Mislocation Errors Research Articles

Mitigating the effect of errors in source parameters on seismic (waveform) tomography

SUMMARYWe investigate the effect of errors in earthquake source parameters on the tomographic inverse problem and propose mitigation strategies for avoiding artefacts caused by such errors. In global catalogues, mislocation errors can amount to tens of kilometres both horizontally and vertically, while fault plane uncertainties can be of the order of tens of degrees. We conduct a perturbation study investigating both errors in the source location and in the moment tensor. Spatial perturbations of 5 km and fault plane perturbations of 5° result in measured time-shifts of the order of 0.5 to several seconds, which in five iterations lead to artefacts with amplitudes of the order of 0.5–1 per cent spanning up to several hundreds of kilometres. Larger perturbations (e.g. 20 km) lead to artefacts similar in amplitude (∼5 per cent) to the features judged to be interpretable in tomographic models. This can be further exacerbated by the cumulative effect of systematic errors. Mitigation strategies consist of removing a region around the source from the gradient and discarding traces where amplitudes are comparatively small. The most problematic type of error is a horizontal mislocation, because its imprint is not removed by such measures—discarding a ‘suspicious’ event may be the only option if no trustworthy ground truth is available. Although this study focuses on (adjoint) waveform tomography, a large part of the results are equally valid for any other type of imaging method that is based on time- and/or phase-shift measurements. The concerns and mitigation strategies presented here therefore have broader applicability.

Can Anthropometry be Used to Dictate Participant-Specific Thigh Marker Placements Which Minimize Error in Hip Joint Center Estimation?

Specific participant characteristics may be leveraged to dictate marker placements which reduce soft tissue artifact; however, a better understanding of the relationships between participant characteristics and soft tissue artifact are first required. The purpose of this study was to assess the accuracy in which measures of whole-body and thigh anthropometry could predict mislocation error of the hip joint center, tracked using skin-mounted marker clusters. Fifty participants completed squatting and kneeling, while pelvis and lower limb motion were recorded. The effect of soft tissue artifact was estimated from 6 rigid thigh marker clusters by evaluating their ability to track the position of the hip joint center most like the pelvis cluster. Eighteen backward stepwise linear regressions were performed using 10 anthropometric measures as independent variables and the mean of the peak difference between the thigh and pelvis cluster-tracked hip joint centers. Fourteen models significantly predicted error with low to moderate fit (R = .38-.67), explaining 14% to 45% of variation. Partial correlations indicated that soft tissue artifact may increase with soft tissue volume and be altered by local soft tissue composition. However, it is not recommended that marker placement be adjusted based on anthropometry alone.

Lamb Waves and Adaptive Beamforming for Aberration Correction in Medical Ultrasound Imaging.

Phase aberration in transcranial ultrasound imaging (TUI) caused by the human skull leads to an inaccurate image reconstruction. In this article, we present a novel method for estimating the speed of sound and an adaptive beamforming technique for phase aberration correction in a flat polyvinylchloride (PVC) slab as a model for the human skull. First, the speed of sound of the PVC slab is found by extracting the overlapping quasi-longitudinal wave velocities of symmetrical Lamb waves in the frequency-wavenumber domain. Then, the thickness of the plate is determined by the echoes from its front and back side. Next, an adaptive beamforming method is developed, utilizing the measured sound speed map of the imaging medium. Finally, to minimize reverberation artifacts caused by strong scatterers (i.e., needles), a dual probe setup is proposed. In this setup, we image the medium from two opposite directions, and the final image can be the minimum intensity projection of the inherently co-registered images of the opposed probes. Our results confirm that the Lamb wave method estimates the longitudinal speed of the slab with an error of 3.5% and is independent of its shear wave speed. Benefiting from the acquired sound speed map, our adaptive beamformer reduces (in real time) a mislocation error of 3.1, caused by an 8 mm slab, to 0.1 mm. Finally, the dual probe configuration shows 7 dB improvement in removing reverberation artifacts of the needle, at the cost of only 2.4-dB contrast loss. The proposed image formation method can be used, e.g., to monitor deep brain stimulation procedures and localization of the electrode(s) deep inside the brain from two temporal bones on the sides of the human skull.

