Thrust Faults Research Articles

EARTHQUAKE FOCAL PARAMETERS in the CRIMEAN-BLACK SEA REGION in 2018–2019

The results of calculation and analysis of spectral and dynamic parameters of the sources (М0,r0, , , ησ, r, ū, Eu и Mw) of 24 Crimean earthquakes for 2018–2019 in the range of energy classes KП=5.8–11 are presented. 157 station amplitude spectra of P- and S- seismic waves recorded at seven regional digital seismic stations were used for calculations. The determination of dynamic parameters of the sources was carried out using the Brune theoretical dislocation model. The average values of the dynamic parameters of earthquake sources for 2018–2019 were in most cases estimated for several stations and for different types of waves, which ensured a small value of the degree of scattering of individual estimates. For the studied 2018–2019 earthquakes, the average values of the seismic moment М0, the radius of the circular dislocation r0, and the stress drop  were within the confidence intervals of the long-term dependencies М0(KП), r0 (KП) and (KП). For five strongest earthquakes of 2018 (January 31, April 24, September 9, September 13, and October 15 with KП=10.5–11) and two earthquakes of 2019 (May 8 and December 4), focal mechanism solutions were obtained within the framework of the double dipole model. Type of movement in the source of January 31, 2018 earthquake is a strike-slip with a normal fault component, of September 9 and September 13, 2018 – a normal fault, of April 24 and October 15, 2018, as well as May 8 and December 4, 2019 – a reverse fault. The spectral composition of seismic oscillations was additionally studied from the energy spectra of 15 earthquakes using records at the Alushta station located at distances 5–285 km from source zones. At the qualitative level, a shift of the spectrum maximum (fqmax) towards higher frequencies for weak shocks and close epicentral distances.

A MODEL OF THE LATE MESOZOIC AND CENOZOIC THERMOTECTONIC EVOLUTION OF THE PRE-MESOZOIC BASEMENT ROCKS IN SOUTH TUVA

Thermotectonic modeling was performed for the crystalline rocks of South Tuva using the apatite fission-track analysis. Thermotectonic modeling made it possible to visualize the Late Mesozoic and Cenozoic cooling history of the Pre-Mesozoic basement rocks, and to reconstruct the chronology and scale of the denudational processes over the last 125 myr and the evolution of paleorelief of South Tuva over the last 100 myr. The modeling results depicted several Mesozoic-Cenozoic episodes of cooling due to differential denudation and exhumation of the Pre-Mesozoic basement rocks. A differential denudation is related to an asynchronous activation of fault structures controlling the tectonic evolution of South Tuva. It is shown that the Early Cretaceous (~125–100 Ma) activation of the Agar-Dag-Oka thrust fault zone could result from the post-collisional processes after the collision between Siberia and Amuria and/or consecutive collision between the Cimmerian blocks. An intense activation of the Agar-Dag-Oka fault zone in the Late Cretaceous (~100–75 Ma), accompanied by significant basement rock exhumation in the eastern South Tuva to absolute heights of 1200 m, could be caused by the Karakoram-Pamir collision in the south of Eurasia. The Late Cenozoic (25–0 Ma) activation of the main fault zones of South Tuva represents a far-field effect of the Indo-European collision on the southern Eurasian continent. At the same time, there were the maximum basement uplift in the junction zone between the South Tannuola and Ubsunur-Bii-Khem fault zones and the transformation of relief of South Tuva from moderately dissected, with absolute heights of 500 to 1400 m, to modern, with absolute heights of 800 to 2600 m.

Novel corrugated tube–rubber–concrete flexible joint for lining water conveyance tunnels crossing reverse Faults: Numerical analysis of dislocation resistance performance

When water conveyance tunnels cross seismic fault fracture zones, significant deformation may occur, threatening the structural integrity of the tunnel. To resolve this problem, a novel corrugated tube–rubber–concrete flexible joint (CTRCFJ) for improving fault resistance is proposed for the first time. The effectiveness of the CTRCFJ was evaluated using advanced three-dimensional non-linear finite element analysis. The design parameters of the CTRCFJ, including rubber width, corrugated tube interval, and corrugated tube width, were selected based on the distribution of the axial bending moment of the lining structure. An orthogonal test was performed to determine the optimal combination of parameters. The effects of the number of crests, different steel grades, and wall thickness of the corrugated tube on the fracture resistance of the CTRCFJ are investigated. Results show that the CTRCFJ can effectively improve the dislocation resistance performance of composite lining water conveyance tunnels crossing reverse faults by reducing axial compression and bending strain. This study provides a reference for the structural design of composite lining structures that can cross reverse faults.

