Vertical Crustal Displacements Research Articles

An EOF and SVD analysis of interannual variability of GPS coordinates, environmental parameters and space gravity data

Eleven years, 1999–2010, of GPS positions of stations located in Europe and the Mediterranean were analyzed together with time series of atmospheric pressure, terrestrial water storage, and surface mass anomalies provided by the GRACE gravity mission. The Empirical Orthogonal Functions (EOF) technique was applied to single variables data series detrended and de-seasoned to identify the main modes of interannual variability in both time and space. For the GPS coordinates, the analysis has revealed the presence of significant interannual fluctuations which were also identified in the time series of the environmental parameters and of the space gravity data. A prominent feature common to the main modes of the time components of all variables is a slope inversion occurring around 2003–2004. During 2003 most of the European continent was affected by a severe drought. A second type of analysis was performed by applying the Singular Value Decomposition (SVD) approach to a few series of variable pairs to study the coupled space/time variability. This mathematical tool is used to examine possible cause-effect physical relationships between variables pairs. The analysis shows, for example, for the atmospheric pressure and the up coordinate that the first two SVDs account for about 97% of the total covariance. The clear anticorrelation observed between the two SVD1 spatial patterns represents the vertical crustal displacements associated with variations in atmospheric pressure. East–West (EW) and North–South (NS) gradients of the environmental parameters and of the GRACE surface mass anomalies were computed and compared to the EOFs of the east and north GPS coordinates respectively. Significant correlations were found, in particular, between the EW atmospheric pressure gradient and the east EOFs and between the GRACE EW and NS gradients and the east and north EOFs respectively. Significant correlations were also identified between the Multivariate ENSO Index (MEI) and the EOFs of GPS coordinates.

Isostatic stability of the East Antarctic station Dumont d'Urville from long-term geodetic observations and geophysical models

Geodetic measurements of the vertical crustal displacement collocated with absolute gravity changes provide a discriminatory measurement of present-day glacial changes, versus more deeply seated rock motions caused by glacial isostatic adjustment (GIA). At the East Antarctic station of Dumont d’Urville, we compare the displacements derived from continuous DORIS (1993.0– 2006.0) and Global Positioning System (GPS) (1999.0–2005.7) data, and observed changes in absolute gravity (2000–2006), with the predicted vertical displacement and change in gravity from GIA modelling. The geodetic results have mutual self-consistency, suggest station stability and provide upper bounds on both GIA and secular ice mass changes. The GIA models tend to predict amplitudes of rock motion larger than those observed, and we conclude that this part of Antarctica is probably experiencing a slight gain in ice mass, in contrast to West Antarctica.

Dependence of waveform of near-field coseismic ionospheric disturbances on focal mechanisms

AbstractUsing Total Electron Content (TEC) measurements with Global Positioning System we studied ionospheric responses to three large earthquakes that occurred in the Kuril Arc on 04 October 1994, 15 November 2006, and 13 January 2007. These earthquakes have different focal mechanisms, i.e. high-angle reverse, low-angle reverse, and normal faulting, respectively. TEC responses to the 2006 and 2007 events initiated with positive and negative changes, respectively. On the other hand, the initial TEC changes in the 1994 earthquake showed both positive and negative polarities depending on the azimuth around the focal area. Such a variety may reflect differences in coseismic vertical crustal displacements, which are dominated by uplift and subsidence in the 2006 and 2007 events, respectively, but included both in the 1994 event.

Isostatic stability of the East Antarctic station Dumont d’Urville from long-term geodetic observations and geophysical models

Geodetic measurements of the vertical crustal displacement collocated with absolute gravity changes provide a discriminatory measurement of present-day glacial changes, versus more deeply seated rock motions caused by glacial isostatic adjustment (GIA). At the East Antarctic station of Dumont d’Urville, we compare the displacements derived from continuous DORIS (1993.0– 2006.0) and Global Positioning System (GPS) (1999.0–2005.7) data, and observed changes in absolute gravity (2000–2006), with the predicted vertical displacement and change in gravity from GIA modelling. The geodetic results have mutual self-consistency, suggest station stability and provide upper bounds on both GIA and secular ice mass changes. The GIA models tend to predict amplitudes of rock motion larger than those observed, and we conclude that this part of Antarctica is probably experiencing a slight gain in ice mass, in contrast to West Antarctica.

