Figure 7: Recent horizontal and vertical ground deformation velocity vectors in the Houston-Galveston area derived from extensometer and GPS observations (2006–2012). The horizontal velocity vectors have been transformed to the stable Houston reference frame (SHRF). 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].