Perceptual Learning of Visual Span Improves Chinese Reading Speed.

Evidence has indicated that the size of the visual span (the number of identifiable letters without movement of the eyes) and reading speed can be boosted through perceptual learning in alphabetic scripts. In this study, we investigated whether benefits of perceptual learning could be extended to visual-span size and sentence reading (all characters are presented at the same time) for Chinese characters and explored changes in sensory factors contributing to changes in visual-span size following training. We randomly assigned 26 normally sighted subjects to either a control group (n = 13) or a training group (n = 13). Pre- and posttests were administered to evaluate visual-span profiles (VSPs) and reading speed. Training consisted of trigram (sequences of three characters) character-recognition trials over 4 consecutive days. VSPs are plots of recognition accuracy as a function of character position. Visual-span size was quantified as the area under VSPs in bits of information transmitted. A decomposition analysis of VSPs was used to quantify the effects of sensory factors (crowding and mislocation). We compared the size and sensory factors of visual span and reading speed following training. Following training, the visual-span size significantly increased by 11.7 bits, and reading speed increased by 50.8%. The decomposition analysis showed a significant reduction for crowding (-13.1 bits) but a minor increase in the magnitude of mislocation errors (1.46 bits) following training. These results suggest that perceptual learning expands the visual-span size and further improves Chinese text sentence-reading speed, indicating that visual span may be a common sensory limitation on reading that can be overcome with practice.

The Multiple Object Test as a Performance Based Tool to Assess Cognitive Driven Activity of Daily Living Function inParkinson's Disease.

There is need for multidimensional quantitative assessment of cognitive driven activities of daily living (ADL) functions in Parkinson's disease (PD). To determine whether there is an ADL profile related to cognitive impairment in PD assessed by the Multiple Object Test (MOT). We assumed MOT performance to be lower in PD patients versus controls and in PD patients with more severe cognitive impairment. 50 PD patients with no cognitive impairment (PD-NC), 54 patients with PD-mild cognitive impairment (PD-MCI), 29 with Parkinson's disease dementia (PDD), and 40 healthy controls (HC) were investigated. Besides comprehensive cognitive testing, the MOT, a performance based test consisting of five routine tasks (e.g., preparing a cup of coffee), was applied. Quantitative (total errors and time) and qualitative (error type) MOT parameters were analyzed. Total time and number of MOT errors was increased in PD patients compared to controls (p < 0.001). These parameters also differentiated PDD patients from other cognitive groups (p < 0.05). No control subject had ≥ 4 errors in the MOT, but 30% of PD patients, especially PDD, scored above this cut-off. Omission (p < 0.001) and mislocation (p < 0.03) errors were more prominent in PDD than other cognitive groups. Perplexity errors did not differ between PD-MCI and PDD but between PD-NC and PDD (p = 0.01). MOT parameters discriminating between cognitive groups correlated mainly with lower test performance in psychomotor speed and executive function. Performance based testing is promising to identify quantitative and qualitative ADL aspects differentiating between different cognitive groups which might be helpful for an early detection of PDD.

Integrating Older Survey Data into Modern Research Paradigms

AbstractThe data from older archaeological surveys are incredibly important resources, often containing our only information about sites that have been destroyed or that are now inaccessible. These surveys occurred before the advent of GPS technology, however, so their spatial accuracy is often uncertain. Many types of locational errors accumulate in such “legacy” datasets, so using them in modern GIS-based spatial analyses is frequently problematic. Many of the sources of error can be identified and quantified, however, and systematic and random errors (derived mainly from Cartesian, rounding, and human error) can largely be mitigated by scanning the original field maps, georectifying the maps to trusted imagery, and then digitizing sites directly. The remaining “mislocation” errors derive from difficulty identifying locations in the field. The original survey notes may contain clues about mislocation error, but it is impossible to mitigate these errors without re-recording site locations with more accurate survey instruments. Instead, I advocate the use of GIS-based models to estimate the influence of specific surveying practices on site location accuracy. These models can provide a standardized, quantifiable measure of mislocation error in a legacy dataset, which can help guide its use in modern GIS analyses that require accurate site locations.

