Vertical Component Of Displacement Research Articles

Geometrically coherent continuous deformation in the volume surrounding a seismically imaged normal fault-array

We calculated an apparent dip attribute, which was used to ascertain the spatial distribution of fault-related continuous deformation. The vertical component of displacement calculated from the continuous deformation acts to “fill-in” missing displacement in the fault-throw profile. This result shows that apparently complex 3D patterns of continuous strain in the volumes surrounding the fault-array developed as part of a single, geometrically coherent fault-array. However, if this component of continuous deformation was not added to the throw profile, the fault-array could have been misinterpreted as a series of isolated fault segments with coincidental overlaps. This technique permits the analysis of continuous deformation structures, which are up to an order of magnitude smaller than previously described. In the study area, these structures are interpreted as small fault-propagation folds, forming in a shale-dominated cover sequence. The fault-propagation folds above the upper tip line of the mapped fault-array bifurcate upwards from the fault surface into three coherent lobes and resemble secondary fault segments. The near-constant along-strike length of the region of continuous deformation throughout the syn-rift sequence implies that the length of the fault-array was established at an early stage in its growth, prior to the establishment of a seismically-visible fault surface.

Marine palaeoseismology from very high resolution seismic imaging: the Gondola Fault Zone (Adriatic foreland)

AbstractWe present a marine palaeoseismology analysis of a dense network of very high resolution seismic profiles along the Gondola Fault Zone (GFZ), a right‐lateral, E–W‐striking, active fault system in the Adriatic foreland. This case‐study aims to show how time and space variations in the activity of a dominantly right‐lateral fault system can be assessed using the vertical component of slip. The GFZ has been investigated for a length of 50 km. It includes two parallel subvertical fault sets and two main anticlines. The late Middle Pleistocene to Holocene vertical component of displacement along the fault is bell‐shaped, suggesting that in the long‐term the fault zone acts as a single, kinematically coherent structure. Slip rates are 0–0.18 mm a−1 and vary temporally on individual segments. This variability is consistent with a model in which individual fault segments rupture independently during earthquakes with magnitudes up to 6.4 and 1.3–1.8 ka recurrence intervals.

Utilização das transformadas de Laplace e Fourier-Bessel na modelagem de meios elásticos delgados

Existem diferentes aspectos que devem ser considerados na modelagem numerica dos campos de onda conectados com reservatorios delgados em subsuperficie. Este trabalho descreve os processos de propagacao das ondas sismicas a partir do sistema das equacoes de Lame. Os resultados obtidos sao ascomponentes horizontal e vertical do deslocamento, importantes para a analise do levantamento sismico multicomponente. A fim de proporcionar resultados mais proximos do experimento real, na formulacao matematica do problema usamos uma fonte enterrada, do tipo centro de expansao. A solucao do problema, construido no dominio espectral a partir das transformadas de Laplace temporal e de Fourier-Bessel espacial, e estudada em detalhes para provar sua aplicabilidade na solucao de problemas dinâmicos diretos e inversos da sismica. Neste caso uma atencao especial e dada a analise da influencia da parte real do parâmetro de Laplace nasolucao do problema direto, utilizada para a construcao de sismogramas multicomponentes sinteticos. Neste artigo, tambem, discutimos os aspectos computacionais do esquema proposto e realizamos varias analises dos campos das ondas registrados. Os resultados alcancados demonstraram o potencial do metodo para auxiliarno processo de caracterizacao de reservatorios delgados em comparacao com os metodos potenciais, de raio e de diferencas finitas.

1205 高速鉄道車両用腰掛の振動解析モデルを用いた設計指標の検討(OS1-1:乗心地・快適性,OS1:交通・物流システムの高速化,利便性,快適性の向上,オーガナイズド・セッション(OS),第18回交通・物流部門大会(TRANSLOG2009))

The seats for high speed railway vehicle have vibration characteristics which induce high frequency and torsional vibration. That has a possibility to disturb the ride comfort. To analyze the vibrations mechanisms and to obtain useful information for seat design considering ride comfort, the seat model which has nine-degree-of-freedom is suggested. Backrest and seat base of the seat were modeled by the model, which includes out-of-plane and vertical displacement components of backrest, vertical, longitudinal, pitch, roll and yaw motions of seat base. It can describe the vibration characteristics of the seat against the floor acceleration input. By using the model, the relationship between model parameters and vibration characteristics of the seat was investigated.

