An expanded body-wave data set for the 4 February 1976 Guatemalan earthquake is analyzed by iterative, multiple-station inversion to provide enhanced resolution of the rupture process of this important strike-slip event. The body-wave data set used in an earlier study of this event, in which a predominantly unilateral, westward-propagating rupture was proposed, actually does not have sufficient resolution to reliably map the spatial heterogeneity for the source process. The expanded azimuthal coverage of the new data set provides better spatial resolution of the primary rupture characteristics. The Guatemalan earthquake can be modeled as an asymmetric bilateral rupture extending eastward and westward along the Motagua fault, with the largest episode of moment release occurring ≈90 km west of the epicenter, near a change in strike in the surface faulting. The overall rupture velocity is about 3.5 km/sec, and the total moment is 3.7 × 1027 dyne cm. Inversions with composite fault models having a second focal mechanism appropriate for the western end of the fault are consistent with the data, but are not clearly required. The characterization of the Guatemalan earthquake as an irregular bilateral rupture agrees with the variable co-seismic surface displacements measured along the fault outcrop as well as with an earlier surface-wave investigation, and is consistent, in a general sense, with previous characterizations of the irregular rupture processes of other large strike-slip earthquakes such as the 1972 Sitka, Alaska and the 1980 Eureka, California events.

First Page Preview

First page PDF preview
You do not currently have access to this article.