Vertical Land Motion Rates Research Articles

Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast.

Coastal communities are vulnerable to multihazards, which are exacerbated by land subsidence. On the US east coast, the high density of population and assets amplifies the region's exposure to coastal hazards. We utilized measurements of vertical land motion rates obtained from analysis of radar datasets to evaluate the subsidence-hazard exposure to population, assets, and infrastructure systems/facilities along the US east coast. Here, we show that 2,000 to 74,000 km2 land area, 1.2 to 14 million people, 476,000 to 6.3 million properties, and >50% of infrastructures in major cities such as New York, Baltimore, and Norfolk are exposed to subsidence rates between 1 and 2 mm per year. Additionally, our analysis indicates a notable trend: as subsidence rates increase, the extent of area exposed to these hazards correspondingly decreases. Our analysis has far-reaching implications for community and infrastructure resilience planning, emphasizing the need for a targeted approach in transitioning from reactive to proactive hazard mitigation strategies in the era of climate change.

20thto 21stCentury Relative Sea and Land LevelChanges in Northern California:Tectonic Land Level Changes and theirContribution to Sea-Level Rise, Humboldt BayRegion, Northern California

Sea-level changes are modulated in coastal northern California by land-level changes due to the earthquake cycle along the Cascadia subduction zone, the San Andreas plate boundary fault system, and crustal faults. Sea-level rise (SLR) subjects ecological and anthropogenic infrastructure to increased vulnerability to changes in habitat and increased risk for physical damage. The degree to which each of these forcing factors drives this modulation is poorly resolved. We use NOAA tide gage data and ‘campaign’ tide gage deployments, Global Navigation Satellite System (GNSS) data, and National Geodetic Survey (NGS) first-order levelling data to calculate vertical land motion (VLM) rates in coastal northern California. Sea-level observations, highway level surveys, and GNSS data all confirm that land is subsiding in Humboldt Bay, in contrast to Crescent City where the land is rising. Subtracting absolute sea-level rate (~1.99 mm/year) from Crescent City (CC) and North Spit (NS) gage relative sea-level rates reveals that CC is uplifting at ~2.83 mm/year and NS is subsiding at ~3.21mm/year. GNSS vertical deformation reveals similar rates of ~2.60 mm/year of uplift at Crescent City. In coastal northern California, there is an E-W trending variation in vertical land motion that is primarily due to Cascadia megathrust fault seismogenic coupling. This interseismic subsidence also dominates the N-S variation in vertical land motion in most of the study region. There exists a second-order heterogeneous N-S trend in vertical land motion that we associate to crustal fault-related strain. There may be non-tectonic contributions to the observed VLM rates.

Constraint of glacial isostatic adjustment in the North Sea with geological relative sea level and GNSS vertical land motion data

SUMMARYIn this study, we focus on improved constraint of the glacial isostatic adjustment (GIA) signal at present-day, and its role as a contributor to present-day sea level budgets. The main study area extends from the coastal regions of northwestern Europe to northern Europe. Both Holocene relative sea level (RSL) data as well as vertical land motion (VLM) data are incorporated as constraints in a semi-empirical GIA model. 71 geological rates of GIA-driven RSL change are inferred from Holocene proxy data and 108 rates of vertical land motion from GNSS provide an additional measure of regional GIA deformation. Within the study area, the geological RSL data complement the spatial gaps of the VLM data and vice versa. Both data sets are inverted in a semi-empirical GIA model to yield updated estimates of regional present-day GIA deformations. A regional validation using tide gauges is presented for the North Sea, where the GIA signal may be complicated by lateral variations in Earth structure and existing predictions of regional and global GIA models show discrepancies. The model validation in the North Sea region suggests that geological data are needed to fit independent estimates of GIA-related RSL change inferred from tide gauge rates, indicating that geological rates from Holocene data do provide an important additional constraint for data-driven approaches to GIA estimation.