Neogene faulting, basin development, and relief generation in the southern Klamath Mountains (USA)

Abstract Development and evaluation of models for tectonic evolution in the Cascadia forearc require understanding of along-strike heterogeneity of strain distribution, uplift, and upper-plate characteristics. Here, we investigated the Neogene geologic record of the Klamath Mountains province in southernmost Cascadia and obtained apatite (U-Th)/He (AHe) thermochronology of Mesozoic plutons, Neogene graben sediment thickness, detrital zircon records from Neogene grabens, gravity and magnetic data, and kinematic analysis of faults. We documented three aspects of Neogene tectonics: early Miocene and younger rock exhumation, development of topographic relief sufficient to isolate Neogene graben-filling sediments from sources outside of the Klamath Mountains, and initiation of mid-Miocene or younger right-lateral and reverse faulting. Key findings are: (1) 10 new apatite AHe mean cooling ages from the Canyon Creek and Granite Peak plutons in the Trinity Alps range from 24.7 ± 2.1 Ma to 15.7 ± 2.1 Ma. Inverse thermal modeling of these data and published apatite fission-track ages indicate the most rapid rock cooling between ca. 25 and 15 Ma. One new AHe mean cooling age (26.7 ± 3.2 Ma) from the Ironside Mountain batholith 40 km west of the Trinity Alps, combined with previously published AHe ages, suggests geographically widespread latest Oligocene to Miocene cooling in the southern Klamath Mountains province. (2) AHe ages of 39.4 ± 5.1 Ma on the downthrown side and 22.7 ± 3.0 Ma on the upthrown side of the Browns Meadow fault suggest early Miocene to younger fault activity. (3) U-Pb detrital zircon ages (n = 862) and Lu-Hf isotope geochemistry from Miocene Weaverville Formation sediments in the Weaverville, Lowden Ranch, Hayfork, and Hyampom grabens south and southwest of the Trinity Alps can be traced to entirely Klamath Mountains sources; they suggest the south-central Klamath Mountains had, by the middle Miocene, sufficient relief to isolate these grabens from more distal sediment sources. (4) Two Miocene detrital zircon U-Pb ages of 10.6 ± 0.4 Ma and 16.7 ± 0.2 Ma from the Lowden Ranch graben show that the maximum depositional age of the upper Weaverville Formation here is younger than previously recognized. (5) A prominent steep-sided negative gravity anomaly associated with the Hayfork graben shows that both the north and south margins are fault-controlled, and inversion of gravity data suggests basin fill is between 1 km and 1.9 km thick. Abrupt elevation changes of basin fill-to-bedrock contacts reported in well logs record E-side-up and right-lateral faulting at the eastern end of the Hayfork graben. A NE-striking gravity gradient separates the main graben on the west from a narrower, thinner basin to the east, supporting this interpretation. (6) Of fset of both the base of the Weaverville Formation and the cataclasite-capped La Grange fault surface by a fault on the southwest margin of the Weaverville basin documents 200 m of reverse and 1500 m of right-lateral strike-slip motion on this structure, here named the Democrat Gulch fault; folded and steeply dipping strata adjacent to the fault confirm that faulting postdated deposition of the Weaverville Formation. Based on these findings, we suggest that Miocene rock cooling recorded by AHe ages, accompanying graben formation, and development of topographic relief record early to middle Miocene initiation of underplating or “subcretion” in the southern Cascadia subduction zone beneath the southern Klamath Mountains.

Holocene paleoearthquakes activity in the Nieru graben, southern Tibet

The Yadong-Gulu Rift (YGR) is the longest and most prominent rift in southern Tibet. While 14 large historical earthquakes have occurred on the northern-central segment of the YGR, historical or paleoearthquake records along the southern segment remain poorly understood. The spatial discrepancy of large earthquakes has significant implications for assessing seismic hazards along the entire YGR. To address this knowledge gap, this study presents the paleoseismic events for the first time in the Nieru graben located along the southern segment of the YGR. The excavation of a paleoseismic trench reveals two Holocene earthquakes with calibrated radiocarbon dates constraining the timing of the two events to be after 4084-3954 cal yr BP. The paleoearthquake had a magnitude of M 7. The study shows that the southern segment of the YGR experienced strong paleoseismic events, except for the Relong graben. Considering the high present extension rate of the southern rifts and the magnitude of the paleoseismic events along the Nieru graben, the southern segment of the YGR holds the potential for producing large earthquakes. Furthermore, the ongoing tectonic deformation in the area, coupled with stress changes from large earthquakes on Himalayan thrust faults, may increase the likelihood of future rupture along the active faults in the Nieru graben.

