Land-surface Subsidence Research Articles

Resolving the contributing factors to Mississippi Delta subsidence: Past and Present

AbstractTo date, quantification of individual components that contribute to shallow and deep‐seated subsidence in passive margin deltas worldwide has proven problematic. A new, regional gridded chronostratigraphic dataset for the Lower Mississippi Delta region, derived from 80,928 well reports across the northern Gulf of Mexico (GOM), has bridged the disparity between geodetic mean rates measuring total land surface subsidence across annual‐to‐decadal timescales and the deep‐seated stratigraphic subsidence rates that record isostatic response over timescales of >104 years. Through a quantitative assessment of gridded chronostratigraphic surfaces, sections, and subsidence rates extending from the Middle Pleistocene (0.58 Ma) to the Late Pliocene (3.85 Ma), we identify both temporal and spatial variability in deep‐seated subsidence across the northern GOM. Targeted deep‐seated subsidence data extracted across prior GOM Holocene sea‐level sample locations have revealed more than an order of magnitude greater rates of isostatic compensation in the Mississippi depocentre versus similar GOM sea‐level control sites in Florida and Alabama, casting doubt on efforts towards a representative Holocene sea‐level curve. Spatial variability in subsidence was also assessed locally in both the strike and dip directions to assess the contributions of growth faults. Fault throw displacement magnitude was discovered to decrease with depth, accounting for less than half of the total deep‐seated subsidence record of the Middle Pleistocene. Temporal subsidence complexities were also revealed including a direct, inverse logarithmic relationship between subsidence rate and time indicating variable subsidence component controls across different timescales. Despite the spatial and temporal complexities, this dataset serves as the first regional baseline for deep‐seated subsidence rates across the northern GOM.

Effects of ferric sulfate and polyaluminum chloride coagulation enhanced treatment wetlands on Typha growth, soil and water chemistry

Land surface subsidence is a concern in many deltas worldwide as it contributes to water quality degradation, loss of fertile land and increased potential for levee failure. As a possible solution to these concerns, on-site coagulation enhanced treatment wetlands (CETWs), coagulation water treatment followed by wetland passage serving as a settling basin, were implemented in a field-scale study located on a subsided island of the Sacramento-San Joaquin Delta in northern California under three treatments; coagulation with polyaluminum chloride (PAC), coagulation with ferric sulfate and an untreated control. Because CETWs offer a relatively novel solution for water quality improvement and subsidence reversal due to its low-infrastructure requirements and in-situ nature, effects from these systems remain uncharted and they may have adverse effects on plant biomass production that also contribute to sediment accretion. This study focuses on the effect CETWs had on the growth of Typha spp.; the dominant vegetation in the wetlands. Plant growth parameters and nutrient content were measured in conjunction with soil, pore water and surface water chemistry. Soil analysis indicated there was no intermixing of newly formed flocs and original soil material. Where there was significant deposition of floc, PAC treatment reduced phosphate concentrations and ferric sulfate treatment increased total Fe concentrations in surrounding water compared to the control. Results indicated coagulation treatments had no negative effects on Typha leaf nutrient content, Typha growth or allometric parameters. Additionally, no signs of plant toxicity such as necrosis, wilting or chlorosis were observed in any of the treatments. Overall, this study suggests that CETWs are viable treatment option for water quality improvement and sediment accretion while having no negative impact on the growth of Typha plants.

Assessment of Land Surface Subsidence Due to Underground Metal Mining Using Integrated Spaceborne Repeat-Pass Differential Interferometric Synthetic Aperture Radar (DInSAR) Technique and Ground Based Observations

Differential interferometric synthetic aperture radar (DInSAR) is a novel remote sensing technique to measure earth surface deformation. It is capable of obtaining dense information related to the deformation of a large area efficiently, economically and effectively. Therefore, DInSAR is a promising technology for monitoring the earth surface deformation related to some natural hazardous events, such as earthquake, volcano eruption, land subsidence, landslide. In present study, Conventional DInSAR technique have been applied to a mineral rich zone, coming under the Khetri copper belt, a part of Northern Aravali range of hillocks in India, predominant with mining activities since late 1960’s to address the possibility of deformation phenomena due to hard rock underground metal mining. Four interferometric SAR data sets of Radarsat-2 was used for the study area to address the subsidence/uplift phenomena. Further, results obtained from conventional DInSAR technique using Radarsat-2 data sets compared with results obtained from ground based observation technique for its validity. In both the techniques, deformation results obtained in terms of average subsidence rate in mm (quarterly basis) of points under study within mining zone of Mine-A has well agreed to each other. Further, it has been observed that average subsidence rate in mm (quarterly basis) obtained from space based observation and ground based observation are 5.6 and 6.67, respectively over the points under study in mining zone of Mine-A.

