Traceable Length Research Articles

Clustering of earthquakes along the Pidima-Anthia normal fault: New data from palaeoseismology and tectonic geomorphology and their significance on the earthquake's regularity and recurrence across southern Greece

The Pidima-Anthia Fault provides an opportunity to unravel the long palaeoseismic records of the Eastern Messinia Fault Zone (EMFZ) that defines the western border of the Taygetos Mtn range in Peloponnese (southern Greece). This fault zone is segmented and includes a complex system of primarily normal fault segments dipping westwards with a strike of NNW-SSE to N–S, with a traceable length from 6 to 10 km. We applied geomorphological and palaeoseismological analysis across the Pidima-Anthia Fault. The palaeoseismological trench performed across the Pidima-Anthia Fault provide evidence for five M > 6.4 earthquakes hosted on this fault and indicate an apparent slip rate of 0.23 mm/a. Geomorphologically, based on modelling the triangular facets, we estimated the slip rate as 0.28–0.44 mm/a. These data highlight that the slip rate of the fault is remarkably stable for the approximately 17 ka period, and that this duration is enough for a morphogenic active fault to create seismic landscapes. The earthquake history of the Pidima-Anthia Fault allows its comparison with six other known faults that dominate the earthquake history of southern Greece. The pattern of earthquake history in southern Greece shows clustering features (“Wallace-type” behaviour) during Late Quaternary. In particular, the Pidima-Anthia Fault's seismic history resembles with time predictable earthquakes and clustering during the Holocene. Overall, clustering appears prevalent in earthquake behaviour in southern Greece. However, the Pidima-Anthia Fault during the current period (i.e., post 1 ka A.D.)does not display cluster time-predictable behaviour and a strong earthquake can happen at any time.

Mapping the near‐surface trace of the seismically active Kachchh Mainland Fault and its lateral extension in the blind zone, Western India

ABSTRACTThe W–WNW‐striking Kachchh Mainland Fault (KMF) is the largest intra‐basinal fault in the Kachchh Rift Basin (KRB) located at the western continental margin of the Indian plate, and is responsible for several historic earthquakes, including the 2001 Bhuj earthquake and the 1956 Anjar earthquake. The objective of the study is to constrain the precise location and near‐surface characteristics of the KMF using field and ground penetrating radar (GPR) studies. Efforts were also made to ascertain and map the eastward continuity of the KMF. The fault has a prominent geomorphic expression up to the east of Devisar, where the KMF scarp finally dies out. The KMF marks the lithotectonic contact between Mesozoic rocks in the south and Tertiary rocks in the north. The segmented nature of the KMF has been previously attributed to transverse faults, complex deformation zones and heterogeneous assemblages of unconformable Quaternary deposits. Eight survey sites between Nirona and Sikra were chosen for near‐surface investigation of KMF using GPR. Comparatively, high‐amplitude radar reflections were received from well‐compacted sand‐ and shale‐rich Mesozoic rocks, whereas low‐amplitude weak reflections were observed from softer and clay‐rich Tertiary rocks. In the upper section of the GPR profiles, Quaternary deposits display low‐ to moderate‐amplitude semi‐continuous to wavy reflections. The traceable length of the KMF has been extended eastward by ∼20 km through the current study, which is considered a blind zone as feeble surficial evidence is present, but the fault trace is confirmed near the surface using GPR. The eastern part of the KMF is inferred to be a near‐vertical north‐dipping normal fault based on GPR data analysis. The tendency of the KMF to transform into a reverse fault in the vicinity of the intersection with transverse faults implies zones of relatively higher stress accumulation that might activate and trigger devastating earthquakes in the future.

Robust phase-stepping interferometry for traceable length measurements in a Hilger–Watts gauge-block interferometer

We demonstrate a simple adaptation of the venerable Hilger–Watts gauge-block interferometer capable of performing automated, traceable calibrations of gauge block length by phase-stepping interferometry (PSI). We discuss the selection of robust PSI filtering algorithms to counteract in software the flaws of the hardware implementation, including markedly non-sinusoidal fringes and inhomogeneous phase step size. We find that the length measurement errors attributable to the phase measurement can be reduced to 0.6 nm, even with a simple retrofit to an instrument not originally designed for PSI.