Assessment of Future Flood Hazards for Southeastern Texas: Synthesizing Subsidence, Sea‐Level Rise, and Storm Surge Scenarios

AbstractRecent hurricanes highlight shortcomings of flood resilience plans in Texas that can worsen with climate change and rising seas. Combining vertical land motion (VLM) with sea‐level rise (SLR) projections and storm surge scenarios for the years 2030, 2050, and 2100, we quantify the extent of flooding hazards. VLM rates are obtained from GNSS data and InSAR imagery from ALOS and Sentinel‐1A/B satellites. VLM is resampled and projected on LIDAR topographic data, then multiple inundation and flooding scenarios are modeled. By the year 2100, over 76 km2 are projected to subside below sea level. Subsidence increases the area of inundation over SLR alone by up to 39%. Under the worst‐case composite scenario of an 8‐m storm surge, subsidence, and the SLR RCP8.5, the total affected area is 1,156 km2. These models enable communities to improve flood resiliency plans.

Revisiting Vertical Land Motion and Sea Level Trends in the Northeastern Adriatic Sea Using Satellite Altimetry and Tide Gauge Data

We propose a revisited approach to estimating sea level change trends based on the integration of two measuring systems: satellite altimetry and tide gauge (TG) time series of absolute and relative sea level height. Quantitative information on vertical crustal motion trends at six TG stations of the Adriatic Sea are derived by solving a constrained linear inverse problem. The results are verified against Global Positioning System (GPS) estimates at some locations. Constraints on the linear problem are represented by estimates of relative vertical land motion between TG couples. The solution of the linear inverse problem is valid as long as the same rates of absolute sea level rise are observed at the TG stations used to constrain the system. This requirement limits the applicability of the method with variable absolute sea level trends. The novelty of this study is that we tried to overcome such limitations, subtracting the absolute sea level change estimates observed by the altimeter from all relevant time series, but retaining the original short-term variability and associated errors. The vertical land motion (VLM) solution is compared to GPS estimates at three of the six TGs. The results show that there is reasonable agreement between the VLM rates derived from altimetry and TGs, and from GPS, considering the different periods used for the processing of VLM estimates from GPS. The solution found for the VLM rates is optimal in the least square sense, and no longer depends on the altimetric absolute sea level trend at the TGs. Values for the six TGs’ location in the Adriatic Sea during the period 1993–2018 vary from −1.41 ± 0.47 mm y−1 (National Research Council offshore oceanographic tower in Venice) to 0.93 ± 0.37 mm y−1 (Rovinj), while GPS solutions range from −1.59 ± 0.65 (Venice) to 0.10 ± 0.64 (Split) mm y−1. The absolute sea level rise, calculated as the sum of relative sea level change rate at the TGs and the VLM values estimated in this study, has a mean of 2.43 mm y−1 in the period 1974–2018 across the six TGs, a mean standard error of 0.80 mm y−1, and a sample dispersion of 0.18 mm y−1.

Uncertainty Estimation in Regional Models of Long‐Term GIA Uplift and Sea Level Change: An Overview

AbstractThis work provides a comparison of four approaches that can be used to describe uncertainty in models of the long‐term glacial isostatic adjustment (GIA) process. The four methods range from pessimistic to optimistic representations of GIA uncertainty. Each estimation method is applied to selected one dimensional GIA model predictions and compared with vertical land motion data from Global Positioning System (GPS) measurements across Fennoscandia and North America. The methods are evaluated relative to two main properties: (1) their expected ability to separate non‐GIA from GIA signals and (2) their estimated statistical appropriateness given a specific GIA model and data set. For the first point, non‐GIA signals are considered isolated from the long‐term (millennial time scale) GIA signal at sites where measurement and model uncertainties do not overlap. Across methods, the frequency and accuracy with which non‐GIA signals are separated from GIA signals in GPS data display both consistent similarities and disparities. For the second point, we compare model predictions with rates of vertical land motion and relative sea level change that have been cleaned of non‐GIA signals to determine the most appropriate value of model uncertainty and relate the findings to the four approaches. Best fit inferences suggest that within deglaciation centers, GIA model uncertainty is up to ~2 mm/yr (vertical land motion). Likewise, away from the former ice sheet centers, GIA uncertainty for relative sea level change is inferred to be ~0.3–0.5 mm/yr along the U.S. East Coast and ~0.6–0.8 mm/yr in the North Sea.