Recent activity of the regional geologic structures in western Slovenia

Several important geological structures in the western Slovenia were identified as active and their activity was quantified. Geologic interpretation is based on the analysis of repeated leveling line campaigns data along the Sečovlje-Bled polygon. Taking into account the limitations of the method - only the vertical component of displacement is measured - the following structures were identified as active: a juvenile syncline between Strunjan and Koper, the Kras Imbricate Structure, the Divača fault, the Raša fault, the Southalpine Front and the Julian Alps thrust. Vertical movement rate is relative, calculated with respect to the benchmark in Sečovlje. The largest uplift rate difference between Sečovlje and Bled is 7 mm/a.Vertical Geodynamic Activity (VGA) is introduced as a link between geologic interpretation of geodetic measurements on one side and possible applications on the other as well as a mean of comparison between tectonically active regions.

Interaction of a surface wave with a dislocation

The scattering of a surface wave by a pinned edge dislocation in a semi-infinite, homogeneous, isotropic, three-dimensional elastic solid is investigated analytically and numerically. An incident wave excites the dislocation that responds by oscillating as a string endowed with mass, line tension, and damping. The oscillations of the stringlike dislocation generate secondary (``scattered'') elastic waves that are the primary object of interest in this study. The back reaction of the re-emitted waves on the dislocation dynamics is neglected, but the wavelength of the radiation is allowed to be large, comparable, or small compared to the length of the dislocation. In view of recent experimental visualizations of these phenomena, we focus particularly on the field behavior at the free surface near the dislocation, and not just on the far field. For the same reason, it is the vertical component of displacement at the free surface that is studied in detail. An efficient numerical procedure for the computation of the appropriate components of the Green's function, using a Filon quadrature for the integration of rapidly oscillating functions, is developed. The numerics is validated with known analytical expressions. The secondary radiation generated by the response of the dislocation to the incident wave is also calculated numerically, and the results are also validated by comparing them with the analytical expressions that can be obtained when the radiation wavelength is very long compared to dislocation length. The interference pattern between incident wave and secondary wave that is generated at the free surface is studied in detail and found to depend strongly not only on wavelength and dislocation geometry (length and orientation) but also on dislocation depth, with the response of the dislocation being a particularly sensitive function of such depth. Results are compared with recent experiments of Shilo and Zolotoyabko [Phys. Rev. Lett. 91, 115506 (2003)] that report visualizations of the surface-wave--dislocation interaction using stroboscopic x-ray imaging. A satisfactory agreement is found. Dislocation velocities of a few percent of the speed of sound and viscosity coefficients of about ${10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\mathrm{Pa}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$ are inferred.

Paleoseismic evidence of great surface rupture earthquakes along the Indian Himalaya

Toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system, we describe the late Quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the Himalayan Frontal Thrust (HFT) system of India. Our observations span a distance of ∼250 km along strike of the HFT. Uplifted and truncated fluvial terrace deposits resulting from the Holocene displacements on the HFT are preserved along canyons of the Ghaggar, Markanda, Shajahanpur, and Kosi Rivers. Dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of ∼4–6 mm/yr, which when assumed to be the result of slip on an underlying thrust dipping at ∼20°–45° are equivalent to fault slip rates of ∼6–18 mm/yr or shortening rates of ∼4–16 mm/yr. Trench exposures reveal the HFT to fold and break late Holocene surface sediments near the cities and villages of Chandigarh, Kala Amb, Rampur Ganda, Lal Dhang, and Ramnagar. Radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after ∼A.D. 1200 and before ∼A.D. 1700. Uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous. Trench exposures and vertical separations measured across scarps at Rampur Ganda, Lal Dhang, and Ramnagar are interpreted to indicate single‐event displacements of ∼11–38 m. Dividing the observed single‐event vertical components of displacement by the estimated longer‐term uplift rates indicates ∼1330–3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements. Surface rupture appears to not have occurred during the historical 1905 Kangra (Mw = 7.7), 1934 Bihar‐Nepal (Mw = 8.1), and 1950 Assam (Mw = 8.4) earthquakes, which also occurred along the Himalayan front. Yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the HFT. We suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the HFT greater than the ∼250 km we have studied.

