Maximum Slip Research Articles

Research on Interface Slip of Composite Reinforced Steel Truss-Concrete Test Beam and Its Calculation and Analysis Method

In this study, a model of test beam in negative moment area is designed, and the slip characteristics of test beam under overlimit static load and variable amplitude cyclic load are studied, respectively. By constructing the relationship between shear stiffness and slip parameters of the test beam, the deformation calculation method of the test beam under different fatigue cycles is derived, and the accuracy of the calculation model is verified by experiments. The results show that the maximum slip value (0.038 mm) of static load after 10,000 times of limited fatigue load is increased by 58.3% compared with that before overlimit fatigue load is applied (0.024 mm). When the fatigue cycle is 0-2 million times, the total slip is between 0.019 and 0.026 mm and the residual slip percentage is between 4.17 and 8.33%. The maximum residual values are 0.022 mm, 0.027 mm, and 0.028 mm after 1.5 times, 2 times, and 3 times of overload and variable amplitude fatigue loads, respectively, and the slip values have no obvious fluctuation, all of which show good working performance. The average value of the ratio between the deformation value and the measured value of composite beams is 0.89, and the standard deviation is 4.86%. When the fatigue loading times are more than 2.8 million, the ratio between the calculated value and the measured value is less than 0.85, so the adaptability of the calculation model has certain limitations. On the whole, the calculation model proposed in this study fully considers the factors such as the stiffness and fatigue loading times of composite beams, and the error between the calculated results and the measured results is within 5%, with high accuracy, which can be used as a reference for the actual design.

Role of Poroelasticity During the Early Postseismic Deformation of the 2010 Maule Megathrust Earthquake

AbstractMegathrust earthquakes impose changes of differential stress and pore pressure in the lithosphere‐asthenosphere system that are transiently relaxed during the postseismic period primarily due to afterslip, viscoelastic and poroelastic processes. Especially during the early postseismic phase, however, the relative contribution of these processes to the observed surface deformation is unclear. To investigate this, we use geodetic data collected in the first 48 days following the 2010 Maule earthquake and a poro‐viscoelastic forward model combined with an afterslip inversion. This model approach fits the geodetic data 14% better than a pure elastic model. Particularly near the region of maximum coseismic slip, the predicted surface poroelastic uplift pattern explains well the observations. If poroelasticity is neglected, the spatial afterslip distribution is locally altered by up to ±40%. Moreover, we find that shallow crustal aftershocks mostly occur in regions of increased postseismic pore‐pressure changes, indicating that both processes might be mechanically coupled.

Surroundings affect slip length dynamics in nanoscale friction through contact stiffness and damping

Friction force microscopy (FFM) explores the interaction in a sliding contact on the nanoscale, providing information on the frictional dynamics and lateral contact stiffness with lattice resolution. Recent FFM measurements on a NaCl crystal immersed in liquid (ethanol) surroundings displayed an increase of the effective contact stiffness, Keff, with the applied load, differently from similar measurements performed under ultra-high vacuum (UHV) conditions, where Keff showed negligible load dependency. Additionally, under UHV conditions multiple slip length friction with increasing load was reported, while in ethanol surroundings only single (lattice unit length) slips were observed. Our current understanding of this behavior relates the transition from single jumps to multiple jumps dynamics to the normal load (manifested through the amplitude of the interaction potential at the contact, U0) and to the damping of the system. Here we have incorporated the effect of the load dependency on both U0 and Keff within Prandtl—Tomlinson based simulations, accompanied by variations in the damping coefficient of the system. Introducing the experimentally observed load dependency to Keff resulted indeed in single slip jumps at critical damping, while multiple slip jumps were obtained at constant Keff. The average slip length increased with the normal load, particularly when the system became underdamped. Our work provides a glimpse on the relation between the characteristic observables in atomic-scale sliding friction (maximal slip forces, stiffness, and slip dynamics) with respect to their governing parameters (corrugation energy, effective stiffness, and damping). While common understanding in nanotribology relates the effect of surrounding media mainly to the interaction potential at the contact, here we show that the media can also greatly affect the elastic interaction, and consequently play an important role on the transition from single to multiple stick-slip.

