Structural Analysis and Morphotectonic Interpretation of Ain Sifni Anticline, Northern Iraq

Ain Sifni anticline is located in northern Iraq within High Folded Zone. It contains some tectonic deformations that need to study to determine the source and mechanism of these deformations concerning the geological setting of the study area. This study includes structural and morphotectonic interpretations for the Ain Sifni anticline, such as the visual & digital interpretation of satellite images and the Digital Elevation Model interpretation. These parameters are used to identify the morphogenic criteria and subsequently, to conclude a morphotectonic aspect of the deformations in the Ain Sifni anticline. Because of the regional tectonic evolution in this area, the structural and morphotectonic analysis of this anticline shows much evidence of morphological changes at the southeastern plunge area of the anticline within the Injana and Mukdadiya formations in comparison to the northwestern plunge area of the anticline. In addition, two recent water gaps have been recognized at the southeastern plunge area, one is confirmed and the other is proposed, and then a wind gap has been recognized in the middle of the anticline. A relation has been established between these morphotectonic features with the lateral propagation of the anticline towards the southeast, due to the regional tectonic deformation. A significant main fault has also been detected as a dextral strike-slip fault perpendicular to the fold axis of the anticline. This fault caused a difference in the vergency of the anticline and deformed the outcrops of formations in the study region.

Coseismic fault-slip distribution of the 2019 Ridgecrest Mw6.4 and Mw7.1 earthquakes

The 2019 Ridgecrest, California seismic sequence, including an Mw6.4 foreshock and Mw7.1 mainshock, represent the largest regional seismic events within the past 20 years. To obtain accurate coseismic fault-slip distribution, we used precise positioning data of small earthquakes from January 2019 to October 2020 to determine the dip parameters of the eight fault geometry, and used the Interferometric Synthetic Aperture Radar (InSAR) data processed by Xu et al. (Seismol Res Lett 91(4):1979–1985, 2020) at UCSD to constrain inversion of the fault-slip distribution of both earthquakes. The results showed that all faults were sinistral strike-slips with minor dip-slip components, exception for dextral strike-slip fault F2. Fault-slip mainly occurred at depths of 0–12 km, with a maximum slip of 3.0 m. The F1 fault contained two slip peaks located at 2 km of fault S4 and 6 km of fault S5 depth, the latter being located directly above the Mw7.1hypocenter. Two slip peaks with maximum slip of 1.5 m located 8 and 20 km from the SW endpoint of the F2 fault were also identified, and the latter corresponds to the Mw6.4 earthquake. We also analyzed the influence of different inversion parameters on the fault slip distribution, and found that the slip momentum smoothing condition was more suitable for the inversion of the earthquakes slip distribution than the stress-drop smoothing condition.

Travel Time Tomography to Delineate 3-D Regional Seismic Velocity Structure in the Banyumas Basin, Central Java, Indonesia, Using Dense Borehole Seismographic Stations

The Banyumas Basin is a tertiary sedimentary basin located in southern Central Java, Indonesia. Due to the presence of volcanic deposits, 2-D seismic reflection methods cannot provide a good estimation of the sediment thickness and the subsurface geology structure in this area. In this study, the passive seismic tomography (PST) method was applied to image the 3-D subsurface Vp, Vs, and Vp/Vs ratio. We used 70 seismograph borehole stations with a recording duration of 177 days. A total of 354 events with 9, 370 P and 9, 368 S phases were used as input for tomographic inversion. The checkshot data of a 4, 400-meter deep exploration well (Jati-1) located within the seismic network were used to constrain the shallow crustal layer of the initial 1-D velocity model. The model resolution of the tomographic inversions was assessed using the checkerboard resolution test (CRT), the diagonal resolution element (DRE), and the derivative weight sum (DWS). Using the obtained Vp, Vs, and Vp/Vs ratio, we were able to sharpen details of the geological structures within the basin from previous geological studies, and a fault could be well-imaged at a depth of 4 km. We interpreted this as the main dextral strike-slip fault that controls the pull apart process of the Banyumas Basin. The thickness of the sediment layers, as well as its layering, were also could be well determined. We found prominent features of the velocity contrast that aligned very well with the boundary between the Halang and Rambatan formations as observed in the Jati-1 well data. Furthermore, an anticline structure, which is a potential structural trap for the petroleum system in the Banyumas Basin, was also well imaged. This was made possible due to the dense borehole seismographic stations which were deployed in the study area.

