The rupture process of the destructive July 16, 1990, Luzon, Philippin
es, earthquake is analyzed using a long-period surface wave spectral i
nversion technique to estimate the average source properties and a bro
adband body wave and surface wave empirical Green function technique t
o investigate the slip distribution. The average source model has a se
ismic moment of 4.2+/-0.1 x10(20) N m (M(W)=7.7), a total duration of
30 to 35 s, a left lateral strike-slip focal mechanism with strike, ph
i=153 degrees, dip, delta=89 degrees, and rake, lambda=16 degrees, and
a north-northwestward directivity. These results are consistent with
previous work on the Luzon earthquake. However, the broadband analysis
indicates that, for periods longer than about 20 s, the teleseismic s
ource time function is characterized by a single, relatively smooth pu
lse of energy release with azimuthal variations in duration of 24 to 6
0 s. This contrasts with previous body wave results that inferred two
discrete pulses of energy release. The simpler source process is infer
red as a result of using empirical Green functions rather than standar
d theoretical Green functions for a layered crustal model, and by cons
idering only the seismic energy with periods longer than 20 s. The Luz
on earthquake began rupturing bilaterally, but evolved into a predomin
antly northwest directed rupture that extended for 75 to 100 km. The l
argest slip (10-15 m) occurred about 25 km northwest of the epicenter,
beyond which the slip decreased gradually as the rupture propagated i
nto a restraining bend. The peak slip at depth appears to exceed the s
urface rupture by a factor of 2 to 3. There is little evidence for sig
nificant energy release later than 50 s after the rupture initiated.