Coseismic deformation and slip distribution of the 2017 Mw 6.3 Jinghe, Xinjiang, western China earthquake based on InSAR observations: a buried reverse event on previously unknown fault

SUMMARY The 2017 Mw 6.3 Jinghe earthquake occurred in the orogenic zone of the North Tianshan mountain range, Xinjiang, western China. No evident surface rupture was identified by field investigation conducted immediately after the earthquake. We investigate the coseismic and post-seismic deformation fields due to the Jinghe event using the C-band Sentinel-1 SAR imagery, and further analyse its causative fault. The Generic Atmospheric Correction Online Service for InSAR (GACOS) model is employed to remove the atmospheric phase delay of multiple InSAR deformation maps. Coseismic deformation fields are resolved by averaging the high quality deformation maps. A nonlinear inversion scheme is used to find the optimized fault geometry in a layered elastic crust. The results imply that the Jinghe earthquake is characterized by thrust faulting, with striking and dipping angles of ∼62° and ∼28°, respectively. Subsequently coseismic slip distribution is estimated using the steepest descent method program, constrained by the derived coseismic deformation fields. The inversion results show that the average slip is ∼0.08 m and the average rake angle is ∼98°. The maximum slip is ∼0.24 m, located at the depth of 12.9 km. The moment magnitude is estimated to be Mw 6.38. The fault geometry is generally consistent with the relocated aftershocks distribution. Both the InSAR-derived deformation field and the aftershock distribution indicate that the Jinghe earthquake is attributed to a previously unknown buried fault beneath the Yongji fold with a strike of 62°. No significant post-seismic deformation is identified in the zone of coseismic deformation. This study shows that the Jinghe earthquake is a typical inland thrust event in the North Tianshan area, which is affected by south to north compression due to the Indian-Eurasian collision.

Effects of Uniform Load on Externally Post-tensioning Composite Beams under Multiple Degrees of Shear Connection

Composite beams (steel and concrete) are used widely as the main structural elements in flexure in bridges and buildings. Such structures' design life would be decreased if the loads increased or if environmental deterioration could occur. Such modifications can reduce the strength of these members and therefore need to be considered for replacement or retrofitting.The current study presents an evaluation of the effect of shear connection with its different degrees from partial to full for the composite beams strengthened with post-tensioning tendons. It is known by design that the use of partial shear connection in composite beams requires that the sliding capacitance of the shear connectors shouldn’t be less than the maximum slip so that the composite section can reach the ultimate design load. The degree of shear connection over which the composite section is designed, as well as the span length of the beam, are the most important factors governing the maximum slip limit. This study was performed using numerical modelling by the finite element analysis method to simulate the bending behaviour of composite steel beams under uniform loading cases which were strengthened with three shapes of tendons profiles. The results of two finite element models have been compared with experimental results obtained from previous literature related to the same topic. This comparison was made to ensure the efficiency, effectiveness, and accuracy of the model used, using ANSYS Workbench Software.

Coseismic Rupture Model and Tectonic Implications of the January 7 2022, Menyuan Mw 6.6 Earthquake Constraints from InSAR Observations and Field Investigation

A Mw 6.6 earthquake struck Menyuan, Qinghai, China, on 7 January 2022. To determine the rupture parameters of this event, the coseismic InSAR deformation fields were mapped and further employed to estimate the focal mechanism. The best-fitting solution emphasized that the 2022 Menyuan earthquake ruptured at the junction of the Tuolaishan fault and the Lenglongling fault. Both rupturing faults were dominated by sinistral strike-slip, and the main slip was concentrated on the shallow part of the rupture plane. The latter was the main rupture segment with a strike of 106° and a dip of 86°. The slip mainly occurred at depths of 0–8 km, and the rupture was exposed at the surface. The maximum slip reached ~3.5 m, which occurred mainly at a depth of 4 km. Joint analysis of the optimal slip model, relocated aftershocks, Coulomb stress change, and field observation suggested that the strain energy in the Tuolaishan fault may not have been fully released and needs further attention. Moreover, the 2022 Mw6.6 Menyuan earthquake caused a significant stress loading effect on the western Tuolaishan fault and eastern Lenglongling fault, which implies that the 2022 event increased the seismic hazard in these regions.