WE‐C‐103‐10: Lung Density Standard Reference for Medical Computed Tomography

Purpose: To report to the quantitative imaging community that Standard Reference Material™ 2088, Density Standard for Medical Computed Tomography, is in the final stages of certification. The SRM 2088 can be used to determine the radiodensity scale in medical computed tomography (CT) in the range of lung tissue, partially supplementing the quantitative imaging effort championed by the Quantitative Imaging Biomarkers Alliance (QIBA) to specifically address the standardization of lung density measurements using CT. Methods: The SRM consists of a set of five rigid polyurethane foam blocks, approximately 5 cm × 4 cm × 2 cm, with densities ranging from 0.06 to 0.30 g/cm3 corresponding to HU values nominally from −950 and −695. A total of 200 blocks makes up the 40 packaged units, each containing 5 blocks of the 5 unique densities. Among these, 15 (3 from each density level) were randomly selected to have their physical density determined by SI traceable length and mass measurements. The measured densities of these blocks and their corresponding HU value obtained in a CT measurement serve as the calibration for assigning a density value to the entire 200 blocks. In addition, 3 units randomly selected were measured in the NIST standard beam qualities to obtain the mass attenuation coefficient. The linear attenuation coefficient, the lot averaged path length along the x‐ray beam, and the assigned mass density were used to obtain the mass attenuation coefficient. Results: Based on rigorous statistical analyses, all 200 blocks in the 40 units are issued a certified physical density in kg/m3, and the entire lot of the SRM is issued a mass attenuation coefficient, in kg/m2, for each of the four standard beam qualities. Conclusion: SRM 2088 allows an SI‐traceable calibration of densities observed in a CT in the density range of lung tissue.

Investigation of dynamics-induced errors of long line scale calibration systems

The article treats the issue of embedding the traceable length metrology directly into technological process by performing precise dynamic measurements of line scale in real industrial environment. It addresses the error-related problems specific to line scale calibration in dynamic mode of operation that are caused primarily by static and dynamic loads as well as geometrical deviations of the calibration system components. Introducing the dynamic regime of calibration leads to the dynamic calibration error originating due to vibration sources in the structure. This term should be considered and implicated in the measurement uncertainty budget. A new 3D finite element model has been developed in order to both investigate the influence of dynamical excitations of a long stroke comparator structure and evaluate possible influence of vibrations on geometrical dimensions of the line scale. The experiments have been conducted on the new interferometer-controlled comparator setup with a moving microscope in order to evaluate the performance of the precision scale calibration process.

Frequency stabilized three mode HeNe laser using nonlinear optical phenomena

Accurate and traceable length metrology is employed by laser frequency stabilization. This paper describes a laser frequency stabilization technique as a secondary standard with a fractional frequency stability of 5.2x10(-10) with 2 mW of power, suitable for practical applications. The feedback stabilization is driven by an intrinsic mixed mode signal, caused by nonlinear optical phenomena with adjacent modes. The mixed mode signals are described theoretically and experimentally verified.

Three-dimensional Reconstructed Contrast–enhanced MR Angiography for Internal Iliac Artery Branch Visualization before Uterine Artery Embolization