Estimation of Land Surface Subsidence Induced by Hydrocarbon Production in the Niger Delta, Nigeria, Using Time-Lapse Orthometric Leveling Data

Time-lapse orthometric levelling measurements, acquired in 1988 and 2003 in the south-east Niger Delta basin, are used to estimate surface subsidence resulting from hydrocarbon withdrawal. The value of the subsidence was determined by finding the differences from the orthometric heights in the base and the monitor surveys. The elevation ranges between -30m along river channels and 3m for the base 3D survey while that for the monitor survey shows elevation of -27m to 5m. Hydrocarbon production in reservoir under this area was 89.52stb/day initially and declined to 13.92stb/day, and the reservoir pore-fluid pressure depletion is only 674psi, initially at 3833psi but dropped to 3159psi in 15 years. The results from the analysis show that the rate of land subsidence at each location of levelling varies from 66.67mm yr-1 to 200.00mm/yr with an average of 86.00mmyr-1. When comparing the land subsidence trend, hydrocarbon production and reservoir pressure declines, there is no positive correlation between the three phenomena. This is an indication that land subsidence is localized where the measurements are carried out mainly in river channels and slopes caused by erosion, and not on a regional scale. The results of this work can be used for engineering and environmental works.

Satellite-based Estimates of Ground Subsidence in Ordos Basin, China

Abstract This paper reports the findings based on ALOS-1 and GRACE satellite data for the purpose of monitoring land surface subsidence due to groundwater extraction and underground mining activities in the Ordos Basin, China. 42 ALOS-1 PALSAR data (22 images from Frame 790 while 20 scenes from Frame 780) acquired between 8 January 2007 and 19 January 2011 are utilized in the time-series InSAR (TS-InSAR) analysis while the total water storage observations derived from the Gravity Recovery and Climate Experiment (GRACE) satellite data are integrated with hydrological modeling results (for soil moisture modelling) to estimate the groundwater depletion rate. Since the results have vast difference in spatial resolution between GRACE (~300 km) and InSAR (~10’s of meters), the two measurements are not comparable over the same region. Instead, we applied them to Haolebaoji surrounding region and ALOS covered area, respectively. The groundwater change series of about –7.3 mm yr–1 between December 2006 and June 2012 is detected, which is then being exploited to explain the groundwater induced subsidence in Haolebaoji, Inner Mongolia. Within ALOS covered region, time-series analysis was carried out to explain the local subsidence. Then the total area size of underground mining sites is estimated, and we concluded that human involved activities contribute a lot to the total velocity and this part of subsidence should be excluded before estimating the final mean velocity (–4.9 mm yr–1 in vertical direction) when comparing with GRACE-based groundwater depletion series. Last but not least, some suggestions are given on how to make a rational comparison between the InSAR derived mean velocity with GRACE-based groundwater depletion trend together. This study could help the local government and associated geotechnical engineers to have a better understanding of the groundwater induced subsidence in this region.

Population Dynamics of Microorganism and Greenhouse Gas Emission By Applying Chicken Manure in Peat Soil

<em>Peat land accumulates organic materials and emits greenhouse gas (GHG). Agricultural activities in peat land cause the subsidence of peat land surface and the loss of carbon in the form of GHG. Appropriate management of peat land for agriculture would reduce GHG emission. This research aims to understand the microorganism population dynamics and emission of GHG on the treatment of chicken manure application in peat land. The research was conducted in the GHG Laboratory of Indonesia Agricultural Environment Research Institute (IAERI) in 2012 using peat material taken from Jabiren, Central Kalimantan. The experiment was done by incubating peat soil for 2 months with the treatment of chicken manure application and without manure. The incubation experiment was conducted by using paralon PVC pipe. Parameters observed included pH, Eh, bacteria population and fungi, as well as GHG flux (CO<sub>2</sub>, CH<sub>4 </sub>and N<sub>2</sub>O). GHG samples taking method was used a sealed containment. The research result showed at the peat given chicken manure treatment, bacteria population decreased at the end of incubation; fungi population, however, increased. The application of chicken manure on peat land planted rubber trees and pineapples would reduce GHG emission by 12.8% as compared without manure application.</em>