Surface Displacement and Source Parameters of the 2021 Bandar-e Genaveh, Iran, Earthquake Determined from InSAR Observations

On 18 April 2021, a MW 5.8 earthquake occurred near the city of Bandar-e Genaveh, southwestern Iran. Four synthetic aperture radar (SAR) images, acquired from Sentinel-1 (ESA Copernicus project) satellites in ascending and descending orbits, were used to get two displacement maps, catching the surface co-seismic effects through the two-pass InSAR technique. Modeling the deformation patterns using equations for a shear dislocation in elastic half-space allowed the source parameters and the slip distribution of the seismogenic source to be determined. We calculated that the rupture occurred on a reverse fault extending NW-SE, gently dipping NE and with a maximum slip reaching about 1 m. The northeast and low-dip angle of this fault are also consistent with the tectonics of the region, which is subject to deformation and shortening along the northern margin of the Arabian plate. Our estimations of the fault parameters agree with the Zagros Foredeep reverse fault. We additionally processed four other SAR images to investigate the possibility that the Mw 5.0 aftershock, which occurred about one month later, induced surface effects visible with InSAR. This analysis, however, did not provide any clear conclusions.

Analysis of coseismic slip distributions and stress variations of the 2019 Mw 6.4 and 7.1 earthquakes in Ridgecrest, California

Exploring spatiotemporal variations in the regional stress field is critical for understanding the interactions between active tectonic plates. On July 4 and 6, 2019, strike-slip earthquakes of Mw 6.4 sinistral and 7.1 dextral, respectively, occurred in Ridgecrest, California, which provided an appropriate condition for studying conjugate earthquake stress variation. In this study, we used GNSS coseismic displacement to invert the coseismic slip distributions of each earthquake. According to the spatiotemporal distribution, the focal mechanisms were divided into three time periods and five subareas. Therefore, spatiotemporal variations of the stress field were calculated. Results indicate that the two earthquakes were not purely strike-slip, but had minor dip-slip components. The maximum slips of the Mw 6.4 foreshock and the Mw 7.1 mainshock were 0.7 and 3.1 m, respectively. Areas of significant stress variations corresponded to areas of larger slip distributions. During the three time periods, the maximum horizontal stress (SHmax) direction in each subarea first experienced counterclockwise and then clockwise rotation; the SHmax direction of the foreshock epicenter region changed from 3.8° to 2.8° to 5.8°. After the mainshock, the SHmax of the foreshock epicenter region rotated clockwise by ~3.0°, the deviatoric stress was ~4.5 MPa, and the stress drop in the epicenter region of the mainshock was ~4.3 MPa, from which we can judge that the stress was almost completely released. Six months before the earthquakes, the b value began to change markedly, while it stabilized after the earthquakes. In the dextral shear zone formed by the relative motions of the Pacific and North American plates, the cumulative stress tends to be jointly regulated by NW–SE and NE–SW oriented conjugate fractures. These two Ridgecrest earthquakes are a phenomenon of stress regulation.

Seismic faults of the 2022 <italic>M</italic>w 6.6 Menyuan, Qinghaiearthquake and their implication for the regionalseismogenic structures

