Rates Of Vertical Movement Research Articles

付加体の構造侵食による前弧の構造発達

This paper proposes a new model for the evolution of geologic structures in forearcs concerning subduction erosion after tectonic accretion. The model was generated from a high-pressure (HP) metamorphic unit, in which the early history of frontal offscraping accretion is recorded, in the Kamuikotan Zone of central Hokkaido. It was transported from the trench to the interior of the subduction zone during a non-accretionary stage, and the process is regarded to be subduction erosion and subsequent underplating re-accretion at greater depths. This mode of material transport persuasively explains the common and abundant occurrences of terrigenous meta-clastic rocks in HP subduction complexes, in spite of common evidence that sediments had been scraped off at much shallower depths as seen in coeval non-metamorphic accretionary units. It is thus suggested that significant amounts of HP metasediments originated from tectonically eroded materials of the frontal accretionary complex, instead of rocks directly underplated from the subducted slab. Subduction erosion in Hokkaido occurred contemporaneously with the exhumation of a higher-grade HP unit with similar rates of vertical movement of opposite senses. It suggests that exhumation was a counter flow of subduction erosion: the higher-grade rocks were lifted up by the insertion and accumulation of tectonically eroded rocks at depths, and were unroofed by lateral extension of the oversteepened non-accretionary wedge. This model can also explain common flat-lying structures of accretionary and subduction complexes exposed on land. They originally had rather high-angle structures formed by lateral shortening during early accretionary stages, and then were tilted trench-ward by the removal of materials near the trench by subduction erosion and their underplating at rear-side portions during the subsequent non-accretionary stages.

Petrological and geochronological constraints on the formation, subduction and exhumation of the continental crust in the southern Sulu orogen, eastern-central China

Detailed petrological, geochemical and geochronological studies were carried out for the core samples from the Chinese Continental Scientific Drilling Main Hole (CCSD-MH) with a final depth of 5158 m. This borehole has penetrated into an ultrahigh-pressure (UHP) metamorphic slice consisting mainly of eclogites, gneisses, garnet–pyroxenites and garnet–peridotites. Geochemical characteristics indicate that their protoliths are igneous rocks, and occur in a continental rifting tectonic setting. Quartz-, rutile- and ilmenite-rich eclogites from 0 to 710 m occur as alternating layers; the eclogites, together with interlayers of peridotites and gneisses form a layered ultramafic–mafic–acidic intrusion, which was formed by extensive fractional crystallization of basaltic magma in continental environments. The granitic gneisses from 1190 to 1505 m and 3460 to 5118 m show affinity to within-plate granite, whereas the granitic gneisses from 710 to 1190 m and 1505 to 3460 m exhibit characteristics of volcanic-arc granite. Zircon U–Pb dating demonstrates that the magmatic zircon cores, which have relatively high Th/U ratios (mostly > 0.4), from both eclogites and gneisses, yield the same age at c. 788.8 Ma, suggesting that the protoliths of UHP rocks were formed by bimodal magmatism in Neoproterozoic rifting tectonic zones along the northern margin of the Yangtze Plate, in response to the breakup of the supercontinent Rodinia. U–Pb dating of metamorphic zircons with coesite and other eclogite-facies mineral inclusions and with relatively low Th/U ratios (mostly < 0.14) gives similar Triassic ages, which define two main zircon-forming events at 221.1 Ma and 216.7 Ma. We suggest that the older weighted mean age represents the peak-UHP metamorphic event at a pressure of 5.0 GPa (corresponds to ∼ 165 km depth), whereas the younger mean age reflects the UHP/HP retrograde event at a pressure 2.8 GPa (∼ 92 km depth). Therefore, a maximum rate of vertical movement during early exhumation of the UHP rocks from the Sulu orogen would be 17 mm/year, which is quite similar to initial exhumation rates (16 to 35 mm/year) of many UHP terranes in the world.

Vertical movements of North Sea cod

Various air-breathing marine vertebrates such as seals, turtles and seabirds show dis- tinct patterns of diving behaviour. For fish, the distinction between different vertical behaviours is often less clear-cut, as there are no surface intervals to differentiate between dives. Using data from acoustic tags (n = 23) and archival depth recorders attached to cod Gadus morhua (n = 92) in the southern North Sea, we developed a quantitative method of classifying vertical movements in order to facilitate an objective comparison of the behaviour of different individuals. This method expands the utilisation of data from data storage tags, with the potential for a better understanding of fish behaviour and enhanced individual based behaviour for improved ecosystem modelling. We found that cod were closely associated with the seabed for 90% of the time, although they showed distinct seasonal and spatial patterns in behaviour. For example, cod tagged in the southern North Sea exhib- ited high rates of vertical movement in spring and autumn that were probably associated with migra- tion, while the vertical movements of resident cod in other areas were much less extensive and were probably related to foraging or spawning behaviours. The full reasons underlying spatial and tempo- ral behavioural plasticity by cod in the North Sea warrant further investigation.

