Geostatistic Analysis of Long-Term Subsidence effects on Isostasy of Long Island Applying Continuous GPS Displacement Rates using R
Abstract:
Long Island has experienced subsidence since the last ice age when the large Laurentide ice sheet covered most of New York State and readjusted after it melted. This process of readjustment of the land is known as isostasy, the equilibrium position where a body of land should sit between the surface above and below. However, the region is not upliftingaftertheweightoftheicemeltedbut rather continues to subside even after this event took place. Modern human environmental interferences, particularly groundwater overpumping, causes uneven land deformation that heightens risks of landslides, sinkholes, and other geohazards (U.S. Geological Survey, n.d.). Central Long Island, with its many residential properties, hasahighdemandforgroundwater,leadingto the overpumping of aquifers in certain areas. This excessive withdrawal may contribute to gradual subsidence in parts of the region. In contrast, areas within New York City and Montauk Point exhibit significant subsidence rates despite lower residential groundwater extraction. This is likely due to reliance on upstate water sources, heavy infrastructure, and high population density. While Montauk Point is less populated than central and western Long Island, it still experiences notable subsidence, possibly due to reduced aquifer pumping, which allows underlying geological formations to compact under their own weight. To capture these spatial variations in land motion, we analyzed continuous GPS records from multiple stations across differing time intervals. Rather than restricting our study to a common observation window, we considered each station’s full operational timeline to assess overall trends.
Background of Study:
Parag, A. S.
1Dept. Geology, Environment and Sustainability, Hofstra University, NY, USA. . 2Dept. Information Systems, Analytics, and Supply Chain Management, Rider University, NJ, USA.
Figure 1: These geostatistical graphs display the up components of each station and their vertical movements within their various ranges. Some stations range from 1995-1998 and variations within the 2000s. The x-axis is time in years and the y-axis is the vertical displacement in meters (m).
Results:
➢ Long Island has been subsiding since the last ice age due to glacialisostaticadjustment.
Method/Materials:
GPS displacement data from 12 Long Island stations were retrieved usingRfromtheNevadaGeodeticLaboratory.(Fig.1) DataprocessingandcleaningusedRpackages.
➢ Custom function (GPS_dwd) structured data into northward, eastward, andupwarddisplacementcomponents.
➢ Missing values were interpolated, and stations with excessive data issues(MOR6,QYNS)wereexcluded.
➢ Outliers were removed using Z-score normalization (values beyond ±3 standarddeviations).
➢ Noise reduction applied using Kolmogorov-Zurbenko (KZ) filtering (365daywindow,3replications).
➢ Wavelet Spectrum (WaveletComp) detected periodic signals in Up, North,andEastdisplacementcomponents.(Fig.2)
➢ Linear regression (lm function) calculated vertical displacement rates fromsmootheddata.
➢ Geostatistical interpolation (IDW method) mapped subsidence patterns usingthegstatandsppackages.
➢ GIS visualization (leaflet package) created an interactive map showing GPSstationlocationsanddisplacementrates.(Fig.3)
Acknowledgements:
Credit Authorship Contribution Statement:
Discussion/ Conclusion:
A GIS-interpolated map of average displacement rates reveals localized areas of significant subsidence, illuminating the combined effects of natural isostatic processes and human-induced stresses. Findings support the need for strategic groundwater management and infrastructure planning to reduce further land subsidence and its associated hazards in this vulnerable coastalsetting.
GeostatisticalAnalysis:
➢ Displays vertical movements of stations overtime(1995-1998&2000s).
SubsidenceTrends:
➢ Glacial isostasy causes land to subside under ice weight and upliftwhentheicemelts.
➢ Unlike expected uplift, the region continues to subside, suggesting additionalcontributingfactors.
➢ Groundwater overpumping may lead to uneven land deformation, increasing geohazard risks like landslides and sinkholes formed by underground erosion and sedimentcollapse.
➢ This study uses GPS data to detect ongoing vertical land movements beyond 2005–2020 research.
➢ GIS-interpolated maps highlight localized subsidence patterns, linking natural and human-
➢ Highestsubsidence(~-2mm/yr)nearNYC& eastern Long Island; central Long Island shows lower subsidence with occasional uplift.
StationObservations:
➢ NYBR(NYC):Stronglong-termsubsidence.
➢ MNP1 (Eastern Long Island): Gradual downward trend but higher subsidence ratesthancentralstations.
➢ NYEL,NYPD,ZNY1(CentralStations):Lower subsidencerateswithslightupliftperiods.
WaveletSpectrumAnalysis:
➢ Up Component: Multiple peaks, indicating periodic oscillations in vertical displacement. Clustering of peaks suggests seasonalandsub-annualcycles.
➢ North Component: Low but visible longterm periodic movements in the northward
➢ NYC has the highest subsidence due to infrastructure weight and limited groundwaterextraction.
➢ Central Long Island shows slight uplift, likelyfromgroundwateroverpumping.
➢ Eastern Long Island subsides despite low population, possibly due to retained groundwaterweight.
➢ Subsidence may be influenced by groundwater and human activity, not tectonicfactors.
➢ GPS data analysis confirms sinking rates,averaging1.6mm/year,withsome areasexceeding3cm/decade.
➢ KZ filtering (365-day) removes noise, preserving long-term displacement trends.
➢ Subsidence varies across regions, with NYC and Montauk Point sinking more thancentralLongIsland.
➢ Wavelet spectrum analysis identifies periodic land displacement possibly influenced by groundwater, temperature,andsubsidence.
➢ Vertical (Up) motion shows stronger oscillationsthanhorizontalcomponents.