To evaluate the feasibility of three-dimensional (3D) reconstructed contrast-enhanced (CE) magnetic resonance (MR) angiography in mapping the pelvic arteries in women before uterine artery embolization (UAE). CE MR angiography studies before UAE in 49 women (age range, 38-57 years; mean, 47.04 y +/- 4.7 [SD]) who underwent UAE for uterine leiomyomas between February 2005 and February 2007 were retrospectively evaluated by two radiologists in consensus. Studies were performed on a 1.5-T MR unit with a 3D fast low-angle shot sequence in the coronal direction. Reconstruction was performed with 3D computed tomographic angiography reconstruction software. In the current study, 98 internal iliac arteries (IIAs) from 49 women were studied. The superior and inferior gluteal arteries were visualized in all cases (N = 98; 100%), the lateral sacral artery in 86 cases (88%), the iliolumbar artery in 84 (86%), the obturator artery in 81 (83%), the internal pudendal artery in 96 (98%), and the uterine artery in 95 (97%). The superior vesical and middle rectal arteries were seen in 21 (21%) and 11 (11%) cases, respectively. The mean length of the uterine artery was 12.56 cm (range, 4.6-22.2 cm), and it showed the longest traceable length among all branches. The uterine artery showed five patterns of origin. The superior gluteal artery showed constant origin from the posterior division of the IIA, whereas the iliolumbar and obturator arteries showed the most variations in origin. Three-dimensional reconstructed CE MR angiography can detect most branches of the IIA in addition to their point of origin. Therefore, it can be used as a mapping tool of the pelvic arterial tree before UAE.

Self-calibration of dual-actuated single-axis nanopositioners

The rapid growth in nanosciences and technology has increased the need for high-precision nanopositioning stage technology, an important aspect of which is calibration to a traceable length standard with nanometre resolution. Direct calibration of the entire displacement range to a traceable length standard is generally difficult and time consuming because of the dearth of suitable and stable references and the need to remove all environmental disturbances during the calibration procedure. This paper introduces an approach to implementing self-calibration on a single-axis, dual-actuated, nanopositioning stage. It demonstrates how dual actuation on such a system can be used to implement the transitivity and redundancy conditions required for dimensional self-calibration so that only a single scaling input is required. The approach is verified by a series of simulations and experiments to demonstrate repeatable self-calibration of the axis to within 1 nm over a displacement range of 30 µm.

The Koryak strong earthquake of April 20 (21), 2006: Preliminary results

A number of terrain features and objects of the settlements of Tilichiki and Korf and the village of Khailino in the epicentral zone of the strongest earthquake in the north of the Kamchatka region were examined in the first days after the earthquake. Primary and secondary coseismic ruptures were identified on the surface. An outcrop of the seismic source was discovered in the form of an extended seismic fault about 140 km in traceable length. The settlements were inspected for the purpose of elucidating the macroseismic effect, structural maps were compiled, and the main types of ruptures were identified. The network of seismic stations on Kamchatka and in eastern Russia recorded a few thousand aftershocks. The gathered data provide insight into the structure of the source and its tectonic position at the Asian active continental margin.

Combined optical and X–ray interferometry for high–precision dimensional metrology

The requirement for calibrating transducers having subnanometre displacement sensitivities stimulated the development of an instrument in which the displacement is measured by a combination of optical and X–ray interferometry. The need to combine both types of interferometry arises from the fact that optical interferometry enables displacements corresponding to whole numbers of optical fringes to be measured very precisely, but subdivision of an optical fringe may give rise to errors that are significant at the subnanometre level. The X–ray interferometer is used to subdivide the optical fringes. Traceability to the meter is achieved via traceable calibrations of the lattice parameter of silicon and of the laser frequency. Polarization encoding and phase modulation allow the optical interferometer to be precisely set on a specific position of the interference fringe—the null point setting. The null point settings in the interference fringe field correspond to dark or bright fringes. Null measurement ensures maximum possible noise rejection. However, polarization encoding makes the interferometer nonlinear, but all nonlinearity effects are effectively zero at the fringe set point. The X–ray interferometer provides the means for linear subdivision of optical fringes. Each X–ray fringe corresponds to a displacement that is equal to the lattice parameter of silicon, which is ca .0.19 nm for the (220) lattice planes. For displacements up to 1 m the measurement uncertainties at 95% confidence level are ± 30 pm, and for displacements up to 100 m and 1 mm the uncertainties are ± 35 and ± 170 pm, respectively. Important features of the instrument, which is located at the National Physical Laboratory, are the silicon monolith interferometer that both diffracts X–rays and forms part of the optical interferometer, a totally reflecting parabolic collimator for enhancing the usable X–ray flux and the servo–control for the interferometers.