Sense Of Slip Research Articles

Determination of the long-term slip rate of a fault in a slowly deforming region based on a reconstruction of the landform and provenance

Determining slip rates is essential for assessing earthquake hazards and understanding their recurrence intervals. However, in regions characterized by slow deformation, the long intervals between seismic events present challenges in understanding the long-term seismic behavior. This study focused on the Yangsan Fault (YF) on the Korean Peninsula, which is a major active fault in a slowly deforming area. We identified paleo-surface ruptures and validated stratigraphic evidence of paleo-earthquakes by geomorphological analyses and trench surveys along the YF. Landform restoration analyses indicate a lateral offset of ~320 m, which is supported by downstream changes in gravel composition in channels that cross the YF. Our investigation into the notable changes in gravel composition within channels forming in the alluvial fan revealed sediments with compositions unlikely to originate from the current topography. Observations of the sediment composition in channels within the alluvial fan, flowing from east to west, suggest a dextral slip sense focused around the YF. The minimum slip rate for the lateral offset was calculated to be 0.38–0.57 mm/yr using a burial age of ca. 698 ka for a gravel deposit exposed in a trench wall. The results show the importance of using diverse approaches to mitigate methodological uncertainties in measuring fault displacements and ages, particularly when determining the long-term slip rate in intraplate settings.

Midcrustal moderate-size earthquake occurrence in paleovolcanic structures off Jeju Island, South Korea

A series of midcrustal moderate-size earthquakes occurred in the Korean Peninsula recently. A midcrustal ML4.9 strike-slip earthquake with a fault-plane strike in N-S occurred on December 14, 2021 at the southwestern offshore region of Jeju Island, South Korea. The fault plane orientation and slip sense (faulting mechanism) hardly conform with the regional stress field. The deep focal depth and N-S directional strike-slip motion require transient changes in the medium properties and stress field. Strong ground motions of the midcrustal earthquake induce preferential dynamic stress changes in NE-SW direction, triggering subsequent aftershocks in NE-SW-directional adjacent faults. Both the static and dynamic stress changes caused by the mainshock contribute to the aftershock sequence. The number and focal depths of aftershocks decrease with distance from the mainshock. The different fault-plane orientations between the mainshock and aftershocks suggest earthquake nucleations in independent fault structures. The mainshock occurred in aseismic midcrustal paleovolcanic structure on the outskirt of a high seismicity region. The ML4.9 earthquake suggests possible nucleation of earthquake in seismically-inactive paleotectonic structures, successively incurring aftershocks conforming to the ambient stress. The mainshock and aftershocks suggest that paleotectonic structures may behave as source structures to spawn earthquakes.

Variations in Subsidence Patterns in the Gulf of Mexico Passive Margin From Airborne‐LiDAR Data and Time Series InSAR: Baton Rouge Case Study

AbstractThe Coast of Louisiana is affected by accelerating sea level rise compounded by land subsidence, leading to land loss. Vertical crustal motions in the region are caused by natural and anthropogenic processes that vary temporally and spatially across the Gulf of Mexico. We investigate the role of growth faulting contributions to subsidence in a case study of Baton Rouge, where two E‐W striking, down‐to‐the‐south normal faults, the Denham Springs and Baton Rouge faults, cut compacted Pleistocene strata, and where sediment compaction should be minimal. We used InSAR time series and LiDAR differencing data spanning 1999–2020 to quantify modern vertical and horizontal displacements. After calibration with GNSS data, both methods reveal similar spatial patterns in ground motion, with the faults delimiting areas with different absolute rates. On average the area north of the Baton Rouge fault is subsiding faster than the south, opposite to the long‐term sense of fault slip. LiDAR mean vertical rates range between −5 to −11 mm/y and −2.4 to −7 mm/y. InSAR time‐series mean rates in the LOS direction range between −10.9 to −13.6 mm/y and −8 to −10.6 mm/y, respectively, for the north and south areas. Subsidence in the northern area likely is controlled by groundwater level changes caused by pumping as indicated by groundwater extraction models. The southern area average is likely influenced by the injection of fluids. Our results suggest volumetric changes caused by fluid extraction and injection in regions separated by growth faults that are creeping to accommodate the spatial variations in subsidence.

