dataset to develop a static 3D geomechanical model to predict the spatially continuous distribution of undisturbed in situ stress state and evaluate the reactivation risk of major fault zones. Compared to the point-wise stress information, the spatially continuous in situ stress state provides an effective tool for planning subsurface operations and assessing seismic hazards in areas where no stress information is available. The developed model was validated against a comprehensive calibration dataset including results from geophysical logging, borehole deformation, and fault-slip analysis, in situ hydrofracturing measurements, distribution of subsidence, microseismicity, and observations from coal mining activities. Consequently, interpretation and assessment of the model results including their uncertainties, reliability, limitations, and perspectives are discussed. The possible applications of the model approach for seismic hazard prediction and utilization of deep geothermal energy in the Ruhr region are outlined.

The structural pattern and tectonic evolution of the Muráň fault revealed by geological data, fault-slip analysis, and paleostress reconstruction (Western Carpathians)

The structural pattern and tectonic evolution of the Muráň fault revealed by geological data, fault-slip analysis, and paleostress reconstruction (Western Carpathians)

Pre-evaluation of fault stability for underground mining based on geomechanical fault-slip analysis

In underground near-fault mining, fault reactivation is related to many kinds of mine disasters such as mine water inrush, mine earthquakes, gas outburst, rock burst, roof collapse. pre-evaluation of fault stability in the pre-mining phase is of great significance for predicting possible mine fault-related disasters. In this study, based on the geomechanical analysis of fault slip tendency, a technique to the pre-mining evaluation of fault stability under Andersonian stress system was introduced by extending the original Morris’s theory of fault slip-tendency, effects of fault orientation, in-situ stress and pore fluid pressure on fault stability were analyzed. Taking Shilin coal mine as the research background, a pre-evaluation on the stability of all 15 faults distributed in the whole coalfield at the mining depths of 369 and 514 m was conducted, the analysis results demonstrated that all faults in the Shilin coalfield are quite stable at the two mining depths. The work presented in this study is practical and can provide a quantitative geomechanical way in the analysis of pre-mining fault stability and in the risk pre-assessment of fault-related mine disasters.

Kinematic analysis of fault-slip data in the Nanling Tectonic Belt and Cretaceous to Paleogene tectonic evolution of the Central South China Block

• Six tectonic events were inversed from fault-slip analysis in the Nanling Tectonic Belt. • Four Cretaceous tectonic events resulted from the Paleo-Pacific subduction . • Two Paleogene tectonic events were due to the far field effect of the India-Asia collision. Cretaceous tectonic events and Cenozoic geodynamics of the central South China Block are still under debate. A long-term extensional regime or two extension-contraction tectonic cycles were proposed for the Cretaceous tectonic evolution. While Cenozoic geodynamics of the central South China Block were ascribed to the Pacific subduction or the far field effect of the India-Asia collision. Kinematic analysis of fault-slip data were carried out for the Cretaceous to Paleogene Chaling-Yongxing Basin and the Lianshan-Yangshan Domain in the Nanling Tectonic Belt. Kinematic analysis of fault-slip data (409 groups of faults and striations) reveal four Cretaceous tectonic events and two Paleogene tectonic events. i) The early Early Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which generated NE-striking boundary normal faults of Early Cretaceous basins. ii) The late Early Cretaceous strike-slip regime is characterized by a N-S horizontal maximum principal stress and a E-W horizontal minimum principal stress, which led to tectonic inversion of Early Cretaceous extensional basins and nearly N-S-striking folding of the Lower Cretaceous. iii) The early Late Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which activated the NE-striking boundary normal faults of Late Cretaceous basins. And iv) the latest Late Cretaceous strike-slip regime is characterized by NW-SE horizontal maximum principal stress and a NE-SW horizontal minimum principal stress, which led to tectonic inversion of Late Cretaceous extensional basins and NNE-striking folding of the Upper Cretaceous. Orientations of maximum or minimum principal stresses imply that two extension-contraction tectonic cycles during the Cretaceous resulted from the Paleo-Pacific subduction. Two Paleogene tectonic events are v) the strike-slip regime characterized by NE-SW horizontal maximum principal stress and a NW-SE horizontal minimum principal stress, and vi) the subsequent extensional regime represented by a NE-SW minimum principal stress and a vertical maximum principal stress. The former generated NW-striking reverse faults and reactivated strike-slipping of NE- and NW-striking conjugate faults whereas the latter formed NW-striking normal faults in the Lower Paleogene clastic rocks. Orientations of maximum or minimum principal stresses indicate that two Paleogene tectonic events in the central South China Block were attributed to the far field effect of the India-Asia collision and subsequent stress relief.

