Quantifying active deformation within the Southwestern Foothills of Taiwan, from incised fluvial terraces and sedimentary data

2020 ◽  
Author(s):  
Philippe Steer ◽  
Valentine Lefils ◽  
Martine Simoes ◽  
J. Bruce H. Shyu ◽  
Magali Rizza ◽  
...  
Keyword(s):  
Coastal Plain ◽  
Active Faults ◽  
Active Regions ◽  
Sedimentary Facies ◽  
Tectonic Uplift ◽  
Mountain Range ◽  
Active Deformation ◽  
Fluvial Terraces ◽  
Base Level ◽  
Shortening Rate

<p>The Taiwan mountain range stands as one of the most active regions on Earth. With an overall shortening rate of ~40 mm/yr and an average erosion rate of ~4 mm/yr, this mountain range appears ideal to better understand the interactions between tectonics and surface processes, and how these shape active landscapes. Here we explore the geomorphic and sedimentary record of active deformation within the Southwestern Foothills of Taiwan, and we quantify from there the kinematics of active faults. In particular, we investigate the downstream portion of the meandering Tsengwen river - one of the largest rivers of this region - where we identify and correlate remnants of 7 terrace levels, progressively abandoned over the last ~5 kyr. The incision of these terraces is interpreted as being controlled to the first-order by folding and uplift related to underlying active faults. The evolution of the river is reconstructed from correlated terrace remnants, and our results indicate that the overall river sinuosity and gradient did not vary significantly during the past ~5 kyr in response to tectonics. Incremental tectonic uplift is retrieved from terrace incision corrected for sedimentation at the mountain front, and is used to derive the incremental shortening since terrace abandonment. Downstream, within the Coastal Plain, the Tsengwen river reaches its base level and aggrades. Sedimentary facies within boreholes of the Coastal Plain record vertical displacements relative to sea level, spatially consistent with potential blind active faults. When corrected for eustatic variations, these data allow for quantifying tectonic uplift rates within the Coastal Plain over the last ~20 kyr. Taken altogether, our quantitative analysis of the Tsengwen river record, from terrace incision to dowsntream aggradation, reveals that the most frontal active faults absorb a shortening rate of at least ~35 mm/yr, that is most of - if not all -  the shortening rate to the absorbed across the whole mountain range.</p>

Investigating lateral variations in the kinematics of active deformation along the Western Kunlun mountain front (Xinjiang, China): structural and morphological analysis of the Hotan anticline

2020 ◽  
Author(s):  
Christelle Guilbaud ◽  
Martine Simoes ◽  
Laurie Barrier ◽  
Jérôme Van der Woerd ◽  
Guillaume Baby ◽  
...  
Keyword(s):  
Morphological Analysis ◽  
Mountain Range ◽  
Thrust Sheet ◽  
Active Deformation ◽  
Fluvial Terraces ◽  
Structural Style ◽  
Western Kunlun ◽  
Mountain Front ◽  
Surface Geology ◽  
Lateral Variations

<p>The Western Kunlun Range is a mountain range located at the northwestern boundary of the Tibetan Plateau, facing the Tarim Basin. Our previous combined structural and morphological investigations of the mountain front, nearby the city of Pishan where a Mw 6.4 earthquake occurred in 2015, revealed the existence of a duplex uplifting Cenozoic strata, in which only the most frontal blind ramp is presently active and slips at a probable rate of 2 to 2.5 mm/yr. Located ~100 km further east along the mountain front, the Hotan anticline seems to present a different structure from surface geology, as older strata from Mesozoic and Paleozoic outcrop. Additionally, some authors proposed that the deformation would be here accommodated by a large blind basement thrust sheet, in clear contrast with the duplexes documented further west.</p><p>To further document potential lateral variations in the structural style and how they may affect the kinematics of active deformation along the mountain front of the Western Kunlun, we carry out a structural and morphological analysis of the Hotan anticline. We build structural cross-sections based on seismic reflection profiles, and calculate the incremental uplift recorded by dated fluvial terraces to quantify shortening rates over the last ~300 kyr. Our analysis reveals that a duplex structure, located below the basement thrust sheet, presently accommodates active deformation at a rate of 0.5 to 2.5 mm/yr, with a preferred rate of ~1.6 to 2.3 mm/yr. In more detail, uplifted terraces reveal that all ramps of the duplex are active in the case of the Hotan anticline, while only the most frontal ramp is documented as active in the case of the Pishan anticline further west. These results indicate that the style and rate of active shortening are rather homogeneous all along the mountain front, in contrast with the first impression provided by surface geology. Moreover, the discrepancy between surface geology and active morphology reveals progressive structural changes over geological times, from a blind basement ramp to duplexes. However, in the details, active deformation still remains segmented as its partitioning on the various ramps of the duplexes is variable along strike.</p>

