Rupture Length Research Articles

Anatomical and biomechanical characteristics of fibularis longus tendon used for cruciate ligaments reconstruction

Abstract Introduction: Arthroscopic reconstruction of the cruciate ligament of the knee becomes routine with modern techniques and special instruments. However, the source of materials for this procedure has always been an eternal issue that affects the surgeons decision. The two peroneal tendons on the lateral side of the lower leg have the same function of plantar flexion and foot eversion. The fibularis longus tendon has been used for reconstruction such as the lateral collateral ligaments of the ankle or the Achilles tendon. Patients and methods: Descriptive cross-sectional study on twenty fresh cadavers were selected randomly for taking the fibularis longus tendon at the Department of Anatomy of the University of Medicine and Pharmacy, Ho Chi Minh City from January to July, 2022. Specimens with intact leg to lower knee segment were not crushed, well preserved and had never been used in previous studies. Results: Fibularis longus tendon length was 29,25 ± 2,1cm; the distances from fibularis longus tendon to deep fibular nerve and superficial fibular nerve was 71.1±8.63mm respectively, no split (longitudinal tear) was observed, the maximum tensile strength was 1170,4 ±203N, the maximum length of rupture 14,29 ± 3,88 mm. Conclusion: There was no split of fibularis longus tendon. Also no sign of impact on adjacent anatomy structures was found. The maximum tensile strength was equivalent to other grafts, such as the Hamstrings and patellar tendons. Its a potential source for arthroscopic reconstruction of the cruciate ligament Keywords: knee arthroplasty, fibularis longus tendon, grafts, Hamstrings tendon

Airborne LiDAR-Based Mapping of Surface Ruptures and Coseismic Slip of the 1955 Zheduotang Earthquake on the Xianshuihe Fault, East Tibet

ABSTRACTSurface ruptures and coseismic slip distributions of large earthquakes are the keys to understanding earthquake rupture processes, analyzing rupture history of associated faults, and assessing earthquake hazards. Detailed mapping of surface ruptures of large historical earthquakes is needed but is difficult in remote regions. The 1955 Ms 7.5 Zheduotang earthquake occurred in a prominent restraining bend of the central sinistral Xianshuihe fault and within a high-relief and densely vegetated mountain range. This study characterizes the 1955 earthquake surface rupture via 50 cm resolution airborne light detection and ranging (LiDAR) data, combined with field investigations. Our mapping of geomorphic features showed that relatively fresh mole tracks and fault scarps are still preserved beneath the dense vegetation cover. The 1955 earthquake ruptured at least 30 km in length, which consisted of four sections separated by stepovers or changes in the strike. Overall, the multistranded rupture was more complex than that of other historical earthquakes to the northwest along the Xianshuihe fault but consistent with its local structural setting. We collected 47 LiDAR-derived and 48 field-based left-lateral (with minor vertical) measurements. The clustering of the smallest offsets suggests that the average sinistral coseismic displacement of the 1955 earthquake was ∼2.1 m based on LiDAR-derived data and ∼1.5 m based on field measurements. This difference highlights the ambiguity and difficulties associated with surface rupture investigations of historical earthquakes decades after the event. The rupture length (∼30 km) and average sinistral displacement (1.5–2.1 m) suggest a moment magnitude of 6.6–7.4 based on empirical relationships of strike-slip earthquakes worldwide. The magnitude is smaller than the widely accepted Ms 7.5 in the catalog, suggesting that the previously reported magnitude was possibly overestimated. Our data have implications for the seismic hazard evaluation of the Sichuan–Tibet railway, which passes through the northern part of the ruptured fault.

Rupture Process of the 2022 Mw6.6 Menyuan, China, Earthquake from Joint Inversion of Accelerogram Data and InSAR Measurements

We obtained the rupture process and slip distribution of the 2022 Mw6.6 Menyuan earthquake by jointly inverting accelerogram data and InSAR measurements. The near-field InSAR measurements provide good constraints on the shallow slip distributions (<6 km). The accelerogram data enable us to better resolve the deeper coseismic slip (>6 km). The combination of two types of data provided improved constrains on slip distribution of the 2022 Menyuan earthquake. The results from joint inversion of InSAR and accelerogram data reveal a 26-km-long rupture length, which roughly agrees with the mapped length from the optically identified surface rupture trace and the InSAR deformation field. We imaged a major asperity with a dimension of 14 × 6 km at 4 km depth updip of the hypocenter. The maximum slip is estimated to be 3.8 m at 4 km depth. The duration of the 2022 Menyuan earthquake is ~14 s, and 90% of the seismic moment is released in the first 10 s. The total seismic moment is estimated to be 1.31 × 1 × 1019 N·m, equivalent to a moment magnitude of Mw6.7. Our results highlight that the moderate but shallow rupture during the 2022 Menyuan earthquake could intensify the seismic damage on the surface, confirmed by field investigations.

