Horizontal Slip Rate Research Articles

Surface rupturing earthquakes along the eastern Rhine Graben Boundary Fault near Ettlingen-Oberweier (Germany)

The eastern Rhine Graben Boundary Fault (eastern RGBF) forms the eastern margin of the Upper Rhine Graben (URG), the most seismically active area in the plate interiors of Europe. Despite seismic activity posing a significant threat to the densely populated URG and critical facilities therein, only a few studies have documented the paleoearthquake history and associated seismic hazard, focusing mainly on the western margin. We present the results of the first paleoseismological trenching ever conducted on the central section of the eastern RGBF. Following high-resolution near-surface geophysical studies, we excavated six trenches near Ettlingen-Oberweier (south of Karlsruhe, Germany) on one of its secondary fault strands. The nearly-vertical fault is transtensional left-lateral and splits into several NNW-SSE en échelon branches, forming a negative flower structure. Stratigraphic and structural relationships along with radiocarbon and Optically Stimulated Luminescence dating reveal a minimum of three surface-rupturing paleoearthquakes with a Mw of potentially 6.5 ± 0.5, occurring from old to young, >56 ka (EX), between 54 and 19 ka (EY), and between 15 and 1 ka (EZ). The events are poorly constrained in age due to erosional unconformities. Based on the cumulative vertical separation of 1.2 ± 0.3 m, we calculate an average vertical slip rate of 0.02 ± 0.005 mm/yr. From a horizontally offset alluvial channel, we infer a cumulative left-lateral slip of 5.9 ± 0.7 m and derive an average horizontal slip rate of 0.1 ± 0.01 mm/yr. The average net slip rate is 0.1 ± 0.02 mm/yr for the past 59.5 ± 3.8 ka. This value represents a minimum slip rate for the eastern RGBF, considering slip distribution within the different fault strands of the fault system. Our findings highlight the seismic potential of the eastern RGBF, providing new evidence of the Late Pleistocene and Holocene tectonic activity of its central section.

Oblique Collision of the Bahamas Platform at the Northern Boundary of the Caribbean Plate Recorded by the Late Cenozoic Coastal Terraces of SE Cuba

AbstractThe southeastern tip of Cuba Island is limited to the south by the N‐Caribbean boundary. By revisiting the impressive sequences of coastal terraces of this region, we decipher the Quaternary deformation pattern of this plate boundary. We present a detailed mapping of coastal terraces uplifted over a hundred kilometers of coastline, and U/Th dating. At Punta de Maisí, the deformation pattern shows (a) a faster uplift close to the transform boundary and (b) a northward propagation of folding produced by the convergence of the Bahamas platform toward the Caribbean plate. Along the southern coast of Punta de Maisí, the sequence displays 29 coastal terraces up to 520 m in elevation and a upper Pleistocene uplift rate of 0.23 ± 0.07 mm yr−1. We interpret this deformation as resulting from an offshore north‐dipping reverse fault near the coast. This uplift rate corresponds to 3% to 1.6% of the short‐term horizontal slip rate of Septentrional Oriente Fault Zone (10 ± 0.1 mm yr−1). Along the northern coast of Punta de Maisí, the sequence displays height coastal terraces up to 220 m in elevation and the uplift rates amount to 0.1 ± 0.05 mm yr−1 and likely result from the reverse faulting and folding associated with the offshore North Hispaniola Fault Zone. Uplift rates quickly decrease to the West, in agreement with the westward decrease in the activity of the North Hispaniola Fault Zone due to the docking of the Bahamas Platform against Cuba, while the platform more gently underthrusts Cuba to the East.

