Figure 1: Map showing contours of the average subsidence rate (mm/year) during the time span from 2006 to 2012. The contours are derived from subsidence observed from 72 GPS stations and 13 borehole extensometers. The red lines represent the locations of about 150 principle faults mapped by USGS in the Houston area using airborne LIDAR data collected after tropical storm Allison in 2001 [19]. The tan blobs represent the locations of salt domes [20].