RUPTURE PROCESS OF THE 1990 LUZON, PHILIPPINES (M(W)=7.7), EARTHQUAKE

Citation
Aa. Velasco et al., RUPTURE PROCESS OF THE 1990 LUZON, PHILIPPINES (M(W)=7.7), EARTHQUAKE, J GEO R-SOL, 101(B10), 1996, pp. 22419-22434
Citations number
40
Categorie Soggetti
Geochemitry & Geophysics
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
ISSN journal
21699313 → ACNP
Volume
101
Issue
B10
Year of publication
1996
Pages
22419 - 22434
Database
ISI
SICI code
2169-9313(1996)101:B10<22419:RPOT1L>2.0.ZU;2-P
Abstract
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.