Rupture Process of the 1995 Antofagasta Subduction Earthquake ( M w = 8.1)

Abstract

A finite-source rupture model of the July 30, 1995, M w = 8.1 Antofagasta (Northern Chile) subduction earthquake is developed using body and surface waves that span periods from 20 to 290 s. A long-period (150–290 s) surface-wave spectral inversion technique is applied to estimate the average finite-fault source properties. Deconvolutions of broadband body waves using theoretical Green’s functions, and deconvolutions of broadband fundamental mode surface waves using empirical Green’s functions provided by a large aftershock, yield effective source time functions containing periods from 20 to 200 s for many directivity parameters. The source time functions are used in an inverse radon transform to image a one-dimensional spatial model of the moment rate history. The event produced a predominantly unilateral southward rupture, yielding strong directivity effects on all seismic waves with periods less than a few hundred seconds. The aftershock information, spectral analysis, and moment rate distribution indicate a rupture length of 180-200 km, with the largest slip concentrated in the first 120 km, a rupture azimuth of 205° ± 10° along the Chilean coastline, and a rupture duration of 60–68 s with a corresponding average rupture velocity of 3.0–3.2 km/s. The overall rupture character is quite smooth, accentuating the directivity effects and reducing the shaking intensity, however there are three regions with enhanced moment rate distributed along the rupture zone: near the epicenter, 50 to 80 km south of the epicenter, and 110 to 140 km south of the epicenter.