One-segment Model Research Articles

Sensitivity of InSAR and teleseismic observations to earthquake rupture segmentation

SUMMARYEarthquakes often rupture across more than one fault segment. If such rupture segmentation occurs on a significant scale, a simple point-source or one-fault model may not represent the rupture process well. As a consequence earthquake characteristics inferred, based on one-source assumptions, may become systematically wrong. This might have effects on follow-up analyses, for example regional stress field inversions and seismic hazard assessments. While rupture segmentation is evident for most Mw > 7 earthquakes, also smaller ones with 5.5 < Mw < 7 can be segmented. We investigate the sensitivity of globally available data sets to rupture segmentation and their resolution to reliably estimate the mechanisms in presence of segmentation. We focus on the sensitivity of InSAR (Interferometric Synthetic Aperture Radar) data in the static near-field and seismic waveforms in the far-field of the rupture and carry out non-linear and Bayesian optimizations of single-source and two-sources kinematic models (double-couple point sources and finite, rectangular sources) using InSAR and teleseismic waveforms separately. Our case studies comprises of four Mw 6–7 earthquakes: the 2009 L’Aquila and 2016 Amatrice (Italy) and the 2005 and 2008 Zhongba (Tibet) earthquakes. We contrast the data misfits of different source complexity by using the Akaike informational criterion (AIC). We find that the AIC method is well suited for data-driven inferences on significant rupture segmentation for the given data sets. This is based on our observation that an AIC-stated significant improvement of data fit for two-segment models over one-segment models correlates with significantly different mechanisms of the two source segments and their average compared to the single-segment mechanism. We attribute these modelled differences to a sufficient sensitivity of the data to resolve rupture segmentation. Our results show that near-field data are generally more sensitive to rupture segmentation of shallow earthquakes than far-field data but that also teleseismic data can resolve rupture segmentation in the studied magnitude range. We further conclude that a significant difference in the modelled source mechanisms for different segmentations shows that an appropriate choice of model segmentation matters for a robust estimation of source mechanisms. It reduces systematic biases and trade-off and thereby improves the knowledge on the rupture. Our study presents a strategy and method to detect significant rupture segmentation such that an appropriate model complexity can be used in the source mechanism inference. A similar, systematic investigation of earthquakes in the range of Mw 5.5–7 could provide important hazard-relevant statistics on rupture segmentation. In these cases single-source models introduce a systematic bias. Consideration of rupture segmentation therefore matters for a robust estimation of source mechanisms of the studied earthquakes.

InSAR and GPS derived coseismic deformation and fault model of the 2017 Ms7.0 Jiuzhaigou earthquake in the Northeast Bayanhar block

On 8 August 2017, a Ms7.0 earthquake stroke the city of Jiuzhaigou, Sichuan, China. The Jiuzhaigou earthquake occurred on a buried fault in the vicinity of three well-known active faults and this event offers a unique opportunity to study tectonic structures in the epicentral region and stress transferring. Here we present coseismic displacement field maps for this earthquake using descending and ascending Sentinel-1A Interferometric Synthetic Aperture Radar (InSAR) data. Deformation covered an area of approximately 50 × 50 km, with a maximum line-of-sight (LOS) displacement of ~22 cm in ascending and ~14 cm in descending observations on the west side of the source fault. Based on InSAR and Global Positioning System (GPS) measurements, both separately and jointly, we constructed a one-segment model to invert the coseismic slip distribution and dip angle of this event. Our final fault slip model suggests that slip was concentrated at an upper depth of 15 km; there was a maximum slip of ~1.3 m and the rupture was dominated by a left-lateral strike-slip motion. The inverted geodetic moment was approximately 6.75 × 1018 Nm, corresponding to a moment magnitude of Mw6.5, consistent with seismological results. The calculated static Coulomb stress changes indicate that most aftershocks occurred in stress increasing zones caused by the mainshock rupture; the Jiuzhaigou earthquake has brought the western part of the Tazang fault 0.1–0.4 MPa closer to failure, indicating an increasing seismic hazard in this region. The Coulomb stress changes caused by the 2008 Mw7.8 Wenchuan earthquake suggest that stress loading from this event acted as a trigger for the Jiuzhaigou earthquake.

A methodology for estimating valgus stress during baseball pitching with one-segment model

A methodology for estimating valgus stress during baseball pitching with one-segment model

Two-Segment Foot Model for the Biomechanical Analysis of Squat.