Linking Earthquake Magnitude‐Frequency Statistics and Stress in Visco‐Frictional Fault Zone Models

AbstractThe ability to estimate the likelihood of given earthquake magnitudes is critical for seismic hazard assessment. Earthquake magnitude‐recurrence statistics are empirically linked to stress, yet which fault‐zone processes explain this link remains debated. We use numerical models to reproduce the interplay between viscous creep and frictional sliding of a fault‐zone, for which inter‐seismic locking becomes linked to stress. The models reproduce the empirical stress‐dependent earthquake magnitude distribution observed in nature. Stress is related to the likelihood a fault section is near frictional failure, influencing likely rupture lengths. An analytical model is derived of a fault consisting of identical patches, each with a probability of inter‐seismic locking. It reproduces a similar magnitude‐recurrence relationship, which may therefore be caused by probabilistic clustering of locked fault patches. Contrasts in earthquake statistics between regions could therefore be explained by stress variation, which has future potential to further constrain statistical models of regional seismicity.

Rupture Directivity of the 2021MW6.0 Yangbi, Yunnan Earthquake

AbstractThe 2021MW6.0 Yangbi, Yunnan strike‐slip earthquake occurred on an unmapped crustal fault near the Weixi‐Qiaoho‐Weishan Fault along the southeast margin of the Tibetan Plateau. Using near‐source broadband seismic data from ChinArray, we investigate the spatial and temporal rupture evolution of the mainshock using apparent moment‐rate functions (AMRFs) determined by the empirical Green's function (EGF) method. Assuming a 1D line source on the fault plane, the rupture propagated unilaterally southeastward (∼144°) over a rupture length of ∼8.0 km with an estimated rupture speed of 2.1 km/s to 2.4 km/s. A 2D coseismic slip distribution for an assumed maximum rupture propagation speed of 2.2 km/s indicates that the rupture propagated to the southeast ∼8.0 km along strike and ∼5.0 km downdip with a peak slip of ∼2.1 m before stopping near the largest foreshock, where three bifurcating subfaults intersect. Using the AMRFs, the radiated energy of the mainshock is estimated as ∼. The relatively low moment scaled radiated energyof 1.5 × 10−5and intense foreshock and aftershock activity might indicate reactivation of an immature fault. The earthquake sequence is mainly distributed along a northwest‐southeast trend, and aftershocks and foreshocks are distributed near the periphery of the mainshock large‐slip area, suggesting that the stress in the mainshock slip zone is significantly reduced to below the level for more than a few overlapping aftershock to occur.

Rapid Source Determination of the 2021 Mw 7.4 Maduo Earthquake by a Dense High-Rate GNSS Network in the Tibetan Plateau

Abstract High-rate Global Navigation Satellite Systems (GNSS) observations from an integrated network in the Tibetan plateau were used for rapid source determination of the 2021 Mw 7.4 Maduo earthquake. Constrained by high-rate displacements from nine stations near the source, the magnitude was essentially determined as early as 20 s after the origin time (OT), whereas the 39-s-long rupture propagated only approximately halfway, and together with the epicenter location and rupture length, they were completely determined 29 s after the OT or 10 s before the rupture completion. In addition, to test the capability and feasibility of current GNSS networks for rapid source determination in the Tibetan plateau, two experiments were further implemented to invert source parameters by real observations at farther sites and synthetic observations induced by an Mw 7.0 modeled earthquake. The results demonstrate that current GNSS networks are capable and feasible to provide rapid source determination and earthquake early warning in approximately 30 s after the OT for large earthquakes (Mw 7.0+) based on current station density, spatial coverage and communication conditions in the Tibetan plateau.