Current active fault distribution and slip rate along the middle section of the Jiali-Chayu fault from Sentinel-1 InSAR observations (2017–2022)

The Jiali-Chayu fault, situated on the eastern side of the eastern Himalayan syntaxis, is the southeastern margin of the large strike-slip fault zone of the Jiali Fault. The study of the distribution and activity within this fault zone is imperative for a comprehensive understanding of the tectonic movement patterns in the southeastern Tibetan Plateau. Previous studies have established that the kinematic characteristic of the Jiali-Chayu fault diverges significantly from that of other segments within the Jiali fault. Nonetheless, the current tectonic characteristics, including the slip sense, slip rate, and geometric deformation of this fault, are still not well resolved, leading to divergent interpretations regarding its contemporary activity intensity. This paper introduced an optimized time-series InSAR method with phase compensation designed for regions characterized by low coherence and exhibiting slow deformation. Using Sentinel-1 SAR data from both ascending and descending orbits spanning the period between 2017 and 2022, we successfully derived deformation rates for the middle part of the Jiali-Chayu fault at a spatial resolution of 150 m. The slip and dip rates of active faults are determined by considering the fault movement rates from two different observation angles, in conjunction with strike angle and the assumed dip angle of the fault. The results show that the deformation rates of the three branches are very different, with F2-1 and F2-2 exhibiting notable activity, while other areas exhibit relatively weaker activity. The strike-slip rates for F2-1 and F2-2 faults range between 3.6 and 5.3 mm/a and 3.05 to 5.13 mm/a, respectively, while their respective dip-slip rates fall within the range of 1.1–2.7 mm/a and 2.99–5.02 mm/a. In accordance with the fault slip directions, we classify the F2-1 fault as a sinistral (left-lateral) strike-slip fault and the F2-2 fault as a dextral (right-lateral) strike-slip fault. This study addresses a gap in remote sensing methods for detecting active fault activity in this region, providing a systematic foundation for identifying weak activity characteristics within the fault zone.Graphical

Mismatch between Actual and Perceived Sense of Slip Detrimentally Influences Postural Stability in Older workers

Age-associated impairment of proprioception and decreased sensitivity to underfoot pressure, may have serious problems for the elderly for their ability to “correctly” judge or perceive the degree of slipperiness, while walking on an inclined slippery surface, such as a ramp. The present study focuses on investigating the role of age-associated influences on workers’ ability to perceive surface slipperiness and its impact on postural balance and slip and fall events while negotiating a ramp. The study was carried out on 32 younger and 33 older workers. All workers’ postural balance and slip/fall events were objectively quantitated with a human motion analysis system and subjectively measured with the perceived sense of slip/fall (PSOF) tool respectively, while they walked up and down a ramp (on a level surface or 0, or at 10, 15, and 20 degrees) on 2 surface coefficient of frictions (dry: 0.76-1.06; moderately slippery: 0.19-0.21). While slip rating scores for the dry surface were comparable between the groups, the older workers significantly (p=0.046) underestimated the slippery surface. The deviation of the subjective surface slipperiness rating from the mean (DSSSR) for each surface was calculated. As expected, the older workers’ objective measure of postural balance was poorer than the younger group when they negotiated the slippery ramp surface. Repeated measure logistic regression analysis showed that the younger group was more likely to slip but much less likely to fall as DSSSR increased. Therefore, a mismatch between perception of slippery surface risk and the actual risk may jeopardize workers’ ability to safely negotiate a slippery ramp surface and thereby make them more susceptible to slip-related fall-injuries.