Analysis of the fault slip, creep, and coupling characteristics of the Maomaoshan-Laohushan-Haiyuan Fault using InSAR and GNSS measurements

Line-of-sight Interferometric Synthetic Aperture Radar (InSAR) observations are affected by long-wavelength errors and the inaccurate estimation of vertical deformation, thereby restricting horizontal slip rate estimations for strike-slip faults, such as the Maomaoshan-Laohushan-Haiyuan Fault (MMS-LHS-HY). To overcome this limitation, herein, InSAR (2016–2022) and Global Navigation Satellite System (GNSS) observations were combined and the Least Squares Variance Component Estimation (LS-VCE) method was used to obtain the Three-Dimensional (3-D) deformation field of the Haiyuan fault zone; subsequently, the slip-rate and coupling distributions were inverted. The results showed that: (1) Compared with the GNSS and leveling deformation velocities, the residuals of the 3-D deformation field obtained using the LS-VCE method combined with the GNSS and InSAR observations reached an RMS of 1 mm/a, significantly better than the deformation field obtained without GNSS data. (2) Vertical deformation from InSAR observations led to over- or under-estimation of the fault strike-slip rate, with the maximum influence on the shallow creep rate of 2.1 mm/a. (3) Based on the 3-D deformation field, fault slip rate, locking depth, and fault creep characteristics obtained from the elastic dislocation and elastic block models were consistent with each other. (4) The strike-slip rate of the MMS-LHS-HY fault gradually decreased from west to east, whereas the thrust rate gradually increased in the same direction. (5) Based on the 3-D deformation field, the creep range of the LHS fault was ∼40 km, with the mean shallow creep rate reaching 2.5 ± 0.1 mm/a, notably larger than the creep rate obtained by ascending InSAR observation alone.

Holocene Activity of the Wudaoliang–Changshagongma Fault of the Eastern Tibetan Plateau

The Wudaoliang–Changshagongma fault is one of the NW-trending faults located within the southern Bayan Har Block of the Tibetan Plateau in China. In this paper, we used high-resolution imagery and digital elevation model data to study the geomorphological and geological characteristics of the fault. Furthermore, the result also determined the fault trace and estimated the average horizontal slip rate of the fault since the late Quaternary to have been 2.6 ± 0.6 mm/a. This slip rate is approximately equivalent to that of the Awancang, Madoi–Garde, and Dari faults, which are also located within the block. Furthermore, the slip rates of these faults obtained by remote sensing and geological methods are consistent with GPS observations. It indicates that tectonic deformation within the block is continuous and diffuse. Using trenching study results and sedimentary radiocarbon dating, we identified four paleoearthquake events that occurred at 42,378–32,975, 33,935–20,663, 5052–4862, and after 673–628 cal BP, respectively. The recurrence intervals of large earthquakes on the faults within the block are much longer than those of the boundary faults, and the slip rates are also smaller, indicating that faults within the block play a regulatory role in the tectonic deformation of the Bayan Har Block.

Seismotectonics, Geomorphology and Paleoseismology of the Doroud Fault, a Source of Seismic Hazard in Zagros

In this study, the active tectonics, paleoseismicity, and seismic hazards of the Doroud Fault are examined through high-resolution satellite image interpretations, field investigations, outcrop and trench excavations, and the dating of geochronology samples. The Doroud Fault (DF), one of the essential segments of the Main Recent Fault in the northern margin of the Zagros mountain range, has a historical and instrumental background of high seismicity. We present the first constraints from tectonic geomorphology and paleoseismology along the Doroud Fault near the capital city of Dorud. Detailed observations from satellite imagery, field investigations, real-time kinematic (RTK) measurements, paleoseismological trenching, the radiocarbon (C14), and optically stimulated luminescence (OSL) as ages allowed us to map the fault in detail, describe and characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements, paleoseismicity, and magnitude, as well as recurrence interval) relevant to the recent seismic activity of the Doroud Fault during the late Holocene as one of the most important seismogenic faults in Zagros. Modern alluvial terraces of gullies and loess accumulations are systematically deflected and/or offset with co-seismic rupture, landslides, and scarps, indicating that the Doroud Fault has been active in the late Quaternary and is characterized by dextral strike–slip movements with a normal component. In addition, our findings provide a comprehensive analysis of the fault displacement, the timing of paleoearthquakes, and the right-lateral slip rate of the Doroud Fault. The late Holocene slip rate of the Doroud Fault using the OSL dating the gully is as follows: the minimum and maximum horizontal slip rates are estimated to be 1.82 and 2.71 mm/yr, and vertical slip rates of 1.03 and 1.53 mm/yr are calculated for the past 4600 ± 900 years in the middle segment of the fault. This study focused on a paleoseismological trench within the archeological sites of Darbe-Astaneh. The central portion of the fault has historically hosted more than nine earthquakes in the last 66 ka years, according to the study’s findings. According to paleoseismology studies, the Doroud Fault has the seismic capability to cause earthquakes with a magnitude of more than 7.4 and a total slip rate of about 3.83 ± 0.1 m. The average recurrence interval for the identified paleoearthquakes is approximately 104 ± 7 years.