Length of labour using vaginal misoprostol or dinoprostone for induction at various gestational ages: A retrospective cohort study

Introduction Induction of labour is a common procedure performed on labour and delivery. There are multiple ways to achieve cervical ripening, however, no studies have evaluated these methods based on a patient's gestational age. The goal of this study is to compare the length of labour at specific gestational ages in women being induced with either vaginal misoprostol or the dinoprostone insert. Methods A retrospective cohort study of 3774 singleton pregnancies from 2009 to 2019 at a health system with tertiary care and community hospitals was conducted. The primary outcome was time to insertion of medication to time to vaginal delivery. Secondary outcomes included length of first and second stages of labour, length of rupture of membranes, mode of delivery, neonatal Apgar scores at 1 and 5 min and neonatal intensive care unit admission. A generalized linear model was utilised for continuous outcomes and a logistic regression model was used for binary outcomes. Results Across all gestational ages, women who received vaginal misoprostol had a shorter labour course than women who received dinoprostone (in hours, preterm 18.2 vs. 26.3 p < 0.01, term 15.9 vs. 24.4 p < 0.01, late term 17.6 vs. 22.3 p < 0.01). Patients that received misoprostol had a shorter first stage of labour (in hours, preterm 18.2 vs. 25.7 p < 0.01, term 15.3 vs. 23.6 p < 0.01, late term 16.5 vs. 21.1 p < 0.01) and second stage of labour in the term and late term group (term 20.5 vs. 30.0 min. p < 0.01, late term 30.0 vs. 47.0, p = 0.05). Patients that received dinoprostone at term had higher odds of undergoing caesarean section (odds ratio (95% confidence interval): 1.34 (1.06, 1.70)). Conclusion Patients that received vaginal misoprostol was associated with shorter labour course across all gestational ages. Patients that received dinoprostone at term had an increased risk of caesarean section.

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.

New Insights Into the Paleoseismic History of the Mae Hong Son Fault, Northern Thailand

The Mae Hong Son Fault (MHSF) is a north-trending active fault in northern Thailand. The largest earthquake ever recorded in Thailand occurred in February 1975 with a magnitude of 5.6 and was associated with the southern end of the MHSF. Paleoearthquake magnitudes, recurrence intervals, and slip rates for the MHSF are evaluated using the morphological characteristics of the MHSF aided with a 12.5-m-resolution digital elevation model (DEM) and using fault trenching. Morphotectonic analysis, including studies of offset streams, linear valleys, triangular facets, and fault scarps, helps illustrate dextral fault movements within the MHSF zone. Two separated N–S trending basins, the Mae Hong Son to the north and the Mae Sariang to the south, are present along the MHSF. Between these basins, fault displacements decrease toward the Khun Yuam area. Surface rupture length investigation from fault segments in both basins indicates maximum credible earthquake magnitudes between 5.8 and 6.3. Fault trenching and road-cut studies show that nine earthquakes occurred along the MHSF over the past ∼43 ka. Optically stimulated luminescence (OSL) dating help define the timing of the earthquakes to ∼43, ∼38, ∼33, ∼28, ∼23, ∼18, ∼13, ∼8, and ∼3 ka. The recurrence interval of earthquakes on the Mae Hong Son Fault is ∼5,000 years and the fault has a slip rate of ∼0.04–0.15 mm/a.

Source Characteristics of the Shallow 2019 Ms 6.0 Changning, China, Earthquake Sequence in the Salt Mining Area

AbstractThe 17 June 2019 Ms 6.0 Changning earthquake occurred on the southern margin of the Sichuan basin in China, which breaks the historical record for the largest earthquake in the Sichuan basin. Based on the abundant local seismic, strong motion, and Interferometric Synthetic Aperture Radar line of sight displacement data, we investigate the detailed source characteristics of this earthquake sequence. We determine focal mechanisms of 68 ML≥2.0 aftershocks with P wave first-motion polarities and S/P amplitude ratios. The triangle diagram of focal mechanisms shows that 82% of the aftershocks have thrust faulting mechanisms. The spatial distribution of aftershocks together with the determined focal mechanisms indicates that this earthquake sequence was mainly controlled by the southeast–northwest-extended faults. In addition, the revealed diversity of aftershock focal mechanisms implies that some small subsidiary faults with different geometries and motion features have likely been ruptured. The kinematic finite-fault joint inversion results reveal a complex rupture process of the mainshock on two fault segments with different geometries. The rupture initiated on the southeastern fault segment with a gentle dip angle and then jumped to the vertical northwestern fault segment. The main rupture length and duration are approximately 11 km and 8 s, respectively. The released total scalar seismic moment during the rupture process is 4.6×1017 N·m, corresponding to a moment magnitude of Mw 5.7. Our results suggest that the nucleation and the rupture initiation and propagation of the 2019 Ms 6.0 Changning earthquake sequence were likely controlled by the intrinsic structure and stress heterogeneities of the involved seismogenic faults, as well as the variation in pore-fluid pressure caused by the long-term water injection in the Changning salt mining area and adjacent areas.