Interpretasi Struktur Geologi Berdasarkan Fault Fracture Density (FFD) dan Implikasinya Terhadap Potensi Likuefaksi di Daerah Kalibening, Kabupaten Banjarnegara, Jawa Tengah

ABSTRAK Keberadaan struktur geologi sering dikaitkan dengan bencana tanah longsor dan gempa bumi. Daerah Kalibening merupakan lokasi yang cukup menarik untuk dilakukan penelitian terkait hal tersebut. Daerah ini tersusun atas satuan batuan berumur Pleistosen dan Resen. Berdasarkan stratigrafinya, batuan tersebut terpotong oleh struktur sesar. Hal ini berarti menjadikan sesar di daerah tersebut termasuk dalam kategori sesar aktif. Morfologi yang tinggi dengan suatu cekungan di tengahnya mengindikasikan bahwa daerah tersebut pembentukannya dipengaruhi oleh sesar. Penelitian ini bertujuan untuk menentukan pola struktur geologi yang mengontrol daerah penelitian. Untuk menentukan pola struktur geologi, digunakan metode pemetaan struktur Fault Fracture Density (FFD) yang dikombinasikan dengan peta residual anomali Bouguer dan peta kelurusan hillshade. Secara umum, hal yang paling penting dalam mempelajari struktur geologi adalah geometri elemen struktur. Model konseptual struktur geologi selanjutnya digunakan untuk menganalisis potensi likuefaksi yang ada pada daerah penelitian. Interpretasi struktur menunjukkan adanya sesar mendatar dekstral yang diikuti sesar-sesar penyerta dan cekungan pull-apart yang diduga merupakan hasil pensesaran normal yang timbul dari mekanisme strike-slip. Sesar mendatar dekstral ini menghasilkan cekungan yang terisi oleh sedimen lepas yang rentan mengalami likuefaksi jika terjadi gempa bumi dan gerakan tanah. Kajian ini menyimpulkan bahwa daerah Kalibening rentan terjadi likuefaksi karena adanya pergerakan sesar mendatar dekstral, sedimen lepas yang mendominasi daerah penelitian, dan muka air tanah yang dangkal. ABSTRACT The existence of geological structures is often associated with landslides and earthquakes. The Kalibening area is an interesting location for research on that purpose. This area is composed of Pleistocene and Recent rocks units. Based on its stratigraphy, the rocks in the area are truncated by fault structure. It means that the fault in the area is categorized as an active fault. The high morphology and a basin existence on its center indicate that the area formation was controlled by faults. The research is carried out to determine the trend of the geological structures that control the study area. To determine the trend of the geological structure, a structural mapping method of Fault Fracture Density (FFD) map combined with the Bouguer anomaly residual map and hillshade lineaments map is used. In general, the most important thing in the study of structural geology is the geometry of the structural elements. The conceptual model of geological structures is subsequently used to analyze the liquefaction potential of the study area. The interpretation of the structures shows the existence of dextral strike-slip fault followed by companion faults and pull-apart basin that is inferred as the result of normal faulting in the strike-slip mechanism. The dextral strike-slip fault produces a basin filled with loose sediment that is prone to liquefaction in the event of an earthquake and ground motion. This study concludes that the Kalibening area is prone to liquefaction due to the existence of the movement of dextral strike-slip fault, loose sediments that dominate the study area, and shallow groundwater table.

