Geodetic observations using the Global Positioning System (GPS) and other t
echniques record a high rate of north-south shortening in an east-southeast
-trending, 5-40-km-wide belt in northern metropolitan Los Angeles, Californ
ia. Downtown Los Angeles is observed to be converging upon the southern San
Gabriel Mountains at 6 mm/yr. Aside from the elastic strain that will be r
eleased during earthquakes rupturing the san Andreas and San Jacinto faults
, east-west lengthening across northern metropolitan Los Angeles is minor,
<2.5 mm/yr. Therefore north-south shortening is accommodated mainly by vert
ical crustal thickening.