Recent temporal changes in the stress state and fault reactivation assessment of HTB underground gas storage in China associated with gas injection and extraction

The stress state variations due to seasonal injection and extraction of gas in HTB underground gas storage (HTB-UGS) were estimated, as well as the fault-slip analysis of the main fault, to understand how gas injection and extraction result in earthquakes. The stress state at different depths at the time of a complete depletion in 2012 was first estimated using image-logged borehole breakout data and stress inversions of focal mechanism solutions. Further, the temporal variations of the stress state caused by changes in the pore pressure due to gas injection and extraction were estimated based on a simple pore pressure-stress coupling assumption. The fault reactivation/slip tendency temporal changes and their possible relation with seismicity in this area were analyzed. Results revealed that the stress orientation in the reservoir layer was around N21°E−N23°E, which was consistent with the tectonic stress prevailing direction. The stress regime varied between reverse and strike-slip faulting stress regimes during the gas injection and extraction cycles. The main fault-slip tendency initially decreased continuously with gas production and then increased with gas injection. Earthquake sequences appeared when the slip tendency increased to a critical value of 0.45 ± 0.03.

Modelling of fault reactivation mechanisms and associated induced seismicity in rocks with different elastic materials

The mechanical failure of fault plane during fluid injection can be conveniently approached by numerical methods, and the results can be applied in fault slip analysis to determine the corresponding magnitude of induced seismicity. During hydrofracturing, when faults are present and the fluid is injected into the fault, micro-seismic events are possible, although the magnitude is often somewhat larger than those associated with micro-seismic events produced from regular hydraulic fracturing because of the larger surface area available for fault rupture. This study considers the rate at which the changing elastic properties of materials influences the magnitude of seismic event during fault injection. The simulation is carried out under varying injection flow rates from 0.18 kg/s to 0.3 kg/s, and the thermo-hydro-mechanical (THM) model in FLAC3D is adopted. As the material elastic moduli increase significantly under isothermal injection, the resulted non-uniformity in the fault slip timing affects the magnitude of injection-induced seismicity. Rocks with lower moduli produced higher slip distance and seismicity during shear failure. However, in the coupled thermal case, the magnitudes of seismicity during injection are largely enhanced at lower elastic properties, which suggests that the energy of accumulated fluid pressure produces a larger rupture and longer slip displacement in cold injection than in the isothermal case. The resulting volumetric strain, both in the fault zone and in the matrix, is higher in lower moduli, meanwhile, it is much developed in non-isothermal injection as a result of the rock's response to the sum effect of thermal strain and the stress-induced strain.