Endoscopic resection of bladder urothelial neoplasm in a child: a case report

Bladder tumour, especially urothelial neoplasm, is a very rare condition in paediatric age. That is why true and accurate information on biological grade of malignancy and, correspondingly, the surgical management is absent. However, the majority of physicians take the view that this type of tumour has a low grade of malignization and recurrence, even after the endoscopic excision of neoplasm in paediatric patients. Purpose - to describe a clinical case of surgical management of the bladder urothelial neoplasm in a child by means of minimally invasive equipment. Clinical case. Endoscopic methods of surgical treatment are widely used in paediatric patients with the urinary tract conditions in our clinic. The transcutaneous surgical treatment of bladder conditions has been employed in paediatric patients since 2010. For example, it was used for the removal of ureterolith impacted in the bladder neck and foreign bodies of the bladder, as well as the bladder urothelial neoplasm excision. We also tried to use it for visualisation of the posterior urethra rupture length through a cystoscope, which was put into the epicystostomic hole of the posterior urethra together with the simultaneous urethroscopy (for the purpose of the directed illumination during the urethroscopy). However, due to the long length of the posttraumatic urethrostenosis, it was impossible to achieve the illumination and catheterisation of the urethra during the urethroscopy in the site of damage. The clinical case of the minimally invasive resection of the bladder urothelial neoplasm in a child is presented in the article. Minimally invasive techniques give the opportunity to perform even the radical operations with the perfect cosmetic result and minimal injury that is very important in the paediatric patients. The research was carried out in accordance with the principles of the Helsinki Declaration. The informed consent of the patient was obtained for conducting the studies. No conflict of interests was declared by the authors. Key words: bladder neoplasm, transcutaneous cystoscopy, neuromuscular bladder dysfunction, children.

Discrete Element Modeling of a Subduction Zone with a Seafloor Irregularity and its Impact on the Seismic Cycle

AbstractSeafloor irregularities influence rupture behavior along the subducting slab and in the overriding plate, thus affecting earthquake cycles. Whether seafloor irregularities increase the likelihood of large earthquakes in a subduction zone remains contested, partially due to focus put either on fault development or on rupture pattern. Here, we simulate a subducting slab with a seafloor irregularity and the resulting deformation pattern of the overriding plate using the discrete element method. Our simulations illustrate the rupture along three major fault systems: megathrust, splay and backthrust faults. Our results show different rupture dimensions of earthquake events varying from tens to ca. 140 km. Our results suggest that the recurrence interval of megathrust events with rupture length of ca. 100 km is ca. 140 years, which is overall comparable to the paleoseismic records at the Mentawai area of the Sumatran zone. We further propose the coseismic slip amounts decrease and interseismic slip amounts increase from the surface downwards gradually. We conclude that the presence of seafloor irregularities significantly affects rupture events along the slab as well as fault patterns in the overriding plate.

XYtracker: a new approach to estimate fault rupture extent in real time for large earthquakes