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.

TOPO-EUROPE: The geoscience of coupled deep Earth-surface processes

TOPO-EUROPE addresses the 4-D topographic evolution of the orogens and intra-plate regions of Europe through a multidisciplinary approach linking geology, geophysics, geodesy and geotechnology. TOPO-EUROPE integrates monitoring, imaging, reconstruction and modelling of the interplay between processes controlling continental topography and related natural hazards. Until now, research on neotectonics and related topography development of orogens and intra-plate regions has received little attention. TOPO-EUROPE initiates a number of novel studies on the quantification of rates of vertical motions, related tectonically controlled river evolution and land subsidence in carefully selected natural laboratories in Europe. From orogen through platform to continental margin, these natural laboratories include the Alps/Carpathians–Pannonian Basin System, the West and Central European Platform, the Apennines–Aegean–Anatolian region, the Iberian Peninsula, the Scandinavian Continental Margin, the East-European Platform, and the Caucasus–Levant area. TOPO-EUROPE integrates European research facilities and know-how essential to advance the understanding of the role of topography in Environmental Earth System Dynamics. The principal objective of the network is twofold. Namely, to integrate national research programs into a common European network and, furthermore, to integrate activities among TOPO-EUROPE institutes and participants. Key objectives are to provide an interdisciplinary forum to share knowledge and information in the field of the neotectonic and topographic evolution of Europe, to promote and encourage multidisciplinary research on a truly European scale, to increase mobility of scientists and to train young scientists. This paper provides an overview of the state-of-the-art of continental topography research, and of the challenges to TOPO-EUROPE researchers in the targeted natural laboratories.

Active deformation front delineated by drainage pattern analysis and vertical movement rates, southwestern Coastal Plain of Taiwan

Orogenesis in Taiwan results from an arc-continent collision between the Eurasian plate and the Philippine Sea plate. The southwestern part of Taiwan absorbs active shortening as evidenced by rapid crustal deformation and frequent earthquakes. Southwestern Taiwan may be subdivided into three tectonic–geomorphic domains, including the plain (PL), the tilted tableland (TT), and the low hills (LH), based on geomorphology, drainage pattern and stratigraphic records. The PL domain is the westernmost and is characterized by meandering rivers with relatively low surface slope and river gradient, but high river sinuosity. The TT domain has slightly tilted terraces with river meanders and many tributaries are developed on its surface. Anomalous river sinuosity occurs as a result of active tectonics. The LH domain has higher elevation and deformed geomorphic surfaces associated with a dissected landscape. This domain also has high stream gradients with low sinuosity which may indicate active deformation. We define crustal deformation, using Holocene deposits and radiocarbon dating in addition to geomorphic analysis that suggests a blind thrust may exist between the PL and TT domains. This blind thrust may indicate the position of the active deformation front of the orogenic belt of southwest Taiwan.

Quaternary erosion-induced isostatic rebound in the western Alps

The high elevation and deep incision of the Alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates. Normal faulting and horizontal extension, however, dominate current tectonic activity, and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations. Here we test the idea that enhanced Quaternary erosion of the Alps and isostatic compensation of the mass removed can account for the distribution of present-day geodetically measured rates of vertical movement in the western Alps. Using geophysical relief and Kuhlemann's estimated average erosion rate for the Alps, we quantify the spatial distribution of erosion and the volume of eroded rock, respectively. From these, we obtain a map of rock eroded within a given time span. The calculated isostatic response of the Alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the Alpine lithosphere reaches a maximum of [~]500 m since 1 Ma in the inner Swiss Alps, and vertical movement extends across the entire belt, including peri-Alpine basins. Assuming a steady erosion rate since 1 Ma, this rebound accounts for half of the measured vertical motion of 1.1 mm/yr in the southern Valais. Thus, a significant fraction ([~]50%) of the present-day vertical movement results from the isostatic response to enhanced erosion during Plio-Quaternary time

Depth and movement behaviour of the Pacific sleeper shark in the north‐east Pacific Ocean