Tectonic geomorphology and Quaternary fault slip rates in the Tsambagarav Massif, Mongolian Altai

AbstractThe NNW‐striking Mongolian Altai is a Late Cenozoic dextral strike–slip deformation belt affected by the far‐field stress caused by the collision between India and Eurasia. The Tsambagarav Massif is bounded by faults, has a triangular plan shape, and attains the highest elevation of the belt. This massif is adjacent to the central segment of the Hovd fault, which is the largest fault in the Mongolian Altai. Here, we use 10Be surface exposure dating, radiocarbon dating, and paleoseismic trenching to reveal deformation patterns and Quaternary slip rates for two range‐bounding faults: the Tsambagarav dextral reverse fault and the Lower thrust fault. The Lower thrust exhibits thrusting motion along the low‐angle structural fabric of the basement rock and cuts Quaternary alluvial fan deposits, vertically offsetting their surfaces by 3.9–5.1 m, with fault scarps extending several kilometres along‐strike. The Tsambagarav dextral reverse fault is characterized by strike–slip motion along the high‐angle structural fabric of basement rock. Various surface deformation features indicate recent dextral strike–slip, including displacements of Late Quaternary moraine by ~50 m. Dividing the measured displacements by 10Be surface exposure ages of alluvial fan surfaces (for the Lower thrust) and moraine (for the Tsambagarav dextral reverse fault) gives a reverse slip rate of 0.3–1.7 mm/yr for the Lower thrust and a horizontal slip rate of 1.7–2.6 mm/yr for the dextral reverse fault. Radiocarbon ages of animal bones in a pond deposit accumulated along an associated tensional crack indicate that the last earthquake that caused a surface rupture occurred between 1924 and 1708 cal yr BP. Our study suggests that strain partitioning has occurred on the faults of the Tsambagarav Massif.

Late Quaternary fault activity and deformation mechanism in the eastern Tibet Plateau (Dari fault, Bayan Har Block)

The Dari fault is one of several large NW-trending left-lateral strike-slip faults with Holocene activity inside the Bayan Har Block in the east of the Tibetan Plateau. Through interpretation of high-resolution images, field investigations, and trench excavations, we estimated that the average horizontal slip rate has been 2.6 ± 0.6 mm/y since the late Quaternary. We also identified three earthquake events dated to 15,609–12,658 cal BP, 6741–5074 cal BP, and 1947 AD. The large NW-trending strike-slip faults (such as the Awancang fault, Madoi–Gardê fault, Dari fault, and Wudaoliang–Changshagongma fault, which are located in the Bayan Har Block, eastern Tibetan Plateau) all exhibit late Quaternary activity, and appear to have divided the Bayan Har Block into several subblocks. The faults transmit crustal deformation from the interior of the block to the Longriba fault, and the long-term tectonic deformation is converted into vertical uplift in the Longmen Shan region.