A comparison of annual vertical crustal displacements from GPS and Gravity Recovery and Climate Experiment (GRACE) over Europe

We compare approximately 3 years of GPS height residuals (with respect to the International Terrestrial Reference Frame) with predictions of vertical surface displacements derived from the Gravity Recovery and Climate Experiment (GRACE) gravity fields for stations in Europe. An annual signal fit to the residual monthly heights, corrected for atmospheric pressure and barotropic ocean loading effects, should primarily represent surface displacements due to long‐wavelength variations in water storage. A comparison of the annual height signal from GPS and GRACE over Europe indicates that at most sites, the annual signals do not agree in amplitude or phase. We find that unlike the annual signal predicted from GRACE, the annual signal in the GPS heights is not coherent over the region, displaying significant variability from site to site. Confidence in the GRACE data and the unlikely possibility of large‐amplitude small‐scale features in the load field not captured by the GRACE data leads us to conclude that some of the discrepancy between the GPS and GRACE observations is due to technique errors in the GPS data processing. This is evidenced by the fact that the disagreement between GPS and GRACE is largest at coastal sites, where mismodeling of the semidiurnal ocean tidal loading signal can result in spurious annual signals.

Vertical crustal displacements due to surface fluid changes

Using the model data for surface mass changes of the atmosphere, ocean, soil moisture and snow depth, the vertical crustal displacements of 25 ficual stations in China were calculated according to the loading theory. From the spectral analysis of the results, we can see that the periods of displacements are 12 months and the semi-periods are 6 months. The results also show that the maximum seasonal displacements can reach 20 mm and even larger. The covariance analyses and significance tests show that the coefficients of 96 percent of the stations are significant at the 0.1 significance level. The results show that one of the reasons of the vertical crustal displacements is the changing surface fluid loads.

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.

Coastal deformation between the Versilia and the Garigliano plains (Italy) since the last interglacial stage

AbstractThe opening of the north‐central Tyrrhenian Sea is the result of the Cretaceous–Paleogene alpine collision, which triggered a series of regional uplift, subsidence and transcurrent tectonic mechanisms along the coastal Tyrrhenian sectors of peninsular Italy. These tectonic processes, in conjunction with the effects of glacio‐ and hydro‐isostasy during the Quaternary, produced substantial crustal responses that, in some cases, reached metres in extent. In the study of coastal neotectonics, geomorphological markers of the last interglacial maximum, corresponding to marine isotope stage 5.5, are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr. Through altimetrical, palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913, combined with an additional set of data reported here, a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern Tuscany and southern Latium is presented. The reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors. This has been done by carefully choosing the eustatic marker, among those available at each study site, in order to minimize the margin of error associated with the measurements. Copyright © 2003 John Wiley & Sons, Ltd.

Slip kinematics and dynamics during and after the 1995 October 9Mw=8.0 Colima-Jalisco earthquake, Mexico, from GPS geodetic constraints

We use horizontal and vertical crustal displacements derived from GPS measurements at 26 sites in western Mexico to study the coseismic and post-seismic kinematics and dynamics of the 1995 October 9 (Mw = 8.0) Colima–Jalisco earthquake along the Middle America Trench. The measurements bracket the entire landward edge of the approximately 150 km long rupture zone and span a 4 yr period for most sites. We solve for the temporal evolution of slip along the subduction interface by inverting GPS displacements for the coseismic and four post-seismic intervals (March 1995–March 1999), subject to the assumption that the crust responds elastically to slip along a shallow-dipping, curved subduction interface. Coseismic rupture of up to 5 m was largely focused above depths of 20 km and was limited to a 120–140 km long segment of the subduction zone. Within one week of the earthquake, post-seismic slip migrated downdip to depths of 16–35 km, where it has since decayed logarithmically. We also find evidence for shallow aseismic slip during 1996 or early 1997 northwest of the coseismic rupture zone and increasingly widespread relocking of shallow regions of the subduction interface after early 1997. The relative lack of afterslip in shallow regions of the subduction interface suggests that the interface lies in the unstable frictional regime and hence is strongly coupled between earthquakes. By 1999, the cumulative slip moment associated with post-seismic slip equaled ∼70 per cent of the coseismic moment, with nearly all of this slip occurring downdip from the coseismic rupture zone. The migration of slip after the earthquake to a deeper and presumably velocity-strengthening area of the subduction interface and the logarithmic decay of afterslip conform to the qualitative and quantitative predictions of a model in which the fault kinematics are prescribed by rate- and state-variable frictional laws. However, misfits to the geodetic displacements exceed the average displacement uncertainties for all epochs, implying one or more of the following: (1) the elastic response is heterogeneous due to slip along unmodelled upper crustal faults or variations in the elastic properties of the crust; (2) other post-seismic mechanisms such as viscoelastic or poroelastic effects contribute to or possibly dominate the post-seismic response; (3) we have underestimated the uncertainties in the GPS displacements.