New tectonic configuration in NW Iran: Intracontinental dextral shear between NW Iran and SE Anatolia

The Main Recent Fault (MRF) is a major active strike-slip fault system at the NE border of the Arabian platform and Central Iran. Both geometry and kinematics of the fault system is rather well known along its central part and at its SE termination, while its possible continuation to the northwest is ambiguous. Moreover, less regard has been paid to possible relationships between this major intracontinental fault system and other strike-slip faults in NW Iran – SE Anatolia. This paper investigates both the structural pattern and kinematics of deformation in the region to the north of latitude 37°N, between the North Tabriz Fault and the MRF. We followed this goal through detailed fault mapping, structural field measurements, and fault-slip analyses, complemented by the reconstruction of cumulative geomorphic offsets along the main fault segments. The collected data sets have led us to propose a new tectonic model for the northwest corner of the Arabia – Central Iran collision zone. Our results reveal that the intracontinental dextral shear between Arabia-Central Iran, which is mainly localized along the MRF, continues to the north of latitude 37°N along a branch of the Neotethyan suture penetrating into SE Anatolia. The dextral fault system abruptly dies out at latitude 37.5° N joining two NNW-striking normal fault zones, which accommodate the dextral translation of Central Iran relative to Arabia through ESE-trending extension. The region in NW Iran and SE Anatolia is affected by a heterogeneous active stress field due to different tectonic processes such as tectonic escape, block translation, and localized extension. The dynamics of these processes is either directly governed by the Arabia – Eurasia oblique convergence or indirectly controlled by frontal collision and pure shear deformation in central Anatolia.

Fault reactivation and propagation in the northern Adamello pluton: The structure and kinematics of a kilometre-scale seismogenic source

The northern Adamello batholith (European Southern Alps) is crosscut by E-W trending pseudotachylyte-bearing paleoseismic fault zones composed of multiple subparallel fault strands. The main faults are the Gole Strette Fault Zone (GSFZ), here discussed in detail, and the Gole Larghe Fault Zone (GLFZ). The western ending of the GSFZ intersects the propagation of the Gallinera Thrust, a regional structure of Late Cretaceous age, which was truncated and dismembered by the late Eocene - early Oligocene emplacement of the Adamello batholith. Fault slip analysis and paleostress reconstruction suggest that the GSFZ and the Gallinera Thrust were both active during dextral transpression related with Oligocene orogen-parallel shearing along the Periadriatic Fault System. The remnants of the Gallinera Thrust within the Adamello were reactivated as dextral-reverse faults and do not include pseudotachylytes. The pseudotachylyte-bearing GSFZ shows changing structural features from west to east: the fault dip angle decreases from 80° to 45°, the slip vector passes from strike-slip (pitch of 20°) to oblique (pitch of 35° to 45°), and the fault zone thickness increases (> 800 m at the intersection with the GLFZ). The GSFZ is an immature and strong fault as indicated by (i) the local geometry controlled by precursor joints; (ii) the along-strike segmentation; and (iii) the spread of seismogenic faults into wide fault zones.

Paleostress reconstruction of faults recorded in the Nied\u017awiedzia Cave (Sudetes): insights into Alpine intraplate tectonic of NE Bohemian Massif

Brittle structures identified within the largest karstic cave of the Sudetes (the Niedźwiedzia Cave) were studied to reconstruct the paleostress driving post-Variscan tectonic activity in the NE Bohemian Massif. Individual fault population datasets, including local strike and dip of fault planes, striations, and Riedel shear, enabled us to discuss the orientation of the principal stresses tensor. The (meso) fault-slip data analysis performed both with Dihedra and an inverse method revealed two possible main opposing compressional regimes: (1) NE–SW compression with the formation of strike-slip (transpressional) faults and (2) WNW–ESE horizontal compression related to fault-block tectonics. The (older) NE-SW compression was most probably associated with the Late Cretaceous–Paleogene pan-regional basin inversion throughout Central Europe, as a reaction to ongoing African-Iberian-European convergence. Second WNW–ESE compression was active as of the Middle Miocene, at the latest, and might represent the Neogene–Quaternary tectonic regime of the NE Bohemian Massif. Exposed fault plane surfaces in a dissolution-collapse marble cave system provided insights into the Meso-Cenozoic tectonic history of the Earth’s uppermost crust in Central Europe, and were also identified as important guiding structures controlling the origin of the Niedźwiedzia Cave and the evolution of subsequent karstic conduits during the Late Cenozoic.