3D geomechanical modeling of the Xianshuihe fault zone, SE Tibetan Plateau: Implications for seismic hazard assessment

The Xianshuihe fault on the southeastern margin of the Tibetan Plateau is one of the most active intracontinental faults worldwide. At least 16 strong earthquakes (M > 6.5) have occurred on this fault since 1327 CE. To reasonably assess the future seismic hazard of this fault region, it is essential to gain a comprehensive knowledge of the fault kinematics and stress state. In this study, we developed a fine 3D geomechanical model of the Xianshuihe fault and its adjacent area, and obtained a spatially continuous contemporary kinematics and crustal background stress field of this region. Our modeled results show that the slip rate of the Xianshuihe fault is as high as 11 mm/a on the northwestern segment and generally decreases to ~9 mm/a on the southeastern segment (i.e. Moxi fault). The Yulongxi fault, a branch oblique to the Moxi fault, has different slip senses in different segments with a very low horizontal slip rate (<0.6 mm/a). In terms of stress, the study area is dominated by a transtensional faulting stress regime with E-W-trending maximum horizontal stress SH, indicating the study area is mainly subjected to an E-W compression and N-S extension. Localized normal and thrust faulting regimes appear alternately along the Xianshuihe fault, showing an inhomogeneous stress state. The high normal stresses on the Songlinkou-Selaha segment and the Moxi fault combined with their relatively high slip rates, make us speculate that these two segments have the potential to produce strong earthquakes in the future. A relatively high seismic hazard is also ascribed to the Yulongxi fault based on the analysis of its geological and geodynamic environment.

Co-seismic rupture of the 2021, Mw7.4 Maduo earthquake (northern Tibet): Short-cutting of the Kunlun fault big bend

We report detailed field measurements of the 2021, Mw7.4 Maduo earthquake surface rupture south of the Kunlun fault, near the northern boundary of Tibet's Bayan Har block. In the field, the dominantly left-lateral surface rupture length was ∼151 km, along the poorly known Jiangcuo fault, with maximum horizontal and vertical displacements of ∼2.1±0.2 to 2.9±0.2 m (up to 3.6±0.2 m at one site) and ∼1.2±0.2 to 1.8±0.2 m, respectively. The rupture, which propagated bilaterally from a roughly central epicenter, terminated in well-defined, ∼20 km-long horsetail splays, as predicted by Coulomb stress failure, consistent with the very young age of the still growing Jiangcuo fault, which may be trying to bypass the Anyemaqen restraining bend in order to connect directly the Kokoxili and Maqen segments of the main Kunlun fault. 14C dating at one site (Cuoerjiala) implies long return times (≥6500 years) for M7+, Maduo-type earthquakes, in keeping with a slow horizontal slip rate of ∼0.55±0.03 mm/yr and the subdued geomorphic expression of the fault. In the broader Tibetan tectonics framework, the Jiangcuo fault may be better interpreted as a kinematic streamlining of the Kunlun fault bend, rather than a result of diffuse deformation across the Bayan Har terrane.

Late Quaternary Slip Rate of the Zihong Shan Branch and Its Implications for Strain Partitioning Along the Haiyuan Fault, Northeastern Tibetan Plateau

AbstractGeometrical complexities such as bends and branches are ubiquitous along strike‐slip faults. Understanding strain partitioning between the different fault strands along such sections is key to assessing kinematics and evolution through time of a fault system and related seismic hazards. The Haiyuan fault, one of the longest strike‐slip faults of the Tibetan Plateau, has developed a multi‐stranded complex fault geometry along the Hasi Shan restraining bend. In this study, we quantified the slip rate of the ∼50‐km‐long Zihong Shan fault, which is the poorly‐known southernmost fault strand of the Hasi Shan restraining bend. We computed high‐resolution DEMs and orthophotos to document the offset landforms along this fault using drone surveys. At selected sites with well‐preserved offset geomorphic markers, we quantified displaced terraces and channels using microtopography analysis. We dated the abandonment age of these terraces using 10Be cosmogenic depth profiles and OSL dating techniques. It yields a left‐lateral slip rate of 1.9 ± 0.6 mm/yr since ∼13 ka, which is similar to the rate of the main Hasi Shan branch that ruptured during the 1920 Haiyuan earthquake. The minimum total horizontal slip rate system summed over the multiple strands of the Haiyuan fault at the Hasi Shan restraining bend is 4.1 ± 0.6 mm/yr, without considering the vertical deformation rate of these fault strands. The rate is thus slightly smaller than, but comparable to, slip‐rates determined along the rest of the Haiyuan fault, east and west of the Hasi Shan restraining bend.