Seismic Behavior Along a Fault Segment in an Active Continental Collision Zone: New Paleoseismic and Structural Data of the Pamir Frontal Thrust in the Alai Valley, Kyrgyzstan, Central Asia.

2020 ◽  
Author(s):  
Magda Patyniak ◽  
Angela Landgraf ◽  
Atyrgul Dzhumabaeva ◽  
Alana M. Williams ◽  
Sultan Baikulov ◽  
...  
Keyword(s):  
Seismic Behavior ◽  
Alluvial Fan ◽  
Tien Shan ◽  
Luminescence Dating ◽  
Mountain Range ◽  
Fault Segment ◽  
Fluvial Terraces ◽  
The North ◽  
Collision Zone ◽  
Shortening Rate

<p>The Pamir Frontal Thrust (PFT) constitutes the northernmost boundary of the Pamir mountain range at the NW edge of the India-Eurasia collision zone. Due to the ongoing collision this active system propagates into and overthrusts the Quaternary deposits of the Alai Valley, an intermontane basin separating the Pamir from the Tien Shan in the north. Geodetic data across the Central Pamir document a shortening rate of 25 mm/yr, with a dramatic decrease of ~10 mm over a short distance across the northernmost Trans-Alai range (250 km aperture); this suggests that almost half of the shortening in the greater Pamir – Tien Shan collision zone is absorbed along the PFT.</p><p>Consequently, the frontal thrusts must accommodate a significant amount of slip and may be capable of generating ≥M7 earthquakes in this part of the orogen. In contrast to similar tectonic settings along the Himalayan megathrust, the present-day seismicity in the Pamir apparently does not reflect the long-term deformation history. Despite few studies in the late 20<sup>th</sup> century, and an extensive data base of recent earthquakes, the relationships between seismicity and the geometry of the thrust zone are not well understood. In this context our study aims to improve the understanding of the earthquake geology of the PFT by asking two principal questions: (1) How much of the PFT is activated during an earthquake rupture? (2) Does the paleoseismic slip history agree with the geodetically-derived shortening rate?</p><p>Here, we present our results of five analyzed paleoseismic trenches that reveal the youngest manifestation of thrusting along the central segment of the PFT. We combined field-based observations with a TanDEM-X data, UAV-based DEMs, and dGPS profiling for an offset analysis along the fault scarp. The interpretation of the trench stratigraphy and event horizons in the context of these tectonic landforms was combined with radiocarbon and luminescence dating to develop an earthquake chronology.</p><p>We find robust evidence for at least three surface-rupturing events during the past 6 kyr. At least one event can be recognized in all five trenches separated by ~10 km, indicating a full-length activation of the central fault segment during rupture. Ages obtained from uplifted fluvial terraces coupled with the total cumulative fault offset indicate a Holocene slip rate of up to 3.5 mm/yr. Based on dip-slip motion offsets per event we estimated an average earthquake paleo-magnitude ranging between M6.5-7.0.</p><p>Despite the regional extent of the central PFT, and a rather high displacement gradient across it, our results suggest a seismic behavior characterized by strong surface-rupturing earthquakes, short surface ruptures, and low slip rates. Earthquakes along this structure do not cover the total geodetic shortening, which suggests that a strongly segmented PFT system may be linked with active seismogenic deformation in the alluvial-fan covered piedmont regions to the north. However, the preservation potential for fault scarps in the piedmont may be low in this highly dynamic environment due to climate-driven fluvial and glacial processes in the high sectors of the Pamir.</p>

Assessing the seismic hazards associated with one of the largest active thrust sheets: the case of the slowly deforming Western Kunlun mountain range (Xinjiang, China).