APPLICATION OF SURFACE CONSISTENT AMPLITUDE CORRECTION (SCAC) IN THE "HRNR" FIELD

This research aims to enhance the quality of 3D onshore seismic data and understand subsurface structures in a study area. We implemented the Surface Consistent Amplitude Correction (SCAC) method in seismic data processing. This study's results demonstrate that using SCAC significantly improves the quality of seismic data amplitudes, especially in eliminating previously disruptive noise in the analysis. Following the application of SCAC, seismic data amplitudes become clearer and stronger. The interpretation of the enhanced seismic data with SCAC revealed the presence of a significant geological structure, namely a reverse fault, which has significant implications for subsurface understanding. The location of this reverse fault was identified at inline 190 within the CMP range of 60 to 120, with time domain depths ranging from 150 ms to 1250 ms in the southwestern part of the cross-section. This research highlights that SCAC plays a key role in enhancing seismic data resolution and enables the identification of reverse faults that were previously challenging to discern. These findings make a crucial contribution to understanding subsurface geology in the study area and hold significant potential in the context of natural resource exploration. This study firmly establishes that SCAC is an effective tool in improving seismic data quality and revealing important geological structures, especially reverse faults, which can be a primary focus in subsurface geological studies in this research area.

New insight on the structural architecture of northern Tunisia with a multidisciplinary approach: Association of Miocene piggy-back basin and active Plio-quaternary out-of-sequence thrusts

In order to better understand the intricate structural architecture of northern Tunisia, we use a multidisciplinary approach that includes field observations, geomorphic, sedimentological, and gravity data across this area. We offer a model of progressive thrusting in which four deformation phases occurred in the context of plate convergence (i) Uplift of the Jebel Ichkeul Triassic succession via a NE-trending thrust fault during the Eocene; (ii) Advance of Numidian thrust sheets during the late Oligocene-Middle Miocene, causing the formation of the Lake Ichkeul/Jalta as being piggy-back basin; (iii) Initial out-of-sequence thrusting during the Late Miocene, resulting in the formation of the Sejnane and El Mejel basins with syntectonic Pliocene infill; and (iv) Subsequent out-of-sequence thrusting during the Early Pleistocene, leading to the formation of the Oued (River) Zyatine basin with a syntectonic Quaternary deposits. We used the gravity data analysis to mark the thicknesses of syntectonic deposits and their bounding thrust faults. The kinematic analysis indicates the occurrence of progressive multiphase out-of-sequence thrusting events with thrusts verging to the southeast. The combination of climate and mechanical fractures induced gradually long-term damage and changed the original landscape of the evidenced out-of-sequence thrusts. Furthermore, the existence of local normal faults in the backlimbs and reverse faults in the forelimbs, together with the drainage network type, earthquakes, the slope erosion, and the aggraditional terrace system, implies a gradual landscape evolution of thrust topography. This physical evolution occurred following an active tectonics across the exhibited out-of-sequence thrusting since the Pliocene.

Analogue modelling of basin inversion: implications for the Araripe Basin (Brazil)