Distribution of the Surface Ruptures in the Kalaotoa Due to the 2021 M w 7.3 Flores Sea Earthquake, Indonesia

A magnitude 7.3 earthquake occurred at precisely 11:20 on December 14, 2021, within the Flores Sea region of Indonesia, precipitating a consequential landslide event. This seismic incident induced the creation of an extensive rupture zone spanning approximately 8 kilometers along the Kalaotoa fault (KF) system, which exhibits an NNE-NW-SSE trend. The objective of this study was to concentrate specifically on the Kalaotoa Island vicinity, situated approximately 40 kilometers from the earthquake’s epicenter, encompassing meticulous orientation and comprehensive field surveys conducted during the reconnaissance phase. The results of the ground assessment have been combined with spatial analysis data to ascertain the configuration and dispersion of ruptures subsequent to the earthquake, thus delineating the affected region as a prospective area susceptible to seismic events and subsequent calamities. In the vicinity proximate to the northern epicenter, fractures resulting from the seismic activity were consolidated, exhibiting considerable devastation in the form of ground fissures, rock avalanches, landslides, and structural collapses, and were predominantly oriented in a roughly NE-SW direction. Notably significant are the southern beaches of Lato’do and the eastern extremity of the rupture zone in the Lembang Mate’ne area, where coastal transgression and extensive inundation during high tides have been observed due to subsidence of 1.2 meters since the 2021 Flores Sea earthquake. Horizontal displacement around Kalaotoa Port, north of the Karumpa-Kawawo area. Displacement distribution, slip sense, and crustal deformation after earthquake propagate unilaterally to the north, resulting in a movement of the northeast side of the fault concerning SE.

Refined Earthquake Focal Mechanism Catalog for Southern California Derived With Deep Learning Algorithms

AbstractEarthquake focal mechanisms, determined with P‐wave polarities and S/P amplitude ratios, are primary data for analyzing fault zone geometry, sense of slip, and the crustal stress field. Solving for the focal mechanisms of small earthquakes is often challenging because phase arrivals and first‐motion polarities are hard to be separated from noise. To overcome this challenge, we implement convolutional‐neural‐network algorithms (Ross, Meier, & Hauksson, 2018, Ross, Meier, Hauksson, & Heaton, 2018, https://doi.org/10.1029/2017jb015251, https://doi.org/10.1785/0120180080) to detect additional phases and polarities. Using both existing and these new data, we build a high‐quality focal mechanism catalog of 297,478 events that occurred from 1981 to 2021 in southern California with the HASH method of Hardebeck and Shearer (2002), https://doi.org/10.1785/0120010200, Hardebeck and Shearer (2003), https://doi.org/10.1785/0120020236. The new focal mechanism catalog is overall consistent with the standard catalog (Yang et al., 2012, https://doi.org/10.1785/0120110311) but includes 40% more focal mechanisms, and is more consistent with moment tensor solutions derived using waveform‐fitting methods. We apply the new catalog to identify changes in focal mechanism properties caused by the occurrences of large mainshocks such as the 2010 Mw7.2 El Mayor‐Cucapah and 2019 Mw7.1 Ridgecrest earthquakes. Such changes may be associated with co‐seismic stress drops, post‐seismic deformation processes, and static stress changes on a regional scale. The new high‐resolution catalog will contribute to improved understanding of the crustal stress field, earthquake triggering mechanisms, fault zone geometry, and sense of slip on the faults in southern California.

Drainage divide migration in response to strike-slip faulting: An example from northern Longmen Shan, eastern Tibet

Drainage divides can become unstable due to tectonic disturbances and therefore can be used to constrain past tectonic activity. However, many studies have focused mainly on the influence of vertical motion with less attention on the drainage divide response to strike-slip faulting. How the drainage divide response to strike-slip faulting is still uninvestigated. Here we analyze the drainage divide stability along the Beichuan-Yingxiu Fault, an active dextral strike-slip fault with a reverse component in the Longmen Shan, on the eastern margin of the Tibetan Plateau. Based on activity of the Beichuan-Yingxiu Fault and response of the local landscape, we have identified a site in the Guixi area where a river capture event may occur in the near future, and a site in the Leigu area where a river capture event may have occurred. We used the χ-plot and Gilbert metrics methods to measure drainage divide stability at these two sites. The results show that (1) drainage divides near active strike-slip faults will be unstable before and after a capture event in response to strike-slip faulting and (2) before a capture event, the drainage divide on opposing sides of the strike-slip fault will migrate in opposite directions. This study systematically reveals the drainage divide migration generated in response to strike-slip faulting. We suggest that the drainage divide stability has the potential to be used to identify strike-slip fault activity and slip sense.