2020 ◽  
Author(s):  
Martine Simoes ◽  
Christelle Guilbaud ◽  
Jerome van der Woerd ◽  
Laurie Barrier ◽  
Roxane Tissandier ◽  
...  
Keyword(s):  
Tarim Basin ◽  
Active Faults ◽  
Seismic Hazards ◽  
Spatial Gradient ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Thrust Sheet ◽  
Fluvial Terraces ◽  
Western Kunlun ◽  
Mountain Front

<p><span lang="EN-US">The Western Kunlun Range (WKR) is a slowly converging orogen located along the northwestern edge of the Tibetan Plateau, facing the Tarim Basin. The recent Mw 6.4 2015 Pishan earthquake along the mountain front recalls that this region remains seismically active, despite little or moderate historical seismicity. Its low deformation rates can be hardly retrieved from current geodetic data, placing limited constraints on the potential interseismic loading of the region. This is particularly critical as recent structural investigations report the existence of an extremely wide (~150-180 km) frontal thrust sheet, whose dimensions would imply the possibility of major M ≥ 8 earthquakes in the case that it is locked and slips during one single seismic event.</span></p> <p><span lang="EN-US">To place further constraints on the seismic hazards of this region, we have conducted morphological and structural analyses of active faults to unravel the geomorphic record of active deformation cumulated other multiple seismic events at specific sites. To do so, field observations, seismic profiles and high-resolution Pléiades images and DEMs were combined together with the dating of fluvial terraces. We find that shortening rates have been of 0.5-2.5 mm/yr, with most probable values of ~2 mm/yr over the last ~300-500 kyr. Our detailed morphological investigations further indicate that this shortening is variably partitioned on one or several blind ramps along the mountain front, and from there is transmitted forward all the way to the deformation front, ~150-180 km further north. As such, this extremely wide single frontal thrust sheet stands most probably as the largest active thrust sheet in the world!</span></p> <p><span lang="EN-US">Finally, previously published GPS velocity fields highlight a 2-3 mm/yr gradient in horizontal velocities across the WKR and southern Tarim basin when combined and expressed in a stable Tarim reference. Such gradient, unseen from previous analyses, is consistent with our morphological results on shortening rates. Most importantly, this spatial gradient in velocities may suggest that the frontal thrust sheet is presently partly locked, questioning the possibility of mega-earthquakes in the region.</span></p>

GPS-DERIVED SECULAR VELOCITY FIELD AROUND SANGIHE ISLAND AND ITS IMPLICATION TO THE MOLUCCA SEA SEISMICITY

GEOMATIKA ◽  
2020 ◽  
Vol 26 (2) ◽  
pp. 107
Author(s):  
Leni Sophia Heliani ◽  
Cecep Pratama ◽  
Parseno Parseno ◽  
Nurrohmat Widjajanti ◽  
Dwi Lestari
Keyword(s):  
Surface Displacement ◽  
Active Regions ◽  
Least Square ◽  
The Other ◽  
Gps Data ◽  
West Side ◽  
Active Deformation ◽  
Secular Motion ◽  
Small Change ◽  
Linear Least Square