Abstract. Basin inversion is a process that takes place when a sedimentary basin is subjected to compressional stresses resulting in the reactivation of pre-existing faults and/or the localization of deformation along new reverse faults. The Araripe Basin (NE Brazil) is an example of a Cretaceous intracontinental aborted rift, with its sedimentary infill found at ca. 1000 m altitude, 500 m above the host basement. Post-rift basin inversion has been proposed by previous authors as the cause of this topographic high, but how inversion affected this basin remains a matter of debate, with the following two end-member scenarios: reactivation of pre-existing normal faults leading to local uplift or regional uplift and differential erosion. Neither end-member fully explains the observations from seismic and field data. In this study, we, therefore, conducted analogue models to explore how basin inversion in the Araripe Basin could have taken place. We present two series of crustal-scale brittle–viscous experiments: (i) extension followed by compression without sedimentation, with a variation in divergence and convergence directions (orthogonal or 45∘ oblique); and (ii) extension with syn-rift sedimentation followed by compression, with the same variation in rifting and inversion directions. We found that orthogonal rifting without sedimentation forms throughgoing graben boundary faults, whereas oblique rifting initially creates en échelon faults that eventually link up, creating large graben boundary faults. Rift basins with syn-rift sedimentation evolved in a similar fashion; however, sedimentary loading resulted in increased subsidence. During both oblique and orthogonal inversion, most shortening was accommodated along new low-angle reverse faults. Significant intra-graben fault reactivation occurred in all models without syn-rift sedimentation. By contrast, orthogonal inversion of models with syn-rift sedimentation did not reactivate rift faults, whereas only a minor reactivation of rift faults took place during oblique inversion since the sediments strengthened the otherwise weakened basin, thus acting as a buffer during convergence. Based on our modelling results, we propose an alternative scenario for the evolution of the Araripe Basin, involving oblique inversion and the development of low-angle reverse faults, which better fits observations from seismic lines and field data from the region.

Ramps as modifiers of deformation of mass-transport deposits flow cells: A case study in the Santos Basin, SE Brazil

Mass-transport deposits (MTDs) are one of the several deepwater deposits and correspond to an important part of the gravitational sedimentation in the basins. MTDs register several pieces of evidence about their formation, which can indicate flow direction, level of internal deformation, and position in the deposit, for example. During the transport process, the flow can interact with the substrate and change its characteristics. Consequently, different structures are formed internally and in the basal surface according to the flow modification. In this study, 3D seismic data located in the northern Santos Basin was used to investigate the relationships between different MTD kinematic structures and styles of basal interaction. After conducting a comprehensive interpretation of the deposit, which involved morphological analysis, examination of basal and upper surfaces, and the assessment of internal facies distribution, we proceeded to correlate various structural elements, with the purpose of providing a clearer understanding of the sedimentation processes that took place within the deposit. On the basal surface, three distinct features (grooves, striations, and deformational elements) along with ramps, were interpreted. Apart from this, the distribution of large and small-size blocks, and normal and reverse faults within this MTD indicates that there were major changes in the flow behavior during the transport. Thus, we propose a model for the MTD transformation which considers ramp generation as a modifier of the MTD deformation and, consequently, as responsible for creating second-order flow cells, facilitating the substrate deformation, and providing erosive blocks near the flow base. In this model, the studied MTD was divided in five zones according to the nature of basal interaction. Typically, these zones are border by ramps. The variation in the internal structures suggest fluctuations in the flow velocity. Altogether, our findings indicate that the flow exhibited a compartmentalized behavior, giving rise to second-order flow cells.

Interpretation and mapping of geologic structure in the Bali Basin based on integrated gravity, magnetic, and seismic data analysis

The Bali Basin is located in the Sunda-Banda back-arc from subduction along the Sunda Arc to continental collision along the Banda Arc. Still, its geologic structural patterns have yet to be mapped and discussed in detail as the transition zone. An integrated approach involving magnetic, gravity, and seismic data analysis was undertaken to discover these structures that potentially impact the surrounding area. The magnetic anomalies indicate that the thrust fault structure beneath the north coast of the islands of Bali and Lombok vertically displaces the basement on the seabed. The interpretation, verified with gravity and seismic reflection profiles, indicates a significant, tight, and well-developed expression of blind thrust faulting. Gravity data delineate the basin bedrock surface 6 km beneath the south Bali Basin, where seismic sections show five Cenozoic sedimentary sequences more than 2000 m thick, filling a highly deformed and faulted Cretaceous bedrock sequence. The seismic-gravity model shows sedimentation-related subsidence from basin filling followed by tectonics inversion.