<p indent="0mm">The <italic>M</italic>w 6.6 Menyuan earthquake occurred on January 8th of 2022 on the northern margin of Menyuan Basin, Qinghai. It was followed by over 600 aftershocks with magnitudes of up to <italic>M </italic>5.1. The mainshock was located on the Lenglongling (LLLF) segment of the Qilian-Haiyuan (QLHYF) sinistral fault system, a 127-km-long active fault with a characteristic event of <italic>M</italic>w 7.3–7.5. In this study, we used seismic and geodetic data for the characterization of this seismic event and its large aftershocks. Using the seismic data and the CAPjoint inversion method, we obtained the centroid depths and focal mechanisms of the mainshock and the 17 largest (<italic>M</italic>s<x content-type="symbol">³</x>3.0) aftershocks. We determined that the mainshock was a strike-slip event with a moment magnitude of 6.58, centroid depth of <sc>4 km,</sc> and the two nodal planes of 197°/83°/–162° and 104°/72°/–7°. Most of the estimated aftershocks were also strike-slip events located at depths ranging from <sc>3–9 km</sc> at the periphery of the earthquake centroid. We analyzed the rupture directivity of the two large aftershocks (<italic>M</italic>s 5.2 and <italic>M</italic>s 4.8) with the azimuthal variation of source duration and found that both events ruptured <sc>1.5–2.0 km</sc> segments along the sinistral fault plane. We also processed Sentinel-1 SAR data acquired on tracks 026, 033, and 128 using an automated InSAR processing package, pSAR. The SAR-derived results that include subpixel offsets, coherence maps, and differential interferometry consistently reveal two major surface rupture segments that correlate with a step-over of Tuolaishan fault and the western segment of LLLF, respectively. We performed a geodetic inversion of the ascending and descending coseismic InSAR observations using a geodetic inversion package PSOKINV in order to determine geometric parameters and subsurface slip on the fault. During the inversion, the surface fault traces were fixed based on the observations from the subpixel offsets and coherence maps produced from the SAR data. The geodetic inversion indicates that the sinistral strike-slips on the two steep-dipping fault segments are responsible for the mainshock, having three distinct slip patterns with a maximum slip of about <sc>4 m</sc> at a depth of <sc>4 km,</sc> which is consistent with the seismic solutions. The geodetic moment from the slip model was 1.58×10¹⁹ Nm, corresponding to <italic>M</italic>w 6.68, which is slightly greater than <italic>M</italic>w 6.58 estimated from the seismic data. We also compared the seismic source solutions produced by the different seismic methods to the multiple earthquake fault segments inferred from the InSAR results obtained in this study. We found that the significant variations of the seismic solutions from P first motion polarizations, CAPjoint, GCMT and USGS W-phase are mainly due to the different periods of the seismic data used in the inversions. The solution derived from the P first motions is consistent with the fault F1 determined from the offset maps presented in this study that corresponds to the step-over of Tuolaishan fault. With longer periods, the seismic focal mechanism solutions turn out closer to the epicenter of the earthquake. This could help with the understanding of seismic solutions for other earthquakes, particularly those with significant strike variations along the rupture. Combining with regional tectonic structures and historical earthquakes, e.g., the 1986 and 2016 <italic>M</italic>s 6.4 thrust-slip Menyuan earthquakes, we suggest that an asymmetrical flower structure along QLHYF may have been a key model for unleashing the regional strain. The coseismic slip-derived stress analysis indicates that the earthquake significantly increased the Coulomb stress in the vicinity of the hypocenter, particularly at the western end of the earthquake rupture, where few aftershocks were observed, drawing our attention to the increased seismic risk in that region.

Development and analysis of the two-regime transient tyre model for combined slip

This paper refines the two-regime transient theory developed by Romano et al. [Romano L, Bruzelius F, Jacobson B. Unsteady-state brush theory. Vehicle Syst Dyn. 2020;59:11–29. DOI: 10.1080/00423114.2020.1774625.] to include the effect of combined slip. A nonlinear system is derived that describes the non-steady generation of tyre forces and considers the coupling between the longitudinal and lateral characteristics. The proposed formulation accounts for both the carcass and the bristle dynamics, and represents a generalisation of the single contact point models. A formal analysis is conducted to investigate the effect of the tyre carcass anisotropy on the properties of the system. It is concluded that a fundamental role is played by the ratio between the longitudinal and lateral relaxation lengths. In particular, it is demonstrated that the maximum slip that guarantees (partial) adhesion conditions does not coincide with the stationary value and decreases considerably for highly anisotropic tyres. The dissipative nature of the model is also analysed using elementary tools borrowed from the classic theory for nonlinear systems. A comparison is performed against the single contact point models, showing a good agreement especially towards the full-nonlinear one. Furthermore, compared to the single contact point models, the two-regime appears to be able to better replicate the exact dynamics of the tyre forces predicted by the complete brush theory. Finally, the transient model is partially validated against experimental results.