Some geomorphological perspectives on the structure associated with the Petrinja M6.2 earthquake in Croatia

<p>After the earthquake of 29/12/2020 in Petrinja (ML6.2, ImaxVIII-IX EMS), an attempt was made to characterize the active structure associated with the earthquake. As a first step towards this goal, we performed a geomorphological analysis in order to contribute to the identification and characterization of the surface expression of the active Pokupsko dextral strike-slip fault. We focused on the area between the southernmost parts of Vukomeričke Gorice and the southernmost parts of Hrastovica Mountain, where the NW-SE striking Pokupsko fault has slipped during and after the recent earthquake (Ganas et al., 2021). Using available 1 : 5 000 scale topographic maps and various 10 m resolution digital elevation model visualizations, we mapped lineaments that could represent relatively recently active fault segments. We used a quantitative approach to perform stream sinuosity analysis (e.g., Leopold et al., 1964; Zamolyi et al., 2010) on major streams crossing the structure to identify distinct changes in channel patterns that may be associated with vertical movement along the predominantly strike-slip fault. We observed changes in the shape of the valleys, especially the changes in width, height, and direction. By summarizing various geomorphological indicators of active fault segmentation at the surface with available geological data (Pikija, 1987) and so far limited field observations, we provide insights into the structure of the Pokupsko fault.<br>Preliminary results show good agreement between lineament mapping, changes in valley shape, changes in the stream sinuosity index, and (to some extent) previously mapped faults. In addition, some of the changes in stream sinuosity correspond to locations where coseismic surface ruptures occurred during the December 29 earthquake (Budić et al., this session; Pollak et al., 2021). Results suggest that the several-kilometer-wide zone of uplifted Neogene deposits results from the dextral-transpressive structure, which at the surface consists of a series of subparallel fault strands branching off the main fault that runs along the SE slopes of the Hrastovica Mountain. The SW-most fault strands are associated with significant changes in the shape of the valleys: the wide valleys of Petrinjčica, Utinja and Šanja change to narrow and deeply incised as they cross the uplifted structure. Paleocene and Eocene rocks, which otherwise underlie the Neogene, outcrop in the NE parts of the fluvial breakthrough valleys, indicating the uplift of the Hrastovica Mountain. Topographic data show a decrease of the mountain range elevation towards the SW. This evidence suggests that the main fault runs on the NE side of the mountain, strikes NW-SE and dips steeply towards the SW. The fault strike deviates between Župić and Farkašić. The fault plane solution for the December 29 earthquake suggests a nearly pure strike-slip fault, while geomorphic evidence strongly indicates areas of active uplift along the fault, further supported by the general antiformal structure. We interpret this as an indication of either a general current transpressional character of the fault or as local kinematic variations due to segmentation and changes in the strike of the fault; further analyses are pending.</p>

Bridging the Gap between Seismicity and Exhumed Faults: Insights from a Seismically Active Strike-Slip Fault Zone in the Rawil Depression (Northern Valais, Switzerland)