Tracking California's sinking coast from space: Implications for relative sea-level rise.

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, records of high-resolution vertical land motion rates are scarce due to sparse instrumentation, and hazards to coastal communities are underestimated. Here, we considered a ~100-km-wide swath of land along California's coast and performed a multitemporal interferometric synthetic aperture radar (InSAR) analysis of large datasets, obtaining estimates of vertical land motion rates for California's entire coast at ~100-m dimensions-a ~1000-fold resolution improvement to the previous record. We estimate between 4.3 million and 8.7 million people in California's coastal communities, including 460,000 to 805,000 in San Francisco, 8000 to 2,300,00 in Los Angeles, and 2,000,000 to 2,300,000 in San Diego, are exposed to subsidence. The unprecedented detail and submillimeter accuracy resolved in our vertical land motion dataset can transform the analysis of natural and anthropogenic changes in relative sea-level and associated hazards.

Constraining Interseismic Deformation of the Cascadia Subduction Zone: New Insights From Estimates of Vertical Land Motion Over Different Timescales

AbstractWe determine late Holocene (past 4 kyr) vertical land motion (VLM) rates from relative sea level observations along the coastline of western North America and compare these to contemporary (decadal‐scale) rates inferred from Global Positioning System data. The residual rates (contemporary minus late Holocene) indicate uplift at most locations, which likely reflects short‐term signals associated with the Cascadia subduction earthquake cycle and processes that were recently activated. Regarding the latter, we model and remove the signals associated with ground water extraction and twentieth‐century glacier retreat, which have a significant influence in, respectively, California and southern British Columbia. We interpret the remaining signal as being dominated by interseismic deformation associated with the locking of the Cascadia megathrust. A preliminary comparison of this signal with output from a model of interseismic deformation indicates good agreement at most locations within a range of key model parameter values. This agreement is particularly encouraging as the locking model is based on the inversion of only horizontal land motion observations. Considering the data‐model fit at all locations, preference was found for models featuring nearly full locking to a relatively shallow depth (<30 km), although the locking state preference is variable along the coast and not strong. The best fitting parameter set varies considerably from site to site, and no set of parameter values was able to capture the residual VLM rates in northwestern Vancouver Island. Our study indicates that the residual VLM data provide useful constraints for megathrust locking models of Cascadia subduction.

Virtual Tide Gauges for Predicting Relative Sea Level Rise

AbstractWe present a Bayesian method to map contemporary rates of relative sea level change using a joint inversion of vertical trends from tide gauges, GPS time series, and satellite radar altimetry measurements. Tide gauge measurements constrain rates of relative sea level change on decadal to secular time scales at a few hundred sites sparsely distributed along coastlines. Predicting the rates of relative sea level change from historical tide gauge measurements is difficult due to the paucity and uneven distribution of sites with high quality records. Since the late twentieth century, deployments of GPS stations have enabled accurate determination of the rates of vertical land motion. A series of satellite radar altimetry missions provide continuous and global monitoring of geocentric sea level changes since the launch of TOPEX/Poseidon in 1992. By combining these three observations types into a single Bayesian inversion, we construct continuous maps of rates of relative sea level change, geocentric sea level change, and vertical land motion assuming linear trends, with robust estimates of uncertainties at regional scales. Cross‐validation tests show that reliable predictions of relative sea level changes are still provided where only GPS and satellite altimetry data are used, suggesting this method is viable for studying potential sea level risk for communities where historical tide gauge data are not available. Our results provide spatially and temporally consistent estimates of the various contributions to relative sea level changes.