We present a methodology for estimating fault geometry and utilizing the distance to the fault for the shaking estimation to improve the accuracy of real-time shaking estimates for large earthquakes. Most of the earthquake early warning system currently estimates the seismic intensity with the ground-motion prediction equations (GMPE) as a function of the hypocenter distance. However, using the fault distance computed from a finite source model can improve the accuracy of the shaking intensity estimation for large earthquakes. This study proposes a novel methodology, XYtracker, to estimate the surface projection of the fault extent and real-time seismic intensity. For large earthquakes, high-frequency ground motions tend to saturate over the magnitude range and strongly correlate with fault distance. As a result, this work can achieve the fault extent using seismic intensity and GMPE. We considered three types of fault models: point-source, line-source, and rectangle-source model. We found the most probable model parameters for each model by minimizing the residual sum of squares between the observed and estimated seismic intensities. The Akaike Information Criterion selected the most probable model among them. The strong motion data set of the 2008 Wenchuan, 2011 Tohoku, and 2016 Kumamoto earthquakes was used to test our methodology. The new method for estimating the fault geometry can obtain the ongoing rupture length and direction using the strong motion data. The model selection scheme with the Akaike Information Criterion selected the finite-source model to explain the shaking distribution. Results revealed that this new approach performed well in estimating the fault dimension. The method can promote the accuracy of the seismic intensity estimation for future large earthquakes, including the subduction earthquakes.Graphical

The Factors Associated with the Length of the Third Stage of Labour: A Descriptive-Analytical Study

Background: Several risk factors have been identified for postpartum hemorrhage, one of which being the duration of the third stage of labour. This stage refers to the interval between the expulsion of the fetus to the expulsion of the placenta. Some bleeding occurs in this stage due to the separation of the placenta. Objective: This study aimed to identify the factors associated with the length of the third stage of labour. Methods: In this cross-sectional study, 300 women hospitalized for vaginal birth were selected via convenience sampling. The study data were collected using a researcher-made questionnaire. The data were then analyzed using univariate and multivariate linear regression analyses. Results: The mean (SD) age of the participants was 26.41 (6.26) years. Investigation of the relationship between the study variables and the time of placental separation indicated that a minute increase in the length of membrane ruptures caused a 0.003 minute decrease in the time of placental separation. However, this time increased by 2.75, 6.68, and 2.86 minutes in the individuals without history of abortion, those with history of stillbirth, and those who had not received hyoscine, respectively. The results of multivariate analysis indicated that suffering from preeclampsia or hypertension, history of stillbirth, not receiving hyoscine, and not receiving misoprostol increased the length of the third stage by 4.40, 8.55, 2.38, and 6.04 minutes, respectively. Conclusion: Suffering from preeclampsia and having the history of stillbirth increased and using hyoscine and misoprostol decreased the length of the third stage of labour. However, no significant relationship was found between the length of the third stage of labour and mother’s age, gestational age, parity, mother’s body mass index, mother’s chronic disorders, history of manual placenta removal, length of the first and second stages, membranes rupture, induction, amount of oxytocin after delivery, and infant’s weight and gender.

Fifteen years of Environmental Seismic Intensity (ESI-07) scale: Dataset compilation and insights from empirical regressions

The Environmental Seismic Intensity scale (ESI-07), published 15 years ago under the umbrella of INQUA (International Union for Quaternary Research), is solely based on earthquake effects on the natural environment. ESI-07 provides complementary information with respect to other macroseismic scales, in particular those stemming from the original Mercalli scale, which are mainly based on effects on manmade structures. We collect information on 157 earthquakes, occurred between 300 AD and 2020, that have been studied using the ESI-07 scale. The ESI-07 epicentral intensity can be assigned based on linear or areal features (e.g., length of surface rupture, area affected by environmental effects); this value is generally in good agreement, or slightly larger, than estimates provided using other macroseismic scales. Higher discrepancies are found for earthquakes with ESI-07 epicentral intensity above X, where other scales tend to saturate, as expected based on the original definition of the Mercalli-family intensity scales. We develop scaling relations among ESI-07 epicentral intensity and moment magnitude, surface rupture length and affected area. After critically evaluating the scientific literature, we argue that the ESI-07 reached its original goals and proved to be particularly useful for the documentation of earthquake damage i) in remote regions, ii) in the case of strong events, where other scales saturate, and iii) in the region closer to the epicenter. Finally, we identify gaps where to focus future efforts, such as the integration of remote sensed datasets in ESI-07 assignment and the refinement of empirical regressions.