Nonpilot directional protection of a microgrid

AbstractProtection of an islanded inverter‐based microgrid is challenging because of variable and small fault current contribution of inverter‐based resources (IBR) and the absence of sequence currents. This paper proposes a fast and robust nonpilot directional protection scheme to address this challenge. This scheme relies on support vector machines (SVM) and the harmonic current injection capability of IBRs. Examining the harmonic currents measured by a relay during a fault shows that harmonic currents have similar magnitudes but different orientation under forward and reverse faults. Additionally, harmonic currents have similar orientation but different magnitudes under forward faults at different locations along the protected line. Using this, six SVMs are trained for each relay, given that there are three main types of faults (three‐phase‐to‐ground, line‐to‐line, and line‐to‐ground): three as directional elements and three as zone detection elements. A fault is detected and classified by the undervoltage element of a relay. Then, the measured harmonic currents are routed to the appropriate directionality and zone detection SVMs to facilitate proper relay coordination. The performance of the proposed method is evaluated on the CIGRE North American MV distribution benchmark system under various types of contingency scenarios using PSCAD/EMTDC software.

The geomorphology and neotectonics of the Vaalputs Radioactive Waste Disposal Facility site, Namaqualand, South Africa: Palaeoseismological and geodynamic implications

Abstract The safe disposal of radioactive waste products remains a challenging and controversial issue, yet their burial in a stable geological environment is the option favoured by most countries. Past investigations of the Vaalputs facility in South Africa’s semi-arid Bushmanland Plateau demonstrated its suitability for the disposal of low-level, short-lived (<300 years) radioactive waste, but also the need for more data on hazardous seismotectonic and climatic processes for the potential storage of longer-lived spent nuclear fuel. We review and then provide new information on the regional geomorphological and morphotectonic features of the Bushmanland Plateau, focusing on pedogenic features and compressive shear fractures in the trenches excavated over the past two decades. The fractures, provisionally dated between ~75 ka and ~46 ka, resemble east-verging thrust faults of limited horizontal displacement (≤1 m) and die out at depths of 4 m. Having discounted a pedogenic origin, the shear fractures likely represent stress relief structures triggered by the seismogenic reactivation of one of the Quaternary active faults in the area. The most likely candidate is the Santab Fault Zone (SFZ), which has a strike length ≥20 km and a throw of up to ~5 m at its closest point (8 km) to the Vaalputs site. Regional remote sensing and off-site investigations in the Bushmanland Plateau relate the neotectonic episodes at Vaalputs and environs to a late Pleistocene climax of the Namaqualand seismic source zone. This zone is characterised by the Wegener Stress Anomaly, a long-lived ~northwest-southeast oriented compression that, at its apex in the Late Santonian, caused large scale folding and thrusting not only in Bushmanland and parts of central-southern Namibia, but also swept across the entire African plate.

New Insights Into the Active Tectonics of the Northern Canadian Cordillera From an Enhanced Earthquake Catalog

AbstractSeismic activity in the Northern Canadian Cordillera is characterized by diffuse earthquakes that extend hundreds of km northwest from the Yakutat collision zone. We use 25 months of broadband seismic data from Mackenzie Mountain Earthscope Project (MMEP), USArray Transportable Array (TA), and permanent Canadian National Seismic Network stations to present a local earthquake catalog with high sensitivity to small regional events. Deep learning techniques are adopted for both seismic phase detection and association. Event relocations are performed to provide well constrained estimates of earthquake depth distributions. Clusters of seismicity spanning the upper crust are located in the central Richardson Mountains, along the Tintina fault, and in the northeast Selwyn Basin. These clusters suggest that the core of the Richardson Anticlinorium is tectonically active and that the Tintina fault is a locus for low levels of active deformation. We interpret seismicity in the northeast Selwyn Basin as primarily occurring in the hanging wall of the Plateau thrust fault and suggest that some combination of localized duplex structures and lithological strength contrasts both within the Selwyn Basin and between abutting Paleozoic shelf sequences may be responsible for seismicity in the Mackenzie Mountain foreland.

The Crustal Magmatic Structure Beneath the Denali Volcanic Gap Imaged by a Dense Linear Seismic Array

AbstractThe crustal structure in south‐central Alaska has been influenced by terrane accretion, flat slab subduction, and a modern strike‐slip fault system. Within the active subduction system, the presence of the Denali Volcanic Gap (DVG), a ∼400 km region separating the active volcanism of the Aleutian Arc to the west and the Wrangell volcanoes to the east, remains enigmatic. To better understand the regional tectonics and the nature of the volcanic gap, we deployed a month‐long north‐south linear geophone array of 306 stations with an interstation distance of 1 km across the Alaska Range. By calculating multi‐component noise cross‐correlation and jointly inverting Rayleigh wave phase velocity and ellipticity across the array, we construct a 2‐D shear wave velocity model along the transect down to ∼16 km depth. In the shallow crust, we observe low‐velocity structures associated with sedimentary basins and image the Denali fault as a narrow localized low‐velocity anomaly extending to at least 12 km depth. About 12 km, below the fold and thrust fault system in the northern flank of the Alaska Range, we observe a prominent low‐velocity zone with more than 15% velocity reduction. Our velocity model is consistent with known geological features and reveals a previously unknown low‐velocity zone that we interpret as a magmatic feature. Based on this feature's spatial relationship to the Buzzard Creek and Jumbo Dome volcanoes and the location above the subducting Pacific Plate, we interpret the low‐velocity zone as a previously unknown subduction‐related crustal magma reservoir located beneath the DVG.