An experiment to test satellite radar interferometry-observed geodetic ties to remotely monitor vertical land motion at tide gauges

Abstract The nature and linearity of vertical land motion (VLM) impacting the global sea level record from tide gauges is not well known, but remains of importance to understand long-term changes to sea level. Local surveys are required to directly measure VLM at tide gauges relative to a global reference frame, but this is limited by the lack of differential VLM measurements between tide gauges and continuously operating GPS (cGPS) stations that are not co-located, i.e., fixed to the tide gauge structure. We present results from an experiment using satellite radar interferometry (InSAR) scenes acquired from the TerraSAR-X satellite mission to test whether InSAR could replace repeat geodetic levelling as a ‘geodetic tie’ between cGPS stations and tide gauges. Comparisons are made among TerraSAR-X (TSX), cGPS and tide gauge minus altimetry VLM estimates for the Hillarys and Fremantle tide gauges (Perth, Western Australia), which are used as test sites for this method. The results suggest agreement between differential TSX and altimetry minus tide gauge VLM rates, but systematic offsets among the absolute/geocentric rates where the TSX is referenced to IGS08 at the PERT cGPS. The TerraSAR-X VLM at the Fremantle tide gauge for the period 7 October 2012 to 7 October 2017 is +0.45 ± 0.40 mm/yr (referenced to IGS08 at PERT cGPS), although this should be treated cautiously over this short period, and because VLM at Fremantle and Hillarys appears to be non-linear over time. We infer from this that the uncertainties in TerraSAR-X differential VLM rates are comparable to those from the highest quality repeat levelling, although the uncertainty approaches 1 mm/yr if the reference point uncertainty of the TSX and cGPS is considered when transformed to a terrestrial reference frame.

Vertical land motion in the Southwest and Central Pacific from available GNSS solutions and implications for relative sea levels

SUMMARYCoastal populations are impacted by relative sea level variations, which consist both of absolute sea level variations and of vertical land motions. This paper focuses on the Southwest and Central Pacific region, a recognized vulnerable region to sea level rise and where a large range of vertical land motion dynamics is observed. We analyse vertical displacement rates obtained from Global Navigation Satellite Systems (GNSS) by different analysis centres. We study the role played by modelled parameters, such as step discontinuities (due to equipment changes, earthquakes, etc.), in the position time-series analysis. We propose a new modelling approach based on a joint inversion of GNSS position time-series from different analysis centres. The final uncertainty on the vertical land motion rates is estimated as a combination of the uncertainty due to the GNSS data processing itself and the uncertainty due to the stability of the reference frame in which the GNSS data are expressed. We find that the dominant trend in the Southwest and Central Pacific is a moderate subsidence, with an average rate of −1.1 mm yr–1, but significant variations are observed, with displacement rates varying from an uplift of 1.6 ± 0.3 mm yr–1 to a subsidence of −5.4 ± 0.3 mm yr–1. Taking into account the geodynamic context, we assess, for each station, the relevance of current estimates of linear vertical displacement rate and uncertainty for forecasting future coastal sea levels.

Sea level changes and vertical land motion from altimetry and tide gauges in the Southern Levantine Basin

We have investigated the sea level rise (SLR) in the Southern Levantine region of the Mediterranean Sea during the period 1993–2015 using satellite altimetry and tide gauge data. Satellite altimetry indicated a positive SLR with a mean of 3.51 ± 0.62 mm/year, which is slightly higher than the global averaged mean SLR that was reported about 3.19 ± 0.63 (Chambers et al., 2017). The rates of vertical land motion (VLM rate) have been estimated from the trend of de-seasoned sea level difference (altimetry minus TG) time series at the 6 selected TG sites. Land subsidence was found to occur at three stations along the Nile Delta coast (Rosetta, Burullus and Damietta) and at one station in Israel (Hadera). Most of the previous studies in the Mediterranean Sea indicated that there are no sufficient tide gauge data in the Southern and Eastern Mediterranean Sea. So, this investigation offers valuable sea level information that can be applied in a wide range of climatology, related environmental issues, for example; land subsidence, inundation, and global warming in the southern Levantine basin.