Satellite‐linked radio telemetry was used to study the geographic movements and vertical movement behaviour of the Pacific sleeper shark Somniosus pacificus. The fish were tagged near Steller sea lion Eumetopias jubatus rookeries in the Gulf of Alaska during periods when Steller sea lions pups were most vulnerable to predation; when Steller sea lion pups first enter the water (July to August) and when Steller sea lion pups are weaned (April to May). Final locations recovered from most Pacific sleeper sharks (76%) were within 100 km of release locations, 16% were within 100–250 km and 8% were within 250–500 km. The most striking behavioural feature was their extensive, nearly continuous vertical movements. Median daily depth range was 184 m; the most time (61%) was spent between 150 and 450 m, but ascents above 100 m were common (58% of days). Median vertical movement rate was 6 km day−1 and steady. The longest period of continuous vertical movement (&gt; 60 m h−1) was 330 h. Systematic vertical oscillations were most common (60%), followed by diel vertical migrations (25%) and irregular vertical movements (15%). The Pacific sleeper sharks travelled below the photic zone during the day and approached the surface at night. Pacific sleeper sharks appear to employ a stealth and ambush hunting strategy that incorporates slow vertical oscillations to search for prey, and cryptic colouration and cover of darkness to avoid detection by potential prey. The depth and geographic range of Pacific sleeper shark and Steller sea lions overlap near four important Steller sea lion rookeries in the northern Gulf of Alaska, so the potential exists for predation to occur. None of the tissues in the stomachs of the 198 Pacific sleeper sharks collected during a companion diet study, however, were identified as Steller sea lion.

Tectonic and climatic controls on coastal sedimentation: The Late Pliocene–Middle Pleistocene of northeastern Rhodes, Greece

The Late Pliocene to Middle Pleistocene coastal sediments of northeastern Rhodes (Greece) were deposited in an active tectonic setting. They provide an excellent opportunity to investigate the relative roles played by climate and tectonics in sedimentary processes. The tectono-sedimentary organization of these deposits is revised in the light of an integrated study combining data from field investigations, sedimentology, bio- and magnetostratigraphy, radiometric dating, palaeoecology, and palynology. Three lithostratigraphic units are recognised: the Rhodes Formation, the newly defined Ladiko–Tsampika Formation, and the Lindos Acropolis Formation. A major erosional surface separates the Rhodes Formation from the Ladiko–Tsampika Formation, which was deposited in deep and narrow palaeovalleys. The Rhodes Formation (Late Pliocene to 1.4–1.3 Ma) comprises three Members: the Kritika, the Lindos Bay clay and the Cape Arkhangelos calcarenite. The shallow-water clastic sediments of the Ladiko–Tsampika Formation (1.3 to 0.3 Ma) are subdivided into two Members: the Ladiko (mostly sandy) and the Tsampika (predominantly clayey). The Lindos Acropolis Formation is Late Pleistocene in age. Two major transgression–regression cycles occurred prior to the Lindos Acropolis cycle. The deposition of the first cycle (Rhodes Formation) is tectonically controlled, with very high rates of vertical movements (2.6–5.2 mm/year). The second cycle (Ladiko–Tsampika Formation) records sea-level changes controlled by slow vertical motions (around 0.16 mm/year) and glacio-eustatic events with 40-kyr and 100-kyr periods. Finally, the tectonic and sedimentary evolution of Rhodes is integrated into the geodynamic context of the eastern Aegean fore-arc.

Hinterland geology and continental margin growth: the case of the Gioia Basin (southeastern Tyrrhenian Sea)

Abstract The Gioia Basin is a small trough located in the southeastern Tyrrhenian Sea between the Aeolian island arc and Sicily and Calabria. It is experiencing a post-rift margin evolution, while tectonic deformation and high rates of vertical movement are still affecting the Sicilian and Calabrian mainland. The analysis of the evolution of the post-rift depositional systems along the various sectors of the Gioia Basin margin has been carried out through the combined interpretation of multibeam bathymetry and seismic reflection data. Two seismic units have been identified and their component geomorphological elements ascertained through the analysis of seismic facies distribution. In general, the depositional architecture of the margin, the sedimentary environments and facies and related geomorphological elements that are active in the shaping of the margin appear to be mainly controlled by the physiography of the basin itself and by the geology of the hinterland that results from the structural evolution of the adjacent land areas. An evolution from a generalized slope bypass setting to a prograding offlapping slope architecture is recognized and explained as due to the transition from an out-of-grade to a graded profile progressing from the early post-rift stage to the later margin growth stage. Along the Sicilian margin, a constructional apron, mainly consisting of channel levee deposits, makes up much of the studied sedimentary package and reflects a high sediment supply related to the large size of river catchments on land. In contrast, the northeastern Sicilian basin sector is a destructional margin that flanks a region where small river drainage systems result in a low sediment supply to the basin and a continued high uplift rate promotes slope instability; as a consequence, the basin infill is here almost completely made up of mass-wasting deposits. In the Calabrian margin, a first phase of low sediment supply probably coinciding with the filling of the further inland Gioia Tauro half-graben was followed by the establishment of the Gioia-Mesima channel-canyon system that, furnishing an effective sediment flux to the margin, allows the formation of an intraslope depositional body consisting of channelized turbidite lobes.