<p><em>Sangihe-Moluccas region is the most active seismicity in Indonesia. Between 2015 to 2018 there is four M6 class earthquake occurred close to the Sangihe-Moluccas region. These seismic active regions representing active deformation which is recorded on installed GPS for both campaign and continuous station. However, the origin of those frequent earthquakes has not been well understood especially related to GPS-derived secular motion. Therefore, we intend to estimate the secular motion inside and around Sangihe island. On the other hand, we also evaluate the effect of seismicity on GPS sites. Since our GPS data were conducted on yearly basis, we used an empirical global model of surface displacement due to coseismic activity. We calculate the offset that may be contained in the GPS site during its period</em><em>. </em><em>We remove the offset and estimate again the secular motion using linear least square. Hence, in comparison with the secular motion without considering the seismicity, we observe small change but systematically shifting the motion. We concluded the seismicity in the Molucca sea from 2015 to 2018 systematically change the secular motion around Sangihe Island at the sub-mm level. Finally, we obtained the secular motion toward each other between the east and west side within 1 to 5.5 cm/year displacement. </em></p>

Analysis of potential seismic sources of tsunamis in the Black Sea region, using data from various catalogues

2021 ◽  
Author(s):  
Emil Oynakov ◽  
Liliya Dimitrova ◽  
Lyubka Pashova ◽  
Dragomir Dragomirov
Keyword(s):  
Black Sea ◽  
Scientific Evidence ◽  
Active Faults ◽  
Active Regions ◽  
The Black Sea ◽  
Earthquake Catalogues ◽  
Crimean Peninsula ◽  
Black Sea Region ◽  
Global Science ◽  
Using Data

&lt;p&gt;Low-laying territories along the Black Sea coastal line are more vulnerable to the possible high (long) waves due to tsunami events caused by strong earthquakes in the active seismic regions. Historically, such events are rare in the Black Sea region, despite some scientific evidence of tsunamis and their recordings through continuous sea-level observations with tide gauges built in certain places along the coast. This study analyses seismic data derived from different international earthquake catalogues - NEIC, ISC, EMSC, IDC and Bulgarian national catalogue (1981 - 2019). A catalogue of earthquakes within the period covering the historical to the contemporary seismicity with magnitudes M &amp;#8805; 3 is compiled. The data are processed applying the software package ZMAP, developed by Stefan Wiemer (http://www.seismo.ethz.ch/en/research-and-teaching/products-software/software/ZMAP/index.html). The catalogues' completeness is calculated to assess the reliability of the historical data needed to assess the risk of rare tsunami events. The prevailing part of the earthquakes' epicentres are in the seismically active regions of Shabla, the Crimean peninsula, the east and southeast coast of the Black Sea forming six main clusters, which confirmed previous studies in the region. In these areas, several active and potentially active faults, which can generate tsunamigenic seismic events, are recognized.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgements: &lt;/strong&gt;The authors would like to thank the Bulgarian National Science Fund for co-funding the research under the Contract &amp;#1050;&amp;#1055;-&amp;#1057;&amp;#1045;-&amp;#1050;&amp;#1054;&amp;#1057;&amp;#1058;/8, 25.09.2020, which is carried out within framework of COST Action 18109 &amp;#8220;Accelerating Global science In Tsunami HAzard and Risk analysis&amp;#8221; (AGITHAR; https://www.agithar.uni-hamburg.de/).&lt;/p&gt;

scholarly journals Estimation of absolute stress in the hypocentral region of the 2019 Ridgecrest, California, earthquakes

2020 ◽  
Author(s):  
Yuri Fialko
Keyword(s):  
Seismic Data ◽  
Plate Tectonics ◽  
Active Faults ◽  
Active Regions ◽  
Seismogenic Zone ◽  
Shear Stresses ◽  
Strong Earthquakes ◽  
Frictional Strength ◽  
Tectonically Active ◽  
Weak Fault

