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"Thrust faults"
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Active faulting and seismicity, Northwest Pakistan: a case study of Peshawar Basin Pakistan
Active Faults in urban and densely populated areas are of great importance to understand, as these faults may be of high risk to life and property. Peshawar Basin covers Peshawar, the capital of Khyber Pakhtunkhwa, and other populated areas of the Swabi, Mardan, Nowshera, and Charsadda districts. This research article focuses on active faulting and seismic activity in the Peshawar Basin. Fault causes a sudden release of energy in the form of an earthquake when stress exceeds the Strength of a rock. More than 12,000 earthquakes have been reported in the Peshawar Basin, ranging from 1 to 5.7 on the Richter scale. The shallow nature of these earthquakes is a clear indication of ongoing tectonic activity in the region, resulting in active faults in the Peshawar Basin. Intense Field observations and detailed Digital Elevation Model (DEM) analysis analysis confirm active faults in the Peshawar Basin. Field observations of Peshawar Basin cover the study of infrastructures along the active faults where only 10% of the rocks are exposed. Fracture data was collected from infrastructure and this data was carefully analyzed as well. Based on this analysis six active faults are marked. Charsada-Takhbhai Fault, Mardan Fault, Pir Piai Fault, and Swabi Fault are marked as normal, whereas Pir Sabak and Ghorghushti Fault are thrust faults in nature. Normal faults and tilting were also observed in the alluvial deposits, on a small scale, but it is a manifestation of the same phenomenon on a larger scale in the Peshawar Basin. In the Southern part of the Peshawar Basin, active faults were identified and recognized in the near past. This research is significant because it covers the whole Peshawar Basin and this study was never done before. This research shows that these active faults particularly the Swabi fault may be of high risk to the world’s largest earth-filled Tarbela dam and surrounding areas. Subsidence of more than 2 cm per year is observed in the area along the Swabi and Ghoghasti faults.
Journal Article
From oblique thrust to strike-slip fault; progressive stages of an accretionary wedge development
Accretionary wedges of orogenic belts develop differently based on the direction of thrusting, which can be perpendicular to oblique to the belt. In the case of oblique thrusting, stress partitioning occurs, which dissects the accretionary wedge, changes the tectonic regime from thrusting to strike-slip, and causes the external parts to rotate laterally. The relationship between stress partitioning and external rotation is not yet fully understood and has typically been studied separately. This study investigates the Falkenstein-Mikulov fault zone in the Outer Western Carpathians (OWC) wedge as an illustrative example of the relationship between partitioning and rotation. Using a prominent limestone marker horizon and a multidisciplinary approach-including geomorphological analysis, geological mapping, paleostress analysis, and shallow and deep-seismic geophysical surveys-we defined the fault zone's unique arcuate geometry and identified several stages of tectonic activity. Paleostress inversion reveals multiple tectonic phases highlighting a transition from thrusting to strike-slip faulting. After thrusting (Phase D1), transversal strike-slip faults segmented the wedge coinciding with significant counterclockwise rotational patterns (Phase D2). Finally, during Phase D3, an arcuate strike-slip fault zone parallel to thrusting direction evolved, also revealing rotation of 12° over a distance of 10 km. These phases interplayed in the accretionary wedge at the same time, and their apparent succession is the result of shifting of the tectonic activity during the progressive development of the wedge. Thus, the thrusting activity in the front of the wedge was followed by rotational motion along the lateral ramps and finalized by parallel strike-slip faulting. This model explains how accretionary wedges undergo external rotation due to curved strike-slip faulting in the final stages of thrusting and has significant implications for understanding the broader tectonic evolution of accretionary wedges worldwide.
Journal Article
DInSAR Analysis of Ground Deformation Induced by the 2023 Al Haouz Earthquake, Morocco
The study investigates the co-seismic ground deformation induced by the Mw 7.2 Al Haouz earthquake that occurred on September 8, 2023, in the Al Haouz region of Morocco. The research employs Differential Interferometric Synthetic Aperture Radar (DInSAR) analysis of Sentinel-1A satellite images acquired before and after the mainshock to map co-seismic deformation patterns and estimate displacement fields. Through this approach, distinct fringe patterns were revealed, indicating significant crustal deformation, with a maximum uplift of approximately 24 cm in the line-of-sight (LOS) direction near the epicenter. Notably, incomplete fringes indicating subsidence were observed in both the northern and southern portions of the fringe lobe, with an associated displacement of approximately 5 cm. The deformation pattern is consistent with a thrust fault mechanism along an ENE-trending reverse fault, forming a horst-pop-up structure. Our findings provide significant insights into the seismogenic fault system and regional tectonics, improving our understanding of earthquake mechanics in this intraplate context and demonstrating the effectiveness of DInSAR in capturing detailed snapshots of co-seismic deformation associated with the devastating event. Additionally, these results have important implications for seismic hazard assessment and disaster risk reduction in Morocco's tectonically active regions.