Seismic swarms in the Pollino seismic gap: Positive fault inversion within a popup structure

Seismic swarms frequently occur along continental fault systems and their relation with large earthquakes is often contradictory. Such a case is documented in the Pollino mountain range of southern Italy, a decoupling zone where the belt-normal stretching drastically rotates accommodating the differential SE-retreat of the Ionian slab. The paucity of historical large earthquakes has led to hypothesize the presence of a seismic gap. A long-lasting seismic swarm that climaxed with a ML = 5.2 earthquake in October 2012 was therefore thought as a possible signal of an impending large earthquake filling the gap. Seismicity data collected during a 4-years long monitoring are a powerful microscope to look through the seismic swarm. In this study, we present accurate relocations for 2385 earthquakes and high-resolution Vp and Vp/Vs models of the fault system. Seismicity occurred on two separate normal faults that were formerly part of a thrusts and back-thrusts system, originally formed as a pop-up at restraining bends of the Pollino fault, a wrench fault system that inverted the original left lateral sense of slip accommodating a differential motion induced by the southward retreat of the Ionian slab.

Structural Study of the Late Oligocene-Early Miocene Sequence in Khabaz Oil Field, NE of Iraq

Khabaz Oil Field is located in Kirkuk, about 20 Km southwest of Kirkuk City between Jambour and Bai Hassan oil fields. Tectonically, it is located on the Unstable Shelf within the Low Folded Zone (Zagros Fold Belt). Six wells in Khabaz oil field with two seismic lines (Line K8 and KK54) are used to conduct the geometric analysis, which include the description of fold and fault systems for the purpose of understanding the structural setting of Jeribe (Early Miocene) and Azkand (Late Oligocene) formations in this field. Khabaz structure is a double plunging positively inverted subsurface asymmetrical anticline influence the whole pre-Holocene sedimentary sequence. The interlimb angle of this structure ranges between 137º to 151º which is classified as a gentle anticline. The dip values of the axial surface range between 82 – 84º, so it can be classified as an upright fold with a general trend NW-SE. The core of the anticline is bounded by two high angle dipping reverse fault splay dipping toward each other. These faults pushed the core of the anticline upward with respect to the limbs of the structure. The Southwestern limb is affected by several high angle inverted faults that were possibly bifurcated from one or two major faults. The Northeastern limb is also influenced by a series of high angle reverse, some are dipping toward the core of the structure and few others are dipping toward the limbs. Some of these faults especially those influenced the southwestern limb of the anticline were inherited from the original normal faults that bounding the graben structure developed during the deposition of the Shiranish Formation. During the Late Plio-Plistocene contraction phase, the sense of slip on these faults were inverted and the faults migrated upward into the Tertiary sequence resulting in the formation of the positively inverted structure.

Tectonic geomorphology and prehistoric earthquakes of the West Helanshan fault, West Ordos, and its implications for regional tectonics and seismic hazard

The West Helanshan fault is situated at the junction of the northeastern Tibetan Plateau, Alxa, and Ordos blocks, providing an opportunity to investigate the deformation in the transitional zone between the contractional northeastern Tibetan Plateau and extensional North China. Using field investigations and satellite imagery interpretations, we determined detailed geometry and kinematics of the West Helanshan fault. The West Helanshan fault is divided into three segments, including the northern, middle, and southern segments, based on varying fault strike, slip sense, and geomorphic expression. The northern and middle segments are dominated by right-lateral strike-slip motion as indicated by linear fault traces, horizontally offset streams and terrace risers, relatively insignificant vertical offset, and frequently changing facing direction of fault scarps. The late Quaternary right-slip rate is estimated to be 0.2–0.4 mm/yr, which is relatively low comparing with other strike-slip faults in the northeastern Tibetan Plateau, based on 10Be-dated offset fluvial/alluvial surfaces. The southern segment shows conspicuous fault scarps with significant systematic vertical offset, which has a reverse component as revealed in the trench. The timing of the most recent earthquake revealed in the trench is constrained to be between 6.2 ± 0.7 ka and 5.9 ± 0.4 ka. Notably, the West Helanshan fault cuts through the city center of Azuoqi town, which is the capital of Azuoqi county and has about 100,000 residents, carrying high potential earthquake hazard in the future. Finally, combining the regional fault geometry and kinematics with GPS observations, we propose a limited north-northeastward extrusion model for the southern Alxa Block.