Squat exercise is acquiring interest in many fields, due to its benefits in improving health and its biomechanical similarities to a wide range of sport motions and the recruitment of many body segments in a single maneuver. Several researches had examined considerable biomechanical aspects of lower limbs during squat, but not without limitations. The main goal of this study focuses on the analysis of the foot contribution during a partial body weight squat, using a two-segment foot model that considers separately the forefoot and the hindfoot. The forefoot and hindfoot are articulated by the midtarsal joint. Five subjects performed a series of three trials, and results were averaged. Joint kinematics and dynamics were obtained using motion capture system, two force plates closed together, and inverse dynamics techniques. The midtarsal joint reached a dorsiflexion peak of 4°. Different strategies between subjects revealed 4° supination and 2.5° pronation of the forefoot. Vertical GRF showed 20% of body weight concentrated on the forefoot and 30% on the hindfoot. The percentages varied during motion, with a peak of 40% on the hindfoot and correspondently 10% on the forefoot, while the traditional model depicted the unique constant 50% value. Ankle peak of plantarflexion moment, power absorption, and power generation was consistent with values estimated by the one-segment model, without statistical significance.

Efficient Computation of Thermoacoustic Modes in Industrial Annular Combustion Chambers Based on Bloch-Wave Theory

Most annular combustors feature a discrete rotational symmetry so that the full configuration can be obtained by copying one burner-flame segment a certain number of times around the circumference. A thermoacoustic model based on the Helmholtz equation then admits special solutions of the so-called Bloch type that can be obtained by considering one segment only. We show that a significant reduction in computational effort for the determination of thermoacoustic modes can be achieved by exploiting this concept. The framework is applicable even in complex cases including an inhomogeneous temperature field and a frequency-dependent, spatially distributed flame response. A parametric study on a three-dimensional combustion chamber model is conducted using both the full-scale chamber simulation and a one-segment model with the appropriate Bloch-type boundary conditions. The results for both computations are compared in terms of mode frequencies and growth rates as well as the corresponding mode shapes. The same is done for a more complex industrial configuration. These comparisons demonstrate the benefits of the Bloch-wave based analysis.

Toward a realistic optoelectronic-based kinematic model of the hand: representing the transverse metacarpal arch reduces accessory rotations of the metacarpophalangeal joints

A kinematic model representing the versatility of the human hand is needed to evaluate biomechanical function and predict injury risk in the workplace. We improved upon an existing optoelectronic-based kinematic hand model with grouped metacarpals by defining segmented metacarpals and adding the trapeziometacarpal joint of the thumb. Eight participants performed three static postures (neutral pose, cylinder grip, cap grip) to evaluate kinematic performance of three different models, with one, two, and four metacarpal segment(s). Mean distal transverse metacarpal arch angles in the four-segment metacarpal model were between 22.0° ± 3.3° (neutral pose) and 32.1° ± 3.7° (cap grip). Representation of the metacarpals greatly influenced metacarpophalangeal joint rotations. Both the two- and four-segment metacarpal models displayed significantly lower metacarpophalangeal joint ‘supination’ angles (than the one-segment model) for the fourth and fifth fingers. However, the largest reductions were for the four- versus one-segment models, with mean differences ranging from 9.3° (neutral pose) to 17.0° (cap grip) for the fourth finger and 16.3° (neutral pose) to 33.0° (cylinder grip) for the fifth finger. MCP joint abduction/adduction angles of the fourth and fifth fingers also decreased with segmentation of the metacarpals, although the lowest magnitudes generally occurred in the four-segment model. Overall, the four-segment metacarpal model produced the lowest accessory rotations in non-dominant axes, and best matched previous radiological studies that found MCP joint pronation/supination angles were typically less than 10°. The four-segment metacarpal model, with improved anatomic fidelity, will better serve future studies of detailed actions of the hand in clinical or work applications.