An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

Present-day climate-change-related ice-melting induces elastic glacial isostatic adjustment (GIA) effects, while paleo-GIA effects describe the ongoing viscous response to the melting of late-Pleistocene ice sheets. The unloading initiated an uplift of the crust close to the centers of former ice sheets. Today, vertical land motion (VLM) rates in Fennoscandia reach values up to around 10 mm/year and are dominated by GIA. Uplift signals from GIA can be computed by solving the sea-level equation (SLE), 
 
 
 
 S
 ˙
 
 
 
 = 
 
 
 
 N
 ˙
 
 
 
 − 
 
 
 
 U
 ˙
 
 
 
 . All three quantities can also be determined from geodetic observations: relative sea-level variations (
 
 
 
 S
 ˙
 
 
 
 ) are observed by means of tide gauges, while rates of absolute sea-level change (
 
 
 
 N
 ˙
 
 
 
 ) can be observed by satellite altimetry; rates of VLM (
 
 
 
 U
 ˙
 
 
 
 ) can be determined by GPS (Global Positioning System). Based on the SLE, 
 
 
 
 U
 ˙
 
 
 
 can be derived by combining sea-surface measurements from satellite altimetry and relative sea-level records from tide gauges. In the present study, we have combined 7.5 years of CryoSat-2 satellite altimetry and tide-gauge data to estimate linear VLM rates at 20 tide gauges along the Norwegian coast. Thereby, we made use of monthly averaged tide-gauge data from PSMSL (Permanent Service for Mean Sea Level) and a high-frequency tide-gauge data set with 10-min sampling rate from NMA (Norwegian Mapping Authority). To validate our VLM estimates, we have compared them with the independent semi-empirical land-uplift model NKG2016LU_abs for the Nordic-Baltic region, which is based on GPS, levelling, and geodynamical modeling. Estimated VLM rates from 1 Hz CryoSat-2 and high-frequency tide-gauge data reflect well the amplitude of coastal VLM as provided by NKG2016LU_abs. We find a coastal average of 2.4 mm/year (average over all tide gauges), while NKG2016LU_abs suggests 2.8 mm/year; the spatial correlation is 0.58.

The glacial isostatic adjustment signal at present day in northern Europe and the British Isles estimated from geodetic observations and geophysical models

Abstract. The glacial isostatic adjustment (GIA) signal at present day is constrained via the joint inversion of geodetic observations and GIA models for a region encompassing northern Europe, the British Isles, and the Barents Sea. The constraining data are Global Positioning System (GPS) vertical crustal velocities and GRACE (Gravity Recovery and Climate Experiment) gravity data. When the data are inverted with a set of GIA models, the best-fit model for the vertical motion signal has a χ2 value of approximately 1 and a maximum a posteriori uncertainty of 0.3–0.4 mm yr−1. An elastic correction is applied to the vertical land motion rates that accounts for present-day changes to terrestrial hydrology as well as recent mass changes of ice sheets and glaciered regions. Throughout the study area, mass losses from Greenland dominate the elastic vertical signal and combine to give an elastic correction of up to +0.5 mm yr−1 in central Scandinavia. Neglecting to use an elastic correction may thus introduce a small but persistent bias in model predictions of GIA vertical motion even in central Scandinavia where vertical motion is dominated by GIA due to past glaciations. The predicted gravity signal is generally less well-constrained than the vertical signal, in part due to uncertainties associated with the correction for contemporary ice mass loss in Svalbard and the Russian Arctic. The GRACE-derived gravity trend is corrected for present-day ice mass loss using estimates derived from the ICESat and CryoSat missions, although a difference in magnitude between GRACE-inferred and altimetry-inferred regional mass loss rates suggests the possibility of a non-negligible GIA response here either from millennial-scale or Little Ice Age GIA.