Does rapid change in ice loading modulate strain accumulation and release in glaciated, tectonically active regions

There are major glaciated regions of the world that are also seismologically active. Changes in the thickness of ice due to glacier surges, advances, or retreats produce stress changes that may be a significant fraction of the tectonic stress accumulated during an earthquake cycle. The changes in ice loading can affect both the normal and shear stress on a fault with stresses being enhanced or reduced depending on glacier and fault geometry. The stress change has a nearly instantaneous elastic component and a longer time‐scale viscoelastic component. Thus I propose that glacier motion can produce geodetically significant horizontal and vertical crustal displacements and can affect strain, strain rate, and the time of occurrence of earthquakes. In regions that are not tectonically active, rapid ice motion can also produce locally significant and geodetically detectable crustal deformations.

Crustal tilting derived from Holocene sea‐level observations along the east coast of Hokkaido in Japan and upper mantle rheology

Late Holocene sea‐level observations at sites along the east coast of Hokkaido in Japan indicate a gradual decrease of the altitude of relative sea‐level eastward toward the tip of Nemuro Peninsula. These observations in seismically active areas can be explained by glaciohydroisostatic adjustment due to the last déglaciation for an Earth model with a thin lithosphere of 30–40 km thickness and with no low viscosity layer, or with a 25 km lithosphère overlying a low viscosity layer less than 50 km, although more data as a function of time are needed to distinguish these models. Thus the vertical crustal displacement associated with the subduction of the Pacific plate seems to has not been cumulated on a time scale of 103–104 years.

Constraints on Alleghanian vertical displacements in the southern Appalachian Piedmont, based on aluminum-in-hornblende barometry

Aluminum-in-hornblende barometry of Alleghanian granitoid plutons in the southern Appalachian Piedmont provides new constraints on synorogenic, vertical crustal displacements. Systematic differences in depths of emplacement between plutons in the Carolina slate belt and the Charlotte and Kings Mountain belts appear to confirm previously proposed Alleghanian folding of earlier isothermal surfaces. The Kiokee and Raleigh belts represent ductile horsts that have undergone as much as 18.5 and 15.1 km, respectively, or normal displacement along boundary faults prior to late Allegbanian dextral shearing. Plutons in or near the Eastern slate and Belair belts were emplaced at depths similar to those in the Carolina slate belt. Plutons partly or completely covered by Atlantic Coastal Plain sediments, however, appear to have been emplaced deeper and earlier, perhaps reflecting uplift prior to Alleghanian time. Geothermal gradients for the various lithotectonic belts estimated from these data are consistent with the previously recognized decrease in Alleghanian metamorphic overprinting away from the Kiokee-Raleigh belt thermal axis.

Late Cenozoic turbidite and contourite deposition in the southern Brazil Basin

Piston and giant gravity cores, together with 3.5 kHz and seismic profiles, reveal a complex pattern of dispersal of bioclastic calcareous turbidites in the southern Brazil Basin. Extensive canyons up to 500 m deep dissect the steep north flank of the Rio Grande Rise, and serve as conduits for turbidity currents which have eroded modern sediments as well as outcrops of Tertiary and late Cretaceous strata. The resulting turbidites are up to several meters thick in channel axes, and commonly several cm thick at distances up to hundreds of km from the canyon source region. Individual turbidity currents were apparently sufficiently strong to transport fine-grained components several hundred meters upslope and several hundred km laterally across the Brazil Basin. The lithology of both proximal and distal turbidites, their presence well below the modern CCD, and the lack of correspondence between their presence and that of displaced Antarctic diatoms, verifies that these calcareous deposits are not products of episodic Antarctic Bottom Water flow, but originated from a shallow-water source area. The late Pleistocene and Holocene witnessed major turbidity current episodes at intervals on the order of 50,000 yrs, with at least two episodes coinciding approximately with interglacials following Terminations I and II. Sediments older than isotopic stage 8 (∼275,000 yrs B.P.) include thinly-laminated “contourites”. We interpret these units as intervals of normal pelagic sedimentation which were subsequently reworked under the influence of AABW pulses. Episodes of intensified AABW flow may have immediately preceded the onset of major glacial episodes, extending corrosive eastward-flowing AABW to relatively shallow depths (4200—4300 m) along the north flank of the Rio Grande Rise. The undercutting of outcropping strata by chemical dissolution at the base of the faulted north flank has probably played a critical role in the initiation of canyon-cutting. Episodic slumping due to oversteepening and the generation of debris flows progressively enlarged the canyons upslope in a dendritic pattern and gradually extended the canyons to shallower elevations on the Rise. Vertical crustal displacements associated with the Rio Grande Fracture Zone have controlled the pathway of AABW in the southern Brazil Basin, and accentuated the steep relief on the north flank of the Rise. These two processes have been essential conditions for the extensive canyon cutting and subsequent dispersal of carbonate turbidites over the Brazil Basin.