Mechanisms of late Quaternary fault throw‐rate variability along the north central Gulf of Mexico coast: implications for coastal subsidence

AbstractQuaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 103 to 105 year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year−1 during the late Holocene, ca. 0.03 mm year−1 during the last glacial and at least 0.07 mm year−1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.

Reconstructing DEM using TLS point cloud data and NURBS surface

Underground coal mining inevitably results in land surface subsidence. Acquiring information on land surface subsidence is important in the detection of surface change. However, conventional data acquisition techniques cannot always retrieve information on whole subsidence area. This study focuses on the reconstruction of a digital elevation model (DEM) with terrestrial laser scanning (TLS) point cloud data. Firstly, the methodology of the DEM with terrestrial 3-dimensional laser scanning is introduced. Then, a DEM modeling approach that involves the application of curved non-uniform rational B-splines (NURBS) surface is put forward. Finally, the performance of the DEM modeling approach with different surface inverse methods is demonstrated. The results indicate that the DEM based on the point cloud data and curved NURBS surface can achieve satisfactory accuracy. In addition, the performance of the hyperbolic paraboloid appears to be better than that of the elliptic paraboloid. The reconstructed DEM is continuous and can easily be integrated into other programs. Such features are of great importance in monitoring dynamic ground surface subsidence.

The influence of morphological changes of small lowland river on discharge rate

Abstract The influence of morphological changes of small lowland river on discharge rate. The aim of the study was the comparison of the changes of cross-sections and longitudinal profile of the Mała river at the distance of 600 m. The paper presents the geometry changes of the river from field measurements made in 2013 in comparison with design assumptions from 1967 which were implemented in 1971. The four (available historical) cross-sections (hm 7+700, 7+800, 7+900, 8+000) and longitudinal profile (hm 7+700÷8+300) of the river were analysed and compared. The large scale of subsidence of the land surface on both banks was observed (even to 0.5 m). Probably it is the effect of peat shrinkage and mineralization processes of organic soils. The bottom of the Mała river was still located at the same altitude in sand deposits in the analysed period 1971-2013. The designed slope of bottom of the Mała river equals 0.7‰ (1967) and present slope (2013) was estimated to be around 1‰. The subsidence of peat layers on both river banks, changes in cross-sections’ parameters (present irregular shapes in comparison with designed trapezoidal cross-sections) caused the reduction of cross-sectional area and water discharge of about 40-50% in comparison with parameters designed in 1967 and made in 1971.

Understanding subsidence in the Mississippi Delta region due to sediment, ice, and ocean loading: Insights from geophysical modeling

AbstractThe processes responsible for land surface subsidence in the Mississippi Delta (MD) have been vigorously debated. Numerous studies have postulated a dominant role for isostatic subsidence associated with sediment loading. Previous computational modeling of present‐day vertical land motion has been carried out in order to understand geodetic data. While the magnitudes of these measured rates have been reproduced, the model parameter values required have often been extreme and, in some cases, unrealistic. In contrast, subsidence rates in the MD on the 103 year timescale due to delta loading estimated from relative sea level reconstructions are an order of magnitude lower. In an attempt to resolve this conflict, a sensitivity analysis was carried out using a spherically symmetric viscoelastic solid Earth deformation model with sediment, ice, and ocean load histories. The model results were compared with geologic and geodetic observations that provide a record of vertical land motion over three distinctly different timescales (past 80 kyr, past 7 kyr, and past ~15 years). It was found that glacial isostatic adjustment is likely to be the dominant contributor to vertical motion of the Pleistocene and underlying basement. Present‐day basement subsidence rates solely due to sediment loading are found to be less than ~0.5 mm yr−1. The analysis supports previous suggestions in the literature that Earth rheology parameters are time dependent. Specifically, the effective elastic thickness of the lithosphere may be <50 km on a 105 year timescale, but closer to 100 km over 103 to 104 year timescales.