Determining the slip rate of the Kendeng Fault in East Java through GPS observations

The Kendeng Fault is recognized as an extension of the Flores back-arc thrust, primarily exhibiting thrust fault behavior. However, prior research has indicated the presence of a significant right-lateral shear component along this fault. While no significant seismic events have been documented in recent years, historical records suggest that the region experienced significant seismic events prior to the 20th century, necessitating a careful consideration of the earthquake hazard associated with this fault. The question arises whether the absence of recent seismic activity is a consequence of energy accumulation or gradual energy release. Our investigation utilizes GPS data collected over a four-year period starting in 2016 to determine the slip rate of the Kendeng Fault. Our findings indicate that the slip rate along the Kendeng Fault is approximately 0.45 ± 0.07 cm/year. These results provide valuable insights into the behavior of the Kendeng Fault and contribute to a better understanding of its seismic potential and associated risks.

Current deformation in eastern part of Java derived from GPS observation 2017-2022

The eastern part of Java Island is a prone area with high seismic potential. Geologically, the seismicity in this area is dominated by the subduction zone in southern Java, reverse faults structure in the north extending along east to west part of Java Islands, and normal faults in Pasuruan and Probolinggo. Several studies have indicated the potential of earthquakes associated with these sources. The geodetic technique is employed to monitor the deformation activity in the eastern part of Java to understand the characteristics. We utilized the continuous GPS stations operated by Geospatial Agency of Indonesia (BIG) and processed them using the GAMIT/GLOBK software. The processing incorporates the IGS stations surrounding Indonesia. We also used precise orbit and 2nd-order ionospheric correction. The processing produces the velocity in the ITRF2014 reference frame, which generally indicates the south-eastward velocity up to 29 mm/year, mainly influenced by block rotation. Velocity referenced to the Sunda block shows a distinguished pattern between southern Java and northern Java. The velocity pattern in the southern part of Java tends to move northwest with a velocity variation of 3-6 mm/year, while several north stations show a velocity pattern to the south with a variation of 2-4 mm/yr. The strain analysis shows different patterns between eastern and western regions and different characteristics of southern and northern regions. Mainly the deformation is dominated by the compression due to the subduction in the south. Meanwhile, near to the central Java the deformation patterns significantly change due to the appearance of the east-west extension. The result indicates the different distinguished characteristics of the deformation source in the eastern part of Java. This result will have implications for seismic hazard analysis as a contribution to disaster risk reduction in the future.

Three-dimensional finite-element modeling of Coulomb stress changes on normal and thrust faults caused by pore fluid pressure changes and postseismic viscoelastic relaxation

Abstract The analysis of Coulomb stress changes has become an important tool for seismic hazard evaluation because such stress changes may trigger or delay subsequent earthquakes. Processes that can cause significant Coulomb stress changes include coseismic slip and transient postseismic processes such as poroelastic effects and viscoelastic relaxation. However, the combined influence of poroelastic effects and viscoelastic relaxation on co- and postseismic Coulomb stress changes has not been systematically studied so far. Here, we use three-dimensional finite-element models with arrays of normal and thrust faults to investigate how pore fluid pressure changes and viscoelastic relaxation overlap during the postseismic phase. In different experiments, we vary the permeability of the upper crust and the viscosity of the lower crust or lithospheric mantle while keeping the other parameters constant. In addition, we perform experiments in which we combine a high (low) permeability of the upper crust with a low (high) viscosity of the lower crust. Our results show that the coseismic (i.e., static) Coulomb stress changes are altered by the signal from poroelastic effects and viscoelastic relaxation during the first month after the earthquake. For sufficiently low viscosities, the Coulomb stress change patterns show a combined signal from poroelastic and viscoelastic effects already during the first postseismic year. For sufficiently low permeabilities, Coulomb stress changes induced by poroelastic effects overlap with the signals from viscoelastic relaxation and interseismic stress accumulation for decades. Our results imply that poroelastic and viscoelastic effects have a strong impact on postseismic Coulomb stress changes and should therefore be considered together when analyzing Coulomb stress transfer between faults.