Journal Article
A Blind Thrust Fault Ruptured During the 10 October 2018 Situbondo, East Java, Indonesia, Earthquake Estimated Using GNSS Data
The 2018 Situbondo earthquake occurred along an unidentified fault source in East Java, Indonesia. Historical records from 1821 to 2018 show that no earthquakes before 2018 were recorded in this region. In this study, we use Global Navigation Satellite System (GNSS) data to estimate the coseismic displacements of stations in the study region. Significant coseismic displacements were estimated for stations located south of the epicenter. Using focal mechanism as preliminary information for the fault geometry, we conduct coseismic slip inversion on two possible fault sources, i.e., a northward dipping fault and a southward dipping fault. The seismic moment of the southward dipping fault, which is 2.7 × 10
18
N·m (equivalent to
Mw
6.2), is identical to the seismic moment from the seismic analysis. Also, displacement model of the southward dipping fault model better fit data than the northward dipping fault. We also find that high slip is concentrated at depths greater than 9 km. Our assessment of the fault suggests that it could rupture every 700 to 1700 years. Since the dilatation rate to the west from the epicenter is much higher, our result emphasizes the urgent need for further investigation of the Kendeng thrust, which may affect the megacity of Surabaya.
Journal Article
Main drivers of drainage pattern development in onshore Makran Accretionary Wedge, SE Iran
Over time, river networks achieve a specific pattern as determined by the function of several factors such as climate, tectonic, geological structures, topography, lithology, and base-level fluctuations. The relative importance of mentioned factors on drainage systems was studied to determine the controlling factors of their heterogeneity across the tectono-stratigraphic zones of onshore Iranian Makran. We applied structural, geomorphological, and climate analysis. Results indicate that the dendritic patterns of N-S flowing rivers in the western part of Iranian Makran are mostly controlled by the Minab-Zendan Fault activity and distribution of olistostrome cover, whereas the dominant trellis patterns in the eastern part are controlled by the well-developed thrust fault-related fold systems. The channel steepness pattern demonstrates that the high values are mostly localized in the hanging wall of thrust and normal faults. Accordingly, the topographic profiles of the steep rivers show the old stages of incision in the Inner and Outer Makran. However, some rivers of the Coastal Makran are in the young stage of incision, where the normal faults are located and active. The sediment connectivity index shows that the Inner Makran has a high potential of sediment supplies, while the Outer Makran intra-mountain basins and the Coastal-plain are more prone to sediments accumulation. Our findings reveal that the river patterns and landscape evolution in the Inner and Outer Makran are controlled by thrust faults, olistostrome and related mini-basins, while rivers in the Coastal Makran are governed by activity of Pliocene–Pleistocene normal faults.
Journal Article
Postseismic Coulomb stress changes on intra-continental dip-slip faults due to viscoelastic relaxation in the lower crust and lithospheric mantle: insights from 3D finite-element modelling
Earthquakes in the brittle upper crust induce viscoelastic flow in the lower crust and lithospheric mantle, which can persist for decades and lead to significant Coulomb stress changes on receiver faults located in the surrounding of the source fault. As most previous studies calculated the Coulomb stress changes for a specific earthquake in nature, a general investigation of postseismic Coulomb stress changes independent of local geological conditions is still lacking for intra-continental dip-slip faults. Here we use finite-element models with normal and thrust fault arrays, respectively, to show that postseismic viscoelastic flow considerably modifies the original coseismic Coulomb stress patterns through space and time. Depending on the position of the receiver fault relative to the source fault, areas with negative coseismic stress changes may exhibit positive postseismic stress changes and vice versa. The lower the viscosity of the lower crust or lithospheric mantle, the more pronounced are the transient stress changes in the 1st years, with the lowest viscosity having the largest effect on the stress changes. The evolution of postseismic Coulomb stress changes is further controlled by the superposition of transient stress changes caused by viscoelastic relaxation (leading to stress increase or decrease) and the interseismic strain accumulation (leading to a stress increase). Stress changes induced by viscoelastic relaxation can outweigh the interseismic stress increase such that negative Coulomb stress changes can persist for decades. On some faults, postseismic relaxation and interseismic strain accumulation can act in concert to enhance already positive Coulomb stress changes.