Monitoring subsurface coal fires in Jharia coalfield using observations of land subsidence from differential interferometric synthetic aperture radar (DInSAR)

Coal fires in the Jharia coalfield pose a serious threat to India’s vital resource of primary coking coal and the regional environment. In order to undertake effective preventative measures, it is critical to detect the occurrence of subsurface coal fires and to monitor the extent of the existing ones. In this study, Differential Interferometric Synthetic Aperature Radar (DInSAR) technique has been utilized to monitor subsurface coal fires in the Jharia coalfield. Results showed that majority of the coal fire-related subsidence were concentrated on the eastern and western boundaries of the coalfield. The magnitude of subsidence observed was classified into high (10–27.8 mm), low (0–10 mm) and upliftment (−10–0 mm). The results were strongly supported by in situ observations and satellite-based thermal imagery analysis. Major subsidence was observed in the areas with repeated sightings of coal fire. Further, the study highlighted on the capability of the methodology for predicting potential coal fire zones on the basis of land surface subsidence only. The results from this study have major implications for demarcating the hazardous coal fire areas as well as effective implementation of public safety measures.

Influence of growth faults on coastal fluvial systems: Examples from the late Miocene to Recent Mississippi River Delta

The details of how fluvial systems respond to spatial changes in land-surface subsidence produced by active faulting remain incompletely understood. Here, we examine the degree to which the positioning of individual channels and channel-belts is affected by local maxima in subsidence associated with the hanging walls of growth faults. The channel forms and faults are imaged using a seismic volume covering 1400km2 of Breton Sound and Barataria Bay in southern Louisiana, USA. We look at the consequences of interactions between channels, channel-belts, and faults in late Miocene to Recent strata. More than fifty individual channels that crossed the traces of active growth faults were examined. Of these channels, only three appear to have been redirected by the faults. There also appeared to be no systematic change in the cross-sectional geometries of channels or channel-belts associated with crossing a fault, though the orientation of the channel-belts appears to be more influenced by faulting than the orientation of individual channels. Seven out of ten mapped channel-belts appear to have been steered by growth faults. We propose that channel belts are more likely to be influenced by faults than individual channels because channel-belts are longer lived features, unlikely to shift their overall position before experiencing a discrete faulting event. In addition, the style of influence in the few cases where an individual channel is affected by a fault is different from that of larger systems. While downstream of a fault channel-belts generally become oriented perpendicular to fault strike, the individual channels are directed along the hanging wall of the fault, running parallel to the fault trace. We relate this to the ratio of the length-scale of fault rollover relative to the channel or channel-belt width. Fluvial-fault interactions with higher values for this ratio are more likely to be carried parallel to the fault trace than systems with lower ratio values.

Land subsidence caused by solution mining in the Mogilno salt dome

Occurrence of land surface subsidence is a result of rock salt extraction. The process is observed by geodetic measurements. On the Paledzie I salt mining field, such measurements are conducted every five years. The most recent series of measurements was carried out in 2009. The analysis of land levelling results indicated that a twin-centre subsidence is still being formed above the salt mining area. Its maximum load on the SW side of the salt dome did not exceed -100 mm in 1986-2009. The second subsidence centre behind the NE edge pillar is 50% smaller than the first one. Along with extraction moving up to shallower areas of the salt bed, the rate of land surface subsidence is increasing, with the decreasing perimeter of the depression. The indicators that describe the land surface subsidence – vertical displacement of benchmarks and the caverns volume – are presented on the function of time and a parameter, determining the distance from the measurement point to the exploitation field edges.