S/P Amplitude Ratios Derived from Single-Component Seismograms and Their Potential Use in Constraining Focal Mechanisms for Microearthquake Sequences

Abstract Focal mechanisms, which reflect the sense of slip in earthquakes, provide important constraints for understanding crustal tectonics and earthquake source physics, including the interactions among earthquakes during mainshock–aftershock sequences or seismic swarms. Focal mechanisms of small (magnitude ≲3.5) earthquakes are usually determined by first-motion P-wave polarities, sometimes supplemented by the ratio of S-wave to P-wave amplitudes (S/P). However, focal mechanisms of such events can be difficult to reliably constrain, particularly with sparse recording networks or very small magnitude events. Here, we describe a method for deriving S/P amplitude ratios from P/P and S/S amplitude ratios measured on single seismic components between pairs of nearby events, as is often performed during correlation-based earthquake detection and relocation. These measurements can be transformed into relative S/P amplitude ratios, or they can be combined with a smaller number of traditional S/P amplitude ratios to provide a single-channel estimation of full S/P ratios, even for low signal-to-noise-ratio events not routinely cataloged and not amenable to traditional S/P ratio processing. This approach has the potential to greatly expand the applicability of S/P amplitude ratios, providing additional constraints for focal mechanisms of small earthquakes, particularly for spatially concentrated seismicity sequences.

A Shallow and Left‐Lateral Rupture Event of the 2021 Mw 5.3 Baicheng Earthquake: Implications for the Diffuse Deformation of Southern Tianshan

AbstractOn 24 March 2021, an Mw 5.3 earthquake struck northwest Baicheng, located in the Kuqa fold‐and‐thrust belt (FTB), northwest China. In the current study, interferometric synthetic aperture radar (InSAR) data were used to investigate the associated fault rupture solution (dip, dip direction, and slip sense), to determine the geometry of the seismogenic structure; the high‐resolution images of the surface rupture were obtained using an unmanned aerial vehicle (UAV). This geometric model, along with the co‐seismic slip distribution from the InSAR data, and deformation characteristics of co‐seismic surface rupture revealed that: (a) it was a shallow event, the focal depth was 0.5–2 km, and the co‐seismic slip was distributed in the 0–7 km range with high dip angles (66°, 70°). (b) A 4‐km long surface rupture with obvious left‐lateral strike‐slip was distributed on the surface, and the maximum strike‐slip displacement and width were 0.79 and 0.7 m, respectively. This left‐lateral strike‐slip event indicates that the relative motion between the Tianshan and Tarim blocks is a continuous and diffuse deformation process. The study shows that, when evaluating the earthquake risk of the Kuqa FTB, we should consider both the front position of the fault outburst and the internal compressional salt‐related structures, which can also produce moderate to strong earthquakes.

Theatrical Adaptation Of Philippa Pearce’s Tom’s Midnight Garden A Chronotopic Study

Literary adaptation is the transformation of a specific work to another genre or medium. It is not a mere process of replication or interpretation but one of innovation and creativity. As a process, adaptation has become prevalent through ages, and this has resulted in plethora of unconventional stories devised by creative adapters. Many stories, especially classics, are revisited and revived by innovative adapters. An outstanding classic, Philippa Pearce’s novel Tom’s Midnight Garden (1958) has been adapted for the stage for the first time by David Wood in 2001under the same title. As there is hardly any existing criticism which tackles the adaptation between Pearce’s source novel and Wood’s play, this paper aims at exploring the relationship between the two genres and showing how David Wood invigorates the novel’s sense of adventure and time slip in an impressive theatrical adaptation. Moreover, it attempts to illuminate the discrepancies between writing narrative and writing for the theater, and to prove whether Wood, in his adaptation, incorporates the effective rudiments of the new media with the fidelity to the original story. Along with Linda Hutcheon’s theory of adaptation, other critical perspectives of different critics will be used. In addition to adaptation, the paper aims at tracing the use of Bakhtin’s chronotope, literally the interplay of time and space, in Philippa Pearce’s Tom’s Midnight Garden, and to realize how it is efficiently revealed in David Wood’s reduced adaptive play.