Journal Article
A study of the relationship between the pressuremeter modulus and the preconsolidation pressure around a thrust fault
The study area is in a zone under the influence of the Lake Van water changes and the Van fault, which caused a destructive earthquake in 2011. Due to the level changes of Lake Van, sediments with different thicknesses as well as grain sizes were deposited in this region and the characteristics of these sediments were significantly affected by the morphology and lake water fluctuations in the past. A total of six boreholes were drilled along a 3-km line within the study area to determine the preconsolidation pressure (σpc) and the pressuremeter test values of the clayey levels of old lake deposits—which are known to have different physical and mechanical properties—with hopes to gain an insight on how they influence the mechanical tests performed in the field and in laboratory conditions. The relationship between these values was also statistically evaluated. When both datasets were evaluated together, it was determined that the stresses in the area close to the Van Thrust Fault plane caused deformations in the soil, which in turn affected the hanging-wall block of the thrust fault in particular. The inspection of EM and σpc values for the area within the primary compression zone of the Van Fault revealed that both values of the boreholes on the footwall block were higher compared to other boreholes close to the lake (southwest). This finding indicates that the fault stresses at the footwall block of the fault plane enhance the mechanical characteristics of the soil. The data obtained were also evaluated using regression analysis. Relationships between all available data were investigated and a high coefficient of determination was derived between the Menard deformation modulus (EM) and the preconsolidation (σpc) pressure.
Journal Article
Study on co-seismic energy losses from hypocenter to ocean bottom for Sumatra earthquake 2004 using 3-D crustal deformation model
Our co-seismic GRACE gravity data (Level 2 ‘RL_05’ data product “GX-OG-_2-GSM) for Sumatra earthquake 2004 is obtained by differencing monthly gravity field average for November 2004 from that of January 2005 and band-pass filtering (17–30, degrees and orders) in spectral domain. Here we propose an 11-layered 3-D thrust fault gravity model based on several co-seismic rupture models in literature. Previously we have covered the 3-D modelling details and its inferences like slip rate, seismic moment, momentum etc. in our published literature. Further we extend the inferences through our model for this case study. Here, we have estimated the layer-wise energy distribution by undertaking two types energy loss one is spherical spreading and second absorption with constrained by literature. We have computed layer-wise energy loss, equivalent energy, differential pressure, slip rate, ultimate slip and work done. The computed differential pressure and work done for Sumatra Earthquake 2004 are 1.7552 × 108 N/m2 and 1.657 × 1018 J, respectively. We also estimated the absorption coefficient (calculated absorption coefficients) from our model to honour the slip rate of Sumatra earthquake 2004. The differential pressure is estimated for ocean bottom and sea level surface. The volumetric analysis is also provided for entire 3-D body (layer-wise) using excess mass of our model. The computed differential pressure indeed corresponds to an area pulse at ocean bottom that led to a Tsunami generation.
Journal Article
Normal faults near the top of footwall of Ramgarh Thrust along Kosi River valley, Kumaun Lesser Himalaya
Conjugate sets of normal faults formed in the Quaternary fan sediments lying near the top of footwall rocks of the Ramgarh Thrust are analysed. These faults are recognized on left hillslope of Kosi River valley, Kumaun Lesser Himalaya. The Ramgarh Thrust marks the mountain front of the uplifted Central Crystallines, which have been under thrust along the Ramgarh Thrust by its footwall of the Nagthat Formation belonging to the Lesser Himalayan Sequence. The existence of a regional-scale footwall anticlinal structure along the Kosi River suggests that the compressional stress regime is active in the subsurface region related to the Himalayan thrust tectonics. Analysis of structural data reveals that the normal faults have been formed by pure shear due to gravity. The WNW–ESE trending normal faults are recognized within the Quaternary fan deposit and also at the top of the country rocks just below and adjacent to the fan deposit. Therefore, it is interpreted that the deformation related to N–S extensional tectonics has taken place at the uppermost crustal level due to gravity, where influence of the Himalayan subsurface compressional tectonics is no more significant.
Journal Article