The Influence of Sediment Isostatic Adjustment on Sea Level Change and Land Motion Along the U.S. Gulf Coast

AbstractSea level rise presents a hazard for coastal populations, and the Mississippi Delta (MD) is a region particularly at risk due to the high rates of land subsidence. We apply a gravitationally self‐consistent model of glacial and sediment isostatic adjustment (SIA) along with a realistic sediment load reconstruction in this region for the first time to determine isostatic contributions to relative sea level (RSL) and land motion. We determine optimal model parameters (Earth rheology and ice history) using a new high‐quality compaction‐free sea level indicator database. Using the optimal model parameters, we show that SIA can lower predicted RSL in the MD area by several meters over the Holocene and so should be taken into account when modeling these data. We compare modeled contemporary rates of vertical land motion with those inferred using GPS. This comparison indicates that isostatic processes can explain the majority of the observed vertical land motion north of latitude 30.7°N, where subsidence rates average about 1 mm/yr; however, subsidence south of this latitude shows large data‐model discrepancies of greater than 3 mm/yr, indicating the importance of nonisostatic processes. This discrepancy extends to contemporary RSL change, where we find that the SIA contribution in the Delta is on the order of 10−1 mm/yr. We provide estimates of the isostatic contributions to 20th and 21st century sea level rates at Gulf Coast Permanent Service for Mean Sea Level tide gauge locations as well as vertical and horizontal land motion at GPS station locations near the MD.

Vertical land motion along the Black Sea coast from satellite altimetry, tide gauges and GPS

Tide gauge records comprise of relative sea level change and vertical land motion, while satellite altimetry provides absolute sea level change in the Earth’s center fixed frame. Accordingly, the difference of both observations can be used to estimate geocentric vertical land motion along the coasts. In this paper, the vertical land motion rates are investigated at 13 tide gauge sites along the Black Sea coast by analyzing differences between Tide Gauge (TG) and Satellite Altimetry (SA) observations. Furthermore, the estimated vertical motion rates are compared with those from nearby the Global Positioning System (GPS) measurements. The results show general consistence with the present geodynamics in the Black Sea coastal region. For example, our estimates support the general subsidence at Bourgas and Varna.

A data-driven model for constraint of present-day glacial isostatic adjustment in North America

Geodetic measurements of vertical land motion and gravity change are incorporated into an a priori model of present-day glacial isostatic adjustment (GIA) in North America via least-squares adjustment. The result is an updated GIA model wherein the final predicted signal is informed by both observational data, and prior knowledge (or intuition) of GIA inferred from models. The data-driven method allows calculation of the uncertainties of predicted GIA fields, and thus offers a significant advantage over predictions from purely forward GIA models. In order to assess the influence each dataset has on the final GIA prediction, the vertical land motion and GRACE-measured gravity data are incorporated into the model first independently (i.e., one dataset only), then simultaneously. The relative weighting of the datasets and the prior input is iteratively determined by variance component estimation in order to achieve the most statistically appropriate fit to the data. The best-fit model is obtained when both datasets are inverted and gives respective RMS misfits to the GPS and GRACE data of 1.3 mm/yr and 0.8 mm/yr equivalent water layer change. Non-GIA signals (e.g., hydrology) are removed from the datasets prior to inversion. The post-fit residuals between the model predictions and the vertical motion and gravity datasets, however, suggest particular regions where significant non-GIA signals may still be present in the data, including unmodeled hydrological changes in the central Prairies west of Lake Winnipeg. Outside of these regions of misfit, the posterior uncertainty of the predicted model provides a measure of the formal uncertainty associated with the GIA process; results indicate that this quantity is sensitive to the uncertainty and spatial distribution of the input data as well as that of the prior model information. In the study area, the predicted uncertainty of the present-day GIA signal ranges from ∼0.2–1.2 mm/yr for rates of vertical land motion, and from ∼3–4 mm/yr of equivalent water layer change for gravity variations.

