SPATIAL AND TEMPORAL DISTRIBUTION OF SLIP FOR THE 1992 LANDERS, CALIFORNIA, EARTHQUAKE

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.