Large Surface‐Rupture Gaps and Low Surface Fault Slip of the 2021 Mw 7.4 Maduo Earthquake Along a Low‐Activity Strike‐Slip Fault, Tibetan Plateau

AbstractBased on field investigations, interpretations of high‐resolution UAV images, and analyses of available InSAR data, we mapped the fault geometry and surface ruptures of the 2021 Mw 7.4 Maduo earthquake that occurred on a low‐activity strike‐slip fault within the Tibetan Plateau. The results indicate that (a) the earthquake activated a fault that is ∼161 km long and has complicated structural geometry; (b) the surface rupture occurs over a distance of 148 km, but is separated into three distinct segments by two large gaps (38 and 20 km, respectively); (c) within the surface‐rupture segments, the horizontal and vertical displacements are typically 0.2–2.6 m (much lower than the InSAR‐based slip maximum of 2–6 m at depth) and ≤0.4 m, respectively. The two large gaps of the Maduo surface rupture represent the two largest surface‐rupture discontinuities of strike‐slip earthquakes ever documented, and coincide with structurally complicated fault portions and near‐surface soft sediments.

Slip Kinematics of the 2021 Yangbi Earthquake: Fore-Main-Aftershock Sequence Rupture along an Unknown Secondary Fault of the Weixi–Qiaohou Fault

Abstract On 21 May 2021, an earthquake sequence occurred at the Weixi–Qiaohou fault that is considered as a boundary of the Chuandian block in Southwest China, providing a significant opportunity to understand the seismogenic tectonics of the fault and its secondary faults. We used Interferometric Synthetic Aperture Radar and Global Navigation Satellite System observations to obtain surface displacements and slip kinematics of the Mw 6.1 mainshock. The Mw 6.1 event ruptured along a previously unknown secondary fault of the Weixi–Qiaohou fault; this newly identified southwest-dipping fault is dominated by right-lateral strike slip with a small normal component. Fault slip was concentrated between depths of 3 and 8 km, with a maximum slip of ∼0.8 m. Given that there is minor slip and lack of foreshocks and aftershocks rupture in 0–3 km depth, a systemic shallow slip deficit is observed in the depth. In addition, stress change simulations suggest that the Mw 5.4 foreshock promoted the Mw 6.1 event. The increased coulomb stress change region extends approximately 16 km (from 25.65° N to 25.52° N) along the Weixi–Qiaohou fault triggered by the Mw 6.1 mainshock. Combined with modeling results of the Yangbi earthquake sequence and magnetotelluric model across the Weixi–Qiaohou fault, the fore-main-aftershock sequence initiate in depths of 8–16 km (corresponding to relatively low resistivity) and further promote larger slip upward along depths of 3–8 km (relatively high resistivity). Finally, aftershocks rupture and release stress below slip depths of the mainshock.

Coseismic fault slip inversion of the 2013 Lushan Ms 7.0 earthquake based on the triangular dislocation model

The 2013 Lushan Ms 7.0 earthquake occurred on the Longmenshan thrust tectonic zone, a typical blind reverse-fault type earthquake that caused the death of nearly 200 people. The investigation of the fault geometry and fault slip distribution of this earthquake is important for understanding the seismogenic tectonic type and seismic activity mechanism of the Longmenshan Fault Zone. In this paper, for the fault geometry of the Ms 7.0 earthquake in Lushan, the geometric parameters of the planar fault are inverted based on the rectangular dislocation model using GPS coseismic displacement data, and on this basis, a curved fault steeply-dipping on top and gently-dipping at depth is constructed by combining the aftershock distribution. The GPS and leveling data are used to invert the slip distribution of the curved fault for the Lushan Ms 7.0 earthquake. The results show that the fault is dominated by reverse slip with a small amount of sinistral rotation, and there is a peak slip zone with a maximum slip of 0.98 m, which corresponds to a depth of ~ 13.50 km, and the energy released is 1.05 × 1019 N/m with a moment magnitude of Mw 6.63. Compared with the planar rectangular dislocation model, the curved fault model constructed by using triangular dislocation elements can not only better approximate the fault slip, but also better explain the observed surface displacement, and the root mean square error of the GPS and leveling data fitting is reduced by 1.3 mm and 1.9 mm, respectively. Both the maximum slip and moment magnitude of the fault based on the inversion of the curved structure are slightly larger than the results based on the planar structure.