<p>The Rawil depression north of the Rhone Simplon fault zone (southwestern Swiss Alps) was host of the Mw = 5.8 Sion earthquake in 1946 (Fäh et al., 2011). It is nowadays one of the seismically most active regions in Switzerland and seismicity forms a cluster, which is elongated approximately in WSW-ENE direction over 40-50 km. In November 2019, a remarkable earthquake sequence occurred within the center of this cluster north of the village of Anzère, with more than 300 earthquakes up to ML = 3.3 recorded by the Swiss Seismological Service within 20 days.</p><p>Detecting associated full-scale 3D fault patterns solely based on earthquake hypocenters is challenging because of commonly too limited spatial resolution and insufficient number of seismic events. Within the framework of SeismoTeCH, we aim to improve these limitations by a combination of high-precision hypocenter relocation techniques, reconstruction of subsurface fault patterns and correlative links between surface and subsurface data. Assuming that a fault is seismically active multiple times and that the seismic stress-release is initiated at different locations along the fault, we can calculate 3D fault plane orientations from the hypocenter locations. Together with the 17 focal mechanisms derived for the Anzère sequence, we are able to gain geometrical and kinematic information of the seismic faults in 3D. Our analysis reveals a seismically active transpressional step-over structure within a dextral strike-slip fault zone. With remote sensing and field observations, we detect exhumed faults with similar orientations and kinematics that presumably represent step-over structures, interconnecting previously known strike-slip fault zones.</p><p>Although seismic activity occurs at depths between 3-5 km, we conclude that the observed surface fault systems in the Rawil depression can be correlated in terms of fault patterns with those assumed at depth. The linkage of the recent seismicity with structural observations of exhumed, potentially paleo-seismic faults in combination with recent hypocenter relocation techniques therefore have great potential to provide further insights into fault linkage and earthquake rupturing processes.</p><p> </p><p><strong>References</strong></p><p>Fäh, D., Giardini, D., Kästli, P., Deichmann, N., Gisler, M., Schwarz-Zanetti, G., Alvarez-Rubio, S., Sellami, S., Edwards, B., Allmann, B., Bethmann, F., Wössner, J., Gassner-Stamm, G., Fritsche, S., Eberhard, D., 2011. ECOS-09 Earthquake Catalogue of Switzerland Release 2011. Report and Database. Public catalogue, 17.4.2011. Swiss Seismological Service ETH Zürich, Report SED/RISK/R/001/20110417.</p>

Mapping the Lithological Features and Ore-Controlling Structures Related to Ni–Cu Mineralization in the Eastern Tian Shan, NW China from ASTER Data

The study of lithological features and tectonic evolution related to mineralization in the eastern Tian Shan is crucial for understanding the ore-controlling mechanism. In this paper, the lithological features and ore-controlling structure of the Huangshan Ni–Cu ore belt in the eastern Tian Shan are documented using advanced spaceborne thermal emission and reflection radiometer (ASTER) multispectral data based on spectral image processing algorithms, mineral indices and directional filter technology. Our results show that the algorithms of b2/b1, b6/b7 and b4/b8 from ASTER visible and near-infrared (VNIR)- shortwave infrared (SWIR) bands and of mafic index (MI), carbonate index (CI) and silica index (SI) from thermal infrared (TIR) bands are helpful to extract regional pyroxenite, external foliated gabbro bearing Ni–Cu ore bodies as well as the country rocks in the study area. The detailed interpretations and analyses of the geometrical feature of fault system and intrusive facies suggest that the Ni–Cu metallogenic belts are related to Carboniferous arc intrusive rocks and Permian wrench tectonics locating at the intersection of EW- and NEE-striking dextral strike-slip fault system, and the emplacement at the releasing bends in the southern margin of Kanggur Fault obviously controlled by secondary faults orthogonal or oblique to the Kanggur Fault in the post-collision extensional environment. Therefore, the ASTER data-based approach to map lithological features and ore-controlling structures related to the Ni–Cu mineralization are well performed. Moreover, a 3D geodynamic sketch map proposes that the strike-slip movement of Kanggur Fault in Huangshan-Kanggur Shear Zone (HKSZ) during early Permian controlled the migration and emplacement of three mafic/ultramafic intrusions bearing Ni–Cu derived from partial mantle melting and also favored CO2-rich fluids leaking to the participation of metallogenic processes.

Syncing fault rock clocks: Direct comparison of U-Pb carbonate and K-Ar illite fault dating methods