Direct Inversion Method of Fault Slip Analysis to Determine the Orientation of Principal Stresses and Relative Chronology for Tectonic Events in Southwestern White Mountain Region of New Hampshire, USA

The orientation and relative magnitudes of paleo tectonic stresses in the western central region of the White Mountains of New Hampshire is reconstructed using the direct inversion method of fault slip analysis on 1–10-m long fractures exposed on a series of road cuts along Interstate 93, just east of the Hubbard Brook Experimental Forest in North Woodstock, NH, USA. The inversion yields nine stress regimes which identify five tectonic events that impacted the White Mountain region over the last 410 Ma. The inversion method has potential application in basin analysis.

Assessment of pore pressure, wellbore failure and reservoir stability in the Gabo field, Niger Delta, Nigeria - Implications for drilling and reservoir management

This work investigates a 3400m thick Tertiary succession from the prolific Gabo hydrocarbon field in the Niger Delta and presents a well-scale geomechanical model to address the pore pressure, borehole stability and fault slip potential attributes. The Tertiray stratigraphy is dominated by cyclic clastic sedimentation and it produces hydrocarbon from the Eocene Agbada Formation. An average vertical stress gradient of 0.85-0.90 PSI/feet is interpreted from the density logs. Extensive direct downhole measurements indicate a sub-hydrostatic pressure gradient of 0.325 PSI/feet in the Upper Agbada reservoir sands, while the lower producers are presently in hydrostatic regime (0.435 PSI/feet). Pore pressure against the shales are estimated by Eaton’s disequilibrium compaction method, which are found to be mildly overpressured (0.49 PSI/feet). The minimum horizontal stress (Shmin) gradient ranges between 0.59 and 0.70 PSI/feet. Wellbore stability is addressed by the Mohr-Coulomb failure model and the assessed failures are corroborated with the caliper log observations. Drilling mud weight used in the studied wells were found to be less than the shale collapse pressure gradient, resulting in selective wellbore over-gauging in the Eocene shales, intercalated with the sandstone reservoir intervals. Safe and effective downhole pressure window is inferred from the interpreted pore pressure, collapse pressure and Shmin to avoid any kick, loss or compressive wellbore failures by optimum mud weight designing. Inferences on drilling optimization are discussed which will be helpful for better planning of the infill injector wells. A fault slip analysis indicates that pore pressure could be increased by 1100-1200 PSI during the repressurization in the Upper and Lower Agbada reservoirs without inducing reservoir instabilities as well as caprock failure.

Reconstruction of the stress regime in the Jiaolai Basin, East Asian margin, as decoded from fault-slip analysis

The East Asian margin has experienced a complex tectonic history since the Mesozoic and has developed a complex basin-mountain system. The Jiaolai Basin, which is located on the East Asian margin, is a typical Mesozoic rift basin that has undergone multiple tectonic episodes. Here, using field geological surveys, effective stress inversions, and accurate chronological data, we recognize six tectonic episodes that have occurred in the Jiaolai Basin since the Cretaceous: E-W extension (135-121 Ma), which controlled the early deposition of the Laiyang Group; NW-SE extension (120-93 Ma), which controlled the late deposition of the Laiyang Group and the eruption of the volcanic rocks in the Qingshan Group; NE-SW compression (92-86 Ma), which produced folding of the Qingshan Group and its underlying strata and the formation of the unconformity surface between the Wangshi and the Qingshan Groups; N-S extension (85-60 Ma), which controlled the deposition of the Wangshi Group; NW-SE compression (60-55 Ma), which produced the unconformity between the Wangshi Group and the Wutu Group; and NE-SW extension (ca. < 55 Ma), which controlled the deposition of the Wutu Group. Considering the subduction history of the Izanagi plate and the Pacific plate, the activities of these plates may have primarily controlled the temporal variation in the intraplate paleostress regime in the East Asian margin.