Sensory and cognitive influences on the training-related improvement of reading speed in peripheral vision

Reading speed in normal peripheral vision is slow but can be increased through training on a letter-recognition task. The aim of the present study is to investigate the sensory and cognitive factors responsible for this improvement. The visual span is hypothesized to be a sensory bottleneck limiting reading speed. Three sensory factors-letter acuity, crowding, and mislocations (errors in the spatial order of letters)-may limit the size of the visual span. Reading speed is also influenced by cognitive factors including the utilization of information from sentence context. We conducted a perceptual training experiment to investigate the roles of these factors. Training consisted of four daily sessions of trigram letter-recognition trials at 10° in the lower visual field. Subjects' visual-span profiles and reading speeds were measured in pre- and posttests. Effects of the three sensory factors were isolated through a decomposition analysis of the visual span profiles. The impact of sentence context was indexed by context gain, the ratio of reading speeds for ordered and unordered text. Following training, visual spans increased in size by 5.4 bits of information transmitted, and reading speeds increased by 45%. Training induced a substantial reduction in the magnitude of crowding (4.8 bits) and a smaller reduction for mislocations (0.7 bits), but no change in letter acuity or context gain. These results indicate that the basis of the training-related improvement in reading speed is a large reduction in the interfering effect of crowding and a small reduction of mislocation errors.

A "fuller" report on mislocation errors in visual crowding

A "fuller" report on mislocation errors in visual crowding

Seismic imaging in hardrock environments: The role of heterogeneity?

We investigate the effect of petrophysical scale parameters and structural dips on wave propagation and imaging in heterogeneous media. Seismic wave propagation effects within the heterogeneous media are studied for different velocity models with scale lengths determined via stochastic analysis of petrophysical logs from the Matagami mine, Quebec, Canada. The elastic modeling study reveals that provided certain conditions of the velocity fluctuations are met, strong local distortions of amplitude and arrival times of propagating waves are observed as the degree of scale length anisotropy in the P-wave velocity increases. The location of these local amplitude anomalies is related to the dips characterizing the fabric of the host rocks. This result is different from the elliptical shape of direct waves often defined by effective anisotropic parameters used for layered media. Although estimates of anisotropic parameters suggest weak anisotropy in the investigated models, these effective anisotropic parameters often used in VTI/TTI do not sufficiently describe the effects of scale length anisotropy in heterogeneous media that show such local amplitude, travel time, and phase distortions in the wavefields.Numerical investigations on the implications for reverse time migration (RTM) routines corroborate that mean P-wave velocity of the host rocks produces reliable imaging results. Based on the RTM results, we postulate the following: weak anisotropy in hardrock environments is a sufficient assumption for processing seismic data; and seismic scattering effects due to velocity heterogeneity with a dip component is not sufficient to cause mislocation errors of target structures as observed in the discrepancy between the location of the strong seismic reflections associated to the Matagami sulfide orebody and its true location. Future work will investigate other factors that may provide plausible explanations for these mislocation problems, with the objective of providing a mitigation strategy for incorporation into the seismic data processing sequence when imaging in hardrock settings.