Fault Activation in Central Mongolia during the Holocene: Results of Study of the Mogod Earthquake Ruptures

Abstract —In order to determine the seismotectonic activity of faults in the Holocene, we performed trench studies of the ruptures produced by the catastrophic Mogod earthquake (5 January 1967, M = 7.5–7.8, I0 = 9–10) in the junction zone of the N–S striking Hulzhin Gol fault and the NW striking Tullet fault. Paleoseismic interpretation of seismic-deformation sections and radiocarbon dating of the samples allowed determining the kinematics and obtaining, for the first time, the absolute ages of paleoevents preceding the Mogod earthquake. Analysis of the tectonic conditions for realization of earthquake sources has shed light on the complex structure of ruptures in the area of the Mogod earthquake epicenter, within which three segments differing in the displacement amplitudes and kinematics have been identified. The research data indicate the repeated activation of the Tulet and Hulzhin Gol faults in the Late Pleistocene–Holocene. The absolute age of the latest activation is 596–994 AD for the Tulet fault and 11,379–6235 BC for the Hulzhin Gol fault. The cumulative deformation from paleoearthquakes in the trench sections in the Tulet fault zone points to at least two displacements of thrust kinematics, with the latest of them having an amplitude of 2.8 m. The paleoearthquake in the Hulzhin Gol fault zone is characterized by the presence of lateral slip. The amplitudes of deformations attest to earlier earthquakes similar in energy to the 1967 Mogod event or even stronger in the fault node. The obtained data on the timing of these earthquakes and the amplitudes of the accompanying displacements made it possible to estimate slip rates along the faults: 0.2–0.3 m/kyr horizontal-slip rates on the Hulzhin Gol fault and 0.5–0.7 m/kyr vertical-slip rates on the Tulet fault.

Segmentation and Holocene Behavior of the Middle Strand of the North Anatolian Fault (NW Turkey)

AbstractThe North Anatolian Fault (NAF) in the Marmara region is composed of three parallel strands all separated by ∼50 km. The activity of the middle strand, which borders the southern edge of the Marmara Sea, is much debated because of its present‐day very low seismicity. This contrasts with historical, archeological and paleoseismological evidence, which suggest several destructive earthquakes have occurred during the last 2000 years. Our study aims to better constrain seismic hazard on the middle strand by exploring its Holocene paleoseismicity. For this, we mapped 148 km of the eastern part of the middle strand, using high‐resolution satellite imagery. A series of landforms offset by the middle strand activity have been systematically measured to recover the past ruptures. Three Late Pleistocene‐Holocene terraces have been dated with the terrestrial cosmogenic nuclide method, constraining a horizontal slip rate of mm/yr. The statistical analysis of the offsets evidences several major ruptures preserved in the landscape, with coseismic lateral displacements ranging between 3 and 6.5 m. This corresponds to Mw ∼7.3 earthquakes able to propagate along several fault segments. Historical seismicity and paleoseismology data suggest that the last large earthquakes along the middle strand of the NAF (MNAF) happened in 1065 CE and between the 14th and 18th centuries CE. Since then, the MNAF may have accumulated enough stress to generate a destructive rupture.