Joint inversion of InSAR, local seismic and teleseismic data sets for the rupture process of the 2020 Mw 6.3 Yutian earthquake and its implications

On 25 June 2020, a Mw 6.3 earthquake struck Yutian county. The earthquake nucleated on a normal fault in the northwestern Tibetan Plateau. Through jointly inverting local seismic and teleseismic waveform data as well as Interferometric Synthetic Aperture Radar (InSAR) Line-of-Sight (LOS) displacement data, the spatiotemporal rupture properties of this earthquake were resolved to investigate and better understand regional crustal extension mechanisms. Inversion results show that this event ruptured along one main asperity concentrated within a depth range of 4.1–13.3 km with a maximum slip of ~0.9 m. The rupture front propagated initially around the hypocenter and then unilaterally toward the north. The whole process lasted approximately 8 s and released a total scalar seismic moment of 3.2 × 1018 Nm (Mw 6.3). The energy-based average stress drop was estimated in the range of 1.9–3.0 MPa. The radiation efficiency was estimated to be 10.0–15.8%, which is relatively low, demonstrating that most of the accumulated strain energy dissipated during rupturing. We suggest that the earthquake was possibly related to the nearby Cenozoic volcano in consideration of the dissipated rupture of the source and the west-dipping causative fault located on the western edge of the volcano. Both the westward motion of the western Kunlun block and the eastward motion of the Kunlun-Qaidam block were responsible for the EW-trending crustal extension in the Yutian district. We supposed that the 2020 normal faulting earthquake was primarily attributed to the different velocities of the Kunlun-Qaidam block moving eastward. Additionally, according to an analysis of coseismic Coulomb stress interactions, the previous 2008 Mw 7.1, 2012 Mw 6.2, and 2014 Mw 6.9 Yutian earthquakes contribute small Coulomb stress disturbance on the hypocenter of the 2020 Mw 6.3 Yutian earthquake which suggest that previous Yutian earthquakes have a limited effect on triggering the 2020 event.

Coseismic and Postseismic Fault Kinematics of the July 22, 2020, Nima (Tibet) Ms6.6 Earthquake: Implications of the Forming Mechanism of the Active N‐S‐Trending Grabens in Qiangtang, Tibet

AbstractThe N‐S‐trending grabens, the most prominent active structures in the Tibetan plateau, contain important information about the evolution and deformation mechanism of the plateau. The Ms6.6 earthquake that occurred in Nima, Qiangtang on July 22, 2020, provides an opportunity to investigate the kinematics of the grabens. Here, we use field survey and interferometric synthetic aperture radar to study the structural style, coseismic and postseismic deformation, fault slip, and stress changes of the Nima earthquake. The N‐S‐trending Qomo Ri graben (QRG) and the normal faults on the east and west sides are kinematically correlated with the NE‐trending sinistral Jiangaizangbu River and West Yibug Caka faults. The QRG is characterized by an extensional strike‐slip duplex and negative flower structure. The maximum coseismic deformation of the Nima earthquake is 29.4 cm in the line‐of‐sight direction observed by Sentinel‐1 ascending images. The coseismic slip model demonstrates that the NE20–30°‐striking fault caused the Nima earthquake has a maximum slip of 1.39 m and a main slip area at 4–12 km depth. The seismological fault may transit from a moderately dipping normal fault near the surface to a steeper strike‐slip fault at depth. Obvious postseismic deformation was observed in the stress‐enhancement area. The afterslip model shows that the mainshock fault is correlated with parallel normal faults to its west. We infer that the QRG was formed by local E‐W‐trending extension at the joints of the left‐stepping sinistral fault system, and the active normal faulting in the Qiangtang block favors stress localization.

