TS10.1

The Tien Shan are an intracontinental mountain belt experiencing shortening as a result of far field deformation from the ongoing India-Eurasian collision. At the longitude of Kyrgyzstan the Tien Shan accommodate ~20 mm/yr of shortening. In central Kyrgyzstan, the most well studied faults include the northwest-striking right-lateral Talas Fergana fault and the series of east-striking reverse & thrust faults that form the basins and subranges that accommodate most of this compression. Yet in satellite imagery, some of the most prominent fault ruptures appear on a series of east-northeast-striking left-lateral strike slip faults. Little is known about the paleoseismology, rate of slip, or tectonic role of these faults. Here we present new drone-based high resolution topography and imagery along with geomorphic, geochronology, paleoseismic, and slip rate data for four of these sinistral faults. The studied faults are in the Aksay, Kazarman, Issyk Kul, and Song Kol basins. These data reveal that each fault has produced Holocene surface ruptures with single event displacements as great as 5-7 m along faults as long as ~100 km, corresponding to M~7.5 earthquakes. We propose a structural model to explain how these faults may have evolved from reverse faults that have rotated about their horizontal axis and then reactivated as strike slip faults due to their optimal alignment in the current stress field. How the existence of these faults affects seismic hazards is a question of discussion, as they are currently not considered in the regional strain budget that is largely based on compression.

How to cite: Pierce, I., Abdrakhmatov, K., Baikulov, S., Rakhmedinov, E., Tilek Kyzy, G., Johnson, B., Seitz, G., Arrowsmith, R., Rizza, M., and Walker, R.: Sinistral Strike Slip Faults of the Kyrgyz Tien Shan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-529, https://doi.org/10.5194/egusphere-egu22-529, 2022.

The tectonic landscape of the Himalayas is mainly depicted by the E-W trending major regional thrusts, the southernmost being the Himalayan frontal Thrust (HFT) or the Main Frontal Thrust (MFT. But there are also out of sequence transverse faults and back thrusts that play important role in strain adjustment.

The map traces of thrust faults make cuspate-lobate patterns suggesting differential fault growth. These orogen-scale curvatures at an intermediate scale are expressed as salients and recesses. Salients are normally associated with mountain fronts defined by frontal imbricate faults, whereas recesses are open to the foreland. Himalayan salients, recesses, and associated cross-structures help in determining the deformation kinematics along the length of the Himalayan arc over space and time.

In the Eastern Himalaya, east of the Tista River, the sequential and out-of-sequence structures are well observed in the Jaldhaka recess. Here the splay on the HFT is marked by southerly sloping Chalsa and Matiali scarps whereas the northerly sloping Thaljhora scarp represents the Frontal Back Thrust (FBT).

In this study, we are presenting the geometry and structural detail of the back thrust below the Thaljhora scarp. The attitude of the thrust plane, folding of the bedding, and displacement is evident from an excavated trench perpendicular to the strike of the fault scarp. The folded beds join against the thrust plane to form a piggyback structure. The thrust plane dips 20⁰ → S. The maximum displacement of the bed is recorded at 4.5cm along the thrust plane. There are liquefaction structures, convolute laminations and flame structures within the deformed sediments. The attitude of the gentler limb of the fold is about 40⁰→S and that of the steeper climb is around 55-60 degrees towards North.

From earlier works (Guha et al. 2010, Singh et al, 2016, Goswami et al., 2019) the age of deposition of different sediments of this area varies from 70ka to 22ka. The oldest sediment here from the north bank of Thaljhora River, below the deformed boulder bed, is around 70 ka., eastward from the same bank from an upper stratum, comprising of black sandy clay dated around 27ka, a black clay around 6m high from the river bed, on the Thaljhora scarp itself dated as around 37 ka whereas from somewhere within that scarp dated as around 22ka. From the present study, the sediments which are deformed and displaced gives the depositional dates varying from 14 to 17ka. So, it can be said that the faulting or thrusting which has formed the scarp is at least as young as 14ka.

The movement on the splay of HFT in the adjacent Matiali fan started earlier than 70 ka and the major upliftment forming the T2 terrace was around 20ka.

The movement along the Thaljhora fault started somewhere between 20-30ka. This movement may have started to adjust the stress along the northerly dipping fault. These two northerly and southerly dipping thrust systems may be interpreted as a conjugate thrust which maybe adjust the stress in this particular area.

How to cite: Chakrabarti Goswami, C., Jaiswal, M., Dasgupra, S., and Singh, A.: Paleoseismological findings along the identified back thrust in the Eastern Himalayan foothills near the India-Bhutan border, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4432, https://doi.org/10.5194/egusphere-egu22-4432, 2022.