The dependence of crowding on flanker complexity and target-flanker similarity

We examined the effects of the spatial complexity of flankers and target-flanker similarity on the performance of identifying crowded letters. On each trial, observers identified the middle character of random strings of three characters ("trigrams") briefly presented at 10° below fixation. We tested the 26 lowercase letters of the Times Roman and Courier fonts, a set of 79 characters (letters and non-letters) of the Times Roman font, and the uppercase letters of two highly complex ornamental fonts, Edwardian and Aristocrat. Spatial complexity of characters was quantified by the length of the morphological skeleton of each character, and target-flanker similarity was defined based on a psychometric similarity matrix. Our results showed that (1) letter identification error rate increases with flanker complexity up to a certain value, beyond which error rate becomes independent of flanker complexity; (2) the increase of error rate is slower for high-complexity target letters; (3) error rate increases with target-flanker similarity; and (4) mislocation error rate increases with target-flanker similarity. These findings, combined with the current understanding of the faulty feature integration account of crowding, provide some constraints of how the feature integration process could cause perceptual errors.

Very preliminary reference Moon model

The deep structure of the Moon is a missing piece to understand the formation and evolution of the Earth–Moon system. Despite the great amount of information brought by the Apollo passive seismic experiment (ALSEP), the lunar structure below deep moonquakes, which occur around 900 km depth, remains largely unknown. We construct a reference Moon model which incorporates physical constraints, and fits both geodesic (lunar mass and polar moment of inertia, and Love numbers) and seismological (body wave arrivals measured by Apollo network) data. In this model, the core radius is constrained by the detection of S waves reflected from the core. In a first step, for each core radius, a radial model of the lunar interior, including P and S wave velocities and density, is inverted from seismic and geodesic data. In a second step, the core radius is determined from the detection of shear waves reflected on the lunar core by waveform stacking of deep moonquake Apollo records. This detection has been made possible by careful data selection and processing, including a correction of the gain of horizontal sensors based on the principle of energy equipartition inside the coda of lunar seismic records, and a precise alignment of SH waveforms by a non-linear inversion method. The Very Preliminary REference MOON model (VPREMOON) obtained here has a core radius of 380 ± 40 km and an average core mass density of 5200 ± 1000 kg/m 3. The large error bars on these estimates are due to the poorly constrained S-wave velocity profile at the base of the mantle and to mislocation errors of deep moonquakes. The detection of horizontally polarized S waves reflected from the core and the absence of detection of vertically polarized S waves favour a liquid state in the outermost part of the core. All these results are consistent, within their error bars, with previous estimates based on lunar rotation dissipation ( Williams et al., 2001) and on lunar induced magnetic moment ( Hood et al., 1999).

Where does attention go when you blink?

Many studies have shown that covert visual attention precedes saccadic eye movements to locations in space. The present research investigated whether the allocation of attention is similarly affected by eye blinks. Subjects completed a partial-report task under blink and no-blink conditions. Experiment 1 showed that blinking facilitated report of the bottom row of the stimulus array: Accuracy for the bottom row increased and mislocation errors decreased under blink, as compared with no-blink, conditions, indicating that blinking influenced the allocation of visual attention. Experiment 2 showed that this was true even when subjects were biased to attend elsewhere. These results indicate that attention moves downward before a blink in an involuntary fashion. The eyes also move downward during blinks, so attention may precede blink-induced eye movements just as it precedes saccades and other types of eye movements.

Precision of position signals for letters

Accurate reading of words and text relies on reliable identification of letters in left-to-right order. Previous studies have shown that people often make letter-reversal errors when identifying strings of letters away from fixation. These errors contribute to a decline in letter identification performance away from fixation. This study tests the hypothesis that these errors are due to decreased precision (increased position noise) in the coding of letter position in the periphery. To test our hypothesis, we measured observers’ performance for identifying pairs of adjacent letters presented within eight letter positions left and right of fixation. The task was to name the two letters of each pair, from left to right. Responses were scored in two ways for each letter position: (1) letters were identified correctly and in the correct position, and (2) letters were identified correctly but in the wrong position. The ratio of these two scores, when subtracted from 1, gives the empirical rate of mislocation errors. Our primary finding shows that the coding of letter position becomes increasingly imprecise with distance from fixation. A model in which the encoded position of each letter is independent and Gaussian distributed, and in which the spread of the distribution governs the precision of localizing the letter accounts for the empirical rate of mislocation errors. We also found that precision of letter position coding scales with letter size but the precision does not improve with the use of a pre-cue.