Reactivation Potential of Intraplate Faults in the Western Quebec Seismic Zone, Eastern Canada

AbstractThe intraplate western Quebec seismic zone (WQSZ) in eastern Canada experiences moderate seismicity that mainly results from reactivation of inherited structures under the present‐day, NE‐SW‐striking regional maximum horizontal stress (SH) and, possibly to a minor extent, through stress perturbations in response to glacio‐isostatic adjustment. This work comprises the first numerical stress simulation‐based study that predicts the preferred spatial distribution, trends, and sense of slip of contemporary fault reactivation, which may have implications for possible fault segmentation patterns in the WQSZ. We show that mostly NNW‐SSE to NW‐SE‐striking faults exhibit the highest slip tendency values. Spatial patterns of slip tendency and kinematics of reactivation are consistent with the observed seismicity. In an area where Quaternary‐active faults have yet to be systematically identified, we have narrowed down areas to focus on for more detailed, future neotectonic investigations that could provide sound foundation for seismic hazard assessments. This study demonstrates the applicability of slip tendency analysis to identifying potentially active faults in stable continental regions worldwide.

Estimation of Absolute Stress in the Hypocentral Region of the 2019 Ridgecrest, California, Earthquakes

AbstractStrength 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 most debated quantities in geophysics. Direct measurements of stresses acting at seismogenic depths are largely lacking. Seismic data (in particular, earthquake focal mechanisms) have been used to infer orientation of the principal stress axes. I show that the focal mechanism data can be combined with information from precise earthquake locations to place constraints not only on the orientation, but also on the magnitude of absolute stress at depth. The proposed method uses relative attitudes of conjugate faults to evaluate the amplitude and spatial heterogeneity of the deviatoric stress and frictional strength in the seismogenic zone. Relative fault orientations (dihedral angles) and sense of slip are determined using quasi‐planar clusters of seismicity and their composite focal mechanisms. The observed distribution of dihedral angles between active conjugate faults in the area of Ridgecrest (California, USA) that hosted a recent sequence of strong earthquakes suggests in situ coefficient of friction of 0.4–0.6, and depth‐averaged shear stress on the order of 25–40 MPa, intermediate between predictions of the “strong” and “weak” fault theories.

Focal Mechanisms of Intraslab Earthquakes: Insights From Pseudotachylytes in Mantle Units

AbstractDevastating seismic events occur mainly in subduction zones, and a significant percentage of them are intraslab earthquakes. The geologic record of these events holds valuable information that needs to be investigated for a comprehensive seismic risk assessment. Here we investigate pseudotachylytes formed in oceanic peridotites and that are interpreted to result from intraslab seismic rupture. Each vein has recorded the seismic slip direction and slip sense of a single coseismic shear‐heating event. The well‐preserved exposures, showing individual veins up to 7 m in length and about 3 cm in width, of Cima di Gratera, in the Schistes Lustrés ophiolitic units of Corsica, offer unparalleled opportunities to investigate intraslab rupture kinematics in mantle rocks. The principal ferromagnetic phase in these rocks is a Ti‐poor magnetite. We use the anisotropy of magnetic susceptibility (AMS) recorded in pseudotachylyte generation veins (bulk susceptibilities range from 600 to 20,000 × 10−6 [SI] volume, with P′ ranging from 1.05 to 2.5) to reconstruct the co‐seismic deformation parameters, that is, fault plane attitude, direction and sense of slip. These new results, internally consistent at the vein level, span across oblate and prolate symmetries and reveal that seismic deformation recorded in these veins was kinematically diverse and included mostly normal mechanisms acting along the same subduction zone. In addition, our investigations show that the magnetic fabric of peridotite‐hosted pseudotachylytes provides key information bearing on the complex dynamics of frictional melts at a unprecedently high spatial resolution.