Salt Eruptions and Their Role in the Shaping of the Oil Trapping for Selected Fields in Eastern Iraq

This research had been achieved using 2D seismic sections to study the presence of subsurface salty bodies in the Khashim Al-Ahmer, Galabat, Injana fields as a case study. The selected oil fields is located to the northeast of Baquba city within Diyala Governorate. The study aims to determine the salt accumulations of the selected fields and their role in the formation of oil traps. The interpretation of seismic data was focused on two reflectors Fatha and Jeribe Formations which belong to the lower and Middle Miocene. Structurally, Two systems of reversal faults are affecting the fields, according to seismic sections, the first represents thrust faults affected on the top part of Fatha (Red Beds & Seepage) and the layers above with large displacements and trending in an NW-SE orientation; The separation surface of these faults is the salt bed in the Fatha Formation. the second represents reversal faults affected on the lower section of Fatha (Transition beds) and the layers beneath with high displacements. The research concludes Petroleum flow from the source was directed by the faults created by the broad Zagros tectonism to Miocene and younger traps, also seal fracturing exceeds vertical petroleum flow. The differences in fault types are caused by the presence of a salt bed within the Fatha Formation and the high variation in its thickness at the crest and flanks. So, the main recommendation of research is to implement a 3D seismic survey covering these fields to determine salt body areas.

Late Miocene to present synchronous extension and contraction in the eastern Pamir: Insights from inversion of thermochronologic data across the southern Muztaghata dome

Late Cenozoic gneiss domes cover ∼30% of the surface of the Pamir salient in the northwestern end of the India−Asia collision zone. The highest peaks of the Pamir are in the east, where the ∼250-km-long, ∼N−S-trending Kongur Shan extensional system controls the topography. We combined 115 new apatite (U-Th-Sm)/He and zircon (U-Th)/He single-grain dates from 18 samples and previous thermochronologic data with three-dimensional thermokinematic models to constrain the thermo-tectonic history of the southern portion of the Muztaghata dome, one of the largest gneiss domes in the eastern Pamir. The new cooling dates from the western boundary of the southern Muztaghata dome generally increase with distance from the southern Kongur Shan fault and are related to normal faulting along the fault at near-surface levels over the last 6.5 m.y. The new dates across the central−eastern portion of the dome outline the previously recorded U-shaped date pattern at a higher spatial resolution. The modeling indicates that this pattern is most likely the result of uplift and erosion above a flat-ramp-flat thrust fault at depth over the last 7 m.y. Modeling does not resolve how topographic changes may have affected the observed distribution of cooling dates, but it indicates a faster thrust-slip rate associated with an increase in relief and a slower one associated with steady-state topography. Our results suggest that the modern topography along the southern Muztaghata dome, similar to the rest of the eastern Pamir salient, is shaped by normal faulting at shallow depth, but its growth may still be governed by contraction and crustal thickening at depth.

GEOMORPHIC INDICES AND FAULT SEGMENTATION INDICATION OF MENANGA FAULT AT PESAWARAN, LAMPUNG

Remote sensing and GIS are playing important roles in geomorphology and hazard risks analysis. Pesawaran area located near the Menanga Fault and recently on the risk of earthquake that happened along this fault. Thus, it is essential to investigate the area actively affected by Menanga Fault as preliminary research about hazard risk related to Menanga Fault. The morphometry method based on DEMNAS and Landsat 8 was applied to evaluate the zone affected by Menanga Fault, and fracture data analysis was conducted to consider the possibility of fault segmentation resulting from its mechanism. The study area can be divided into 3 zones; zone A is greatly affected by Menanga Fault activity, zone B is affected by Menanga Fault and Mt. Pesawaran development, and zone C is tectonically less affected. Zone A landforms were not only formed as a result of Menanga Thrust fault but also the strike-slip fault segment. Fault segmentation exists in this zone with different mechanisms (strike-slip and dip-slip), producing lineaments with different trends, and differentiation of river patterns.