Control of pre-existing fabric in fracture formation, reactivation and vein emplacement under variable fluid pressure conditions: an example from Archean greenstone belt, India

Abstract. Most of the upper crustal fluid flows are strongly influenced by the pre-existing fractures/foliations in the rocks under a certain state of tectonic stress and fluid pressure condition. In the present study, we analyzed a wide range of crosscutting fractures that are filled with quartz veins of variable orientations and thicknesses, from the gold-bearing massive metabasalts (supracrustals) of the Chitradurga Schist Belt adjacent to the Chitradurga Shear Zone (CSZ), Western Dharwar Craton, southern India. The study involves the following steps: (1) analyzing the internal magnetic fabric, using anisotropy of magnetic susceptibility (AMS) studies, and determining strength of the host metabasalts, (2) quantifying the fluid pressure condition through lower hemisphere equal area projection of pole to veins by determining the driving pressure ratio (R′), stress ratio (ϕ), and susceptibility to fracturing, and (3) deciphering the paleostress condition using fault-slip analysis. We interpret the NNW–SSE to NW–SE (mean 337/69∘ NE) oriented magnetic fabric in the rocks of the region as having developed during regional D1/D2 deformation on account of NE–SW shortening. However, D3 deformation manifested by NW–SE to E–W shortening led to the sinistral movement along CSZ. As a consequence of this sinistral shearing, fractures with prominent orientations formed riedel shear components, with CSZ as the shear boundary. Subsequently, all the pre-existing fabrics along with the riedel shear components were reactivated and vein emplacement took place through episodic fluid pressure fluctuation from high to low Pf at shallow depth (∼ 2.4 km). However, NNW–SSE orientations were prone to reactivate under both high- and low-Pf conditions, thereby attaining maximum vein thickness along these orientations. The deduced paleostress from fault-slip analysis along with the kinematics of the fractures and veins are in good agreement with previously estimated regional tectonics. Thus, integrating multiple domains of studies helps in the logical interpretation of fluid flow conditions and vein emplacement mechanisms in the study area that has not been ventured before.

Structural Analysis of the Western Afar Margin, East Africa: Evidence for Multiphase Rotational Rifting

AbstractThe Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N‐S striking WAM is still actively deforming and is characterized by NNW‐SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first‐ever borehole‐calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large‐scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.

Short communication: A semiautomated method for bulk fault slip analysis from topographic scarp profiles

Abstract. Manual approaches for analyzing fault scarps in the field or with existing software can be tedious and time-consuming. Here, we introduce an open-source, semiautomated, Python-based graphical user interface (GUI) called the Monte Carlo Slip Statistics Toolkit (MCSST) for estimating dip slip on individual or bulk fault datasets that (1) makes the analysis of a large number of profiles much faster, (2) allows users with little or no coding skills to implement the necessary statistical techniques, (3) and provides geologists with a platform to incorporate their observations or expertise into the process. Using this toolkit, profiles are defined across fault scarps in high-resolution digital elevation models (DEMs), and then relevant fault scarp components are interactively identified (e.g., footwall, hanging wall, and scarp). Displacement statistics are calculated automatically using Monte Carlo simulation and can be conveniently visualized in geographic information systems (GISs) for spatial analysis. Fault slip rates can also be calculated when ages of footwall and hanging wall surfaces are known, allowing for temporal analysis. This method allows for the analysis of tens to hundreds of faults in rapid succession within GIS and a Python coding environment. Application of this method may contribute to a wide range of regional and local earthquake geology studies with adequate high-resolution DEM coverage, enabling both regional fault source characterization for seismic hazard and/or estimating geologic slip and strain rates, including creating long-term deformation maps. ArcGIS versions of these functions are available, as well as ones that utilize free, open-source Quantum GIS (QGIS) and Jupyter Notebook Python software.