Improved Ground Subsidence Monitoring Using Small Baseline SAR Interferograms and a Weighted Least Squares Inversion Algorithm

We present the application of a weighted least squares (WLS) method based on image mode interferometric data to monitor the spatiotemporal evolution of land surface subsidence in Mashhad valley, northeast Iran. The technique is based on an appropriate combination of differential interferograms produced by image pairs with small orbital separation to limit the spatial decorrelation phenomena. Our data consist of 17 ASAR single-look-complex images acquired from a descending orbit by the European ENVISAT satellite in image mode (I2), spanning a time interval from June 2004 to November 2007. Fifty-three reliable differential interferograms with relatively little noise and a continuous unwrapped phase are constructed from this data set and are analyzed using a WLS adjustment technique to produce time series of the displacement field. The time-series analysis suggests that the subsidence occurs within a northwest–southeast elongated elliptically shaped bowl along the axis of Mashhad valley. The maximum accumulated subsidence during the 1260-day period reaches approximately 86 cm, located northeast of Mashhad city. The comparison between SAR-interferometry time-series results with continuous Global Positioning System measurements yields an estimated root-mean-square error of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 1.0 cm.

Modeling the subsidence of peat soils in the Dutch coastal area

In large parts of the western coastal region of the Netherlands peat soils occur. Historic land use resulted in decomposition of organic matter and compaction of these soils and as a consequence the land surface subsided. Along with sea level rise and tectonic subsidence since the end of the Weichselian ice-age, this resulted in a country where one-third of the land lies below mean sea level. Global warming will accelerate the sea level rise and land subsidence due to peat oxidation, leading to elevated risks of flooding and increasing upward seepage of brackish and nutrient rich ground water. In the Polder Groot-Mijdrecht near Amsterdam the land surface is currently between 5 and 6.5m below sea level. For this polder we calibrated a model for the land surface subsidence. The subsidence rate is modeled using a differential equation accounting for the peat oxidation and other processes causing land surface subsidence. The model input consists of information on (i) the thickness of peat layers derived from soil surveys in 1964 and 1967; (ii) the regulated surface water levels in a network of drainage ditches, and (iii) the initial elevation measured between 1954 and 1968 at 1423 locations. The model was calibrated on the elevation measurements in 2005 and on the peat thickness from a recent soil survey in 2005. The subsidence between 1954 and 2005 as predicted with the model was validated with a subsample of 100 points out of the 1423 locations. The average rate of predicted subsidence between 1954 and 2005 was approximately 5mmyear−1. In soils containing peat layers the predicted subsidence rate due to peat oxidation was up to 8mmyear−1. On the contrary, at locations without peat the predicted subsidence rate was only 0.7mmyear−1. The model accounted for 78% of the variance of the historic subsidence, and the root mean squared error of the predicted elevation in 2005 was 94mm. Model forecasts of the cumulative subsidence between 2005 and 2020 for the eastern half of the study area where still thick peat layers occur, were over 80cm. In areas where peat layer in the soil profile are absent the forecasted cumulative subsidence was 10mm. The case study shows that the simple process model, when calibrated on local data, can help in evaluating flooding risks and in taking long-term strategic decisions on water management and land use in peat areas.

Probabilistic longevity estimate for the LUSI mud volcano, East Java

Abstract: A new method for estimating the duration of a mud volcano eruption is applied to the LUSI mud volcano in East Java. The estimate is based upon carbonates at depths in the range 2500–3500 m being the water source, with an estimated area of 100–600 km 2 , thickness of 0.2–1.0 km, porosity of 0.15–0.25, an initial pressure between 13.9 and 17.6 MPa, and a separate, shallower source of mud ( c . 1200–1800 m depth). The resulting 50 percentile for the time it takes for flow to decline to &lt;0.1 Ml day −1 is 26 years. By analogy with natural mud volcanoes it can be expected to continue to flow at lower rates for thousands of years. Assuming subsidence rates of between 1 and 5 cm day −1 , land surface subsidence of between c . 95 and c . 475 m can be expected to develop within the 26 year time period.

Inherited drainage - paleochannels and preferential groundwater flow

It is suggested that in a localized remnant of Kalahari sand at Dufuya, central Zimbabwe, groundwater flows in an integrated pattern inherited from the paleochannel network of the underlying gneiss. Contact springs occur at discrete localities along the Kalahari sand/gneiss boundary and are associated with spring sapping and land surface subsidence. Subsidence is presumed to be due to preferential solute removal by leaching and dissolution as a result of concentration of groundwater flow within the buried paleochannel network and the location of the springs is presumed to occur where the paleochannel network intersects the Kalahari sand/gneiss boundary. Over time the surficial Kalahari sand is preferentially removed along these buried drainage lines by spring sapping and headwards erosion, exposing the gneiss. Multi-electrode direct current resistivity profiling and radar have been used to map the sub-surface, revealing the topography of the basement and nature of the Kalahari cover. Coincidence of gneiss basement depressions with the spring sites, leached sands and subsidence zones suggests inheritance of the gneiss fluvial paleochannel network pattern by the present day groundwater flow. Washed sand and gravel intersected in shallow boreholes in these areas provides further evidentiary support for the concept of inherited drainage.

