Genetic Inversion of a Synthetic Aperture Radar Interferogram to constrain the slip over the fault during the June 28, 1992, Landers, California, Earthquake.
A Synthetic Aperture Radar interferogram
of the Landers earthquake region (Massonnet
et al, 1993) is inverted to constrain
the slip distribution over the fault.
We use several hundred data points in the
image of the change in the distance
between the ground and the satellite ERS-1,
due to the earthquake rupture and the postseimic
relaxation. A genetic inversion (Lomax and
Sneider 1994) is used to find a set of acceptable
slip models. The slip distribution found at the
top of the fault shows a concentration of models
in a range of 1 meter and is in agreement with
the slip measured directly by geologists in
the field. The spread of slip distribution
increase with depth and span a 4-meter slip
length at the bottom of the fault (16 km deep).
A 3-asperity model is simulated to test the inversion accuracy. This synthetic test confirms that the slip is well constrained in the upper part of the fault and that the resolution decreases as depth increases, with models becoming rather random at the deepest part of the fault.
GPS data have also been inverted with this method, and the results are comparable to those obtained with the interferogram. However, the spread obtained with GPS is larger. Those tests show that interferometric data can be used to constrain the slip on the fault more accurately than classical geodetic inversions which use GPS data.
The models obtained are in accord with teleseismic and strong motion inversions. This suggests that the postseismic slip over 14 months in the upper part of the fault is very small compared to the coseismic slip.