Accurate Location of Synthetic Acoustic Emissions and Location Sensitivity to Relocation Methods, Velocity Perturbations, and Seismic Anisotropy

Acoustic emission (AE) monitoring is a non-invasive method of monitoring fracturing both in situ, and in experimental rock deformation studies. Until recently, the major impediment for imaging brittle failure within a rock mass is the accuracy at which the hypocenters may be located. However, recent advances in the location of regional scale earthquakes have successfully reduced hypocentral uncertainties by an order of magnitude. The least-squares Geiger, master event relocation, and double difference methods have been considered in a series of synthetic experiments which investigate their ability to resolve AE hypocentral locations. The effect of AE hypocenter location accuracy due to seismic velocity perturbations, uncertainty in the first arrival pick, array geometry and the inversion of a seismically anisotropic structure with an isotropic velocity model were tested. Hypocenters determined using the Geiger procedure for a homogeneous, isotropic sample with a known velocity model gave a RMS error for the hypocenter locations of 2.6 mm; in contrast the double difference method is capable of reducing the location error of these hypocenters by an order of magnitude. We test uncertainties in velocity model of up to ±10% and show that the double difference method can attain the same RMS error as using the standard Geiger procedure with a known velocity model. The double difference method is also capable of precise locations even in a 40% anisotropic velocity structure using an isotropic model for location and attains a RMS mislocation error of 2.6 mm that is comparable to a RMS mislocation error produced with an isotropic known velocity model using the Geiger approach. We test the effect of sensor geometry on location accuracy and find that, even when sensors are missing, the double difference method is capable of a 1.43 mm total RMS mislocation compared to 4.58 mm for the Geiger method. The accuracy of automatic picking algorithms used for AE studies is ±0.5 µs (1 time sample when the sampling rate is 0.2 µs). We investigate how AE locations are effected by the accuracy of first arrival picking by randomly delaying the actual first arrival by up to 5 time samples. We find that even when noise levels are set to 5 time samples the double difference method successfully relocates the synthetic AE.

Voluntary eyeblinks disrupt iconic memory

In the present research, we investigated whether eyeblinks interfere with cognitive processing. In Experiment 1, the participants performed a partial-report iconic memory task in which a letter array was presented for 106 msec, followed 50, 150, or 750 msec later by a tone that cued recall of onerow of the array. At a cue delay of 50 msec between array offset and cue onset, letter report accuracy was lower when the participants blinked following array presentation than under no-blink conditions; the participants made more mislocation errors under blink conditions. This result suggests that blinking interferes with the binding of object identity and object position in iconic memory. Experiment 2 demonstrated that interference due to blinks was not due merely to changes in light intensity. Experiments 3 and 4 demonstrated that other motor responses did not interfere with iconic memory. We propose a new phenomenon, cognitive blink suppression, in which blinking inhibits cognitive processing. This phenomenon may be due to neural interference. Blinks reduce activation in area V1, which may interfere with the representation of information in iconic memory.

Locating and modeling regional earthquakes with two stations

We developed a new technique CAPloc to retrieve full source parameters of small seismic events from regional seismograms, which include origin time, epicenter location, depth, focal mechanism, and moment magnitude. Despite rather complicated propagation effects at short periods, a simple localized one‐dimensional model can well explain signals of periods 3–10 s if we break the three‐component records into different segments and allow differential time shifts among them. These differential time shifts, once established from a calibration process or a well‐determined tomographic map, can be used together with P wave travel times to refine an event's location. In this study, we tested whether our new method could produce satisfactory results with as few as two stations, so that we can improve source estimates of poorly monitored events with sparse waveform data. We conducted the test on 28 events in the Tibetan Plateau. The focal mechanisms and locations determined from only two stations agree well with those determined from a whole PASSCAL array. In particular, our new method produces better locations than International Seismological Centre, with the average mislocation error reduced from ∼16 to ∼5 km. We also tested whether an event's depth and mechanism can be determined separately from its epicenter relocation in a two‐step approach. We find that the two‐step approach does not always give the correct solution, but the reliability of a solution can be evaluated using a reduced chi‐square value.