Active tectonics along the Khazar fault (Alborz, Iran)

The Alborz Mountain accommodates some of the convergence between Central Iran and Eurasia, is characterized by active range-parallel fold and thrust structures. At present, the kinematics of the range involves a strain partitioning mechanism and clockwise rotation of the South Caspian Basin. Range-parallel, left-lateral strikeslip faulting dominates the central part of the mountain range, while reverse faulting affects its northern and southern borders. Several slip-rate studies have been carried out along active faults in the internal and southern parts of the range. However, the characteristics of the main northern bounding fault (the Khazar [Persian: Caspian] Fault) remain poorly known. Our analysis provides new constraints on the activity of this fault. We first show that the fault generally is a hidden thrust fault, often associated with fault-bend and fault-propagation folds (forebergs). In the central part of the fault, the radiocarbon dating of an uplifted terrace allows estimating minimum vertical and average horizontal slip rates of 2.0 ± 0.5 mm/yr and 3 mm/yr respectively. hence, minimum slip rate along the fault reach to 3.6 mm/yr. About 150 km further east, near the city of Behshahr, within the archeological site of Gohar-Tappe, a paleoseismological trench study on a young detachment fold suggests that at least 5 events occurred in the past 5,300 years, 3 of them with surface-rupturing between 5300- and 3900-years cal BP, our results confirm that the Khazar Fault is a major active structure in northern Iran, and represents a significant seismic hazard for the entire Central Alborz region.

Morphotectonics and Slip rate of the Khazar fault in Central Alborz, (North of Iran)

The Alborz mountain range accommodates some of the convergence between Central Iran and Eurasia. At present, the kinematics of the range involves a strain partitioning mechanism, and is associated with clockwise rotation of the South Caspian Basin. left-lateral strike-slip faulting is present along the entire of its central part, while reverse faulting is affects its northern and southern borders. Several slip-rate studies have been carried out along active faults in the internal and southern parts of the range. Our analysis provides new constraints on the activity of this important active thrust fault. We show that the fault generally is a hidden thrust fault, often associated with fault-bend and fault-propagation folds (forebergs). In the central part of the fault near Chamestan, radiocarbon dating on an old elevated terrace allows estimating the minimum vertical slip of 2.0± 0.5 mm / year. Considering a 34 degree slope for the fault, the minimum horizontal slip rate will be 3 mm/yr and the minimum slip rate along the fault plane will be up to 3.6 mm / year. Our results confirm that the Khazar Fault is a major active structure in northern Iran, and represents a significant seismic hazard for the entire Central Alborz region.

Late Pleistocene‐Holocene Slip Rates in the Northwestern Zagros Mountains (Kurdistan Region of Iraq) Derived From Luminescence Dating of River Terraces and Structural Modeling

AbstractA significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold‐Thrust Belt. However, the spatial and temporal distribution of active shortening within the belt, especially in its NW part, is not yet well constrained. We determined depositional ages of uplifted river terraces crossing the belt along the Greater Zab River using luminescence dating. Kinematic modeling of the fault‐related fold belt was then used to calculate long‐term slip rates during the Late Pleistocene to Holocene. Our results provide new insight into the rates of active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 1.46 ± 0.60 mm a−1 of slip, while a more external basement fault further to the SW accommodates less than 0.41 ± 0.16 mm a−1. Horizontal slip rates related to detachment folding of two anticlines within the Zagros Foothills are 0.40 ± 0.10 and 1.24 ± 0.36 mm a−1. Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and in the distribution of uplifted terraces. In the southwestern part, the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment. In the NE, deformation is associated with slip on basement thrusts. Our study sheds light on the distribution of shortening in the Zagros Mountains and helps to understand the regional tectonic system. Our results may be the foundation for a better seismic hazard assessment of the entire area.