Decomposing InSAR LOS displacement into co-seismic dislocation with a linear interpolation model: A case study of the Kunlun Mountain M S=8.1 earthquake

It has always been a difficult problem to extract horizontal and vertical displacement components from the InSAR LOS (Line of Sight) displacement since the advent of monitoring ground surface deformation with InSAR technique. Having tried to fit the firsthand field investigation data with a least squares model and obtained a preliminary result, this paper, based on the previous field data and the InSAR data, presents a linear cubic interpolation model which well fits the feature of earthquake fracture zone. This model inherits the precision of investigation data; moreover make use of some advantages of the InSAR technique, such as quasi-real time observation, continuous recording and all-weather measurement. Accordingly, by means of the model this paper presents a method to decompose the InSAR slant range co-seismic displacement (i.e. LOS change) into horizontal and vertical displacement components. Approaching the real motion step by step, finally a serial of curves representing the co-seismic horizontal and vertical displacement component along the main earthquake fracture zone are approximately obtained.

Markers of the last interglacial sea-level high stand along the coast of Italy: Tectonic implications

A compilation of the Marine Isotope Substage (MIS) 5.5 high stand (∼125 Ka) sites spanning the coastline of Italy allows a picture of the vertical displacement pattern affecting the Central Mediterranean coasts since the Late Pleistocene to be drawn. For each of the 246 listed sites, the accurate elevation of the high stand is defined through well-known markers. Coupled with a refined age assessment locally supported by new radiometric dating, these markers provide robust constraints on deformation. Significant alongshore differences in site elevation between +175 and −125 m a.s.l. resulted from the interplay of regional and local tectonic processes, including faulting and volcanic deformation. Whereas most of Sardinia's coasts and the northern Tyrrhenian Sea coasts are tectonically stable, the central Tyrrhenian Sea coasts display stable promontories, subsiding plains, and localized centres of weak uplift. Subsidence of the plains is related to extensional faulting locally enhanced by volcano-tectonic collapse, and weak uplift arising from magmatic processes. Rapid uplift of southern Calabria, northeast Sicily and the Jonian sea coasts probably reflects the extent of deep crustal delamination. The central Adriatic Sea shows weak thrust-related uplift, but foreland flexure in northern Adriatic and possibly southwestern Sicily results in locally intense regional subsidence. The rapidly uplifting regions are well correlated with the sectors of higher seismic release and surface horizontal motion documented by geodetic velocities. In this light, the MIS 5.5 marker indicates with a relatively high spatial resolution the vertical component of tectonic displacement and provides insight into the long-term tectonic processes of the Central Mediterranean orogen.

Paleoseismic evidence of legendary earthquakes: The apparition of Archangel Michael at Monte Sant'Angelo (Italy)

The Gargano promontory, a carbonate massif belonging to the Adria microplate, the foreland of both the Apenninic and Dinaric mountain chains, is a well-known seismogenic area, with historic earthquake up to Imax=X MCS (July 30,1627, M=6.7). Nevertheless, paleoseismic data on the region are still scarce, and no trench fault stratigraphy has been analysed along the major, E–W trending, right-lateral strike-slip fault system that cuts through the whole massif, the South Gargano Line (SGL). The over 60 km long on-shore trace of the SGL, the Mattinata Fault, is clearly segmented. This study focused on the eastern active fault segment, the Monte Sant'Angelo Fault (MSA), to verify the associated seismic potential.Analysis of contemporary descriptions of the August 10,1893 earthquake (M=5.2) coupled with field-work allowed identification of surface faulting along the MSA. Along the fault there is paleoseismic evidence of the occurrence of larger earthquakes. After collecting geomorphic evidence of paleo-earthquakes, we selected two trench sites at the base of two prominent fault escarpments, where the MSA is characterized by significant vertical components of fault displacement. The preliminary results demonstrate that: i) the recent vertical slip-rate of the MSA range between 0.2–0.3 and 0.7 mm/yr; ii) the MSA moves with incremental slip episodes, with vertical surface offset up to several decimeters; iii) based on the stratigraphic and geomorphic evidence of surface faulting observed and assuming a rupture length of around 20+ km, the seismic potential of the MSA segment would be similar to that displayed by the western SGL segment during the 1627 event.A large earthquake on the MSA is reported only in ancient legends, the most relevant of which being the one describing the apparition of Archangel Michael at Monte Sant'Angelo traditionally dated AD 493. Using a multidisciplinary approach, combining paleoseismic and historical data it has been possible to interpret the legend, and hereby identify an event of surface faulting before 8th century AD. A recent scarplet, up to 1 m high, on the MSA can be seen to be related to this legendary earthquake, which in turn seems to correspond to the maximum possible magnitude. Geologic phenomena observed during the earthquake at the site of the sanctuary appear to lie at the very origin of the veneration of the place.