GPS monitoring of vertical ground motion in northern Ardenne–Eifel: five campaigns (1999–2003) of the HARD project

We present the HARD project of GPS monitoring of vertical ground motion in NE Ardenne and Eifel (western Europe). Its main purposes are to get a better insight into the present-day rates of vertical ground motion in intraplate settings and to identify the various causes of these motions. Since 1999, we have carried out yearly campaigns of simultaneous GPS measurements at 12 sites situated so as to sample the different tectonic subunits of the study area and especially to record potential displacements across the seismogenic Hockai fault zone. Five campaigns (1999–2003) have been processed currently. Key issues of the data processing with the Gamit software are discussed and first results are presented. Though temporally consistent in many cases, the obtained vertical motion rates are spatially highly variable. They are also much too high (several mm/year) to support a tectonic interpretation, and a long-term influence of groundwater level variations is proposed to account for the observed motions. This influence should be distinguished from seasonal variations and from inter-survey variations linked to the varying degree of soil and subsoil drying off during the successive spring surveys.

Sea-level change along the Italian coast for the past 10,000 yr

Relative sea-level change along the Italian coast and adjacent seas—the combined result of eustasy, glacio-hydro-isostasy and vertical tectonic motion—exhibits considerable spatial and temporal variability throughout the Holocene. The tectonic contribution can be evaluated from the elevation of MIS 5.5 shoreline-markers that are well developed in many localities and the eustatic and isostatic contributions can be predicted from models of ice sheets and earth rheology. Discrepancies between observed Holocene sea levels and model predicted values provide the information for refining the model parameters, including the tectonic rates of vertical movement. Recent and new Holocene and MIS 5.5 information from 30 sites in Italy has been evaluated and compared with model results to calibrate the predictive model. The resulting parameters for the earth rheology and for the eustatic (ice-volume equivalent) sea-level function are consistent with results from regions outside of the Mediterranean and reflect global values. Using the calibrated model parameters the relative sea-level change due to eustasy and the concomitant isostasy is predicted across the central Mediterranean region. Holocene tectonic rates of vertical motion are also given for the Italian coastal zone. At most sites where the MIS 5.5 shoreline occurs above or below its ‘tectonically stable’ position, the inferred rates of vertical crustal displacements are consistent with the assumption that average rates for the past ∼125,000 years are comparable to the average Holocene rates, but at some locations in eastern Sicily and southern Calabria the Holocene rates exceed the longer term average rates.

Use of data storage tags to quantify vertical movements of cod: effects on acoustic measures

Abstract Depth data from archival tagging studies of cod (Gadus morhua) were used in three different analyses with the aim of testing basic assumptions of cod behaviour. Examination of post-release depth profiles from cod tagged in the Barents, North, and Irish Seas revealed that some cod underwent a post-release period of adaptation to increasing depth as they readjusted their buoyancy to its pre-tagging level. This depth adaptation behaviour was characterized by gradually increasing mean depth, and enabled the calculation of neutral-buoyancy compliant descent rates, which were less than 1 m h−1. Estimated rates of vertical movement were shown to be highly dependent upon the frequency at which depth was sampled. Maximum estimated rates of ascent and descent from sampling intervals of 10 or 15 min were inconsistent with the maintenance of neutral buoyancy, but estimates from sampling intervals greater than 1 h were not. Calculation of tilt angles using depth data sampled at 10-s intervals showed that cod were often tilted more than 5° relative to the horizontal, and that this effect was more pronounced at night. These findings suggest that basic assumptions regarding cod physiology and behaviour require revision if the accuracy and precision of acoustic methods are to be improved.