The timing of slip on brittle faults in Earth’s upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials is the most explicit approach. Here we make a direct comparison between K-Ar dating of fault gouge clay (authigenic illite) and U-Pb dating of carbonate slickenfibers and veins from the same fault. We have dated fault generated materials from the Big Creek fault, a northwest-striking, dextral strike-slip fault system in Yukon Territory, Canadian Cordillera. Both methods yielded dates at ca. 73 Ma and ca. 60–57 Ma, representing at least two periods of fault slip that form part of a complex fault and fluid-flow history. The Cretaceous result lies within previous indirect estimates for major slip on the fault. The Paleocene–Eocene result coincides with the estimated timing of slip of the nearby Tintina and Denali faults, which are crustal-scale, northwest-striking dextral faults, indicating Big Creek fault reactivation during regional faulting. The coincidence of periods of carbonate-crystallizing fracturing and fluid flow with intervals of seismic, gouge-generating slip supports the fault valve model, where fault strength is mediated by fluid pressures, and fluid emplacement requires seismic pumping in otherwise impermeable aseismic fault zones. The reproducibility of slip periods for distinct fault-generated materials using different decay systems indicates that these methods provide complimentary results and can be reliably applied to date brittle fault slip, opening new opportunities for investigating fault conditions with associated mineralizing fluid events.

Evidence for Large Holocene Earthquakes along the Denali Fault in Southwest Yukon, Canada

ABSTRACT The Yukon–Alaska Highway corridor in southern Yukon is subject to geohazards ranging from landslides to floods and earthquakes on faults in the St. Elias Mountains and Shakwak Valley. Here we discuss the late Holocene seismic history of the Denali fault, located at the eastern front of the St. Elias Mountains and one of only a few known seismically active terrestrial faults in Canada. Holocene faulting is indicated by scarps and mounds on late Pleistocene drift and by tectonically deformed Pleistocene and Holocene sediments. Previous work on trenches excavated against the fault scarp near the Duke River reveals paleoseismic sediment disturbance dated to ∼300–1,200, 1,200–1,900, and 3,000 years ago. Re-excavation of the trenches indicates a fourth event dated to 6,000 years ago. The trenches are interpreted to show a negative flower structure produced by extension of sediments by dextral strike-slip fault movement. Nearby Crescent Lake is ponded against the fault scarp. Sediment cores reveal four abrupt sediment and diatom changes reflecting seismic shaking at ∼1,200–1,900, 1,900–5,900, 5,900–6,200, and 6,500–6,800 years ago. At the Duke River, the fault offsets sediments, including two White River tephra layers (∼1,900 and 1,200 years old). Late Pleistocene outwash gravel and overlying Holocene aeolian sediments show in cross section a positive flower structure indicative of post-glacial contraction of the sediments by dextral strike-slip movement. Based on the number of events reflecting ∼M6, we estimate the average recurrence of large earthquakes on the Yukon part of the Denali fault to be about 1,300 years in the past 6,500–6,800 years.

The November 2019 Seismic Sequence in Albania: Geodetic Constraints and Fault Interaction

The seismic sequence of November 2019 in Albania culminating with the Mw = 6.4 event of 26 November 2019 was examined from the geodetic (InSAR and GNSS), structural, and historical viewpoints, with some ideas on possible areas of greater hazard. We present accurate estimates of the coseismic displacements using permanent GNSS stations active before and after the sequence, as well as SAR interferograms with Sentinel-1 in ascending and descending mode. When compared with the displacements predicted by a dislocation model on an elastic half space using the moment tensor information of a reverse fault mechanism, the InSAR and GNSS data fit at the mm level provided the hypocentral depth is set to 8 ± 2 km. Next, we examined the elastic stress generated by the Mw = 7.2 Montenegro earthquake of 1979, with the Albania 2019 event as receiver fault, to conclude that the Coulomb stress transfer, at least for the elastic component, was too small to have influenced the 2019 Albania event. A somewhat different picture emerges from the combined elastic deformation resulting after the two (1979 and 2019) events: we investigated the fault geometries where the Coulomb stress is maximized and concluded that the geometry with highest induced Coulomb stress, of the order of ca. 2–3 bar (0.2–0.3 MPa), is that of a vertical, dextral strike slip fault, striking SW to NE. This optimal receiver fault is located between the faults activated in 1979 and 2019, and very closely resembles the Lezhe fault, which marks the transition between the Dinarides and the Albanides.