Sensitivity of electrical resistivity tomography data to electrode position errors

Limitations of imaging using electrical resistivity tomography (ERT) arise because of the difficulty of quantifying the reliability of tomographic images. A major source of uncertainty in tomographic inversion is data error. Data error due to electrode mislocations is characterized by the sensitivity of electrical potential to both source and receiver positions. This sensitivity is described by a scattering-type equation and, therefore, depends not only on source—receiver separation, but also on the location and magnitude of contrasts in electrical conductivity. At the overlapping scales of near-surface environmental and engineering geophysical surveys, for which electrodes may be close to the target and experiment dimensions may be on the same order as those of the target, errors associated with electrode mislocations can significantly contaminate the ERT data and the reconstructed electrical conductivity. For synthetic experiments, variations in the data due to electrode mislocation are comparable in magnitude to typical experimental noise levels and, in some cases, may overwhelm variations in the data due to changes in material properties. Furthermore, the statistical distribution of electrode mislocation errors can be complicated and multimodal such that bias may be introduced into the ERT data. The resulting perturbations of the reconstructed electrical conductivity field due to electrode mislocations can be significant in magnitude with complex spatial distributions that are dependent both on the model and the experiment.

Pelvic Width Predicts Hip Joint Center Location In Children

A precise estimate of the locations of the hip joint centers (HJC) is necessary when estimating in-vivo joint reaction forces and moments. Errors in timing and magnitude of hip joint moments have been reported to be up to 25% due to a HJC mislocation error of 30mm (Stagni,2000). While methods exist to predict HJC's based on pelvic width in adults, their applicability to children has not been reported. PURPOSE To determine how accurately MRI measures of pelvic width predict HJC locations in children. METHODS MRI's of the pelvic region were acquired from 10 healthy normal girls (9.6±0.9yrs; 141.0±9.4cm; 37.0±7.1kg; mean ± SD). The T1-weighted images were sampled from the coronal plane at 4mm intervals. Two slices were identified and exported into an imaging program for measurement: 1) the slice through the centers of the femoral heads and 2) the most anterior slice in which the left ASIS was visible. The reference frame was defined as: × = positive anterior, Y = positive left, and Z = positive superior. Fiduciary marks on the MRI's were used to calculate a scaling factor from pixels to SI units (1px = 0.5mm). Pelvic width was defined as the distance between the left and right ASIS. Because the MRI's only contained the two HJC's and the left ASIS, bilateral symmetry about the midpoint between HJC's was assumed in calculating the pelvic width. The displacement from the left ASIS to the left HJC was expressed in each direction as a percentage of the calculated pelvic width. The mean percentages in each direction were then used to predict the left HJC location of each subject. T-tests were used to determine if there were differences between the measured and predicted HJC locations in each direction (p<0.05). RESULTS The location of the left HJC relative to the left ASIS was −21.5±2.9%, −14.5±2.6%, and −32.8±4.9% of the pelvic width (18.1±1.4cm) in the X, Y, and Z directions, respectively. The magnitudes of the errors in predicted HJC location based on these percentages were 4.3±2.4mm (p<0.89), 3.5±2.7mm (p<0.89) & 6.8±5.1mm (p<0.91) in the X, Y, and Z directions, respectively for a total error of 9.8±4.3mm. CONCLUSION The location of the HJC relative to the ASIS as a percentage of pelvic width in these children was similar to that determined previously for adults. Our results also agree with Bell (1990) and Seidel (1995) in that the pelvic width best predicted the HJC along the axis it is parallel to. While the HJC prediction error was greater in the × and Z directions, the overall magnitude of the errors was quite small. Prediction of HJC location based on pelvic width is thus appropriate in computing the joint kinetics of children. International Society of Biomechanics Dissertation Grant.