A geophysically constrained large ensemble analysis of the deglacial history of the North American ice-sheet complex

Past reconstructions of the deglaciation history of the North American (NA) ice-sheet complex have relied either on largely unconstrained and limited explorations of the phase space of solutions produced by glaciological models or upon geophysical inversions of relative sea-level (RSL) data which suffer from incomplete geographic coverage of the glaciated regions, load history amplitude/timing ambiguities, and a lack of a priori glaciological self-consistency. As a first step in the development of a much more highly constrained deglaciation history, we present a synthesis of these two previously disjoint methodologies based on a large ensemble of glacial cycle simulations using a three-dimensional thermo-mechanically coupled ice-sheet model. Twenty glacial system model parameters, chosen so as to best cover the true deglacial phase space, were varied across the ensemble. Furthermore, a new high-resolution digitized ice margin chronology was imposed on the model in order to significantly limit the uncertainties associated with deglacial climate forcing. The model is simultaneously constrained by a large set of high-quality RSL histories, a space geodetic observation of the present-day rate of vertical motion of the crust from Yellowknife and a traverse of absolute gravity measurements from the west coast of Hudson Bay southward into Iowa. The general form of the Last Glacial Maximum (LGM) ice topography that ensues when model results are subject to geophysical constraints is an ice sheet dominated by a large (3.3– 4.3 km maximum ice thickness) Keewatin dome to the west of Hudson Bay connected to a major ice ridge running southeast to the Great Lakes, together with a Hudson Bay region that has relatively thin ice and an Arctic region heavily incised by open water and/or ice shelves. Geographically restricted fast flows due to sub-glacial till deformation are shown to be critical to obtaining such a multi-domed late glacial Laurentide Ice Sheet structure, one that has been previously inferred on the basis of geomorphological data and that is required to fit the geophysical constraints. Our results further suggest that the NA contribution to LGM eustatic sea-level drop is likely to be in the range of 60– 75 m .

Erosional feedbacks and the oscillation of ice masses

An analytical solution to the development of a glacier or ice sheet in a region where the underlying rock rises steadily shows that the ice mass oscillates in size, independefntly of changes in the climate, in response to a feedback in which ice thickness is linked to topography by ice‐induced erosion. The rate of vertical movement of the underlying rock uplift and the parameters governing ice erosion, ablation, and precipitation determine the period of oscillation. Two‐dimensional numerical simulations show that the tectonic uplift rate is the most important control on the period of oscillation and that the feedback period is likely to be between 10 and 100 kyr. An examination of sediment data from the Deep Sea Drilling Project shows evidence of ice mass oscillations in the Chugach‐St. Elias Mountains and in the Himalayas with periods consistent with those produced by the proposed mechanism. Localized changes in glacial extent may not therefore always be the consequence of climate change, and care must be taken in interpreting evidence of glacial advance and retreat.

Tide gauge records of uplift along the northern Pacific‐North American plate boundary, 1937 to 2001

Vertical crustal motions at 15 sites along the northern Pacific‐North America plate boundary are determined using relative sea level changes from tide gauge records. Our analysis is based on monthly mean sea levels, from which barometric pressure and seasonal effects are removed. The records are corrected for common‐mode oceanographic variations. These records are statistically examined for non‐linear behavior related to glacial isostatic, tectonic and postseismic effects. To estimate land uplift rates, the local effect of global sea level rise is removed from the relative sea level rates. Slow rates of vertical motion are observed along the southern strike‐slip plate boundary. The extremely rapid uplift of the northern strike‐slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater‐glacier retreat in Glacier Bay and regional post‐Little Ice Age deglaciation. Isostatic modeling indicates a mantle viscosity of ∼2 × 1019–5 × 1019 Pa s, similar to that found elsewhere along the Pacific‐North America plate margin. At Yakutat, near the transition of plate motion from strike‐slip to subduction, complex non‐linear behavior is evident, with a significant change in uplift rate following the 1979 St. Elias earthquake. Non‐linear uplift rates are predominant within the 1964 Great Alaskan earthquake near‐field. Rapid uplift at Kodiak during a 3.5 year period starting mid‐1964 totaled 47 ± 8 cm. Anchorage, Seward and Seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid‐1972. Since mid‐1972, uplift rates have increased steadily at Anchorage, Seward, Cordova, and Valdez. During this period Nikiski and Kodiak show decreasing uplift rates.