Simple methods for evaluating accommodation space formation in coastal wetlands

Land-surface subsidence and erosion are the principal processes that form accommodation space in interior coastal wetlands when they are converted to open water. The relative contribution of subsidence and erosion to wetland loss can be estimated by comparing elevations and vertical offsets of stratigraphic contacts that are correlated between adjacent sediment cores. Accommodation-space measurements assume that wetland-sediment thicknesses and the elevation of stratigraphic contacts were originally nearly uniform over short horizontal distances (tens to hundreds of meters). The accommodation space attributable to erosion equals the difference in wetland-sediment thickness between wetland cores and adjacent open-water cores taken at formerly emergent wetland sites. The accommodation space attributable to subsidence equals the elevation difference of a stratigraphic marker correlated between the two cores using the wetland core as the reference standard. Together, subsidence plus erosion at an open-water core location equals the accommodation space created by land loss, which is the difference between the adjacent emergent wetland elevation and the existing water depth.

The legacy of wetland drainage on the remaining peat in the Sacramento — San Joaquin Delta, California, USA

Throughout the world, many extensive wetlands, such as the Sacramento-San Joaquin Delta of California (hereafter, the Delta), have been drained for agriculture, resulting in land-surface subsidence of peat soils. The purpose of this project was to study the in situ effects of wetland drainage on the remaining peat in the Delta. Peat cores were retrieved from four drained, farmed islands and four relatively undisturbed, marsh islands. Core samples were analyzed for bulk density and percent organic carbon. Macrofossils in the peat were dated using radiocarbon age determination. The peat from the farmed islands is highly distinct from marsh island peat. Bulk density of peat from the farmed islands is generally greater than that of the marsh islands at a given organic carbon content. On the farmed islands, increased bulk density, which is an indication of compaction, decreases with depth within the unoxidized peat zone, whereas, on the marsh islands, bulk density is generally constant with depth except near the surface. Approximately 55-80% of the original peat layer on the farmed islands has been lost due to land- surface subsidence. For the center regions of the farmed islands, this translates into an estimated loss of between 2900-5700 metric tons of organic carbon/hectare. Most of the intact peat just below the currently farmed soil layer is over 4000 years old. Peat loss will continue as long as the artificial water table on the farmed islands is held below the land surface.

Land subsidence induced by groundwater extraction and building damage level assessment — a case study of Datun, China

As in many parts of the world, long-term excessive extraction of groundwater has caused significant land-surface subsidence in the residential areas of Datun coal mining district in East China. The recorded maximum level of subsidence in the area since 1976 to 2006 is 863 mm, and the area with an accumulative subsidence more than 200 mm has reached 33.1 km2 by the end of 2006. Over ten cases of building crack due to ground subsidence have already been observed. Spatial variation in ground subsidence often leads to a corresponding pattern of ground deformation. Buildings and underground infrastructures have been under a higher risk of damage in locations with greater differential ground deformation. Governmental guideline in China classifies building damages into four different levels, based on the observable measures such as the width of wall crack, the degree of door and window deformation, the degree of wall inclination and the degree of structural destruction. Building damage level (BDL) is estimated by means of ground deformation analysis in terms of variations in slope gradient and curvature. Ground deformation analysis in terms of variations in slope gradient has shown that the areas of BDL III and BDL II sites account for about 0.013 km2 and 0.284 km2 respectively in 2006, and the predicted areas of BDL (define this first) III and II sites will be about 0.029 km2 and 0.423 km2respectively by 2010. The situation is getting worse as subsidence continues. That calls for effective strategies for subsidence mitigation and damage reduction, in terms of sustainable groundwater extraction, enhanced monitoring and the establishment of early warning systems.