East Tacheng (Qoqek) Fault Zone: Late Quaternary Tectonics and Slip Rate of a Left‐Lateral Strike‐Slip Fault Zone North of the Tian Shan

AbstractAlthough the Tacheng Basin may play an important role in accommodating crustal shortening north of the Tian Shan and west of the Junggar Basin based on observations of several conspicuous surface ruptures in satellite imagery, little is known about its late Quaternary tectonic activity. We analyze the tectonic geomorphology of the East Tacheng fault zone, including the subparallel NE‐SW trending East Tacheng and Wuerkashier faults, using field observations, interpretations of satellite imagery, and construction of decimeter‐scale digital elevation models from unmanned aerial vehicle surveys. Geomorphological features such as displaced stream channels and terrace risers, negligible vertical offset, opposite facing directions of a single fault scarp, and linear fault traces suggest that the East Tacheng fault is a nearly pure left‐lateral subvertical strike‐slip fault. The late Quaternary horizontal slip rate is estimated to be 0.4–2.0 mm/year, likely ∼0.7 mm/year. Paleoearthquake studies in trenches reveal that the most recent earthquake occurred between 3.1 and 0.5 ka. The Wuerkashier fault, which shows pristine surface ruptures along a total length of ∼67 km, is also a nearly pure left‐lateral strike‐slip fault. The most recent earthquake along this fault is dated to be 7.9–0.5 ka. Combining GPS velocity and active fault kinematics in the northern Tian Shan and western Junggar, we suggest that the western Junggar is controlled by regional N‐S crustal shortening related to the India‐Eurasia collision, and the reactivated Paleozoic fault zones in the western Junggar play a key role in transferring deformation northeastward into the Altai and Mongolia.

Late Pleistocene-Holocene characteristics of the North Anatolian Fault at Adapazarı Basin: evidence from the age and geometry of the fluvial terrace staircases

The Late Pleistocene-Holocene evolution of the Adapazarı Basin was investigated using the stratigraphy, geometry, and absoluteluminescence dating of the 4-step fluvial terrace staircases of the Sakarya River. The results revealed that the fluvial cycle was primarily related to relative sea level changes of the Black Sea. The initiation of deposition and the abandonment ages of the terraces indicated relative high stands during marine isotope stage (MIS) 5a (~84-72 ka), 3 (40-30 ka), and 1 (9 ka-recent). The erosional periods in between the terrace steps reflected the response of the Sakarya River to the significantly low stands of the sea. The spatiotemporal position of the high terraces (T4 and T3) yielded an average of 0.78 ± 0.03 mm/year, and uniform and aseismic rock uplift rate for the NW part of the Anatolian Plate bounded by the North Anatolian Fault, which ruptured during the 1999 İzmit earthquake. The lower terrace (T1) was previously used to determine the horizontal slip rate of the Sapanca-Akyazı segment of the earthquake rupture and reported as 16.7 + 3.6/-2.5 mm/year. Further displacement measurements from the surfaces of T2 and T1 yielded a vertical slip rate of 1.49 ± 0.2 mm/year, calculated for the Late Holocene. Extrapolation of these 2 vertical rates to the south and north of the fault zone, in time and space, used in conjunction with the stratigraphy and geometry of the Adapazarı Basin, provided an estimation constraining the timing of the initiation of the fault to 450 ± 50 ka and the total thickness of the basin to ~1100 m.

The Late Quaternary dip–slip characteristics of the left-lateral strike-slip Yuanmou fault, the southwestern margin of the north–south seismic belt of China