A glacial isostatic adjustment model for the central and northern Laurentide Ice Sheet based on relative sea level and GPS measurements

The thickness and equivalent global sea level contribution of an improved model of the central and northern Laurentide Ice Sheet is constrained by 24 relative sea level histories and 18 present-day GPS-measured vertical land motion rates. The final model, termed Laur16, is derived from the ICE-5G model by holding the timing history constant and iteratively adjusting the thickness history, in four regions of northern Canada. In the final model, the last glacial maximum (LGM) thickness of the Laurentide Ice Sheet west of Hudson Bay was ~3.4-3.6 km. Conversely, east of Hudson Bay, peak ice thicknesses reached ~4 km. The ice model thicknesses inferred for these two regions represent, respectively, a ~30 per cent decrease and an average ~20-25 per cent increase to the load thickness relative to the ICE-5G reconstruction, which is generally consistent with other recent studies that have focussed on Laurentide Ice Sheet history. The final model also features peak ice thicknesses of 1.2-1.3 km in the Baffin Island region, a modest reduction relative to ICE-5G and unchanged thicknesses for a region in the central Canadian Arctic Archipelago west of Baffin Island. Vertical land motion predictions of the final model fit observed crustal uplift rates well, after an adjustment is made for the elastic crustal response to present-day ice mass changes of regional ice cover. The new Laur16 model provides more than a factor of two improvement of the fit to the RSL data (?2 measure of misfit) and a factor of nine improvement to the fit of the GPS data (mean squared error measure of fit), compared to the ICE-5G starting model. Laur16 also fits the regional RSL data better by a factor of two and gives a slightly better fit to GPS uplift rates than the recent ICE-6G model. The volume history of the Laur16 reconstruction corresponds to an up to 8 m reduction in global sea level equivalent compared to ICE-5G at LGM.

Estimation of vertical land movement rates along the coasts of the Gulf of Mexico over the past decades

We estimated the vertical land movement rates at tide gauge stations along the Gulf of Mexico (GOM) coasts. A novel approach suggested by Kuo et al. (2004, 2008) for combining satellite altimetry and tide gauge data was applied. The obtained vertical land motion rates were compared with the GPS vertical velocities measured at Galveston, Grand Isle, Dauphin Island, Pensacola and Key West stations. The estimated vertical rates range from slow subsidence in the South of Florida and Veracruz to high subsidence rates in Texas and Louisiana where some of the tide gauges subside at the rate of up to 7mm/yr. A small but noticeable uplift in the NE of the Gulf was detected at Cedar Key and Apalachicola and a very low subsidence at Pensacola tide gauge. We suppose there are some local tectonic processes which contribute significantly to the land movement at these stations. Comparison with the post-glacial rebound model ICE5G-VM2 predictions shows that the drivers of the subsidence on the GOM shelf are of local nature. The resulted absolute sea level rise along the GOM coast was estimated to be about 2.0±0.4mm/yr.

Estimates of vertical land motion along the southwestern coasts of Turkey from coastal altimetry and tide gauge data

The differences between coastal altimetry and sea level time series of tide gauges in between March 1993 and December 2009 are used to estimate the rates of vertical land motion at three tide gauge locations along the southwestern coasts of Turkey. The CTOH/LEGOS along-track coastal altimetry retrieves altimetric sea level anomalies closer to the coast than the standard along-track altimetry products. However, the use of altimetry very close to the coast is not found to improve the results. On the contrary, the gridded and interpolated AVISO merged product exhibits the best agreement with tide gauge data as it provides the smoothest variability both in space and time compared with along track altimetry data. The Antalya gauge to the south (in the Mediterranean Sea) and the Mentes/Izmir gauge to the west (in the Aegean Sea) both show subsidence while the Bodrum tide gauge to the south (in the Aegean Sea) shows no significant vertical land motion. The results are compared and assessed with three independent geophysical vertical land motion estimates like from GPS. The GIA effect in the region is negligible. The VLM estimates from altimetry and tide gauge data are in good agreement both with GPS derived vertical velocity estimates and those inferred from geological and archaeological investigations.