Orogen‐Parallel Westward Oblique Uplift of the Qinling Basement Complex in the Core of the Qinling Orogen (China): An Example of Oblique Extrusion of Deep‐Seated Metamorphic Rocks in a Collisional Orogen

Both vertical uplift and lateral extrusion of rocks in convergent orogens have been widely documented. This article, using the basement core of the Qinling orogen as an example, demonstrates orogen‐parallel westward uplift with both vertical and horizontal displacement components. The Qinling complex of the Qinling orogen is a tectonic slice of a Precambrian crystalline basement. It is an elongate lens between younger terranes bounded by the Shangdan suture to the south and by the Zhuxia zone to the north. During the middle Paleozoic, the complex underwent large‐scale orogen‐parallel westward oblique ductile uplift. Supporting evidence for this includes the following: (1) opposite shear senses of the two bounding shear zones, i.e., the thrust‐sinistral shear on the south and thrust‐dextral shear on the north; (2) well‐developed eastward plunging (orogen‐parallel) A‐type structures in the complex, such as stretching lineation and sheath folds; (3) strong decompression metamorphism of the complex from 0.66 GPa to 0.45 GPa and eclogites decompressed from 1.2 GPa to 0.5 GPa; and (4) eastward migration in the emplacement of synkinematic granitic plutons. Integrated analysis of PT evolution paths suggests a vertical uplift of the basement complex relative to adjacent Paleozoic supracrustal rocks ranging from 15 to 40 km. Coeval west‐directed horizontal displacement is then estimated to range from 32 to 86 km and total oblique displacement from 36 to 95 km, using an average 25° plunge of mineral stretching lineations in the boundary shear zones. This oblique uplift could be explained by soft oblique extrusion derived from a scissors‐like (or zipped) subduction/collision between the North and South Qinling belts. Because plate boundaries are usually irregular and nonparallel both in the vertical and horizontal, orogen‐parallel oblique uplift (soft oblique extrusion) may be widespread in collisional orogens.

HVSR prospecting in multi-layered environments: An example from the Tyrnavos Basin (Greece)

The Tyrnavos Basin (Central Greece) is an E-W trending graben bordered by two major antithetic sets of right-stepping dip-slip normal faults that began forming during Middle Pleistocene as a consequence of the N-S extension which affected the whole Aegean Region. This Quaternary structure is superimposed on the Pliocene-Early Pleistocene NW-SE trending Larissa Basin, approximately 700–800 m deep. Seismic activity is instrumentally well documented within and surrounding the investigated area. Based on structural, morphotectonic and palaeoseismological data, several structures previously characterised as active faults have been investigated by applying the HVSR method. This method is commonly used to map the thickness of sedimentary layers in a basin based on the variation of the fundamental 1-D frequency. The polyphased structural evolution and the consequently complex geological setting do not allow for the contouring of a unique continuous surface. We therefore developed a new interpretation technique for statistically significant HVSR peaks, in order to obtain 2-D sections that can be interpreted in a seismic-like fashion. We applied this technique across the major active faults bordering the basin. The results confirm their occurrence at depth and document the important vertical component of displacement.

General methods for the determination of the stiffness tensor and mass density of thin films using Brillouin light scattering: Study of tungsten carbide films

Methods of film preparation and data evaluation are presented to determine the stiffness tensor and mass density of thin films using Brillouin light scattering from surface phonons. The combined use of stepped films of progressively increasing thickness $d,$ and an optimized variation of the magnitude of the surface wave vector ${q}_{\ensuremath{\parallel}}$ provides a particularly wide range of uniformly distributed values of the product ${q}_{\ensuremath{\parallel}}d$ in the study of the velocity dispersion of the observed surface acoustic waves. Furthermore by the independent variation of ${q}_{\ensuremath{\parallel}}$ and $d,$ the microstructure can be assessed as a function of film thickness. In the present case of tungsten carbide (WC) films on a silicon substrate, being a slow-on-fast system, the Rayleigh mode and several Sezawa modes are observed. Using the extensive velocity dispersion data, five independent material parameters of the WC films, i.e., four elastic constants and the mass density, are determined by two independent approaches. One employs a least-squares fit to the experimental velocity dispersion curves to determine these material parameters, whereas the other investigates the structure of the parameter space in the vicinity of the solution being sought by a Monte Carlo technique. Both approaches yield identical and self-consistent results. In a Green's-function formulation that uses the vertical displacement component of the acoustic excitations at the free surface, the experimental Brillouin spectra are simulated in the discrete as well as in the continuous part of the mode spectrum.

