Dj. Wald et Th. Heaton, SPATIAL AND TEMPORAL DISTRIBUTION OF SLIP FOR THE 1992 LANDERS, CALIFORNIA, EARTHQUAKE, Bulletin of the Seismological Society of America, 84(3), 1994, pp. 668-691
We have determined a source rupture model for the 1992 Landers earthqu
ake (M(W) 7.2) compatible with multiple data sets, spanning a frequenc
y range from zero to 0.5 Hz. Geodetic survey displacements, near-field
and regional strong motions, broadband teleseismic waveforms, and sur
face offset measurements have been used explicitly to constrain both t
he spatial and temporal slip variations along the model fault surface.
Our fault parameterization involves a variable-slip, multiple-segment
, finite-fault model which treats the diverse data sets in a self-cons
istent manner, allowing them to be inverted both independently and in
unison. The high-quality data available for the Landers earthquake pro
vide an unprecedented opportunity for direct comparison of rupture mod
els determined from independent data sets that sample both a wide freq
uency range and a diverse spatial station orientation with respect to
the earthquake slip and radiation pattern. In all models, consistent f
eatures include the following: (1) similar overall dislocation pattern
s and amplitudes with seismic moments of 7 to 8 x 10(26) dyne-cm (seis
mic potency of 2.3 to 2.7 km3); (2) very heterogeneous, unilateral str
ike slip distributed over a fault length of 65 km and over a width of
at least 15 km, though slip is limited to shallower regions in some ar
eas; (3) a total rupture duration of 24 sec and an average rupture vel
ocity of 2.7 km/sec; and (4) substantial variations of slip with depth
relative to measured surface offsets. The extended rupture length and
duration of the Landers earthquake also allowed imaging of the propag
ating rupture front with better resolution than for those of prior sho
rter-duration, strike-slip events. Our imaging allows visualization of
the rupture evolution, including local differences in slip durations
and variations in rupture velocity. Rupture velocity decreases markedl
y at shallow depths, as well as near regions of slip transfer from one
fault segment to the next, as rupture propagates northwestward along
the multiply segmented fault length. The rupture front slows as it rea
ches the northern limit of the Johnson Valley/Landers faults where sli
p is transferred to the southern Homestead Valley fault; an abrupt acc
eleration is apparent following the transfer. This process is repeated
, and is more pronounced, as slip is again passed from the northern Ho
mestead Valley fault to the Emerson fault. Although the largest surfac
e offsets were observed at the northern end of the rupture, our modeli
ng indicates that substantial rupture was also relatively shallow (les
s than 10 km) in this region.