Los Angeles, Calif., is one of the world’s largest metropolitan areas
with a population of about 15 million people. The urban areas mostly
cover the coastal plains and lie within the inland valleys. The
intervening and adjacent mountains are generally too rugged for much
urban development. This is in large part because the mountains are
#8220;young,” meaning they are still building (and eroding) in this
seismically active (earthquake prone) region.
Earthquake faults commonly lie between the mountains and the
lowlands. The San Andreas fault, the largest fault in California,
likewise divides the very rugged San Gabriel Mountains from the
low-relief Mojave Desert, thus forming a straight topographic boundary
between the top center and lower right corner of the image. We present
this perspective image from NASA’s Shuttle Radar
Topography Mission (SRTM) with a graphic overlay
that maps faults that have been active in Late Quaternary times (white
lines). The fault database was provided by the U.S. Geological Survey.
The Landsat image used here was acquired on May 4, 2001, about seven
weeks before the summer solstice, so natural terrain shading is not
particularly strong. It is also not especially apparent given a view
direction (northwest) nearly parallel to the sun illumination (shadows
generally fall on the backsides of mountains). Consequently, topographic
shading derived from the SRTM elevation model was added to the Landsat
image, with a false sun illumination from the left (southwest). This
synthetic shading enhances the appearance of the topography.
View width 134 kilometers (83 miles); view distance 150 kilometers (93 miles)
34.3 degrees North latitude, 118.4 degrees West longitude
View west-northwest, 1.8 X vertical exaggeration
Landsat Bands 3, 2+4, 1 as red, green, blue, respectively
Original Data Resolution:
SRTM 1 arcsecond (30 meters or 98 feet), Landsat 30 meters (98 feet)
Earthquake faults active in Late Quaternary times Date Acquired: February 2000 (SRTM), May 4, 2001 (Landsat).