Occurrence of Land Subsidence in the west Valley


Historically, more than 18 feet of land subsidence has occurred in the west Valley, mostly the result of the heightened agricultural periods. However, with increasing urbanization of the Valley, a declining water table contines to promote subsidence.

This project proposes to define the structural and/or hydrologic controls on the magnitude and geometry of the subsidence bowl that has developed near Olive Avenue and 71st Street in Peoria, Arizona. Although the mechanics of subsidence are fairly well understood, complexities arise when trying to understand why certain areas are more susceptible to land deformation, particularly in the Basin and Range province where 2000 feet of alluvium with no defined stratigraphy is common. Through the use of geophysical data, radar images, drill core and well data, a more complete understanding of the local conditions that aid in the occurrence of subsidence can be sought. This information can then be used to assist local municipalities in determining groundwater withdrawal and recharge potential from specific well locations.



Use of InSAR Images
Interferometric Synthetic Aperture Radar (InSAR) images are being used to help detect and characterize the occurrence of subsidence across the valley. This image corresponds to a period from 1992 to 2000 and a displacement scale of ~ 5 cm for each full color, thus, illustrating a maximum subsidence of almost 45cm. The images are made up of an array of XYZ data, and when two images are subtracted, the difference in values corresponds to the amount of displacement that has occurred since the previous acquisition. The graph corresponds to the amount of displacement that occurred between each acquistion (~ every 15 months) along the black NW-SE trending profile line. This is being used to look at both the spatial and temporal changes in deformation.




Correlation to Changes in Water Table Elevation

This image is used to illustrate the lack of correlation between the declining water table elevation and the amount of deformation. The contour lines represent the change (~decline) in feet of the water table from 1983 to 2000. The greatest decline (~160 ft) occurred in the NW corner of the image, while the area around the subsidence bowl experience ~50 ft. Drill logs and hydrogeologic reports will be further investigated to determine the influence of the stratigraphy.

Use of Gravity
A gravity survey, completed by Maurice Tatlow of ADWR, is currently being corrected and analyzed to determine depth to bedrock, and whether the bedrock topography has an influence on the shape and susceptibility of this deformation.



Acknowledgements:
 The InSAR images were provided by Maurice Tatlow of the Arizona Department of Water Resources (ADWR). They were produced by VEXCEL Corporation for ADWR in accordance with the NASA BAA Grant.


Links:
Environmental Geophysics Research page
Active Tectonics Research Group homepage
Department of Geological Sciences

Page last modified March 28, 2005
Comments? Questions? Email: Amanda Perkins