Present day strike-slip deformation within the southern part of the İzmir-Balıkesir Transfer Zone based on GNSS data and implications for seismic hazard assessment in western Anatolia

Herein, a combined analysis of Global Navigation Satellite System-derived strain rate maps, in accordance with recent seismicity, was presented to reveal that the N-S extension is accommodated primarily by strike-slip faulting of the İzmir-Balıkesir Transfer Zone (İBTZ), where a counter clockwise rotation (~25-100°/Myr) along the vertical axis is dominant. The results indicated that strike-slip segments within the İBTZ show variable transport sense and amount of slip along them, and they connect by hard linkage relay ramps with the dip to oblique slip normal faults. According to the strain map, the Karaburun Peninsula has the largest strain rates, at 137 nano strain (nstrain)/yr extension (NE-SW) and 126 nstrain/yr (NW-SE) compression. To the south, the largest strain areas begin to shrink where the NW-trending sinistral Riedel Fault is located. The smallest strains in the region were measured on the NE-trending Tuzla Fault, compatible with the right lateral component. Based on this, the northern part of the Karaburun Peninsula has the shortest recurrence period in the region. The geodetic earthquake recurrence periods throughout the region comprise 800 yr for magnitudes 7 and above and 70 year for magnitudes between 6 and 7. The period was calculated as 30 years for M > 5.5 (with 99% probability) and 100 years for M > 6 (with 95% probability). These were consistent with the geodetic earthquake recurrence periods (25-30 years for M > 5.5 and 80-100 years for M > 6). This result showed that the seismic hazard sources in the region have increased the earthquake risk, which may cause loss of life and property in the near future.

Lower Portion Rupture of a Thrust Fault during the 2017 Mw 6.3 Jinghe Earthquake: Implications to Seismic Hazards in the Tian Shan Region

AbstractThe 2017 Mw 6.3 Jinghe earthquake represents one of the few large earthquakes that are well recorded by seismic instruments and Interferometric Synthetic Aperture Radar (InSAR) observations in the seismically active Tian Shan region. In this study, we use the rupture fault solution (dip, dip direction, and slip sense) from seismologic and InSAR results, along with analysis of our collected surface mapping data, to determine the subsurface fault-plane geometry of the seismogenic Jinghenan fault. This geometric model, integrated with the coseismic slip distribution from seismologic and InSAR data, reveals that: (1) the Jinghenan fault extends downward from the land surface at a dip of ∼46° S (upper ramp), then bends to ∼42° S (lower ramp) at the depth of 9–13 km; (2) the coseismic rupture is confined within the Jinghenan lower ramp, and its upper limitation is approximately coincident with the fault-bend location. This coseismic rupture pattern and seismic behavior can be broadened to other active thrust faults within the Tian Shan, suggesting that, during moderate-strong earthquakes, such faults may only rupture partially in the down-dip extension, and the unruptured fault portion remains to pose high-seismic risk in the future.

Dynamic crystal plasticity modeling of single crystal tantalum and validation using Taylor cylinder impact tests

In this work, we extend a dislocation-density based constitutive theory for the dynamic thermomechanical behavior of crystals to body centered cubic (BCC) tantalum. Strain rate and temperature dependence of the slip resistance in the model is incorporated via an expression for the state-dependent instantaneous saturation dislocation density and a dynamic recovery fraction that affects the rate of generation of immobile dislocation density. Crystallographic slip along 111 on the {110} or {112} planes as well as their combination are examined. The Schmid stress serves as the driving force for dislocation motion and the twinning/anti-twinning sense of slip on {112} planes is accounted for by introduction of Peierls stress that depends upon this sense. The model parameters are calibrated using a two-stage Bayesian approach against experimentally generated uniaxial stress-strain compression curves at quasi-static and high strain rates over a range of temperatures. Velocity-time histories from single crystal flyer plate impact experiments were also used to parameterize this model. The calibrated model was applied to simulate previous Taylor cylinder impact experiments. Our results show that the model must include slip on {110} and {112} planes and also account for the twinning versus anti-twinning sense of slip on {112} planes, to appropriately represent the orientation dependence of the flow stress and match the deformed geometry of the single crystal Taylor cylinders.