An Elasto-Plastic Analysis of Thermoplastic Composite Cantilever Beam Loaded by a Single Force at Its Free End

In the present study, an elastic–plastic stress analysis is carried out on a high-density thermoplastic-based composite cantilever beam loaded by a single force at its free end. An analytical solution is performed for satisfying both the governing differential equation in the plane stress case and boundary conditions for small plastic deformations. The solution is carried out under the assumption of the Bernoulli–Navier hypotheses. The composite material is assumed to be strain-hardening. The Tsai–Hill theory is used as a yield criterion. The residual stress component of x are determined for 0, 30, 45, 60 and 90 orientation angles. It is found that the intensity of the residual stress is maximum at the upper and lower surfaces of the beam. The horizontal displacement component of u is greater than the vertical displacement component of v.

Fundamental Study on Vibration Diagnosis for High Speed Rotational Machine using Wavelet Transform

In this paper we presented results of fundamental study to introduce the wavelet transform to vibration diagnosis for high-speed rotational machine such as steam turbine, gas turbine, and generator and so on. It is required to detect and distinguish typical vibration of high-speed rotational machine accurately in order to diagnose the machine. The wavelet transform is used in many fields because it is able to visualize phenomenon in time-frequency domain and to detect the beginning time and the duration of it. We made a model rotor supported with two journal bearings to simulate contact vibration, clearance vibration, and oil whip. The vibration phenomena were measured with vertical and horizontal displacement meters at the rotor and vertical and horizontal accelerometers at the rotor bearing and visualized in the time-frequency domain by the wavelet transform. It is found that the dynamic spectra obtained by the wavelet transform of the vertical and horizontal components of displacement and acceleration signals are different for each vibration phenomenon, therefore, this method is able to distinguish each kind of vibration phenomenon. Each vibration phenomenon can be detected and distinguished at the early stage.

The moving-load problem in soil dynamics—the vertical displacement approximation

The moving point load problem in soil dynamics is analyzed in the vertical particle displacement approximation. Prior to its motion, the load is stationary. From the instant at which it is set into motion it moves, with constant speed, along a straight path on the (horizontal) planar surface of a semi-infinite elastic medium. The modified Cagniard method for solving transient wave problems is used to determine closed-form expressions for the vertical component of the particle displacement from the elastodynamic wave equation of which only the vertical component is taken into account. The relevant approximation is standard in soil dynamics. Both the cases of “subsonic” and “supersonic” surface load speeds are considered. Methods to include losses in the model are briefly discussed. The study has been initiated with a view to the application of the results to the analysis of the ground motion generated by high-speed trains traveling on a poorly consolidated soil.

Quaternary vertical offset and average slip rate of the Nojima Fault on Awaji Island, Japan

Abstract Drilling was carried out to penetrate the Nojima Fault where the surface rupture occurred associated with the 1995 Hyogo‐ken Nanbu earthquake. Two 500 m boreholes were successfully drilled through the fault zone at a depth of 389.4 m. The drilling data show that the relative uplift of the south‐east side of the Nojima Fault (south‐west segment) was approximately 230 m. The Nojima branch fault, which branches from the Nojima Fault, is inferred to extend to the Asano Fault. From the structural contour map of basal unconformity of the Kobe Group, the vertical component of displacement of the Nojima branch–Asano Fault is estimated to be 260–310 m. Because the vertical component of displacement on the Nojima Fault of the north‐east segment is a total of those of the Nojima Fault of the south‐west segment and of the Nojima branch–Asano Fault, it is estimated to total to 490–540 m. From this, the average vertical component of the slip rate on the Nojima Fault is estimated to be 0.4–0.45 m/103 years for the past 1.2 million years.