Abstract. The tectonically active western coast of South America is characterized by the accumulation of deformation that contributes to permanent uplift of the Andean forearc at glacial-cycle timescales. However, the individual mechanisms responsible for long-term coastal uplift are still debated, mostly because analyses at continental-scale have not been carried out as yet. In coastal realms, permanent deformation is often estimated from marine terraces, which depict the interplay between wave erosion, tectonic uplift, and sea-level changes. Based on ~2000 elevation measurements of last interglacial marine terraces, we performed wavelength analyses using fast Fourier transforms. We compared the resulting uplift-rate signal with various tectonic processes and subduction parameters associated with the accumulation of permanent deformation. We detected a constant background signal of uplift along the South American margin (median rate: 0.22 mm/yr), which is disturbed by short-, intermediate- and long-wavelength changes between ~20 and ~800 km wavelengths, with the most prominent wavelengths at scales of ~500 km. Similarities between the wavelength spectra of uplift rate and signals from tectonic parameters suggest potential correlations, although multiple individual mechanisms usually contribute to a larger wavelength peak or to a certain range of wavelengths. For instance, crustal faulting is responsible for short-wavelength deformation (<100 km) and strong megathrust earthquakes (M_W>7.5) mostly cover wavelength ranges from ~100 to 200 km, despite reaching wavelengths over 600 km as well. The subduction of bathymetric anomalies and the extent of interseismic locking correlate with intermediate wavelengths (~200 to ~500 km), whereas residual gravity anomalies, basal friction, and background seismicity correlate with long-wavelength deformation (>500 km). We suggest that the constant background signal of uplift rate results from two possible mechanisms: (a) a combination of multiple processes acting at different wavelengths, times and locations over millennial timescales or (b) a single unidentified process acting homogeneously along the western South American margin. With this study, we highlight the application of novel signal analysis approaches to elucidate the mechanisms driving surface deformation in subduction zones on different spatial and temporal scales.

How to cite: Freisleben, R., Jara-Muñoz, J., Melnick, D., Strecker, M., and van der Beek, P.: Tectonic processes responsible for various wavelengths of permanent deformation on the western coast of South America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11435, https://doi.org/10.5194/egusphere-egu22-11435, 2022.

The Salar de Atacama (SdA) endorheic basin is a low topographic anomaly located in the Central Andes forearc, and it has been suggested as an independent block that subsides with respect to their neighbouring morpho-structures: Cordillera de Domeyko at the west, and the Altiplano and Puna volcanic plateaus to the east. Within the SdA depression, we focus on the Cordillera de la Sal (CdS), a ridge that emerges at its western margin and extends to the northeast for more than 100 km towards the volcanic arc, where the SdA basin closes. The core of the CdS ridge is formed by a fold-and-thrust belt affecting the Oligocene-Miocene continental sedimentary sequences of the San Pedro Formation. Unconformably overlaying this sequence, Upper Miocene-Pliocene tuffs and clastics with varying intensities of deformation are recognised along the northern segment of CdS, where it ends covered by the volcanic arc.

The deformation of CdS and the western border of the SdA have been suggested as a consequence of the inversion of a normal fault that delimits the basin or as an eastward propagation of the thrusting of Cordillera de Domeyko. Moreover, the presence of salt intervals and domes within the San Pedro Formation made some authors propose the existence of halokinesis. In the present work, we aim to investigate the actual tectonic regime of the CdS fold-and-thrust belt. Our objective is to determine spatial and temporal strain variability of CdS to contribute to the understanding of how this mountain belt evolved and how deformation is partitioned at its northern prolongation under the volcanic edifices.

Detailed geological mapping and the construction of seriated cross-sections will allow us to determine variable spatial patterns of deformation affecting the tuff-rich succession, spanning from 9 to 1 Ma. In addition, we will obtain temporal patterns of deformation at the scale of 10³ to 10⁵ yr using tectonic geomorphology indicators, such as deformed strath terraces and Holocene salt cave conduits.

Our preliminary results suggest that a compressional tectonic regime is progressively deforming the Upper Miocene-Pleistocene succession of CdS. Moreover, the evolution of drainages from the south-facing slope of the volcanic arc towards the SdA competed with the folds and thrusts, and the major channels developed along thrusts and synclines. This competition is going on also in the Middle to Late Pleistocene as documented by deformed fluvial strath terraces, which we are currently dating with Infra-Red Stimulated Luminescence. The age assessment of deformed terraces and cave conduits will allow us to model the slip rates of the thrust structures at different time scales.

How to cite: Guzmán-Marín, P., Picotti, V., Schmidt, C., and King, G.: Variability of active deformation of the Cordillera de la Sal fold-and-thrust belt, Salar de Atacama, Central Andes, Chile. Preliminary data on deformed fluvial features., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12690, https://doi.org/10.5194/egusphere-egu22-12690, 2022.