State-Dependent Delay Influenced Drill-String Oscillations and Stability Analysis

In this paper, the authors present a discrete system model to study the coupled axial–torsional dynamics of a drill string. The model is developed taking into account state-dependent time delay and nonlinearities due to dry friction and loss of contact. Simulations are carried out by using a 32-segment model with 128 states. Bit bounce is observed through time histories of axial vibrations, while stick-slip phenomenon is noted in the torsion response. The normal strain contours of this spatial–temporal system demonstrate the existence of strain wave propagation along the drill string. The shear strain wave exhibits features of wave nodes and wave loops along the drill string, which indicate that the torsional motion has the properties of a standing wave. When the penetration rate is varied, qualitative changes are observed in the system response. The observed behavior includes chaotic and hyperchaotic dynamics. Stability analysis reveals a stable region for the degenerate one-segment model. This stable region becomes infinitesimally small, as the resolution of spatial discretization is increased. This finding suggests that drill-string motions have a high likelihood of being self-exited in practical drilling operations.

A-priori and post-hoc segmentation in the design of healthy eating campaigns

Nutrition-oriented public health campaigns – both communication and intervention initiatives – often target particular demographic groups, for example schoolchildren, adults at workplaces, older women, presuming that the members of these groups are homogenous with respect to healthy eating. Although such practice may be justifiable from the practical point of view, it is unclear how effective these implicit segmentations are. In this study the authors argue that it is important to transcend demographic boundaries and to further segment demographic groups. A study with 13–15-year-old adolescents is used to prove that segmentation generates valuable insights for planning promotion of healthy eating. Four types of predictive segmentation models are compared – a one-segment model, an a-priori segmentation based on demographic variables, an a-priori segmentation based on behavioural variables and a post-hoc segmentation. The results of the study show that it is useful and also ethical to differentiate people using segmentation methods, since it facilitates reaching more vulnerable segments of society that in general resist change. It also demonstrates that post-hoc segmentation is more helpful for designing healthy eating campaigns.

The Dynamics of Postural Sway Cannot Be Captured Using a One-Segment Inverted Pendulum Model: A PCA on Segment Rotations During Unperturbed Stance

Research on unperturbed stance is largely based on a one-segment inverted pendulum model. Recently, an increasing number of studies report a contribution of other major joints to postural control. Therefore this study evaluates whether the conclusions originating from the research based on a one-segment model adequately capture postural sway during unperturbed stance. High-pass filtered kinematic data (cutoff frequency 1/30 Hz) obtained over 3 min of unperturbed stance were analyzed in different ways. Variance of joint angles was analyzed. Principal-component analysis (PCA) was performed on the variance of lower leg, upper leg, and head-arms-trunk (HAT) angles, as well as on lower leg and COM angle (the orientation of the line from ankle joint to center of mass). It was found that the variance in knee and hip joint angles did not differ from the variance found in the ankle angle. The first PCA component indicated that, generally, the upper leg and HAT segments move in the same direction as the lower leg with a somewhat larger amplitude. The first PCA component relating ankle angle variance and COM angle variance indicated that the ankle joint angle displacement gives a good estimate of the COM angle displacement. The second PCA component on the segment angles partly explains the apparent discrepancy between these findings because this component points to a countermovement of the HAT relative to the ankle joint angle. It is concluded that postural control during unperturbed stance should be analyzed in terms of a multiple inverted pendulum model.

Estimation of multiple heat-flux components at the metal/mold interface in bar and plate aluminum alloy castings

In the present investigation, a serial solution of the inverse heat-conduction problem (IHCP) is extended for Al-3 pct Cu-4.5 pct Si alloy square bars and rectangular plates cast in metal molds. The metal/mold interface was divided into three segments, viz., the half face, the quarter face, and the corner. The heat-flux transients during casting solidification were then estimated at these segments. Three configurations were considered, viz., (1) one boundary segment for the whole length on the interface, (2) two boundary segments delineating two heat-flux components, and (3) three boundary segments leading to three heat-flux components. In order to identify the most acceptable spatial distribution of interface heat flux, two types of analyses were performed on the results of the IHCP, viz., convergence of absolute error in the computed and the measured temperatures at the sensor locations and total heat energy transferred across the boundary from the casting to the mold. The error convergence at the thermocouple locations was more or less identical for all the three cases in both bars and plates. However, the total heat absorbed by the mold, in the case of the one-segment model in bars and the three-segment model in plates, was found to be a minimum. This indicated that the interface heat flux did not show any spatial distribution in the case of bars, while a distinct spatial distribution could be identified in the case of plates. The individual heat fluxes at the different interface segments for the plate casting showed a peak within 3 to 3.5 seconds of pouring, after which it reduced and reached stable values in about 200 seconds. The maximum heat flux occurred at the corner segment. The analysis of heat-flux gradients showed that the air gap initiated at the corner and spread toward the center.