The North–South Seismic Belt distributed along the eastern margin of the Tibetan Plateau is a regional-scale seismically active zone. The Yuanmou Fault, located at the junction of the North–South Seismic Belt and the Central Yunnan Sub-Block, is an important boundary of earthquakes distribution and topography. Therefore, the studying of the Late Quaternary activity of the Yuanmou Fault is of great significance to understand the regional geodynamic mechanism and its efforts on the regional tectonic activities, seismic distribution and future risk. Based on field observations and analysis of earthquake geology and tectonic geomorphology and the dating results of Quaternary chronology, together with the previous studies, revealed that: (1) the fluvial terrace T1 was cut by the Yuanmou fault on the northern section of Jiangbian, and the most recent earthquake event happened about 7 ka B.P. age on the Jiangbian–Luochuan segment. (2) Based on the offset measurement and dating results of deformed terraces, the horizontal and vertical average slip rate of the Yuanmou fault were determined to be ~ 1.0 mm/year and ~ 0.1 mm/year, respectively. (3) Moreover, the latest activity time of the southern segment of the Yuanmou Fault is late Pleistocene, indicating the segmentation between the northern and southern segments of the Yuanmou Fault. (4) The differential activity intensity and activity ways of the Yuanmou Fault on different segments is probably associated with the change of local stress. Therefore, these findings concerning with seismic activities and activity segmentation of the Yuanmou Fault reveal the complexity of the regional dynamic mechanisms and provide a new insight for exploring regional differences in the tectonic deformation mechanisms of the southeastern margin of the Tibetan Plateau during the Late Cenozoic.

Constraining Late Quaternary Crustal Shortening in the Eastern Qilian Shan From Deformed River Terraces

AbstractThe Qilian Shan, located in the northeastern Tibet, is under strong tectonic activity and earthquake motion due to the propagation of the plateau. At the mountain front of the eastern Qilian Shan, the Tongziba River, in the southern Zhangye Basin, flows northward and successively cuts the Minle‐Damaying Fault and the Yonggu Anticline, two parallel structures within the Frontal Thrust system of the Qilian Shan. Here we present a detailed record of seven strath terraces of this river that documents the history of active deformation of the two structures. Based on the estimated crustal shortening distance from the deformed terraces and the terrace formation age constrained by AMS14C and optically stimulated luminescence (OSL) dating, a horizontal slip rate of 1.4 ± 0.5 mm/year of the Minle‐Damaying Fault is constrained since 16.7 ± 1.8 kyr, and a shortening rate of 1.3 ± 0.4 mm/year across the Yonggu Anticline has been estimated in a similar time frame, respectively. In total, the shortening rate across the mountain front is estimated to be 2.7 ± 0.6 mm/year. GPS data show a similar modern shortening rate in this area, which indicates the rate of crustal shortening may be comparable in the modern and 104‐year scales. Our study supports a higher crustal shortening rate along the mountain front of the eastern Qilian Shan than that of the western Qilian Shan since the Late Quaternary.

Late Quaternary transpressional earthquakes on a long-lived intraplate fault: A case study of the Southern Yangsan Fault, SE Korea

The NNE–SSW-striking Yangsan Fault in southeastern Korea has been regarded as one of the most prominent seismogenic structures in the Korean Peninsula on the basis of instrumental and historical seismicity, and paleoseismic records along the fault zone. Its seismic behavior is, however, still uncertain due to long recurrence intervals of strong earthquakes and insufficient historical and geologic records. We conducted a detailed paleoseismic investigation, including an 8 m-deep excavation, in order to understand recent earthquake-faulting events along the Southern Yangsan Fault. Our observations indicate that at least two and possibly four dominantly strike-slip surface-faulting events have occurred along a subsidiary fault in the eastern boundary of the fault valley since the late Pleistocene. Stratigraphic features and OSL ages of the stratigraphy exposed in the trenches indicate that the most recent rupture(s) occurred after 29.2 ± 1.4 ka and the timing of earlier ruptures are constrained to between 70.0 ± 3.7 ka and 29.2 ± 1.4 ka. Using a contact of the oldest dated unit that has at least 7.5 m of vertical separation, we calculate a minimum vertical slip rate during the late Quaternary of 0.11 mm/yr. The minimum horizontal slip rate is presumed to be two times that of the vertical slip rate based on striations observed on clasts next to the fault core. We also propose that the late Quaternary earthquake-faulting kinematics along the Yangsan Fault, expressed as contractional dextral slip with east-side-up geometry, is strongly dependent on a pre-existing fault zone architecture with a strike of N10–20°E that dips to the east, and the direction of neotectonic maximum horizontal stress (ENE–WSW to E–W).