In order to investigate crustal deformation within the upper plate of the Ionian Subduction Zone (ISZ) at different time scales, we have (i) mapped and modelled sequence of Late Quaternary raised marine terraces tectonically deformed by the West Crati normal fault, in northern Calabria, and (ii) refined geodetic rates of crustal extension from continuous GNSS measurements. Indeed, this region experienced damaging earthquakes such as the “1184 Valle del Crati” (M 6.7) and the “1638 Crotonese” (M 6.7) events, possibly on the West Crati Fault; however, an in-depth evaluation of the deformation rates inferred from geologic and GNSS data has not yet been performed. Furthermore, fault slip-rates and earthquake recurrence intervals for the understudied West Crati Fault are still debated and poorly-constrained. Raised Late Quaternary marine terraces are preserved on the footwall of the West Crati Fault; however, it is still debated if the “local” effect of the footwall uplift is affecting the “regional” signal of uplift likely related to the deformation associated either with the subduction or mantle upwelling processes. Within the investigated region lying in the northern part of the uplifting Calabrian-Peloritani Arc there are 32 regionally distributed permanent GNSS stations, for 18 of which the coordinate time series are adequately long (at least 4.5 years) to allow the study of the crustal kinematics. The data of these 18 stations are used to geodetically estimate fault slip-rates and then earthquake recurrence intervals for the West Crati Fault, with the aim of at least partially solve the aforementioned problem of the poor constrains. In particular, velocity and strain across this fault, based on reasonable hypotheses about the fault dip and the mechanical properties of the involved material, are computed starting from GNSS data about the surface kinematics.

Our preliminary results show that GIS-based elevations of Middle to Late Pleistocene palaeoshorelines, as well as temporally constant uplift rates, vary along the strike of the West Crati Fault, mapped on its footwall. This suggests that the fault slip-rate governing seismic hazard has also been constant through time, over multiple earthquake cycles. We then suggest that our geodetically-derived fault slip-rate for the West Crati Fault may be a more than reasonable value to be used over longer time scales for an improved seismic hazard approach, allowing to derive new earthquake recurrence intervals. These results thus suggest a significant yet understudied seismic hazard for the investigated area also because the regional extension might be likely accommodated by a few more active faults across-strike in northern Calabria. These facts highlight the importance of mapping crustal deformation within the upper plate above subduction zones to avoid unreliable interpretations relating to the mechanism controlling regional uplift.

How to cite: Meschis, M., Teza, G., Elia, L., Lattanzi, G., Di Donato, M., and Castellaro, S.: Refining rates of active crustal deformation in the upper plate of subduction zones, implied by geologic and geodetic data: The E-dipping West Crati Fault, southern Italy., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3588, https://doi.org/10.5194/egusphere-egu22-3588, 2022.

The coastal morphology of islands may furnish valuable information regarding deformation rates, their controlling mechanisms and the dynamics of the upper crust in offshore areas along subduction zones. Here we study active deformation and faulting at glacial-cycle time scales in the Kythira island, located at the western part of the Hellenic subduction zone, between Crete Island and the Peloponnese. The island exposes an outstanding sequence of more than twelve successive levels of marine terraces that depict the Pleistocene active uplift of the island. The marine terraces are offset by several NNW-SSE and NNE-SSW active faults. We use high-resolution topography combined with morphometric analysis to map the sequence of marine terraces and active faults. We divide the marine terrace sequence into two groups, the higher marine terraces (260 – 480 masl) include polygenic rasa surfaces, the lower terraces (20 – 220 masl) are characterized by staircase morphologies. Based on a proposed correlation with sea level curves, we estimated ages ranging between MIS 17 and MIS 22 (712 – 1000 ka) for the higher terraces and between MIS 5 and MIS 15 (125 – 620 ka) for the lower terraces. We focus on the two main faults of the island, defined as F1 and F2, they display right- and left-lateral and dip slip displacements, offsetting the marine terrace risers and treads and producing local drainage anomalies. Based on the proposed terrace ages we derived preliminary heave rates between 0.3 and 0.5 m/ka for the right-lateral fault F1 and between 0.8 and 1 m/ka for the left-lateral fault F2. Mean throw rates vary between 0.01 m/ka and 0.03 m/ka for F1 and F2 respectively. We link the activity of these faults with the occurrence of intermediate-depth and strong magnitude earthquakes such as the Mw 6.6 and 6.7 occurred in the area of Kythira in 1903 and 2006, respectively. Further dating of marine terrace deposits and surfaces, and structural analysis will be carried soon to refine our preliminary estimates. Our work emphasizes on the importance of studying islands to elucidate vertical and horizontal deformation rates in offshore areas of subduction zones.

How to cite: Jara-Muñoz, J., Tsanakas, K., Karymbalis, E., Yildirim, C., Pedoja, K., Batzakis, D.-V., and Griva, D.: Quantifying active faulting using marine terraces, Kythira island, Greece, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11349, https://doi.org/10.5194/egusphere-egu22-11349, 2022.