Understanding historical earthquakes by mapping coseismic landslides in the Loess Plateau, northwest China

AbstractLocating the epicenters and quantifying the magnitudes of historical earthquakes are important, yet difficult, tasks. These tasks often entail estimating seismic intensities based on written documentation, which suffers from biases and uncertainties that are difficult to evaluate. However, past strong earthquakes may trigger numerous landslides that remain in the landscape to the present day, whose number and distribution are correlated with the magnitude and location of the earthquakes. Thus, mapping historical coseismic landslides may provide a useful tool for re‐evaluating the magnitudes of historical earthquakes. We use remote sensing images to map landslides in the southern Loess Plateau, China. We suggested thatc. 5000 preserved landslides are related to the 734ceTianshui earthquake. These landslides are densely distributed along a c. 70‐km‐long section of the West Qinling Fault. Based on the assumption that the length of the zone in which substantial landslides occurred is equal to the fault rupture length, we estimated aMwof 7.2 for the 734ceTianshui event, which is similar to previous estimates (Mw = 6.8–7.5). We confirmed that the 1920ceHaiyuan, 1718ceTongwei, and 1654ceLixian earthquakes did not contribute to the historical landslides observed in the study area by combination of the mapping and Chinese related literature. We estimated anMwof 7.0 for the 1654ceLixian earthquake, which is lower than previous estimates (Mw = 8.0). We suggest that coseismic landslide of medium and large sizes with areas &gt; 104 m2can be used as a criterion to locating and quantifying historical earthquakes, thereby reducing uncertainties in the estimated magnitudes of historical earthquakes that lack instrument records.

Seismotectonic characterization of the 1948 (MW 6.9) Anta earthquake, Santa Bárbara System, central Andes broken foreland of northwestern Argentina

The region of the Andean back-arc of northwestern Argentina has been struck by several magnitude ≥6 crustal earthquakes since the first historically recorded event in 1692. One of these events corresponds to the Anta earthquake on 25 August 1948, with epicenter in the Santa Bárbara System causing three deaths and severe damage in Salta and Jujuy provinces with maximum Modified Mercalli seismic intensities (MMI) of IX. We collected and digitized analog seismograms of this earthquake from worldwide seismic observatories in order to perform first-motion analysis and modeling of long-period teleseismic P-waveforms. Our results indicate a simple seismic source of M0 = 2.85 × 1019 N m consistent with a moment magnitude Mw = 6.9. We have also tested for the focal depth determining a shallow source at 8 km with a reverse focal mechanism solution with a minor dextral strike-slip component (strike 20°, dip 30°, rake 120°) from the best fit of waveforms. Using magnitude-size empirical relationships, the comparison of the obtained Mw 6.9 magnitude value and the ca. 10,000 km2 area of MMI ≥ IX from our seismic intensity map, which was obtained from newspaper and many historical reports, indicates a rupture length of 42 ± 8 km for the Anta earthquake. We show our results in a 3D geological model around the epicentral area, which integrates modern seismicity, geological data, and information of a previously studied east-west cross section located a few kilometers south of the 1948 epicenter. The integration of all available information provides evidence of the re-activation of the Pie de la Sierra del Gallo fault during the 1948 Mw 6.9 shallow earthquake; this thrust fault bounds the Santa Bárbara System along its western foothill.

Resolving the location of small intracontinental earthquakes using Open Access seismic and geodetic data: lessons from the 2017 January 18mb 4.3, Ténéré, Niger, earthquake

SUMMARYA low-magnitude earthquake was recorded on 2017 January 18, in the Ténéré desert in northern Niger. This intraplate region is exceptionally sparsely covered with seismic stations and the closest open seismic station, G.TAM in Algeria at a distance of approximately 600 km, was unusually and unfortunately not operational at the time of the event. Body-wave magnitude estimates range from mb 4.2 to mb 4.7 and both seismic location and magnitude constraints are dominated by stations at teleseismic distances. The seismic constraints are strengthened considerably by array stations of the International Monitoring System for verifying compliance with the Comprehensive Nuclear Test-Ban-Treaty. This event, with magnitude relevant to low-yield nuclear tests, provides a valuable validation of the detection and location procedure for small land-based seismic disturbances at significant distances. For seismologists not in the CTBT system, the event is problematic as data from many of the key stations are not openly available. We examine the uncertainty in published routinely determined epicentres by performing multiple Bayesloc location estimates with published arrival times considering both all published arrival times and those from open stations only. This location exercise confirms lateral uncertainties in seismologically derived location no smaller than 10 km. Coherence for interferometric synthetic aperture radar in this region is exceptionally high, and allows us to confidently detect a displacement of the order 6 mm in the time frame containing the earthquake, consistent with the seismic location estimates, and with a lateral length scale consistent with an earthquake of this size, allowing location constraint to within one rupture length (≤5 km)—significantly reducing the lateral uncertainty compared with relying on seismological data only. Combining Open Access-only seismological and geodetic data, we precisely constrain the source location, and conclude that this earthquake likely had a shallow source. We then discuss potential ways to continue the integration of geodetic data in the calibration of seismological earthquake location.