Abstract Strength of the upper brittle part of the Earth's lithosphere controls deformation styles in tectonically active regions, surface topography, seismicity, and the occurrence of plate tectonics, yet it remains one of the least constrained and most debated quantities in geophysics. Seismic data (in particular, earthquake focal mechanisms) have been used to infer orientation of the principal stress axes. Here I show that the focal mechanism data can be combined with information from precise earthquake locations to place robust constraints not only on the orientation, but also on the magnitude of absolute stress at depth. The proposed method uses machine learning to identify quasi-linear clusters of seismicity associated with active faults. A distribution of the relative attitudes of conjugate faults carries information about the amplitude and spatial heterogeneity of the deviatoric stress and frictional strength in the seismogenic zone. The observed diversity of dihedral angles between conjugate faults in the Ridgecrest (California, USA) area that hosted a recent sequence of strong earthquakes suggests the effective coefficient of friction of 0.4-0.6, and depth-averaged shear stresses on the order of 25-40 MPa, intermediate between predictions of the "strong" and "weak" fault theories.

scholarly journals Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan/mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (Northern Pyrenees, France)

2016 ◽  
Author(s):  
Margaux Mouchené ◽  
Peter van der Beek ◽  
Sébastien Carretier ◽  
Frédéric Mouthereau
Keyword(s):  
Numerical Modelling ◽  
Temporal Variations ◽  
Tectonic Activity ◽  
Mountain Range ◽  
Stream Network ◽  
Mountainous Catchment ◽  
Isostatic Rebound ◽  
Base Level ◽  
Alluvial Terraces

Abstract. Alluvial megafans are sensitive recorders of landscape evolution, controlled by autogenic processes and allogenic forcing and influenced by the coupled dynamics of the fan with its mountainous catchment. The Lannemezan megafan in the northern Pyrenean foreland was abandoned by its mountainous feeder stream during the Quaternary and subsequently incised, leaving a flight of alluvial terraces along the stream network. We explore the relative roles of autogenic processes and external forcing in the building, abandonment and incision of a foreland megafan using numerical modelling and compare the results with the inferred evolution of the Lannemezan megafan. Autogenic processes are sufficient to explain the building of a megafan and the long-term entrenchment of its feeding river at time and space scales that match the Lannemezan setting. Climate, through temporal variations in precipitation rate, may have played a role in the episodic pattern of incision at a shorter time-scale. In contrast, base-level changes, tectonic activity in the mountain range or tilting of the foreland through flexural isostatic rebound appear unimportant.

A discussion concerning the floor of the northwest Indian Ocean - The recent sedimentary facies of the Persian Gulf region

1966 ◽  
Vol 259 (1099) ◽  
pp. 291-298 ◽  
Keyword(s):  
Indian Ocean ◽  
Coastal Plain ◽  
Persian Gulf ◽  
Barrier Islands ◽  
Sedimentary Facies ◽  
Dune Sand ◽  
Gulf Region ◽  
Marginal Sea ◽  
The Indian Ocean ◽  
The Persian Gulf

The Persian Gulf, which is a shallow marginal sea of the Indian Ocean, is an excellent model for the study of some ancient troughs. It is bordered on the west by the Arabian Precambrian shield and on the east by the Persian Tertiary fold mountains. Persia is an area of extensive continental deposition. It is bordered by a narrow submarine shelf. The deeper trough of the Persian Gulf lying along the Persian Coast seaward of the shelf is floored by marly sediments. East of this, the Arabian shelf is covered with skeletal calcarenites and calcilutites. To the northwest is the Mesopotamian alluvial plain and deltaic lobe. Arabia is bordered on the Persian Gulf littoral by a coastal complex of carbonate environments. Barrier islands, tidal deltas (the site of oolitic calcarenite formation) and reefs protect lagoons where calcilutites, pelletal-calcarenites and calcilutites and skeletal calcarenites and calcilutites are forming. There are Mangrove swamps, extensive algal flats and broad intertidal flats bordering the lagoons and landward sides of the islands. A wide coastal plain, the sabkha, borders the mainland. Here evaporation and reactions between the saline waters percolating from the lagoons, and calcium carbonate deposited during a seaward regression, leads to the production of evaporitic minerals including anhydrite, celestite, dolomite, gypsum and halite. Inland, wide dune sand areas pass into the outwash plains skirting the mountain rim of Arabia.

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