The Crete Isl. (Greece) Mw6.0 Earthquake of 27 September 2021: Expecting the Unexpected

The 27 September 2021 damaging mainshock (Mw6.0) is the first known strong earthquake that ruptured the Arkalochori area, Crete Isl., Greece, during the entire historical period, making it an unexpected event in the long-term sense. The area is characterized by the presence of the normal active Kastelli Fault (KF) striking NNE-SSW and dipping towards ~WNW. The KF, of surface exposure only ~6 km, at its southern tip is truncated by the nearly perpendicular active Nipiditos fault. The main shock was preceded by foreshock activity lasting for ~3.9 months, thus the mainshock turned out to be an expected event in the short-term sense. Maximum ground subsidence of ~20 cm was estimated from InSAR images, but this also incorporates deformation that may have been caused by the largest aftershock (Mw5.1) of 28 September 2021. The fault model produced from the inversion of InSAR observations indicated strike 216°, dip towards ~NW at angle 53°, rake −95°, and is consistent with fault-plane solutions obtained from routine moment tensor analysis. The geodetic seismic moment calculated from the Okada’s formalism is 1.14 × 1018 N·m (Mw6.0), while a maximum slip of 1.03 m was found at depths from 3.5 km to 5 km. The entire aftershock epicenters cloud strikes in a ~SW-NE direction but is distributed in two clusters, the southern and the northern ones. The foreshock cloud, the main slip patch, the deformation area, and the strongest aftershocks all fall within the southern cluster. The foreshocks concentration at the deepest edge of the main slip patch was a foreshadow of the mainshock nucleation area. The northern cluster, which is very likely due to the gradual expansion of aftershocks, is situated in the KF hanging wall block. To interpret the main seismic slip in the southern cluster area we propose the existence of a buried KF segment at the SSW-wards prolongation of the emerged at the surface segment. Assuming a rectangular seismic fault stress drop Δσ~7 bars was found. However, for a circular fault area, which in this case is more realistic, we get Δσ = 55 bars. This is a relatively large value for Greek earthquakes but is explainable by increased fault rigidity as a result of the long repeat time of strong earthquakes in KF.

Research on deformation characteristics of the 2021 Qinghai Maduo MS7.4 earthquake through coseismic dislocation inversion

Over the past 70 years, the Qinghai Maduo Ms7.4 earthquake (May 22, 2021) has been the only earthquake with a magnitude of ≥7 that has occurred within the Bayan Har Block. To investigate the deformation process of this earthquake, we acquired the Interferometric Synthetic Aperture Radar (InSAR) coseismic deformation field based on Sentinel-1 SAR images, which showed that the maximum line of sight (LOS) displacement was ~1 m. By combining this information with the results of our field investigation, the fault slip distributions were obtained by inversion using the single- and double-fault models, wherein the latter model showed better inversion results than that of the former. According to the inversion results, the overall rupture pattern was predominantly left-lateral strike-slip, with a released seismic moment of ~Mw7.5. Specifically, the principal seismogenic fault had a strike of 283°, dip of 91°, and maximum slip of 4.87 m; the branch fault along the eastern segment of the rupture had a strike of 110°, dip of 94°, and maximum slip of 2 m. Conversely, the results derived from the Global Navigation Satellite System (GNSS) strain rate field before the earthquake indicated that the Maduo earthquake occurred in East Kunlun,which is characterized by the largest maximum shear strain rate. The strain accumulation rate (~2.5 × 10−8/yr) was significantly lower than that of the Xianshuihe fault zone on the southern boundary of the Bayan Har block and the East Kunlun fault zone on its northern boundary. Furthermore, pre-seismic deformation near the seismogenic fault was relatively gentle, showing partial late seismogenic characteristics.

Source characteristics of the Mw 6 Mutatá earthquake, Murindo seismic cluster, northwestern Colombia

The Mutatá earthquake is a Mw 6 earthquake which occurred in northwestern Colombia on September 14, 2016. This region is located at the junction between three tectonic plates, namely the South American, Nazca and Caribbean plates, and the Chocó-Panamá and Northern Andes Blocks. This event took place in the Murindo seismic zone, a zone characterized by a high seismic activity involving the Uramita fault zone, which defines the contact between the two blocks. In this study, we relocate the mainshock – aftershocks sequence and analyze the source characteristics of the Mutatá earthquake. Using data from the Colombian Seismological National Network, and after re-picking the 411 events, we obtain absolute locations exhibiting a NW-SE oriented cloud, with the mainshock being located 8 km away from its original location and at a depth of 17.6 km. The event cloud is situated at the intersection of three faults with different orientations, the NNW-SSE Uramita Fault, a NW-SE fault, and a NNE-SSW inferred fault. Using data coming from 8 broad-band seismographs within 300 km of the mainshock, we perform moment tensor and kinematic slip distribution inversions. The moment tensor inversion points to an event centroid at 20 km depth, with a predominantly double-couple mechanism. The fault orientations in the area, NW-SE orientation of the event cloud, and hypocenter – centroid technique, indicate that the NW-SE nodal plane likely corresponds to the fault plane giving a right-lateral strike-slip mechanism on a SW dipping plane. The rupture model estimated on this plane shows different slip patches, one being close to the mainshock centroid, and few other patches distributed around the mainshock except to the southeast where most of the aftershocks are located. The maximum slip for this model is approximately 0.16 m. The source characteristics of the 2016 Mutatá earthquake suggest then that secondary faults within the Murindo seismic zone can generate large earthquakes, potentially consisting in an important source of seismic hazard in this region.