Geodetic leveling and its applications

The inherent precision of spirit leveling has preserved its utility as a geodetic measurement system for over a century. While various instrumental and procedural modifications designed to enhance this precision have been introduced over the years, the basic measurement system has remained virtually unchanged since the mid‐nineteenth century. Possible systematic error has dictated the majority of the procedural and instrumental requirements associated with geodetic leveling; the physical source(s) of several of these errors remain poorly understood. Statistically independent random errors, which accumulate according to the square root of the survey distance, are generally controlled through redundancy and procedural randomization; they range from 0.5 mm L1/2 for the highest‐order modern leveling to about 6 mm L1/2 for the lowest‐order nineteenth‐century geodetic surveys, where L is the survey distance in kilometers. Height differences are conceptually distinct from observed or measured elevation differences in the sense that the former are uniquely defined, whereas the latter are path dependent, a distinction that arises from the nonparallelism of the equipotential surfaces of the earth’s gravity field. The number of possible height systems is virtually limitless. They include the systems of geopotential numbers and dynamic heights; although neither of these systems is geometrically informative, each provides perfectly valid height characterizations that may be especially useful in the solution of certain physical problems. The most generally used system of heights is the orthometric height system; the resulting heights are true geometric heights above the geoid. Normal height systems are referred to the quasi‐geoid rather than the geoid. Each of the various height systems meets the requirement of uniqueness, and none can be viewed as being conceptually superior. Conversion of the observed elevation differences obtained from leveling into uniquely defined height differences requires the application of a gravity‐dependent correction. Because gravity coverage in North America was generally sparse until recently, an approximation for this correction, which provides for the effects of the poleward covergence of the equipotential surfaces, has usually been used on this continent. Heights have been traditionally referred to mean sea level as a datum, a usage that implies coincidence between mean sea level and the geoid (or quasi‐geoid). Because the determination of mean sea level is dependent on the length of the observation period, because its definition makes no allowance for vertical crustal displacements or changes in eustatic sea level, and because its definition disregards the demonstrable existence of sea surface topography, local mean sea level generally departs from the geoid. This introduces errors in computed heights that probably equal or exceed those due to leveling. Repeated levelings continue to provide the best basis for determining terrestrial vertical displacements. These displacements are necessarily measured with respect to the time‐dependent (instantaneous) geoid. Analysis of changes in the orthometric correction and changes in the geoid as a function of changes in gravity indicates that height determinations are almost insensitive to temporal variations in gravity. The simplest and probably the most accurate procedure for determining vertical displacements is based on direct comparisons between observed elevations derived from repeated levelings along the same line. The estimated errors associated with these displacements are a function of the precision of the utilized levelings and have been shown to be much smaller than those associated with heights. A smoothed representation of the vertical displacement field can be obtained by the fitting of a mathematical surface to the results of segmented relevelings. Surface‐fitting techniques usually tend to subdue short‐wavelength features, but they are especially useful in depicting artificially induced subsidence and broadly defined tectonic uplift or collapse.

A wave-like pattern of holocene crustal warping in eastern Asia

Radiocarbon dating of coral and marine molluscs from raised beaches along the coasts of Taiwan, the Ryukyu Islands and Honshu indicates apparently regular vertical crustal displacements during the Holocene. The crustal warping seemingly followed a wave-like pattern corresponding to a broad sine curve with a wave height of about 20 m and wave length of 760 km. It is estimated that the wave migrated southward at a rate of approximately 114 m per year.

Areas of tectonic activity in the United States as indicated by earthquake epicenters

A study based on earthquake occurrences in the United States shows several zones of continuing seismic activity. Over the past 30 years there is a suggestion of systematic variations in seismic activity following what appears to be a three‐year cycle which is superimposed on a longer period. Areas of activity can not be related to either geologic age or type of structure. In California transcurrent movement on known faults is associated with seismic activity. In the other western states activity is associated with the boundaries of areas of epeirogenic uplift and subsidence and appears to involve predominantly vertical crustal displacement. In the Midcontinent area activity for the most part is associated with positive crystalline rock tectonic elements and their borders. In the Appalachian area activity is associated with the zones of overthrusts and shear. A conspicuous zone of earthquakes paralleling the Appalachians from Missouri to the St. Lawrence River valley while not related to known geologic controls does follow a zone of better‐than‐normal seismic transmissibility. The depth of focus varies from area to area and appears to be related directly to crustal thickness and possibly also changes in crustal rigidity with depth. No direct relation is noted between areas of isostatic unbalance and seismic activity or variations in degree of seismic activity with changes in crustal thickness. For the most part, it appears local stress conditions are dominant in causing earthquakes.

Vertical Crustal Displacement in the Seismic Region of Itô, on the East Coast of the Idu Peninsula

Vertical Crustal Displacement in the Seismic Region of Itô, on the East Coast of the Idu Peninsula