Pelvic Width Predicts Hip Joint Center Location In Children

A precise estimate of the locations of the hip joint centers (HJC) is necessary when estimating in-vivo joint reaction forces and moments. Errors in timing and magnitude of hip joint moments have been reported to be up to 25% due to a HJC mislocation error of 30mm (Stagni,2000). While methods exist to predict HJC's based on pelvic width in adults, their applicability to children has not been reported. PURPOSE To determine how accurately MRI measures of pelvic width predict HJC locations in children. METHODS MRI's of the pelvic region were acquired from 10 healthy normal girls (9.6±0.9yrs; 141.0±9.4cm; 37.0±7.1kg; mean ± SD). The T1-weighted images were sampled from the coronal plane at 4mm intervals. Two slices were identified and exported into an imaging program for measurement: 1) the slice through the centers of the femoral heads and 2) the most anterior slice in which the left ASIS was visible. The reference frame was defined as: × = positive anterior, Y = positive left, and Z = positive superior. Fiduciary marks on the MRI's were used to calculate a scaling factor from pixels to SI units (1px = 0.5mm). Pelvic width was defined as the distance between the left and right ASIS. Because the MRI's only contained the two HJC's and the left ASIS, bilateral symmetry about the midpoint between HJC's was assumed in calculating the pelvic width. The displacement from the left ASIS to the left HJC was expressed in each direction as a percentage of the calculated pelvic width. The mean percentages in each direction were then used to predict the left HJC location of each subject. T-tests were used to determine if there were differences between the measured and predicted HJC locations in each direction (p<0.05). RESULTS The location of the left HJC relative to the left ASIS was −21.5±2.9%, −14.5±2.6%, and −32.8±4.9% of the pelvic width (18.1±1.4cm) in the X, Y, and Z directions, respectively. The magnitudes of the errors in predicted HJC location based on these percentages were 4.3±2.4mm (p<0.89), 3.5±2.7mm (p<0.89) & 6.8±5.1mm (p<0.91) in the X, Y, and Z directions, respectively for a total error of 9.8±4.3mm. CONCLUSION The location of the HJC relative to the ASIS as a percentage of pelvic width in these children was similar to that determined previously for adults. Our results also agree with Bell (1990) and Seidel (1995) in that the pelvic width best predicted the HJC along the axis it is parallel to. While the HJC prediction error was greater in the × and Z directions, the overall magnitude of the errors was quite small. Prediction of HJC location based on pelvic width is thus appropriate in computing the joint kinetics of children. International Society of Biomechanics Dissertation Grant.

Applicability of 3D Modeling Techniques in Creating Single-Station Locations: A Test Case in Southern Asia

Conventional multistation location estimation is not possible for small earthquakes and explosions recorded at only a single seismic station. We present a novel method of estimating epicentral distance by integrating observed travel times ( Lg-Pn and Sn-Pn ) measured on three-component (3C) single-station data with theoretical travel times for the same phase combinations determined from 3D velocity models. Theoretical travel times for the body-wave phases are estimated using raytracing through a 3D P - and S -wave velocity model, while the travel times for Lg are estimated either using raytracing techniques or with a constant velocity determined from synthetics. Backazimuths are determined by applying polarization techniques on 3C data. The backazimuth and distance are then used to determine the epicenter for the event. The results of applying this 3D single-station location methodology to well-located events in southern Asia show mislocation errors that are typically less than 6% of the total propagation path distance. Online Material: Event database with estimated arrival times and backazimuth.