Recurrence and Clustering of Large Earthquakes along the Northern Boundary of Ordos Block: Constraining Paleoearthquakes by an Improved Multiple Trench Constraining Method

AbstractTectonic belts along active tectonic block boundaries comprise one or more active faults; along which, large earthquakes recur. Therefore, it is important to establish the recurrence behavior of large earthquakes along such boundary zones for studying their characteristics and developments. Many paleoearthquake studies make it possible to investigate the recurrence behavior of large earthquakes along the northern boundary of the Ordos block (NBOB). Based on the previous studies, data from 52 trenches were collected to reconstruct prehistoric earthquakes using an improved multiple trench constraining method. This method is based on paleoearthquake indicators and trench location distribution to constrain the rupture time and length, thereby reducing the selection bias of fixed rupture length to construct additional rupture scenarios. The results suggest that the NBOB comprises four normal faults (from west to east): the Langshan Piedmont Fault (LPF), Sertengshan Piedmont Fault (SPF), Wulashan Piedmont Fault (WPF), and Daqingshan Piedmont Fault (DPF); along which, six, seven, eight, and six paleoearthquakes have occurred within approximately 15,000 yr, respectively. In addition, recurrence behaviors of the individual faults exhibit remarkable periodicity. The regional fault network along the NBOB reveals clustered characteristics with six clusters propagating either westward or eastward and a recurrence time of approximately 1,300 yr. Large earthquake events have occurred along the LPF, WPF, and DPF according to the most recent cluster; however, earthquakes were absent along the SPF, and no evidence of large earthquakes was observed along the NBOB after the 849 CE earthquake. Thus, we discuss the possibility of occurrence of large earthquakes along the SPF after the 849 CE earthquake based on earthquake recurrence and cluster migration behavior. Additional research is required to assess the potential risk of the occurrence of a large earthquake along the SPF in the future.

High-Detail Fault Segmentation: Deep Insight into the Anatomy of the 1983 Borah Peak Earthquake Rupture Zone (Mw 6.9, Idaho, USA)

Abstract Following observations made in a survey campaign along the Lost River Fault (Idaho, USA) in 2019, we integrate both original and previously published data to obtain a detailed segmentation of the fault sections that failed in the 1983 Borah Peak earthquake (Mw 6.9). The earthquake ruptured the topographic surface with an oblique-normal faulting mechanism, activating two SW-dipping fault segments (Thousand Springs and Warm Springs) and a branching SSW-dipping fault (Arentson Gulch Fault) and producing coseismic surface ruptures with up to 3 m of vertical separation. We augment the 1983 earthquake description by interpreting high-resolution topography and fault mapping. We use quality vertical separation data, rupture zone width measurements, and fault slip data to analyze major and minor structural-geometric complexities, highlighting a partition of the deformation and a fault segmentation into four detail levels (i.e., segments, sections, subsections, and sectors). Our work provides new details of the 1983 Borah Peak earthquake, constraints for paleoseismic and seismotectonic studies, and a methodological approach applicable in other areas of the world. Our fault-slip data show variations along fault-strike that we interpret as kinematic partitioning. In 1983, the main southern segment had a large rupture zone width, while the northern segment localized the deformation. The distributed ruptures accommodate a large portion of the rupture length (~19.5 km versus 31 km for the main rupture) and displacement (~66%). 83% of the surface faulting and 80% of the displacement are located at the hanging wall of the main rupture. There is a strong correlation between vertical separation, rupture zone width, rupture position (footwall or hanging wall), and fault geometry. We highlight the control of the obliquity and kinematic partitioning in the surface expression of the earthquake propagation. We interpret the coseismic (i.e., 1983) and long-term (i.e., Quaternary) behavior, showing that the two activated segments had similar cumulated behaviors in distributing the deformation between synthetic and antithetic ruptures, despite the different geometries. Our results have implications for fault rupture behavior with application to rupture hazard.