Paleoseismicity of the northern Horohoro Fault, Taupo Volcanic Zone, New Zealand

Trench excavations have provided constraints on the recent paleoseismic history of the northern Horohoro Fault, one of the faults of the Taupo Fault Belt (TFB), a belt of northeast‐striking normal faults that run along the axis of the Taupo Volcanic Zone (TVZ). We excavated two trenches across the northernmost part of the fault where it displaces two Quaternary terraces of different ages. The trench exposures reveal a series of alluvial and volcanic fall deposits, ranging in age from c. 25 to 1.75 ka, that are vertically displaced across the steeply southeast‐dipping fault. The trench data confirm that the fault is active and indicate that it has ruptured at least three times within the last c. 26 000 yr and twice within the last c. 15 700 yr, with an average vertical component of displacement of c. 1.1 m per rupture. The most recent surface rupture occurred between 1750 and 8050 yr ago. Because the fault has ruptured within the last 20 000 yr, we consider it to be part of the modern TFB, the region that accommodates most of the modern extension in the TVZ. The post‐c. 25 ka vertical displacement rate on the northern Horohoro Fault, which runs along the northwest boundary of the TFB, is 0.14–0.2 mm/yr at the trench site, lower than that of many of the faults within the modern TFB. It is unclear if the whole Horohoro Fault or just the northern section is active. If the latter, then the fault may only be accommodating strain associated with a bend or step in the TFB near Rotorua.

A late Quaternary extension rate in the Taupo Volcanic Zone, New Zealand, derived from fault slip data

A northwest‐southeast oriented extension rate from faulting for a time‐averaged period of c. 50 000 yr (10 000–64 000 yr), across the Ngakuru‐Waikite depression (modern Taupo Fault Belt, central Taupo Volcanic Zone), has a best estimate of 1.9 mm/yr (in a range of 1.2–2.8 mm/ yr) in the near surface, but increases to a best estimate of 6.4 mm/yr (in a range of 3.6–10.2 mm/yr) at seismogenic depths of 6–10 km. We obtain this result by summing the vertical components of fault displacement across known‐age surfaces, or as the vertical component of displacement in stratigraphic units of known age, within the 14 km wide zone of active normal faulting. We convert the summed vertical slip rate of 7.2 ± 0.4 mm/yr to dip‐slip displacement rate and to northwest‐southeast extension by estimating a range of possible fault plane dips at the surface and at seismogenic depth. Fault displacement at seismogenic depth in large events is on average 1.6 times larger than at the surface, and for earthquake magnitudes of A/6.8 and smaller, about one‐third of the displacement occurring with the whole Gutenburg & Richter distribution of earthquakes in the modern Taupo Fault Belt will not rupture to the ground surface. Fault dip averages c. 75° in the near surface, but is poorly constrained at seismogenic depth in the Taupo Fault Belt. From a variety of local and literature considerations, we propose a dip of c. 60° at seismogenic depth in the Taupo Fault Belt. Our observations suggest only a minor component of extension at the surface (c. 5%) is contributed by small scale faulting below our observation threshold of 0.1–0.5 m of fault slip. The c. 4.5 mm/yr difference in extension rate between seismogenic depth and the ground surface may represent the surface extension rate caused by a combination of opening of extension fractures and penetrative grain‐scale extensional deformation.

Direction-dependent distortions of retinocentric space in the visuomotor transformation for pointing.

The aim of this study was to: (1) quantify errors in open-loop pointing toward a spatially central (but retinally peripheral) visual target with gaze maintained in various eccentric horizontal, vertical, and oblique directions; and (2) determine the computational source of these errors. Eye and arm orientations were measured with the use of search coils while six head-fixed subjects looked and pointed toward remembered targets in complete darkness. On average, subjects made small exaggerations in both the vertical and horizontal components of retinal displacement (tending to overshoot the target relative to current gaze), but individual subjects showed considerable variations in this pattern. Moreover, pointing errors for oblique retinal targets were only partially predictable from errors for the cardinal directions, suggesting that most of these errors did not arise within independent vertical and horizontal coordinate channels. The remaining variance was related to nonhomogeneous, direction-dependent distortions in reading out the magnitudes and directions of retinal displacement. The largest and most consistent nonhomogeneities occurred as discontinuities between adjacent points across the vertical meridian of retinotopic space, perhaps related to the break between the representations of space in the left and right cortices. These findings are consistent with the hypothesis that at least some of these visuomotor distortions are due to miscalibrations in quasi-independent visuomotor readout mechanisms for "patches" of retinotopic space, with major discontinuities existing between patches at certain anatomic and/or physiological borders.