Crustal uplift in the south central Alaska subduction zone: New analysis and interpretation of tide gauge observations

We have examined tide gauge measurements of apparent sea level height in south central Alaska to determine the history of crustal uplift subsequent to the 1964 Prince William Sound earthquake. There are spatial and temporal variations in the uplift rate since the 1994 earthquake that depend on the location of the tide gauge relative to the coseismic rupture features. At Seward, on the eastern side of the Kenai Peninsula, we find slow uplift that is consistent with elastic strain accumulation at the locked North American‐Pacific Plate boundary. Conversely, at Seldovia and Nikiski, on the western side of the Kenai Peninsula, we find persistent rapid uplift of ∼10 mm yr−1 that may be longterm transient response to the earthquake but that cannot be sustained over the entire several hundred year recurrence interval for a great earthquake. Farther to the southwest, at Kodiak, the rate of uplift is several millimeters per year but has slowed significantly over the past three and a half decades. To the east of the Kenai Peninsula we find subsidence at Cordova and an uncertain behavior at Valdez. At Cordova, and to a lesser extent Valdez, there is a mathematically significant time dependence, although the evidence for the time dependence is less compelling than at Kodiak. At Anchorage, there is little evidence of vertical motion since the earthquake. The along‐strike spatial variability in the relaxation time of the rates of vertical motion since the 1964 earthquake may be related to variations in the updip coseismic slip during the megathrust event.

A 4,700-Year Record of Lake Level and Isostasy for Lake Michigan

Four relative lake-level curves (RLLCs), produced from five sites bordering Lake Michigan, show similar timings of high and low lake-levels during the late Holocene. However, glacial isostatic-adjustments and possibly tectonism experienced at each site are superimposed on these records of relative lake-level change. This effect causes the RLLCs to diverge from each other with time. The absolute magnitudes of lake-level fluctuations for the late Holocene can only be determined by quantifying and subtracting the component of vertical ground-movement from each RLLC. Both an exponential rate and a constant-rate equation for a shoreline undergoing isostatic adjustment were used to model vertical movement for each site. Results show that for at least the last 4,000 calendar years (cal BP) of record, vertical movement in Lake Michigan has obeyed both types of equations. The two models yield similar results because rates of vertical movement of the shorelines around Lake Michigan are small and the time frame for which lake-level data are available is so short that the exponential nature of isostatic change is not expressed. Except for the southern shore of Lake Michigan, all the study sites have experienced uniform isostatic uplift consistent with trends reported by the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data (1977) and Tushingham (1992). The southern shore of Lake Michigan, however, experienced a change in uplift rate relative to the Port Huron outlet about 1,400 cal BP. The residuals between the calculated rates of vertical movement at each site and its corresponding RLLC are a record of water-level change experienced at each site. Within the resolution of the technique used to construct the RLLCs, all the residual curves should be, and are, similar. A Fourier smoothing of the combined residual curves yields a “eustatic” lake-level curve for Lake Michigan over the past 4,700 cal BP. The results of the Fourier smoothing identify major lake-level fluctuations such as the Nipissing II and Algoma phases of ancestral Lake Michigan. The technique also resolves lower magnitude and shorter duration quasi-periodic lake-level fluctuations of about 160 years (120 to 200 years).

Current vertical movement demonstrated by comparative levelling in Brittany (northwestern France)

The current vertical movement of the Earth's crust is demonstrated through comparative levelling. The two methods presented are complementary. First we constructed a profile along traverses in order to highlight localized features such as recurrent faulting or block tilting. Second we produced a map of relative current vertical movement rates and their error coefficients using a geostatistical kriging method. These methods were applied to Brittany (northwestern France) and revealed that (1) the ancient NW–SE Rance and Morlaix faults are presently reactivated, and (2) the west of the region is tilted with uplift which is interpreted as a lithospheric deformation.

Distribution of vertical crustal movement rates in the Tohoku district, Japan, predicted by least-squares collocation

Least-squares prediction using an empirically deduced local covariance function was performed to investigate the temporal change in the rates of vertical crustal movements in the Tohoku district, Japan. Levelling data covering an area of approximately 450 × 275 km2 observed between 1966 and 1995 were used and the results shown in the form of contour maps. Firstly we derived a covariance function of the rates of vertical crustal movement with a Gaussian form function. We used this function to estimate the spatial distribution of the rates of vertical crustal movements. By the present method, a steady tilt of the Tohoku district to the east, toward the Japan Trench and an areal uplift in the southwestern part were well reproduced. Moreover, a significant temporal change in vertical movement rates is clearly seen.