Kinematics of the 30 October 2020 Mw 7.0 Néon Karlovásion (Samos) earthquake in the Eastern Aegean Sea: Implications on source characteristics and dynamic rupture simulations

We resolve source mechanism and rupture process for the Néon Karlovásion, Samos Mw 7.0 earthquake that struck Greek-Turkish border regions on 30th October 2020 acquired from kinematic joint inversion of teleseismic body-waves and near-field strong ground-motion waveforms. The optimal kinematic finite-fault slip model indicates a planar E-W striking north-dipping normal faulting mechanism with strike ϕ = 270° ± 5°; dip δ = 35° ± 5°; rake λ = −94° ± 5°; centroid depth h = 11 ± 2 km; duration of the source time function STF = 26 s and seismic moment Mo = 3.34 × 1019 Nm equivalent to Mw = 7.0. Our final finite- fault slip models exhibit two main asperities within a depth range from ~20 km to the surface. The dynamic rupture model exposes an initial heterogeneous stress distribution with variations up to 25 MPa. The near-field strong motion waveforms constrained the slip model suggesting up-dip and westward propagation of the bilateral rupture pattern with a maximum slip of 3.2 m, illuminated by back-projection (BP) analysis. The high-frequency (HF) back-projected rupture showed a predominantly E-W striking component (~75%) with directivity of 277° that propagates to the surface along a 60 km long and 24 km wide fault plane in 20 s at a slower speed range of 1.0–2.0 km/s. This well constrains the coseismic slip region where the aftershock sequence confirms distributed deformation. Our back-projection analyses elucidates a dominant HF rupture stage (0–13 s) tracked first on the epicentre area and further along the downdip in the region of maximum coseismic slip indicating ~15 km of persistent rupture. The latter HF emissions (13–20 s) remark a speed of about 3.0 km/s and a westward extension of the rupture up to 30 km from the preceding rupture segment to shorelines at the northeast of the Ikaria Island.

InSAR Constrained Downdip and Updip Afterslip Following the 2015 Nepal Earthquake: New Insights into Moment Budget of the Main Himalayan Thrust

We use ALOS-2 and Sentinel-1 data spanning 2015–2020 to obtain the post-seismic deformation of the 2015 Mw 7.8 Nepal earthquake. ALOS-2 observations reveal that the post-seismic deformation was mainly distributed in four areas. A large-scale uplift deformation occurred in the northern subsidence area of the co-seismic deformation field, with a maximum uplift of ~80 mm within 4.5 yr after the mainshock. While in the southern coseismic uplift area, the direction of the post-seismic deformation is generally opposite to the co-seismic deformation. Additionally, two notable deformation areas are located in the region around 29° N, and near the MFT, respectively. Sentinel-1 observations reveal post-seismic uplift deformation on the north side of the co-seismic deformation field with an average rate of ~20 mm/yr in line-of-stght. The kinematic afterslip constrained by InSAR data shows that the frictional slip is distributed in both updip and downdip areas. The maximum cumulative afterslip is 0.35 m in downdip areas, and 0.2 m in the updip areas, constrained by the ALOS measurements. The stress-driven afterslip model shows that the afterslip is distributed in the downdip area with a maximum slip of 0.3 m during the first year after the earthquake. Within the 4.5 yr after the mainshock, the estimated moment released by afterslip is ~1.5174 × 1020 Nm,about 21.2% of that released by the main earthquake.